Heinkel 100D Stunt
The inverted gull-shape wing is pronounced just enough to enhance
the scale appearance. Flap sizes and deflection ratios were carefully
considered.
The He 100D’s finish is left matte, with recessed panel lines.
Although designed for Stunt, the model’s outline is accurate enough
to warrant using authentic insignia.
THE HEINKEL HE 100D is a little-known,
seldom modeled aircraft that could have
become the mainstay of the Luftwaffe during
World War II. It was built as follow-up to the
He 112: Heinkel’s original design entry when
the Reich Air Ministry issued specifications
for a new fighter in 1935.
The He 100, sometimes designated “He
113,” was in many ways superior to the
Messerschmitt Me 109, which had initially
won the Reich Air Ministry’s competition
over the He 112. But Heinkel was not
awarded a production contract, mostly
because of politics. As with the Bell P-39,
there was little margin for weight-increasing
modifications.
For a short time, clipped-wing
preproduction model He 100V8 held an
absolute world speed record at 463.92 mph.
For more information, see Schiffer Military
History volume 52 and Aero Publishers
number 12.
You never forget your first love; that is
certainly true of my experience in model
aviation. I was an avid CL Precision
Aerobatics (Stunt) builder and flier from 1960
until 1966. During those formative years, I
devoured every article I could find about
aerodynamics, especially pertaining to Stunt
application.
During the next 30 years, I alternated
between activity and inactivity in CL and RC
because of military service, college, raising a
family, and work. However, I followed the
design articles—especially those by Al Rabe.
I agreed with the direction he was taking
Stunt design.
I learned about the He 100 while
researching for an RC Scale Focke-Wulf Fw
190D. Later I acquired a 1/5-scale He 100D
from Dennis Wann in Bryan, Ohio. I loved it
and kept thinking that it deserved to be made
an incarnation of a close-to-scale Stunter,
although that would be a challenge.
I got fired up and started drawing after the
2002 Nats. Then the balsa chips started
flying.
Large models fly better because of a
somewhat more favorable Reynolds number.
My bad shoulder did not want the pull of a
.60 engine, so I compromised on a .51, which
I already had. Rather than force a scale
appearance on a set of Stunt design numbers,
I worked backward. I altered scale threeviews
as little as possible to arrive at what my
instincts told me would work.
In relation to the fuselage, I redrew and
resized the wing many times. This resulted in
approximately a 10% enlargement, with a
slight chord widening and a modest decrease
in the outer panels’ taper. I retained the
inverted gull wing and split flaps to preserve
the aircraft’s essential character, although it
was obvious that it was going to present some
challenges.
I employed a Southwick Skylark airfoil
with the LE radius blunted to reduce pitch
sensitivity. The TE was shortened to fit my
planform, and that yielded a 22% airfoil less
flaps. At that point I had a 57.5-inch
wingspan with approximately 570 square
inches of area. Yikes! The model had a long
wing and a good airfoil, but not a lot of area.
More deviation from scale was
unacceptable, so I was going to have to
design my way around this problem. I kept
thinking, high-aspect-ratio wings are more
efficient, so why do Stunters have low aspect
ratios? From that point on, weight reduction
became Priority One.
No topic has generated more ink in Stunt
discussions than wing imbalance vs. tip
weight. Married to that is the issue of flap
differential, either through area or movement.
In a sharp corner, we want both wings
pitching equally without introducing yaw and
roll forces, which are difficult to trim out of
all maneuvers.
I don’t think the outboard wing generates
as much additional lift from moving in a
radius as some think. In a sharp turn, the need
for a clean pitch change completely overrides
the radius of the flight path. Most of the
traditionally used wing imbalance is actually
compensating for line weight and tug.
The Heinkel’s right outboard panel is
shortened by 5/8 inch, with 17/8 ounces of tip
weight, and the flaps are equal. This proved to
give clean squares and triangles in flighttesting.
The fuselage profile is scale, except for 1/4
inch that was shaved off the bottom of the
fuselage and 3/8 inch that has been removed
from the top of the fin. The fuselage width
was reduced 7/8 inch.
The stabilizer was enlarged but is not as
large as on most of today’s Stunters. I thought
it was unnecessary, because a long tail
movement requires less force for pitch
stability and pitch change. The elevator was
enlarged by borrowing area from the
stabilizer. The balances were retained for
scale effect.
I used 37° maximum flap deflection for
45° elevator deflection. I wanted to avoid
stalling the wing and losing airspeed in tight
turns but knew I needed to move that long tail
in a hurry.
A plus for the Heinkel is that the low
thrustline falls on the wing. Once I built a
T-Bird II to look like a Goodyear racer,
which lowered the thrustline to the wing.
It flew better.
A Stunter with warbird appeal that is outside the typical lines
I had a Sterling Spitfire that flew poorly. I
made a similar change, with remarkable
improvement. The engine, tank, and spinner
fall near the wing, giving a favorable vertical
CG in spite of the tall fuselage profile.
The He 100D employs a wide-blade,
large-diameter, low-pitch propeller (Graupner
12 x 5). This allows the airplane to fly at a
modest speed, but the wide center-section of
the wing and tail would get a large volume of
faster airflow and help compensate for a small
wing and long tail.
Slightly more than 1° of engine side thrust
was used to hold the Heinkel on the lines at a
lower speed in overhead maneuvers. Very
little rudder offset is used. I’m letting the
engine do the work for me, and I don’t
consider side thrust to be a loss of efficiency;
it doesn’t create the problems that flap
differential and rudder offset do.
Please realize that any airplane is an
aerodynamic package. Making any one of
these changes on an existing design may or
may not improve it. Together they have
worked well for the Heinkel He 100D Stunt.
CONSTRUCTION
This section will focus on important points
that differ from the usual. Because of closer
adherence to scale dimensions, weight and
alignment become especially important.
Wing: The wing’s construction uses 1/4 x 2
balsa sheet on edge over the plans, which
doubles as building fixture and LE and TE.
Hal deBolt pioneered this method. I refined
it by putting 5/16-inch “feet” on the top and
bottom of each end of the fixture pieces.
That makes it possible to use less than
straight wood without introducing stresses
when attempting to straighten it. Lines
drawn on the center of the width of the
fixture pieces from end to end used for rib
placement determine straightness.
Set a small adjustable square—to be
used as a gauge—to 25/8 inches, and sand all
the fixture ends to the same height. If this
was a typically flat Stunt wing, all lines
would be in the center at 15/16 inches from
the top and bottom edges. Those lines would
be drawn by connecting marks placed at
both ends and each fixture piece. These end
marks can be placed with better accuracy
using the adjustable square as a gauge.
To accommodate the anhedral and
dihedral, the mark at the anhedral break
(top-view aircraft centerline) should be 1/8
inch above the true fixture centerline (17/16
inches above the plans surface). The centersection
leading the TEs have no wing sweep
or taper, so there does not need to be a joint
in the fixture at the anhedral break.
Place the anhedral mark accordingly.
Then the marks at the dihedral breaks
(which do have a joint) are 5/16 inch lower
than the anhedral mark (11/8 inches above
the plans surface).
Mark the tips 3/8 inch higher than the
dihedral joint marks (11/2 inches above the
plans surface). By connecting these marks,
you have your centerline for rib placement
with anhedral and dihedral built in.
Centerlines are carefully placed on each
rib, and they can be glued in place on the
LE and TE by matching lines. Ribs can be
positioned accurately over the plans by
extending a line up from the plans onto the
LE and TE with a square.
Now the wing can be built in one piece.
You can remove it from the building surface
to facilitate control installation, etc. Just
make sure it is pinned flat while you are
gluing all sheeting and capstrips.
The wing should lay flat up or down
with all feet touching the work surface
without being forced. If it lays flat one way
but not the other, the work surface may be
untrue or your fixture ends are unequal in
height.
If the wing warps when off the work
surface, there will be a consistent imbalance
in the up and down position. After
thoroughly checking, pin it down and finish
sheeting it. Whichever the case, determine
the problem and correct it.
This system will show you any errors. If
you use it properly, you cannot build an
untrue wing. When completely sheeted and
capped, remove the excess fixture material
and shape the LE and TE. You may need to
read the section about wing construction
several times while referring to the plans
and photos to make complete sense of it.
Control System: The control system requires
split flap horns. I used a Tom Morris flap
horn for the right flap with the left side cut
off. Only this horn is connected to the
bellcrank. It is also connected through the 1-
inch hole to the elevator horn, which is a
Morris adjustable set for 45°, when the flap is
at 37°.
A Tom Morris 1-inch elevator horn is
used for the left flap with the right side cut
off. A pushrod connects it as a soldered Y
joint to the elevator pushrod roughly 10
inches back. There is no play, rotational
inaccuracy, or differential using this setup.
The outer flaps are slaved by a 1/16-inchdiameter
music-wire pin that enters the
female receptacle (Du-Bro threaded brass
connector). The female end is installed first,
approximately two-thirds of the way back
from the hinge line.
Carefully start a pilot hole with a straight
pin, and then use progressively larger drill
bits, turning them with your fingertips. This
allows you to make precise adjustments.
The connector will require a stepped hole
to fit properly and tight. Before pressing it in
place, make pinholes in the flap surface to
wick in cyanoacrylate glue. Adhere this after
it is in place. Temporarily mount the flaps
with strong-tack masking tape, to simulate
cloth hinges. Carefully mark the male pin’s
position, and then inset it in the same manner
as you did the female, but do not glue.
The gap between the flaps is a strong 1/16
inch, but it must bevel to approximately 5/32
inch at the rear to accommodate up
movement. In neutral, the pin must enter the
brass receptacle by roughly 5/32 inch. Neutral
fit should be perfect. Sand the flap LEs
slightly, if needed for adjustments.
Test for up and down with your tape
hinges tightly in place. They will bind
because of the geometry involved. Use a drill
bit to slightly oval the mouth of the brass
coupler to the front and rear. Remove the
male pin, and slightly bevel and round the
bottom and rear of its end. Reinstall and test.
Close observation will show you where to
make small changes until it is right. If you
mess up, make a new pin. Be patient; this is
work, but not as much as a 32-coat paint job.
When you are sure it is right, glue the flap
in with cyanoacrylate. As a precaution, dig a
trench in the bottom of the flap and expose
part of the pin, and fill the trench with epoxy
flush to the surface. This will ensure that the
pin will not loosen with time. (Something I
did not do and now need to.)
Permanently mount the flaps with Tom
Morris Dacron hinges, which will allow more
freedom of movement. It also allows for
slight inaccuracy in the male and female
parts.
Fuselage: The main fuselage sides should be
medium-weight, firm-grain 3/32 balsa. Thicker
wood is unnecessary. Smaller airplanes use
1/2-inch-thick material, because they are not
as tall in profile. There is a lot of wood here
as long as it is kept rigid; think in terms of
trusses and I-Beams.
The engine mounts are offset 1/16 inch to
the inboard side. This allows side thrust and
still puts the spinner at the centerline. The 1/2-
inch square stabilizer center TE edge is hard
balsa. All the rest is light contest balsa.
The radius of the fin LE is offset slightly,
to direct more air on the inboard side. The fin
is glued in place with the LE offset 1/32 inch
inboard. The rudder is offset to the outboard
3/32 inch and the scale trim tab is offset a
“bunch.”
The landing-gear legs and their composite
trunion mount (taken from a set of B&D
retracts) were inset into a plywood pocket
mounted in the wing. A piece of 1/16 plywood
angled from the back of the top spar to the
front of the bottom spar forms the back wall
of this pocket and doubles as shear webbing
for the wing.
The wing center spars should be spruce
or bass. The axles fall just below the LE, and
the gear extends 41/4 inches from wing to
axle. A traditional torsion gear and block may
be used. I like this better.
Finish: Light, light, light! The entire bare
Heinkel was painted with one coat of
AeroGloss clear. I painted 1/2-ounce glass
cloth on the fuselage, with finishing resin
thinned 50% with denatured alcohol. When
cured, I applied a second coat to fill the pores.
Then I sanded until the cloth’s surface was
cut.
I covered all open surfaces with Polyspan
filled with three coats of AeroGloss clear.
Chart tape simulates the scale panel lines. I
applied one generous coat of Perfect Primer
and then removed the chart tape to give the
panel lines depth. Then I applied two coats of
scale-accurate Perfect military flat. Except for
markings, that’s it. The He 100D is extremely
light and scale.
If I haven’t upset anyone yet, I may now.
The rule book stipulates that the airplane be
judged for perfection of appearance; nowhere
does it mention a high-gloss mirror finish. As
much as I loved those mirror finishes, an
accurate military finish on a warbird should
score as well as a nonrealistic high gloss. In
this case, weight and scale appearance enter
the equation.
I thank the following: John Florio
(deceased), for being my mentor in the early
years; Dave Gatewood (deceased), for getting
me back into Stunt and his support during this
project’s design and building phases; Jack
Sheeks, for his support in test-flying and
encouragement to publish the design; and
Bob Hunt for being open-minded and
enthusiastic after test-flying the prototype.
Good luck with your Heinkel. Please call
or write if you have questions or comments; I
don’t have a computer, so I rarely check Email.
MA
Daniel L Grotzinger
6710 Greenshire Dr.
Indianapolis IN 46220
(317) 585-4808
[email protected]
Sources:
Tom Morris Accessories:
J & J Hobbies—Control Line Central
(505) 332-8007
www.clcentral.com
B&D Enterprises
(304) 753-4636
http://bdretracts.com
Edition: Model Aviation - 2009/01
Page Numbers: 28,29,30,31,32,33,34,36
Edition: Model Aviation - 2009/01
Page Numbers: 28,29,30,31,32,33,34,36
Heinkel 100D Stunt
The inverted gull-shape wing is pronounced just enough to enhance
the scale appearance. Flap sizes and deflection ratios were carefully
considered.
The He 100D’s finish is left matte, with recessed panel lines.
Although designed for Stunt, the model’s outline is accurate enough
to warrant using authentic insignia.
THE HEINKEL HE 100D is a little-known,
seldom modeled aircraft that could have
become the mainstay of the Luftwaffe during
World War II. It was built as follow-up to the
He 112: Heinkel’s original design entry when
the Reich Air Ministry issued specifications
for a new fighter in 1935.
The He 100, sometimes designated “He
113,” was in many ways superior to the
Messerschmitt Me 109, which had initially
won the Reich Air Ministry’s competition
over the He 112. But Heinkel was not
awarded a production contract, mostly
because of politics. As with the Bell P-39,
there was little margin for weight-increasing
modifications.
For a short time, clipped-wing
preproduction model He 100V8 held an
absolute world speed record at 463.92 mph.
For more information, see Schiffer Military
History volume 52 and Aero Publishers
number 12.
You never forget your first love; that is
certainly true of my experience in model
aviation. I was an avid CL Precision
Aerobatics (Stunt) builder and flier from 1960
until 1966. During those formative years, I
devoured every article I could find about
aerodynamics, especially pertaining to Stunt
application.
During the next 30 years, I alternated
between activity and inactivity in CL and RC
because of military service, college, raising a
family, and work. However, I followed the
design articles—especially those by Al Rabe.
I agreed with the direction he was taking
Stunt design.
I learned about the He 100 while
researching for an RC Scale Focke-Wulf Fw
190D. Later I acquired a 1/5-scale He 100D
from Dennis Wann in Bryan, Ohio. I loved it
and kept thinking that it deserved to be made
an incarnation of a close-to-scale Stunter,
although that would be a challenge.
I got fired up and started drawing after the
2002 Nats. Then the balsa chips started
flying.
Large models fly better because of a
somewhat more favorable Reynolds number.
My bad shoulder did not want the pull of a
.60 engine, so I compromised on a .51, which
I already had. Rather than force a scale
appearance on a set of Stunt design numbers,
I worked backward. I altered scale threeviews
as little as possible to arrive at what my
instincts told me would work.
In relation to the fuselage, I redrew and
resized the wing many times. This resulted in
approximately a 10% enlargement, with a
slight chord widening and a modest decrease
in the outer panels’ taper. I retained the
inverted gull wing and split flaps to preserve
the aircraft’s essential character, although it
was obvious that it was going to present some
challenges.
I employed a Southwick Skylark airfoil
with the LE radius blunted to reduce pitch
sensitivity. The TE was shortened to fit my
planform, and that yielded a 22% airfoil less
flaps. At that point I had a 57.5-inch
wingspan with approximately 570 square
inches of area. Yikes! The model had a long
wing and a good airfoil, but not a lot of area.
More deviation from scale was
unacceptable, so I was going to have to
design my way around this problem. I kept
thinking, high-aspect-ratio wings are more
efficient, so why do Stunters have low aspect
ratios? From that point on, weight reduction
became Priority One.
No topic has generated more ink in Stunt
discussions than wing imbalance vs. tip
weight. Married to that is the issue of flap
differential, either through area or movement.
In a sharp corner, we want both wings
pitching equally without introducing yaw and
roll forces, which are difficult to trim out of
all maneuvers.
I don’t think the outboard wing generates
as much additional lift from moving in a
radius as some think. In a sharp turn, the need
for a clean pitch change completely overrides
the radius of the flight path. Most of the
traditionally used wing imbalance is actually
compensating for line weight and tug.
The Heinkel’s right outboard panel is
shortened by 5/8 inch, with 17/8 ounces of tip
weight, and the flaps are equal. This proved to
give clean squares and triangles in flighttesting.
The fuselage profile is scale, except for 1/4
inch that was shaved off the bottom of the
fuselage and 3/8 inch that has been removed
from the top of the fin. The fuselage width
was reduced 7/8 inch.
The stabilizer was enlarged but is not as
large as on most of today’s Stunters. I thought
it was unnecessary, because a long tail
movement requires less force for pitch
stability and pitch change. The elevator was
enlarged by borrowing area from the
stabilizer. The balances were retained for
scale effect.
I used 37° maximum flap deflection for
45° elevator deflection. I wanted to avoid
stalling the wing and losing airspeed in tight
turns but knew I needed to move that long tail
in a hurry.
A plus for the Heinkel is that the low
thrustline falls on the wing. Once I built a
T-Bird II to look like a Goodyear racer,
which lowered the thrustline to the wing.
It flew better.
A Stunter with warbird appeal that is outside the typical lines
I had a Sterling Spitfire that flew poorly. I
made a similar change, with remarkable
improvement. The engine, tank, and spinner
fall near the wing, giving a favorable vertical
CG in spite of the tall fuselage profile.
The He 100D employs a wide-blade,
large-diameter, low-pitch propeller (Graupner
12 x 5). This allows the airplane to fly at a
modest speed, but the wide center-section of
the wing and tail would get a large volume of
faster airflow and help compensate for a small
wing and long tail.
Slightly more than 1° of engine side thrust
was used to hold the Heinkel on the lines at a
lower speed in overhead maneuvers. Very
little rudder offset is used. I’m letting the
engine do the work for me, and I don’t
consider side thrust to be a loss of efficiency;
it doesn’t create the problems that flap
differential and rudder offset do.
Please realize that any airplane is an
aerodynamic package. Making any one of
these changes on an existing design may or
may not improve it. Together they have
worked well for the Heinkel He 100D Stunt.
CONSTRUCTION
This section will focus on important points
that differ from the usual. Because of closer
adherence to scale dimensions, weight and
alignment become especially important.
Wing: The wing’s construction uses 1/4 x 2
balsa sheet on edge over the plans, which
doubles as building fixture and LE and TE.
Hal deBolt pioneered this method. I refined
it by putting 5/16-inch “feet” on the top and
bottom of each end of the fixture pieces.
That makes it possible to use less than
straight wood without introducing stresses
when attempting to straighten it. Lines
drawn on the center of the width of the
fixture pieces from end to end used for rib
placement determine straightness.
Set a small adjustable square—to be
used as a gauge—to 25/8 inches, and sand all
the fixture ends to the same height. If this
was a typically flat Stunt wing, all lines
would be in the center at 15/16 inches from
the top and bottom edges. Those lines would
be drawn by connecting marks placed at
both ends and each fixture piece. These end
marks can be placed with better accuracy
using the adjustable square as a gauge.
To accommodate the anhedral and
dihedral, the mark at the anhedral break
(top-view aircraft centerline) should be 1/8
inch above the true fixture centerline (17/16
inches above the plans surface). The centersection
leading the TEs have no wing sweep
or taper, so there does not need to be a joint
in the fixture at the anhedral break.
Place the anhedral mark accordingly.
Then the marks at the dihedral breaks
(which do have a joint) are 5/16 inch lower
than the anhedral mark (11/8 inches above
the plans surface).
Mark the tips 3/8 inch higher than the
dihedral joint marks (11/2 inches above the
plans surface). By connecting these marks,
you have your centerline for rib placement
with anhedral and dihedral built in.
Centerlines are carefully placed on each
rib, and they can be glued in place on the
LE and TE by matching lines. Ribs can be
positioned accurately over the plans by
extending a line up from the plans onto the
LE and TE with a square.
Now the wing can be built in one piece.
You can remove it from the building surface
to facilitate control installation, etc. Just
make sure it is pinned flat while you are
gluing all sheeting and capstrips.
The wing should lay flat up or down
with all feet touching the work surface
without being forced. If it lays flat one way
but not the other, the work surface may be
untrue or your fixture ends are unequal in
height.
If the wing warps when off the work
surface, there will be a consistent imbalance
in the up and down position. After
thoroughly checking, pin it down and finish
sheeting it. Whichever the case, determine
the problem and correct it.
This system will show you any errors. If
you use it properly, you cannot build an
untrue wing. When completely sheeted and
capped, remove the excess fixture material
and shape the LE and TE. You may need to
read the section about wing construction
several times while referring to the plans
and photos to make complete sense of it.
Control System: The control system requires
split flap horns. I used a Tom Morris flap
horn for the right flap with the left side cut
off. Only this horn is connected to the
bellcrank. It is also connected through the 1-
inch hole to the elevator horn, which is a
Morris adjustable set for 45°, when the flap is
at 37°.
A Tom Morris 1-inch elevator horn is
used for the left flap with the right side cut
off. A pushrod connects it as a soldered Y
joint to the elevator pushrod roughly 10
inches back. There is no play, rotational
inaccuracy, or differential using this setup.
The outer flaps are slaved by a 1/16-inchdiameter
music-wire pin that enters the
female receptacle (Du-Bro threaded brass
connector). The female end is installed first,
approximately two-thirds of the way back
from the hinge line.
Carefully start a pilot hole with a straight
pin, and then use progressively larger drill
bits, turning them with your fingertips. This
allows you to make precise adjustments.
The connector will require a stepped hole
to fit properly and tight. Before pressing it in
place, make pinholes in the flap surface to
wick in cyanoacrylate glue. Adhere this after
it is in place. Temporarily mount the flaps
with strong-tack masking tape, to simulate
cloth hinges. Carefully mark the male pin’s
position, and then inset it in the same manner
as you did the female, but do not glue.
The gap between the flaps is a strong 1/16
inch, but it must bevel to approximately 5/32
inch at the rear to accommodate up
movement. In neutral, the pin must enter the
brass receptacle by roughly 5/32 inch. Neutral
fit should be perfect. Sand the flap LEs
slightly, if needed for adjustments.
Test for up and down with your tape
hinges tightly in place. They will bind
because of the geometry involved. Use a drill
bit to slightly oval the mouth of the brass
coupler to the front and rear. Remove the
male pin, and slightly bevel and round the
bottom and rear of its end. Reinstall and test.
Close observation will show you where to
make small changes until it is right. If you
mess up, make a new pin. Be patient; this is
work, but not as much as a 32-coat paint job.
When you are sure it is right, glue the flap
in with cyanoacrylate. As a precaution, dig a
trench in the bottom of the flap and expose
part of the pin, and fill the trench with epoxy
flush to the surface. This will ensure that the
pin will not loosen with time. (Something I
did not do and now need to.)
Permanently mount the flaps with Tom
Morris Dacron hinges, which will allow more
freedom of movement. It also allows for
slight inaccuracy in the male and female
parts.
Fuselage: The main fuselage sides should be
medium-weight, firm-grain 3/32 balsa. Thicker
wood is unnecessary. Smaller airplanes use
1/2-inch-thick material, because they are not
as tall in profile. There is a lot of wood here
as long as it is kept rigid; think in terms of
trusses and I-Beams.
The engine mounts are offset 1/16 inch to
the inboard side. This allows side thrust and
still puts the spinner at the centerline. The 1/2-
inch square stabilizer center TE edge is hard
balsa. All the rest is light contest balsa.
The radius of the fin LE is offset slightly,
to direct more air on the inboard side. The fin
is glued in place with the LE offset 1/32 inch
inboard. The rudder is offset to the outboard
3/32 inch and the scale trim tab is offset a
“bunch.”
The landing-gear legs and their composite
trunion mount (taken from a set of B&D
retracts) were inset into a plywood pocket
mounted in the wing. A piece of 1/16 plywood
angled from the back of the top spar to the
front of the bottom spar forms the back wall
of this pocket and doubles as shear webbing
for the wing.
The wing center spars should be spruce
or bass. The axles fall just below the LE, and
the gear extends 41/4 inches from wing to
axle. A traditional torsion gear and block may
be used. I like this better.
Finish: Light, light, light! The entire bare
Heinkel was painted with one coat of
AeroGloss clear. I painted 1/2-ounce glass
cloth on the fuselage, with finishing resin
thinned 50% with denatured alcohol. When
cured, I applied a second coat to fill the pores.
Then I sanded until the cloth’s surface was
cut.
I covered all open surfaces with Polyspan
filled with three coats of AeroGloss clear.
Chart tape simulates the scale panel lines. I
applied one generous coat of Perfect Primer
and then removed the chart tape to give the
panel lines depth. Then I applied two coats of
scale-accurate Perfect military flat. Except for
markings, that’s it. The He 100D is extremely
light and scale.
If I haven’t upset anyone yet, I may now.
The rule book stipulates that the airplane be
judged for perfection of appearance; nowhere
does it mention a high-gloss mirror finish. As
much as I loved those mirror finishes, an
accurate military finish on a warbird should
score as well as a nonrealistic high gloss. In
this case, weight and scale appearance enter
the equation.
I thank the following: John Florio
(deceased), for being my mentor in the early
years; Dave Gatewood (deceased), for getting
me back into Stunt and his support during this
project’s design and building phases; Jack
Sheeks, for his support in test-flying and
encouragement to publish the design; and
Bob Hunt for being open-minded and
enthusiastic after test-flying the prototype.
Good luck with your Heinkel. Please call
or write if you have questions or comments; I
don’t have a computer, so I rarely check Email.
MA
Daniel L Grotzinger
6710 Greenshire Dr.
Indianapolis IN 46220
(317) 585-4808
[email protected]
Sources:
Tom Morris Accessories:
J & J Hobbies—Control Line Central
(505) 332-8007
www.clcentral.com
B&D Enterprises
(304) 753-4636
http://bdretracts.com
Edition: Model Aviation - 2009/01
Page Numbers: 28,29,30,31,32,33,34,36
Heinkel 100D Stunt
The inverted gull-shape wing is pronounced just enough to enhance
the scale appearance. Flap sizes and deflection ratios were carefully
considered.
The He 100D’s finish is left matte, with recessed panel lines.
Although designed for Stunt, the model’s outline is accurate enough
to warrant using authentic insignia.
THE HEINKEL HE 100D is a little-known,
seldom modeled aircraft that could have
become the mainstay of the Luftwaffe during
World War II. It was built as follow-up to the
He 112: Heinkel’s original design entry when
the Reich Air Ministry issued specifications
for a new fighter in 1935.
The He 100, sometimes designated “He
113,” was in many ways superior to the
Messerschmitt Me 109, which had initially
won the Reich Air Ministry’s competition
over the He 112. But Heinkel was not
awarded a production contract, mostly
because of politics. As with the Bell P-39,
there was little margin for weight-increasing
modifications.
For a short time, clipped-wing
preproduction model He 100V8 held an
absolute world speed record at 463.92 mph.
For more information, see Schiffer Military
History volume 52 and Aero Publishers
number 12.
You never forget your first love; that is
certainly true of my experience in model
aviation. I was an avid CL Precision
Aerobatics (Stunt) builder and flier from 1960
until 1966. During those formative years, I
devoured every article I could find about
aerodynamics, especially pertaining to Stunt
application.
During the next 30 years, I alternated
between activity and inactivity in CL and RC
because of military service, college, raising a
family, and work. However, I followed the
design articles—especially those by Al Rabe.
I agreed with the direction he was taking
Stunt design.
I learned about the He 100 while
researching for an RC Scale Focke-Wulf Fw
190D. Later I acquired a 1/5-scale He 100D
from Dennis Wann in Bryan, Ohio. I loved it
and kept thinking that it deserved to be made
an incarnation of a close-to-scale Stunter,
although that would be a challenge.
I got fired up and started drawing after the
2002 Nats. Then the balsa chips started
flying.
Large models fly better because of a
somewhat more favorable Reynolds number.
My bad shoulder did not want the pull of a
.60 engine, so I compromised on a .51, which
I already had. Rather than force a scale
appearance on a set of Stunt design numbers,
I worked backward. I altered scale threeviews
as little as possible to arrive at what my
instincts told me would work.
In relation to the fuselage, I redrew and
resized the wing many times. This resulted in
approximately a 10% enlargement, with a
slight chord widening and a modest decrease
in the outer panels’ taper. I retained the
inverted gull wing and split flaps to preserve
the aircraft’s essential character, although it
was obvious that it was going to present some
challenges.
I employed a Southwick Skylark airfoil
with the LE radius blunted to reduce pitch
sensitivity. The TE was shortened to fit my
planform, and that yielded a 22% airfoil less
flaps. At that point I had a 57.5-inch
wingspan with approximately 570 square
inches of area. Yikes! The model had a long
wing and a good airfoil, but not a lot of area.
More deviation from scale was
unacceptable, so I was going to have to
design my way around this problem. I kept
thinking, high-aspect-ratio wings are more
efficient, so why do Stunters have low aspect
ratios? From that point on, weight reduction
became Priority One.
No topic has generated more ink in Stunt
discussions than wing imbalance vs. tip
weight. Married to that is the issue of flap
differential, either through area or movement.
In a sharp corner, we want both wings
pitching equally without introducing yaw and
roll forces, which are difficult to trim out of
all maneuvers.
I don’t think the outboard wing generates
as much additional lift from moving in a
radius as some think. In a sharp turn, the need
for a clean pitch change completely overrides
the radius of the flight path. Most of the
traditionally used wing imbalance is actually
compensating for line weight and tug.
The Heinkel’s right outboard panel is
shortened by 5/8 inch, with 17/8 ounces of tip
weight, and the flaps are equal. This proved to
give clean squares and triangles in flighttesting.
The fuselage profile is scale, except for 1/4
inch that was shaved off the bottom of the
fuselage and 3/8 inch that has been removed
from the top of the fin. The fuselage width
was reduced 7/8 inch.
The stabilizer was enlarged but is not as
large as on most of today’s Stunters. I thought
it was unnecessary, because a long tail
movement requires less force for pitch
stability and pitch change. The elevator was
enlarged by borrowing area from the
stabilizer. The balances were retained for
scale effect.
I used 37° maximum flap deflection for
45° elevator deflection. I wanted to avoid
stalling the wing and losing airspeed in tight
turns but knew I needed to move that long tail
in a hurry.
A plus for the Heinkel is that the low
thrustline falls on the wing. Once I built a
T-Bird II to look like a Goodyear racer,
which lowered the thrustline to the wing.
It flew better.
A Stunter with warbird appeal that is outside the typical lines
I had a Sterling Spitfire that flew poorly. I
made a similar change, with remarkable
improvement. The engine, tank, and spinner
fall near the wing, giving a favorable vertical
CG in spite of the tall fuselage profile.
The He 100D employs a wide-blade,
large-diameter, low-pitch propeller (Graupner
12 x 5). This allows the airplane to fly at a
modest speed, but the wide center-section of
the wing and tail would get a large volume of
faster airflow and help compensate for a small
wing and long tail.
Slightly more than 1° of engine side thrust
was used to hold the Heinkel on the lines at a
lower speed in overhead maneuvers. Very
little rudder offset is used. I’m letting the
engine do the work for me, and I don’t
consider side thrust to be a loss of efficiency;
it doesn’t create the problems that flap
differential and rudder offset do.
Please realize that any airplane is an
aerodynamic package. Making any one of
these changes on an existing design may or
may not improve it. Together they have
worked well for the Heinkel He 100D Stunt.
CONSTRUCTION
This section will focus on important points
that differ from the usual. Because of closer
adherence to scale dimensions, weight and
alignment become especially important.
Wing: The wing’s construction uses 1/4 x 2
balsa sheet on edge over the plans, which
doubles as building fixture and LE and TE.
Hal deBolt pioneered this method. I refined
it by putting 5/16-inch “feet” on the top and
bottom of each end of the fixture pieces.
That makes it possible to use less than
straight wood without introducing stresses
when attempting to straighten it. Lines
drawn on the center of the width of the
fixture pieces from end to end used for rib
placement determine straightness.
Set a small adjustable square—to be
used as a gauge—to 25/8 inches, and sand all
the fixture ends to the same height. If this
was a typically flat Stunt wing, all lines
would be in the center at 15/16 inches from
the top and bottom edges. Those lines would
be drawn by connecting marks placed at
both ends and each fixture piece. These end
marks can be placed with better accuracy
using the adjustable square as a gauge.
To accommodate the anhedral and
dihedral, the mark at the anhedral break
(top-view aircraft centerline) should be 1/8
inch above the true fixture centerline (17/16
inches above the plans surface). The centersection
leading the TEs have no wing sweep
or taper, so there does not need to be a joint
in the fixture at the anhedral break.
Place the anhedral mark accordingly.
Then the marks at the dihedral breaks
(which do have a joint) are 5/16 inch lower
than the anhedral mark (11/8 inches above
the plans surface).
Mark the tips 3/8 inch higher than the
dihedral joint marks (11/2 inches above the
plans surface). By connecting these marks,
you have your centerline for rib placement
with anhedral and dihedral built in.
Centerlines are carefully placed on each
rib, and they can be glued in place on the
LE and TE by matching lines. Ribs can be
positioned accurately over the plans by
extending a line up from the plans onto the
LE and TE with a square.
Now the wing can be built in one piece.
You can remove it from the building surface
to facilitate control installation, etc. Just
make sure it is pinned flat while you are
gluing all sheeting and capstrips.
The wing should lay flat up or down
with all feet touching the work surface
without being forced. If it lays flat one way
but not the other, the work surface may be
untrue or your fixture ends are unequal in
height.
If the wing warps when off the work
surface, there will be a consistent imbalance
in the up and down position. After
thoroughly checking, pin it down and finish
sheeting it. Whichever the case, determine
the problem and correct it.
This system will show you any errors. If
you use it properly, you cannot build an
untrue wing. When completely sheeted and
capped, remove the excess fixture material
and shape the LE and TE. You may need to
read the section about wing construction
several times while referring to the plans
and photos to make complete sense of it.
Control System: The control system requires
split flap horns. I used a Tom Morris flap
horn for the right flap with the left side cut
off. Only this horn is connected to the
bellcrank. It is also connected through the 1-
inch hole to the elevator horn, which is a
Morris adjustable set for 45°, when the flap is
at 37°.
A Tom Morris 1-inch elevator horn is
used for the left flap with the right side cut
off. A pushrod connects it as a soldered Y
joint to the elevator pushrod roughly 10
inches back. There is no play, rotational
inaccuracy, or differential using this setup.
The outer flaps are slaved by a 1/16-inchdiameter
music-wire pin that enters the
female receptacle (Du-Bro threaded brass
connector). The female end is installed first,
approximately two-thirds of the way back
from the hinge line.
Carefully start a pilot hole with a straight
pin, and then use progressively larger drill
bits, turning them with your fingertips. This
allows you to make precise adjustments.
The connector will require a stepped hole
to fit properly and tight. Before pressing it in
place, make pinholes in the flap surface to
wick in cyanoacrylate glue. Adhere this after
it is in place. Temporarily mount the flaps
with strong-tack masking tape, to simulate
cloth hinges. Carefully mark the male pin’s
position, and then inset it in the same manner
as you did the female, but do not glue.
The gap between the flaps is a strong 1/16
inch, but it must bevel to approximately 5/32
inch at the rear to accommodate up
movement. In neutral, the pin must enter the
brass receptacle by roughly 5/32 inch. Neutral
fit should be perfect. Sand the flap LEs
slightly, if needed for adjustments.
Test for up and down with your tape
hinges tightly in place. They will bind
because of the geometry involved. Use a drill
bit to slightly oval the mouth of the brass
coupler to the front and rear. Remove the
male pin, and slightly bevel and round the
bottom and rear of its end. Reinstall and test.
Close observation will show you where to
make small changes until it is right. If you
mess up, make a new pin. Be patient; this is
work, but not as much as a 32-coat paint job.
When you are sure it is right, glue the flap
in with cyanoacrylate. As a precaution, dig a
trench in the bottom of the flap and expose
part of the pin, and fill the trench with epoxy
flush to the surface. This will ensure that the
pin will not loosen with time. (Something I
did not do and now need to.)
Permanently mount the flaps with Tom
Morris Dacron hinges, which will allow more
freedom of movement. It also allows for
slight inaccuracy in the male and female
parts.
Fuselage: The main fuselage sides should be
medium-weight, firm-grain 3/32 balsa. Thicker
wood is unnecessary. Smaller airplanes use
1/2-inch-thick material, because they are not
as tall in profile. There is a lot of wood here
as long as it is kept rigid; think in terms of
trusses and I-Beams.
The engine mounts are offset 1/16 inch to
the inboard side. This allows side thrust and
still puts the spinner at the centerline. The 1/2-
inch square stabilizer center TE edge is hard
balsa. All the rest is light contest balsa.
The radius of the fin LE is offset slightly,
to direct more air on the inboard side. The fin
is glued in place with the LE offset 1/32 inch
inboard. The rudder is offset to the outboard
3/32 inch and the scale trim tab is offset a
“bunch.”
The landing-gear legs and their composite
trunion mount (taken from a set of B&D
retracts) were inset into a plywood pocket
mounted in the wing. A piece of 1/16 plywood
angled from the back of the top spar to the
front of the bottom spar forms the back wall
of this pocket and doubles as shear webbing
for the wing.
The wing center spars should be spruce
or bass. The axles fall just below the LE, and
the gear extends 41/4 inches from wing to
axle. A traditional torsion gear and block may
be used. I like this better.
Finish: Light, light, light! The entire bare
Heinkel was painted with one coat of
AeroGloss clear. I painted 1/2-ounce glass
cloth on the fuselage, with finishing resin
thinned 50% with denatured alcohol. When
cured, I applied a second coat to fill the pores.
Then I sanded until the cloth’s surface was
cut.
I covered all open surfaces with Polyspan
filled with three coats of AeroGloss clear.
Chart tape simulates the scale panel lines. I
applied one generous coat of Perfect Primer
and then removed the chart tape to give the
panel lines depth. Then I applied two coats of
scale-accurate Perfect military flat. Except for
markings, that’s it. The He 100D is extremely
light and scale.
If I haven’t upset anyone yet, I may now.
The rule book stipulates that the airplane be
judged for perfection of appearance; nowhere
does it mention a high-gloss mirror finish. As
much as I loved those mirror finishes, an
accurate military finish on a warbird should
score as well as a nonrealistic high gloss. In
this case, weight and scale appearance enter
the equation.
I thank the following: John Florio
(deceased), for being my mentor in the early
years; Dave Gatewood (deceased), for getting
me back into Stunt and his support during this
project’s design and building phases; Jack
Sheeks, for his support in test-flying and
encouragement to publish the design; and
Bob Hunt for being open-minded and
enthusiastic after test-flying the prototype.
Good luck with your Heinkel. Please call
or write if you have questions or comments; I
don’t have a computer, so I rarely check Email.
MA
Daniel L Grotzinger
6710 Greenshire Dr.
Indianapolis IN 46220
(317) 585-4808
[email protected]
Sources:
Tom Morris Accessories:
J & J Hobbies—Control Line Central
(505) 332-8007
www.clcentral.com
B&D Enterprises
(304) 753-4636
http://bdretracts.com
Edition: Model Aviation - 2009/01
Page Numbers: 28,29,30,31,32,33,34,36
Heinkel 100D Stunt
The inverted gull-shape wing is pronounced just enough to enhance
the scale appearance. Flap sizes and deflection ratios were carefully
considered.
The He 100D’s finish is left matte, with recessed panel lines.
Although designed for Stunt, the model’s outline is accurate enough
to warrant using authentic insignia.
THE HEINKEL HE 100D is a little-known,
seldom modeled aircraft that could have
become the mainstay of the Luftwaffe during
World War II. It was built as follow-up to the
He 112: Heinkel’s original design entry when
the Reich Air Ministry issued specifications
for a new fighter in 1935.
The He 100, sometimes designated “He
113,” was in many ways superior to the
Messerschmitt Me 109, which had initially
won the Reich Air Ministry’s competition
over the He 112. But Heinkel was not
awarded a production contract, mostly
because of politics. As with the Bell P-39,
there was little margin for weight-increasing
modifications.
For a short time, clipped-wing
preproduction model He 100V8 held an
absolute world speed record at 463.92 mph.
For more information, see Schiffer Military
History volume 52 and Aero Publishers
number 12.
You never forget your first love; that is
certainly true of my experience in model
aviation. I was an avid CL Precision
Aerobatics (Stunt) builder and flier from 1960
until 1966. During those formative years, I
devoured every article I could find about
aerodynamics, especially pertaining to Stunt
application.
During the next 30 years, I alternated
between activity and inactivity in CL and RC
because of military service, college, raising a
family, and work. However, I followed the
design articles—especially those by Al Rabe.
I agreed with the direction he was taking
Stunt design.
I learned about the He 100 while
researching for an RC Scale Focke-Wulf Fw
190D. Later I acquired a 1/5-scale He 100D
from Dennis Wann in Bryan, Ohio. I loved it
and kept thinking that it deserved to be made
an incarnation of a close-to-scale Stunter,
although that would be a challenge.
I got fired up and started drawing after the
2002 Nats. Then the balsa chips started
flying.
Large models fly better because of a
somewhat more favorable Reynolds number.
My bad shoulder did not want the pull of a
.60 engine, so I compromised on a .51, which
I already had. Rather than force a scale
appearance on a set of Stunt design numbers,
I worked backward. I altered scale threeviews
as little as possible to arrive at what my
instincts told me would work.
In relation to the fuselage, I redrew and
resized the wing many times. This resulted in
approximately a 10% enlargement, with a
slight chord widening and a modest decrease
in the outer panels’ taper. I retained the
inverted gull wing and split flaps to preserve
the aircraft’s essential character, although it
was obvious that it was going to present some
challenges.
I employed a Southwick Skylark airfoil
with the LE radius blunted to reduce pitch
sensitivity. The TE was shortened to fit my
planform, and that yielded a 22% airfoil less
flaps. At that point I had a 57.5-inch
wingspan with approximately 570 square
inches of area. Yikes! The model had a long
wing and a good airfoil, but not a lot of area.
More deviation from scale was
unacceptable, so I was going to have to
design my way around this problem. I kept
thinking, high-aspect-ratio wings are more
efficient, so why do Stunters have low aspect
ratios? From that point on, weight reduction
became Priority One.
No topic has generated more ink in Stunt
discussions than wing imbalance vs. tip
weight. Married to that is the issue of flap
differential, either through area or movement.
In a sharp corner, we want both wings
pitching equally without introducing yaw and
roll forces, which are difficult to trim out of
all maneuvers.
I don’t think the outboard wing generates
as much additional lift from moving in a
radius as some think. In a sharp turn, the need
for a clean pitch change completely overrides
the radius of the flight path. Most of the
traditionally used wing imbalance is actually
compensating for line weight and tug.
The Heinkel’s right outboard panel is
shortened by 5/8 inch, with 17/8 ounces of tip
weight, and the flaps are equal. This proved to
give clean squares and triangles in flighttesting.
The fuselage profile is scale, except for 1/4
inch that was shaved off the bottom of the
fuselage and 3/8 inch that has been removed
from the top of the fin. The fuselage width
was reduced 7/8 inch.
The stabilizer was enlarged but is not as
large as on most of today’s Stunters. I thought
it was unnecessary, because a long tail
movement requires less force for pitch
stability and pitch change. The elevator was
enlarged by borrowing area from the
stabilizer. The balances were retained for
scale effect.
I used 37° maximum flap deflection for
45° elevator deflection. I wanted to avoid
stalling the wing and losing airspeed in tight
turns but knew I needed to move that long tail
in a hurry.
A plus for the Heinkel is that the low
thrustline falls on the wing. Once I built a
T-Bird II to look like a Goodyear racer,
which lowered the thrustline to the wing.
It flew better.
A Stunter with warbird appeal that is outside the typical lines
I had a Sterling Spitfire that flew poorly. I
made a similar change, with remarkable
improvement. The engine, tank, and spinner
fall near the wing, giving a favorable vertical
CG in spite of the tall fuselage profile.
The He 100D employs a wide-blade,
large-diameter, low-pitch propeller (Graupner
12 x 5). This allows the airplane to fly at a
modest speed, but the wide center-section of
the wing and tail would get a large volume of
faster airflow and help compensate for a small
wing and long tail.
Slightly more than 1° of engine side thrust
was used to hold the Heinkel on the lines at a
lower speed in overhead maneuvers. Very
little rudder offset is used. I’m letting the
engine do the work for me, and I don’t
consider side thrust to be a loss of efficiency;
it doesn’t create the problems that flap
differential and rudder offset do.
Please realize that any airplane is an
aerodynamic package. Making any one of
these changes on an existing design may or
may not improve it. Together they have
worked well for the Heinkel He 100D Stunt.
CONSTRUCTION
This section will focus on important points
that differ from the usual. Because of closer
adherence to scale dimensions, weight and
alignment become especially important.
Wing: The wing’s construction uses 1/4 x 2
balsa sheet on edge over the plans, which
doubles as building fixture and LE and TE.
Hal deBolt pioneered this method. I refined
it by putting 5/16-inch “feet” on the top and
bottom of each end of the fixture pieces.
That makes it possible to use less than
straight wood without introducing stresses
when attempting to straighten it. Lines
drawn on the center of the width of the
fixture pieces from end to end used for rib
placement determine straightness.
Set a small adjustable square—to be
used as a gauge—to 25/8 inches, and sand all
the fixture ends to the same height. If this
was a typically flat Stunt wing, all lines
would be in the center at 15/16 inches from
the top and bottom edges. Those lines would
be drawn by connecting marks placed at
both ends and each fixture piece. These end
marks can be placed with better accuracy
using the adjustable square as a gauge.
To accommodate the anhedral and
dihedral, the mark at the anhedral break
(top-view aircraft centerline) should be 1/8
inch above the true fixture centerline (17/16
inches above the plans surface). The centersection
leading the TEs have no wing sweep
or taper, so there does not need to be a joint
in the fixture at the anhedral break.
Place the anhedral mark accordingly.
Then the marks at the dihedral breaks
(which do have a joint) are 5/16 inch lower
than the anhedral mark (11/8 inches above
the plans surface).
Mark the tips 3/8 inch higher than the
dihedral joint marks (11/2 inches above the
plans surface). By connecting these marks,
you have your centerline for rib placement
with anhedral and dihedral built in.
Centerlines are carefully placed on each
rib, and they can be glued in place on the
LE and TE by matching lines. Ribs can be
positioned accurately over the plans by
extending a line up from the plans onto the
LE and TE with a square.
Now the wing can be built in one piece.
You can remove it from the building surface
to facilitate control installation, etc. Just
make sure it is pinned flat while you are
gluing all sheeting and capstrips.
The wing should lay flat up or down
with all feet touching the work surface
without being forced. If it lays flat one way
but not the other, the work surface may be
untrue or your fixture ends are unequal in
height.
If the wing warps when off the work
surface, there will be a consistent imbalance
in the up and down position. After
thoroughly checking, pin it down and finish
sheeting it. Whichever the case, determine
the problem and correct it.
This system will show you any errors. If
you use it properly, you cannot build an
untrue wing. When completely sheeted and
capped, remove the excess fixture material
and shape the LE and TE. You may need to
read the section about wing construction
several times while referring to the plans
and photos to make complete sense of it.
Control System: The control system requires
split flap horns. I used a Tom Morris flap
horn for the right flap with the left side cut
off. Only this horn is connected to the
bellcrank. It is also connected through the 1-
inch hole to the elevator horn, which is a
Morris adjustable set for 45°, when the flap is
at 37°.
A Tom Morris 1-inch elevator horn is
used for the left flap with the right side cut
off. A pushrod connects it as a soldered Y
joint to the elevator pushrod roughly 10
inches back. There is no play, rotational
inaccuracy, or differential using this setup.
The outer flaps are slaved by a 1/16-inchdiameter
music-wire pin that enters the
female receptacle (Du-Bro threaded brass
connector). The female end is installed first,
approximately two-thirds of the way back
from the hinge line.
Carefully start a pilot hole with a straight
pin, and then use progressively larger drill
bits, turning them with your fingertips. This
allows you to make precise adjustments.
The connector will require a stepped hole
to fit properly and tight. Before pressing it in
place, make pinholes in the flap surface to
wick in cyanoacrylate glue. Adhere this after
it is in place. Temporarily mount the flaps
with strong-tack masking tape, to simulate
cloth hinges. Carefully mark the male pin’s
position, and then inset it in the same manner
as you did the female, but do not glue.
The gap between the flaps is a strong 1/16
inch, but it must bevel to approximately 5/32
inch at the rear to accommodate up
movement. In neutral, the pin must enter the
brass receptacle by roughly 5/32 inch. Neutral
fit should be perfect. Sand the flap LEs
slightly, if needed for adjustments.
Test for up and down with your tape
hinges tightly in place. They will bind
because of the geometry involved. Use a drill
bit to slightly oval the mouth of the brass
coupler to the front and rear. Remove the
male pin, and slightly bevel and round the
bottom and rear of its end. Reinstall and test.
Close observation will show you where to
make small changes until it is right. If you
mess up, make a new pin. Be patient; this is
work, but not as much as a 32-coat paint job.
When you are sure it is right, glue the flap
in with cyanoacrylate. As a precaution, dig a
trench in the bottom of the flap and expose
part of the pin, and fill the trench with epoxy
flush to the surface. This will ensure that the
pin will not loosen with time. (Something I
did not do and now need to.)
Permanently mount the flaps with Tom
Morris Dacron hinges, which will allow more
freedom of movement. It also allows for
slight inaccuracy in the male and female
parts.
Fuselage: The main fuselage sides should be
medium-weight, firm-grain 3/32 balsa. Thicker
wood is unnecessary. Smaller airplanes use
1/2-inch-thick material, because they are not
as tall in profile. There is a lot of wood here
as long as it is kept rigid; think in terms of
trusses and I-Beams.
The engine mounts are offset 1/16 inch to
the inboard side. This allows side thrust and
still puts the spinner at the centerline. The 1/2-
inch square stabilizer center TE edge is hard
balsa. All the rest is light contest balsa.
The radius of the fin LE is offset slightly,
to direct more air on the inboard side. The fin
is glued in place with the LE offset 1/32 inch
inboard. The rudder is offset to the outboard
3/32 inch and the scale trim tab is offset a
“bunch.”
The landing-gear legs and their composite
trunion mount (taken from a set of B&D
retracts) were inset into a plywood pocket
mounted in the wing. A piece of 1/16 plywood
angled from the back of the top spar to the
front of the bottom spar forms the back wall
of this pocket and doubles as shear webbing
for the wing.
The wing center spars should be spruce
or bass. The axles fall just below the LE, and
the gear extends 41/4 inches from wing to
axle. A traditional torsion gear and block may
be used. I like this better.
Finish: Light, light, light! The entire bare
Heinkel was painted with one coat of
AeroGloss clear. I painted 1/2-ounce glass
cloth on the fuselage, with finishing resin
thinned 50% with denatured alcohol. When
cured, I applied a second coat to fill the pores.
Then I sanded until the cloth’s surface was
cut.
I covered all open surfaces with Polyspan
filled with three coats of AeroGloss clear.
Chart tape simulates the scale panel lines. I
applied one generous coat of Perfect Primer
and then removed the chart tape to give the
panel lines depth. Then I applied two coats of
scale-accurate Perfect military flat. Except for
markings, that’s it. The He 100D is extremely
light and scale.
If I haven’t upset anyone yet, I may now.
The rule book stipulates that the airplane be
judged for perfection of appearance; nowhere
does it mention a high-gloss mirror finish. As
much as I loved those mirror finishes, an
accurate military finish on a warbird should
score as well as a nonrealistic high gloss. In
this case, weight and scale appearance enter
the equation.
I thank the following: John Florio
(deceased), for being my mentor in the early
years; Dave Gatewood (deceased), for getting
me back into Stunt and his support during this
project’s design and building phases; Jack
Sheeks, for his support in test-flying and
encouragement to publish the design; and
Bob Hunt for being open-minded and
enthusiastic after test-flying the prototype.
Good luck with your Heinkel. Please call
or write if you have questions or comments; I
don’t have a computer, so I rarely check Email.
MA
Daniel L Grotzinger
6710 Greenshire Dr.
Indianapolis IN 46220
(317) 585-4808
[email protected]
Sources:
Tom Morris Accessories:
J & J Hobbies—Control Line Central
(505) 332-8007
www.clcentral.com
B&D Enterprises
(304) 753-4636
http://bdretracts.com
Edition: Model Aviation - 2009/01
Page Numbers: 28,29,30,31,32,33,34,36
Heinkel 100D Stunt
The inverted gull-shape wing is pronounced just enough to enhance
the scale appearance. Flap sizes and deflection ratios were carefully
considered.
The He 100D’s finish is left matte, with recessed panel lines.
Although designed for Stunt, the model’s outline is accurate enough
to warrant using authentic insignia.
THE HEINKEL HE 100D is a little-known,
seldom modeled aircraft that could have
become the mainstay of the Luftwaffe during
World War II. It was built as follow-up to the
He 112: Heinkel’s original design entry when
the Reich Air Ministry issued specifications
for a new fighter in 1935.
The He 100, sometimes designated “He
113,” was in many ways superior to the
Messerschmitt Me 109, which had initially
won the Reich Air Ministry’s competition
over the He 112. But Heinkel was not
awarded a production contract, mostly
because of politics. As with the Bell P-39,
there was little margin for weight-increasing
modifications.
For a short time, clipped-wing
preproduction model He 100V8 held an
absolute world speed record at 463.92 mph.
For more information, see Schiffer Military
History volume 52 and Aero Publishers
number 12.
You never forget your first love; that is
certainly true of my experience in model
aviation. I was an avid CL Precision
Aerobatics (Stunt) builder and flier from 1960
until 1966. During those formative years, I
devoured every article I could find about
aerodynamics, especially pertaining to Stunt
application.
During the next 30 years, I alternated
between activity and inactivity in CL and RC
because of military service, college, raising a
family, and work. However, I followed the
design articles—especially those by Al Rabe.
I agreed with the direction he was taking
Stunt design.
I learned about the He 100 while
researching for an RC Scale Focke-Wulf Fw
190D. Later I acquired a 1/5-scale He 100D
from Dennis Wann in Bryan, Ohio. I loved it
and kept thinking that it deserved to be made
an incarnation of a close-to-scale Stunter,
although that would be a challenge.
I got fired up and started drawing after the
2002 Nats. Then the balsa chips started
flying.
Large models fly better because of a
somewhat more favorable Reynolds number.
My bad shoulder did not want the pull of a
.60 engine, so I compromised on a .51, which
I already had. Rather than force a scale
appearance on a set of Stunt design numbers,
I worked backward. I altered scale threeviews
as little as possible to arrive at what my
instincts told me would work.
In relation to the fuselage, I redrew and
resized the wing many times. This resulted in
approximately a 10% enlargement, with a
slight chord widening and a modest decrease
in the outer panels’ taper. I retained the
inverted gull wing and split flaps to preserve
the aircraft’s essential character, although it
was obvious that it was going to present some
challenges.
I employed a Southwick Skylark airfoil
with the LE radius blunted to reduce pitch
sensitivity. The TE was shortened to fit my
planform, and that yielded a 22% airfoil less
flaps. At that point I had a 57.5-inch
wingspan with approximately 570 square
inches of area. Yikes! The model had a long
wing and a good airfoil, but not a lot of area.
More deviation from scale was
unacceptable, so I was going to have to
design my way around this problem. I kept
thinking, high-aspect-ratio wings are more
efficient, so why do Stunters have low aspect
ratios? From that point on, weight reduction
became Priority One.
No topic has generated more ink in Stunt
discussions than wing imbalance vs. tip
weight. Married to that is the issue of flap
differential, either through area or movement.
In a sharp corner, we want both wings
pitching equally without introducing yaw and
roll forces, which are difficult to trim out of
all maneuvers.
I don’t think the outboard wing generates
as much additional lift from moving in a
radius as some think. In a sharp turn, the need
for a clean pitch change completely overrides
the radius of the flight path. Most of the
traditionally used wing imbalance is actually
compensating for line weight and tug.
The Heinkel’s right outboard panel is
shortened by 5/8 inch, with 17/8 ounces of tip
weight, and the flaps are equal. This proved to
give clean squares and triangles in flighttesting.
The fuselage profile is scale, except for 1/4
inch that was shaved off the bottom of the
fuselage and 3/8 inch that has been removed
from the top of the fin. The fuselage width
was reduced 7/8 inch.
The stabilizer was enlarged but is not as
large as on most of today’s Stunters. I thought
it was unnecessary, because a long tail
movement requires less force for pitch
stability and pitch change. The elevator was
enlarged by borrowing area from the
stabilizer. The balances were retained for
scale effect.
I used 37° maximum flap deflection for
45° elevator deflection. I wanted to avoid
stalling the wing and losing airspeed in tight
turns but knew I needed to move that long tail
in a hurry.
A plus for the Heinkel is that the low
thrustline falls on the wing. Once I built a
T-Bird II to look like a Goodyear racer,
which lowered the thrustline to the wing.
It flew better.
A Stunter with warbird appeal that is outside the typical lines
I had a Sterling Spitfire that flew poorly. I
made a similar change, with remarkable
improvement. The engine, tank, and spinner
fall near the wing, giving a favorable vertical
CG in spite of the tall fuselage profile.
The He 100D employs a wide-blade,
large-diameter, low-pitch propeller (Graupner
12 x 5). This allows the airplane to fly at a
modest speed, but the wide center-section of
the wing and tail would get a large volume of
faster airflow and help compensate for a small
wing and long tail.
Slightly more than 1° of engine side thrust
was used to hold the Heinkel on the lines at a
lower speed in overhead maneuvers. Very
little rudder offset is used. I’m letting the
engine do the work for me, and I don’t
consider side thrust to be a loss of efficiency;
it doesn’t create the problems that flap
differential and rudder offset do.
Please realize that any airplane is an
aerodynamic package. Making any one of
these changes on an existing design may or
may not improve it. Together they have
worked well for the Heinkel He 100D Stunt.
CONSTRUCTION
This section will focus on important points
that differ from the usual. Because of closer
adherence to scale dimensions, weight and
alignment become especially important.
Wing: The wing’s construction uses 1/4 x 2
balsa sheet on edge over the plans, which
doubles as building fixture and LE and TE.
Hal deBolt pioneered this method. I refined
it by putting 5/16-inch “feet” on the top and
bottom of each end of the fixture pieces.
That makes it possible to use less than
straight wood without introducing stresses
when attempting to straighten it. Lines
drawn on the center of the width of the
fixture pieces from end to end used for rib
placement determine straightness.
Set a small adjustable square—to be
used as a gauge—to 25/8 inches, and sand all
the fixture ends to the same height. If this
was a typically flat Stunt wing, all lines
would be in the center at 15/16 inches from
the top and bottom edges. Those lines would
be drawn by connecting marks placed at
both ends and each fixture piece. These end
marks can be placed with better accuracy
using the adjustable square as a gauge.
To accommodate the anhedral and
dihedral, the mark at the anhedral break
(top-view aircraft centerline) should be 1/8
inch above the true fixture centerline (17/16
inches above the plans surface). The centersection
leading the TEs have no wing sweep
or taper, so there does not need to be a joint
in the fixture at the anhedral break.
Place the anhedral mark accordingly.
Then the marks at the dihedral breaks
(which do have a joint) are 5/16 inch lower
than the anhedral mark (11/8 inches above
the plans surface).
Mark the tips 3/8 inch higher than the
dihedral joint marks (11/2 inches above the
plans surface). By connecting these marks,
you have your centerline for rib placement
with anhedral and dihedral built in.
Centerlines are carefully placed on each
rib, and they can be glued in place on the
LE and TE by matching lines. Ribs can be
positioned accurately over the plans by
extending a line up from the plans onto the
LE and TE with a square.
Now the wing can be built in one piece.
You can remove it from the building surface
to facilitate control installation, etc. Just
make sure it is pinned flat while you are
gluing all sheeting and capstrips.
The wing should lay flat up or down
with all feet touching the work surface
without being forced. If it lays flat one way
but not the other, the work surface may be
untrue or your fixture ends are unequal in
height.
If the wing warps when off the work
surface, there will be a consistent imbalance
in the up and down position. After
thoroughly checking, pin it down and finish
sheeting it. Whichever the case, determine
the problem and correct it.
This system will show you any errors. If
you use it properly, you cannot build an
untrue wing. When completely sheeted and
capped, remove the excess fixture material
and shape the LE and TE. You may need to
read the section about wing construction
several times while referring to the plans
and photos to make complete sense of it.
Control System: The control system requires
split flap horns. I used a Tom Morris flap
horn for the right flap with the left side cut
off. Only this horn is connected to the
bellcrank. It is also connected through the 1-
inch hole to the elevator horn, which is a
Morris adjustable set for 45°, when the flap is
at 37°.
A Tom Morris 1-inch elevator horn is
used for the left flap with the right side cut
off. A pushrod connects it as a soldered Y
joint to the elevator pushrod roughly 10
inches back. There is no play, rotational
inaccuracy, or differential using this setup.
The outer flaps are slaved by a 1/16-inchdiameter
music-wire pin that enters the
female receptacle (Du-Bro threaded brass
connector). The female end is installed first,
approximately two-thirds of the way back
from the hinge line.
Carefully start a pilot hole with a straight
pin, and then use progressively larger drill
bits, turning them with your fingertips. This
allows you to make precise adjustments.
The connector will require a stepped hole
to fit properly and tight. Before pressing it in
place, make pinholes in the flap surface to
wick in cyanoacrylate glue. Adhere this after
it is in place. Temporarily mount the flaps
with strong-tack masking tape, to simulate
cloth hinges. Carefully mark the male pin’s
position, and then inset it in the same manner
as you did the female, but do not glue.
The gap between the flaps is a strong 1/16
inch, but it must bevel to approximately 5/32
inch at the rear to accommodate up
movement. In neutral, the pin must enter the
brass receptacle by roughly 5/32 inch. Neutral
fit should be perfect. Sand the flap LEs
slightly, if needed for adjustments.
Test for up and down with your tape
hinges tightly in place. They will bind
because of the geometry involved. Use a drill
bit to slightly oval the mouth of the brass
coupler to the front and rear. Remove the
male pin, and slightly bevel and round the
bottom and rear of its end. Reinstall and test.
Close observation will show you where to
make small changes until it is right. If you
mess up, make a new pin. Be patient; this is
work, but not as much as a 32-coat paint job.
When you are sure it is right, glue the flap
in with cyanoacrylate. As a precaution, dig a
trench in the bottom of the flap and expose
part of the pin, and fill the trench with epoxy
flush to the surface. This will ensure that the
pin will not loosen with time. (Something I
did not do and now need to.)
Permanently mount the flaps with Tom
Morris Dacron hinges, which will allow more
freedom of movement. It also allows for
slight inaccuracy in the male and female
parts.
Fuselage: The main fuselage sides should be
medium-weight, firm-grain 3/32 balsa. Thicker
wood is unnecessary. Smaller airplanes use
1/2-inch-thick material, because they are not
as tall in profile. There is a lot of wood here
as long as it is kept rigid; think in terms of
trusses and I-Beams.
The engine mounts are offset 1/16 inch to
the inboard side. This allows side thrust and
still puts the spinner at the centerline. The 1/2-
inch square stabilizer center TE edge is hard
balsa. All the rest is light contest balsa.
The radius of the fin LE is offset slightly,
to direct more air on the inboard side. The fin
is glued in place with the LE offset 1/32 inch
inboard. The rudder is offset to the outboard
3/32 inch and the scale trim tab is offset a
“bunch.”
The landing-gear legs and their composite
trunion mount (taken from a set of B&D
retracts) were inset into a plywood pocket
mounted in the wing. A piece of 1/16 plywood
angled from the back of the top spar to the
front of the bottom spar forms the back wall
of this pocket and doubles as shear webbing
for the wing.
The wing center spars should be spruce
or bass. The axles fall just below the LE, and
the gear extends 41/4 inches from wing to
axle. A traditional torsion gear and block may
be used. I like this better.
Finish: Light, light, light! The entire bare
Heinkel was painted with one coat of
AeroGloss clear. I painted 1/2-ounce glass
cloth on the fuselage, with finishing resin
thinned 50% with denatured alcohol. When
cured, I applied a second coat to fill the pores.
Then I sanded until the cloth’s surface was
cut.
I covered all open surfaces with Polyspan
filled with three coats of AeroGloss clear.
Chart tape simulates the scale panel lines. I
applied one generous coat of Perfect Primer
and then removed the chart tape to give the
panel lines depth. Then I applied two coats of
scale-accurate Perfect military flat. Except for
markings, that’s it. The He 100D is extremely
light and scale.
If I haven’t upset anyone yet, I may now.
The rule book stipulates that the airplane be
judged for perfection of appearance; nowhere
does it mention a high-gloss mirror finish. As
much as I loved those mirror finishes, an
accurate military finish on a warbird should
score as well as a nonrealistic high gloss. In
this case, weight and scale appearance enter
the equation.
I thank the following: John Florio
(deceased), for being my mentor in the early
years; Dave Gatewood (deceased), for getting
me back into Stunt and his support during this
project’s design and building phases; Jack
Sheeks, for his support in test-flying and
encouragement to publish the design; and
Bob Hunt for being open-minded and
enthusiastic after test-flying the prototype.
Good luck with your Heinkel. Please call
or write if you have questions or comments; I
don’t have a computer, so I rarely check Email.
MA
Daniel L Grotzinger
6710 Greenshire Dr.
Indianapolis IN 46220
(317) 585-4808
[email protected]
Sources:
Tom Morris Accessories:
J & J Hobbies—Control Line Central
(505) 332-8007
www.clcentral.com
B&D Enterprises
(304) 753-4636
http://bdretracts.com
Edition: Model Aviation - 2009/01
Page Numbers: 28,29,30,31,32,33,34,36
Heinkel 100D Stunt
The inverted gull-shape wing is pronounced just enough to enhance
the scale appearance. Flap sizes and deflection ratios were carefully
considered.
The He 100D’s finish is left matte, with recessed panel lines.
Although designed for Stunt, the model’s outline is accurate enough
to warrant using authentic insignia.
THE HEINKEL HE 100D is a little-known,
seldom modeled aircraft that could have
become the mainstay of the Luftwaffe during
World War II. It was built as follow-up to the
He 112: Heinkel’s original design entry when
the Reich Air Ministry issued specifications
for a new fighter in 1935.
The He 100, sometimes designated “He
113,” was in many ways superior to the
Messerschmitt Me 109, which had initially
won the Reich Air Ministry’s competition
over the He 112. But Heinkel was not
awarded a production contract, mostly
because of politics. As with the Bell P-39,
there was little margin for weight-increasing
modifications.
For a short time, clipped-wing
preproduction model He 100V8 held an
absolute world speed record at 463.92 mph.
For more information, see Schiffer Military
History volume 52 and Aero Publishers
number 12.
You never forget your first love; that is
certainly true of my experience in model
aviation. I was an avid CL Precision
Aerobatics (Stunt) builder and flier from 1960
until 1966. During those formative years, I
devoured every article I could find about
aerodynamics, especially pertaining to Stunt
application.
During the next 30 years, I alternated
between activity and inactivity in CL and RC
because of military service, college, raising a
family, and work. However, I followed the
design articles—especially those by Al Rabe.
I agreed with the direction he was taking
Stunt design.
I learned about the He 100 while
researching for an RC Scale Focke-Wulf Fw
190D. Later I acquired a 1/5-scale He 100D
from Dennis Wann in Bryan, Ohio. I loved it
and kept thinking that it deserved to be made
an incarnation of a close-to-scale Stunter,
although that would be a challenge.
I got fired up and started drawing after the
2002 Nats. Then the balsa chips started
flying.
Large models fly better because of a
somewhat more favorable Reynolds number.
My bad shoulder did not want the pull of a
.60 engine, so I compromised on a .51, which
I already had. Rather than force a scale
appearance on a set of Stunt design numbers,
I worked backward. I altered scale threeviews
as little as possible to arrive at what my
instincts told me would work.
In relation to the fuselage, I redrew and
resized the wing many times. This resulted in
approximately a 10% enlargement, with a
slight chord widening and a modest decrease
in the outer panels’ taper. I retained the
inverted gull wing and split flaps to preserve
the aircraft’s essential character, although it
was obvious that it was going to present some
challenges.
I employed a Southwick Skylark airfoil
with the LE radius blunted to reduce pitch
sensitivity. The TE was shortened to fit my
planform, and that yielded a 22% airfoil less
flaps. At that point I had a 57.5-inch
wingspan with approximately 570 square
inches of area. Yikes! The model had a long
wing and a good airfoil, but not a lot of area.
More deviation from scale was
unacceptable, so I was going to have to
design my way around this problem. I kept
thinking, high-aspect-ratio wings are more
efficient, so why do Stunters have low aspect
ratios? From that point on, weight reduction
became Priority One.
No topic has generated more ink in Stunt
discussions than wing imbalance vs. tip
weight. Married to that is the issue of flap
differential, either through area or movement.
In a sharp corner, we want both wings
pitching equally without introducing yaw and
roll forces, which are difficult to trim out of
all maneuvers.
I don’t think the outboard wing generates
as much additional lift from moving in a
radius as some think. In a sharp turn, the need
for a clean pitch change completely overrides
the radius of the flight path. Most of the
traditionally used wing imbalance is actually
compensating for line weight and tug.
The Heinkel’s right outboard panel is
shortened by 5/8 inch, with 17/8 ounces of tip
weight, and the flaps are equal. This proved to
give clean squares and triangles in flighttesting.
The fuselage profile is scale, except for 1/4
inch that was shaved off the bottom of the
fuselage and 3/8 inch that has been removed
from the top of the fin. The fuselage width
was reduced 7/8 inch.
The stabilizer was enlarged but is not as
large as on most of today’s Stunters. I thought
it was unnecessary, because a long tail
movement requires less force for pitch
stability and pitch change. The elevator was
enlarged by borrowing area from the
stabilizer. The balances were retained for
scale effect.
I used 37° maximum flap deflection for
45° elevator deflection. I wanted to avoid
stalling the wing and losing airspeed in tight
turns but knew I needed to move that long tail
in a hurry.
A plus for the Heinkel is that the low
thrustline falls on the wing. Once I built a
T-Bird II to look like a Goodyear racer,
which lowered the thrustline to the wing.
It flew better.
A Stunter with warbird appeal that is outside the typical lines
I had a Sterling Spitfire that flew poorly. I
made a similar change, with remarkable
improvement. The engine, tank, and spinner
fall near the wing, giving a favorable vertical
CG in spite of the tall fuselage profile.
The He 100D employs a wide-blade,
large-diameter, low-pitch propeller (Graupner
12 x 5). This allows the airplane to fly at a
modest speed, but the wide center-section of
the wing and tail would get a large volume of
faster airflow and help compensate for a small
wing and long tail.
Slightly more than 1° of engine side thrust
was used to hold the Heinkel on the lines at a
lower speed in overhead maneuvers. Very
little rudder offset is used. I’m letting the
engine do the work for me, and I don’t
consider side thrust to be a loss of efficiency;
it doesn’t create the problems that flap
differential and rudder offset do.
Please realize that any airplane is an
aerodynamic package. Making any one of
these changes on an existing design may or
may not improve it. Together they have
worked well for the Heinkel He 100D Stunt.
CONSTRUCTION
This section will focus on important points
that differ from the usual. Because of closer
adherence to scale dimensions, weight and
alignment become especially important.
Wing: The wing’s construction uses 1/4 x 2
balsa sheet on edge over the plans, which
doubles as building fixture and LE and TE.
Hal deBolt pioneered this method. I refined
it by putting 5/16-inch “feet” on the top and
bottom of each end of the fixture pieces.
That makes it possible to use less than
straight wood without introducing stresses
when attempting to straighten it. Lines
drawn on the center of the width of the
fixture pieces from end to end used for rib
placement determine straightness.
Set a small adjustable square—to be
used as a gauge—to 25/8 inches, and sand all
the fixture ends to the same height. If this
was a typically flat Stunt wing, all lines
would be in the center at 15/16 inches from
the top and bottom edges. Those lines would
be drawn by connecting marks placed at
both ends and each fixture piece. These end
marks can be placed with better accuracy
using the adjustable square as a gauge.
To accommodate the anhedral and
dihedral, the mark at the anhedral break
(top-view aircraft centerline) should be 1/8
inch above the true fixture centerline (17/16
inches above the plans surface). The centersection
leading the TEs have no wing sweep
or taper, so there does not need to be a joint
in the fixture at the anhedral break.
Place the anhedral mark accordingly.
Then the marks at the dihedral breaks
(which do have a joint) are 5/16 inch lower
than the anhedral mark (11/8 inches above
the plans surface).
Mark the tips 3/8 inch higher than the
dihedral joint marks (11/2 inches above the
plans surface). By connecting these marks,
you have your centerline for rib placement
with anhedral and dihedral built in.
Centerlines are carefully placed on each
rib, and they can be glued in place on the
LE and TE by matching lines. Ribs can be
positioned accurately over the plans by
extending a line up from the plans onto the
LE and TE with a square.
Now the wing can be built in one piece.
You can remove it from the building surface
to facilitate control installation, etc. Just
make sure it is pinned flat while you are
gluing all sheeting and capstrips.
The wing should lay flat up or down
with all feet touching the work surface
without being forced. If it lays flat one way
but not the other, the work surface may be
untrue or your fixture ends are unequal in
height.
If the wing warps when off the work
surface, there will be a consistent imbalance
in the up and down position. After
thoroughly checking, pin it down and finish
sheeting it. Whichever the case, determine
the problem and correct it.
This system will show you any errors. If
you use it properly, you cannot build an
untrue wing. When completely sheeted and
capped, remove the excess fixture material
and shape the LE and TE. You may need to
read the section about wing construction
several times while referring to the plans
and photos to make complete sense of it.
Control System: The control system requires
split flap horns. I used a Tom Morris flap
horn for the right flap with the left side cut
off. Only this horn is connected to the
bellcrank. It is also connected through the 1-
inch hole to the elevator horn, which is a
Morris adjustable set for 45°, when the flap is
at 37°.
A Tom Morris 1-inch elevator horn is
used for the left flap with the right side cut
off. A pushrod connects it as a soldered Y
joint to the elevator pushrod roughly 10
inches back. There is no play, rotational
inaccuracy, or differential using this setup.
The outer flaps are slaved by a 1/16-inchdiameter
music-wire pin that enters the
female receptacle (Du-Bro threaded brass
connector). The female end is installed first,
approximately two-thirds of the way back
from the hinge line.
Carefully start a pilot hole with a straight
pin, and then use progressively larger drill
bits, turning them with your fingertips. This
allows you to make precise adjustments.
The connector will require a stepped hole
to fit properly and tight. Before pressing it in
place, make pinholes in the flap surface to
wick in cyanoacrylate glue. Adhere this after
it is in place. Temporarily mount the flaps
with strong-tack masking tape, to simulate
cloth hinges. Carefully mark the male pin’s
position, and then inset it in the same manner
as you did the female, but do not glue.
The gap between the flaps is a strong 1/16
inch, but it must bevel to approximately 5/32
inch at the rear to accommodate up
movement. In neutral, the pin must enter the
brass receptacle by roughly 5/32 inch. Neutral
fit should be perfect. Sand the flap LEs
slightly, if needed for adjustments.
Test for up and down with your tape
hinges tightly in place. They will bind
because of the geometry involved. Use a drill
bit to slightly oval the mouth of the brass
coupler to the front and rear. Remove the
male pin, and slightly bevel and round the
bottom and rear of its end. Reinstall and test.
Close observation will show you where to
make small changes until it is right. If you
mess up, make a new pin. Be patient; this is
work, but not as much as a 32-coat paint job.
When you are sure it is right, glue the flap
in with cyanoacrylate. As a precaution, dig a
trench in the bottom of the flap and expose
part of the pin, and fill the trench with epoxy
flush to the surface. This will ensure that the
pin will not loosen with time. (Something I
did not do and now need to.)
Permanently mount the flaps with Tom
Morris Dacron hinges, which will allow more
freedom of movement. It also allows for
slight inaccuracy in the male and female
parts.
Fuselage: The main fuselage sides should be
medium-weight, firm-grain 3/32 balsa. Thicker
wood is unnecessary. Smaller airplanes use
1/2-inch-thick material, because they are not
as tall in profile. There is a lot of wood here
as long as it is kept rigid; think in terms of
trusses and I-Beams.
The engine mounts are offset 1/16 inch to
the inboard side. This allows side thrust and
still puts the spinner at the centerline. The 1/2-
inch square stabilizer center TE edge is hard
balsa. All the rest is light contest balsa.
The radius of the fin LE is offset slightly,
to direct more air on the inboard side. The fin
is glued in place with the LE offset 1/32 inch
inboard. The rudder is offset to the outboard
3/32 inch and the scale trim tab is offset a
“bunch.”
The landing-gear legs and their composite
trunion mount (taken from a set of B&D
retracts) were inset into a plywood pocket
mounted in the wing. A piece of 1/16 plywood
angled from the back of the top spar to the
front of the bottom spar forms the back wall
of this pocket and doubles as shear webbing
for the wing.
The wing center spars should be spruce
or bass. The axles fall just below the LE, and
the gear extends 41/4 inches from wing to
axle. A traditional torsion gear and block may
be used. I like this better.
Finish: Light, light, light! The entire bare
Heinkel was painted with one coat of
AeroGloss clear. I painted 1/2-ounce glass
cloth on the fuselage, with finishing resin
thinned 50% with denatured alcohol. When
cured, I applied a second coat to fill the pores.
Then I sanded until the cloth’s surface was
cut.
I covered all open surfaces with Polyspan
filled with three coats of AeroGloss clear.
Chart tape simulates the scale panel lines. I
applied one generous coat of Perfect Primer
and then removed the chart tape to give the
panel lines depth. Then I applied two coats of
scale-accurate Perfect military flat. Except for
markings, that’s it. The He 100D is extremely
light and scale.
If I haven’t upset anyone yet, I may now.
The rule book stipulates that the airplane be
judged for perfection of appearance; nowhere
does it mention a high-gloss mirror finish. As
much as I loved those mirror finishes, an
accurate military finish on a warbird should
score as well as a nonrealistic high gloss. In
this case, weight and scale appearance enter
the equation.
I thank the following: John Florio
(deceased), for being my mentor in the early
years; Dave Gatewood (deceased), for getting
me back into Stunt and his support during this
project’s design and building phases; Jack
Sheeks, for his support in test-flying and
encouragement to publish the design; and
Bob Hunt for being open-minded and
enthusiastic after test-flying the prototype.
Good luck with your Heinkel. Please call
or write if you have questions or comments; I
don’t have a computer, so I rarely check Email.
MA
Daniel L Grotzinger
6710 Greenshire Dr.
Indianapolis IN 46220
(317) 585-4808
[email protected]
Sources:
Tom Morris Accessories:
J & J Hobbies—Control Line Central
(505) 332-8007
www.clcentral.com
B&D Enterprises
(304) 753-4636
http://bdretracts.com
Edition: Model Aviation - 2009/01
Page Numbers: 28,29,30,31,32,33,34,36
Heinkel 100D Stunt
The inverted gull-shape wing is pronounced just enough to enhance
the scale appearance. Flap sizes and deflection ratios were carefully
considered.
The He 100D’s finish is left matte, with recessed panel lines.
Although designed for Stunt, the model’s outline is accurate enough
to warrant using authentic insignia.
THE HEINKEL HE 100D is a little-known,
seldom modeled aircraft that could have
become the mainstay of the Luftwaffe during
World War II. It was built as follow-up to the
He 112: Heinkel’s original design entry when
the Reich Air Ministry issued specifications
for a new fighter in 1935.
The He 100, sometimes designated “He
113,” was in many ways superior to the
Messerschmitt Me 109, which had initially
won the Reich Air Ministry’s competition
over the He 112. But Heinkel was not
awarded a production contract, mostly
because of politics. As with the Bell P-39,
there was little margin for weight-increasing
modifications.
For a short time, clipped-wing
preproduction model He 100V8 held an
absolute world speed record at 463.92 mph.
For more information, see Schiffer Military
History volume 52 and Aero Publishers
number 12.
You never forget your first love; that is
certainly true of my experience in model
aviation. I was an avid CL Precision
Aerobatics (Stunt) builder and flier from 1960
until 1966. During those formative years, I
devoured every article I could find about
aerodynamics, especially pertaining to Stunt
application.
During the next 30 years, I alternated
between activity and inactivity in CL and RC
because of military service, college, raising a
family, and work. However, I followed the
design articles—especially those by Al Rabe.
I agreed with the direction he was taking
Stunt design.
I learned about the He 100 while
researching for an RC Scale Focke-Wulf Fw
190D. Later I acquired a 1/5-scale He 100D
from Dennis Wann in Bryan, Ohio. I loved it
and kept thinking that it deserved to be made
an incarnation of a close-to-scale Stunter,
although that would be a challenge.
I got fired up and started drawing after the
2002 Nats. Then the balsa chips started
flying.
Large models fly better because of a
somewhat more favorable Reynolds number.
My bad shoulder did not want the pull of a
.60 engine, so I compromised on a .51, which
I already had. Rather than force a scale
appearance on a set of Stunt design numbers,
I worked backward. I altered scale threeviews
as little as possible to arrive at what my
instincts told me would work.
In relation to the fuselage, I redrew and
resized the wing many times. This resulted in
approximately a 10% enlargement, with a
slight chord widening and a modest decrease
in the outer panels’ taper. I retained the
inverted gull wing and split flaps to preserve
the aircraft’s essential character, although it
was obvious that it was going to present some
challenges.
I employed a Southwick Skylark airfoil
with the LE radius blunted to reduce pitch
sensitivity. The TE was shortened to fit my
planform, and that yielded a 22% airfoil less
flaps. At that point I had a 57.5-inch
wingspan with approximately 570 square
inches of area. Yikes! The model had a long
wing and a good airfoil, but not a lot of area.
More deviation from scale was
unacceptable, so I was going to have to
design my way around this problem. I kept
thinking, high-aspect-ratio wings are more
efficient, so why do Stunters have low aspect
ratios? From that point on, weight reduction
became Priority One.
No topic has generated more ink in Stunt
discussions than wing imbalance vs. tip
weight. Married to that is the issue of flap
differential, either through area or movement.
In a sharp corner, we want both wings
pitching equally without introducing yaw and
roll forces, which are difficult to trim out of
all maneuvers.
I don’t think the outboard wing generates
as much additional lift from moving in a
radius as some think. In a sharp turn, the need
for a clean pitch change completely overrides
the radius of the flight path. Most of the
traditionally used wing imbalance is actually
compensating for line weight and tug.
The Heinkel’s right outboard panel is
shortened by 5/8 inch, with 17/8 ounces of tip
weight, and the flaps are equal. This proved to
give clean squares and triangles in flighttesting.
The fuselage profile is scale, except for 1/4
inch that was shaved off the bottom of the
fuselage and 3/8 inch that has been removed
from the top of the fin. The fuselage width
was reduced 7/8 inch.
The stabilizer was enlarged but is not as
large as on most of today’s Stunters. I thought
it was unnecessary, because a long tail
movement requires less force for pitch
stability and pitch change. The elevator was
enlarged by borrowing area from the
stabilizer. The balances were retained for
scale effect.
I used 37° maximum flap deflection for
45° elevator deflection. I wanted to avoid
stalling the wing and losing airspeed in tight
turns but knew I needed to move that long tail
in a hurry.
A plus for the Heinkel is that the low
thrustline falls on the wing. Once I built a
T-Bird II to look like a Goodyear racer,
which lowered the thrustline to the wing.
It flew better.
A Stunter with warbird appeal that is outside the typical lines
I had a Sterling Spitfire that flew poorly. I
made a similar change, with remarkable
improvement. The engine, tank, and spinner
fall near the wing, giving a favorable vertical
CG in spite of the tall fuselage profile.
The He 100D employs a wide-blade,
large-diameter, low-pitch propeller (Graupner
12 x 5). This allows the airplane to fly at a
modest speed, but the wide center-section of
the wing and tail would get a large volume of
faster airflow and help compensate for a small
wing and long tail.
Slightly more than 1° of engine side thrust
was used to hold the Heinkel on the lines at a
lower speed in overhead maneuvers. Very
little rudder offset is used. I’m letting the
engine do the work for me, and I don’t
consider side thrust to be a loss of efficiency;
it doesn’t create the problems that flap
differential and rudder offset do.
Please realize that any airplane is an
aerodynamic package. Making any one of
these changes on an existing design may or
may not improve it. Together they have
worked well for the Heinkel He 100D Stunt.
CONSTRUCTION
This section will focus on important points
that differ from the usual. Because of closer
adherence to scale dimensions, weight and
alignment become especially important.
Wing: The wing’s construction uses 1/4 x 2
balsa sheet on edge over the plans, which
doubles as building fixture and LE and TE.
Hal deBolt pioneered this method. I refined
it by putting 5/16-inch “feet” on the top and
bottom of each end of the fixture pieces.
That makes it possible to use less than
straight wood without introducing stresses
when attempting to straighten it. Lines
drawn on the center of the width of the
fixture pieces from end to end used for rib
placement determine straightness.
Set a small adjustable square—to be
used as a gauge—to 25/8 inches, and sand all
the fixture ends to the same height. If this
was a typically flat Stunt wing, all lines
would be in the center at 15/16 inches from
the top and bottom edges. Those lines would
be drawn by connecting marks placed at
both ends and each fixture piece. These end
marks can be placed with better accuracy
using the adjustable square as a gauge.
To accommodate the anhedral and
dihedral, the mark at the anhedral break
(top-view aircraft centerline) should be 1/8
inch above the true fixture centerline (17/16
inches above the plans surface). The centersection
leading the TEs have no wing sweep
or taper, so there does not need to be a joint
in the fixture at the anhedral break.
Place the anhedral mark accordingly.
Then the marks at the dihedral breaks
(which do have a joint) are 5/16 inch lower
than the anhedral mark (11/8 inches above
the plans surface).
Mark the tips 3/8 inch higher than the
dihedral joint marks (11/2 inches above the
plans surface). By connecting these marks,
you have your centerline for rib placement
with anhedral and dihedral built in.
Centerlines are carefully placed on each
rib, and they can be glued in place on the
LE and TE by matching lines. Ribs can be
positioned accurately over the plans by
extending a line up from the plans onto the
LE and TE with a square.
Now the wing can be built in one piece.
You can remove it from the building surface
to facilitate control installation, etc. Just
make sure it is pinned flat while you are
gluing all sheeting and capstrips.
The wing should lay flat up or down
with all feet touching the work surface
without being forced. If it lays flat one way
but not the other, the work surface may be
untrue or your fixture ends are unequal in
height.
If the wing warps when off the work
surface, there will be a consistent imbalance
in the up and down position. After
thoroughly checking, pin it down and finish
sheeting it. Whichever the case, determine
the problem and correct it.
This system will show you any errors. If
you use it properly, you cannot build an
untrue wing. When completely sheeted and
capped, remove the excess fixture material
and shape the LE and TE. You may need to
read the section about wing construction
several times while referring to the plans
and photos to make complete sense of it.
Control System: The control system requires
split flap horns. I used a Tom Morris flap
horn for the right flap with the left side cut
off. Only this horn is connected to the
bellcrank. It is also connected through the 1-
inch hole to the elevator horn, which is a
Morris adjustable set for 45°, when the flap is
at 37°.
A Tom Morris 1-inch elevator horn is
used for the left flap with the right side cut
off. A pushrod connects it as a soldered Y
joint to the elevator pushrod roughly 10
inches back. There is no play, rotational
inaccuracy, or differential using this setup.
The outer flaps are slaved by a 1/16-inchdiameter
music-wire pin that enters the
female receptacle (Du-Bro threaded brass
connector). The female end is installed first,
approximately two-thirds of the way back
from the hinge line.
Carefully start a pilot hole with a straight
pin, and then use progressively larger drill
bits, turning them with your fingertips. This
allows you to make precise adjustments.
The connector will require a stepped hole
to fit properly and tight. Before pressing it in
place, make pinholes in the flap surface to
wick in cyanoacrylate glue. Adhere this after
it is in place. Temporarily mount the flaps
with strong-tack masking tape, to simulate
cloth hinges. Carefully mark the male pin’s
position, and then inset it in the same manner
as you did the female, but do not glue.
The gap between the flaps is a strong 1/16
inch, but it must bevel to approximately 5/32
inch at the rear to accommodate up
movement. In neutral, the pin must enter the
brass receptacle by roughly 5/32 inch. Neutral
fit should be perfect. Sand the flap LEs
slightly, if needed for adjustments.
Test for up and down with your tape
hinges tightly in place. They will bind
because of the geometry involved. Use a drill
bit to slightly oval the mouth of the brass
coupler to the front and rear. Remove the
male pin, and slightly bevel and round the
bottom and rear of its end. Reinstall and test.
Close observation will show you where to
make small changes until it is right. If you
mess up, make a new pin. Be patient; this is
work, but not as much as a 32-coat paint job.
When you are sure it is right, glue the flap
in with cyanoacrylate. As a precaution, dig a
trench in the bottom of the flap and expose
part of the pin, and fill the trench with epoxy
flush to the surface. This will ensure that the
pin will not loosen with time. (Something I
did not do and now need to.)
Permanently mount the flaps with Tom
Morris Dacron hinges, which will allow more
freedom of movement. It also allows for
slight inaccuracy in the male and female
parts.
Fuselage: The main fuselage sides should be
medium-weight, firm-grain 3/32 balsa. Thicker
wood is unnecessary. Smaller airplanes use
1/2-inch-thick material, because they are not
as tall in profile. There is a lot of wood here
as long as it is kept rigid; think in terms of
trusses and I-Beams.
The engine mounts are offset 1/16 inch to
the inboard side. This allows side thrust and
still puts the spinner at the centerline. The 1/2-
inch square stabilizer center TE edge is hard
balsa. All the rest is light contest balsa.
The radius of the fin LE is offset slightly,
to direct more air on the inboard side. The fin
is glued in place with the LE offset 1/32 inch
inboard. The rudder is offset to the outboard
3/32 inch and the scale trim tab is offset a
“bunch.”
The landing-gear legs and their composite
trunion mount (taken from a set of B&D
retracts) were inset into a plywood pocket
mounted in the wing. A piece of 1/16 plywood
angled from the back of the top spar to the
front of the bottom spar forms the back wall
of this pocket and doubles as shear webbing
for the wing.
The wing center spars should be spruce
or bass. The axles fall just below the LE, and
the gear extends 41/4 inches from wing to
axle. A traditional torsion gear and block may
be used. I like this better.
Finish: Light, light, light! The entire bare
Heinkel was painted with one coat of
AeroGloss clear. I painted 1/2-ounce glass
cloth on the fuselage, with finishing resin
thinned 50% with denatured alcohol. When
cured, I applied a second coat to fill the pores.
Then I sanded until the cloth’s surface was
cut.
I covered all open surfaces with Polyspan
filled with three coats of AeroGloss clear.
Chart tape simulates the scale panel lines. I
applied one generous coat of Perfect Primer
and then removed the chart tape to give the
panel lines depth. Then I applied two coats of
scale-accurate Perfect military flat. Except for
markings, that’s it. The He 100D is extremely
light and scale.
If I haven’t upset anyone yet, I may now.
The rule book stipulates that the airplane be
judged for perfection of appearance; nowhere
does it mention a high-gloss mirror finish. As
much as I loved those mirror finishes, an
accurate military finish on a warbird should
score as well as a nonrealistic high gloss. In
this case, weight and scale appearance enter
the equation.
I thank the following: John Florio
(deceased), for being my mentor in the early
years; Dave Gatewood (deceased), for getting
me back into Stunt and his support during this
project’s design and building phases; Jack
Sheeks, for his support in test-flying and
encouragement to publish the design; and
Bob Hunt for being open-minded and
enthusiastic after test-flying the prototype.
Good luck with your Heinkel. Please call
or write if you have questions or comments; I
don’t have a computer, so I rarely check Email.
MA
Daniel L Grotzinger
6710 Greenshire Dr.
Indianapolis IN 46220
(317) 585-4808
[email protected]
Sources:
Tom Morris Accessories:
J & J Hobbies—Control Line Central
(505) 332-8007
www.clcentral.com
B&D Enterprises
(304) 753-4636
http://bdretracts.com
Edition: Model Aviation - 2009/01
Page Numbers: 28,29,30,31,32,33,34,36
Heinkel 100D Stunt
The inverted gull-shape wing is pronounced just enough to enhance
the scale appearance. Flap sizes and deflection ratios were carefully
considered.
The He 100D’s finish is left matte, with recessed panel lines.
Although designed for Stunt, the model’s outline is accurate enough
to warrant using authentic insignia.
THE HEINKEL HE 100D is a little-known,
seldom modeled aircraft that could have
become the mainstay of the Luftwaffe during
World War II. It was built as follow-up to the
He 112: Heinkel’s original design entry when
the Reich Air Ministry issued specifications
for a new fighter in 1935.
The He 100, sometimes designated “He
113,” was in many ways superior to the
Messerschmitt Me 109, which had initially
won the Reich Air Ministry’s competition
over the He 112. But Heinkel was not
awarded a production contract, mostly
because of politics. As with the Bell P-39,
there was little margin for weight-increasing
modifications.
For a short time, clipped-wing
preproduction model He 100V8 held an
absolute world speed record at 463.92 mph.
For more information, see Schiffer Military
History volume 52 and Aero Publishers
number 12.
You never forget your first love; that is
certainly true of my experience in model
aviation. I was an avid CL Precision
Aerobatics (Stunt) builder and flier from 1960
until 1966. During those formative years, I
devoured every article I could find about
aerodynamics, especially pertaining to Stunt
application.
During the next 30 years, I alternated
between activity and inactivity in CL and RC
because of military service, college, raising a
family, and work. However, I followed the
design articles—especially those by Al Rabe.
I agreed with the direction he was taking
Stunt design.
I learned about the He 100 while
researching for an RC Scale Focke-Wulf Fw
190D. Later I acquired a 1/5-scale He 100D
from Dennis Wann in Bryan, Ohio. I loved it
and kept thinking that it deserved to be made
an incarnation of a close-to-scale Stunter,
although that would be a challenge.
I got fired up and started drawing after the
2002 Nats. Then the balsa chips started
flying.
Large models fly better because of a
somewhat more favorable Reynolds number.
My bad shoulder did not want the pull of a
.60 engine, so I compromised on a .51, which
I already had. Rather than force a scale
appearance on a set of Stunt design numbers,
I worked backward. I altered scale threeviews
as little as possible to arrive at what my
instincts told me would work.
In relation to the fuselage, I redrew and
resized the wing many times. This resulted in
approximately a 10% enlargement, with a
slight chord widening and a modest decrease
in the outer panels’ taper. I retained the
inverted gull wing and split flaps to preserve
the aircraft’s essential character, although it
was obvious that it was going to present some
challenges.
I employed a Southwick Skylark airfoil
with the LE radius blunted to reduce pitch
sensitivity. The TE was shortened to fit my
planform, and that yielded a 22% airfoil less
flaps. At that point I had a 57.5-inch
wingspan with approximately 570 square
inches of area. Yikes! The model had a long
wing and a good airfoil, but not a lot of area.
More deviation from scale was
unacceptable, so I was going to have to
design my way around this problem. I kept
thinking, high-aspect-ratio wings are more
efficient, so why do Stunters have low aspect
ratios? From that point on, weight reduction
became Priority One.
No topic has generated more ink in Stunt
discussions than wing imbalance vs. tip
weight. Married to that is the issue of flap
differential, either through area or movement.
In a sharp corner, we want both wings
pitching equally without introducing yaw and
roll forces, which are difficult to trim out of
all maneuvers.
I don’t think the outboard wing generates
as much additional lift from moving in a
radius as some think. In a sharp turn, the need
for a clean pitch change completely overrides
the radius of the flight path. Most of the
traditionally used wing imbalance is actually
compensating for line weight and tug.
The Heinkel’s right outboard panel is
shortened by 5/8 inch, with 17/8 ounces of tip
weight, and the flaps are equal. This proved to
give clean squares and triangles in flighttesting.
The fuselage profile is scale, except for 1/4
inch that was shaved off the bottom of the
fuselage and 3/8 inch that has been removed
from the top of the fin. The fuselage width
was reduced 7/8 inch.
The stabilizer was enlarged but is not as
large as on most of today’s Stunters. I thought
it was unnecessary, because a long tail
movement requires less force for pitch
stability and pitch change. The elevator was
enlarged by borrowing area from the
stabilizer. The balances were retained for
scale effect.
I used 37° maximum flap deflection for
45° elevator deflection. I wanted to avoid
stalling the wing and losing airspeed in tight
turns but knew I needed to move that long tail
in a hurry.
A plus for the Heinkel is that the low
thrustline falls on the wing. Once I built a
T-Bird II to look like a Goodyear racer,
which lowered the thrustline to the wing.
It flew better.
A Stunter with warbird appeal that is outside the typical lines
I had a Sterling Spitfire that flew poorly. I
made a similar change, with remarkable
improvement. The engine, tank, and spinner
fall near the wing, giving a favorable vertical
CG in spite of the tall fuselage profile.
The He 100D employs a wide-blade,
large-diameter, low-pitch propeller (Graupner
12 x 5). This allows the airplane to fly at a
modest speed, but the wide center-section of
the wing and tail would get a large volume of
faster airflow and help compensate for a small
wing and long tail.
Slightly more than 1° of engine side thrust
was used to hold the Heinkel on the lines at a
lower speed in overhead maneuvers. Very
little rudder offset is used. I’m letting the
engine do the work for me, and I don’t
consider side thrust to be a loss of efficiency;
it doesn’t create the problems that flap
differential and rudder offset do.
Please realize that any airplane is an
aerodynamic package. Making any one of
these changes on an existing design may or
may not improve it. Together they have
worked well for the Heinkel He 100D Stunt.
CONSTRUCTION
This section will focus on important points
that differ from the usual. Because of closer
adherence to scale dimensions, weight and
alignment become especially important.
Wing: The wing’s construction uses 1/4 x 2
balsa sheet on edge over the plans, which
doubles as building fixture and LE and TE.
Hal deBolt pioneered this method. I refined
it by putting 5/16-inch “feet” on the top and
bottom of each end of the fixture pieces.
That makes it possible to use less than
straight wood without introducing stresses
when attempting to straighten it. Lines
drawn on the center of the width of the
fixture pieces from end to end used for rib
placement determine straightness.
Set a small adjustable square—to be
used as a gauge—to 25/8 inches, and sand all
the fixture ends to the same height. If this
was a typically flat Stunt wing, all lines
would be in the center at 15/16 inches from
the top and bottom edges. Those lines would
be drawn by connecting marks placed at
both ends and each fixture piece. These end
marks can be placed with better accuracy
using the adjustable square as a gauge.
To accommodate the anhedral and
dihedral, the mark at the anhedral break
(top-view aircraft centerline) should be 1/8
inch above the true fixture centerline (17/16
inches above the plans surface). The centersection
leading the TEs have no wing sweep
or taper, so there does not need to be a joint
in the fixture at the anhedral break.
Place the anhedral mark accordingly.
Then the marks at the dihedral breaks
(which do have a joint) are 5/16 inch lower
than the anhedral mark (11/8 inches above
the plans surface).
Mark the tips 3/8 inch higher than the
dihedral joint marks (11/2 inches above the
plans surface). By connecting these marks,
you have your centerline for rib placement
with anhedral and dihedral built in.
Centerlines are carefully placed on each
rib, and they can be glued in place on the
LE and TE by matching lines. Ribs can be
positioned accurately over the plans by
extending a line up from the plans onto the
LE and TE with a square.
Now the wing can be built in one piece.
You can remove it from the building surface
to facilitate control installation, etc. Just
make sure it is pinned flat while you are
gluing all sheeting and capstrips.
The wing should lay flat up or down
with all feet touching the work surface
without being forced. If it lays flat one way
but not the other, the work surface may be
untrue or your fixture ends are unequal in
height.
If the wing warps when off the work
surface, there will be a consistent imbalance
in the up and down position. After
thoroughly checking, pin it down and finish
sheeting it. Whichever the case, determine
the problem and correct it.
This system will show you any errors. If
you use it properly, you cannot build an
untrue wing. When completely sheeted and
capped, remove the excess fixture material
and shape the LE and TE. You may need to
read the section about wing construction
several times while referring to the plans
and photos to make complete sense of it.
Control System: The control system requires
split flap horns. I used a Tom Morris flap
horn for the right flap with the left side cut
off. Only this horn is connected to the
bellcrank. It is also connected through the 1-
inch hole to the elevator horn, which is a
Morris adjustable set for 45°, when the flap is
at 37°.
A Tom Morris 1-inch elevator horn is
used for the left flap with the right side cut
off. A pushrod connects it as a soldered Y
joint to the elevator pushrod roughly 10
inches back. There is no play, rotational
inaccuracy, or differential using this setup.
The outer flaps are slaved by a 1/16-inchdiameter
music-wire pin that enters the
female receptacle (Du-Bro threaded brass
connector). The female end is installed first,
approximately two-thirds of the way back
from the hinge line.
Carefully start a pilot hole with a straight
pin, and then use progressively larger drill
bits, turning them with your fingertips. This
allows you to make precise adjustments.
The connector will require a stepped hole
to fit properly and tight. Before pressing it in
place, make pinholes in the flap surface to
wick in cyanoacrylate glue. Adhere this after
it is in place. Temporarily mount the flaps
with strong-tack masking tape, to simulate
cloth hinges. Carefully mark the male pin’s
position, and then inset it in the same manner
as you did the female, but do not glue.
The gap between the flaps is a strong 1/16
inch, but it must bevel to approximately 5/32
inch at the rear to accommodate up
movement. In neutral, the pin must enter the
brass receptacle by roughly 5/32 inch. Neutral
fit should be perfect. Sand the flap LEs
slightly, if needed for adjustments.
Test for up and down with your tape
hinges tightly in place. They will bind
because of the geometry involved. Use a drill
bit to slightly oval the mouth of the brass
coupler to the front and rear. Remove the
male pin, and slightly bevel and round the
bottom and rear of its end. Reinstall and test.
Close observation will show you where to
make small changes until it is right. If you
mess up, make a new pin. Be patient; this is
work, but not as much as a 32-coat paint job.
When you are sure it is right, glue the flap
in with cyanoacrylate. As a precaution, dig a
trench in the bottom of the flap and expose
part of the pin, and fill the trench with epoxy
flush to the surface. This will ensure that the
pin will not loosen with time. (Something I
did not do and now need to.)
Permanently mount the flaps with Tom
Morris Dacron hinges, which will allow more
freedom of movement. It also allows for
slight inaccuracy in the male and female
parts.
Fuselage: The main fuselage sides should be
medium-weight, firm-grain 3/32 balsa. Thicker
wood is unnecessary. Smaller airplanes use
1/2-inch-thick material, because they are not
as tall in profile. There is a lot of wood here
as long as it is kept rigid; think in terms of
trusses and I-Beams.
The engine mounts are offset 1/16 inch to
the inboard side. This allows side thrust and
still puts the spinner at the centerline. The 1/2-
inch square stabilizer center TE edge is hard
balsa. All the rest is light contest balsa.
The radius of the fin LE is offset slightly,
to direct more air on the inboard side. The fin
is glued in place with the LE offset 1/32 inch
inboard. The rudder is offset to the outboard
3/32 inch and the scale trim tab is offset a
“bunch.”
The landing-gear legs and their composite
trunion mount (taken from a set of B&D
retracts) were inset into a plywood pocket
mounted in the wing. A piece of 1/16 plywood
angled from the back of the top spar to the
front of the bottom spar forms the back wall
of this pocket and doubles as shear webbing
for the wing.
The wing center spars should be spruce
or bass. The axles fall just below the LE, and
the gear extends 41/4 inches from wing to
axle. A traditional torsion gear and block may
be used. I like this better.
Finish: Light, light, light! The entire bare
Heinkel was painted with one coat of
AeroGloss clear. I painted 1/2-ounce glass
cloth on the fuselage, with finishing resin
thinned 50% with denatured alcohol. When
cured, I applied a second coat to fill the pores.
Then I sanded until the cloth’s surface was
cut.
I covered all open surfaces with Polyspan
filled with three coats of AeroGloss clear.
Chart tape simulates the scale panel lines. I
applied one generous coat of Perfect Primer
and then removed the chart tape to give the
panel lines depth. Then I applied two coats of
scale-accurate Perfect military flat. Except for
markings, that’s it. The He 100D is extremely
light and scale.
If I haven’t upset anyone yet, I may now.
The rule book stipulates that the airplane be
judged for perfection of appearance; nowhere
does it mention a high-gloss mirror finish. As
much as I loved those mirror finishes, an
accurate military finish on a warbird should
score as well as a nonrealistic high gloss. In
this case, weight and scale appearance enter
the equation.
I thank the following: John Florio
(deceased), for being my mentor in the early
years; Dave Gatewood (deceased), for getting
me back into Stunt and his support during this
project’s design and building phases; Jack
Sheeks, for his support in test-flying and
encouragement to publish the design; and
Bob Hunt for being open-minded and
enthusiastic after test-flying the prototype.
Good luck with your Heinkel. Please call
or write if you have questions or comments; I
don’t have a computer, so I rarely check Email.
MA
Daniel L Grotzinger
6710 Greenshire Dr.
Indianapolis IN 46220
(317) 585-4808
[email protected]
Sources:
Tom Morris Accessories:
J & J Hobbies—Control Line Central
(505) 332-8007
www.clcentral.com
B&D Enterprises
(304) 753-4636
http://bdretracts.com