IN THE LAST column, I discussed a few of the many reasons to
consider electric power for CL Precision Aerobatics (Stunt)
competition. I’m sold on the concept to the point where I’ve sold
all of my competition glow engines, pipes and headers, and glow
propellers. I have kept my Classic and Old Time Stunt glow
engines, however, because I don’t believe in flying these vintage
events using electric power.
My first experience with competition-level electric aerobatic
flight was, as I described last time, the installation of an AXI
2826-10 motor into my formerly glow-powered Genesis Extreme.
We simply gutted the maple engine mounts from the nose using a
hand grinder fitted with a Perma-Grit sanding drum. There was
lots of smoke and a weird smell ...
Dean Pappas and I decided to install a vertical motor-mount
plate that would allow us to use the rear-mounting scheme with
the AXi and install a propeller adapter on the bell of the motor.
This worked okay, but in time we learned that the precessive loads
imposed by the propeller caused the rear bearing mount to fail.
After 70-90 flights, the bearing started to spin in its mount.
When that happened, a shrill howl was emitted, canceling out the
whole noise-reduction concept—not to mention that the motor
was then useless. I don’t know about you, but I want significantly
more than 70-90 flights from a motor.
We lived with this for a short while, as I decided to try out for
the 2006 US F2B
(FAI Stunt) team a
few weeks after
making the switch.
Immediately before
leaving for the
Team Selection that
year, a bearing
started to spin and howl.
I installed a new motor before leaving for the Team Trials and
used it in practice. Then I changed the motor again the evening
before the contest started, just to be sure.
I admit that at that time we didn’t confess to anyone the
problem we had discovered. We were almost sure we could solve
it quickly.
Real life got in the way of development for quite awhile, and I
actually went to the 2006 F2B World Championship in Spain in
2006 with the original motor-mount setup—and many spare
motors. After that contest, real life stayed in the way for a while
longer. Then finally, the internal bell went “ding.” It was time to
fix this problem.
Dean sent me some photos he found on the Internet of a
stamped sheet-metal cradle that allows an outrunner motor to be
mounted with the stationary end forward and allows the shaft at
the rear to be supported by a bearing. It was robust and was made
for larger outrunner motors and use in large RC Aerobatics
(Pattern) models. It was beautiful, but it looked way too heavy for
our purposes.
I asked Dean if we could use this same basic concept but make
it much lighter. We kicked it around a lot and then realized that
we were overdesigning it; fancy alignment was not required.
An outrunner motor is built with a large bearing at the
stationary end and a second, smaller bearing at the end of a
tubular central pylon. That pylon flexes with the propeller’s
extreme gyroscopic loads, which loosens the smaller bearing.
In all fairness, the manufacturers never designed these bearing
Electric power for competition Stunt
[[email protected]]
Control Line Aerobatics Bob Hunt
Also included in this column:
• Scary-smooth motor mount
Buddy Wieder constructed a test bed unit to ensure that the
yoke-mounted rear-bearing-support idea would work on Bob
Hunt’s AXI 2826-10. It did!
The unit that was installed in the airplane was made by interlockmounting
the front and rear motor-mount formers to a baseplate
made from 1/8 light plywood.
The motor has been installed and the yoke bearing plate has been
bolted to the aft former. Notice the timer that is mounted to the
bottom of the 1/8 light-plywood plate.
November 2009 145
11sig5.QXD_00MSTRPG.QXD 9/24/09 3:56 PM Page 145
supports for Stunt maneuvering. Our RC
Pattern brethren learned that the supports
didn’t stand up to snap-roll loads either.
All we needed was a bearing to
support the aft end of the main shaft. The
propeller shaft would be supported by
bearings that were twice as far apart as
before.
Dean came up with the idea of using a
ball-bearing slip fit mounted into a
plywood yoke that could, in turn, be
bolted to a plywood fuselage former that
was glued in aft of the motor-mount bay.
The bearing would allow the shaft to
self-align top to bottom and side to side. It
would self-align, and the propeller shaft’s
bending loads would be supported in part
by the airframe.
There was no need for a front-to-aft
anchoring of the shaft where it passed
through this bearing, as it would float
axially, eliminating yet another precision
alignment step. Because we are lazy, we
mounted the rear bearing to the original
propeller-shaft adapter.
A ubiquitous skateboard-wheel bearing
was used—only a much better grade. It
required a small sleeve to be turned, to
make up the difference between the
propeller adapter OD and the bearing ID.
(Thank you, lathe-man Tom Hampshire.)
We made a test bed unit, to see if this
concept was feasible, before retrofitting
the Genesis Extreme for a second time.
Being short on time, I delegated this chore
to Buddy Wieder, who had flown the
Genesis Extreme when it was fitted with
the first electric setup, and he loved it. He
decided to use electric power in his new
Stunt model, so he was drafted into the
development program.
Buddy, who used to be a mechanicaldrawing
teacher, made some
measurements, drew gorgeous plans, and
quickly built the test bed unit pictured.
We installed a battery and the speed
control, bolted the unit to a sturdy table
outside, hit the switch, and ran.
The motor did its programmed spoolup
and jumped to flight-speed rpm. It was
scary smooth. We ran the test bed unit
dozens of times. Although we could not
approximate the maneuvering loads that a
model would experience during normal
pattern flight, we were convinced that it
would work perfectly in actual use.
Again, the Genesis Extreme’s nose
was gutted (with much less smoke and
smell this time, since we had only to
remove one plywood motor-mount
former) and prepared to accept a newconcept
front-end design. This time we
decided to make the battery accessible
from the top.
Not only would that allow me to
change the battery without turning the
model on its back between flights, but it
would also allow me to package the speed
control and the timer and all of the wires
in the airplane’s bottom block, below the
battery. This would clean up the look of
the installation a great deal.
It was decided to interlock the vertical
motor-mount plate and the rear yoke
mount former to a horizontal 1/8 lightplywood
plate. Using this process, we
could align everything outside the aircraft
and then simply line up the light-plywood
plate inside the front of the airplane to
two lines—one drawn on each plywood
doubler—that were parallel to the
centerline of the wing.
Once everything was aligned, the unit
could be tack-glued in place, to allow a
final alignment check, and then epoxied
permanently in place.
We did all of the preceding, and it
worked perfectly. And it was extremely
easy. It was much easier than installing
the traditional maple engine mounts in a
Stunt model’s nose. And the horizontal
plate, once glued in place, made the nose
area extremely rigid.
A new lower cowl block was carved
and fitted. The airscoop inlet at the front
of the cowl block was bifurcated (I’ve
always wanted to use that word in a
column) with balsa diverters, to allow
cooling air to get to the motor bay and the
battery compartment.
Before permanently gluing this block
to the Genesis, I mounted our new betatest
timer to the horizontal plate and cut
holes to allow access to it, for
programming and up-and-down rpm
(electronic needle valve) adjustment from
the right side of the model. The deadman’s
switch holes were cut below the
plate, and they exit on the left side of the
fuselage.
A new top block section was carved
and hollowed and fitted with hold-downs,
to allow it to be removed quickly. As I am
writing this, the nose is being refinished
and I should have finished shots of the
model in the next column—and a flight
report.
To be fair, others figured this out at the
same time we did. Crist Rigotti made a
sheet-metal version of the mount for use
in his new CL Profile Stunter.
You can find photos of the model and
installation and some discussion about it
on the Stunt Hangar online forum. You
will have to log in to that forum to access
the information. It is in the “Gettin’ All
AMPed Up” section. Find the “570
Electric Profile” thread; on page 2 of that
thread, see response #51. If you scroll
down from there, you will find a response
that shows our test bed unit as well.
If you would like to see more photos
of this system’s installation into my
Genesis Extreme as it progressed, please
e-mail me.
Till next time, fly Stunt! MA
Sources:
Stunt Hangar
(314) 774-8910
www.stunthangar.com
Precision Aerobatics Model Pilots’
Association
www.control-line.org
Edition: Model Aviation - 2009/11
Page Numbers: 145,146
Edition: Model Aviation - 2009/11
Page Numbers: 145,146
IN THE LAST column, I discussed a few of the many reasons to
consider electric power for CL Precision Aerobatics (Stunt)
competition. I’m sold on the concept to the point where I’ve sold
all of my competition glow engines, pipes and headers, and glow
propellers. I have kept my Classic and Old Time Stunt glow
engines, however, because I don’t believe in flying these vintage
events using electric power.
My first experience with competition-level electric aerobatic
flight was, as I described last time, the installation of an AXI
2826-10 motor into my formerly glow-powered Genesis Extreme.
We simply gutted the maple engine mounts from the nose using a
hand grinder fitted with a Perma-Grit sanding drum. There was
lots of smoke and a weird smell ...
Dean Pappas and I decided to install a vertical motor-mount
plate that would allow us to use the rear-mounting scheme with
the AXi and install a propeller adapter on the bell of the motor.
This worked okay, but in time we learned that the precessive loads
imposed by the propeller caused the rear bearing mount to fail.
After 70-90 flights, the bearing started to spin in its mount.
When that happened, a shrill howl was emitted, canceling out the
whole noise-reduction concept—not to mention that the motor
was then useless. I don’t know about you, but I want significantly
more than 70-90 flights from a motor.
We lived with this for a short while, as I decided to try out for
the 2006 US F2B
(FAI Stunt) team a
few weeks after
making the switch.
Immediately before
leaving for the
Team Selection that
year, a bearing
started to spin and howl.
I installed a new motor before leaving for the Team Trials and
used it in practice. Then I changed the motor again the evening
before the contest started, just to be sure.
I admit that at that time we didn’t confess to anyone the
problem we had discovered. We were almost sure we could solve
it quickly.
Real life got in the way of development for quite awhile, and I
actually went to the 2006 F2B World Championship in Spain in
2006 with the original motor-mount setup—and many spare
motors. After that contest, real life stayed in the way for a while
longer. Then finally, the internal bell went “ding.” It was time to
fix this problem.
Dean sent me some photos he found on the Internet of a
stamped sheet-metal cradle that allows an outrunner motor to be
mounted with the stationary end forward and allows the shaft at
the rear to be supported by a bearing. It was robust and was made
for larger outrunner motors and use in large RC Aerobatics
(Pattern) models. It was beautiful, but it looked way too heavy for
our purposes.
I asked Dean if we could use this same basic concept but make
it much lighter. We kicked it around a lot and then realized that
we were overdesigning it; fancy alignment was not required.
An outrunner motor is built with a large bearing at the
stationary end and a second, smaller bearing at the end of a
tubular central pylon. That pylon flexes with the propeller’s
extreme gyroscopic loads, which loosens the smaller bearing.
In all fairness, the manufacturers never designed these bearing
Electric power for competition Stunt
[[email protected]]
Control Line Aerobatics Bob Hunt
Also included in this column:
• Scary-smooth motor mount
Buddy Wieder constructed a test bed unit to ensure that the
yoke-mounted rear-bearing-support idea would work on Bob
Hunt’s AXI 2826-10. It did!
The unit that was installed in the airplane was made by interlockmounting
the front and rear motor-mount formers to a baseplate
made from 1/8 light plywood.
The motor has been installed and the yoke bearing plate has been
bolted to the aft former. Notice the timer that is mounted to the
bottom of the 1/8 light-plywood plate.
November 2009 145
11sig5.QXD_00MSTRPG.QXD 9/24/09 3:56 PM Page 145
supports for Stunt maneuvering. Our RC
Pattern brethren learned that the supports
didn’t stand up to snap-roll loads either.
All we needed was a bearing to
support the aft end of the main shaft. The
propeller shaft would be supported by
bearings that were twice as far apart as
before.
Dean came up with the idea of using a
ball-bearing slip fit mounted into a
plywood yoke that could, in turn, be
bolted to a plywood fuselage former that
was glued in aft of the motor-mount bay.
The bearing would allow the shaft to
self-align top to bottom and side to side. It
would self-align, and the propeller shaft’s
bending loads would be supported in part
by the airframe.
There was no need for a front-to-aft
anchoring of the shaft where it passed
through this bearing, as it would float
axially, eliminating yet another precision
alignment step. Because we are lazy, we
mounted the rear bearing to the original
propeller-shaft adapter.
A ubiquitous skateboard-wheel bearing
was used—only a much better grade. It
required a small sleeve to be turned, to
make up the difference between the
propeller adapter OD and the bearing ID.
(Thank you, lathe-man Tom Hampshire.)
We made a test bed unit, to see if this
concept was feasible, before retrofitting
the Genesis Extreme for a second time.
Being short on time, I delegated this chore
to Buddy Wieder, who had flown the
Genesis Extreme when it was fitted with
the first electric setup, and he loved it. He
decided to use electric power in his new
Stunt model, so he was drafted into the
development program.
Buddy, who used to be a mechanicaldrawing
teacher, made some
measurements, drew gorgeous plans, and
quickly built the test bed unit pictured.
We installed a battery and the speed
control, bolted the unit to a sturdy table
outside, hit the switch, and ran.
The motor did its programmed spoolup
and jumped to flight-speed rpm. It was
scary smooth. We ran the test bed unit
dozens of times. Although we could not
approximate the maneuvering loads that a
model would experience during normal
pattern flight, we were convinced that it
would work perfectly in actual use.
Again, the Genesis Extreme’s nose
was gutted (with much less smoke and
smell this time, since we had only to
remove one plywood motor-mount
former) and prepared to accept a newconcept
front-end design. This time we
decided to make the battery accessible
from the top.
Not only would that allow me to
change the battery without turning the
model on its back between flights, but it
would also allow me to package the speed
control and the timer and all of the wires
in the airplane’s bottom block, below the
battery. This would clean up the look of
the installation a great deal.
It was decided to interlock the vertical
motor-mount plate and the rear yoke
mount former to a horizontal 1/8 lightplywood
plate. Using this process, we
could align everything outside the aircraft
and then simply line up the light-plywood
plate inside the front of the airplane to
two lines—one drawn on each plywood
doubler—that were parallel to the
centerline of the wing.
Once everything was aligned, the unit
could be tack-glued in place, to allow a
final alignment check, and then epoxied
permanently in place.
We did all of the preceding, and it
worked perfectly. And it was extremely
easy. It was much easier than installing
the traditional maple engine mounts in a
Stunt model’s nose. And the horizontal
plate, once glued in place, made the nose
area extremely rigid.
A new lower cowl block was carved
and fitted. The airscoop inlet at the front
of the cowl block was bifurcated (I’ve
always wanted to use that word in a
column) with balsa diverters, to allow
cooling air to get to the motor bay and the
battery compartment.
Before permanently gluing this block
to the Genesis, I mounted our new betatest
timer to the horizontal plate and cut
holes to allow access to it, for
programming and up-and-down rpm
(electronic needle valve) adjustment from
the right side of the model. The deadman’s
switch holes were cut below the
plate, and they exit on the left side of the
fuselage.
A new top block section was carved
and hollowed and fitted with hold-downs,
to allow it to be removed quickly. As I am
writing this, the nose is being refinished
and I should have finished shots of the
model in the next column—and a flight
report.
To be fair, others figured this out at the
same time we did. Crist Rigotti made a
sheet-metal version of the mount for use
in his new CL Profile Stunter.
You can find photos of the model and
installation and some discussion about it
on the Stunt Hangar online forum. You
will have to log in to that forum to access
the information. It is in the “Gettin’ All
AMPed Up” section. Find the “570
Electric Profile” thread; on page 2 of that
thread, see response #51. If you scroll
down from there, you will find a response
that shows our test bed unit as well.
If you would like to see more photos
of this system’s installation into my
Genesis Extreme as it progressed, please
e-mail me.
Till next time, fly Stunt! MA
Sources:
Stunt Hangar
(314) 774-8910
www.stunthangar.com
Precision Aerobatics Model Pilots’
Association
www.control-line.org