Aero Mail - 2011/03

136 MODEL AVIATION
Serious Jamboree Sponsor
I was very excited to see last month’s
[the December 2010] issue of Model
Aviation arrive at my door. I was in
attendance for the entire event [the
IRCHA Jamboree], and it was by far the
best ever. The time delay photo of the
night flying helicopter made a great
cover shot!
After I read through the entire article,
I did notice that there was one important
fact that was missing from the coverage of
the event. The Saturday festivities, which
included the “One Competition,” the night
fly and the fireworks display, was cosponsored
by GAUI Helicopters and
Scorpion Precision Industries.
Georges Van Gansen, the owner of
Scorpion, flew over from Hong Kong to
be at the event all week, and in addition to
the sponsorship of the event, brought a
bunch of Scorpion hats, shirts, jackets and
lock strap battery straps to pass out to the
pilots. In addition to GAUI and Scorpion
sponsoring these events, their respective
US distributors, Empire Hobbies and
Innov8tive Designs, also assisted in
putting on a great show.
Georges put in a lot of effort and
finances to help IRCHA 2010 be the best
ever, and I just wanted to make sure he
got proper credit for his contributions to
the event.
As a side note, the three top finishers
of the event, Bobby Watts (1st place),
Kyle Dahl (2nd place) and Daniel Katzav
(3rd place) were all flying Electric
helicopters that were powered with
Scorpion motors!
Thank you so much for your great
coverage of the event and your continued
support of the RC hobby!
Lucien Miller
Innov8tive Designs, Inc.
Vista, California
Gyro Fancy
Great article [“Improve Your
Approach” by Ben Lanterman in the
December 2010 MA]. I have a Great
Planes Cub modified to an L-4. It has
been such an evil ... to get airborne that I
have flown it only 4-5 times in the last
two years.
After reading your article, I went down
to my favorite hobby shop and bought a
JR G 770 3D gyro and installed it.
Absolutely transformed the takeoff! Lined
it up, selected Heading Hold, and it ran
dead straight despite a right cross wind. I
Aero Mail
Continued from page 7
Viewfinder
Sarasota Sunrise
This photo was taken at the Sarasota
Silent Flyers’ field in Bradenton, Florida,
on September 26, 2010, just before sunrise.
I fly my GWS Slow Stick first thing, to
warm up my fingers before flying the more
difficult models. The peace and solitude of
early morning is wonderful to experience,
and the beauty of the scene is breathtaking.
My transmitter is the JR X9303 2.4
GHz, and my receiver is a Spektrum
AR6100e model. The battery is usually a
1300 mAh 3S Li-Poly.
The model is so slow-flying and steady
that I could almost take the photo myself
with a small camera held in my left hand.
Quiet electric models are a nostalgic
reminder of our free flight heritage.
This is the most fun airplane you can
own! MA
—Fred Sgrosso
[email protected]
E-mail your high-resolution
“Viewfinder” photo and a short note
telling the airplane or helicopter story
to [email protected].
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March 2011 137
was so enthralled, I forgot to deselect
Heading Hold until after a very ugly 180
degree turn.
Made several takeoffs afterwards, never
touching the rudder and remembering to
deselect HH after getting airborne; just
great. Makes the plane a joy to fly. Well
worth the money. I may try the E-Flite G
110 next on another plane.
Thanks for such an informative and
helpful article.
Al Shukle
via e-mail
About Those Propellers ...
You have outdone yourself with the
cover for the December, 2010, Model
Aviation magazine! Wow is an
understatement. I was impressed with it as
soon as I saw it come out of my mailbox.
Beautiful! You should take a bow.
On page 150 is a lead in to “Landing
Next Month...” where a beautiful photo of
the Basler BT-67 is shown. I notice the
picture shows five bladed propellers,
apparently replicating the full size aircraft.
Not being an aeronautical engineer, I never
have fully understood how many blades an
aircraft engine needs, and the pitch needed,
diameter, etc.
Four blades for the WWII P-47
apparently works great, even at 30,000 feet,
but required engine turbocharging to get
enough air into the combustion chamber. (I
have built the giant scale 86-inch P-47 of
Top Flite.) But it looks like turbo engines
need even more “bite” to get top speed and
performance from the plane.
Do you have any plans for a short article
on prop selection for propeller driven model
planes? At the low elevation our models fly,
it is apparent 2 blade props work just fine.
However, they don’t look scale. Would my
Top Flite 86-inch P-47 fly with a four blade
prop? And, just for curiosity, why don’t
manufacturers make 4-blade props?
2011 will be my 13th year in the hobby,
and I love it! Model Aviation magazine is a
great source of information, and inspiration,
for me! Keep up the good work!
Herman Burton
via e-mail
The main reasons for using multibladed
propellers on full-size aircraft are
that their smaller diameter (for a given
amount of engine power) reduces tip
speed, and also minimizes the necessary
landing gear strut length.
You probably know that the F4U
“Corsair” employed its
inverted gull wings to permit use of its
huge 3-bladed prop without needing long,
gawky (and heavily-stressed) LG struts.
Had the Corsair (or Thunderbolt, or
Mustang) used 2-bladed props on their
high-powered engines, those would have
required significantly larger diameters to
handle the power—and thus longer LG’s
to provide sufficient ground clearance.
Yet 2-bladed propellers are more
efficient thrust producers than multibladers.
That’s because the fundamental
equation for propeller thrust does not
include the number of blades. In simple
terms, thrust depends on both rpm and
diameter.
It’s proportional to the square of the
rpm, and to the fourth power of the
diameter. For example (in model airplane
sizes), increasing engine speed from
10,000 rpm to 14,140 rpm will double the
thrust; and idling down to 5000 rpm will
result in one fourth the thrust developed
at 10,000.
But diameter has a more profound
effect. If you could spin a 12-inch prop at
the same rpm as a 10-incher (an increase
in diameter of 120%), it would develop
1.2 x 1.2 x 1.2 x 1.2 times as much thrust—
an increase of more than double.
Of course, propeller diameter influences
power absorption, and hence rpm. But in
model sizes, and considering only thrust,
it’s often more efficient to use biggerdiameter
props.
Off the top of my head, consider a
“typical” sport .049 engine. On a 6-inch
prop that might turn 15,000 rpm.
Reducing the diameter to 5 inches might
raise the speed to 18,000 (engine
porting would be the determining factor
here).
Using the relationships given above,
the rpm increase by itself would result in
144% greater thrust. However, the
diameter decrease (by itself) would cause
the thrust to drop to 48% of what it was
with the six-incher. The end result—1.44 x
.48 = about 70% of the thrust produced by
the 6-inch prop at 15K rpm.
Now for pitch! Its effects are largely
independent of diameter. As a very rough
(but quite useful) approximation, the
propeller pitch in inches times its rpm in
thousands equals the maximum speed (in
mph) through the air that can be
achieved.
For example, a model with a 5-inch
pitch prop that’s turning at 10K rpm
cannot exceed 50 mph in flight. (In actual
fact the speed would be lower.) If you
want to fly faster, you can speed up the
engine or increase the pitch.
(Of course, merely changing the pitch
will slow the engine; so reducing the
diameter will be needed to keep rpm up ... )
These are dynamic relationships.
Change one variable and the others
change too.
Two further important considerations:
(1) Model propeller efficiency also
varies. Some brands are much more
efficient than others. Merely calling for a
10-5 prop is not enough to insure
maximal performance.
(2) Engine-powered model airplanes
have (in general) quite high power-toweight
ratios. This permits them to fly
acceptably well with rather inefficient
propeller/engine combinations.
I try for maximum efficiency in my own
models, and usually employ much smaller
engine sizes in them than “the average
modeler” does: .19s and .25s in controlliners
where most flyers use .35 to .40
power, for example.
Joe Wagner
[email protected]
Control Line in Vegas
Many of us came to Las Vegas from
different states. My son, Steve ([862] 221-
1055), and I came from N.J. where in the
East Coast control line planes are as
popular as R/C planes. In fact, in
Pennsylvania, Brodak is the largest
manufacturer and seller of control line
products.
We are long time control line
modelers. I have been flying in the hobby
for 50 years. I am now retired and living
in Las Vegas with my family and would
love to continue my life-long control line
interest.
However, in the short time we have
been here, we found out that there is no
flying allowed in any parks for control
line planes. As per AMA and the safety
concerns, you take a very high risk flying
in a ballpark field.
Clark County of Nevada told us that
the only place in Las Vegas dedicated for
model planes is a place called Bennett
Field. That’s how we came to meet new
friends in the hobby that have the same
interest and respect for fellow modelers.
We asked LVRC President, Tom Brandt,
if he could advise us on where control line
could be flown.
This is where we stand now. Looking
for a dedicated flying site that is both safe
and available to all that take an interest in
control line.
Let’s not stop an active interest in
Model Aviation in Las Vegas due to lack
of a flying site. Control line will grow
here once it has a permanent flying site.
Then we can hold contests and other fun
events. Fellow modelers from California
and Arizona have already shown interest
in coming here to support us.
I hope we all can work together to
encourage a control line field in Las
Vegas. MA
Reuben Mac Bride
[email protected]
(862) 221-1948
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