MegaTech R/C Real World Helicopter Series Bedienungsanleitung PDF herunterladen (Seite 63)

DESIGN AND BUILD AN RC BIRD MODEL

FLYING LIKE A BIRD

It was a calm Saturday morning, and as I walked outside for the

morning paper, I spotted a raven gliding toward me at telephone-pole

height. Although this is a common sight here in the California desert,

I stopped to watch. I had just retired from the Air Force Flight Test

Center as a stability and control flight-test engineer, and now I had time

to expand my interest in bird flight as a new hobby. As I watched, the

raven started a slow bank to the right with its wings fully outstretched.

The turn got steeper and steeper until, at last, the raven dived-head-

first—into the middle of the road, about 30 yards in front of me. I was

dumbfounded. I had never seen a bird crash before!

Span • 4.17 ft. Length • 1.92 ft.

Wing area = 2.78 sq. ft. Aspect ratio = 6.2S

Weight = 1.1 Ib.

BASE-LINE RAVEN

There was no evidence of life after the impact, and I suspected that

the bird had suffered a stroke or a heart attack. In any case, this little

fellow had unwittingly given his life to science. I seized the opportunity

to weigh him and draw an outline of his wings and tail on a sheet of

butcher paper. The dimensions were surprisingly similar to a ^A-size

radio-controlled model that I had been flying. I reasoned that I could

probably learn something about how birds fly by building a glider model

with the same shape, size and planform of a large soaring bird.

I hoped to establish a "base-line" configuration that would fly, even

if I had to cheat a little at the beginning. The starting point was a series

of small, balsa-wood, profile models with 6- to 8-inch spans that I

glided around the living room. I was a little surprised to find that these

models were stable in all axes, even without vertical tails. Lateral

control was an enigma, but I soon discovered that either spoilers or

drag flaps caused the model to turn toward the high-drag wing.

To provide room for the radio gear, I built the prototype Raven

model about 8 percent larger than a real raven. Pitch control was

provided by deflection of the rear portion of the tail, and lateral-

directional control was provided by the use of drag flaps (downward

only) on the bottom of each wing. I built it to be sturdy, since I expected

frequent crashes. The model was launched from the top of a small hill.

It appeared to be stable but glided with a gentle rolling oscillation that

could not be controlled with the drag flaps, so a very small vertical fin

was added. Stable and controllable glides were then possible.

It seems that each successful test produces additional, unanswered

questions, such as: how do birds twist their wingtip feathers to produce

proverse yaw? Does a bird's airfoil really have a reflexed trailing edge

in flight? Do birds adjust the wing sweep at the wingtips as part of the

control mechanism? Of course, there is also a wide variety of species

with various wing shapes to try. I have only begun to explore the

technical aspects of how birds really fly. I am constantly amazed at

the incredible complexity of bird flight, and I marvel at that little

"bird-brain" that's able to coordinate all the required actions.

For the full story, take the "Click Trip"!

The aileron servo for each wing

panel is attached to the root

end of the wing. This keeps the

tips light for better turning per-

formance. A Kimbrough rotary

coupler connects the torque

rod to the servo.

Left: without a vertical fin

and rudder, bird models

can be very difficult to

launch with a bungee

high-start or a winch line.

To improve the ride, you

can use a drop-away

ventral fin like this one

that fits into a slot in the

bottom of the fuselage.

hints spur some interest in building models that look and fly like birds.

The analysis methods mentioned are good starting points, but they do

not ensure that a new bird model will fly well on the first launch. There

is still much to learn about how birds fly.

BUILDING A TURKEY VULTURE

Early flights of my Turkey Vulture model oscillated continuously in roll.

I made three changes to help it fly better. First, I built a new, lighter

wing. Next, I replaced the drag flaps with wingtip-aileron feathers, and

third, I installed Kimbrough rotary-drive couplers to control all moving

surfaces. In its current configuration, the model oscillates lightly in

turbulence, much as a real bird does, but it's easily controlled and will

stabilize nicely in still air.

The model is based on photos of vultures flying in thermals. It is

approximately full size (66-inch span) but is roughly half the weight of a

real turkey vulture. The wing construction incorporates a full-depth spar

and a cambered-wing airfoil with reflex. The fuselage (body) is built with

balsa formers, sheeting and balsa blocks for the head and minor fairing

pieces. I cover my bird models with MonoKote film and paint the heads

to match. This results in a model that is a true floater but does not pene-

trate the wind as well as a model

with less camber. The model handles

ballast well, and this can be used to

somewhat improve penetration. Real

soaring birds reduce their wingspan

and area and increase their wing

sweep when flying straight between

thermals (more options for

experimentation?).

Detailed instructions for building

the Turkey Vulture model

accompany the full-size plan.

You can also view the detailed article

and some related aerodynamic illus-

trations via the "Click Trip" Web

address at the end of this article.

Please let me know, through Model

Airplane News, of your experiences

with bird-like flight. ±

MODELAIRPLANENEWS.COM

For more information and to

see the model fly, click on

the article and videos link.

94 MODEL AIRPLANE NEWS

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