MegaTech R/C Real World Helicopter Series Manual do Utilizador descarregar pdf (Página 61)

DESIGN AND BUILD AN RC BIRD MDDEL

A little more sheeting and a couple

of balsa blocks carved to shape,

and you'll almost be finished.

(horizontal tail that tilts

around a longitudinal

axis for controlling turns)

works OK depending on

the CG location but is not

very powerful. If used

with a pitch-stable air-

CONTROL

Two methods for pitch control

have been tried—a standard

elevator at the rear of the tail

and the single-piece tail hinged

at the wing's trailing edge. The

elevator at the rear is the most

effective.

Because of the large adverse yaw associ-

ated with ailerons, they don't work well

when there is no vertical tail. A rolling tail

Here's the completed fuselage ready to cover with

MonoKote. To make it easier to finish, I simply painted

the head and beak.

plane (forward CG), the model flies well,

but the control action is opposite to the

way birds really fly (the model will turn in

the same direction as the tilted tail, but

During the past 11 years, many encounters have occurred between these models and real birds.

Unfortunately, these encounters are usually spontaneous and take place at a fairly high altitude, so I

have no photographic evidence of them.

There are lots of ravens around here; they are gregarious birds, and quite inquisitive. The models

circle easily and climb with the real birds in thermals. Often, one or two ravens fly formation with the

model and follow it as it circles in a thermal (or, just as often, I follow them). Occasionally, one will

come in quite close. Because the wing loadings of the models are lighter than their real counterparts,

the models can fly more slowly. Sometimes, I slow the model to near-stall and then watch as the poor

birds stall or flap off to one side.

One warm, still day, I thermalled a Raven model with about 25 real ravens for about half an hour. The

entire gaggle got so high that I had trouble distinguishing the model from the real birds. I made step

inputs in roll control, and then flew the bird that rolled abruptly. From my notes on the day of the flight:

"Finally I got too high to see well, so I put in full forward trim and flew straight. One bird followed,

matching the model's speed and descent rate, and joined up in formation. I pulled up into a loop. He

watched, then joined up again. I went into a full-up, full-left spiral for about 5 turns to lose altitude,

then recovered. The raven pulled his wings in and did about 3 half-rolls, then some other maneuvers,

then joined up again. I continued trying to descend, and eventually he left.

"The fixed-geometry, under-cambered wing of the models is no match for the refined, variable-

geometry wing of the real birds in straight, high-speed flight. The model quickly drops below and

behind. On several occasions, ravens have followed the model down to about 20 feet altitude, and

then circled overhead squawking loudly as the model lands. One raven landed nearby and walked all

the way around the model (it was probably puzzled by my belly landing}."

I have also thermalled the Turkey Vulture model with real turkey vultures. The appearance and climb

performance were similar, but real vultures aren't as friendly as ravens; they completely ignored the

model.

I've had the most fun with hawks. They will dive at any of the models (raven, seagull, or turkey vulture) from out of nowhere. They have never touched or damaged a model but

usually go screaming by with their wings folded. I once watched a hawk regain altitude

after the attack and then begin circling off to the side. He stayed there until I did some-

thing abnormal, such as a stall, with the model. He then folded his wings and came right

at the model, aborting at the last minute. I triggered three attacks this way. Apparently,

the hawks thought they were watching a wounded or sick bird. Recently, a hawk zoomed in

and established a position directly above the seagull model just a few inches away. He

stayed in that position for about 15 seconds as I made turns with the model. Eventually,

he flew away. I expected to find claw marks on the model but saw no evidence of any contact. Hawk attacks on the Turkey Vulture model are more cautious—usually from above I

and directly behind. They fly in trail with the model for awhile until they are satisfied that I

it is not a wounded, easy target. I hope to eventually install one of the new, tiny video cameras in a model to document

some of these encounters-up close and personal.

/ used a 0.063-inch-thick piece of aluminum for

my wing dihedral brace. Note that the full-

depth spars slide into place in the slots cut

into the brace.

The wing is built with a front and rear portion

glued to the main spar. Here you see the wing root

and the slots in the ribs for the aluminum brace.

no one will notice!). Drag flaps on the

lower wing surface (or spoilers on the

upper surface) also work well for initiating

turns, but they aren't very efficient or

realistic. Since they rely on dihedral effect

to control turns, they often require larger

wing dihedral than that observed on a

real bird.

Wingtip ailerons (feathers) are the most

bird-like roll-control method. They are

very sensitive to the initial incidence set-

ting of the two ailerons. I use a bias con-

trol through the throttle channel to help

locate the proper angle in flight. For land

birds, use the forward three feathers as a

single aileron surface that rotates around

a spanwise axis (detailed on the plan). For

sea birds, use the outer 22 percent of the

semi-span as an aileron, rotating around a

'ere, the two wing panels have been joined. Note the reflex

hape of the airfoil. The wingtip aileron feathers and the

'ding-edge sheeting still have to be installed.

90 MODEL AIRPLANE NEWS

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