MegaTech R/C Real World Helicopter Series Manuale Utente Scaricare il pdf (Pagina 59)

Even a big old pelican can be

modeled. Notice its graceful

wlngtlp aileron feathers.

PECIFICATIONS

5DEL: Turkey Vulture

ODEL TYPE: bird-like rudderless glider

'INGSPAN: 64 in.

ING AREA: 600 sq. in.

NGTH: 25.5 in.

EIGHT: 2.5 Ib.

ING LOADING: 9.75 oz./sq. ft.

tDIO REQ'D: 2-channel (aileron and elevator)

Herein my seagull model.,Note:that the mbvabte*

wingtip feature, begins at about the gray/black iolbr

Jlne'. (The midspan break in the photo is a fixed

ground-adjustable joint for altering the dihedral.) * V|

COMMENTS: designed by Bob Hoey, this bird-like RC Turkey

Iture uses highly effective wingtip aileron feathers to bank

d turn the model just like a real bird. The model has no

^rtical fin or rudder but is very stable in flight. Built of balsa

and plywood, the model is covered with MonoKote and has a

drop-away ventral fin for bungee high-start launches. It can also

Ib dropped from another airplane. The wing is highly under-

mbered and slightly reflexed. The plan shows the articulated

Bngtip aileron feathers in detail.

DESIGN METHOD

Start by observing and photographing the bird species you wish

to imitate. Try to get bottom, side and front views, but be pre-

pared for a real challenge, since these critters are continuously

changing shape. Slides are best because they can be projected

onto a wall, and your subject's shape can be traced with a pencil.

Varying the projection distance also allows different views to be

scaled to the same size. Use a little artistic license and develop a

3-view.

Next, apply the simplified stability and control criteria

described herein (center of gravity [CG] location, wing dihedral

and sweep). Make design alterations to your 3-view to bring these

numbers within reason. The final step is to design flexibility into

the structure to allow for trial-and-error development of your

design. (Provide for changes in dihedral, CG and tail area, for

example). Gliding flight without a vertical tail is certainly

possible, but stability will be less than that of a typical RC glider.

PITCH AXIS

The complex planform of a bird's wing requires more attention

during the design to properly locate the CG. The wing's mean

aerodynamic chord (MAC) and aerodynamic center (AC) can be

located using the procedure described in the "Click Trip" URL at

the end of this article. First flights should be made with the CG

close to the aerodynamic center. Bird models are typically very

short-coupled in pitch, and the tail area may need to be enlarged,

much like any scale model. A 15- to 20-percent increase will

improve trim ability and require less attention to maintain glide

speed. Using a slightly reflexed airfoil (typical for flying wings)

also avoids large tail deflections.

ROLL-YAW AXIS

The complex shape of a bird's wing, and a bird's lack of a vertical

tail, make the design of the wing critical to successful flight. Wing

sweep and dihedral are the critical features. Dihedral varies over

the span of most bird wings. Land birds (hawks, buzzards, eagles,

etc.) usually have small dihedral near the root and increasing

dihedral near the tip. Sea birds (gulls, pelicans, albatross, etc.), on

the other hand, often have negative dihedral but high sweep in

their outer wing panels. A method for defining the total dihedral

effect for the wing is also described in the "Click Trip." These

calculations are for the wing only and do not account for the

The basic keel and plywood crutch

parts of the fuselage (bird's body).

JUNE 2002 S7

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MegaTech R/C Real World Helicopter Series Manuale Utente Pagina 59

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