MegaTech R/C Real World Helicopter Series Uživatelský manuál stáhnout pdf (Strana 48)

HOW TO

Make Static

Scale Props

The ultimate final touch

by Dick van Mourik

henever I attend a scale meet, I wonder why so

many scale modelers spend so much time installing

features such as sliding canopies and retract doors,

but no one feels the need to upgrade from a plain gray

2-blade 12x6 prop for static judging. The use of static props

doesn't have to be limited to the highest competition models;

scale propellers are major attractions on any aircraft, and they

are more than worth the time it takes to create them.

Constructing static scale props does not require any spe-

cial talent or equipment beyond that possessed by the aver-

age modeler. To help explain the techniques involved, this

article outlines the steps I took in the production of the static

scale prop for my 1/4-scale Zlin Z-50 LS. Give it a try; you'll be

amazed by what you can create with some glass, epoxy and a

little practice!

1 A sketch and several photos of the full-size aircraft at

various angles provided the basis for an accurate plug.

In this case, I was really lucky; the manufacturer of the full-size

plane supplied me with factory information as well as a logo

and identification sticker.

2j The choice of building materials for the plug depends on

the builder's individual preferences. I used a block of hard

polyurethane foam. It is vital that you smooth out the foam as

much as possible. Any imperfections will immediately show up

in the moldings. Careful sanding (start with 400-grit and end with

1200) and polishing will pay off later.

A prop blade is not the easiest part

to form a mold around. To allow for

removal, the molding must be split.

I placed the blade on a bed of

modeling clay, which I then

smoothed out as much as possi-

ble. I placed the whole thing on a

bearer plate made of plastic-

coated fiberboard, onto which I

formed the flange.

Be sure that you liberally treat both the plug and the support with

release agents. I normally use a combination of two: first, I use a spe-

cial mold-release wax that I allow to dry for a few minutes before I

polish it out. Depending on the plug's finish, I may repeat this process

six to 10 times. Second, I carefully apply some poly vinyl alcohol

(PVA) to the plug/mold with a soft, wet sponge. (You could also thin

the PVA to a milk-like consistency and apply it in a single layer with a

dry cloth.) As the water evaporates, it forms a very thin film.

Ultimately, it's the wax that ensures debonding from the resin and

plug, but this film provides an extra measure of safety. I always use a

very thin layer of PVA because any imperfections will clearly show.

When the release agents were

completely dry, I used a soft

brush to gently apply the first layer of

molding compound. Molding com-

pound has a high viscosity and

should be carefully stirred to allow

the hardener to be thoroughly

mixed. To prevent air bubbles, I

always use a small brush in the cor-

ners first. It is best to apply thick layers and avoid retouching the mix-

ture with the brush where it has already been applied. I normally get

a decent result from two layers. Brush the second one on after the

first layer has hardened but before it has fully cured.

When the second coat had

hardened to the stage where it

is sticky, I poured a mixture of

cotton fibers and chopped fiber-

glass strands over the com-

pound. The strands and fibers

ensure a firm bonding between

the compound and resin. When

it had cured, I used a vacuum

cleaner to remove any excess

material.

SB MDDEL AIRPLANE NEWS

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