8

sile

Materials and Methods Grover I. Mitchell Over the past two years the

Answer Department

strength of ten

pounds

solid,

thousand

per square inch

and

twenty

when

thousand

pounds per square inch when

laminated

with

glass

fabric

(forty to fifty percent of the lamination is resin). The speci-

fic gravity

of the

laminate is

about one-half of aluminum. Since the aluminum alloys that

author has investigated a num- can be given a compound shape

ber of new materials which include fiber-glass fabrics, mats and blankets, also laminating resins and expanded plastics. Correspondence from the Of nineteen products investimembers to EAA headquarters continually includes questions gated, seven seem to be adapted to the needs of the small shop. from technical to general in type of information desired. Member The trade journal "Modern Plastics" (575 Madison Ave., Roy M. Prine, a former CAA New York 22, N. Y.) or the agent, has consented to prepare "Thomas Registry of Manufactanswers to any and all questions submitted, so here's your chance urers" will be found helpful for to get the facts. This service is finding sources for materials. open to members only, so state They can be found in the libraries of most cities. your membership number when Of the glass fiber materials, submitting your question. the most valuable types were QUESTION: What are two woven fabrics. The heaviest one restrictions on homebuilt air- being a course weave measuring craft? .013 inches thick which comes ANSWER: There are two rein rolls 44" wide and in tapes strictions - "Initial" and "Modiof one, two, three and four infied". "Initial Restrictions" ap- ches wide. This is available ply during the testing or proving from many boat dealers who period of at least 50 hours fly- stock it for marine use. It has ing time, and limited or restric- a tensile strength of 440 pounds ted operations to Day Visual per linear inch. Another fabric Flight Rules, passenger and car- which is useful in getting a good go carrying being prohibited. surface on laminated articles is The aircraft cannot be used in of fine weave and measures .003 connection with any business. inches thick. It is also used in A limited flight radius is imlaminating prop spinners, fairposed, and any additional reings and other small parts. strictions that may be deemed The laminating resin sold for necessary. boat use (polyesters) are not too After successful and satisfacgood for aircraft use, as they tory completion of this initial contain some volatile solvents, phase, the "Initial Restrictions" shrink during set-up, will dimay be "Modified" to permit solve expanded polystyrene, and continental wide operations or require a long time to set up. flight, except that the aircraft On the other hand these resins cannot be used to carry passenonly cost about eight dollars a gers or cargo for hire. gallon and can be laminated over QUESTION: How many hours wood satisfactorily. The strongest laminating remust a pilot have to fly a homesins are the epoxies. They cost built? about sixteen dollars per gallon, ANSWER: No restriction on this, except that the pilot must but do not shrink, set within have at least a Private Pilot Cer- thirty to forty minutes after tificate valid for the type of air- mixing, and do not damage the expanded polystyrene material, craft to be operated. which is valuable if you wish to QUESTION: Where can the use the sandwich type of conhomebuilt aircraft be flown? struction. By itself it has a tenANSWER: During the "Initial" restriction or testing, provQUESTION: What kind and ing period, flights must not ex- what size of paper must be used ceed a radius of 25 miles from in preparing aircraft drawings the airport, thereafter no flight to notarize them in order to sell area restriction. to some manufacturer? ANSWER: There is no reQUESTION: Is the Stits Playquirement on this. If you have boy a one or two place job? ANSWER: The original Stits a good drawing made that shows all details, the manufacturer or Playboy was certificated as a buyer will do the rest. one place aircraft.

have a tensile strength of for-

ty thousand pounds per square inch or lesss, the laminate compares with it on a strength

weight basis. The epoxy resins have been used for a few years by sheet metal stamping shops for jigs, dies and fixtures. The epoxies we used were packaged and sold by the Renite Company of Lansing, Michigan

and the Rezolin Company. The Renite product is white in color while the Rezolin is yellow and translucent.

Both of them are

applied with a paint brush or roller which must be discarded

after forty minutes of use, as no common solvent will disolve the hard resin.

Of the expanded plastics that were tried, I believe expanded polystyrene is the most adaptive to our needs. We purchased ours from the Dow Chemical Company of Midland, Michigan

under the trade name of "Styrofoam". It is used as flotation in marine equipment. When purchased at their minimum order requirements, it costs a little over two dollars per cubic foot for the lightest which weighs about two pounds per cubic foot, although it can be had in heavier densities at increased cost. In quantity purchases it could be had for about one-half of this. V/hat we bought was 4" x 12" x 36". The largest piece they stock being about 2' x 2 % ' x 9'. Koppers Company of Pittsburg 19, Pa. makes a pellet of polystyrene, trade name "Dylite", that expands many times its size when subject to heat. It can be expanded within a container or mold, density being easily controlled. The last material we will discuss will be polyvinyl alcohol* film. This is useful as a parting medium and it can be stretched over a laminate after the last coat of resin to give a gla=s smooth surface. It is inexpensive and can be obtained at most plastic supply firms. It is also used for packaging food products. Cellophane can be used for a good finish but it does not *Mitchell-Rand Mfg. Co., 51

have the elasticity of the polyvinyl film. Now lets take a few projects to see what can be done with these materials. Lets start with a tank, it could be any shape

from a wing tip tank to one that has to fit into a restricted space behind a firewall. Cut the expanded polystyrene one-eighth inch smaller than the shape of the gas tank wanted and with sand paper round the corners generously and roughly hollow it out so it has a one-inch wall thickness. Wrap the entire

block with a strip of polyvinyl film. Stop the strip at the place the filler pipe is to go and stick a nail down through the film into the block. Cut the fabric to fit the surfaces leaving a two and one-half inch overlap at the joints in the fabric. The .013" glass fabric laminates to .016" thick. Put at least two layers over all surfaces. If you

are replacing an aluminum tank, laminate the wall to twice the thickness of the aluminum and , your fiber glass tank will weigh the same and be as strong. Pull the nail from the middle of the filler opening and enlarge the hole into the block without damaging the polyvinyl film excessively. Pour some lacquer thinner into the tank and the expanded polystyrene block will dissolve. Now the polyvinyl film

can be pulled out through the filler opening and the tank can be washed out with thinner. The filler and drain fittings are silver soldered to perforated stainless steel discs and stuck down with epoxy resin and several layers of fabric two and one-half inches larger than the discs. Large tanks that require baffles can be made in a number of sections and joined with four inch glass cloth tape and resin. This system will give you a smooth surface inside the tank

where it is most important.

A

wing tip tank is made similarly by laminating 4" tape around the form, overlapping it one-half the width of the tape each turn. When you have enough layers on it, wrap it with a strip of polyvinyl film for a smooth exterior right after applying the

last coat of resin. The film comes off easily when the resin is hard. The hoi wire method of cutting expanded polystyrene is as follows: Stretch a piece of nichrome wire from the ceiling down through a hole in your

bench, fasten it underneath with a turnbuckle. Hook up enough voltage to bring the wire to less

Murray St., New York 7, N.Y. than a dull red heat.

When it

9 is at the right temperature it will cut a path the diameter of

the wire. You can use it as you would a band saw for cutting

expanded polystyrene. A model wing section was made by first cutting out of sheet metal a template of the cross section of the wing at each end. Temporarily tack these on both ends of a piece of expanded polystyrene with the reference line of each template level. The two templates are held in contact with the taut hot wire and moved

and resin dust into the air when sanding. Work where you have

two or three minutes.

respirator and coveralls if you

the meantime sprinkle water on the portion of burlap you expect

plenty of fresh air and wear a

do much sanding equipment.

with power

To make a fiber-glass engine

cowling,

take your

stripped

fuselage with the engine mounted in place (drain the oil) and

the tailskid bolted on and hang

Now let

it set for about two minutes, in

to cover with the plaster. Your wife's

clothes

sprinkler

will

work fine. You have about eight minutes to work the plas-

ter before it starts to set, so dump it on the burlap right in the middle of the top of the engine and smear it around a

dry. Sand lightly and repeat the dope. Two to four coats will make it glossy. Sand it lightly with very fine paper. Put on a

coat of paste floor wax, let it dry without polishing, and fol-

low with a second coat polish-

ing it very lightly when it is dry.

The resin suppliers also stock a liquid parting agent that is

sprayed on over the wax. Now if you want only one cowling

it from the ceiling by v-slings at the propeller hub and tailskid. The whole fuselage will turn over easily in the sling. If

little thicker than the projecting

Don't worry if you

can be laminated directly on the form. This will give you a very

exact section for

proper place to balance it. Have

easier than plain plaster of Paris. If you don't get it thick enough

outside can be finished by hand as previously described. When

be cut just as easily as a straight

the cowling as seen in your fullscale side view and top view.

so the wire is guided over the edges of the templates. This will cut an

you, and a tapered section can

.ection.

A pair of wheel pants can be made by cutting sections of polystyrene and assembling them bread and butter fashion using epoxy resin as glue. The outside is easily sanded to shape.

Paint the form with epoxy resin

and laminate on two thicknesses of .013" glass fabric over the outside. Then sand the expanded plastic inside the wheel well clown to the outer covering

above the top of the tire and at

the sides where they are attached to the landing gear. Laminate

two layers of fiber glass to the

expanded plastic inside the wheel well. Reinforce mounting points by laminating to Vs inch thick on the inside of the

it is too much out of balance clamp some weights on it in the prepared exterior templates of

Extend these templates so that

the plaster

from

burlap and wrap them around the cylinders and the rest of the

outer points of the engine to a thickness of one-quarter inch

less than the amount of clearance you want between these

depressions. The wheel pants can be sanded to a smooth surface and painted to match your ship. Making them by this method

so they just clear the template by the thickness of the proposed cowling. Do the same to the outer points of the engine, letting the nailheads stick up the onequarter inch you allowed for the thickness of the plaster.

ed plastic exposed. A putty can

suppliers) and used to fill in any

fills the unused volume inside

the wheel pants with expanded plastic; there is no place for mud or other heavy material to accumulate. If you cut the fabric on the bias, it will form itself over compound shapes easier. Always get all the fabric

cut to shape before mixing any

resin. When you make your first attempt at laminating, have

an assistant so you will be sure to get everything done before the resin sets. With experience

and planning you will be able to

do the laminating on a wheel

pant by yourself. Use protective hand creams and a plastic

you can handle a large batch of

are lightly oiled, hardened plaster will come out when the container is flexed. Repeat this plaster mixing and

prevent

Tie this with wire on six inch centers. Stick some finishing

ers when bolting it to the land-

more experienced you will find

sticking. Stuff the bulk of the space between engine and firewall with wadded up newspapers. Take strips of clean

to

be made of the resin and glass flock (obtainable from the resin

thickness larger than the previous one and use oversize wash-

the next batch can be added right on top of it. As you get

[plaster. Do not mix plaster with

ing gear bracket. Be careful not to leave any of the expand-

Make each added

get it a little thick as this mixture sands down many times

the front can rest on the prop hub and the back on the firewall. Cork up all openings in the engine and grease the propeller shaft and firewall edge

high points and the inside of the cowling. Try your templates to see how much space is left to be filled in and fill it with wads of newspaper to within threefourths of an inch from the template and tie it firmly with strong string or rope. Put on about four layers of burlap strip

wheel pant.

nailheads.

6" wide,

wrapping

it tightly.

nails into the burlap and paper

Now get about fifty pounds

of plaster of Paris and about fifty pounds of pumice, this

shouldn't cost much more than

ten or eleven dollars. Paint stores stock both of these or can

get them for you. Put about

two quarts of cold water in a

basin and shift the mixture of fifty-fifty plaster and pumice

into the water thru a threesixteenths inch screen. When the powder sinks into the water and comes flush with the surface, let it set for about one min-

ute, then stir as rapidly as you

apron when working with lam- can without whipping air into inates. Do not blow the glass it. It will become creamy in

any that is about to set or is hard as it will shorten the set up time. The new

flexible

polyethlene

basins now available are excellent for mixing plaster. If they

pouring until you have built up

the top surface of the engine, then let it dry over night. You

have done about one-third of it so far so look at the plaster you

have left, if two-thirds of it is

unmixed, you'll have enough to finish. The next day turn the

thing over on its side and do

another third.

will finish

work.

The third day

the rough

plaster

Now it must tiry which will take six to eight days. If you can bring the temperature of

the room up to ninety degrees,

it will dry in four or five days.

When it is dry, sand down to the

nailheads. You can use very course sandpaper on the sanding

block at first and progress to the finer

grades as you

proceed.

Sand the plaster to the lines you want your cowling to have. If

you find hollows in the plaster, forget them now and sand down

the high spots. If you take too much off, let it go for now and

finish roughing it out. Then mix some more plaster and while it is setting for two or

three minutes sprinkle water on some of the low spots of the form and put the plaster on to build

them up. It will become firm quickly as the form will soak the water from the new stuff.

Sand it down after it has dried and you will have just about

what you want.

A little more

work will bring it in.

Finish

sanding with No. 320 paper. Blow the dust off and give it

a brush coat of dope and let it

the fiber-glass and epoxy resin

smooth inside surface and the

hard it can be

slit along

the

hood opening and removed. If you want a number of cowlings, make a plaster splash. To do this the surface of the form

you have just built up must represent the outside surface of the cowling, instead of the inside as just described (1/16" lar-

ger). Coat the form with a very thin film of fifty-fifty vaselinekerosene mixture and wipe off any excess.

Dip hemp fibers into a plaster of Paris mix* (no pumice

this time) and pack it 2 Vz" thick over the entire surface, doing one-third of it at a time. After each third is done wire it to the

prop hub and fuselage. Run the

wires from front to back on 4" centers and do not turn it over for the next third until it has set

over night.

When completed and dry, use a skill saw to saw through the plaster and hemp at the hood opening line on the cowling. (This has to be at the widest part of the cowling). Now get two husky assistants and put them on each side of the bottom cowling form. Have them hold it up while you cut the wires. It may need a little encouragement but if you have done everything right it should

drop free.

Steady the fuselage

while the lower half is being removed. Turn the fuselage upside down and repeat the process for the top half. Now set

these, smooth interior up, on a

low table or box. Make some

* United States Gypsum

Co.

puts out a plaster called "HydroStone" that has seven to eight times the strength and hardness of plaster of Paris. Time of set is twenty to thirty minutes. Wrtie to their Industrial Sales Division, 300 West Adams St., Chicago 6, 111. for bulletin No. 16L-13 for mixing instructions and nearest dealer.

Continued on page 13

13

Continued from Page 4 the basic

glass

material and

Hess-Goldsmith and Co.. Inc.,

who manufacture the glass clo'h. Many types and grades of glas~ cloth and bonding agents were tried during the experimentrl trial until one type was found that had the desired qualities and most nearly approached grade A. aircraft fabric but was considerably stronger in both directions. The aircraft dope bonding process was approved in July 1955 and a few months later the Epoxy resin bonding process was developed and approved. Each process has distinct advantages and disadvantages

but if both processes and methods are combined at a slight increase in labor and material, the advantages of both methods can be had. The aircraft selected for the

original experiment was an Aeronca 7 A C with deteriorated fabric which strip tested between 35 - 38 lbs., the structure being satisfactory and airworthy. After completion of the experiment, the reinforced fabric was again strip tested and showed a tensile strength of 165 lbs. in one direction and 125 in the opposite direction. The estimated weight increase was approximately 25-30 lbs. but should decrease as the wet dope dries. Later experimental work using an Epoxy resin indicated that the Epoxy resin method may have many advantages over the aircraft dope as a bonding agent and may likely replace the dope bonding method when the material is more readily obtained and understood. The original experiment was completed in July 1955 and conditionally approved by the CAA in the standard category, the conditions being that evaluation tests and their results to be reported each 90 days for approximately 1 year. This was due to the fact that it was recognized from the results of the experiment that the problems of repairing and reinforcing deteriorated aircraft fabric had several aspects not fully resolved, and until such time as the following questions were answered and the qualities of the Fiberglass cloth resin process was proven by some closely observed tests, it would not be possible for the CAA to grajnt blanket approval of any procesSf'prepare C A M material or issue any specific information to the

industry. A few of the specific questions

for which specific answers must be obtained are as follows:

a. If aircraft dope, plastics or

resins are used as a bonding agent, is the bond of sufficient

strength?

The Parasol Champ!

it created too much turbulence. A smaller windshield is being made, while it is presently being The July, 1955 issue featured flown without any windsheld an Aeronca "Champion" which at all. was modified to a parasol conThe wing tips were also refiguration. The parasol effect moved, and tip plates were then was achieved by cutting the added. fuselage back down, and removJames E. Tyndall of 5606

ing the cabin from the fuselage, b. At what rate will this bond still retaining the wing support deteriorate? structure, rather than construct c. Does the Fiberglass cloth and aircraft laminate have suf- new cabane mounts. The standard "Champion" ficient tear resistance after being

Patterson Avenue in Richmond, Virginia, did this modification

d. When applied over old fabric, can Fiberglass cloth be so attached that after the underlying fabric has completely deteriorated, a satisfactory attachment to the primary structure and the wing ribs be retained?

about the

finished?

e. Will the

Fiberglass cloth

and fabric laminate have sufficient structural integrity when

operated

in

windshield was trimmed off a little, but had to be after the first test flight last fall, because

turbulent air or

acrobatically in or under extreme temperature conditions and rapid temperature changes? To assist the industry in obtaining basic information on

Continued from Page 9 sturdy plaster and hemp fiber feet on them. After these are

set inspect the inside surfaces

and make any necessary repairs.

When dry give it the dope treatment then wax it, and you are

these two processes, The Aviation Glass Cloth Services, 1421 all set to make as many cowlings E. 25th Avenue, North Kansas as you wish in these molds, waxing between each set. After you City, Missouri has prepared a and an assistant have done the kit of instructions and informalaminating, lay in a sheet of poltion at a nominal charge which includes free consultation ser- yvinyl film, and sand bag it until it sets. vice on application problems. Now break off the plaster Glass cloth covering of the from the engine, and sweep all complete aircraft offers wonderthe plaster from the shop. ful possibilities to the experimenter as tremendous strength When you unwrap your engine it will look as good as ever. with extreme lightness can be readily obtained with only a Hard work? Yes, indeed. But fraction of the cost and no spe- no more than forming an aluminum cowl and it requires less cial technique or special tools skill and equipment. If you reare required. Editors note: The writer is a inforce it properly, it will last longer, make a quieter plane, former C.A.A. Aviation Safety hold paint better and will not Agent who has resigned to go suffer from fatigue cracking. into business.

on his Aeronca, for the total

cost amounting to $550.00, which

included the original airplane. The rate of climb and speed are same as any

"Champion",

but

it

other

handles

much better, according to Tyndall. He believes that it has great possibilities as a crop-duster or sprayer. However, Tyndall isn't interested in proving that possibility, but is looking forward to building a "Honey Bee", as soon as the opportunity presents itself. Leo J. Kohn

News Note Hal Sanders and Bill Roden-

berg are quite busy these days restoring a Heath Parasol. The ship has a Continental A-40 engine and prop taken from an old Taylorcraft, as well as the wing

struts which were cut down. The gear is from the T-craft also, but has been cut down 3 inches and the 6 x 6 wheels were retained. More details on this ship will

appear in a future issue. Meanwhile any members in the area

are invited to drop in for a visit. The ship is located in a quon-

set hut on the northwest corner of Centinela and Major Streets,

Culver City, Calif. Hal and Bill

are usually there on Monday evenings.