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.