# Boat fiberglass on aircraft?

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#### BJC

##### Well-Known Member
Supporting Member
I would not use polyester on anything in an airplane
Does anyone know of a source of vinyl ester gel coat?

Thanks,

BJC

#### wsimpso1

##### Super Moderator
Staff member
Does anyone know of a source of vinyl ester gel coat?

Thanks,

BJC

BJC

#### Pops

##### Well-Known Member
Supporting Member
Many commercially made items use polyester resin. Its use in objects that stay submerged for a long time, like boats, has its problems but usually they appear long after the warranty has expired. I am pretty sure the KR series planes were built with fiberglass and polyester resin. It was really when Rutan started using extruded polystyrene foam where Polyester resin was an issue because it would dissolve the foam core. Thus the VariEze and LongEz had to use epoxy resin since it would not harm the core material that was being used.

The other thing to watch out for is whether the resin contains wax to help cure it. This is usually used on the last layup. The previous layups may use a bonding resin without wax which remains tacky for a long time to promote a bond with the next layer. But if you used the resin with wax so that it fully cured and had no tackiness, it would be very difficult indeed to make a secondary bond to that layer because it is so difficult to remove the waxy layer and then one would also need a mechanical bond.

Lots of education needed if one is not to screw it up.
In the 1970's, when I started building my KR-2 there was 2 flying. I built my KR with epoxy resin and don't know of any KR's that was built with polyester resin.
That is how I met Bob Hoover. I was at Oshkosh ( maybe 1974 or 1975 ), and looking at the first KR-2 that I had seen. Had been working on my KR for a couple months. I was looking at everything real close and taking pictures and another man was looking very close and making comments about the construction and the design. We talked back and forth to each other for 15 or 20 minutes without stopping looking at the KR. Finally I looked up and recognized who he was and saw his name tag on the front of his suit. He said he really liked the little airplane and was impressed with the design.

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#### mikoman

##### Well-Known Member
Supporting Member
Aircraft grade glass has fiber bundles (tow) of controlled size woven into a cloth with relatively the same number of tows in both directions. The smaller the tow size, the stronger the laminate. Normal 7781 glass has a tight, orthogonal weave and is approx 10 mils in thickness, dry.
It is the standard woven material in structural designs. It has epoxy sizing for good matrix adhesion.
Polyester resins used on boats are cheaper than epoxies so boatbuilders use plenty of it because they are building up mass and want to keep costs down. Epoxies have higher temp resistance and provide a stronger laminate than polyesters. If you are making an aircraft structural part or repairing one, always use an epoxy matrix. Aeropoxy from Spruce is a good 2-part system with high mechanical properties at reasonable cost. The West Systems work also.
Just picked up a West Systems kit fro Aircraft Spruce prior to holiday weekend, the gallon with fast hardener. It was $168 up from$144 in the prior catalog....Sigh ..I hate supply chain issues LOL

#### BJC

##### Well-Known Member
Supporting Member
Thanks, Bill.

BJC

#### Rik-

##### Well-Known Member
Does anyone know of a source of vinyl ester gel coat?

Thanks,

BJC
North American Composite

BJC

#### BJC

##### Well-Known Member
Supporting Member
Thanks, Rik, but I’m looking to buy in quart quantities.

BJC

#### wsimpso1

##### Super Moderator
Staff member
Can I use boat fiberglass on aircraft? I am thinking it has humidity, fire and low temp/high temp resistance.
Test it first. Some of the "boat cloth" I have seen do not conform well to compound shapes and layup heavy. We do a lot of compound shapes, corners, fillets, etc with glass, so it has to go around corners and conform. Laid up weight with many boat cloths tend to have a larger fraction epoxy than the 50-50 (by weight) we generally achieve with BID and UNI. WEIGHT IS THE ENEMY in airplane construction. Excess epoxy or vinylester resin does nothing for strength or deflections, only makes your bird heavier.

Testing: you are finding out how your candidate resin and cloth compare to our usual BID and UNI, so run some with those as well as with your candidates. For strength tests, I like four-point bending of 4 to 8 ply laminates. Make you controls and your test pieces with the same fiber orientation, cloth weights, and resin systems. Keep track of which are which, and track the results too.

After you try a few different layups with your candidate cloths, weigh them to get fraction epoxy, then test them to make sure the failures are in the fibers. If the resin lets go of the fibers, the surface treatment is not compatible with your resin.

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#### Bob H

##### Active Member
The thicker the woven cloth, the lower the compression strength of the laminate because each fiber tow has to go up and down adjacent tows in the weave. This generates eccentricity of the tow instead of an ideal flat tow. The strongest laminate is made with unidirectional material that has no eccentricity but also has little transverse strength, so the laminate has to have plies in multiple directions to act as an isotropic laminate and that takes time to do. Much easier to use a ply of woven with orthogonal weave and orient plies at 0/90 and +/- 45 deg. to approximate isotropy. When evaluating a new resin system or fiber, you use compression strength as the criteria because if loaded in tension, the laminate is fiber dominated and the matrix/fiber interface is not strained completely. Epoxy matrix is the standard because of it's adherence to fiber interface that provides maximum strength and epoxies have better thermal properties than most other matrix materials like polyesters. And they cost more because of the benefits. All commercial composite aircraft structures use epoxies in the form of prepregs that have toughened resins impregnated into the fibers and this combination provides maximum damage tolerance in service. You can't use a toughened resin system in a wet layup because the viscosity is too high for good impregnation. For maximum laminate strength and highest mechanical properties, you vacuum bag parts and cure in autoclaves at 350F and 100 psi. This gives highest laminate compaction and minimum porosity and highest reliability.

#### dwalker

##### Well-Known Member
Supporting Member
Does anyone know of a source of vinyl ester gel coat?

Thanks,

BJC

US Composites in Florida

#### dwalker

##### Well-Known Member
Supporting Member
When I think of boat glass I think of chopper gun. E Glass in the appropriate weave and weight is perfect for aircraft use. S glass is good for very specific applications where someone has taken into account the increased rigidity. The flex in the E glass makes a Long EZ ride like a fine touring car vs the super stiff carbon-fibre Berkut.
It is always interesting to hear West Marine epoxy referred to as West Systems. I use West myself for various things, but for building actual structural bits I use MGS, which used to be Shell Aero, which I used by the drum making carbon parts for racecars.
Without knowing the type of aircraft or parts being built it is hard to know what is acceptable, that is why there are charts that show all the necessary information from strength at various cure temps, with and without postcure, etc. so that the proper materials can be selected. To attempt to make an accurate answer for whether a product can or should be used without all the information is just... a shot in the dark/guessing game.

#### dwalker

##### Well-Known Member
Supporting Member
Thanks, but I idn’t find any vinyl ester gel coat there.

BJC

TAP used to carry all sorts of stuff but the past few years they have really slimmed down thier offerings.

US Composites has what you are looking for about halfway though the list-

#### BJC

##### Well-Known Member
Supporting Member
US Composites has what you are looking for about halfway though the list-
Couldn't find any vinyl ester gel coat there.

BJC

#### dwalker

##### Well-Known Member
Supporting Member
Couldn't find any vinyl ester gel coat there.

BJC

I thought you were looking for polyester gelcoat. They only have the vinyl Ester resin near as I can tell, but it might be worth a call to them

#### TFF

##### Well-Known Member
Just poking for fun but West System is on the packaging. I think West wins because of accessibility not because it’s the best. Stuff like MGS you have to be in the know. Most homebuilders, although we think we know, really just follow the crowd, which usually means easy to get ahold of and instructions that hold your hand.

#### Rik-

##### Well-Known Member
Thanks, but I idn’t find any vinyl ester gel coat there.

BJC

I’m not certain that vinyl ester exist.

#### wsimpso1

##### Super Moderator
Staff member
Just poking for fun but West System is on the packaging. I think West wins because of accessibility not because it’s the best. Stuff like MGS you have to be in the know. Most homebuilders, although we think we know, really just follow the crowd, which usually means easy to get ahold of and instructions that hold your hand.
MGS was designed as a composite strucural epoxy. West was designed as structural resin for composite reinforced wooden boats. Both have failure strains exceeding those of common woods and fiber reinforcements, have similar moduli, handling, wetout, and cure. They both also have similar reputations for long lived structures in service.

I suspect that all of us would be hard pressed to ever demonstrate in standard strength and fatigue tests of composite laminates that one is significantly better than another.

I suggest that most of us would be far better served by doing test laminates of our candidate resins, and make our choices on how it handles, laminates, working time, part failures in four-point bending, availability, and cost.

I have ProSet and West in my shop. In Proset I have two viscosity resins and three speeds of hardener. In West, I have both hardener speeds and use what suits each job. I also have System Three 5 minute epoxy on hand for fixturing. On the occasion of needing vinylester, I buy it Derakane 411. This covers all of my composite resin needs for my experimental airplane building, repairs and rebuilding of storebought airplane parts, and other composite work. YMMV.

Billski

Staff member
BJC