Fiberglass doors

[Nev]

Has anyone made fiberglass or carbon fiber doors and flown with them successfully?
What are some of the considerations? I'm thinking about whether it would be possible to mold the door and frame together so they're integrated, and then install the acrylic panes from the inside.
Any thoughts on how to attach hardware such as the door hinges, door handle mechanism etc ?
Is there likely to be a weight saving ?

[Battson]

I can only comment of selected parts of this question.

My experience and observations of others here, over the years, has been there's little difference between metal and fiberglass structures in terms of weight and strength. This is looking at wingtips, interior panels, fairings / cowlings, etc. If there are savings or differences, they are usually small compared to the extra effort required. The advantages of fiberglass is no corrosion and easy to make any shape with blended curves.

I think carbon fiber is where the real improvements are hiding.... Hiding behind a big wall of extra complexity and cost for your average Joe

[jaredyates]

We have a set of prototype composite doors on 303ap. Currently the cargo doors are composite and the front doors are original. One takeaway is that they need to have more curve than the airframe in order to make a spring-action to the sealing edges.

[svyolo]

A while back I thought about CF doors. I still might replace the cargo doors in the future after flying. The square CF tubing is stupid expensive. I ran some numbers and I could get most of the weight savings of CF using aluminum tubing, at far less cost. The plexi weighs the same no matter what.

You will add weight to the CF with reinforcing joints etc. AL you just weld.

There are some other threads on this.

[svyolo]

I think composite (not tube based) cargo doors would save a lot of weight well aft of the CG. Front doors are covered in plexi which is heavy. The potential weight savings is less because of the plexi. The cost of square CF tube failed my weight savings/$ test. Square AL tube is MUCH cheaper, but still a lot of work to save a very few pounds. I will do floor boards and cargo doors before front doors. I made one attempt at floor boards, unsuccessful. It will get airborne at first with kit floorboards.

[Nev]

I think composite (not tube based) cargo doors would save a lot of weight well aft of the CG. Front doors are covered in plexi which is heavy. The potential weight savings is less because of the plexi. The cost of square CF tube failed my weight savings/$ test. Square AL tube is MUCH cheaper, but still a lot of work to save a very few pounds. I will do floor boards and cargo doors before front doors. I made one attempt at floor boards, unsuccessful. It will get airborne at first with kit floorboards.

I agree - it was important for me to get flying first. But now I'm interested to see if I can get some gains in design or weight, and also just to have a winter project in the shed.

Any ideas of the differences between carbon fibre and fiberglass? Is there a significant weight difference to offset the cost?

[gregc]

Good explanation of the differences between e glass, s glass, kevlar and carbon fiber - https://youtu.be/KHXVf0SaJpA

[Mark Goldberg]

I know Bob Barrows likes Kevlar on the interior of planes. It doesn't shatter like C/F on impact. Mark

[svyolo]

I tried making a floorboard out of CF cored sandwich. It didn't turn out very good. Later I will give it another try with vacuum bagging. Weight is similar for the same weight cloth. CF is a lot stiffer for the same weight. Fiberglass next, Kevlar not stiff at all. My interior panels are all 1 layer of CF and 1 Kevlar. CF is easy to break. Putting a layer of Kevlar makes it a lot tougher. I like the combo a lot better than 2 layers of FG.

[rodsmith]

I went the carbon/composite route. Between the doors and Hoerner wing tips added a year to my project. Mark had originally said that the composite doors on 303AP saved 25 pounds. I don't believe that is anywhere close to accurate, at least not in my case, I may have saved around 10 pounds. The full lexan front doors don't help with weight. My rear and baggage doors are 3/8" foam with carbon layups on the outside and fiberglass inside. Hard points for hinges / latches were either hard wood inserts or aluminum. My front gull wing doors are square carbon fiber tube frame ($500 worth) and lexan with a fiberglass trim piece over the perimeter. My advice is build per plans or maybe an aluminum frame. If I had built the doors to plans would have been flying awhile already.

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[Nev]

Thanks for all the good info guys. Because my aircraft is now flying I'm not really concerned about the time it would take. I have a few ideas that might be a fun winter project.

When installing a hard point to attach hinges and hardware to, is it simply a matter of fiberglassing a piece of aluminum, steel or wood into the item ? For instance I'm wondering how to make steel hinges for a Seaplane door to fit the exiting fuselage hinges. Does epoxy bond well to steel ?

[rodsmith]

For the gull wing door hinges, I bolted them to the carbon fiber tubes using through bolts. Before I had epoxied them together I had inserted small sections of 5/8" square steel tubing inside the carbon tubes to bolt through. For the composite panels I planed the hardwood to 3/8" and replaced the foam with hard wood at the hinge locations to bolt through. I used 5 min epoxy to glue the hardwood in place before laminating both sides. At the latch location I needed a thinner section so just laminated over a piece of 1/4" aluminum. Epoxy will bond to steel or aluminum if the metal is sufficiently roughed up, think 80 grit sandpaper.

[svyolo]

I don't know how they do it in the aerospace industry, but the marine industry reinforces under laminated sandwiches similar to what you described. Sometimes hard wood, and often just epoxy thickened with high strength filler. Even in the middle of a panel. Drill a hole thru 1 side, then dig out the foam, balsa, etc with a drill and a nail bent 90 deg. Clean it out, fill with thickened epoxy. When cured, drill thru the whole thing. You get a super hard "pad" even in the middle of a large panel.

This might work in a tube as well. Put a small slug of toilet paper on either side of the hole, and fill with epoxy.

[Battson]

The full lexan front doors don't help with weight.

This is a relevant point. The acrylic or lexan are much heavier than a door itself, whatever its made of.

[EBPaul]

I think it’s PPG who makes lightweight plastic I wonder if it’s something that would be available to us

[Battson]

One of our main safety concerns is a window or skylight coming free and damaging the rudder or elevators, causing a departure from controlled flight. I think using the best quality (strong) windows and skylight is important.

[500AGL]

I believe Rob Caldwell’s doors are carbon fiber and I think he may do them again if he had the option, just for the time spent. But perhaps he would, now that he’s learned.

I opted for premade carbon (cored) floorboards, for basic reasons. They have a “finished” surface, and trim to fit somewhat easily. They provide a more “dense” thud if you’re pounding around on them as compared to metal, and perhaps(?) will provide more sound deadening to the cockpit from exterior sound.
As I come from a cub world, many cub guys use these to reduce weight of their wood floorboards.

The first trade off is you can screw them up just as easy and they are very hard to fix and expensive to replace. The second trade off is that they don’t flex to install, so you really have to plan your design or you may be surprised what area ends up with gaps.

Also, if you have factory floor metal check the fit before using it as a pattern. That bit me.

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[rodsmith]

How thick a core do these have?

[500AGL]

Rod maybe -5/16-3/8 overall. I can measure for you.

[svyolo]

I made one attempt at a CF floorboard, I made a couple of mistakes on the layup and I didn't like it. I still want to revisit it eventually. If I do it I will either use one layer of kevlar on bottom laminate as well, or use 1" kevlar tape in a criss cross pattern on the bottom as a safety backup. If the CF breaks, the kevlar will keep it from failing catastrophically. I did that on my cargo tube. Mostly CF, with a small amount of kevlar on the outside. It really "toughens up" CF.

[predragvasic]

robcaldwell has fabricated his own carbon fibre square tubing for the door, and if I recall correctly, his weight savings were around 3 - 4 lbs per door. He explains it in great detail on his YouTube channel:

[500AGL]

rodsmith, 1/4” core and 5/16” overall.
It’s one layer of carbon top and bottom.

[Nev]

Very Nice !

[500AGL]

Nev, it's purchased pieces from Randy at Carbon Concepts in Alaska.