Author Topic: Floor covering.  (Read 5109 times)

Doug Johnson

Floor covering.
« on: August 16, 2011, 06:41:10 PM »
Floor covering.

A while back a friend of mine that lives in Upper Lake, CA had an interesting experience. He was selling his 172 so he took it to a nearby airport that advertised a reasonable price, so it would have a fresh annual. He made arrangements to pick the 172 up in a few days and had his wife pick him up.

When he returned, his wife dropped him off and he expected to fly it home. It seems without calling him, the AI had taken exception to the carpet that was installed. Ron owns a floor covering store and had put in some high priced mohair carpet that was supposed to have minimal chemicals in it. It was not specifically PMA approved and the AI would not sign off the airplane as being airworthy. After some bickering and name calling it was settled that the only thing that kept it from being airworthy was the carpet. Ron whipped out his carpet knife and  proceeded to cut the carpet out in pieces and drop them on the floor. He then asked for his paperwork with the implied threat that more than the carpet would be cut up if it wasn't signed airworthy so he could fly it home.

When I was rebuilding 1233 there weren't any specifically precut floor coverings for the Helio. I looked at a bunch of airplanes for ideas. One that I almost installed was a gray rubber mat that had a raised diamond plate pattern on it. The reason I didn't want to go with a carpet material was because I used the Helio for hauling stuff and I eventually planned to put it on floats. I had put a short nap PMA approved carpet in my 172 and it was a pain to keep clean, and when it snowed or your feet were muddy it got worse.

What I found was a charcoal colored rubber mat with a raised random pattern that was used in trucks and buses and had a DOT commercial fire resistance code very similar to the FAA fire resistance code. It also had a ½ or ¾  inch thick high density closed cell foam on the underside which gave it sound proofing and thermal insulating properties and when you kneel on it, it has a little bit of cushion to it. At first I was going to cut slots so the bottom of the 1400 series seats could bolt flush to the floor but while doing some research on soundproofing I read that in a high noise environment you absorb some noise from the low frequency directly into your body so I decided to use longer bolts and set the seats directly on top of the mat to give them a little more vibration isolation. I also read that a large percentage of the noise in an airplane comes from the fire wall the floor and the rear bulkhead so this floor covering did help considerably with noise. It was also quite easy to keep looking presentable.

But there is a definite weight penalty compared to a thin carpet. I decided I was getting several things that I wanted and the triple weight was worth it.

As always thoughts, comments are invited.

Doug
Doug

Louis

Re: Floor covering.
« Reply #1 on: August 16, 2011, 07:20:22 PM »
I can't see on what ground ( reg) your friend coud not have his 172 with carpet.  There was none reg on flammability on aircraft build before 1990.  Even for commercial with type certificate before some year and below some passenegrs numbers.  I can't see on what spec the carpet could meet, since there is no flammability spec for this 172

For you, i would not take a very long search.  Besides the fact that a non-flammable interior is something that is alway desirable, i am sur it won't change anything in a small plane like a Helio.  Post fire crash are fuel related crash.  Having a carpet non-flammable or not won't make any difference in a crash where fuel is in the cabin.  Good bladder is your best bet to keep the fuel in the wing.  They do work very well for that.  I have a friend that completely destroyed a 180 with bladder tank.  Not a drop of fuel went out.  Another died in a 180 that was manufactured without baldder with integral tank in a hard landing that pop out the inside rib that was holding the fuel.  He had a shower of fuel inside the cabin.  The plane was put on fire for almost three hours.  Nothing was left of him that could not be put in a small garbage bag.  He could had any carpet, he had no chance.  I am sure tne inside flammability is not a factor.

Except for your electricals.  Good wires with the late non-flammable insulation is a plus.  Not for the fire itself, but for the fumes.

Any aramid product ( nomex ) covering flamable object ( cushion ) will gives a very good protection if you allow to smoke cigarette in your plane.

I have put the beaver stuff on my helio.  Heavy, but beautifull.  Non-covered.  no plywood needed under it.  I cary heavy stuff.  Good choice for that.  But if i had to redo it, i think i woud take that honeycomb nomex stuff that weights nothing.  Too expensive on first class suppliers, but you can find it sometimes with defects at "affordable" price.  And it is non-flammable.   But it crhuses under localozed pressure, you need thos wide flange washer

Just some thoughts....

Louis

Doug Johnson

Re: Floor covering.
« Reply #2 on: August 16, 2011, 08:18:24 PM »
I'll have to call Ron it might have just been a good story so I'll have to to be careful in my questions. Or it might have been an attempt by struggling shop to get a couple more bucks and it backfired. I suspect it was one of those events where neither party took time to determine the true facts. A lot of people use that PMA approved for both good and bad and don't even know what it means. Off the top of my head, I don't think I can answer that question. I'll have to look it up.

Parts Manufacturer Approval (PMA) is a combined design and production approval for modification and replacement articles. It allows a manufacturer to produce and sell these articles for installation on type certificated products. Orders 8110.42 and 8120.2 prescribe the approval procedures for FAA personnel and guides applicants in the approval process.

As far as flame resistance I misspoke myself somewhat, because that was what I was concerned about was the noxious fumes.

I've never smoked or allowed any one to smoke in my airplanes. Other places I try not to make to much of an issue of it because I once smoked myself.

Doug
« Last Edit: August 16, 2011, 08:50:01 PM by Doug Johnson »
Doug

Doug Johnson

Re: Floor covering.
« Reply #3 on: August 17, 2011, 07:21:53 PM »
I did some looking around on the web after reading Louis' post on honeycomb material and found Hexcel Fiberlam which is an extremely lightweight flooring that they use in Boeing aircraft.

I wonder if you used it for flooring material and attached it in enough places. If it wouldn't strengthen the frame and floor without increasing the weight.

Doug
Doug

391stol

Re: Floor covering.
« Reply #4 on: August 18, 2011, 12:13:52 PM »
Honeycomb is not a good choice for floor due to the fact that the cells are hollow and if sharp obect are placed on the open part of the cell it will puncture the cell.  Divinycell PVC foam is a better core choice can be purchased in many densities and when sandwhiched with e-glass ,s-glass,carbon or kevlar it makes a very nice flooring and lite.

Doug Johnson

Re: Floor covering.
« Reply #5 on: August 18, 2011, 01:14:09 PM »
Interesting I bet Divinycell PVC foam would have better crush resistance for bolting it down and if you used Kevlar for the top layer and carbon for the bottom layer you'd have a tough lite floor, and if you used low or medium density foam for most of it and glued in strips of high density foam where it bolted down you have even better crush resistance. What do you think? On my plywood floor I used those washers for flat head screws.

You could probably glass in hard points for tie down rings to screw in couldn't you?

How thick would you want to go? When I did the search and found Hexcel Fiberlam they said they used a lower strength but thicker floor in the cargo areas. What's your opinion there?

I also suspect it might get a little expensive using Kevlar and Carbon. But the Kevlar would probably have great wear resistance wouldn't it?

Doug
« Last Edit: August 18, 2011, 01:33:09 PM by Doug Johnson »
Doug

391stol

Re: Floor covering.
« Reply #6 on: August 19, 2011, 09:33:23 AM »
I have made floorboards for cub type planes using 1/4 core or 1/8. In the heavy loaded areas i like to usine 2 sheets of 1/8 with a layer of 6 oz. carbon between.  Kevlar works goodon the underside because if you need to repair it you cannot sand it or anything it just fuzzes up. Sometimes it can be difficult to work with also. The norm for composite planes is a layer of kevlar in the cabin area to protect the pilot/passengers in an accident from all the glass or carbon razors in a crash.  I plan on using FR (fire res.) pvc foam with all carbon. with a FR infusion resin. Not sure of the layup schedule yet it will change through out the plane due to loading needs.  Composites are great because you can match strength and stiffness where needed in area with precision and keep things lite if done properly.  I still think it should not be used for gear legs.

Doug Johnson

Re: Floor covering.
« Reply #7 on: August 20, 2011, 08:05:55 AM »
The floor covering topic started because of my thoughts about the upgross mod and strengthening the frame and worked its way to floorboards.

My thought was that by using more rigid floorboards and attaching it in more points along the edges and on the diagonals you would increase the strength of the frame by increasing lateral rigidity without having to weld sleeves on  the diagonals or increasing wall thickness or putting in the U channel stringers that the seats attach to  in the other bays.

I was surprised that the vertical diagonals in the sides weren’t strengthened as well in the upgross mod.
Maybe that was why Larry said the frame was strong enough but the floor could use some strengthening. I remember that he said he'd looked at a lot of wrecks to reach that conclusion.

I  believe most engineering is much like airplanes a series of compromises to reach an objective.

I went back to the Hexcell site. There was information on Hexply which is cells between metal skins to decrease structural framing by strengthening the skin, and reread the information on flooring. There was also information on glues for attachment. They had different grades of floorboards which seemed to be related to traffic. The flooring used in cargo areas was low traffic but thicker.

It didn't address puncture resistance but it makes me wonder if they don't use a layer  of  PVC foam for puncture resistance on top of the cells to increase rigidity while giving puncture resistance. Maybe that’s why they are thicker.

How do you address wear resistance? I completely misunderstood the properties of Kevlar.

My understanding is that cells give better vertical or bending rigidity than foam in floorboards. But foam has better crush properties which you would need for fasteners in removable floorboards. 

It appears that in permanent or non removable flooring they attach with glue and not fasteners to give lateral rigidity. How do you do repairs if its glued together?

You spoke of fire resistance I recall reading about using ceramic fiber in composite aircraft firewalls to increase its fire resistance but that it had little structural strength. Do they use this in addition to fire resistant foam in firewalls? How do you get structural strength in the firewall?

Doug 
Doug