Quantcast

How should I lay fabric here?

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

Built2Fly

Well-Known Member
Joined
Feb 21, 2020
Messages
92
Location
San Diego, California, USA
I am dry fitting the bottom of the fuselage, trying to figure out the challenges first. So I have this question on what I should do here.

So basically this is the bottom of the fuselage. The whole frame is upside down. Engine (unmounted now) will be on the right hand side, and tail is toward the left hand side. The muffler is hang at the bottom of the fuselage with 4 bolts. The arrow points to one of the bolts. There is an aluminum standoff, and a rubber cushion, with a bolt going through the middle.

20210112_192028.jpg

The aluminum standoffs stand higher than the bottom plane of the fuselage, as shown in the picture below. So my question is whether I should lay fabric (a) like the yellow line below and cut a hole around the standoff, or (b) like the green line between the aluminum and rubber and only need to punch a small hole for the bolt?

20210112_191938.jpg
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
7,481
Location
Saline Michigan
Polyester fabric and paint will both turn to other materials (burn) with typical exhaust system temperatures.

Since the fabric is on the cold side of the rubber isolator, I suspect conducted heat is not a problem.

Exhaust pipes quite hot and radiate heat to the fabric. The further the fabric from the pipe, the less heat has to be handled in the fabric. A radiative heat shield of some sort is likely to be needed. Heat shields are usually metal with either an insulator or an air space between them and the surface being protected. There are two ways of doing this:
  • One is the shield is stainless and close to the hot surface, but they can be fussy, prone to vibration damage, falling off, etc.
  • The other is to put a thin metal shield on the things being protected.
All a matter of which parts are how hot and how close, and no, I am not expert on protecting stuff from exhaust systems, but closer to the engine the hotter the pipes usually are. Thin aluminum along the fabric, glued on with some lines of high temperature silicone and an air gap gives a radiation barrier and an insulator to the fabric below. If you guess too little protection, you will have discolored paint quickly telling you where to enlarge your shield and perhaps requiring a repair. Guess too much and you have a few ounces extra of heat shield.

Billski
 

bmcj

Well-Known Member
HBA Supporter
Joined
Apr 10, 2007
Messages
13,595
Location
Fresno, California
Is this craft built under Part 103 where you have a maximum weight limit? Most aircraft have aluminum (or sometimes composite) cowlings around the hot engine compartment and exhaust areas. If you aren’t absolutely weight restricted, you might consider an aluminum sheet with stiffeners instead of fabric in that lower bay.
 

Built2Fly

Well-Known Member
Joined
Feb 21, 2020
Messages
92
Location
San Diego, California, USA
This is a Hiperlite SNS8. It is an ultralight, but I am also thinking about the option of registering it as EAB. For the sake of simplicity, maybe I can use fabric there as originally designed and keep an eye on it to replace it with sheet metal if it does not go well.

Thanks for the ideas.
 

Victor Bravo

Well-Known Member
HBA Supporter
Joined
Jul 30, 2014
Messages
8,286
Location
KWHP, Los Angeles CA, USA
I would laminate or glue a layer of the thinnest possible metal onto the outside of the fabric as a heat shield, in the immediate area of the exhaust. If you can get .012 or .010" thick aluminum or stainless, then use that. Industrial catalogs like McMaster-Carr have stainless "foil". Even a couple of layers of the heavy duty aluminum foil from a restaurant supply store. Something to reflect and mitigate the heat before it gets to the fabric.
 

Dan Thomas

Well-Known Member
Joined
Sep 17, 2008
Messages
5,608
I wouldn't bond the shield to the fabric. It might reflect some heat but would faithfully conduct the rest of it right into the fabric. Stand it off like Billski says.

If it melts in flight you might have a problem. Could start ripping away from the airplane.
 

Built2Fly

Well-Known Member
Joined
Feb 21, 2020
Messages
92
Location
San Diego, California, USA
How do they do it on the other Hiperlites?
Those are fairly rare. I have never seen a real Hiperlite in life. Online pictures and videos does not show enough details to this scale. It looks that there is no metal heat shield on the underside and it is just fabric. But I am not sure if the fabric is going in (a) or (b) in my first question. From the parts I have, it seems that the shred of fabric left on the bolt is going as the green line in (b). But I do not quite like the way that it pops up on an otherwise flat fabric plane.

I am trying to locate some real flying Hiperlites in my region, but haven't found one yet.
 

Mohawk750

Active Member
Joined
Jan 1, 2021
Messages
38
Location
Ottawa, Ontario
The aluminum standoffs stand higher than the bottom plane of the fuselage, as shown in the picture below. So my question is whether I should lay fabric (a) like the yellow line below and cut a hole around the standoff, or (b) like the green line between the aluminum and rubber and only need to punch a small hole for the bolt?
It's a tricky area but obviously it was covered before and didn't go up 'err down in flames!

I choose option a) allowing the standoff to protrude through the fabric. It looks like there is quite a bit of adjustment in the slotted holes in the muffler attach angles to move the exhaust even further from the surface.

If you still have an issue there are several in expensive heat shield options that fasten to the muffler/pipe not the surface you are trying to protect. Look up "Universal motorbike exhaust heat shield" on Amazon and you will have your choice of black, chrome or corbon fiber or fiberglass heat wrap all for not money.

Mark
 

Built2Fly

Well-Known Member
Joined
Feb 21, 2020
Messages
92
Location
San Diego, California, USA
@Mohawk750, that shield would be a great "after-production" solution. Thanks.

I like the idea of building it as stock as possible, and tried to catch myself from getting too carried away on improvements. That's the fastest way for me to get to a known working configuration, and I can always improve from there later.
 

Rockiedog2

Well-Known Member
HBA Supporter
Joined
Dec 11, 2012
Messages
2,499
Typically glue the fabric to the fuse with it over the standoff and shrink it. Then cut a hole around the standoff and let it come thru. Unless it’s so tall the fabric will go loose. If you don’t cut around it then it will likely wear thru from the buffet on the corner of the standoff.
If it needs a heat shield I would fab up one out of 016 or 020 6061 t6 that fastens to and wraps partially around the exhaust. I would want air between it and both the exhaust and fabric
 
Top