Shrinking Fabric

[503]

An oxy set will do the same job as a heat gun if carefull ,although not recommended

 

 

[M61A1]

Like I say, try a heat gun on a test piece first. heat control is easy, took a lot more heat to melt the fabric there, than I needed to get fabric taught on plane. Don't know about melting glue into the fabric, I used MEK for that. guess there is lots of ways to skin a cat.Andrew

the problem is not about melting the fabric, it's that once you exceed a certain temperature , the fabric permanently loses it's tension. An iron provides a consistent temperature evenly over the surface, to achieve even shrinkage.

 

 

[skippydiesel]

Wow!!!! and here was me thinking I would just get the make & model of a few irons that have been successfully used by others. Dafydd seems to have come closest in this regard.My thanks Dafydd.

 

Just to expand on my situation a little further: I am using the Stewart System - the manual is very comprehensive and goes into some detail regarding iron specifications.

 

I have three irons (in the house) - so far non meet the specs. In the main, the hot plate fails to heat evenly with large variation from side to side & front to back

 

My research to date would suggest:

 

So called "dry irons" seem to be below the 1100 watt minimum requirement.

 

All modern irons have "auto shut off"

 

Regarding "auto shut off" - while I see the benefit in having an iron that is on when you expect it to be so ie continually on (no auto off) I think that an iron with auto off could be managed, it would just require that it be checked for temperature each time you pick it up. Tedious to be sure, but "do able" - I have several thermometers including a cheapy infra red (instant readout) from Super Cheap to assist in temperature monitoring.

 

Pinking Shears ??? - Not sure how we "drifted" on to this - I bought my rotary pinkers through Stewarts

 

Heat gun promoters - I like to flatter myself I think "outside the square" however I feel that this is a step too far - check out the Stewart manual and their very precise temperature requirements for progressive shrinking of fabric and their warning regarding overheating.

 

Anyone like to recommend an iron ie make/model

 

 

[metalman]

I like the utube stuff on the Stewarts system, I have heard of some issues with the top coats, keep us posted it would be good to hear your thoughts. I used the poly fibre stuff and the 2pak paint on mine, pretty happy with the results, but I'd be keen to give the Stewarts a go.

 

Cheers Matty

 

 

[cherk]

Wow!!!! and here was me thinking I would just get the make & model of a few irons that have been successfully used by others. Dafydd seems to have come closest in this regard.My thanks Dafydd.

Anyone like to recommend an iron ie make/model

??

 

http://www.aircraftspruce.com/catalog/cspages/iron.php

 

http://www.aircraftspruce.com/catalog/cspages/sealfabriciron220.php

 

 

[Dafydd Llewellyn]

Wow!!!! and here was me thinking I would just get the make & model of a few irons that have been successfully used by others. Dafydd seems to have come closest in this regard.My thanks Dafydd.Just to expand on my situation a little further: I am using the Stewart System - the manual is very comprehensive and goes into some detail regarding iron specifications.

 

I have three irons (in the house) - so far non meet the specs. In the main, the hot plate fails to heat evenly with large variation from side to side & front to back

 

My research to date would suggest:

 

So called "dry irons" seem to be below the 1100 watt minimum requirement.

 

All modern irons have "auto shut off"

 

Regarding "auto shut off" - while I see the benefit in having an iron that is on when you expect it to be so ie continually on (no auto off) I think that an iron with auto off could be managed, it would just require that it be checked for temperature each time you pick it up. Tedious to be sure, but "do able" - I have several thermometers including a cheapy infra red (instant readout) from Super Cheap to assist in temperature monitoring.

 

Pinking Shears ??? - Not sure how we "drifted" on to this - I bought my rotary pinkers through Stewarts

 

Heat gun promoters - I like to flatter myself I think "outside the square" however I feel that this is a step too far - check out the Stewart manual and their very precise temperature requirements for progressive shrinking of fabric and their warning regarding overheating.

 

Anyone like to recommend an iron ie make/model

If it helps - the little iron I got from Hervey Norman is a Chinese generic basic steam irom, branded "Tru-Flo" (See photos). I don't think it's anything special, but I'm getting satisfactory results on Ceconite 102 with it.

 

I suspect the iron itself is not as critical as how you calibrate it. I used a mercury-in-glass laboratory-style thermometer, with a dab of heat-sink compound as sold by Jaycar - tho I suspect any of the electronic supply companies would have this, and I spent most of an afternoone calibrating it, with the iron sitting on the bulb of the thermometer on some scrap dry rag (i.e. pretty much insulated from the outside air); I used the procedure outlined by the Poly-Fiber catalog. I would suggest from this experience that you need to find the temperature that the iron cuts out on the rise, and the temperature that is cuts back in, on the fall, and do that several times, for each required temperature setting. Then try to adjust the control until it cuts out at the upper limit for the temperature range you are after (Poly-Fiber gives a nominal 225 deg F, 250 deg F and 350 deg F, with some indication of the tolerance); and in general, get the "feel" of how the temperature control actually works.

 

I rather doubt that any iron with an aluminium sole-plate will exhibit much of a temperature range across the sole-plate under the conditions for shrinking fabric, which drag heat out of the iron a lot more slowly than it is designed for when it is operating in steam mode.

 

In any case, the Poly-Fiber instructions are to go right over the surface three times at each temperature, to get the shrinkage even. I did it by the book, and it worked for me.

 

 

 

 

[Yenn]

Use an iron and calibrate it with a jam making thermometer. No problems.

 

 

[Dafydd Llewellyn]

Use an iron and calibrate it with a jam making thermometer. No problems.

Agree - provided you can couple the bulb to the sole plate of the iron with a dab of heat sink compound, which is a thermally-conductive paste. You can buy a tiny tube of this from Jaycar.

 

 

[M61A1]

Agree - provided you can couple the bulb to the sole plate of the iron with a dab of heat sink compound, which is a thermally-conductive paste. You can buy a tiny tube of this from Jaycar.

Also from Jaycar, an inexpensive multimeter, that comes with a K-type temperature probe. They are quite accurate, and are the same type (probes) we use for hot bonded composite repairs. They are a lot hardier than glass thermometers.

 

 

[old man emu]

Some time ago, I posted an article on how to tie the Modified Seine Knot. You might find it useful.

 

http://www.recreationalflying.com.au/threads/a-practical-guide-to-rib-lacing-using-the-modified-seine-knot.16575/

 

Old Man Emu

 

 

[skippydiesel]

Hi Dafydd - my thanks for the Jaycar multimeter suggestion - purchased one for $40 yesterday.

 

Old Man Emu - you may be surprised/horrified/aghast to hear my aircraft, an ATEC Zephy, does not use rib lacing, only heat activated glue. The technique works. The existing fabric has been in place, without problems, for 14 years.

 

 

[Old Koreelah]

Old Man Emu - you may be surprised/horrified/aghast to hear my aircraft, an ATEC Zephy, does not use rib lacing, only heat activated glue. The technique works. The existing fabric has been in place, without problems, for 14 years.

The importance of rib stitching was the subject of much discussion on the Jodel forum a few years back. Hearing about the fabric lifting on one aircraft is enough to get your attention. There is one adhesive which is said to have sufficient peel resistance to do the job: as long as the ribs are wide enough to give plenty of contact area.

 

The Zephyr wing has a fairly narrow chord, so the part behind the spar may not experience as much lifting pressure as other wings.

 

 

[skippydiesel]

OME - dont know enough to comment on other aircraft or the physics /fluid dynamics that may impact on the surfaces - to the best of my knowledge there have been no problems with the Zephyr's ATEC factory applied fabric covered surfaces.

 

I only know of one other Zephyr that has had an owner/after factory applied fabric - to date there have been no problems.

 

As with the other owner, I intend to extend/increase the glued adhesion area (above that of the factory) where this is possible. This is more for "piece of mind" than any factual concerns.

 

The Stewart System people are aware of the Zephyr fabric attachment system and are confident that their adhesive will equal and possibly improve on the ATEC factory applied product.

 

All in all I believe I will end up with an effective & durable finish - my only concern is will the result be esthetically pleasing - I may have to hire a spray painter to do the topcoat(s).

 

 

[Dafydd Llewellyn]

I once had a panel of fabric come off the upper wing surface of an Auster I was flying as a glider tug. It simply tore adjacent to the rib stitching, so I lost the strip between two adjacent ribs, from the leading edge to the aileron shroud. I didn't know about it until after I had landed - tho I noticed a bit more crosswind on the landing than the windsock was showing. The rib stitching contained the failure so it wasn't a problem, in other words. Ever since then, I've been rather fond of rib stitching, if the aircraft has fabric-covered wings . . . it comes under the heading of "cheap insurance", as far as I am concerned. The added drag of rib stitching is only significant for the front part of the wing; aft of the spar, it has no measurable effect. Aesthetics? I can't spell the word . . .

 

 

[skippydiesel]

Hmmm- It would be possible to rib stitch a Zephyr but how do you treat the leading, side & trailing edges of the fabric?

 

An Auster, Cub etc cover the whole wing with fabric, thus managing all edges of the fabric. As far as I know there is no adhesive treatment of the rib to fabric contact surfaces - this is where the rib stitching comes in.

 

The Z utilizes what I call a "patch" fabric cover - that is there is no facility for "locking in/down" by overlapping trailing leading or side edges. The fabric is secured by "glue" on all fabric to wing surface contact points ( leading, trailing, sides and ribs) and it works !

 

 

[Dafydd Llewellyn]

You are pretty much stuck with glue (sorry about that!) at end ribs etc, unless you are using a sewn bag, but usually the fabric is wrapped around an edge before it is glued; this removes the "peeling" load. Also, one normally reinforces that with an overlapping piece of fabric. Glue is pretty reliable so long as it is loaded only in shear; it's unreliable under "peeling" loads. There's no way to wrap the fabric around a rib cap, so you cannot avoid peeling loads there. The width of the rib cap has no effect on the peel strength; "peeling" occurs along the line where the glue is being pulled away, i.e. it's solely a local effect, and the failure simply progresses along the joint as far as it needs to - twice the width does not change the tensile stress in the fabric necessary to start a peeling failure. If you look at the Poly-Fiber manual - I thoroughly recommend it - you will see how they deal with leading & trailing edges etc. Aircraft that have metal skin back to the main spar, and fabric aft of that, normally use some form of mechanical attachment where the fabric joins the metal skin; sometimes by wrapping the fabric around a strip of metal and rivetting that down to the skin, sometimes by metal clips, etcetera. I think you left a couple of words out of your post: "it works - for a while . . . "

 

 

[skippydiesel]

Yes ! for quite a while - 14 years and the only reason I am replacing it now is the paint (over the fabric) & elsewhere is cracking & peeling. I would happily repaint the aircraft without removing the fabric if this seemed to be a viable option.

 

I believe the paint (applied by the original builder) was automotive, modified with extra "elastiser". All things considered, its done quite well.

 

The fabric still seems to be in good condition, however the loss of protective paint will result in accelerated UV damage and the whole aircraft is staring to look a bit tatty - time for a makeover. Add to this that ATEC advise recovering at a very conservative 10 year interval - I assume this is based on the worse case senerio - insufficient UV protection (paint) and outdoor parking.

 

I have researched the matter and come to the conclusion that "traditional" fabric covered aircraft, in the same sort of performance range as the Z , developed their fabric covering systems in the era of organic fabrics and dope shrinking/stiffening. Nothing wrong with this, however times have changed and ATEC seem to have come up with a system that suits their aircraft, current polyester fabrics and heat melt/fix adhesives.

 

14 years without a problem speaks volumes for a very much simpler and lighter system than those employed by older metal or wood framed aircraft.

 

 

[Methusala]

It is neither possible nor prudent to make an argument against one who advocates a 'belt and braces' solution. In my work I have ben asked whether the householder should turn the isolating valve to a dishwasher off when not in use. No win really so I say yes on the small possibility that the inlet system could fail and flood the house. Don

 

 

[Dafydd Llewellyn]

Yes ! for quite a while - 14 years and the only reason I am replacing it now is the paint (over the fabric) & elsewhere is cracking & peeling. I would happily repaint the aircraft without removing the fabric if this seemed to be a viable option.I believe the paint (applied by the original builder) was automotive, modified with extra "elastiser". All things considered, its done quite well.

 

The fabric still seems to be in good condition, however the loss of protective paint will result in accelerated UV damage and the whole aircraft is staring to look a bit tatty - time for a makeover. Add to this that ATEC advise recovering at a very conservative 10 year interval - I assume this is based on the worse case senerio - insufficient UV protection (paint) and outdoor parking.

 

I have researched the matter and come to the conclusion that "traditional" fabric covered aircraft, in the same sort of performance range as the Z , developed their fabric covering systems in the era of organic fabrics and dope shrinking/stiffening. Nothing wrong with this, however times have changed and ATEC seem to have come up with a system that suits their aircraft, current polyester fabrics and heat melt/fix adhesives.

 

14 years without a problem speaks volumes for a very much simpler and lighter system than those employed by older metal or wood framed aircraft.

Simpler - I'd have to accept. I'm re-covering the control surfaces on a TC'ed aircraft, so it HAS to be done "by the book". "The book" in this case is the Poly-Fiber manual, because I'm using their STC, which happens to include my aircraft. However I'm finding that the rib-stitching isn't as big an issue as people seem to imagine; the first couple of ribs, yes it's difficult because you're learning the "knack". After that, it's a breeze. The flat-style lacing thread that Poly-Fiber supply and the hidden-knot technique make the result a lot neater than traditional rib-stitching. I'd still be inclined to use this system even for an experimental homebuilt (if I built one with fabric covering) because it has a fair chance of lasting 30 years, and that means the re-sale value will be a lot better. I do NOT want to have to do it again after 14 years or so. I had an Auster that was covered with Irish Linen (it was an ex-military one - NOT the one that shed a panel) - and its fabric had to be replaced because the automotive paint ringwormed - they always do, sooner or later. So added plasticizer or no, I'd not go there again. Keep the acrylics and polyurethanes for the rigid surfaces, by all means - but NOT for the fabric, so far as I am concerned. I'm also a firm subscriber to aluminium flake as the UV blocker; I've seen enough fabric jobs go the distance with aluminium to not feel like experimenting with anything else. Yes, it costs a bit more initially - tho not in the long term, and yes, I happen to have a forced-air breathing system so the fumes don't bother me - those things are not all that difficult to set up. A chaque'un, son gout; I'd prefer to do it once and do it properly.

 

 

[skippydiesel]

It is neither possible nor prudent to make an argument against one who advocates a 'belt and braces' solution. In my work I have ben asked whether the householder should turn the isolating valve to a dishwasher off when not in use. No win really so I say yes on the small possibility that the inlet system could fail and flood the house. Don

Hi Don - Who is advocating against your "B & B" ? - not me! - I would rib stitch an aircraft designed around such a system - my Z does not employ such.

 

 

[skippydiesel]

Dafydd

 

The UV block issue concerns me - Stewart System (SS) insist that their paint products do not require additional UV protection (even in Australian conditions).

 

I have invested a great deal (by my standards) in the SS, so will follow through, although I confess to continuing disquiet. Time will tell.

 

 

[old man emu]

First rule of aircraft maintenance is: If the manufacturer describes the procedure and materials to carry out a job, then that is the way to do it.

 

Second rule of aircraft maintenance is: If the manufacturer does not describe the procedure and materials to carry out a job, then follow AC43.

 

OME

 

 

[skippydiesel]

First rule of aircraft maintenance is: If the manufacturer describes the procedure and materials to carry out a job, then that is the way to do it.Second rule of aircraft maintenance is: If the manufacturer does not describe the procedure and materials to carry out a job, then follow AC43.

OME

A bit cryptic - Please elaborate.

 

Do you have a strip at Razorback?

 

 

[Chird65]

A bit cryptic - Please elaborate.Do you have a strip at Razorback?

Is this it?

 

http://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.list/parentTopicID/114

 

 

[old man emu]

What that means is that if a manufacturer sets out how a maintenance task is to be done; how often, and using what parts etc, then that is the way the job must be done. On your plane, the manufacturer says to glue the fabric down, shrink and dope. Since there is no mention of stitching, you are not required to do it.

 

If, however you are building something like a Pietenpol AirCamper, there are no manufacturer's instructions on how to carry out the covering process. Therefore you would refer to the FAA Advisory Circular AC43.13-1b.

 

(I don't have a strip. I'm within the Wilton Parachuting Danger Area)

 

OME