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General control line discussion => Open Forum => Topic started by: pipemakermike on April 29, 2015, 07:54:26 AM
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Firstly understand that I live in the UK"
I have been building combat models and covering them with nylon for at least 50 years and I have a pretty well sorted method:-
dope structure, wet nylon in tub of water, lay on towel to remove loose water, lay on model and fix around the edge with more dope pulling tight.
Then leave for some hours to dry when the nylon will be drum tight ready for a couple of coats of thin dope followed by a couple of coats of thicker dope.
This has always worked for me until last year when the covering of my Razorblade 64 (http://www.machineconcepts.co.uk/aeromodelling/razorblade-64.jpg) failed to tighten and no amount of dope would tighten it. The dope didn't seem to go into the weave and just laid on top
I am currently building 4 Supermongers (http://combatflyers.co.uk/files/howto-monger1_slidepic1.png) and am just getting sorted to cover them. I don't want to suffer the same problems again so I have done some experiementing:-
The nylon I had problems with was supplied by Flair and appeared to be OK. I cut a strip 495mm long and 1" wide, soaked it in water for 30mins then laid it on a board to see if it had expanded in length. The result was no change of length.
I did the same test with an offcut of the nylon I used some 20 years ago. the length dry was 310mm and the length wet after 15mins was 317mm. after leaving to dry it shrunk back to 310mm long - much what I was expecting. a shrinksge of 2.25%
Next I cut a new 495 long strip of the Flair material and washed it well in detergent and warm water. This time it had lengthened to 500mm when wet. so a shrinkage of 1% - not ideal but better than the "as suppllied" material.
My suspicion is that modern nylon material is treated with something that stops the nylon thread absorbing water and that is the problem. Raw nylon can expand as much as 5% when immersed in water.
Has any one else seen this problem or any more information.
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I did. So I pulled the fabric off an went with Monokote instead. But what you are describing is exactly the issue I had with some new "nylon" I had tried covering a wing with. It never tightened up after the wing was covered and doped. I also left some wrinkles in place at the time thinking the shrinkage would take it out.
%^@ %^@ ~^
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I have now tested a lot of different nylon offcuts from my scrap covering box some of which I think that I used back in the 60's
I am seeing an expansion when wet of about 2% and that is enough to pull the covering really tight.
The modern stuff doesn't shrink at all unless some other treatment is done. I have tried washing by hand with non-bio Persil liquid. This changed the expansion from zero to 1%. it is possible that a more agressive washing will achieve more.
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I have now tested a lot of different nylon offcuts from my scrap covering box some of which I think that I used back in the 60's
I am seeing an expansion when wet of about 2% and that is enough to pull the covering really tight.
The modern stuff doesn't shrink at all unless some other treatment is done. I have tried washing by hand with non-bio Persil liquid. This changed the expansion from zero to 1%. it is possible that a more agressive washing will achieve more.
Mike,
If it' very humid where you are it's possible that the nylon threads are already saturated before you wet them. Have you tried drying the material in an oven prior to wetting it?
Randy Cuberly
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Will it shrink with heat like polyspan?
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Mike,
If it' very humid where you are it's possible that the nylon threads are already saturated before you wet them. Have you tried drying the material in an oven prior to wetting it?
Randy Cuberly
I am seeing the differences in the different samples in the same environment and late spring in the UK is seldom humid and I am working in a conservatory on a sunny day
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Will it shrink with heat like polyspan?
No but it can be melted<G>
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Have you tried to wash it in hot water then using hot water before you apply it to the airframe? It seems that nylon would not absorb water at all (unlike silk or cotton or silkspan paper) so the only thing could be heat to expand it a bit, then as it cools it should shrink tight. Could the nylon you purchased have some type of waterproofing on it?
Here in the US we tend to use silk, silkspan paper, polyspan or film. I think some a way back used rayon.
Is the nylon lower cost then polyspan or film? Is it lighter weight? Let us know how you make out on this.
Best, DennisT
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Don't know if this will help but in the 70's I covered combat ships with a fabric that was called acetate sheath lining from a local fabric store. We doped it down dry, sprayed with water, it had great shrinkage, than doped as normal. I think I was told it was used to line suit and sportcoat jackets.
Rich
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Have you tried to wash it in hot water then using hot water before you apply it to the airframe? It seems that nylon would not absorb water at all (unlike silk or cotton or silkspan paper) so the only thing could be heat to expand it a bit, then as it cools it should shrink tight. Could the nylon you purchased have some type of waterproofing on it?
Here in the US we tend to use silk, silkspan paper, polyspan or film. I think some a way back used rayon.
Is the nylon lower cost then polyspan or film? Is it lighter weight? Let us know how you make out on this.
Best, DennisT
Nylon is a hydrotropic material and actually contains water within it's molecular structure. Without the water it becomes brittle and loses a lot of it's useful strength. This condition is one of the reasons the old Top Flite, etc props should not be used. As the nylon ages the water is lost and the material becomes brittle. Some of the lost water can be replaced by soaking the material in hot water (at least boiling temperature) for at least 30 minutes.
This raises the question to Mike of How old is the material you're using?
Randy Cuberly
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Mike,
If it' very humid where you are it's possible that the nylon threads are already saturated before you wet them. Have you tried drying the material in an oven prior to wetting it?
Randy Cuberly
That makes sense. It's wet, so dry it in order to to wet it again. Thanks.
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Nylon also takes time to take up water and elongate. Try allowing the nylon samples to soak for an hour, and overnight, and test it again.
Phil
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Mike,
What I think is happening is the manufacturer of the Nylon is using a sizing/fabric lubricant for manufacturing the Nylon cloth. As you have discovered it is interfering with water absorption. The Dacron fabric that we use to cover full-scale airplanes also has a sizing that must be removed prior to applying dope. However, the Dacron fabric is a heat shrunk material so we don't have to wet it prior to covering. I first cover the wing/fuselage/empennage then prior to doping the fabric it must be wiped with a clean rag soaked in & kept wet with MEK which removes the sizing.
For the Nylon material I would wash and rinse it as you are doing to remove the sizing. MEK will not hurt the Nylon and will remove the sizing but be sure to use rubber gloves and do it in a well ventilated area.
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Have you tried to wash it in hot water then using hot water before you apply it to the airframe? It seems that nylon would not absorb water at all (unlike silk or cotton or silkspan paper) so the only thing could be heat to expand it a bit, then as it cools it should shrink tight. Could the nylon you purchased have some type of waterproofing on it?
Here in the US we tend to use silk, silkspan paper, polyspan or film. I think some a way back used rayon.
Is the nylon lower cost then polyspan or film? Is it lighter weight? Let us know how you make out on this.
Best, DennisT
- Nylon absorbs water
- Nylon doesn't heat shrink
- Nylon is significantly stronger than silk and much stronger than silkspan
- Nylon is legal for vintage combat modern films are not
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Mike,
What I think is happening is the manufacturer of the Nylon is using a sizing/fabric lubricant for manufacturing the Nylon cloth. As you have discovered it is interfering with water absorption. The Dacron fabric that we use to cover full-scale airplanes also has a sizing that must be removed prior to applying dope. However, the Dacron fabric is a heat shrunk material so we don't have to wet it prior to covering. I first cover the wing/fuselage/empennage then prior to doping the fabric it must be wiped with a clean rag soaked in & kept wet with MEK which removes the sizing.
For the Nylon material I would wash and rinse it as you are doing to remove the sizing. MEK will not hurt the Nylon and will remove the sizing but be sure to use rubber gloves and do it in a well ventilated area.
Thanks Bill
I plan to cut a couple of pieces oversise then have them in the washing machine for an hour and see how that changes the properties. I do have some MEK and I used to use it as a solvent in the early days of inkjet printin but I agree that it is dangerous stuff.
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Hey Mike:
Just tossing out ideas to try, I have no magic to offer:
If washing the stuff doesn't get things far enough, you might want to try different brands. Really cheap stuff may actually work better for your purposes than stuff that's "premium".
If the MEK doesn't work, or if you want something milder you may also want to try more aggressive detergents, or treatment with mildly acidic or basic solutions (I'm thinking vinegar or washing soda* here, not concentrated muratic acid or lye).
With what little I know about manufacturing cloth I think you're trying the right things.
* Washing soda in the US = sodium carbonate, which is stronger than bicarb.