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Glassfibre covering

what size plane?

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Tony H04/07/2020 14:00:48
870 forum posts
242 photos

Hi All,

Can anyone tell me the minimum size ic plane you can fibreglass cover? I was considering fibreglassing my Sig Kobra 25-35 size plane. Is this going to be too heavy?

Denis Watkins04/07/2020 14:09:36
4536 forum posts
123 photos

See what the boys say Tony

But have made 2 small models unflyable just spraying colour on them !

One in D Day colours could not then get off the ground

Here are your standard specs without adding weight

Wingspan: 45 in 1143 mm
Wing Area: 390 sq in 25.1 dm²
Length: 39.25 in 997 mm
Flying Weight: 3.25 lb 1470 g
Radio Required: 4-Channel (not included)
Recommended Engines: 2-Stroke .19 - .35 (3.1 - 5.7 cc) (not included)

Edited By Denis Watkins on 04/07/2020 14:32:14

Doc Marten04/07/2020 14:26:39
630 forum posts
7 photos

Work out the added weight to give you the overall, then the wing loading if you want to use the scientific method.

Barrie Lever would be a good advisor as he has mountains of knowledge in this.

Edited By Doc Marten on 04/07/2020 14:30:26

Barrie Lever04/07/2020 14:31:05
269 forum posts
50 photos


No minimum size, the weight build up if done correctly is minimal over film and if the model lasts any length of time is probably lighter as no fuel soak takes place and repairs are less likely.

Shout if you need any instruction on glassing.


Cuban804/07/2020 14:33:50
2989 forum posts
1 photos

Just looked at the specs for the Kobra and it's designed as a lightweight model from the outset. 45 inch span and

3 1/4 lbs flying weight. You could use a glass/paint finish but through bitter past experience and with the best will in the world, weight build up can catch you out. With larger models you have to be very ham fisted and clumsy to make an unflyable model with loads of filler/too heavy cloth/ excessive resin not rubbed down sufficiently, and to cap it all, layer after layer of paint, but you risk disaster all the more with a small model, even when taking care. I have produced satisfactory results but only after much experience and learning what works and vice-versa.

If it was my Kobra, I'd pay particular attention to making a nice smooth finish to the airframe and then go with an attractive film colour scheme. If you want to try glassing, make up test pieces from a sheets of 4" wide 1/4 balsa say about a foot long. and try out various techniques to see what you get on with. Practice on a curved sheet as well to get used to manipulating the glass correctly. Go to YouTube and you'll be amazed at how many different ways of glassing there are. Search for a chap called 'Hornitpilot' I find his methods work for me.

Edited By Cuban8 on 04/07/2020 14:42:04

John Stainforth04/07/2020 14:40:25
367 forum posts
64 photos

For the added weight, calculate the surface area of the plane, convert that to weight (knowing the wt/area of the cloth) and double it, because the ideal ratio of resin to cloth is about 1:1. Glassfibre adds a lot of strength to the surface of the plane, so ideally one should try to reduce the amount of weight in the rest of the structure. Admittedly, that is easier said than done!

Richard Clark 204/07/2020 17:04:48
418 forum posts

I've only ever done it once. On the RBC kit 45 inch span 90mm EDF Grumman Panther.

I use Flair 'medium thickness' woven glass and their matching epoxy resin.

It all went fine, wasn't difficult, and the finish was good.

But it turned out to be less 'ding' resistant than doped on heavyweight tissue, was heaver, and added no more strength than the doped on tissue. I won't bother with it again.

Engine Doctor04/07/2020 17:30:05
2533 forum posts
39 photos

I glassed a Peterborough Models Cap 21 years ago then gave it a fancy paint job with two pack car paint sprayed carefully to avoid extra weight. It was heavier but flew fine perhaps a little faster with an old Merco 60 on the front.

The resin is the heavy part and if you soak all the excess resin up with kitchen roll it will keep the weight down.

The model is now living with a club mate and still looks the business.

Edited By Engine Doctor on 04/07/2020 17:31:28

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