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Aeromaster

Simplified version of the classic biplane

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Martin McIntosh16/05/2020 17:16:43
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I would have thought that the PVA would end up as an unsandable surface to cover. Why not Poly-C or similar if you don`t like epoxy resin?

The first foam wing I bought came with a thick bandage and a pack of polyester resin. Some of the hardener must have leaked out of the bottle during transit because the stuff took ages to set, leaked through the veneer and dissolved the wing core!

Polyester would be an alternative to glue though because you do not have to wait long for it to set and is easily sanded. The Halfrauds stuff is fine for this. Epoxy is more fool proof.

Nigel R16/05/2020 23:21:02
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The short answer there is that I don't try sanding it. I've not tried using poly c but I guess it should work as well or better for this job.

Did a bit of trimming of the tissue and then a dry fit of the servo:

Nigel R16/05/2020 23:22:02
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20200516_225129.jpg

FlyinBrian18/05/2020 08:31:45
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4 photos

Nigel - I am impressed by that wing joint

Re: the aileron servo, its a bit late to suggest this but I have found it useful to use two servos in separate rx channels to allow mixing of flaps with elevator, this tightens the looping radius, only needs about c15% mix.on my JR DSX9

I have used two servos on models with torque rods such as you are using simply by installing two servos in the centre of the wing and using each separately to drive a single aileron.

I have used diluted PVA to cover a model with glass fibre, I think it was Resin W and it was fine to sand, I shirked the painting though and finished off with Profilm, I used a quite low heat while covering and it went on well

Nigel R18/05/2020 09:41:50
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Brian,

Thank you. Up close it still looks and feels a little rough, after just the single coat of PVA - there are some loose 'hairs' from the tissue, but when the 'filler' coats of PVA have gone on it is quite smooth, and a few swipes with some 80 grit take the stray hairs off. At that stage I have found film attaches quite well. The 'sticking' part of attaching film needs to be done a bit slower than for normal balsa, but by going slowly it works perfectly well (just like sticking it to ply or hardwood).

Resin W is quite a posh choice smiley

I can always retrofit another servo in the wing centre as you say - I have had this setup in the past.

Bob Cotsford18/05/2020 09:50:45
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I did my Panic with epoxy in the end as the postman dropped of the Z-Poxy finishing resin I had on order. Three layers of 25gm cloth and as you say, it barely needs sanding it blends in so well. A quick swipe to take off the stray strands and that's it.

Brian, did you have any problems with unwanted bubbles using film over PVA/glasscloth? I've used PolyC with glass but only with a paint finish.

Nigel R18/05/2020 09:58:15
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3916 forum posts
678 photos

Bob, did you use actual cloth? I imagine it might be a touch easier to get a good finish.

Martin McIntosh18/05/2020 13:46:45
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1213 photos

Got my moulds at last. On the final spat half I used the new to me gel coat and wish I had tried it years ago because the thing nearly fell out. Not so with the cowl because although I had coated it I waited too long to see how the spat turned out and it no longer had a sticky skin to apply the cloth to so I used my normal home made stuff on top. Two layers of better quality cloth went on. The cowl was very reluctant to part from the mould but with a lot of persuasion from my rubber hammer and various other torture instruments it popped out with only a couple of minor blemishes.

The pic. shows one spat awaiting the join filler and the other one done.aeromaster.jpg

Nigel R18/05/2020 14:29:42
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3916 forum posts
678 photos

Looks nice! yes

Bob Cotsford18/05/2020 17:28:56
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Posted by Nigel R on 18/05/2020 09:58:15:

Bob, did you use actual cloth? I imagine it might be a touch easier to get a good finish.

Yes, it is 25gm woven cloth, the label says that it came from Fighter Aces.

Martin McIntosh18/05/2020 17:46:04
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Nigel, have you just been using tissue as sold by Halfrauds? It has no strength at all but one layer of 25gm cloth is all you need. As I think I said before, my Spitfire has only the two dihedral joints with overlapping 25gm cloth and no braces.

Nigel R18/05/2020 18:59:31
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3916 forum posts
678 photos

I know the tissue is not as strong as cloth before the resin , of whatever type, goes on. I should make a wing and do a destruction test one day. I always figured once it was glued down the strength was about the same.

I didn't get it from halfrauds.

Nigel R19/05/2020 09:36:51
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3916 forum posts
678 photos

Another day, another set of wings joined:

20200518_225604.jpg

One of the few joints I use epoxy for. One does ones best to get a perfect joint... but in this case a strong glue to fill all gaps at that panel joint is required, it is the most critical of joins.

The TE was propped up at the tips, allowing the roots to take whatever angle was required to get parallel tips, as is usual.

Before the top side centre section sheeting was put on, I stuck a knife through the lower side sheeting, to mark out where I should cut the big slot for the ply lug. Which I have now done - before covering the wing up with glass:

20200518_225553.jpg

The ribs have already been part cut through with a razor saw and just need the cut to be completed.

And then, once the resin was dry, the first thin strip of glass and PVA:

20200518_231241.jpg

I put a second coat - filling the weave - on the glass joint of the lower wing, too. It will need more, at least one more coat to be smooth. I think with my last build, I ended up doing three filler coats, as one might expect by the time the final coat goes on it is just a light smear.

Martin McIntosh19/05/2020 18:37:08
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3420 forum posts
1213 photos

This is how I propose to fix my spats to the leg. The GRP piece will be epoxied to the inside. Some 0.3mm brass plate has been sweated to a collet and screwed through to the GRP. This is a mock up with a dummy axle.

aeromaster 005.jpg

aeromaster 006.jpg

About as far as I can get until the wood arrives.

Nigel R20/05/2020 08:46:02
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3916 forum posts
678 photos

They look great Martin. I guess the collet engages with a small flat on the axle to prevent the spats rotating?

FlyinBrian20/05/2020 12:39:39
639 forum posts
4 photos

I have never used spats on my models as I have never had a flying site smooth enough for them to last beyond one flight

Nigel R21/05/2020 09:40:12
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3916 forum posts
678 photos

I got the last layer of glass on the top wing, and did another thin coat of PVA on the bottom wing.

I've now done 3 filler coats on the bottom wing. The coat last night was just the lightest smear over the area of the glass. The only reason I'm making this post is to note that with the high temperatures yesterday, even in the evening sun, out on my patio, the PVA was drying almost as I applied it, and it was quite tricky to get a nice thin even coat on!

I'm now trying to figure out how I can do some sort of test on the strength of this type of joint, without actually breaking a wing in two.

FlyinBrian21/05/2020 18:12:36
639 forum posts
4 photos
Posted by Bob Cotsford on 18/05/2020 09:50:45:

I did my Panic with epoxy in the end as the postman dropped of the Z-Poxy finishing resin I had on order. Three layers of 25gm cloth and as you say, it barely needs sanding it blends in so well. A quick swipe to take off the stray strands and that's it.

Brian, did you have any problems with unwanted bubbles using film over PVA/glasscloth? I've used PolyC with glass but only with a paint finish.

It was probably a couple of weeks between glass/pvaing and film covering, the film (Profilm) went on without too many problems but I kept the heat as low as possible while covering.

Nigel R22/05/2020 06:51:29
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3916 forum posts
678 photos

Sort of made a start on the fuselage last night, after yet more pva on the wings (first filler coat on the top wing this time).

The first generation plan, and the copycat design aeromistress, both show an engine bay of 4" length which is tight for a 60 two stroke let alone anything bigger. This won't fit:

20200521_213833.jpg

it will need 5-1/4" or 5-1/2".

I've been checking and adjusting my hand drawn reproduction plan...

20200521_221600.jpg

Pencil lines on paper don't show too well sad

I've also been making sure the lines of the cowl work ok if I move the thrust line up a bit too account for the inverted motor. It seems nicely with about a 1/2" change.

I'm now ready to start cutting wood and kitting up for the fuselage.

FlyinBrian22/05/2020 09:00:06
639 forum posts
4 photos

Nigel

Take a look at the "Super Aeromaster" plan on Outerzone, My OS91 / ASP 91s had no problems fitting.

My first (original) AM used an HP61F and later an OS61FSR they also fitted OK.

I believe some parts such as the canopy may still be available from Great Planes.

Edited By FlyinBrian on 22/05/2020 09:01:42

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