Who Else Wants a 63" Lavochkin La7 kit?

[Tim Flyer]

Sorry Bob didn’t reply regarding the cowl question. Yes the cowl is formed from polyester. However epoxy is fully compatible with polyester and I will certainly be epoxy coating the Inside on mine plus the balsa baffling . I never use polyester resin on anything much these days as it’s so heavy and smelly (with the exception of car p47 body filler).

[Ron Gray]

Tim, what's the advantage of coating the inside with epoxy?

[Bob Cotsford]

I usualy put a 1" band of 20gm cloth around the inside rear of a glass cowl just to give the mounting screw points a bit more strength, plus a patch around any holes for cylinders, needles etc. to prevent cracks starting. With the need to slide over F1 this might be a problem on this one. I've noticed a few bubbles in the glass on this cowl, nothing on the outside but a full coat of epoxy inside might be a good idea to seal it.

[Cuban8]

I believe that the general consensus is that epoxy can be applied to fully cured polyester, providing that the underlying surface is well prepared. Working the other other way round is the real no no. I was reading up on this a while ago on a boat building website, but the consensus was certainly not 100% from those who had gone down that route for repairs to their polyester glass hulls (not models) and results were not always satisfactory and often resulted after a while, to problems with water ingress.

In my glider guiding days, the chap who used to produce polyester fuselages for Dick Edmonds and Sean Bannister told me that epoxy should never be used in conjunction with polyester as failure of the bond was likely. I ignored his advice and sure enough on one model, some epoxy glassed-in servo bearers popped out of position due to the bond failing, luckily the model could be landed safely by maximum retrimming but it could have been disastrous. I always went with like for like after that, and have never encountered a problem ever since.

We are talking about thirty years ago, so perhaps the chemistry has changed, but might be worth trying a test piece beforehand.

[Tim Flyer]

The only caveat with using epoxy on polyester glass is that the polyester must be fully cured. If slightly sticky, fresh very smooth or greasy the bond will not be good. Critical bonds always need preparation. Epoxy resin is lighter less brittle and far far superior. It has much better moisture barrier and prevents osmosis and makes a smooth impenetrable barrier insid cowls. Epoxy  is routinely used to repair full size ( And model fibreglass boats) . Yes polyester chemistry has changed over the years and boat hulls are thinner now plus the glass woven fabrics available are better. I would not use polyester over epoxy....firstly polyester is more brittle so will crack easily. Full size boats are built with polyester resin due to cost but very very often repaired with epoxy. Just one extra thing to note .  Car body fillers eg isopon P38 etc are mostly polyester resins but can be used on properly cured epoxy as the are more flexible than standard polyester resin. 

Edited By Timothy Harris 1 on 22/02/2018 12:49:24

Edited By Timothy Harris 1 on 22/02/2018 12:50:40

Edited By Timothy Harris 1 on 22/02/2018 13:15:44

[Tim Flyer]

Hi all ! I hope your builds are going we’ll. I have managed to find time with the bad weather to make more progress. I will be finishing Wing to fuselage attachment tonight after glassing the wings last weekend. I must admit I do like fiberglassing! Anyway after doing that I’m veering towards using brown paper to cover the body rather than Solartex . i think it will be more “ding”resistant. I wondered if Deluxe Eze Kote would be ok to use with paper covering or should I buy a tin of PVA and use that slightly thinned instead? . I will post some photos soon🙂

[Ron Gray]

Unfortunately all of my building is on hold at the moment due to family issues so the LA-7 has not progressed. Looking forward to seeing photos of yours Tim but would suggest going down the PVA route, tests I did earlier this year showed me just how good brown paper and PVA is!

[Tim Flyer]

Sorry to hear that Ron . I have managed to get a bit done here and there once wings fixed I will do wing fairing. It’s all bit by bit but I must admit it’s been quite therapeutic. I would have preferred a “built up wing “ and body rather than foam to be honest, but have still enjoyed it.

[Glenn Philbrick]

I'm afraid my LA 7 is still in its box as I am building a Tony Nijhuis Lanc. I have started to experiment with brown paper using 50% PVA as suggested and am quite impressed by the results. I have painted poly-c over the brown paper covering to stiffen it up ready to be rubbed down for priming. I've also applied the paper in 5" wide strips to see if it looks like panel lines on the finished model. A couple of issues I've had so far, do not seal the balsa before applying the PVA it will not bond if the surface is too smooth, the edges of the covering tend to shrink and lift the paper off at the edges. There are some other threads on here about covering with brown paper that are quite useful.

[Tim Flyer]

Hi Glenn, now the Lanc does sound a really big project but I’m sure it will be a superb model . Thank you for your reply and thank You for the tips. I must admit I have also done some experimentation. I had to sand off an unsightly tail fin bulge on the LA7 which meant I had to sand through the veneer to get it looking ok. I reinforced it after sanding by using glass covering cloth coated by gloved hand with neat deluxe aliphatic glue. I then used light filler over the top. It worked very well and the glass cloth was as smooth as when using epoxy but obviously aliphatic is less messy and easier handling. Good luck with the Lanc😊

Edited By Timothy Harris 1 on 20/03/2018 09:11:07

[Tim Flyer]

[Tim Flyer]

Wing located showing cowl slot and strong ply tank floor fitted

[Tim Flyer]

[Tim Flyer]

Underside minus wing. I chose to make a traditional mount for rear wingbolts on f3

[Tim Flyer]

[Tim Flyer]

Front firewall battens and cowl locator.

[Tim Flyer]

Next job is wing fairing down the sides. After that I’m going to glue the split flaps I made onto the bottom of the wing and add edge fairing to them too. 😊

[Bob Cotsford]

I've started wallpapering mine - ok, brown paper but it's the same process. I've got two brands, Sainsbury v Tesco brown parcel paper. I bought the Sainsbury's first, after all their seeded wholemeal is nicer than Tesco's so why not their parcel paper? It turned out that Sainsbury's is an inch narrower than the wing chord hence the Tesco purchase.

The Tesco stuff has no visible grain to it and not much difference between the gloss and matt sides whereas Sainsbury's has both a grain and a glossy side. I tried the Tesco stuff on the tail surfaces using Wilko pva diluted with water by about 10%. It went on nicely, kept it's strength and followed the curves quite easily. I then tried the Sainsbury paper on the fuselage. It doesn't seem as strong when wet and loses it's gloss when it dries. Overall there's not much to choose between them, they both go on ok and will mould to curves quite well. I tried covering the wing fillets as part of the fuselage side, that really took the stretch to it's limit with the paper starting to break up in a couple of small spots but nothing too bad. I've only done one side and the underside so far, taking the paper for the sides onto the centreline of the top.  The fuselage can be done in three large pieces of paper plus a few small odds and ends.

I've stalled a bit the past couple of weeks losing motivation through the lousy weather, I need to get my finger out and put the last piece of paper on the fuselage then get the wing done. I have come to the conclusion that I really do dislike covering and painting!

Edited By Bob Cotsford on 20/03/2018 12:47:00

[Tim Flyer]

Sounds good Bob thanks too for the papering tips! I think I will try Tesco’s on your advice ! I still have plenty of work left with finishing the fairing, fitting the tail and a bit of work installing the wing flaps,iplus a bit more cutting on the cowl but it feels I’m over the peak now. I agree with you on painting I HATE it . I find it the worst aspect of making planes. Plus there are few easily obtainable fuel proof paints. I’m going to use car aerosols on mine and Klear Kote proofer. Covering I quite like especially fibreglass, as to me it’s nearer construction. In fact I glassed the wheel wells and servo boxes rather than using the kits ABS plastic. 

Edited By Timothy Harris 1 on 20/03/2018 13:17:31

Edited By Timothy Harris 1 on 20/03/2018 13:18:05

[Ron Gray]

Don’t forget grease poof paper as an alternative, Paul has used it on his BF110 and 109 and rates it quite highly. Regarding paints and fuel proof, have a look at KlassKote, great range of colours plus fuel proof **LINK** Oracolor paints are also supposed to be fuel proof and available in a range of colours  **Link**

 

Edited By Ron Gray on 20/03/2018 13:36:20

[Tim Flyer]

Cheers Ron I did bag a few tins at wings and wheels, but I’m still an impatient painter...

[Bob Cotsford]

I covered the fiddly bits first

Tesco on the tail, Sainsbury on the fuselage

The first side

I've just covered the second side and for some reason it was more of a struggle than the first. The paper didn't want to go on smoothly, it just wanted to fall apart. Now to see what it looks like when it dries out. I've used glass cloth and PolyC on a few previous models with excellent results. I think I may just use it on the wing.

When it comes to paint, it will be rattle can hi-build primer and paint topped off with rattle can 2K satin lacquer. I'd better get some new filters for my mask.

[Tim Flyer]

Very good finish Bob . Your wing fairing looks very nice too! I have yet to do that. It looks quite fiddly to clamp.

[Bob Cotsford]

Posted by Timothy Harris 1 on 21/03/2018 13:14:36:

Very good finish Bob . Your wing fairing looks very nice too! I have yet to do that. It looks quite fiddly to clamp.

? I covered the wing centre section in clingfilm and loosely bolted it in place, the slipped the glue coated ply bases in between the wing and fuselage then tightened up the wing bolts. I'd marked the thickness of the fuselage side on the inner edges of the ply pieces so I knew how far to slide 'em in. I used the triangle section (with lots of sawcuts) for the narrower front section and soft balsa block for the rear. Glue abrasive paper round a piece of broom stave and have at it for the internal radius. Finish off with a finger full of filler smoothed round.

One point of note - I scored the ply at the wing T/E position and bent it up to match the line of the fuselage.  A 3/32" layer of balsa under this bent up section brings it flush with the wing underside.

Second point - I didn't use the L/E extensions that form the wheel well on the full-size so my wing doesn't overlap the cowl, that made life easier re the fillet.

Edited By Bob Cotsford on 21/03/2018 15:42:24

Edited By Bob Cotsford on 21/03/2018 15:44:57

[Bob Cotsford]

Third point - I extended the ply base for the fillet right to the leading edge sothat the balsa is supported for the full wing chord.

I gave in and I'm using the brown paper on the wing. I've done one half and am waiting for it to dry before hitting the second half.

I think I got things too wet on the underside as the veneer started to split and lift after a few minutes, a firm ironing seems to have flattened it off again. I didn't have this problem on the top of the wing . I was very pleased with the way the wet paper moulded to wingtip curves using a medium-hot covering iron with just a couple of cuts needed on the top surface.