Gary's BT 69" Spitfire Mk1

[Nick Somerville]

Hi Garry, re the fillets: For my Fw 190 and P47 ,that both have a central dihedral I sand back the fuselage outer skin a little more than shown on the plan.  I then glue the wing saddle ply plate to the inside (fus box) only and then mount the wing to the fuselage. With everything measured and checked twice I then pack the small gap with thin strips of scrap balsa  and add several triangular 1/4” soft balsa supports  to hold the saddle tight to the wing. After sanding the triangles with coarse sandpaper wrapped around an appropriate round object its infill/sheeting time. You do need to have finalised the wing fixings first.

[Gary Binnie]

I think I understand what you mean with the centre section sheeting, creating a rebate that the ply fillet base sits in to disguise any step. A worry with that idea is that if the wing bolts break in a bad landing the wing skin might get damaged, some builders have also not built the section of fuselage that fits in to the wing at the trailing edge for the same reason, I've followed that.

 

There should be two former fillet pieces and extensions of two formers to support the ply base and fillets, I did mine in sections of sheet. There's a note on the plan that says something like 'sand fuselage sides for fillets' with an arrow pointing to a diagonal cutaway on the fuselage side, what he meant was remove material all along the top edge of the fillet so that it blends in, took me years to understand that one! I used a drum sander in a cordless drill to carefully create a recess and then used it again to shape the blocked part at the front.

 

I pre-shaped the sheet sections by soaking them in water and wrapping them round food tins with tape and rubber bands, also sanded their inside faces where they meet the ply base and fuselage side after they had dried. Pre-shaping takes the stress out of the part so it shouldn't pull or push anything it's glued to.  The edge of the fillet where it meets the wing skin is sanded to a near razor edge.

 

 

 

 

 

 

[Gary Clark 1]

That makes alot of sense guys, thanks.

 

I decided to plank my fillets instead of a singe sheet but having seen the section sanded out now, thanks to Gary, and also the condition/quality of the fairing being the wing, I feel like that will be better just coming off and starting again too. The photo below shows what I was talking about 

 

you can see what i was talking about regarding the standard of the fairings. I'm

Getting the feeling that tonight will be a night of stripping wood off and back to the bare fuse. Good job I got new blades for my David plane 😄

 

I may as well get it to a standard I'm happy with otherwise it will never get finished 

 

Your photos are really helpful Gary, thanks for putting them up

 

Gary

[Gary Clark 1]

So.......

 

I let the frustration get the better of me and I just kept going with the David plane and removed the fairings

 

 

I wasn't impressed with what was below them but I reckon I can sort it. I cut a new former that was damaged just behind the wing and decided to sort a model for flying tomorrow. I had moved the motor slightly (electric one) and decided to do a quick run to make sure everything was good and straight with no vibration. It was anchored to the front of my bench so just after selecting full power, I was confronted by a flash of white passing me (a ghost would have been less terrifying) which made immediate contact with the big 3 blade prop on my P-47....I obviously stopped the motor immediately to find this

 

 

 

The plan for the spit was blown from the bench and promptly shredded by the prop. You'll be pleased to know that the parts missing from the plan average around 2mm in size so absolutely no chance of patching that up. Sometimes you feel the sky Gods don't want you to finish some models...

 

I know I shouldn't have run the motor inside but this is not on the list of consequences I had in my head

 

I honestly don't know what to do now. I clearly need to get a new plan to continue but tonight does not help my momentum but certainly gave me a frustrated giggle. 

 

Gary

[Peter G Simpson]

The fairing is undoubtedly very frustrating. If you use planking then it is really hard to sand it to a smooth profile without removing too much material. I used pretty much the same process as Gary B, 1/16” balsa sheeting soaked and pre-bent around a Halfords rattle can. I used 1/32 ply base and 1/16 balsa skins that are faired into the ply. There is a step bigger than an actual spitfire panel line, but in practical terms a razor sharp edge would is vulnerable to hangar rash and not really noticeable on the finished model.

 

Something else to consider early on, My first BT Spit had smaller wheels and did tend to nose over if the grass was too long. On a couple of occasions the nose snapped off behind the firewall. This is because that is basically just a 1/4” balsa box. So it is well worth laminating some 1/32 ply with the 1/4” balsa sheet box to reinforce the area. I did go a bit further with mine and substantially redesigned the fuselage construction to reduce tail weight. But used a 1/8” ply structure to support the firewall.   

 

Edited November 12, 2022 by Peter G Simpson

[Gary Binnie]

It's only paper, not fingers! My plan is so brown and faded that it's barely readable. Got to push through setbacks and problem solving, it's all part of the hobby.

 

Many times I have thought about abandoning my build, treating it as a practise run but I have managed to repair or alter problems/poor building and the cost of a new wood pack is probably eye watering. I would like to build BT's larger Mk 9 (if I won the lottery!) as the construction is near identical or his other Spitfires and the Me109E.  

 

On the fairings I glued the ply base on with the wing in place, separated with plastic.  Each section of curved sheeting used half of the former's thickness to sit on.

 

You can make a jig out of floorboard type pine boards to hold the fuselage firmly allowing use of both hands. It uses the firewall motor mount bolt holes or the fuselage can be G clamped using the firewall alone. I made another one for the wing.

 

Chin up!!!

 

1. The fuselage fixed to the bench with the jig, with the wing bolted to it I can work on both hands free.

 

 

2. Jig clamped to the bench for the vertical position.

 

 

3. The wing jig, it uses the wing mount bolt holes and gravity at the front, sitting on door draught excluder pads. The whole model can be supported on this in the flying position and I made it tall enough to allow functional checks of the undercarriage.

 

 

 

4. Adding the fairing ply base.

 

[Gary Clark 1]

Great info there chaps, those photos make things much clearer.

I dried my eyes and got on with it. Got the area around the fairings all cleared up and drew on the position. Turns out they weren't in a symmetrical place anyway so glad I started them again. Thanks to Gary pouting it out, I can sand out the area beneath them. I will cut new 1/32 bases for each side (hopefully I have enough) and I'll glue the front onto the 1/2' balsa in front of the wing which will keep it fixed at the front. I'm actually feeling better about it now I'm starting again around thos area instead of constantly trying to fix problems

 

Gary

[Nigel R]

Sometimes you have to go backwards before you go forwards. 

 

Peter, can you share any details about what you did with the ply firewall area?

 

 

[Peter G Simpson]

15 hours ago, Nigel R said:

Peter, can you share any details about what you did with the ply firewall area?

On my second spitfire i simply sandwiched 1/32” ply between the 1/4” balsa forward fuselage, which is what I recommend to builders of this plan. 

On my most recent build I built the forward fuselage around a 1/8” ply structure shown below.

 

Edited November 13, 2022 by Peter G Simpson

[Nigel R]

That's very neat. Many thanks. 

[Gary Clark 1]

Really Nice Peter, I wish I could this one finished so I can start adjusting the design 😜

 

I've started a little progress on the rebuild of the fairings. Lots of little bits around that area needed sorted and not easy when your trying to do it from a shredded plan!! Hopefully the new one arrives soon.

 

 

 

one side done underneath. I have cut new 1/32 ply bases but I do have a question, how do stop the ply base at the front from turning up? I don't see that it's attached to anything underneath when off the wing, have I understood that correctly. The part I'm talking about below :

 

 

Gary

[Gary Binnie]

Good spot, I had to go 'freestyle' there as well.

 

I made the cross piece (metal plate holder) out of laminated balsa, the rear lamination is 1/8" and set slightly low to form a rebate the same depth of the ply for it to sit on.

 

Excuse the cobwebs and dust!!

 

 

 

[Gary Binnie]

Another reason for laminating the cross piece is that it is cut away in the centre and also has a ply plate let in for the metal plate to screw to, it seemed the easiest and most accurate way to do it.

 

Photo of the parts involved with the thicknesses scribbled on them. The rebate for the ply base was 3/16", not 1/8", I was close!.

 

 

 

With the wing fitted, the gap in the centre is where the steel plate sits.

 

 

 

Edited November 14, 2022 by Gary Binnie

[Gary Clark 1]

That's great help Gary, thanks again. It seems so obvious once you put it up, I'm definitely over thinking this bit so far.

 

 

the back of the fairings is done, waiting for the little bits of filler to dry so I can sand it smoothe but the shape looks OK

 

Hopefully I can get some time tomorrow to get the forward fairing started and be closer to moving on!! 

 

Gary

[Gary Clark 1]

Question, any issues with using 2 thick dowels rather than the metal plate setup? 

[jrman]

I modified a BT P40, using dowels instead of the metal plate with no problems at all. 

[Gary Clark 1]

Thanks jrman, I've done this before too but starting to overtime this build for some reason! I've inlaid 1/8 ply into the 1/2 balsa leading edge and the 1/2 balsa that's attached to the fuselage. My wife is due a baby tomorrow so this may slow me down a little.....

 

Gary

[Gary Binnie]

The metal plate is slotted to allow precise adjustment, I have made this part (but not sure where it is!).

 

No reason why you couldn't use two stub dowels as long as the holes were drilled accurately, it's a feature of Chris Foss designs though on these sport models there's often strips of wing sealing tape to take up any gaps.

 

[Peter G Simpson]

21 hours ago, jrman said:

I modified a BT P40, using dowels instead of the metal plate with no problems at all. 

So did I. On my first spitfire I used the system shown on the plan and interpreted it as having to put a bolt through the leading edge of the wing. It meant taking the cowl off to bolt the wing in place (I probably misunderstood the plan). On my next one and also my P40 I used a pair of dowels in the conventional  way and they always worked fine. 

[Gary Binnie]

My understanding of the plan arrangement is that the metal plate has a tang that the wing slides under (with the fuselage inverted!), the wing is kept square in planform by the tapers on the ends of the  crosspiece and the leading edge cut out, the tang is hidden by the fibreglass cowl.  I would want to let in some spruce or ply though where the tang contacts the wing for longevity.

 

I've seen a version of this with the plate the same but the tang engages in a slot in ply midway between the upper and lower aerofoil surfaces.

 

 

 

[Gary Clark 1]

I've not had anytime over the last 2 weeks as we have welcomed our new son. The carnage has settled down and I've managed to get 10 minutes here and there to tidy the garage and get the bench tidy and ready to continue.

 

 

 

During my many hours of being up at nights and sitting around the hospital, I think I've decided to go for the electron retracts. Does anyone have any suggestions for a better set of retracts? I know we've been through this already but I want to get them ordered soon so I have them for starting the outer wing panels as soon as the fairings are done. 

 

Gary

 

 

Edited November 27, 2022 by Gary Clark 1

[john stones 1 - Moderator]

Congratulations Gary, can't help on the retracts query.

[Jon H]

As John says, congrats on the little one. A new pilot in training?

 

On the retracts, electron are very good and you need 95 degrees for scale on a spit. I need to order some 80 degree jobs for my Bf109 but have been holding off as it is a long way down the build queue 

[Dale Bradly]

Dont get the aliexpress/HK 100deg ones i did, until ive got them sorted at least. (See my seperate thread). If i was doing my BT 64" MkIX now, i would have used electrons, or the eflite 30cc set.

Mine had the same wing mounting arrangement, but i couldnt make it work, so now has a dowel.

Edited November 28, 2022 by Dale Bradly

[Nigel R]

congratulations!