Craig Spence

The kit finally turned up today ? Only a short night building after a late return from work but good to get some parts out. I’ve started on the first hatch and had to do some minor cuts as it’s slightly different from plan. The hatch was later masking tapped to the fuz to hold it in place whilst building. I’ve also noticed that mounting the motor will be tight for drilling but I decided against pre drilling the former to ensure it’s completely center. Before this I also received my hinges from America, there from CB Associates and we’re recommended on the plan. I’m quite keen on them as they seem robust and light weight, also easier to install. The part I’m struggling with is piano hinges for the flaps. Everything in the UK is too bulky for the width of the surface and too heavy. I’ll probably adapt this part of the plan to accommodate another hinging method but we’ll see.

Haven’t posted for a while so here goes. Made the first split flap and I must say I’ve rather enjoyed it. I’ve never built a split flap and further more not from G10. It’s built from .030 G10 for the main flap and the components are .020. Only 1/4” at its thickest it’s quite fiddly to profile the balsa ribs (matchsticks!!!). This will be getting attached with a 5/8” wide or 34mm continuous brass piano hinge with no 4 wood screws. I think once it’s prepared & painted it’ll really look good. Kit should be arriving any day and I can’t wait!

Well, I’m starting to get impatient now whilst waiting for the kit. I’ve laid the first part of the plan on the bench (& gave myself no working room! - I could’ve sorted it out but I’m too tight to use too much plan protector ?), put shallow cuts in the crutch and pinned the crutch to the board. Side view of fuz on the wall for reference and all part patterns cut out and in box for reference. I’ve also thrown together a 1/32nd plastic kit for reference. I won’t say the name of the kit as it is awful and I’ve had to cut, modify and sand to get it all together. I’ve also left parts out in the box which I’ll use for reference as well. Come on kit! Hurry up ?

I’ve done a bit more detailing to the center line tank but will need a lot of finishing work in future. I’ve decided to store it away for now and concentrate on getting the workshop cleared again. I will be getting plans on the table soon and may pin some stuff to it whilst I’m waiting on the kit. I’ll also get ahead of time by starting to cut my planking which I’ll get on later tonight.

Center line tank has had a joining lip installed, hanging brackets and some other minor details. Just gotta wait for some materials before finishing it now, some small tubing for the over flow and a tank fill tube. Roll on getting this kit mid February, I need to start building now!

Small update. So I have acquired a Turnigy 100cc motor but still have to get a suitable speed controller - looking for a 200A one at present which should be ample. I’ve hollowed out the exhaust stacks and made a light balsa former for the center line tank. The former is only there so I can sand flat, I’ll add epoxy and micro balloons to make a strong former and take it back to about 1/4” thickness. Once both shells have been done like this Ill add further strengthening and give it a light sand before adding the lip. I’ll add some details in the coming weeks and this will be stored to one side along with the other pre made parts.

Little bit of work done tonight, sprayed the exhaust stack mounts black and then went to work on the center line tank. The tank is proving to be a pain but after hitting one shell it’s starting to feel like it’s getting there. I have to make up a lip for the tank, I’ll probably do this with strips of 1/6th lite ply and then glue to the edge. Once done I’ll tack the shells together for shaping and then break apart until I build the fuz and figure out a mounting method. The laser cut kit will be arriving mid February now, going nuts waiting for it ?

The one in three out is a general rule of thumb and you are right about the Venturi. I will have to do something similar for the motor and ESC. The Venturi effect on his build will be very good, but personally I don’t think it’ll be focussed enough. Plus the turbulence inside could mess with the carb intake which I’ve had before and had to make a separate intake for the carb. His build is on Facebook if your on there, it’s called “Lee’s P39 Airacobra build” I believe. He is a really good builder ?

There’s a guy in the states who has put the engine behind the cockpit and it really does look great. I have my doubts though, he has made a geared shaft extension with a geared reduction drive using a DLE 50. Works great and I was considering it but I just saw too many issues which until you fly it you won’t know the effects. The weight for one with the extension would be a lot, the cooling would be difficult even with the air intakes. Remember you want 3 times going out what you’ve got coming in. Plus the heat exchange to the inside of the airframe. I really was considering it but too much risk for me. The electric set up will be heavy but an electric motor will be much more efficient, instant power and torque when required. Once I start the actual build I will be doing everything I can to make it as light as possible. I’ve had to do it in the past where I basically remove formers & ribs. It doesn’t save a great deal but does help. I'm also considering a water based finishing system opposed to resin, I’ve never tried it before but I’m guessing it will be easier.

That’s a good insight Jon ? The 1/4 scale is 102” wingspan and around 19kgs. This may go up or down, it all depends on how well I can place the batteries. I worked it out the other night that I will have 13lb of motor and batteries up front, not to mention a huge steel nose retract. It may be the first warbird I’ve built that will need weight on the tail ?

Those spins are horrific! ?

That’s great info for me Jon. I’ve drawn a few conclusions from it as well for my set up. The full size had a huge prop! That coupled with the long nose would cause quite a bit of gyroscopic action as you said. The scale size prop for my model would be 34”!! I initially dropped to a 27”x12” two blade but found the best efficiency with a 23x12. Hopefully this reduces the issue. I’ve heard the electric foamies of the model fly on rails and I’m hoping this is due to a smaller more efficient prop on the front. im also going with a straight thrust line to start with no side or down thrust to start with. I will then adjust as required. Your model looks to be a great set up, is there much room up front with the engine in there?

I’m the same Nigel, I think the full size had a lot of engine/ power issues resulting in stalls. The models shouldn’t suffer the same issues though if the power is right.

Looks great Jon, what size was this one and what power were you using? Im interested in the handling issues to, the full size had plenty but I think that was mainly due to the engine issues. I know they had a habit of tucking out of loops and going into a flat spin but again I think this was due to not enough speed/ power in turn inducing the stall.

Gave the stacks a coat of grey primer this morning & then black. They’ve turned out ok so decided to glue them to their backing. The plans say use 1/8” ply but I’ve used 1/8” balsa, there’s not structural requirement for ply that I can see & worst case I’ll laminate it with 1/16” ply. I’ve also do finished the center line tank finishing work. Next step is to cut it in half & hollow out. Then, there’s a load of work detailing it.

Small updates tonight. Started on cockpit panels but then found a guy who does them so I will be getting him to do once I can find some decent photos of a P39 cockpit. Exhaust stacks have been given a coat of finishing resin with micro balloons, sanded back and filler primed. The center line tank has been filler primed, filler applied and will sand back tomorrow for ? hopefully finishing coats. In other news I’ve decided I will be running a Turnigy Rotomax 100cc (167kv), 200a speed controller with x4 6 cell packs at 6200mah. I will have to go with a two blade prop (27x12 Falcon) opposed to the three blade ?, this is mainly to do with motor cooling. I am having a back plate made up with an impeller which will take air in through the cannon opening in the spinner and push it across the motor. Other cooling options have been considered but will not be as effective. Retracts have finally been sourced, CenturyJet in the US should have the mains on sale at the end of the month so I better put something aside for them

Oh well, one more before the weekend. Tank has the final layer of cloth on and exhausts are first coat sealer (all twelve shaped now). Should have manifolds done early next week.

I’ve added another 2 layers of glass today to the tank but won’t be posting that as it’s same/ same sort of thing until I get filler paint on it. I have however done the first batch of exhaust stacks which is very time consuming. I think I won’t glass these and will probably just seal the grain, sand and prime. hopefully they turn out well. cheers all.

Ive got wood! ? Arrived today from SLEC and all in good order. Today I sanded the first layer of 78gm cloth & as suspected there was a lot of work to do. I used P38 & sanded back to glass and in some areas through it (needed to be done and part of the plan). I’ve now added the second layer of 78gm cloth and will be adding two layers 38gm tomorrow. Once that’s done I can spray, sand, fill repeat. Then cut in half to hollow out. I’ve also cut some more control horns, the plan indicated use of standard ones but I think I can get a better bond with G10 opposed to using screws through a finished surface. Stephen Belshaw, I’ve put photos up of how I do the G10, I use tissue paper to make patterns then glue to the G10, leaves a lovely line to cut to and just peels off after. I’ve also cut the exhaust stack cylinders for the fuselage. I’ll make the body’s for these in the near future. I plan to start striping sheeting soon for the planking, it will save hours before I start. Cheers all.

Cheers Nigel, still undecided which motor set up but will make my mind up in the coming weeks. I want to try and keep it as scale as possible so will be running a three blade prop anywhere between 25” & 27” diameter.

Thanks Graham, very much appreciated ?. I’m hoping I get the laser cut kit soon & can then start the hard part. At present it’s looking like a month. So whilst waiting I intend to do all the fiddly bits.

Thanks Stephen. I use a cutting wheel on my Dremel, cut as close to the line as possible and then sand to the line.

I’ve also finished the 50cals and cut some control horns for the rudder and ailerons from 1/16th G10.

The center line drop tank was sanded this morning, refilled and sanded again. I have now glassed both sides and will run down again tomorrow before adding a heavier filler. I intend to build up 4 or 5 layers of glass cloth (78gm, 78gm, 38gm, 38gm and 38 gm to finish). Once this has been done and sanded I will cut in half and gut it all out, this way I can add hard fixings inside for mounting and also add the scale joining lip.

Latest progress, centre line tank shape complete. Filler applied and will be re-sanded tomorrow for glass. 50 cal gun shrouds primed and will be finished with matte black tomorrow then guns glued inside.