FMS 980mm P-39 mods

[F106DeltaDart]

Over the past 2 weeks, I have been working on a couple of mods for my FMS P-39. This airplane is a great model, but has a few main problems in scale accuracy. First and foremost, the stance of the landing gear was completely wrong. The model sat at a nose level, or even slightly nose down angle. The full-scale sits with a distinctive nose-up stance. In order to replicate this, I shortened the main struts to 2 3/8" from the end to the axle. This looked excellent on the ground, but the mains could no longer retract, since the outer loop of the strut interfered with the retract motor casing. So, I had to hunt down a pair of retracts with the motors on the opposite side of the retract, leaving the gear free of interference. I ended up ordering these as they seemed to be the only pair that fit my requirements: http://www.hobbyking.com/hobbyking/s..._AUW_Max_.html. However, with the motor on the other side, these are much longer than the stock retracts, and the flap servos had to be removed and relocated to accomate the retract body. I also made new gear mounts using 1/8" plywood to hold them in their new position.

The next mod was a correct flap setup. The full scale P-39 used split flaps, not the conventional flaps installed on the model. I cut away most of the flaps, and reattached the upper skin to the wing with balsa joiners. Then, I fabricated the flaps out of .03" styrene and a few small square CF tubes. Still have to mount in the servos and wiring, but the majority of the work is done.

The next mods I will do are a correct exhaust, gear doors, and a repaint. The full scale "Hells Bells" was a P-400, the export version of the P-39 that featured a 12 stack exhaust and it had 12-stack exhaust versus the 6 stack provided with the model. RCG member "Redhood" was kind enough to 3D model the correct exhausts and put them up on shapeways: http://www.shapeways.com/product/XHQ...ionId=60554062. I have them ordered, and should have them in by the end of the week. I'll post more as I make progress on the airplane.

[Prowler901]

Nice work, Delta! She definitely looks much better with your mods. And, the flaps look great. I have a very similar plan for the Wildcat. Looking forward to your updates.

[Westsider]

You were not kidding when you said you were working on a fix for the nose gear. Working is right. Lotta work. You are a mad man. That is really cool.

[F106DeltaDart]

Thanks guys! Prowler, I am really looking forward to your Wildcat build as well, that might be next on the mod list after the P-39, B-17, and LX F-117. Always end up with more projects than time, lol. I just finished getting the flap servos installed and all the wires tucked away. I am planning on a test flight Saturday, and then starting the repaint work. This model is my inspiration for the finished paint job, I hope mine turns out to look even half as nice: http://forum.largescalemodeller.com/...racobra/page-6.

[Prowler901]

Yeah, that guy did an amazing job. I'm sure yours will be awesome as well.

[F106DeltaDart]

On Saturday, I took the P-39 out for the maiden flight after modding. The split flaps were very effective, and ground handling was excellent. However, shortening the mains means your landing have to be spot on 3 points every time. I actually managed to get it down fine on all three, and after rolling 10 ft, it began to shimmy, and the left gear collapsed. Upon further examination, this was due to a design issue in the retract. On the HK retract, there are 2 small, thin arms that connect the trunnion to the slider on the jackscrew. They are made of stamped metal, so you can pretty much pull them apart by hand. So, I am going to have to modify their design if I want this to work. I am going to draw up the arms in CAD and try to get them water jet cut out of steel. Hopefully this resolves the issue, otherwise I will try reconfiguring the stock retracts.

[Prowler901]

Congrats on the maiden! Gear issues seem to be the biggest problem these days. The landing gear is the one part on a plane that needs to be the strongest. There seem to be some serious design issues with most of them.

[F106DeltaDart]

Congrats on the maiden! Gear issues seem to be the biggest problem these days. The landing gear is the one part on a plane that needs to be the strongest. There seem to be some serious design issues with most of them.

I agree. For the most part, I have not had issues with FMS or Freewing/Flightline Retracts, with the exception of FMS rotating retracts that shed their locking pins. Otherwise, the misc. Hobbyking retracts, RClander, Dynam, and LX have all proved to be major maintenance problems.

[F106DeltaDart]

This evening I made some more progress on modding my P-39. I finished painting the new 12-stack exhausts and test fitted them on the aircraft. After some coats of primer, I painted it tamiya metallic grey, than painted over it with a thinned brown color. I am very happy with how they look, and really help give it the appearance of a P-400!

I also rebuilt the stock retracts to accomadate my shorter struts. This was done by completely removing the support wall on the trunnion end of the retract, and reversing the trunnion. This was done using a small belt sander. A new support wall was built of carbon fiber on the motor side of the retract to provide support for the trunnion in the extended position. Now I just have the rebuild the retract mounts in the wings yet again.

[Prowler901]

Nice work on everything there, Delta. The exhaust stacks look very real. Great weathering.

[F106DeltaDart]

Nice work on everything there, Delta. The exhaust stacks look very real. Great weathering.

Thanks Prowler! Hoping to start the airbrushing work tonight.

[F106DeltaDart]

So, instead of getting to airbrushing, I ended up spending most of my night masking off the canopy. Then, I found a new issue with the retracts. Since I reversed the trunnions, now the mains operate opposite of the nose gear. So then I had to rip up the wiring from the wing and pt the mains to a separate port on my RX to reverse them. This process pretty much resulted in the destruction of the servo wiring tape. Any ideas on what type of tape would replace the servo wire tape best?

[Westsider]

What about a decal sheet for the hell's bells? They usually have the servo wire wing tape attached.

[Westsider]

Oh, double yikes. $11.29 and out of stock.

[F106DeltaDart]

Yeah, I'd prefer a cheaper option. The racing decal set is cheaper, but is also out of stock.

[F106DeltaDart]

To do the servo wire tape, I ended up buying a sheet of sticker-backed vinyl paper. It worked perfectly, and looks exactly like the stock tape. I started out on the camouflage as well, but I still have to paint the insignias and the black for the shark mouth.

[Prowler901]

Nice! Where did you get the vinyl?

[F106DeltaDart]

Nice! Where did you get the vinyl?

I got it from Hobby Lobby. I believe it was this stuff: http://www.hobbylobby.com/Scrapbook-...-Vinyl/p/17925.

[Prowler901]

Looks great. How's it taking the paint?

[F106DeltaDart]

The paint is working fine on the tape. No signs of wrinkling or shrinking, and it adheres well. My biggest issue had been the masking tape. Even using delicate surface frog tape, and tacking it, I still have had it take some decent sized chunks of paint off of the aircraft, so I have ended up spraying each color about three time now to correct for masking damage.