I bought a 114" P-38 from an estate. The people selling were not RC folk, so not much help from them regarding the pedigree of the plane. I am fairly certain it is a Robart product, when they built the entire H section from glass. While it looks nice, I have determined that it never was flown ... at least in the condition I found it in. Some other intel is that local folks say the original owner flew a couple P-38s, but not so successfully, and that this one might have been involved in a crash.
I'm reworking her from stem to stern, and am involved with the engine mounts now. I've got a fair amount of experience with large engine installation on 3D birds, but zero with composite construction like this one. I've attached some photos of the "firewall". There is a 1/4" AC ply bulkhead that is very open, and the edges are glassed very well into the fuselage structure. The design, as it stands, is that a second engine bearing assembly which includes a second firewall of 1/2" thickness, is bolted in ten places to the smaller thickness firewall (10-32 sockets heads into blind nuts - I'm not a blind nut fan).
The question - do you guys think this is robust enough for a G62 (which is what is in this plane). It seems to me that the smaller firewall would stress that glass a lot with the engine vibration. I'm used to engine boxes that carry back into the fuse structure to spread the load. However, I know there are lots of large glow engine mounts just like this with far less fiberglass thickness that work just fine.
Anyone have experience with this configuration?

Thanks,
Rikk

Images

Seems like a fine solid set up to me,
and I use blind nuts all the time. The blind nut in there help keep the vibration from wearing enlarged holes in the wood.
Only thing to remember is crank them down hard and back-up all those 10-32s up with a jamb nut or they will shake loose

good luck

Thanks for the reply Scale ... anyone else with an opinion?

Whats the wing span of the plane? Two G62's is going to be a lot of engine. That's enough displacement for a 40+lb plane.

It is a 114" span P-38, which is similar to the Ziroli version, but done in fiberglass. Weight will exceed 40 pounds easily ... more like 45.

That gives you about 2hp per 10lbs. That's more than enough.

Hi Lightning!
If you haven't already purchased G-62s, you might consider a pair of DA-85s for your Robart. They fit nicely in the cowls and weigh about the same as G-62s. I've installed a couple of 85s in my newly built Robart 'cause I wanted to turn near scale props ( two Mejlic 24-12W 3-bladers). If you find G-Pete's thread on his Z P-38M, you'll see he has successfully flown his model with 85s and he appears to be quite happy with the result.

I really would not worry about installing G-62s if that's what you want. If anything, on the Robart 38, I'd consider '62s the minimum powerplants to get good performance out of the model. This is because the Robart 38s DO come out a bit heavier than the Ziroli's BUT you do get a much stronger bird for the extra weight. While I haven't flown my 38 yet, I know a couple of Robart 38 drivers and they have indicated this model is the BEST flying giant scale 38 they own / have owned.

Here's my Robart just out of the shop....


Regards,
Lynn

OK, Lynn, thanks, and you are now officially my best friend. Yours looks very nice indeed, and your comments about the Robart model make me feel much better. I have a wood version in construction (have had for a long time), but I got this one for a song, so it is now first in line.

I have no documentation on this bird, so I need a little advice about "how it is typically done".

First, if you could review the first post, and tell me if your engine mount setup is similar to the photos of mine.
Second ... the outboard wings are plugged in via bayonette plates that go into aluminum channels, which are bolted to wood structure in the fuselages. Not the usual tubes in sleeves. Is yours this way as well?
Finally ... elev/rudder servos. Mine has the rudder servos mounted just aft of the retract door openings, so they have a long (flimsy) pushrod. I am seriously looking at putting all four elev and rud servos in the horizontal stab. I've laid it out and it will work, but I am worried about CG. Four servos in the tail is equivalent to 8 oz, roughly 48 inches aft of the CG. This means, if the bird is balanced before I move the servos aft, I would need nearly a pound 24 inches forward to counter the servos. How did yours balance? Those booms feel very heavy, so I could be making a bad situation worse if it is already tail heavy. Now, the G62s are not light, so maybe they are the offset. No matter what, I'll check balance before I commit to anything, and decide from there, but I'm curious as to how you did yours.

Regarding the DA85's ... maybe someday. I have these G62s (electronic ign) in there now, and unless the general consensus is that they will not fly it, I'm sticking with them.

Regards,
Rikk

Hi Rikk,
My engine mounts appear identical to yours. That's how I knew you had a Robart kit. My motor mounts are however, more like a doubled bulkhead and box set-up. I thought this necessary to deal with the power and vibration of the DA85s (for which they have a deservably strong reputation....which I can neither confirm nor deny....yet).

My model also has the same "bayonette" style wing panel and rear boom servo mounts as yours. I have no concern with either approach. Perhaps Kram can comment on his experiences (Mark, are you lurking about??). Personally, I would not put the elevator and rudder servos in the tail of the boom. With all that engine weight up front, I don't think servo weight would be an issue, but why invite CG problems?I have no reservations about a pushrod and/or pull-pull set-up from the stock servo mount position. This model is a BIG, HEAVY warbird, so I doubt if I'm going to need the throws a direct drive servo would provide in a tail mount. I've no (intentional)plans to 3D my '38.

Having just received my (upgraded) DA85's and custom JTEC mufflers back from the vendors, I haven't had a chance to final check their installation. When I do get around to seeing if the JTEC execution of my mock-up muffler actually DOES fit wholly inside the cowl, I'll take some pictures and post them here in the thread.

Good luck with the refit, Rikk. I'll stay tuned to see how it all turns out......

Regards,
Lynn