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Old Oct 13, 2005, 09:37 PM
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A Not Too Royal P-38

I thought I'd start a build thread for my P-38. I've been wanting to build one forever, but was always afraid to as a slimer because of engine outs. Now that I have a few IC conversions under my belt, and I'm hooked on electrons, a P-38 will make the perfect winter project. Been searching high and low for any kits in the 66 to 76 inch range, but no luck, so I'm going to build it from a set of old Royal plans. Actually, the royal plans are designed more like a tank than an airplane, so I'm really just using the plans for the outlines and cross sections.

I just finished re-drawing all the formers and ribs as I will do them, and got in my wood order with Lone Star. Got nacelles from Fiberglass Specialties and turbochargers and canopy from Wing Mfg. Now I'm anxious for my wood to get here so I can get started.

Royal called for an 8-10 lb. AUW, but I'm pretty confident I can keep it to around 7 lb max. I have some Spring Air retracts laying around, and I have my take on the fowlers figured out. I'm probably going to wind up using AXI 2826/10, with 3S or 4S.

If anyone is interested, I'll post progress and pics as I go. I do have a few scraps laying around, maybe I can at least get started on the stab......
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Old Oct 13, 2005, 11:06 PM
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Santa Clara, CA, USA
Joined Apr 2001
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I'm most definately interested. I've had a special interest in the P-38 ever since reading the (probably fairly corny now) novel "The Last Dogfight" by Martin Cadin almost 30 years ago. I built the guillows kit when I was in 8th grade and powered it with two Cox Tee-Dee 09s for control line, but I never flew it because I never trusted getting both engines to run at the same time. Electric flight certainly makes things better doesn't it?

Will you be planking the fuselage and booms? That'll be quite a bit of work, but certainly well worth it. I'm looking forward to seeing your progress.

Jim
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Old Oct 14, 2005, 12:41 AM
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Great, I am working on a slightly smaller electric P-38 (55" wing span) It will be fun to follow your progress. What did you settle on for a wing span? What scale are the fibre glass parts you bought?

Cheers,

Watts
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Old Oct 14, 2005, 10:50 AM
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It'll have the same WS as the Royal, about 74.5". The fiberglass cowls are still available for the Royal kit, even though you can only find the kits on ebay now (for about $300). Since I wouldn't be using most of the wood in a kit anyway, I'm better off buiding off the plans.

I guess it's a fine line between sheeting and planking, but I'll sheet the booms with 3/32 and the fuse with 1/16, and I'm sure I'll have some planking to do on the compound and tight curves.
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Old Oct 14, 2005, 11:04 AM
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Yep do a thread for us. Very interested. I need to get my Ryan p-38 back on the boards.

Mike
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Old Oct 14, 2005, 12:30 PM
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You betcha - signing up for this!

Ken
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Old Oct 14, 2005, 01:26 PM
Balsa Flies Better!
Stamford, CT
Joined Oct 2000
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That's a project- I know, I built a scale P-38 from an old controline kit. Mine is 60" span- I opted for no flaps and permanent retracts. No glass, I planked everything- took forever, but I must say, it's an airplane I'm fond of. Haven't flown it in a while because I'm waiting for li-poly prices to drop a little further.

I think you might want a little more oomph in your airplane though. Using 3s li-polys per side, you're looking at 100 watts/lb if you hit your weight target, which might be aggressive with retracts. (Don't know here, but my airplane is 4 1/4 lbs without retracts.) Mine flew at 100 watts/lb and was certainly decent, but a little more guts would be welcome. When I li-poly the airplane, it'll go to 150 watts/lb and probably come out a bit lighter, and I'm planning on using 3s packs. Mine has a stall that's scary- drops off on a tip with relatively little warning.

I'd kick around going to a 4s setup- that way you can pull about 35-40A and hit 475-550 watts without too much strain. You'll have performance which will better the glow powered airplane- lighter and probably just as quick or better vertical pull. Believe me, you don't want to be flying a '38 on the back side of the power curve- you're going to be very unhappy if you miss your weight target by a pound, and you're at 350 watt/side at best. A little reserve in the power system isn't a bad thing- especially in a scale twin where you may need a heavy throttle stick. Be careful copying what the 3D and aerobatic guys do- you need more power reserve in your motor. Pick your packs and props first- motors last. A three blader Varioprop would be very cool. I wouldn't count out the Mega 45/3 or Phasor 45/3 either- or maybe look at Astro Bob's new brushless motors- the 25 perhaps?

The K + A kit is a nice way to go for a 55" airplane- lots of glass, much easier build. If I ever dork mine, I'd kick that one around.

But I think there are some larger European glass kits available from JR or HVP. Kind of remember a '38 for twin .40s. Might have to check with mfg directly, kits might be a little challenging to get.

Sam
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Old Oct 14, 2005, 06:50 PM
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Canada, BC, Abbotsford
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I also like the P-38
I would really like to do "Nick Ziroli's" design 114" wing span with a pair of Zenoah 38's in it; but it's waayy out of my price range. I've settled on one designed by "Mike Molt" Parkflyer size 12-14oz all up weight.
Looking forward to watching your's come together.
Rick
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Old Oct 14, 2005, 08:37 PM
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Sam, thanks for the info, I'll keep it in mind. My mass budget is:

LG - 13 oz
Power - 36 oz
Radio and wire - 10.5 oz
flap mechanics - 2 oz
covering - 8 oz
cowls - 4 oz
structure - 38.5 oz
Total = 112 oz

I think I can make 7 lb. most of the weights are actuals. Not sure how I'm going to cover it yet, so that's just a WAG, but, God forbid, I use coverite it would only be about 4 oz.

I have my first pic, I had enough scrap laying around to kit up the stab - 14 ribs, tip, LE, spars. I'll get it on the jig tomorrow.
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Old Oct 15, 2005, 08:23 PM
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Here is a pic of the stab bones. Need to taper the spars to the stab tips, add backers for the hinge points, and do some sanding and it'll be ready for sheeting.

The plans call for a 3/8 X 1/2 trailing edge, 1/8 X 3/16 spars, and 3/32 sheeting. Just a little too much for an e-plane, I went to 1/8 sq spars, 1/8 X 1/2 TE and 1/16 sheeting.

I guess since this is a P-38, I should leave out the puns about the lightening holes.
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Old Oct 18, 2005, 08:01 PM
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The stab bottom is sheeted and the fin is framed. I'm trying to get the mundane parts done first. Who feels like going back to build a rudder after getting all the fun parts like the wing and fuse done? You can see the TE blocks for the hinge points and the TE tri-stock to nest the elevator. The close-together ribs will fit the 1/4 inch fuse backbone as well as the fin stub. I won't sheet the top of the stab until I get everything fit together and make sure I didn't forget something. Nothing worse than having to do surgery later. I think I can fit the rudder control horns within the stab. I'm thinking of putting one HS-225MG centered at the wing dihedral with pull-pull going to each rudder with a pushrod to the retract steering arm. I haven't figured out how to hide the elevator horns yet, though. I'll put one HS-81MG in each fuse for the elevator. I have to do the top and bottom half of the fin separately, otherwise I won't be able to get it on the stab later.

Stab weight so far - 1.6 oz.
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Old Oct 21, 2005, 08:30 PM
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Six hours in the dungeon and.....two fuses worth of formers. Looks like every one of these in the kit was 1/8 ply. I had to re-lay them all out, especially the firewall and the landing gear former. I left the LG former cut high and won't glue it into the fuse until I see where the wing spars line up. That way I can match fit the LG former to the back of the spar and bond them, making for a stronger framework. I left ears on the smaller formers so I can get them onto the jig. The ears will come off after I set a few longerons. There's a little nip in one of the firewalls, oops, ran out of lite ply. I'll patch it once I start getting built up.

I think I'll scan all the parts before assembly, in case I ever need any repairs. Maybe I'll post the scans in case it turns out OK and anyone else wants to try one.
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Old Oct 22, 2005, 02:28 AM
LT
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Joined Jun 2001
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I did buy a Marutaka/Royal kit that someone had started and given up on, hoping to convert it into electric. It was to heavy for my liking and is still laying in my basement, but had I started the kit from scratch I think it would have had much higher chance for sucses.

Are you planning to use a one piece wing with removable tailgroup as per kit drawing, or will you go for a three piece wing?
One thing I noted on my kit is that the 'slott-in system for the tailgroup add quite a lot of tail weight and could probably be lightend considerably with the use of e.g. a cut of piece from a carbon/fiberglass wing joiner as typically used on sailplanes.
By using a 'tube in tube' kind of joiner one could probably have 'JST' connectors for the tail servos running inside the inner tube.

The wing design is surisingly light as it is, but I am sure it can be lightend some more. Regarding the flaps I know that there was an article about fitting Fowler flaps to this spesific kit in an old Traplet RC scale magasine a few years ago. It claimed to be quite lightweight and used a single HS-81 for activating. If there is any interest I can try to dig out the old article.

Best regards
Lars
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Old Oct 23, 2005, 07:53 PM
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Lars, I'm going to permanently attach the wing and tail group, and have removable outer panels for the wing. You're right, the way that Royal/Maratuka had the removable tail set up, there was a lot of ply and hardwood, and I could only imagine the weight. I do like your idea of using CF tubes as a tail attachment, but I'm already commited.

Well, I didn't get as much of a chance as I had hoped to work on it this weekend. But I've got both fuse's formers set up on the jig and the keels and one longeron are in place. If it wasn't for the jig, I guess I'd have built a crutch set up to keep everything aligned. It's nice though, being able to work on both fuses side by side and get as close to a mirror image as I can.

By the way, I scanned the formers for future reference. I'll attach them as well. Oops, they're tif files, I'll have to convert them first.....next time.
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Old Oct 23, 2005, 07:58 PM
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By the way, Lars. Yes, if you could find that fowler flap article, it would be great.
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