Mustang Fever

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I built Jim Ryan's Speed 400 P-38 Lightning about a year and a half ago. It is one of two airplanes I have that I consider to be "without vice". Very well behaved, and very graceful in flight.

Been toying with the idea of scaling the design up to an 80" wingspan, and powering it with a pair of 46s. Jim thinks it would perform well, so here we go. The next post will have some pics of the beginning of the project. Attached now is a pic of my electric Lightning, which spans about 50" and is powered by twin Astro 020 brushless motors.

Mustang Fever

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Installment 1

OK, here we go. Any of you guys with twin building experience, please feel free to jump in and let me know where I might be going wrong here, or make any suggestions you think might be useful.

As I said, the original design was a 50" wingspan for twin electric motors, wing area 340 square inches. It's a sport scale design featuring very simple construction: the wing is sheeted foam core, and the pod and fuses are simple sheet balsa box construction. The plans were featured in Model Airplane News, and can be purchased online from the rcstore.com.

The specs for the 165% version are:
OAL: 58.6"
Wingspan: 80"
Airfoil thickness:
Root: 1.65"
Tip: 0.825"
Airfoil: Eppler 205, 2 degrees washout.
Chord Root: 15.10"
Chord Tip: 8.75
Chord Avg: 11.925"
WA square inch:954
WA square foot: 6.625
Desired WL, foot: 20oz sq foot
Max weight: 132.5 oz (8.3#) Hardware and engines will come to over 80oz, leaving approx 50oz for airframe weight.

Engines: twin Tower 46s w/clamp mounts, sideways mounted with stock mufflers. 3 degrees "out" thrust, both sides. 10x7 3 blade Master Airscrew props.
Engine down thrust: 0
Wing and stab incidence: 0
Dihedral: 3.6 inches, each tip.

Fuse (boom) width, max at wing LE:2.89
Fuse width, at spinner plate: 2.89
Fuse length (sheeted part): 48"
Fuse depth max: 4.87"
Fuse OAL incl fins: 49.91"
Nacelle length, LE forward to spinner plate:

Pod specs:
OAL 30"
Depth 4.95"
Max width: 2.75"
The original design had balsa blocks for nose and tail of the pod, I'm going with built up, hollow, so I will have more room to locate equipment.

Tail Feathers:
Stab: 33.2x5.94" (197 square inches, about 21% of wing area. Good sport flyer ratio, I'm told. My electric Lightning is VERY stable in pitch. With all trims neutral, on a hand launch it just powers away in a level attitude, with no tendency to nose up or down.)
Fins: 10.89 high x 7.67" max chord. Area: no clue. Forgot how to do that kinda figurrin.

Landing gear: Robart 520 retracts with 3/8" od offset RoboStruts.

Construction Notes:
3/32 wing sheeting over white foam cores (CNC Foam Factory) with balsa square stock leading edges
1/4" solid balsa tail feathers
1/8 balsa fuse and pod sides, top and bottom sheeting.
1/4 ply formers forward of LE
3/32 balsa formers aft of TE
Insides of both fuse/booms forward of the LE to be reinforced with fiberglass and epoxy after landing gear blocks and formers are installed. Insides of pod to be reinforced the same way in the nose gear area.
Top and bottom edges of all fuse/pod sides are lined with 1/2" balsa triangle stock. Gaps are left in the stock for installation of the formers.

Pic one shows how I did the plans. Got a copy of the original blueprint made, then cut it up into the various parts so I could blow them up 165% on the do it yourself copiers at OfficeMax. A bit of cutting and pasting is required to get each piece- the fuse booms required four separate sections on the long paper.

The inboard fuse/boom sides have been cut in the second picture. I used 48x6 1/8 balsa. I put the tail of the pattern flush with one end of the sheet, then extended the nose slightly beyond the pattern so as to use all of the 48" sheet. This gives me another 3/4 inch of fuse length ahead of the wing LE, which is needed because the engine/fuel tank installation is going to be tight. (I'm hoping to use 10 oz Sullivan retangular tanks. They are a bit shorter overall than the 8 oz) Whatever happens, I don't want to cut into the LE of the wing to make room for the fuel tank.

Mustang Fever

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Installment 2

Ed Westwood taught me to centerline EVERYTHING when building from plans, so this series of pics shows all of that for the inboard fuselage sides.

#1 A long shot of the centerline/thrustline and former NF-2 and NF-3 locations. The front end of the centerline is located by measuring 1.25" down from the top of the fuse side (half of a 2.5" spinner's diameter). The rear end of the centerline is located at the trailing edge of the wing opening in the fuse side. This is per the original plans, which show the same half spinner OD to wing TE to establish the thrust line. It should be drawn all the way along the fuse sides until it's underneath the stab slot. You know it's correct when the centerline/thrustline is perfectly parallel to the stab slot.

#2 Shows a closer view, with the dimensions involved and the locations of the 1/4" plywood formers NF-2 and NF-3. NF-2 will accept the clamp type engine mount, and the 10 oz Sullivan Rectangular Flex Tank will fit between NF-2 and NF-3. The dimensions shown do not include the thickness of the 1/4 inch formers.

#3 Has the engine and mount sitting in place. Due to muffler interference with the fuse, I abandoned the sideways mount and am going with upright engines. To get sufficient room for the fuel tank, I had to put about a 1" gap between the spinner backplate and the front edge of the 48" long fuse sides. Shouldn't be any trouble to fill this in with balsa block later to make the nose section look nice.

I use the Hobbico clamp type engine mount because it is such a perfect fit with the Tower 46. It self aligns, and there are no holes to drill. It is Tower item number LXL208, and is used on the Superstar and other ARFs. I have ordered the 10 oz tanks (LXFU63) and the 2.5 inch 3 bladed Dubro spinners(LXE155). (Black, because this will be a gloss black P-38M Night Lightning)

adrenalnjunky

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Not to steal your thread - but you mention Ed Westwood - I'm assuming that you're talking about the same ed Westwood that designed the 40 sized RV-6 Plans that I have. Think he's from Spanaway, WA area?

I was hoping you might know a way for me to contact him - I am wanting to build that RV-6, and was hoping that he might have a cowl/canopy for the model (plans mentioned that he would be having some produced)

Thanks so much.

Mustang Fever

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He's the one, Chris. His email is:

[email protected]

I've corresponded with him a lot, and he's really nice and helpful.

fgpierce

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I don't know if you've worked with Carbon fiber before but just a thought on the tank issue. It would be fine to cut the LE at the nacelle if you bridge it with some carbon fiber strips inserted under the sheeting, top and bottom. I built a 80" OV10 Bronco ( Uravich plans) and the wing is built up. The nacelle keys into the LE without giving anything up structurally. In foam core the Carbon fiber would carry the stress without any problem. What are you going to use to secure the balsa to the foam? If you use epoxy you would be able to lay the fiber flat but anything else would require you to sink the fiber on edge down into the core with a slit and a little epoxy to secure it. Two strips, 1/4" wide , top and bottom would be fine.
My friend and I both had KMP P-38s. They flew OK but were crappy quality as far as we're concerned. He now has the VQ P-38 he's assembling and it's really nice. I have the VQ P-61. WoW, what an Adrenalin pumper

Good luck on the project! It looks worthwhile.

Mustang Fever

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Thanks, FQ.

That's some good info on wing reinforcing.

Haven't done anything for a couple weeks, due to family reunions and such.

Took another look at the engine fit, today, and boy, inverted would be the way to go. I had a Tower 46 inverted in a P-51 last year, and it ran fine. I'm not so sure I want to try that with a twin, though. Thoughts, anybody?

JohnBuckner

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Bob I have a Wing P-38 with two TT .46's inverted and they are proving to be absolutely no problem. It was a small challange getting the fuel tanks low enough in the cowlings but has worked nicely. In my case its not neccessary at all to invert the airplane for starting. I do keep hemostats on the feed lines untill starting but the tanks are low enough and syphoning has not been a problem.
When I first completed the airplane I set it up with K&B screamin 48's and these engines just did not like the inverted installation and were never reliable no matter what. So went to the TT's with no problems after the first four flights on the .48's.

John

By the way your project is going to be a really neat airplane[8D]

Mustang Fever

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Thanks, John

I seem to remember from some OS instructions that the pickup tube in the tank (the part of it in the cap) should be about 1/8 to 1/4 inch below the centerline of the spray bar. Does that sound right to you, or should I make it lower with the inverted set up? I have plenty of room to move the tank up and down.

Here's a pic of the trim scheme I'm going to use.

Bob

TLH101

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Centerline of the fuel tank should be even, to 3/8" below the the spray bar in the carburator. If you are doing a stand off scale, you should consider mounting the motors on their sides, to prevent the hassles of inverted motors. Save the inverts for scale models. You will be happier in the long run, unless you have really reliable motors.

Mustang Fever

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Thanks, Terry.

I really think you are right about all this. I've had two inverted engine models, and both of them, regardless of how much time I spent fine tuning, had a tendency to load up at anything other than full throttle. I assume that oil and unburned fuel are accumulating in the cylinder head and muffler, and have to be purged before the engine starts running correctly again. At any rate, both of them would hesitate, sputter and sound very ragged after a part throttle run followed by an attempt to get full power. I don't think I want to deal with that on a twin.

I ordered one of the slimline Pitts mufflers for the OS 46, which also fits my Tower 46s. I think it is skinny enough to get inside the fuses so that a sideways engine mounting will look good. If not, I can always go with upright engines, although they don't look near as nice.

JohnBuckner

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Bob I think one of the the keys to any successful inverted installation is positioning the tank with the same spraybar/tank level relationship in the inverted position that works well in the upright positon. Going by the position of the cap depending on the tank brand and style is not always very accurate. For example a Dubro slant top will be very differant than a Hayes with a center cap and so on.

Having said that I to usually like TLH go for the vertical centerline of the tank but with an inverted setup it does not hurt to error just a little on the low side. I also agree with him on a sideways mount as being an optimum setup for ease of installation and I use it a lot but not all my airplanes. I little commom sense will overcome the usual problems. On my 38 and some other inverted setups there is no need for inverting the airplane to start and a syphon won,t start up unless the airplane is left in the sun for a period and its because of this I do use hemostats when fueled and sitting.

Another problem with sideways mounting on a multi with wingmounted engines is its difficult to install and remove the glow ignitor with one engine being pointed right at the fuselage. For this reason on my two Quads a pair of twin bashes I have mounted with the cylinders about 65 degrees from vertical and this works well to have access to the left side glo plug and with the needles in a convient position. This also reduces the problems of in this case of getting the tanks high enough.

One problem with inverted engines it the difficulty of getting an ignitor on the plug when the airplane is sitting on its gear. First let me say I have always adhered to the KISS principle with multi's and this has worked nicely for me. I am not a fan of onboard glow or remote glow connectors. At least in my case on board glow just covers up poorly tuned engines and the remote connector is just another hassel with more wireing as well as failure mode. The solution in my case came with a new product tower sells for eleven bucks. Its the Tower AAA alkaline ignitor well made of aluminum it is very small diameter and longer than a standard but shorter than the car types. It is ideal for installing with the airplane on the wheels but is not dragging on the ground as the car but very easy to install or remove. I only use it only on the 38 and my Quad so the alkaline batterys are not an issue.


Anyway your 38 is going to be very cool not real scale but probably even more attractive with the long booms and a surefire nice flyer.

My next one due off the boards about half done is a Sig Seniorita that is converted to a glider with full span reflexing ailerons low tricycle gear and a nose tow release for aerotowing intially behind a Spacewalker and later the Quad Cadet it will weight just over two pounds in this configuration. For the good part though with a 15 minute changeover of the gear and four 1/4 twentys attach the bathtub nacelles with two Magnum 30 four strokes.

Keep the photos coming of your project I really like it. Heres my 38 and the Quad a future tow plane:

John

Team Geritol Racing

Mustang Fever

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John:

I hadn't even thought about the distance between the nacelles and the center pod until you brought it up. Rushed right downstairs and measured it on the plans, then multiplied by 165%. Whew. All kinds of room, for a glow driver and the props, which is really what had me going for a bit. About 10 inches, not counting the height of a sideways engine's cylinder head. I think I'll probably go with sideways, although inverted would look better, because, first, the Tower 46s run really well sideways, and two, the slimline pitts muffler will be all but hidden in the fuse. (It will stick out a little on the right side, under the cylinder, but since there's already going to be a hole there for the enigne, it shoudn't matter.) This also gets the exhaust stacks in a area directly under the fuse where the mess is kept to a minimum. (I have a GP DR-1 with a sideways OS 65LA and a pitts muffler, and it is so easy to clean up compared to everything else I have.) If I go with inverted, then I have to use the factory mufflers, and they are huge.

Getting all this input is great. Maybe I won't screw this up afterall.