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Author Topic: Spitfire Mk VII extended wing horizontal stabilizer desing  (Read 271 times)
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Chris A.
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« on: February 12, 2020, 04:37:48 PM »

I'm modifying a Comet Spitfire Mk IX into a long wing Mk VII with the large rudder. I"m sure that the horizontal stabilizer needs to be enlarged for stable flight, but any ideas on the percentage of increase will be appreciated. Wing tips will be brought to lower edge of canopy height. Anyone out there ever built the long wing FF version?
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charlieman
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« Reply #1 on: February 13, 2020, 03:54:41 AM »

I built Comet's "P-51A", their P-47 and the Dauntless, from the old Blue and white boxes. 1966-67. They were stable on their scale areas. In the Model builder plans book, the Spit Mk 1 has enlarged fin/rudder AND stab. Not sure it needs it, but the models do fly well.

I used to fly indoor with a group from Sacramento, Ca. 1978-80. One of the better builder/flyers was Nick Bressi. He would make an oversize horizontal out of light 1/16" sheet slide it in then test fly. Once it was flying to his satisfaction, he would begin to reduce the stab area with scissors until the model was unstable. If the plan stab was larger than the final unstable temp area, he;d' build plan stab to scale outline, use his preset incidence and fly it with confidence. Today, one could easily experiment with foam plate material, instead of balsa.

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Chris A.
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« Reply #2 on: February 13, 2020, 04:38:51 PM »

Charlieman; thanks, I'll be trying your suggestion. The Comet Mk IX fuselage backbone has a slot for the stabilizer that can be lengthened so a "try it" larger stabilizer can be pushed through. I'll also make the slot deeper for incidence trim adjustments.
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charlieman
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« Reply #3 on: February 14, 2020, 03:34:05 PM »

It's been awhile since I built a kit. IIRC, it's usually possible to enlarge the forward end of "slot" in keel, to form a long tri-angle cutout.  When framing stringers (both sides) follow the same cutout, top and bottom. Now,  it's possible to cover to those stringers, which also form a stable lateral stab mount. Shim front of stab (again, both sides) for trim adjustment. Back of stab can be held with dab of rubber cement, or other flex material, to act as a hinge.  When all trim has been established, GLUE the shims in place and cover the cutout.
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lincoln
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« Reply #4 on: February 15, 2020, 01:09:56 AM »

If you have a similar model that flies well, you can compute the tail volume and match that on the new model. You might read How Big the Tail? by Stan Hall. It's about full scale airplanes, but the same principles apply. Easy to find on the net.

William McCombs' book Making Scale Model Airplanes Fly is a good resource for questions like this. According to rumor, it's still being advertised in the NFFS newsletter classifieds. While you're at it, buy a big magnifying glass to read it. It's just a bunch of stapled pages with poor print quality, but it's very useful.
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