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Kadet LT-25 with Kadet LT-40 Wing

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Old 06-14-2018, 01:32 PM
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RandyP
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Default Kadet LT-25 with Kadet LT-40 Wing

Builders,

Thinking about using a extra wing I have from a LT-40 ARF, on a LT-25 Kit I am building. Has anyone tried this before?
Planning on adjusting wing saddle forward as required to keep TE of wing where it is shown on the LT-25 Plans, so that Tail Moment is unchanged. Balance would be where called for on the LT-40 wing Power will be a Saito FA40a. Any thoughts?? Thanks.

Randy
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Old 06-14-2018, 02:12 PM
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I have not tried that, and I wouldn't. Keeping the tail arm the same is not the issue; you have a different wing. If the tail arm of the LT-25 is shorter than that of the LT-40, and if the stab area is less, the CG will need to be farther forward to have the same effect. Also, the point where the engine is mounted will be relatively close to the balance point compared to an LT-40 (aggravated by the smaller tail volume), and the Saito 40a is a light engine, so my guess is you would end up having to add nose weight to get it to balance. I would just build the LT-25 wing and use the Saito 40a. It's a very nice combination. Jim
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Old 06-15-2018, 09:01 AM
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As noted the stock LT-25 is a nice airplane in its own right. My question would be "What do you want to accomplish?" If you can afford the airplanes, "I just wanted to see what would happen" is a valid answer. The process of getting it to fly well will be educational. As long as the C of G is correct relative to the wing, a .40 class engine will fly a .40 class wing. A way to answer the question of "How will it fly?" is to look around for an airplane with similar proportions. The points made above about tail moment and tail volume are relevant. I suspect that the resulting plane would fly kind of like a Slow Poke with undersized control surfaces. Unfortunately, I don't have the source right at hand but there are a sort of set of golden proportions for model airplanes that generally fly well. These proportions vary somewhat with size, speed and task that the aircraft is designed for and designers manipulate one proportion or another to promote various traits in the aircraft. There is, as they say, more than one way to skin a cat, but there is a reason why most airplanes tend to conform to the same general shape and proportion. Experimentation is a part of our hobby and is a way to gain a greater understanding of aerodynamics. On the whole, if you are trying to improve a trainer, I have to agree with Buzzard Bait. If you are trying to thrash together a wing with a partial kit to get one flying airplane, then yeah, it will probably fly. Good luck and have fun.
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Old 06-15-2018, 01:17 PM
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The location of the CG as a proportion of the wing chord does not depend on just the wing, it also depends on the length of the tail arm and the area of the stab. It is proportional to...

stab area/wing area X tail arm/wing chord

So if the tail arm and stab area are reduced compared to the LT-40, the CG position as a proportion of the wing chord will be smaller, i.e., farther forward.
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