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Hob Chpmnk wing lightning?

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Old 03-28-2003, 01:40 PM
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Default Hob Chpmnk wing lightning?

Good day. It appears the wing on this Chipmunk was planned for combat! Geez, its built like a tank. Any ideas for lightening this up?

I was planning on cutting large radius's in between the ribs on all the sheeting. Does this sound exceptable? Has anyone left the sheeting off and connected the ribs by other means? Maybe Wild Fred has some ideas?

Thanks for any input
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Old 03-28-2003, 10:09 PM
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Default Hob Chpmnk wing lightning?

it's pretty overbuilt, but it still comes out acceptably light. I prefer a thinner airfoil, and if building another, I would slice off bottom of ribs and make it flat bottomed. But that's not too big a deal. best thing to do to lighten it is select very light sheeting. You can also increase rib spacing and stuff, but again, it still comes out acceptable as designed. main thing on those is cutting out the ply doublers, most other mods are 1/4 oz. here and there, but they do add up.
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Old 03-29-2003, 12:34 AM
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Default Thinning Flat bottom

I'll bite, you have mentioned before about the thinning and flat bottom. What's your reason? I was mildly hopeful that this would be aerobatic, but the more I'm reading the more the plane was designed for looks in the air. IF that's the case then the flat bottom would make it more stable. Right? Plus increase lift? Making the landings very forgiving? Just speculation.

Thoughts?

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Old 03-29-2003, 01:32 AM
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Default Hob Chpmnk wing lightning?

less drag. It is very aerobatic as is, will loop,roll,spin,invert,snap,avalanch, etc. with stock wing. It won't change the stability noticeably. It will fly faster, corner more nimbly, land better- but make sure you can slow the engine or it will keep flying- even with stock wing!

inverted will still be fine, especially if you sand a little phillips entry into bottom; like seniorita or full size cubs have. I also reflex the ailerons slightly, negates trim change at different throttle settings on flat bottom stuff.

The starfighter is totally flat on the bottom, flies inverted just fine. I just personally find that a flat bottom works better on airplanes .15 size or less. over that, it doesn't work the same. on .25 size or larger, I get the same results using a laminar airfoil. only difference there is that below a certain speed, it sinks rapidly w/ laminar.
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Old 03-29-2003, 06:52 PM
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Default Hob Chpmnk wing lightning?

Thank you for the input. What do you mean reflex the ailerons? and please clarify the Laminar Airfoil.

Ive decided to stay w/the stock rib/wing, but major lightening on the top/bottom leading and trailing edges w/o sacrificing strength.

It calls for reinforcing fiberglass for the middle of the wing. I usually will put a long piece of ply along the spar w/the dihedral to connect the wing halves and glue the heck out of it. I just don't trust the fiber glass thing. Which leads me to another question. Do you need the dihedral?

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Old 03-29-2003, 10:32 PM
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Default Hob Chpmnk wing lightning?

the fiberglas works fine, no problems and lighter than ply.

the h.o.b. kits aren't full span ailerons, but on my full span flat bottom stuff, I set the ailerons both a little above center. the faster it goes, the lower angle of attack, the more effect the reflex has of killing lift. basically, if you dive it vertical and it pulls out, add up on ailerons. if it tucks under, lower them. this works on most planes, by the way!

laminar airfoils are thickest behind the c.g. lower drag, but do "funny" stuff at low speeds in certain instances. The full size p-51 had one of the first, if I am not mistaken. the beercat in my avatar pic also had one, and it was one of the fastest planes that I have ever had. That is what I use on my 25 sized homebuilts a lot.

dihedral is not a must, but helps it track straighter through turns without skidding. taking it out won't make it fly any better, though.
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