Cheranovsky highly tapered planks - Page 2 - RC Groups
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Sep 26, 2012, 06:30 PM
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Foam prototype under construction.

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Oct 09, 2012, 10:00 AM
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Well, the prototype's got wing trouble. I took a chance by mounting the wing "upside down" with the larger KF step on top. The resulting configuration requires a ton of up trim to fly right and has a nasty tip stall. Oh well, I'll probably revisit this design again soon.
Oct 09, 2012, 10:48 AM
Just call me crash for short
Quick61's Avatar
Quote:
Originally Posted by g_munu
Well, the prototype's got wing trouble. I took a chance by mounting the wing "upside down" with the larger KF step on top. The resulting configuration requires a ton of up trim to fly right and has a nasty tip stall. Oh well, I'll probably revisit this design again soon.
One large step on top would not be "upside down". That is simply a KFm2 type airfoil and should be a decent choice for prototyping this sort of wing. i would not give up so easy. Just move the CG back a touch at a time.

Did you test glide the model before truing to take to the sky? I always give my prototypes short test glides (neutral trim) to see how they go. I toss them from the bedroom door onto the bed (soft landing) and see if they come down nose first, tail first, or land flat on their belly. 5 - 10 tosses like that will give you a reasonable idea as to where your CG is, and get you ball parked enough to head out to the field. About the only thing I would of done differently this the wing is given it a KFm4 airfoil as it is a symmetrical type and usually works a bit better with flying wings than the type 2. I personally like using the KF airfoils for prototyping as they are very fast and cheap to build while allowing one to test new designs for flight worthiness.

Mark
Oct 09, 2012, 01:19 PM
You know nothing....
Stuart A's Avatar
And I thought I was the only one using the duvet landing strip.
Stuart
Oct 10, 2012, 10:49 PM
B for Bruce
BMatthews's Avatar
Quote:
Originally Posted by g_munu
Well, the prototype's got wing trouble. I took a chance by mounting the wing "upside down" with the larger KF step on top. The resulting configuration requires a ton of up trim to fly right and has a nasty tip stall. Oh well, I'll probably revisit this design again soon.
Build in more washout. With that extreme a taper and the sweep of the 25% chord line in the outer panels a higher washout twist will both reduce the wing tip stalling AND promote a more pitch stable model.

You may be running into some of the swept wing angle of attack issues related to sweep angle as well. I've done a bit of playing with a test chuckie enough to realize that the effect is quite real and needs to be considered. I've got around 4 degrees of washout on the chuckie and it's not enough. Weather and other duties have prevented me getting back to it. But I've learned enough to suspect that it could easily be an issue in your case. Off the top of my head I'd suggest a good 6 degrees of washout at the tip compared to the gull dihedral break.
Oct 10, 2012, 11:10 PM
Soaring Fanatic!
8thelephant's Avatar
Unique find and nice work so far :-)

-8th


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