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Old May 24, 2013, 01:28 AM
JoethePlumber meet JoetheStack
United States, CA, Pasadena
Joined Apr 2013
81 Posts
Question
flight-test-adjusting CG for speed on flying wing sloper

Howdy folks,

Take a flying wing, vanilla flavor: single-panel, swept, and built from a kit. For example 48" wingspan, 14" root chord, 7" tip chord, and 13.75" sweep. Let's say I build it according to the instructions and set the CG according to the instructions. So now the CG is in exactly the right place, right? Maybe not, evidently it is common to move it according to personal taste, or maybe I'm not so good with a ruler as I think, and my CG position is 5 or 10mm off.

It's a slope glider too, forgot to mention. No motor.

But the CG is pretty close in any case, and I test fly it, and it flies as expected.

But it seems like it could perform better - ok, I confess: I want more speed. So here is my question: If I move the CG fore and aft by small increments and test-fly the wing each time, what flight behavior should I expect and be looking for as, say, the CG goes from a little too far back to a little too far forward, one step at a time?

I've read a fair amount of postings about the dive test, but while I have no doubt it is a good test for various purposes, I don't think it is the complete story regarding the above. Call it a hunch. Plus the slopes I've been flying lately and the conditions are not ideal for doing a lot of steep, long dives.

I've also studied and experimented with the CG calculators. They all rightly claim to calculate a safe or starting point for the CG, and they do not claim to calculate the perfect CG, or the optimal CG, because there are other factors.

When a flying wing is flying "normally", i.e. trimmed and level and speed well above stall, what does the position of the CG affect? Is it the pitch attitude, which therefore requires elevon trim adjustment to maintain level flight? Is it the elevator moment, making the wing more or less sensitive to elevator input? Is it another pitch rotational moment created by the center of lift and the center of gravity not coinciding, and is this necessary due to the flying wing airfoil being a bit special compared with a fuselage aircraft wing?

Before I add lead weight, I want to get the most speed I can from the glider. Then maybe I'll add some lead, and maybe I won't. When I push the stick forward a little, I want to go faster with only a little greater descent angle. Sometimes it seems like I get a lot greater descent angle with only a modest speed increase, so I'm thinking I'm not trimmed quite right.
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Old May 24, 2013, 01:50 AM
I don't like your altitude
Stupot46's Avatar
Joined Sep 2011
3,285 Posts
Welcome to rcg Joe.I'd seen your previous post; you may find answers to both on the Slope forum,or Nurflugal.
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Old May 25, 2013, 02:03 AM
JoethePlumber meet JoetheStack
United States, CA, Pasadena
Joined Apr 2013
81 Posts
Thank you.

Huh - maybe I should post this in the Slope forum instead, or just study harder?

Thanks!
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Old May 26, 2013, 01:25 AM
JoethePlumber meet JoetheStack
United States, CA, Pasadena
Joined Apr 2013
81 Posts
move this thread to Slope?

Ok, so let's say I wanted to move this question to a different forum, Slope. But I do not want to cross-post, where the same post is in two different forums. Is it possible to "move" a thread to a different forum? I mean for a regular user.

Looks like I can edit my posts, so I could delete the content.
Looks like I can close the thread.
So if I delete the content of the original post, and close the thread, then I could post the question on another forum. If this is not correct or there is a better way, please don't hesitate to point it out. Thanks.
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Old May 26, 2013, 01:58 AM
I don't like your altitude
Stupot46's Avatar
Joined Sep 2011
3,285 Posts
http://www.rcgroups.com/site-suggest...omplaints-259/


The place to go.Copy a the link back to here.Frankly I'm surprised someone hasn't helped you by now

http://www.rcgroups.com/modeling-science-136/
A good place for discussing tech.stuff
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