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Another knife edge and coupling query...

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Another knife edge and coupling query...

Old 08-21-2008, 06:27 AM
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Spoiler
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Default Another knife edge and coupling query...

I posted this in reply on another thread. "Wish I knew the secret. My first 27% H9 E260 was, by the time I crashed it, the most perfect k/e flying machine I have ever seen/flown. It had zero coupling in either direction and could also do those lovely flat rudder only turns on rails as a result. This was not due to a fancy set up procedure - it was like this out the box. The replacment with identical set up and cg, is fine right to left , canopy in, but not the other way and has a noticeable tenedency to turn towards the u/c. Once under control its fine but not the no brainer the other one was. Incidence checks out - the only skewness being the slight stab/wing alignment issue when seen from fornt or rear. I wonder if this is a factor... "

I should point that I meant it flies without coupling when flying from right to left canopy in, i.e. right rudder applied, but not when going left to right canopy in, left rudder applied.

Any ideas?
Old 08-21-2008, 08:59 AM
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rmh
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Default RE: Another knife edge and coupling query...

The setup is everything -
once balance is nearly right - and balance is the single most important part - you have to look at any built in trim tweaks as the model when flown in a SKID (and all knife edge and flat turns are skidding).
Your particular tweak can be - prop used (really) - engine alignment- fuselage to wing to stab alignment - on and on
You don't need a trim chart to figure out what is wrong
just try some trim corrections and fly the maneuvers over and over till you see which trims affect the maneuvers - GO EASY on the trims!!! A couple of clicks can make a big difference and you will have to hand correct to fly straight n level.
Jiggering the engine alignment is always a possibility but sort out the easier stuff first.
Also such a thing as relatively large gaps and surface misalignments can cause your problem. also crummy servos and sloppy linkages will unload in different flight attitudes.- changing actual trim conditions.
Old 08-22-2008, 01:02 PM
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Default RE: Another knife edge and coupling query...

I guess I knew some of this already - lots more flying and tweaking needed. have already tried to correct a noticeable stab wing misalignment so we'll see this weekend. Am flying it in an airshow
Old 08-22-2008, 04:51 PM
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da Rock
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Default RE: Another knife edge and coupling query...


ORIGINAL: Spoiler
I should point that I meant it flies without coupling when flying from right to left canopy in, i.e. right rudder applied, but not when going left to right canopy in, left rudder applied.

Any ideas?
Ideas?

Yeah, in KE, the airplane is flying in yaw. Quite a bit of yaw. But as far as propellers are concerned, they couldn't tell yaw from pitch or slip. When they are pitched, the result is called p-effect. Fact is, when they are yawed, the result is also called p-effect. The spiral prop wash however, has a bias. And it adds to the p-effect one direction, but detracts going the other direction. It's also true that a CG that is not directly in line with the wing, and few are, is going to work to create a roll couple. So both the prop wash and a CG not in line with the wing could be something to consider. Any way to predict how much each does and it's effect? Not that I know of, but they are ideas to think about.

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