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Incidence change or downline mix?

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Old 04-27-2008, 01:09 PM
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stek79
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Default Incidence change or downline mix?

Hello Don!

In my pattern plane, I use the classic downline mix in order to achieve a straight downline.

Speaking with a top pilot, he suggested me to remove that mix and to change stab incidence instead. I was willing to give a try to that new (for me) setup, so I changed my stab incidence ad he suggested - stabs LE down. The side effect I was looking for was also a slower downline, since my plane goes down pretty quickly.

Well, I've just flown two days with this new setup. I lowered the LE of my stabs, now I have some down trim on the elvator (let's say about 1mm).

I've found that this setup actually can be used to straighten downlines AND to slower down the plane a bit, which in my case is a good win. The negative issue I've found is the feel of the elevator. Around neutral, it is like having a great amount of expo. So I reduced my expos to ZERO - but the elevator is still too smothed for me, around center. Throws are good, instead.

What do you think Don about this type of setup? Better/worse than the downline mix? Regarding elevator feel, how can I reach a more solid and direct response?


As usual many thanks
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Old 04-28-2008, 03:12 AM
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Don Szczur
 
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Default RE: Incidence change or downline mix?

When I had adjusted the incidence on my (stab) it made the plane look from tail low to tail (normal to high) in straight and level flight. Sometimes planes fly through the air and it looks like the tail is down. Changing the incidence helps that, and thats the main reason I make that adjustment. Regarding your setup, it depends on the plane design, wing and thrust incidence, and weight (to include CG). If you move your CG back it will increase pitch control responsiveness, but its better to have the CG setup per plans of the design. Basically if the plane flies better this way then keep it where you have the incidence and best of luck!

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Old 04-28-2008, 12:49 PM
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Default RE: Incidence change or downline mix?

Thanks Don.

I recall that your Focus had a good amount of downline mix. Why didn't you changed stab incidence instead, in order to achieve a good downline?

That is the point I don't understand. Why many pilots suggest using a downline mix where you can just change your stab incidence - and get rid of that mix?

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Old 04-29-2008, 11:00 PM
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Don Szczur
 
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Default RE: Incidence change or downline mix?

I did not mind the down line mix. On one of my recent planes (I think it was the Focus II or Brio) the stab incidence had a negative effect on the horizontal presentation of the aircraft. I changed the stab incidence so the airplane flies more level (fuselage angle to the ground in horizontal flight) and presented much better in the air. I'm going by memory here. I'll keep these tips in mind for future reference.

Thanks very much,
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