cd3217

My Feedback: (3)

Hi,

Turf landing ripped out the retracts on a Zen 120. Converted to fixed gear with 1/8" 2024 aluminum strap gear just forward of the wing LE. About 25sq in. of area on the strap.

In flying the Zen 120 with the new gear an immediate difference was noted in yaw stability and controllability.....all bad (except for enhanced snap rolls and more predictable stall turns....not enough of a compromise to be a good thing....) The gear acts like a fixed canard. I've only flown it in crosswind sequences (Intermediate) and those of 10 to 30kts. When the airplane track gets displaced, rudder correction is not immediately effective and requires large amounts of input to overcome the displacement..... then of course.... too much reaction. The gear appears to be straight, but I have tweaked it just to see if there was any difference.

I have reduced the gear area to about 17 sq in and removed wheelpants with improved results, but not acceptable yet. My next step is to go to 3/16 wire gear.

I see alot of conversions to retract gear airplanes to fixed gear. Has anyone else experienced yaw problems?
This is the only change I've made and it appears to have ruined the yaw characteristics of this airplane....
I would appreciate any suggestions.

Thanks, Chris

MHester

My Feedback: (1)

That's a new one on me. I know the flying characteristics can change when you go from retracts to fixed, but I've never personally seen it so pronounced as you describe.

Usually they just slow down better, and bump around slightly more in high wind.....and need a bit of retrimming. But usually in my experience, the yaw axis hasn't been affected adversely.

-Mike

Bob Pastorello

My Feedback: (198)

Chris, there are a lot of things that can be going on, but my first guess would be that the area of the vertical fin total, and the percentage of that area that is rudder could be at issue. Total side area aft of the CG could be marginal for yaw stability when the canard was added. I agree with your analogy - the fixed gear stuff is just a canard, and the alignment/airfoil can be pretty important.

If it's possible to temporarily add some rudder area, both in vertical and horizontal, I'd do it, and see what happens.

byoung466

My Feedback: (16)

Chris, did this change the CG at all? I assume you took retracts out which were aft of the new fixed gear location, then added fixed ahead of that.....just a thought.

tph1

My Feedback: (12)

swill has a Zen 120 he converted to fixed gear, see the pic on the TT120 motor thread, he may can help you on the problem

cd3217

My Feedback: (3)

Status: Replaced cut down strap gear with 3/16 wire gear and as expected no more yaw tracking problems. 3/16 wire gear is a little lite for a 10.3 lb airplane on turf. I will use it for now and try a narrower & thicker strap gear if the 3/16" proves to bend too often Probably 1/2 by 3/16 SST will work okay. Another thought is that a gear like the bolly (or any carbon fiber with rounded contours) may minimize the canard effect.

Or maybe this just happened to me for a reason unyet determined
thanks for your help....
Chris