Aircraft rigging with wheel ski's installed, right wing drop

[mdpesky]

Has anyone noticed a difference in aircraft trim/STOL with wheel ski's installed versus no ski's?

Since I installed my Federal AWB2500 wheel ski's, in a Stol my 170B now drops a right wing. To be sure the aircraft rigging was still correct I removed the ski's and verified the aircraft flys straight as an arrow, ball in middle, wings level with no wing drop tendency at all in a power off, power on or with and without flaps! Yet as soon as the skis are re-installed again the right wing drops in the stol???? With or without skis' the aircraft flys well and trims up perfect, its only in the stol it has a tendancy to drop the right wing, all else is normal!

My ski rigging is dead on the money and both ski's are set up exactly the same, no issues there.

Not sure what to do about this latest "Ski set up Challange", hoping someone out there knows if this is normal or???

As always any help or advice is greatly appreciated.

Mark

[blueldr]

Im confused in your use of the word "STOL" in the above.

[mdpesky]

Sorry, poor terminology, its when the aircraft stalls it drops a right wing with skis on versus straight and level with ski's off.

[bagarre]

Slip stream rotation hits the bottom of the left ski differently than the right ski so that in a stall the left side of the plane tends to have slightly more lift resulting in a perceived right wing drop. Russian planes have the opposite problem

¯\_(ツ)_/¯

[mdpesky]

That explanation makes sense but opposite to what we had guessed! We were thinking perhaps the down wash of the airflow coming off the descending prop blade was hitting the top of the right ski pushing down on it, your explanation makes more sense(or maybe a combination of both?).

Its interesting but the wing drop is quite pronounced and certainly means you have to be on your game much more, stalling the aircraft with the ski's on close to the ground could end with a less then desirable result!

I suspect the larger Sea Plane prop also adds to the aerodynamic ghosts playing havoc with what normally is a very docile stall with no tendency to drop a wing to something quite harsh!

I do not remember my original Aero 2000 straight ski's having this problem, I flew those for hundreds of hours in many adverse conditions without ever an issue, the larger AWB2500 certainly are not so forgiving in the stall!

[stogie17]

About to put the AWB 2500s on my 170B. Last year was first with them and I never noticed the wing drop issue. In stalls from slow flight my left wing actually drops first slightly whether wheels ior skis. Never noticed any issues with full stall landings. Rigging was by past owner and checked by my A&P at installation.

[mdpesky]

Stogie

Do you have the larger Sea Plane prop?

Would it be possible to have you conduct a few stall tests before you put your ski's on, then again with the skis mounted just to cross check the differences skis on versus off?

Today I removed my ski's and reconfirmed the aircrafts rigging is dead on, the stall power off and with various RPM's and flap settings is nice and docile. As soon as I put the ski's back on, the right wing has a pronounced drop in the very same tests??

Just would like to know for sure I have a ski rigging issue before I start chasing ghosts and changing things. We were so careful setting up our ski rigging I'm having trouble beleiving thats the problem?

[stogie17]

Sure will. May take a few days as tied up with house building right at the moment. Will take her up for sure before changing to skis. I'm interested to

[mdpesky]

That's great, appreciate it. Please try the stall power off no flaps up to 20 degrees and power on the same.

Did you say you had the larger Sea Plane prop?

[stogie17]

Will try stalls as you mentioned. Yes on prop it is MT carbon.

[mdpesky]

Stogie

Any luck testing out how your plane stalls skis on and off?

Any notible right wing drop with ski's on that isn't there skis off?

[stogie17]

Sorry haven't replied but have skis on mow and plan to fly and check stalls again Sunday. Will let you know.

[stogie17]

Finally got skis on and out today. AC seemed to fly right wing down and out of trim which wa different from last spring when flew last. Fell off to right on stalls. Cycled skis thru a few times and found it stopped. As just installed i think the right ski just was slightly lower when raised and caused problem untill cycled a few times. Check stalls ski up and ski down see if different. My mechs say not much difference in postion will cause out of trim. Good luck

[mdpesky]

Your results are interesting as they have mimicked my last flight test yesterday. This baffled me as my radical right wing drop experienced before was now only subtley noticable as I added flap being more pronounced the more I added but nothing in comparison to what it was doing before(now totally mellow).

Without skis installed flap position had no real noticable affect, the stall remained basically the same with more of a tendancy to slightly favor the left wing(typical).

I can only summize that in my earlier flight tests I must have also had one ski in a different position then the other, perhaps due to some air in the system that wasn't purged out until after a few cycles?

Also as you have found I get higher speed by almost 2 mph with skis down.

I do notice having flown with Ski's, then without and then again with in a short time period the aircraft is a lot mushier and requires more rudder action to keep the ball in the middle then without them, the skis give you the feeling your trying to balance a golf ball on a pin more were in without them installed the aircraft is much more stable.

In any case I really apprerciate your efforts and feedback, being our results are near the same I can conclude I'm not losing my mind and don't need to spend more time re-rigging the rigging.

Thanks so much!

[stogie17]

I agree she flys much mushier. I imagine you had smae issue as me with one ski not coming up exactly the same yntill cyled thru several times. My right ski kept dropping down when packed for several days and I am sure it was out of plane with other ski. Good luck