Pober Junior Ace Heavy Ailerons
I bought a Pober Junior Ace a while back and have found the ailerons to be very heavy in flight. They're rather ineffective giving the plane a "slow and sluggish" feel in roll. This makes flying it rather tiring, especially in turbulence. Also, the ailerons both rise up to a roughly 3/4" negative position in flight. Both are equal and neutral on the ground and I am hesitant to tighten the cables any further because I might pull something loose. Could improper wing wash be the cause? Any input or ideas would be appreciated. This ones got me beat.
If the ailerons are reflexing that much in flight, they will certainly be ineffective and sluggish. What is the cable tension now?
Well, I don't have a tension gauge so my A/I buddy has been advising me. I've set the cable tension to what I believe is the most load I'd want to put against the pulley brakets etc. They're on par with a Cub on the field. It takes considerable force to move the ailerons into their "flight position" on the ground. Also, the more I tighten, the harder the stick force becomes. There's no interference I can find either. I'm just wondering if cable stretch or airframe flex is the issue. It has the correct cable as far as we can tell too. I don't know if it's a quirk of the design but I'm stumped.
I am not familiar with the control system of that particular airplane, but I can suggest some obvious items to look at.
A) I assume that the cables are 1/8" 7x19 and not stiffer types of cable. Yes? Smaller is bad.
B) I believe that pulley diameters should be 35X the cable size for best cable longevity and flex.
So ideally your pulleys should be the 4 1/4" ones for least resistance. You can go smaller but the resistance goes up
and the cable life goes down.
C) The lowest resistance pulleys are the ones with ball bearings. I believe that there are control system pulleys out there
that have bushings rather than bearings. If you have that type, lots of lube might help.
D) The "float' of the ailerons might be the result of the pulley brackets flexing. You should not need huge amounts of
cable tension for the system to do its job. But you are getting slack from somewhere and from the description it is
unlikely to be the cable if the proper cable was used. 7x19 control system cable should handle a 2000lb load.
D) And finally, every once in a while we see an airplane where the cable between the ailerons, the balance cable, has
been twisted around a cable that goes to the control stick or yoke. In the dark of the inside of the wing, more than
one mechanic has made this mistake while snaking the cables into place. And as you add cable tension, resistance
goes up since the two cables are rubbing and abraiding against each other.
Use some webbing to tie the control stick into a fixed position, then have a friend gently push up on an aileron until you see the position that you observe in flight. Then go looking along the cable runs to see what is yielding or interfering.
Best of luck,
Last edited by WLIU; 12-12-2012 at 02:11 PM.
It's got 1/8" 7X19 cable-per print. The pulleys are only 2" though. I've done the "hold the stick" thing and the whole system seems to absorb the flexure although it does take what we feel is a lot of force to simulate the in flight condition. I haven't noted any flex in the pulley brackets. I'll do a very close check of the balance cable run. Your suggestion makes sense about interference. Since this is a low time experimental maybe something is sawing in there. Something I have noticed is that the plane flies with a negative angle of incidence-at least at the outboard ends of the wings. It does this despite the "up" aileron condition. I'll check the cable runs and go from there.
I presume that as you are tightening the cables to pull the ailerons down that you are loosebing the balance cable between the ailerons. I think that the idea that a cable is twisted around something in the wing is more than likely the culprit. That thing ought to be fast with the up aileron in cruise. LOL. I hope you find it. Almost nothing is worse than flying a lousy flying airplane.
Well, the way it's rigged is kind of like an 8 track tape-continuous loop. Tightening one side results in movement of the ailerons so tension must be applied equally. It seems ok as far as tension goes but why the ailerons are able to overcome that tension is beyond me. I flew this afternoon with my wife just to watch the ailerons (and I'm trying to get her to "warm up" to the open cockpit). It was running 85mph+ at a reduced power setting so yes, it's fairly quick. It also flies with a slight negative AOI in cruise despit the aileron postion.
What is the angle of incidence on your wing? It should be 2 deg (compared to the fuselage upper longerons. If the wing incidence is off, you will notice the elevator and horizontal stabilizer not being "faired" (aligned with each other) in cruise.
Adding cable tension will always add control system load (both to the system and the pilot) in all airplanes (it puts more load on all the pulleys). If your ailerons are floating in flight, rig them both down (don't increase the system tension). It also sounds a little like the wings might be improperly twisted (and I don't believe that they are designed with any intentional twist). If you want to experiment, you can also change the leading edge shape of the ailerons (increasing or decreasing control force), seal them (more effective but higher forces) or move the hinge line (less force moving aft - more force moving forward). Enjoy the airplane, and make it yours. That's the beauty of an X airplane!
I'm going to the airport right now to level the plane and do a proper AOI check. There was a plans error common to the rear cabane which resulted in the wing having excessive AOI. I corrected this error and have been adjusting the horizontal for "faired" flight and trim. The reason I mentioned the wing wash was that I thought that excess positive AOI could result in increased pressure on the bottom of the wing-forcing the ailerons up. Just a thought-no science behind it. I'll post my results of the check later today.
For the most part, angle of incidence only establishes the "levelness" of the fuselage in flight. If "q" is forcing the ailerons to move as much as you describe, rerigging them to be streamlined in flight is not going to change how they perform in flight. Think about it, what's going to happen when you deflect the ailerons into the airstream. Dynamic pressure will prevent them from moving proportional to stick movement. You have a control linkage problem.