I bought a Pober Junior Ace a while back and have found the ailerons to be somewhat heavy in flight. Could this be from "standard" ailerons?
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I bought a Pober Junior Ace a while back and have found the ailerons to be somewhat heavy in flight. Could this be from "standard" ailerons?
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 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,
Wes
N78PS
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.
"... rerigging them [ailerons] to be streamlined in flight is not going to change how they perform in flight."
It is a common OEM procedure to intentionally "mis-rig" ailerons to account for "float" in cruise (normally with newer, more aftly loaded airfoils, though). It is also common procedure to mis-rig both ailerons up to unload the outboard wing (increase twist) or both down to load the outboard wing (decrease twist). It is more common to mis-rig ailerons up to produce better stall characteristics (inboard wing will stall before outboard wing). Rigging of ailerons should be independent of control system forces and cable tension (it's a "balanced" system). All flight controls (in this category of airplane) should move lightly and freely on the ground. As others have suggested, check the entire cable routing, you might find that a cable is rubbing or has come off a pulley. I'm looking forward to hearing what you found out at the airport :o)
Hmmm. To clarify, can you confirm the ailerons are heavy in flight, but not while stationary on the ground?Quote:
Originally Posted by pacerpilot
If that's the case, I doubt it's a tension issue. It sounds like the leverage isn't right, or there's supposed to be balance area and there isn't. Or there is something flexing in flight, and adding a ton of friction. There was a fairly popular homebuilt ~30 years ago where the wings would flex in flight and clamp down on the aileron torque tube.
Can you compare as-built vs. the plans to make sure all the control horns, bellcranks, etc. are correct?
If the heavy ailerons only occur in flight, you need to simulate flight conditions on the ground while looking at it. Might be able to just lift the wingtip a bit and look close inside and see if anything is getting fouled.
If worst comes to worst, I'd suggest adding some spades to the ailerons.
Ron Wanttaja
Thanks for all the good suggestions and info. I've checked the cable tension, looked for interference, flexed the structure and looked for interference and, verified all the cables are on the pulleys etc. The airplane is built exactly to plan. I've been reluctant to intentionally "mis-rig" the ailerons because, as noted, that just chases the problem somewhere else. I'd still not have proper response. Just to confirm, the ailerons are only heavy in flight. The controls move freely on the ground. It takes considerable pressure to force the ailerons into their flight position on the ground. It seems to be an aerodynamice force causing the problem-and powerful one. That's why I mentioned wing wash. Are there any Pober drivers in the East Texas or Louisiana area? Maybe a comparison would shed some light.
Yes, that is true of most airfoils and you're probably losing a noticable amount of performance. But the problem is too much elasticity in your control linkage and/or not enough leverage to maintain/move the aerodynamic surface.Quote:
Originally Posted by pacerpilot
Years ago I used to fly a friends Baby Ace and the ailerons were streamlined on the ground and in flight. I also don't recall them being all that heavy in flight.
Perhaps you can email Mr. Paul for more suggestions?
Flying another Pober Jr. Ace is a good idea (or at least calling another owner and talking to him/her). Are the control horns at the stick and the ailerons the proper lengths per the plans? ... and are the throws of both the control surfaces and the control stick proper? Improper lengths will change the gearing ratio (and hence force feel). The Jr. Ace has a big, long wing, and roll inertia is high. Adding a different wingtip will also change the aileron forces. Personally, I find the cub ailerons to be heavy and slow ... including the clipped wing version.
If you can wait until OSH, the person that works in the builders' workshop is an Ace owner/builder extrodinare. He may also be able to shed some light on the situation, too. I am very curious as I did the drawings of the original plans ... updated and converted from original Corben parts and drawings. I need to see if I can find a copy of the drawings laying around the house.
Thanks for all the replies and information guys, I really appreciate it. I've got lots of stuff to ponder on this now. The nice thing is the plane is built perfectly to plan-and I have them as well. I'll keep after it and get it as good as it can be. Again, thanks for the info!
pacerpilot, were you able to resolve this issue? I was reading one of Tony Bingelis's books and he stated that high tension on cables will make the controls feel stiff. I recall, though, that you had checked the tension on the cables.
I still holding my breath on the final outcome! I want to learn what caused the issue ... or if the forces are just high compared to say an RV (which the forces SHOULD be a lot higher than an RV). And the roll rates should be A LOT lower, too :o)
If at Oshkosh 2016, please let me know. I enjoy looking at what wonderful works people have handcrafted that I had a small part in. 316.295.7812
Thanks! (a different) Ron
I appreciate the continued interest guys! As for the aileron issue..., well, I've sort of learned to live with it. From what I/we can determine, the "ratio" of aileron movement to stick movement is kind of high-with standard ailerons. So really what is happening is a "feeling" of heaviness. They're actually moving a lot relative to stick movement and since they don't have the "differential" affect a Friese type ailerons they just feel heavy. The roll rate is typically slow as you'd expect for a slow, heavy, huge winged airplane. I've checked and rechecked the rig, made small adjustments, and now just fly it. I don't think I'll make Osh this hear, maybe next year. It would be fun to run the big green machine to WI and back! I just need to figure out the wind noise issue on my radio. Someday???Quote:
Originally Posted by Ron Blum
You can easily make a couple changes that will change the feel of the controls.Quote:
Originally Posted by pacerpilot
1) I am not sure, but I believe that there are enough "junctions" in the aileron control system that you can make the controls both differential (the "up" aileron goes up more than the "down" aileron goes down) and exponential (the movement of the control stick moves the ailerons less initially then more as the pilot gets toward the stop.
A) Differential - This will also assist with adverse yaw as the "up-going" aileron creates less total delta drag as it goes up, and moving the "down-going" aileron less will create less increased delta drag on the "up" or "outside" wing.
B) Exponential - This will make the ailerons feel lighter when small inputs are made around neutral ... and heavier when OMG (large) inputs are needed. Pilots typically don't guess well on how much force they are putting in during those situations :o)
C) Both differential and exponential movements can be accomplished through using different portions of the control system arcs.
2) The aileron leading edge is also very critical to the "feel" of the flight control. You mentioned Frise ailerons. Depending on how the aileron is hinged, the forces will get lighter as the leading edge changes from: elliptical to circular to bread loaf to squared, as the leading edge shape changes what shape gets exposed (or hidden) to the airstream when the surface is deflected. This is a little more advanced, but Experimental airplanes can make changes with balsa wood (Hobby Lobby 40% off), double stick tape and aluminum tape (both at Dollar Tree).
Bottom Line: You're flying a fun airplane and enjoying it. Why make changes :o)
Hey, Ron Blum, I have a couple questions:
1) I'm building the traditional ailerons and have the ribs made but haven't assembled the aileron, yet. Do you recommend I go with the Friese ailerons?
2) Will you be at the Pober/Acro Sport 'workshop' Tuesday morning (7/26)? If not, I'd like to meet you and visit about my Junior Ace Project.
Thanks!
Terry
1) I need to look at the plans again for a look at the entire aileron system. In other words, I want to see where the system is cable and where it has push-pull rods and bellcranks. The maximum roll rate cannot be changed (without a change in total aileron travel). It would be good for you to talk to other owners/builders to hear/see their comments on the current design and how it flies. I believe that the ailerons are simple with a single, centerline pivot point and a round leading edge. Changing to a Frise aileron would be a little (a lot actually) work, as it would need to be supported from a cantilevered aft upper surface of the rear spar. The rear spar is probably oversized for the loads in that area, but I would be concerned about putting holes (screws) into the top of it. Go figure. An engineer worried about putting holes in primary structure :o)Quote:
Originally Posted by wltrmtty
2) I need to check my plans for Tuesday morning, but I will put the forum high on my list. In other words, I am not sure of my schedule yet, if work has other plans for me at that time or if I have another meeting or forum scheduled for that time :o) Please email me at fly-in-home@att.net or text me at the number previously posted in this forum, and I will make sure that we talk more. I love this stuff! And someone actually building an airplane from plans! My hats off to you!
Thanks,
Ron
I was at the OSH Pober Forum this morning (nice to meet you, Ron), and was talking to Chris Kinnaman about the aileron gap seals on the drawings and it occurred to me, what do you have for gap seals? One advantage of gap seals is aileron authority. There's quite a gap between the wing false spar and the aileron - big air leak.
Effectiveness will be increased ... but so will forces 😝Quote:
Originally Posted by wltrmtty
Quote:
Originally Posted by Ron Blum
Hum, well, I really don't see spades on a Junior Ace aileron.
Now that would get some looks and questions :o)Quote:
Originally Posted by wltrmtty