My Decathlon is pretty much hands off too. Any roll in cruise can be corrected by adjusting the wing strut. Any yaw can be adjusted with the rudder tab. The pitch trim is a rather blunt instrument, but I can usually get it where I want it with gentle taps.
Roll/Aileron Cruise adjustments
- Thread starter Big Ed
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aftCG
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In cruise flight I fly several miles at a time with just my feet on the rudder pedals for course correction, and for pitch adjustments I just lean back and forth in the seat (and easy 100 fpm both directions without resorting to any yoga positions).
Bob Turner
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Several miles? I have gone transcontinental in my J3 touching the stick for landings and takeoffs and an occasional maneuver.
I have a slight left wing low bias at cruise speed. Is adjustment to the wing strut the way that is dealt with?
Truthfully, no idea, I was just talking on the internet. Better ask Bob that one.
Rick Ludtke
Member
What are your ailerons doing in relation to the wing trailing edge? they will fly up normally as much as any slack in the system will allow, which hopefully is a small amount. But if the aileron trailing edges are different left and right, that may provide a clue, especially if you roll to level and look at the trailing edges again.
Rick
Bob Turner
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Rick is the only other guy in the whole world who knows that. It took me six months and lots of strut adjustments to discover mis-matched ailerons on a J3.
I always recommend his test. Nobody understands it.
On the J3, the hinge point is below the entire aileron. A difference of 1/32” side to side is not correctable even with a six inch trim tab.
I always recommend his test. Nobody understands it.
On the J3, the hinge point is below the entire aileron. A difference of 1/32” side to side is not correctable even with a six inch trim tab.
Hi all,
Moved a few posts to address thread drift in the Dynon thread.
Moved a few posts to address thread drift in the Dynon thread.
You would have to assess the angle of incidence for each wing and see if what you find is consistent with the rolling tendency. After we re-attached the wings on my 7ECA it was rolling every so slightly in cruise flight. The angles were consistent so a one half turn of the rod end on each side made it near perfect.
BB57
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There are a couple possibilities that spring to mind:
1) Unequal fuel burn from left and right tanks. In my 7KCAB on a calm day, trimmed for straight and level flight, I can bank slightly left or right by leaning to one side of the cockpit or the other. It's pretty sensitive in that axis, and when you consider how much farther out the fuel is setting in the tanks, a couple gallons difference side to side will give a slight wing low attitude.
2) I also had a slight left wing low bias when I flew my Citabria home after purchasing it, but I also noted the ball was about a half ball right of center in my normal cruise (about 2200 rpm). When I corrected the rudder, it naturally corrected the left wing low attitude. It it were 1/4 or 1/8 of a ball off center a pilot might not notice or care.
In any event, a slight tweak on the trim tab to add a bit more right rudder in cruise fixed the problem at 2200 rpm cruise. However when I cruise at 2450 rpm it needs a touch of left rudder, so it's not that it was "wrong" before, it's that it was set up for a faster cruise speed.
1&2 are just how it is with an aircraft that doesn't have rudder or aileron trim.
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Pilots (and their well meaning but sometimes misguided A&Ps, especially non-pilot A&Ps) can be tempted to mess with the rear strut fork and start playing with the incidence angle on the wing to correct a one wing low cruise condition. That's often a really bad idea as unless the angle of incidence is actually wrong before they start, it creates other much more serious issues.
For example the first 180 hp 7GCBC I ever flew (1985 or so) flew great at cruise, but it would drop a wing in a stall every time. In fact the first time I tried a short field take off in it, (which was my first take off in it) it slammed the left wheel back on the ground as soon as I rotated and needed aggressive control inputs to keep it from skipping off the left side of the runway. In the air it was no better, dropping the left wing in a stall and clearly wanting to depart into a spin if you were not very careful with the rudder. It was just as bad in a full stall, tail wheel first landing, with the same drop the left wing first trait.
One of the high time ag pilots gave me crap about my take off and landing performance after the flight. I didn't bother explaining as it would have been seen as an excuse. I also didn't bother explaining that it was improperly rigged, I just handed him the clipboard and said "show me how short you can get it off the ground". He took me up on that and several off us watched him depart the left side of the (150' wide!) runway skipping on the left main wheel. When he got back we both agreed some moron had increased the incidence angle on the left wing to deal with the additional torque and power of its very healthy 0-360 engine and climb prop (it was set up for banner and glider towing), rather than putting a trim tab on the rudder to allow the rudder to properly address it. Ideally, it would have had a bit of offset in the vertical fin, but that's a much more involved and expensive fix.
Based on that experience, I prefer to confirm proper wing rigging by taking it up and then doing a power off stall to ensure both wings stall at the same time, (with the stick centered and the ball centered with the rudder) and then holding it in the stall to ensure there is no more than the normal tendency to drop a wing, which is easily corrected with small rudder inputs.
Do that before you even consider messing with the angle of incidence on either wing. Then level the aircraft and measure the incidence on each wing to confirm the angle of incidence on the suspect wing really is off, confirm the ailerons are properly rigged, and then - and only then - mess with the strut fork.
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Bob Turner
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I maintain that aileron "rigging" has nothing to do with it.
A good airplane will fly wings level, and go in a straight line, with just gentle rudder pressure. Some think that an airplane should fly straight and level at all speeds and power settings, with hands and feet off the controls. I maintain that is only true at one specific speed, load, and power setting.
Most of the time with Cubs, a differential wash is an attempt to compensate for mis-matched ailerons. A little "tweak," as Bart says, is sometimes necessary, but it should not be excessive.
Opinion, of course.
A good airplane will fly wings level, and go in a straight line, with just gentle rudder pressure. Some think that an airplane should fly straight and level at all speeds and power settings, with hands and feet off the controls. I maintain that is only true at one specific speed, load, and power setting.
Most of the time with Cubs, a differential wash is an attempt to compensate for mis-matched ailerons. A little "tweak," as Bart says, is sometimes necessary, but it should not be excessive.
Opinion, of course.
BB57
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I agree with you when it comes to rudder trim. More power equal more torque along with more airspeed and varying degrees of prop wash effects. There will be one rudder trim tab setting that will produce truly straight flight and a fairly narrow range where flying with your feet on the floor will not create a yaw, that then lowers a wing.
As for aileron rigging, in the end that comes down to getting the stick positioned more or less in the center and ensuring you have equal travel up and down on each side. If the trailing edge of one is 1/32" lower than the other, it might not be correctable with a trim tab, but who cares. It'll be correctable with maybe 1/8" movement of the stick, so why would you even notice?
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Bob Turner
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That was my point. No matter how far out of adjustment the cables are, the ailerons should trail at the same angle wrt the trailing edge. If not, you need different ailerons - has nothing to do with stick position.