Heavier wing high, or heavier wing low?

tawood

tawood

En-Route
Joined
Sep 22, 2015
Messages
2,558
Location
SE Michigan
Display Name
Display name:
Tim
I may have to run another test just to see/verify for myself...

My Cherokee (like all PA28s) carries it’s fuel in its wings, and it always seems somewhat sensitive to fuel imbalances. But I noticed a few times while flying, that it always seems that in order to fly without turning I need to position the heavier wing higher than the lighter wing (which seems opposite from what I would have expected). Is this my imagination or is that correct?
 
Last edited:
tawood said:
I may have to run a test just to see/verify for myself...

My Cherokee (like all PA28s) carries it’s fuel in its wings, and it always seems somewhat sensitive to fuel imbalances. But I noticed a few times while flying, that it always seems that in order to fly without turning I need to position the heavier wing higher than the lighter wing (which seems opposite from what I would have expected). Is this my imagination or is that correct?
Click to expand...
Correct, if you don't coordinate rudder with the aileron too.
 
Ok. I do correct with rudder trim to center the ball. If my fuel is even or close to even, plane flies straight and level. If fuel goes beyond, say, 10 gallons difference between tanks, the plane will fly straight with one wing high / one wing low. If I level the wings with ailerons, then plane turns. So, to stay straight, heavy wing must be high, and ball is centered.
 
I try to never let a 10 gallon imbalance happen in the first place. I switch tanks every thirty minutes, which in my case is only around 4 gallons difference at the most at any one time. Having said that, I'm finding out that Cherokees are notorious for rigging issues, meaning, keeping them rigged properly. I had a heavy wing. IA made an adjustment to fix it. Now I have a yoke that is not centered when flying straight and level. Have adjusted the flaps which almost corrected the yoke problem (need one more turn) but I fear that when this is adjusted I may have a heavy wing again. I'm almost to the point of just starting from scratch.
 
tawood said:
... to stay straight, heavy wing must be high, and ball is centered.
Click to expand...
That's your imagination. If you hold your wings level by using aileron to compensate for a heavy wing you need to compensate for the adverse yaw by using rudder too in order to keep the ball centered. If you bank the airplane to hold your heading you will be in a slip.
 
dtuuri said:
That's your imagination. If you hold your wings level by using aileron to compensate for a heavy wing you need to compensate for the adverse yaw by using rudder too in order to keep the ball centered. If you bank the airplane to hold your heading you will be in a slip.
Click to expand...
Yesterday was dead calm, and I was doing something I normally wouldn’t do, which was running entirely on one tank going to a destination (where I the refilled that tank), then running entirely on the other tank for the ride home. Plane flew hands off at start of flight in each direction, but by the time I reached the destination (and tanks where now 10 gallons different), it was definitely turning when level. I triple checked the ball was centered (it wasn’t at first so it was centered with rudder trim) which once centered then made turning tendency worse. On the return trip it did the same thing, just opposite direction. I may fly again today and run the test again, but most definitely turning when level, once ball was centered. To maintain straight flight, heavy wing had to be held well over the horizon, while lighter wing was held well under. Heavy/lighter wing changed sides near each destination, as did the high side/low side wing.
To get the plane to fly hands off without turning when the fuel was imbalanced, I had to adjust the rudder trim until the ball was way out from centered...in one direction on the way there, and the other on the way back.
It was definitely the opposite of what I expected, as I’ve heard the term “heavy wing” applied to wings that are the lower of two wings of the same plane.
 
Last edited:
Timbeck2 said:
I try to never let a 10 gallon imbalance happen in the first place. I switch tanks every thirty minutes, which in my case is only around 4 gallons difference at the most at any one time. Having said that, I'm finding out that Cherokees are notorious for rigging issues, meaning, keeping them rigged properly. I had a heavy wing. IA made an adjustment to fix it. Now I have a yoke that is not centered when flying straight and level. Have adjusted the flaps which almost corrected the yoke problem (need one more turn) but I fear that when this is adjusted I may have a heavy wing again. I'm almost to the point of just starting from scratch.
Click to expand...
I normally never get more than 5 gallons difference between the two. I normally use my JPI to switch at exactly 5. Yesterday was just unusual as I was running on just one tank out, refilling, then running on only the other tank back.
 
Oh, and last year at annual, I had my mechanic check the rigging with my piper tool. He said it was dead nuts, and even showed me how ailerons and flaps were even/flush...not to mention, as I said, plane flies straight when balanced.
 
tawood said:
Yesterday was dead calm, and I was doing something I normally wouldn’t do, which was running entirely on one tank going to a destination (where I the refilled that tank), then running entirely on the other tank for the ride home. Plane flew hands off at start of flight in each direction, but by the time I reached the destination (and tanks where now 10 gallons different), it was definitely turning when level. I triple checked the ball was centered (it wasn’t at first so it was centered with rudder trim) which once centered then made turning tendency worse. On the return trip it did the same thing, just opposite direction. I may fly again today and run the test again, but most definitely turning when level, once ball was centered. To maintain straight flight, heavy wing had to be held well over the horizon, while lighter wing was held well under. Heavy/lighter wing changed sides near each destination, as did the high side/low side wing.
To get the plane to fly hands off without turning when the fuel was imbalanced, I had to adjust the rudder trim until the ball was way out from centered...in one direction on the way there, and the other on the way back.
It was definitely the opposite of what I expected, as I’ve heard the term “heavy wing” applied to wings that are the lower of two wings of the same plane.
Click to expand...
I'm out of explanations. :(
 
The side without fuel is lighter so it flies faster than the side with fuel. If you step on the rudder on the fast side, both wings will be flying st the same speed and the turn will stop. :rolleyes:
 
dtuuri said:
I'm out of explanations. :(
Click to expand...
I just got off the phone with my mechanic...as I started to explain what I saw, he said it sounded like my turn coordinator wasn't level in my dash, but as I explained it did it in the other direction on the way back, he then said he doesn't think what I'm seeing is possible...I'm definitely a knucklehead at times, so now I've got to run another test to see if I misinterpreted something...
 
tawood said:
I just got off the phone with my mechanic...as I started to explain what I saw, he said it sounded like my turn coordinator wasn't level in my dash, but as I explained it did it in the other direction on the way back, he then said he doesn't think what I'm seeing is possible...I'm definitely a knucklehead at times, so now I've got to run another test to see if I misinterpreted something...
Click to expand...

Check that the TC is really installed correctly. IIRC, the door sills are the leveling point on a Cherokee. Place a level across the door sills to verify plane is level, then look at the ball. If your level isn't long enough, a straight wooden plank across the sills will give you a good base for the level. -Skip
 
In order to keep the plane level the heavier wing will need more aerodynamic force, in this case from the aileron.. that will add more drag to the heavier wing so a "level" plane will actually be pulling you towards the direction of that heavier wing.. so yes it makes sense that the heavier wing must be slightly higher to offset it. If you keep the wings level but counter the turn with rudder than like posted above you'll be in a slip
 
Hmm. How much effect would dihedral have on this? Say right wing is heavy. You use a little left aileron to lift it to level the wings creating adverse yaw to the right. Little left rudder is needed to make the plane fly straight. If you lift the heavy right wing even higher now it has more horizontal component of lift to the left.
 
Tantalum said:
In order to keep the plane level the heavier wing will need more aerodynamic force, in this case from the aileron.. that will add more drag to the heavier wing so a "level" plane will actually be pulling you towards the direction of that heavier wing.. so yes it makes sense that the heavier wing must be slightly higher to offset it. If you keep the wings level but counter the turn with rudder than like posted above you'll be in a slip
Click to expand...

The heavier wing must be higher to offset the adverse yaw of the aileron? I'm not following at all.
 
Skip Miller said:
Check that the TC is really installed correctly. IIRC, the door sills are the leveling point on a Cherokee. Place a level across the door sills to verify plane is level, then look at the ball. If your level isn't long enough, a straight wooden plank across the sills will give you a good base for the level. -Skip
Click to expand...

Door sill is the leveling point in one direction but the one for the turn coordinator is the spar underneath the rear seats.
 
kgruber said:
You need to go out and get your tailwheel endorsement in order to wake up your feet.
Click to expand...
Why “wake up my feet” if the ball is centered?

And I got my tw endorsement about 200 tailwheel hours ago.
 
dmspilot said:
The heavier wing must be higher to offset the adverse yaw of the aileron? I'm not following at all.
Click to expand...
Not even a little bit?

If you lift it even higher you'll add even more adverse yaw but the bank away from the heavier wing will cancel out (so to speak) the adverse yaw so the plane will not want to be turning. Your ball will still not be centered though because now you are flying along in a slight bank but your compass will not show a turn. Most people end up with some combination of slight aileron pressure and rudder trim to "balance" out the plane aerodynamically even though one wing may be 40 lbs heavier. This is why the OP experienced what he experienced
 
tawood said:
Yesterday was dead calm, and I was doing something I normally wouldn’t do, which was running entirely on one tank going to a destination (where I the refilled that tank), then running entirely on the other tank for the ride home. Plane flew hands off at start of flight in each direction, but by the time I reached the destination (and tanks where now 10 gallons different), it was definitely turning when level. I triple checked the ball was centered (it wasn’t at first so it was centered with rudder trim) which once centered then made turning tendency worse. On the return trip it did the same thing, just opposite direction. I may fly again today and run the test again, but most definitely turning when level, once ball was centered. To maintain straight flight, heavy wing had to be held well over the horizon, while lighter wing was held well under. Heavy/lighter wing changed sides near each destination, as did the high side/low side wing.
To get the plane to fly hands off without turning when the fuel was imbalanced, I had to adjust the rudder trim until the ball was way out from centered...in one direction on the way there, and the other on the way back.
It was definitely the opposite of what I expected, as I’ve heard the term “heavy wing” applied to wings that are the lower of two wings of the same plane.
Click to expand...
Flying coordinated “hands off”with a fuel imbalance isn’t going to happen in a properly rigged Cherokee...you need to apply aileron to counter the fuel imbalance, and unless you’ve got aileron trim, you need to use your hands (or knees) to do that. Wings should be level.
 
Last edited:
That's what the rudder trim knob is for but it shouldn't be more than a slight drift without even without trimming. Shifting/gusting wind can make a bigger difference.
 
It's all about balancing forces and moments. Just for convenience let's say it's the right wing that's heavy. Add a little left aileron trim to balance the roll. Now the right aileron is down and when the wings are level the adverse yaw creates a nose-right yawing moment giving you a flat turn and displacing the ball to the left (the ball is a sideforce indicator, not a sideslip indicator). Left rudder to balance the moment gives you right sideforce (sideward 'lift' from the vertical and rudder) which is balanced by raising the right (heavy) wing. Or at least that's one way of looking at it.

You can also trim wings-level with a large weight asymmetry but the ball won't be centered on most airplanes with significant adverse yaw. A similar exercise will show that in a twin with OEI and a yaw string, zero sideslip is not the same as ball-centered (zero sideforce).

Nauga,
and the summation of all fears (and moments)
 
Last edited:
nauga said:
You can also trim wings-level with a large weight asymmetry but the ball won't be centered on most airplanes with significant adverse yaw. A similar exercise will show that in a twin with OEI and a yaw string, zero sideslip is not the same as ball-centered (zero sideforce).
Click to expand...
You mean, I think, "with a large thrust asymmetry," don't you? If rudder is holding the heading, with wings level, the ball should be centered and the sideslip will be to the right in your scenario (either right wing heavy or right engine inop).
 
dtuuri said:
You mean, I think, "with a large thrust asymmetry," don't you? If rudder is holding the heading, with wings level, the ball should be centered and the sideslip will be to the right in your scenario (either right wing heavy or right engine inop).
Click to expand...
With any asymmetry that causes a yawing moment with wings-level. In the OEI case it's the thrust asymmetry, in the fuel case it's the adverse yaw. The resulting rudder deflection to trim causes a sideforce that has to be balanced. There are several ways to do that, one is with ball-centered and wings-level but non-zero sideslip and another is heavy (or dead engine) raised with zero sideslip but the ball not centered.

Nauga,
well-balanced?
 
Last edited:
nauga said:
With any asymmetry that causes a yawing moment with wings-level. In the OEI case it's the thrust asymmetry, in the fuel case it's the adverse yaw. The resulting rudder deflection to trim causes a sideforce that has to be balanced. There are several ways to do that, one is with ball-centered and heavy (or dead engine) raised.
Click to expand...
I always appreciate it when you weigh in on aerodynamic discussions, Nauga. But either I'm not getting it, or you're misspeaking. With a wing raised, the ball shouldn't be centered in non-turning flight, but to my eyes, you're saying it is.
 
dtuuri said:
I always appreciate it when you weigh in on aerodynamic discussions, Nauga. But either I'm not getting it, or you're misspeaking. With a wing raised, the ball shouldn't be centered in non-turning flight, but to my eyes, you're saying it is.
Click to expand...
Ah you are correct, with the dead engine or heavy wing raised the ball will not be centered. Got a bit ahead of myself and thought you were saying that was only the case for a thrust asymmetry.

Nauga,
putting the ass in asymmetric
 
Last edited:
nauga said:
It's all about balancing forces and moments. Just for convenience let's say it's the right wing that's heavy. Add a little left aileron trim to balance the roll. Now the right aileron is down and when the wings are level the adverse yaw creates a nose-right yawing moment giving you a flat turn and displacing the ball to the left (the ball is a sideforce indicator, not a sideslip indicator). Left rudder to balance the moment gives you right sideforce (sideward 'lift' from the vertical and rudder) which is balanced by raising the right (heavy) wing. Or at least that's one way of looking at it.

You can also trim wings-level with a large weight asymmetry but the ball won't be centered on most airplanes with significant adverse yaw. A similar exercise will show that in a twin with OEI and a yaw string, zero sideslip is not the same as ball-centered (zero sideforce).

Nauga,
and the summation of all fears (and moments)
Click to expand...

In the video in this thread https://www.pilotsofamerica.com/com...e-drill-after-losing-one.116015/#post-2658328 the CFI says that coordinated flight is when the ball is pointed straight at the Earth. He says when you lose an engine in a twin you should bank 5 degrees into the good engine. Then use rudder to get the ball pointing straight down, not centered, straight down. It would give you about half a ball off of being centered. This he says is coordinated. That was not passing the logic with me but now I am wondering. I'm having trouble getting the whole picture on all this
 
luvflyin said:
In the video in this thread https://www.pilotsofamerica.com/com...e-drill-after-losing-one.116015/#post-2658328 the CFI says that coordinated flight is when the ball is pointed straight at the Earth. He says when you lose an engine in a twin you should bank 5 degrees into the good engine. Then use rudder to get the ball pointing straight down, not centered, straight down. It would give you about half a ball off of being centered. This he says is coordinated. That was not passing the logic with me but now I am wondering. I'm having trouble getting the whole picture on all this
Click to expand...
I hope Nauga doesn't mind me jumping the route here, but if you want to wrap your mind around it, do this:

Put a model plane [EDIT: A plastic one with hard plastic wheels that slides easily in all directions] on a smooth table top with a sting to pull forward from one wing, simulating the operative engine. As you pull across the table, keep the heading straight with finger pressure to the vertical stab. The plane will slide sidewise, yet hold it's heading. Now you can visualize the relative wind and sideslip and see that the ball will still be pointing at the table. It is "coordinated", but slipping. Banking toward the string would make it "uncoordinated", but streamline the slip (in the air, where bank offsets asymmetrical thrust, i.e., the flat turn, instead of the rudder). So, the CFI in the video was wrong.​
 
Last edited:
You must log in or register to reply here.
Back
Top