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Ball off center in straight and level cruise

lndwarrior

Well Known Member
Both my electric turn and bank AND my Dynon D2 "balls" show the exact same deflection in straight and level cruise. Both balls are reflected about 3/4 Of the ball width to the left.

Is this indicative of a rigging issue, or???

TIA
Gary
 
As a rule, yes you have a rigging issue.

First though, carefully level the airplane laterally on the ground and make certain that the instruments themselves are perfectly level with respect to the airframe.

If everything lines up on the ground, get some balsa wood trailing edge stock (I just checked and amazon sells enough to do 100 or so airplanes for $15).

tape a few inches of the balsa wood on the side away from the ball, make the wedge longer or shorter until the ball is centered in cruise, then seal it with paint and filler and glue it on permanently.

You can also make an aluminum tab, which is more common on certified airplanes, but the balsa wedge IMHO is more aesthetic and easier.
 
I am not an aerospace engineer, but I wonder if the VS offset to counter the effects of P factor is a generic offset, would you think that a 200 HP CS setup would need more offset than say a 160 HP FP setup?
 
I am not an aerospace engineer, but I wonder if the VS offset to counter the effects of P factor is a generic offset, would you think that a 200 HP CS setup would need more offset than say a 160 HP FP setup?

Maybe, but the -6 plans show zero offset, and about 4 to 5 inches of the balsa triangular stock seems to work for most.
 
Try a power off stabilized decent and your ball(s) may center up as is.

True, but how is that relevant to the cruise condition, where engine torque is unavoidable? It's seems to me that what matters is where you spend most of your time, and needing some rudder input for climbs or power off descents is normal and acceptable.

Not picking, just wondering if you know something I don't.
 
I am not an aerospace engineer, but I wonder if the VS offset to counter the effects of P factor is a generic offset, would you think that a 200 HP CS setup would need more offset than say a 160 HP FP setup?

I'm not an aerospace engineer either, but I'd guess that other variables have a much greater effect than available hp. Things like how straight the airframe is, how the gear fairings are mounted, etc.

Even supposedly identical factory aircraft built in hard tooling have trim tabs or eccentrics for adjustment.
 
That's VERY common. Without an adjustable rudder trim there will always be airspeed/power combinations at which your airplane does not fly coordinated hands (or feet ) off. Just think about how much rudder you need in a Vx clime to stay coordinated.

If you look at the forum people have used all kinds of approaches. Rudder tabs or wedges are common. Problem is that they really work only at one speed unless they are adjustable. E.g. you can get yourself coordinated in cruise at a certain power setting but then on descent you won't be.

Personally I like the bungee cord based approach Dan Horton has suggested a while back. Works well on an RV-8 not sure about others. Keeps you coordinated in long cruise flights when you care for feet off operation on autopilot and is out of your way the rest of the time.

Oliver
 
Both my electric turn and bank AND my Dynon D2 "balls" show the exact same deflection in straight and level cruise. Both balls are reflected about 3/4 Of the ball width to the left.

Is this indicative of a rigging issue, or???

TIA
Gary

Yes - but the first step it to figure out what rigging is out.

I recommend you first eliminate the obvious - wheel pants and gear leg fairing. Having them mounted wrong can put the ball way out. Take them off and then fly - is the ball centered or not? If not, then move on to the harder stuff like the VS not properly rigged. Go back to the instructions for when you mounted the VS and measure again.

After you chase these to ground, then consider a rudder trim tab.

Carl
 
Mine is off a half ball to the right in cruise configuration. In climb more, and in descent it requires left rudder. So in cruise, I maintain a little right rudder pressure. No problem. And if I cruise with no pressure on the rudder peddles and the ball is out by a half, there is no discernable change in airspeed. My opinion, don't worry about it. You are going to be on the rudder peddles most of the time anyway.
 
Dumb question

Could an airplane every be flying sideways( fuselage no aligned with airflow) and the wings level and the ball centered?

I was thinking of mis rigged flaps/ailerons such that a slight forward slip is required to maintain wings level. Would the ball be in the center then?
 
Could an airplane every be flying sideways( fuselage no aligned with airflow) and the wings level and the ball centered?
Yes. Easy to demo in a twin with one engine feathered. The large rudder force violates the approximation that rudder torque is important, but rudder force is negligible.
I was thinking of mis rigged flaps/ailerons such that a slight forward slip is required to maintain wings level. Would the ball be in the center then?
I don't think so.
 
Great suggestion! Thanks!

If you use this piece, you can temporarily attach to the rudder using some of the aluminum tape like you use inside the cowling. It will hold but comes off easily when you need to adjust it. Fly the plane. Then trim the tab length as needed. I think I eventually took about an inch off mine before I got the ball centered at cruise. Depends on where you mount the tab. Obviously always mount in the same place during flight trials.

I suggest buying two pieces, one for test and then one for final mount in case you find you've trimmed off too much and the ball goes the other way.

Focus on getting it right for cruise flight as rudder trim will change for other speed regimes.

Good luck.

Chris
 
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Trim Tab

I used a 4" tall piece of aluminum with 1" hanging off the back of the rudder. The bottom of the tab was in approximately alignment equal to the top of the Horizontal stabilizer. The tab was riveted and pro sealed on.

I trimmed for cruise flight power settings since the plane was for long CC flights!! It took me two flight to get needed setting. On climbs and descents you have to fly the rudder but that becomes instinctive.

I should point out, that the plane exhibited the same characteristics without the wheel pants and fairings. After install the same trim was required so I must have got the them installed correctly.

The wedge works well too. Just a matter of aesthetics and personal preference.
 
Mine is off a half ball to the right in cruise configuration. In climb more, and in descent it requires left rudder. So in cruise, I maintain a little right rudder pressure. No problem. And if I cruise with no pressure on the rudder peddles and the ball is out by a half, there is no discernable change in airspeed. My opinion, don't worry about it. You are going to be on the rudder peddles most of the time anyway.

Mine is exactly the same. I plan to re-check everything and install a wedge as needed. Can't stand the ball being off center even with no speed penalty :D
 
Is the ball indicating correctly? There are plenty out there that don't, both glass and steam.
Glider pilots tape a short length of wool to the centre of the canopy which will follow the path of the air. Not sure how the propwash would affect that indication but I can't think of a cheaper or easier thing to try just to confirm the ball is correct.
 
Might want to check into the idea of taping something to the canopy. Not all tape is created equal and some may damage the canopy. I don't have proof, am recalling some glider discussion I had long ago and I won't swear to it.
 
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