RV-9 Flight Testing

[David Burke]

We have been flight testing an RV-9 over here in the U.K. It's got a slight tendancy to roll off to the left . We have trimmed it out with flap and aileron adjustment. On looking at the rear stbd wing mount I am concerned that the wing is slighty down in the rear fitting by about an 1/8 of an inch. Whilst it's not a lot I am pondering whether it's worth lifting the wing by that amount and reaming the holt hole for an oversize bolt

 

[az_gila]

Is it an 1/8...

We have been flight testing an RV-9 over here in the U.K. It's got a slight tendancy to roll off to the left . We have trimmed it out with flap and aileron adjustment. On looking at the rear stbd wing mount I am concerned that the wing is slighty down in the rear fitting by about an 1/8 of an inch. Whilst it's not a lot I am pondering whether it's worth lifting the wing by that amount and reaming the holt hole for an oversize bolt

...out if you do an incidence measurement on each wing?

It could be that the fuselage is not quite symmetrical. The wing incidence measurement is the most accurate.

If you do the measurement every 2 feet or so along each wing, you will be also be able to determine if a wing is twisted.

 

[David Burke]

The wing is a quick build example along with the fuse so I am quite confident on the alignment. It might well be time to remove the wingtips and do another incidence check. I don't like using flap drop to level a wing up because effectively your bleeding off speed at the same time. Thanks for your notes

 

[sjhurlbut]

You don't need to remove the wing tips. See the builders log for how the angle of incidence is set initially. For the RV7 a 3 inch spacer is set on the rear spar and the angle should be zero degrees. Maybe different for -9.

Also the very first thing to check is the trailing edge of the aileron. A minor adjustment to it makes a big difference. My 7A turned left initially and I could adjust the trailing edge of aileron to make it turn right.

A slight turn to the left is fine if the pilot is solo (in left seat), fuel is balanced, and aileron trim can compensate for it.

 

[ClayR_9A]

check the elevators too...

check the trailing edge of the elevators to make sure they're aligned too.

 

[videobobk]

If the turning tendency is slight and there are no other negative tendencies, I would consider adjusting the wing incidence only as a last resort. You could go too far! See if you have ailerons that aren't aligned (up/down) with the flap in flight. See if you turn while holding them aligned. A small tab on the aileron, or even bending the trailing edge VERY slightly to act as a trim tab does wonders. Bend up on the heavy wing aileron trailing edge (or down on the other aileron.) Use a wood block with a groove in it. Do check the alignment of everything first. I do believe you need adjustable aileron trim (electric or manual) on the 9. I did end up with a small bend on an aileron trailing edge. It is very slight and I do exceed Van's speeds, so it doesn't hurt performance. Easy job!

Bob Kelly

 

[yakdriver]

Before you go through all of the above check the ailerons at the hinge line. I would bet that the left aileron is sitting up slightly at the outboard end. Get everything back to neutral and lay a straight edge on top of the wing at the outer hinge and it should be flush. If it is high take the hinge bracket off the aileron and elongate the mounting hole to get the aileron flush. 1/8" makes a huge difference. When you have it where you want it order a new undrilled hinge from Vans and replace the one with the elongated holes. This works! My 7 had a very pronounced roll to the left and moving the left aileron 3/16" made it perfect. My airplane remains trimmed wings level from cruise to stall now. Don

 

[FrankK90989]

My 9

If I am solo with even fuel in both tanks, it will pull slightly to the left. Add one person in the right seat or use the fuel in the left tank, it flys perfectly straight.

 

[Steve]

Check the flaps again

Verify the aileron rigging using Vans alignment tool on both wings. It helps to have a second set of alignment tools (Vans tool and the end rib board).
Then using a protractor, verify both flaps are at the same angle when fully retracted. Adjust the flap pushrods as required. (I adjusted my left flap down 1.5 degrees.) They may not be aligned with the aileron trailing edges anymore but your plane will fly hands-off.

It worked for me,
Steve