Tail Wagging RV-7

[sahrens]

Is the rudder actually in a straight trail position when the pedals are neutral? Watching the video it appears to nose up and slightly roll left as if the counter weight is not doing its job. As if the rudder was slightly off center to the left (left pedal applied.)

Can you feel movement in the rudder cables when the tail is wagging? Push the pedals forward so there is no slack in the cables and light touch one. Is there slight movement in the cable. How tight are your chains? Are the two chains the same length? How are the springs in your cables, they do wear out and after 750 hours in a year they could be worn out.

A solution could be a small strake mounted on the bottom of the fuselage under the elevator. A lot of aircraft use strakes to reduce tail wag / shuffle. I have no idea as to the size needed, but probably not very large.

[Ed_Wischmeyer]

Originally Posted by MacCool

My RV-9A doesn't wag even a little bit, neither visually, reflected in the EFIS/instrumentation, nor seat-of-pants. I've experienced it in some larger airplanes ("Bonanza Boogie") but didn't know it occurs in RV's. Are yaw dampers much of a thing in RV's?

That's what I thought about mine, too, till I saw the video...

[Bruce]

I would check for slightly heavy left wing.

Check radius on ailerons
Hunting for level.

There is play in rigging somewhere.

Also check servos in wing.

My .05
Boomer

[RV7A Flyer]

Originally Posted by D-Dubya

My RV-7 doesn't wag like that, either.

RV-7A here...same thing. Occasionally after getting smacked around by turbulence, but nowhere near that and it damps out quickly. During normal cruise, smooth as silk.

Something is out of whack somewhere on this one...

[MacCool]

Originally Posted by Ed_Wischmeyer

That's what I thought about mine, too, till I saw the video...

I too have seen the video, both from wingtip and tail tie-down, so...pretty confident, but next flight I'll try it making a concerted effort to keep feet off the rudder pedals.

[birddog486]

Originally Posted by sahrens

Is the rudder actually in a straight trail position when the pedals are neutral? Watching the video it appears to nose up and slightly roll left as if the counter weight is not doing its job. As if the rudder was slightly off center to the left (left pedal applied.)

Can you feel movement in the rudder cables when the tail is wagging? Push the pedals forward so there is no slack in the cables and light touch one. Is there slight movement in the cable. How tight are your chains? Are the two chains the same length? How are the springs in your cables, they do wear out and after 750 hours in a year they could be worn out.

A solution could be a small strake mounted on the bottom of the fuselage under the elevator. A lot of aircraft use strakes to reduce tail wag / shuffle. I have no idea as to the size needed, but probably not very large.

It appears the rudder is straight in trail but I don't have a camera I can mount to confirm in flight.

In the video my feet were hard on both pedals. If I step on one side it stops the wag because of the slip but once centered or just left to trail freely the wag will start (in turbulence)

The tail wheel springs and chains are kept fairly loose, probably 1/2" slack which should have no effect on the control surface. Theres no springs on the rudder pedals or cables themselves.

[sahrens]

Originally Posted by birddog486

It appears the rudder is straight in trail but I don't have a camera I can mount to confirm in flight.

In the video my feet were hard on both pedals. If I step on one side it stops the wag because of the slip but once centered or just left to trail freely the wag will start (in turbulence)

The tail wheel springs and chains are kept fairly loose, probably 1/2" slack which should have no effect on the control surface. Theres no springs on the rudder pedals or cables themselves.

I meant the springs at the tail wheel chains. If you are on the pedals there is no slack, so if the chains are different lengths you pull the rudder out of alignment. The aerodynamic force moves the rudder back to neutral but the chain spring pulls it slightly back out of alignment setting up the oscillation. It wouldn't take a lot of rudder deviation to get that much nose movement. But with 1/2" of slack in each chain it may not be the cause.

Just a thought

[rmarshall234]

Somebody earlier mentioned the “ Bonanza Boogie “ and since I own a V-tail, I know it well. If your model-specific suggestions don’t pan out, I suggest a little research on this phenomenon which as I recall, is an inherent instability caused by the flat-bottom design of the fuselage. RVs are pretty flat on the bottom so maybe there’s a correlation. I must be compensating for it with rudder pressure because I don’t even notice it anymore but I don’t ride in the back seat. I put a GoPro on the tailring once and almost got sick watching the video!

[birddog486]

No smoking gun yet but I do see the signature of turbulent air across the rudder after flying through some dirty water.

If someone can compare there Vertical and rudder I'd appreciate it.

My vertical stab is a consistent 1/8" wider than the leading edge of the rudder when in trail top to bottom and with very light pressure on the rudder pedals in flight I can feel it being pulled side to side.

[N16KY]

Is the rudder counterbalance weight tight?