VAF Forums

VAF Forums (https://vansairforce.net/community/index.php)
-   RV General Discussion/News (https://vansairforce.net/community/forumdisplay.php?f=2)
-   -   Dutch roll tendency (https://vansairforce.net/community/showthread.php?t=183271)

birddog486 06-06-2020 06:58 AM

Dutch roll tendency
 
Has anyone found a way to reduce the amount of dutch roll? I've searched the forum but haven't found a lot of info on correcting whatever's causing it.

My RV-7 was rigged per the plans and has flown hands off with the ball centered since first flight (about 60hrs) but, it has quite a bit of dutch roll tendency with and without turbulence.

I flew the first 20hrs. without wheel pants and fairings and was hoping adding them would help but that wasn't the case.

All control surfaces have been checked and adjusted to have almost a perfect shape using a straight edge back to the trailing edge radius. There's also no measurable twist in the wings or control surfaces so I'm stumped.

I've tried using a slight yaw, feet off the pedals and both feet hard on the pedals with nothing solving the issue and possibly making it worse using hard pressure on both pedals.

I'm flying solo with a W&B ARM of about 81.5" except for a couple flights with ballast at gross weight so I'm not sure if W&B has an effect.

Travis

Mel 06-06-2020 07:17 AM

Not necessarily an RV thing.
 
Quote:

Originally Posted by birddog486 (Post 1436740)
Has anyone found a way to reduce the amount of dutch roll? I've searched the forum but haven't found a lot of info on correcting whatever's causing it.
My RV-7 was rigged per the plans and has flown hands off with the ball centered since first flight (about 60hrs) but, it has quite a bit of dutch roll tendency with and without turbulence.
I flew the first 20hrs. without wheel pants and fairings and was hoping adding them would help but that wasn't the case.
All control surfaces have been checked and adjusted to have almost a perfect shape using a straight edge back to the trailing edge radius. There's also no measurable twist in the wings or control surfaces so I'm stumped.
I've tried using a slight yaw, feet off the pedals and both feet hard on the pedals with nothing solving the issue and possibly making it worse using hard pressure on both pedals.
I'm flying solo with a W&B ARM of about 81.5" except for a couple flights with ballast at gross weight so I'm not sure if W&B has an effect.
Travis

It's pretty common on short coupled airplanes.

rvbuilder2002 06-06-2020 10:30 AM

Quote:

Originally Posted by Mel (Post 1436745)
It's pretty common on short coupled airplanes.

Especially short coupled and lower static and dynamically stable airplanes.

In simple terms... RV?s would have much less of the light and responsive handling we all love if they were rock solid like on rails when not being maneuvered.

Mel 06-06-2020 11:50 AM

As Scott says, there is stability at one end of the scale and maneuverability at the other end. Which do you prefer. In my opinion (Which is worth just what you pay for it). The Short-Wing RV series of aircraft are just about at the perfect point.
They are as maneuverable as practical without being unstable.

scsmith 06-06-2020 12:14 PM

Quote:

Originally Posted by birddog486 (Post 1436740)
Has anyone found a way to reduce the amount of dutch roll? I've searched the forum but haven't found a lot of info on correcting whatever's causing it.

My RV-7 was rigged per the plans and has flown hands off with the ball centered since first flight (about 60hrs) but, it has quite a bit of dutch roll tendency with and without turbulence.

I flew the first 20hrs. without wheel pants and fairings and was hoping adding them would help but that wasn't the case.

All control surfaces have been checked and adjusted to have almost a perfect shape using a straight edge back to the trailing edge radius. There's also no measurable twist in the wings or control surfaces so I'm stumped.

I've tried using a slight yaw, feet off the pedals and both feet hard on the pedals with nothing solving the issue and possibly making it worse using hard pressure on both pedals.

I'm flying solo with a W&B ARM of about 81.5" except for a couple flights with ballast at gross weight so I'm not sure if W&B has an effect.

Travis

The two ways to change the design to reduce the dutch roll mode have other consequences for handling. The easier of the two is to make the fin and/or rudder bigger. In the case of the RV-7, you have the option to put the RV-9 rudder on. This will help some, as long as you keep your feet firmly on the rudder pedals. The bigger rudder wont help much if it is swinging back and forth.

The other way to change it is to reduce the dihedral, which makes the airplane less laterally stable and less enjoyable to fly. Also not practical to do on an existing design. Just mentioning it for background.

Robert Sailor 06-06-2020 05:29 PM

Dutch Roll
 
I'm a newer RV pilot but I have lots of time in a variety of aircraft and on my first flight I noticed that familiar little tail wag of an early Bonanza from years ago. Not quite as much as the famous Beech but it was there.
Certainly never stopped me from buying it because the control response was so well balanced plus I just accepted it like I did on the Bonanza and hardly feel it anymore..I really like how the RV flies, near perfect in my opinion.:D

andrewtac 06-06-2020 05:50 PM

how about a yaw damper

luddite42 06-06-2020 06:24 PM

Quote:

Originally Posted by andrewtac (Post 1436918)
how about a yaw damper

The feet do wonders in smoothing out the ride in turbulence.

rvbuilder2002 06-06-2020 08:01 PM

Keeping rudder fixed ( like Steve already mentioned) helps a noticeable amount in turbulence.
If you leave your feet flat on the floor you are essentially reducing the vertical stab area by the rudder size in square inches.

xblueh2o 06-06-2020 10:16 PM

I have noticed the motion you describe in several of the RV models I have flown and I just reverted to my Cessna twin days of "apply pressure to both rudder pedals" technique. It always seemed to stop in about two oscillations. I am surprised that you are not seeing an improvement in motion when pressing on both pedals.


All times are GMT -6. The time now is 02:37 AM.