RV-8 vs RV-8A ride in turbulence

[Ed_Wischmeyer]

Maybe one of the multi-RV-experienced types can answer this one...

I had an RV-8A in Iowa, and the predominant ride in turbulence was in yaw (Dutch roll with predominantly yaw), barely noticeable in the front, annoying to one of my passengers who is a pilot. In the RV-8, flying from Georgia to Michigan earlier this week, the predominant ride in turbulence in the front seat was jostling side to side with little if any apparent yaw or roll coupling.

I'll pay more attention to the ride on the way home tomorrow and the next day; and it's too late to re-examine the -8A ride; but has anybody else seen anything like this? The only really significant aerodynamic differences between the two would seem to be nosewheel on the -8A and wing root / gear leg effects on the -8.

Don't have c.g. information for a solid comparison, but I think the c.g. locations were at least similar.

thanks

Ed Wischmeyer

[flightlogic]

Ed, was your seatbelt on?

[Ed_Wischmeyer]

All five points were on, you bet. Now I need somebody to explain to me what "tighten" means and how to do it...

[Neal@F14]

All the times I flew my friend's RV-8 that I helped build, it had quite a pronounced dutch roll yaw issue in turbulence. It was bad enough that if you kept your feet off the pedals that the yaw would get worse and worse until it stabilized at a certain maximum amplitude and then keep tail-wagging back and forth at that amplitude until you put your feet back onto the pedals and dampened it out yourself. In smooth air it would not dutch roll, it was perfectly stable with feet on the floor.. Thermal turbulence in the Texas summer heat would trigger the ill behavior the most.
Interestingly enough, my -6 with the short tail never does it at all, I can fly it feet on the floor for hundreds of miles at a time with the wing leveler autopilot engaged and the ball stays centered, with no tail wag even in turbulence.

[Kyle Boatright]

Originally Posted by Ed_Wischmeyer

Maybe one of the multi-RV-experienced types can answer this one...

I had an RV-8A in Iowa, and the predominant ride in turbulence was in yaw (Dutch roll with predominantly yaw), barely noticeable in the front, annoying to one of my passengers who is a pilot. In the RV-8, flying from Georgia to Michigan earlier this week, the predominant ride in turbulence in the front seat was jostling side to side with little if any apparent yaw or roll coupling.

I'll pay more attention to the ride on the way home tomorrow and the next day; and it's too late to re-examine the -8A ride; but has anybody else seen anything like this? The only really significant aerodynamic differences between the two would seem to be nosewheel on the -8A and wing root / gear leg effects on the -8.

Don't have c.g. information for a solid comparison, but I think the c.g. locations were at least similar.

thanks

Ed Wischmeyer

Have you examined the profile of the rudder trailing edge? Maybe the two aircraft you've flown are different in that respect.

[David-aviator]

Originally Posted by Kyle Boatright

Have you examined the profile of the rudder trailing edge? Maybe the two aircraft you've flown are different in that respect.

I will ditto that.

If the trailing edge is not flat as per the straight edge ruler specification in the build plan, the dutch roll activity will be excited in turbulence or by kicking the rudder and it won't quit on its own.

[rvbuilder2002]

The only difference between the two models should be on variations caused by slightly different C.G. locations. If C.G.s are nearly the same, the ride results should be the same.

I say should, because there are other variables possible, depending on the build of the airplane. Friction at different points in the control system (rudder hinging being one example), shape of control surface trailing edges, etc. can all have an influance.

One of these days I am going to finally get around to doing a write-up on all of the little things that can have an influance on whether an RV flys like an RV should.

[Michael White]

Originally Posted by Ed_Wischmeyer

All five points were on, you bet. Now I need somebody to explain to me what "tighten" means and how to do it...

If your eyes aren't bulging, they aren't tight enough...

[David Paule]

Originally Posted by Ed_Wischmeyer

All five points were on, you bet. Now I need somebody to explain to me what "tighten" means and how to do it...

Pretty easy. Tighten everything. Then roll upside down and stay there for a few seconds. Roll upright and tighten again.

Repeat until secure.

Generally speaking, people tend to learn that pretty quick - especially if they are in an open cockpit airplane.

Dave

[Pat Stewart]

I have built both and have a few hundred hours in them. Once you break ground I never noticed a difference.