Menu Sign In Contact FAQ
Welcome to our forums

Questions following RV-6 flight.

I was treated to a flight in a Vans Aircraft RV-6 today and came back with an unexpected feeling. I’m hoping that someone on the forum has some experience with these types and can provide some insight.

This particular aircraft is a tailwheel version with an IO-320 and fixed prop. We were two aboard at 90kg each and half fuel.
I know they all vary, and I also know that the general consensus for many home built types is that they are “hot ships” or “not like your Piper” etc, but in this case I’m wondering if all is well?

Take-off, climb out as well as pattern work in general was fine, but the aircraft exhibits incredibly light pitch forces at high speed (above 120 kts). When I say light pitch forces I really mean LIGHT pitch forces. I’ll admit that I’m accustomed to heavier controls (Cessna Citation, Caravans) and normal spam cans (Pipers, Cessnas, Diamonds etc) and I have tried the Giles 202 a few times as well as a few different helicopters. NONE of these aircraft come even close to the behavior of the RV. The Giles had light control forces but you still had to move the stick some distance to make it snap, and helicopters are usually light as well but provide the necessary feedback (in my limited experience).
In the RV, a slight increase in pressure on the controls at 150 kts instantly and abruptly pitched the aircraft one way or the other – without any noticeable movement of the stick. Once slowed below 120 kts, the aircraft behaved “normally” in my view – i.e. required some movement to change pitch although still very light.
It could well be that the aircraft is very close to its aft CG limit, but the pitch trim position appeared to be normal, slightly ahead of neutral in flight.

So, does anyone have experience with these aircraft? Are they really meant to be like this? This is why people think they’re so great? Scared the hell out me!
It seems an impossible aircraft to fly for any length of time at normal cruise speed…

ESSB, Stockholm Bromma

Yes – very responsive at first, but after a few hours I got used to it. When used for touring, an autopilot is strongly recommended.

United Kingdom

Hello Norman,

Responsive is one term I suppose, I would call it nervous…
There is an autopilot fitted and when we engaged it at cruise the aircraft oscillated about the pitch axis probably due to the sensitivity.
Would you say that this is normal?

ESSB, Stockholm Bromma

I’ve not flown a RV-6 but don’t remember feeling great pitch sensitivity in ether the -7 it -8s I’ve flown. I agree that it could be an aft CG issue or just having flown very pitch stable aircraft in the recent past. My flying comes from the opposite end of the spectrum and I remember flying a Cessna single (which I guess is as ‘normal’ as aircraft get) and thinking the pitch forces and static pitch stability were very high in relation to my recent experience.

Last Edited by Silvaire at 09 May 14:29

Thank you for the input Silvaire.
I read somewhere that the -7 is less sensitive in pitch thanks to a longer body (?) and perhaps that is one reason why Vans replaced the 6…
I flew in the RV6 once last year as well and I do remember that it was sensitive but not anywhere near today’s experience. As it turns out, the starter has been replaced since that flight losing about 7kg on the nose and at that time we also had full fuel, so logic says CG was much further forward than today.

ESSB, Stockholm Bromma

I read somewhere that the -7 is less sensitive in pitch thanks to a longer body (?) and perhaps that is one reason why Vans replaced the 6…

A coworker has a -7 now after previously having a -6 and I believe he told me the same thing… I didn’t want to post that for fear of getting it wrong! Same story circulates for the -8 versus -4.

Another friend who is a flying mentor to me (a 70 year old guy who has flown anything with wings, and worked as a Navy test pilot for a while) has an RV-8 and talks about it wagging about a bit in yaw – the same kind of thing you hear about V-tail Bonanzas. He installed some wedges on the trailing edge of the rudder (an old fix to ‘stiffen’ rudder control) and says that worked for him in yaw. He’s happy with pitch control on the -8. He flies the thing all over the map.

Last Edited by Silvaire at 09 May 15:34

There is an autopilot fitted and when we engaged it at cruise the aircraft oscillated about the pitch axis probably due to the sensitivity.

This is a common issue with autopilots which were not configured for the aircraft type. In the certified world, STEC is one example where (apparently) some STCs were generated on the back of others, without sufficient (or any) flight testing which is time consuming because it has to be stable all around the envelope and all speeds from Vs to Vne, and potentially at different altitudes in aircraft where the TAS gain is significant. So porpoising is not unknown.

Control surfaces become more effective at high speeds which increases the proportional gain element of the control loop and at a certain point this will push it into instability.

Solutions include making the P gain low enough to start with (a crude method which gives you poor transient response at low speeds) or making the autopilot know the IAS (as in the KFC325, used in the TBM700 and the early 850) and reduce the gain at high speeds.

The issue occurs in both pitch and roll but is less likely in roll because the loop characteristics are a bit less variable in roll.

But this is nothing new and would have been known in the late 19th century (steam engine governors) and mathematically known since around WW2, so it should not happen in a present-day autopilot installation.

What make of autopilot was it?

Shoreham EGKA, United Kingdom

We discussed adjusting the sensitivity of the autopilot (Trio Ez-3) and the owner will probably look at that.
As it turns out we were a few centimeters ahead of the aft limit today and would have been within the envelope with zero fuel as well, just.
This should be fine, but I really did not like the behavior.. The owner is already talking about changing the light weight starter back to a heavier one to move CG forward a little.

ESSB, Stockholm Bromma

We have a -7 and I don’t find it particularly sensitive in pitch. But, I haven’t flown a -6 to make the comparison.

Oxford and Bidford

Thanks for the input.
I’ll try it again in the not too distant future..

ESSB, Stockholm Bromma
58 Posts
Sign in to add your message

Back to Top