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Rudder pressure concerns RV-6

T

tmendy

Active Member
We are test flying our new -6, in Fallbrook, CA, and are concerned about what seems to be abnormally heavy right rudder pressure for such a small airplane. We have no experience in other 6's to compare. It is an O-320 150hp.

Take off and climb really seem to take almost all the right foot and leg pressure we can muster.


Do any of you drivers out there have an opinion on whether or not this is normal?

Thanks,


Tom M
 
tmendy said:
Do any of you drivers out there have an opinion on whether or not this is normal?

Thanks,

Tom M
Click to expand...

Is that with a CS prop? type of prop?
With no aileron pressure/ heavy wing?? (heavy wing is found more that the need for a heavy rt rudder.)
This is not normal- only medium right foot at initial climb is needed on my and others 6's. How does the ball center in cruse?
 
The RV-6 Rudder comes in varieties (at least 2)

I have the short tail 6 rudder and on takeoff and climb it required a LOT of right rudder. The answer for me was to install a rudder tab. The first was a commercially available (was through VAN's I think) plastic wedge pop riveted to the left side of the rudder. That worked reasonably well but as I modified the airplane for speed things changed and I needed a ground adjustable tab. Toward the lower part of the rudder I cut off a section of skin inserted a trailing edge internal alumimum wedge (not a trim tab) and covered the openings with thicker skins with two stiffeners on each skin. I made a trim tab out of 0.032 2024-T3 aluminum and mounted it with five #8 flathead screws into two tapped holes and three platenuts in a zig-zag pattern. That worked great on first flight. It still uses right rudder (but not so much) on takeoff but the ball is centered in level flight. In the initial rigging I took a lot of care to get everything properly aligned with the reference plane of the canopy deck. In natural position the left wing trailing edge required lifting, what seemed like a lot to me, to get it properly aligned - so from my experience you should not trust the automatic alignment.
IMG_4564.jpg

Bob Axsom
 
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RV6 Rudder Pressure

I have a 150hp in my RV6 as well and do find it takes a considerable amount of right rudder pressure on the climb out. I wouldn't say it is all the strength I can muster but definitely more than most planes I have flown.
 
The RV-6 series, if built according to original plans, have a 0 (zero) degree offset of the VS relative to the fuselage center line. The thought at the time was just add a fixed rudder trim tab if needed.

Later plane designs (RV-7,RV-8,RV-9) have a built-in left offset (1/4 ") where the leading edge of the VS is offset to the left of centerline. This can be seen in the VS attach plate F-781 for the RV-7. This left offset unloads some of the required right rudder needed under high power takeoff & flight (same effect as a rudder trim tab, only not adjustable).

So I bought a flying RV-6A that had a big rudder trim tab; and still needed quite a bit of right rudder, also flew in a slight crab (ball). Wanting to fix some of this, I went through all the rigging and worked on things. I actually found that this particular RV-6A was built with a built-in right VS offset. NOT GOOD. So, I rebuilt it to RV-7 standards & removed the rudder trim tab.

Not suggesting or recommending anything but instead just adding my .02 cents.
 
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They all do.

What you have is a hot rod.:)

I've trained 80 or more guys and to a man, they were all surprised at the large amount of right rudder needed on initial throttle up.

Consider, you have the same size engine as a Skyhawk with one third less size and weight. You ought to feel the rudder needed for a 200 horse RV!!

Methinks that there's nothing wrong with your airplane:)

Best,
 
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Appreciate the feedback

Thanks for all the feedback!

It's a Sterba 70-70 (supposedly) prop. It flies beautifully in the air.

Bob, I'll consider the rudder trim.

Pierre, thanks for the re-assurance, especially with your training history.

Also, since I'm at it, what do guys think is a good cruise prop choice without being too fancy? I've been mulling it over so much and can't make a decision.
 
Catto

Craig will give great performance...he will ask whether you want max cruise or if you do a lot of vertical aerobatics, he'll flatten the pitch for better uphill pull, sacrificing some cruise speed.

We built our -6A to go places FAST and he asked if I'd mind turning it 2700 RPM or so and I said that I would turn those revs. His props are redlined at 3200, so there's not a problem and we ended up with a 201 MPH TAS airplane at 7,500', WOT and 2750 RPM.

That said, we only turned 2200 static and initial take-off but still got off in 800' or less and learned to cruise-climb around 140-150 MPH giving us more RPM's and still around 1500 FPM!

Best,
 
Thanks

Thanks for information on design. It's helpful for understanding the aiplane. We appreciate it.

GrayHawk said:
The RV-6 series, if built according to original plans, have a 0 (zero) degree offset of the VS relative to the fuselage center line. The thought at the time was just add a fixed rudder trim tab if needed.

Later plane designs (RV-7,RV-8,RV-9) have a built-in left offset (1/4 ") where the leading edge of the VS is offset to the left of centerline. This can be seen in the VS attach plate F-781 for the RV-7. This left offset unloads some of the required right rudder needed under high power takeoff & flight (same effect as a rudder trim tab, only not adjustable).

So I bought a flying RV-6A that had a big rudder trim tab; and still needed quite a bit of right rudder, also flew in a slight crab (ball). Wanting to fix some of this, I went through all the rigging and worked on things. I actually found that this particular RV-6A was built with a built-in right VS offset. NOT GOOD. So, I rebuilt it to RV-7 standards & removed the rudder trim tab.

Not suggesting or recommending anything but instead just adding my .02 cents.
Click to expand...
 
Yep................my short tailed 6A had so much rudder pressure required during cruise, that I just let it crab for a while. Installed a temporary wooden wedge by duct taping it on, and then went with the tab as in the pics. Now the ball stays in the center or close to, depending on cruise speed.
With my 180 C/S right rudder is still used for takeoff and climb, but that's expected. And as others have said, it's because the vertical stab has no built in offset.
 
Each plane is different

My Super Six needs far less rudder pressure than I thought it would need. It has an RV8 empanage. The only time that I need excessive rudder is on aggressive takeoffs. (I only did those only in testing) That would be less than a one second power application. I normally use about a three or four second power application. When I flight tested an RV9a, I remember that the right rudder application was more excessive than my Super Six, especially on climbout. The RV9a has a 160 with a wooden prop and is a very straight flier.

Pierre tookoff and climbed with my plane and I am sure he would agree it requires little rudder pressure.

With all that said, it might be a good idea to let a pilot with multiple RV experience fly it, and give you an assessment of its flying qualities. I have never flown any RV that I considered having heavy right rudder pressure.

Steve Barnes "The Builders coach"
 
tmendy said:
Thanks for information on design. It's helpful for understanding the aiplane. We appreciate it.
Click to expand...

GrayHawk said:
The RV-6 series, if built according to original plans, have a 0 (zero) degree offset of the VS relative to the fuselage center line. The thought at the time was just add a fixed rudder trim tab if needed.

Later plane designs (RV-7,RV-8,RV-9) have a built-in left offset (1/4 ") where the leading edge of the VS is offset to the left of centerline. This can be seen in the VS attach plate F-781 for the RV-7. This left offset unloads some of the required right rudder needed under high power takeoff & flight (same effect as a rudder trim tab, only not adjustable).

So I bought a flying RV-6A that had a big rudder trim tab; and still needed quite a bit of right rudder, also flew in a slight crab (ball). Wanting to fix some of this, I went through all the rigging and worked on things. I actually found that this particular RV-6A was built with a built-in right VS offset. NOT GOOD. So, I rebuilt it to RV-7 standards & removed the rudder trim tab.

Not suggesting or recommending anything but instead just adding my .02 cents.
Click to expand...

GrayHawk said:
Here is an image that illustrates the VS offset built into RV-7 & later.

rv7230.jpg
Click to expand...

Just a clarification...
The RV-8(A) plans/design does not call for an offset in the vertical stab.
The design introduction order was RV-8, RV-9, then RV-7. The RV-9 was the first airplane to have vertical stab offset designed in. It was also done on the RV-7 when it was introduced.
 
We modded our -6A

We fitted a -7 vertical fin attach bracket, with the 'jog' in it after being advised by a friend/multi RV builder, to do so. Worked well.

Best,
 
pierre smith said:
We fitted a -7 vertical fin attach bracket, with the 'jog' in it after being advised by a friend/multi RV builder, to do so. Worked well.

Best,
Click to expand...

From what I've seen, there are no speed advantages either way. Must be about the same amount of drag. But with an offset, you can boast that the plane flew hands (and feet) off on the first flight! :D

Personally, I think tabs look cool. Must be the fact that I like the 1940's era aircraft.

L.Adamson
 
Both an off set in engine and tail?

Pierre, it seems that the 6a with the offset engine mount and the offset tail would work against each other. On my plane the 1.5 degree engine offset worked out just about perfect to my surprise and delight.

Steve Barnes "The Builders Coach"
 
Steve Barnes said:
Pierre, it seems that the 6a with the offset engine mount and the offset tail would work against each other. On my plane the 1.5 degree engine offset worked out just about perfect to my surprise and delight.
Click to expand...

The offset engine and vertical stabilizer work together to produce right yaw.
All the the R/C aircraft that I built over the years, also had the engines canted to the right.
 
Since the discussion is touching on rudder trim I would like to add onto this thread to get some insight from anyone more knowledgeable (which is everyone..) than me on the rudder trim tab. I bought a flying RV-6A and just had to reskin the rudder because dufus at an FBO damaged it. I've not re-attached the trim tab yet though. I've got only a slight off center ball and I've not noticed any adverse tendencies with strong (stronger than previously) need for rudder on T/O, cruise or landing. My second post-repair flight had probably the strongest x-wind situation I've dealt with in the 50 hours I've flown the plane and I didn't see any problems there either, just the slightly off-center ball in normal cruise.

I think the trim tab will probably correct the situation but my question is where do I re-attach? It's a wedge type trim tab. Is there something in the build manuals that gives guidance on where to install a trim tab? Both front to back and up and down?

My thanks in advance for anyone's feedback.
 
First off, I am not saying who is right or not, just giving my experience.

Having flown several RV-4s, one -7 and one -6, both my -4 and the -7 have 200hp and CS props, the -6 has 160hp and fixed prop. None of these planes required any heavy rudder pressure to keep them on the runway or center the ball on climb.

One concession we need to realize is no two -4s or -6s are the same, -7s might be more consistent, I don?t know.
 
Avon, we attached the 10deg wedge just above the horizontal stabilizer, figuring that there'd be better air flow and it worked well.

Best,
 
pierre smith said:
Avon, we attached the 10deg wedge just above the horizontal stabilizer, figuring that there'd be better air flow and it worked well.

Best,
Click to expand...

I attached mine just above the rudder bottom fairing. Works well too.
I stuck mine on with some tape and moved it around. It seemed to perform about the same regardless of where I stuck it.
 
My two cents - I have a wedge (and a spring bias rudder trim). If I had a do over, I would definitely do the aluminum tab because the aluminum tab is easy to adjust. The wedge is a PITA to adjust if your trim needs change (mine did).

As to location, mine is low at about the level of the elevator. My reasoning was that that is the widest area of the rudder where the tab has the longest leverage therefore the tab can be smaller and still exert the same force. Don't know how valid that reasoning is but it is a reason. YMMV
 
Thanks Pierre and JonJay for the feedback. The original was stuck on with some two-side foam tape and I'll probably do the same, fly it and maybe try some slight moving around. Hopefully without messing up the shiny new paint.
 
Thank you Gary. I'm seriously thinking of the aluminum ground adjustable tab also for the same reasons you're stating. I just haven't pulled the trigger on one or the other yet. The plane flew great before the damage with the wedge so I may start there and see where it goes.

Appreciate everyone's input.
 
AHaury said:
Thanks Pierre and JonJay for the feedback. The original was stuck on with some two-side foam tape and I'll probably do the same, fly it and maybe try some slight moving around. Hopefully without messing up the shiny new paint.
Click to expand...

I was concerned about my paint so I used blue 3M painters tape and taped over the top of the whole thing. The Double Stick tapes I have used in the past where really sticky.
 
rudder pressure

I'm sure that there is something wrong if the original comment is true. All the leg pressure you can muster is a lot of pressure and must be taking the rudder pedal to the stop. That much deflection of the rudder on take off with a 150 horsepower engine in an RV6 just sounds wrong to me. You've gotten some very good advise from all of these posts. I think the best one said to let someone that has flown several RV6s built like yours fly it and tell you whether it feels normal or not. That pilot will know right away whether you have a problem or not. Nevertheless, good luck and keep your head up. It'll work out.
 
My RV-6 needs a big ol' extra footfull of right rudder immediately as the mains leave the ground or it will dart to the left quite abruptly, also needs a healthy dose of right rudder thru the acceleration in ground effect, and for the initial climb after that. It takes a lot more right rudder than other RVs I've flown. I attribute this to having a wooden prop with an extreme cruise pitch so I'm guessing the prop just has a lot more P-factor going on under these conditions (paperwork says its an Aymar-Demuth 68x74" but feels more like at least 76" of pitch). I've gotten used to it however, but it took me a while.

Once level in flight, it flies feet on the floor with ball in the center. It's got one small wedge-shaped nylon trim tab on the rudder.
 
Fast forward

All,

Fast forward from me starting this thread, closing in on a year, with about a hundred hrs on the 6 now, I'm 100% happy with the airplane.

Thanks to all, especially Pierre's re-assurance about the rudder pressure. I learned pretty quickly thereafter to apply power slowly and let the rudder start to work.

Also, the best advice I got on landing was just to come over the fence with some momentum, 75-80mph, chop power and just hold it off the ground as long as possible until it quits flying. Works fine on our 2,150' strip. I haven't had any problems since. Prior to that I had read so much stuff on landing, I was too jumbled up in thinking too hard pretty much in a panic.

FYI, we don't seem to need rudder trim, but love the electric aileron trim.

Cheers,
 
Hi Tom

Are you still flying with the sterba or did you change.Will have to stop over and see you one of these days.
Tim
6A
 
Get rid of the Sterba prop and invest in a Catto. I gained 8 knots in cruise and increased performance in climb out as well. Best money spent.
 
Thanks

baisicrv said:
Hi Tom

Are you still flying with the sterba or did you change.Will have to stop over and see you one of these days.
Tim
6A
Click to expand...

Also, especially thanks to BASICRV Tim for letting us use his prop until we figure out what to do for a permanent prop.

Tim, I sent you a private message to get together.

FYI, it looks like we're getting 150kts +- 8,600' WOT flying gps rectangles a few times (vans published is 162kts I think) 150hp sterba 70x70
 
Ive had both, and like both for different reasons.

Ive had both a Sterba Prop and and now a Catto.

My RV6a had an Aymar Demuth when I got the plane that decided to crack and chuck a huge chunk out of one blade.

Ed Sterba was the only one to come to my rescue. Everyone else was quoting me 6months + to get me a prop. Ed built me a replacement from scratch and had it shipped to me in a couple of weeks.

It was pitched 70 x 86 for my application and WOT at 8000DA would give me 2540rpm and 160kts solo.

I now have a Catto and am very happy with it. Looks sexy as can be all painted to match the plane and I have the nickel leading edge for rain protection.

With the Catto I now can turn 2680rpm at WOT and 8000DA and get 164kts I also probably picked up about 400 FPM in cruise climb.

Was it worth it? I think that really is a personal decision. If it was just for speed, I should have changing the pitch on the Sterba for more RPM. I never bothered because 95% of the flights I do are local at around 2150rpm burning 5-6gph and doing 120kts to 130kts. That hasn't changed with the new prop. I get almost identical numbers for local flights

YOU just have to decide if the cost is worth it. The nickel leading edge and looks are a big plus. I spent around 4 times as much on the Catto vs the Sterba. I am happy with the new prop and the service I received from Craig. I tell my wife it was absolutely worth the money! but the truth is the Sterba was a fine prop and also definetly worth the money spent on it. ($650 including shipping)
 
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I'm also running an Ed Sterba 68-74 prop on my 0-320 150 HP RV9A. I would love to have a Catto prop but the Ed Sterba prop is doing a great job on my plane and I have a whole $400.00 invested in it. Another RV'er went to a CS prop and sold me his and even had it re-varnished by Ed. If I had a bucket full of cash then sure I would be flying behind a Catto prop but for now I'm a happy camper.
 
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