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RV-6 tail heavy?

Floog

Active Member
RE: RV-6 with 200 HP IO360 angle valve with 3-blade composite prop.
W&B: Pilot, pax, no cargo, 3/4 fuel

In cruise flight yesterday, I looked back at the horizontal stab and noticed the elevator horns were defected UP 1/2" above the stab. Is this 'normal' for a -6?
In my -7, the horns are always flush with the stab no matter how I'm loaded.
I can't imagine a -6 being tail heavy in this configuration.
 
“Normal” can be really hard to define in the homebuilt world with so many options available to every builder, but a very general statement is that -6’s tend to be tail-heavy, while -7’s tend to be nose heavy.

Our -6 with a parallel valve 360 and metal Hartzell C/S gets pretty close to the aft limit with two people and much over 75 lbs - hard to carry much more anyway and stay under gross, but you can load out a typical -7 much easier.
 
RE: RV-6 with 200 HP IO360 angle valve with 3-blade composite prop.
W&B: Pilot, pax, no cargo, 3/4 fuel

In cruise flight yesterday, I looked back at the horizontal stab and noticed the elevator horns were defected UP 1/2" above the stab. Is this 'normal' for a -6?
In my -7, the horns are always flush with the stab no matter how I'm loaded.
I can't imagine a -6 being tail heavy in this configuration.

Assuming you are talking about the top surfaces--that is customarily what I see on my RV-6 when it is loaded. O-320 with metal Sensenich prop.
 
Down elevator in cruise

Yes, it is normal/common for the RV-6 elevator to be trimmed to nose down in cruise flight. This has a lot to do with how the angle of incidence of the horizontal stab is set. Way back when... Vans had instructions on how to adjust that if you had excessive trim. However those instructions have basically been lost by the mothership and they only advise to mess with it if you are running out of trim or something.

Some of us have experimented a bit in this area looking for speed. Obviously running around with the elevator deflected isn't going to be aerodynamically clean. Also I recall, for stability you do want the elevator to have some nose down deflection, so don't go get carried away.

I wish I could recall where I've read all of this. Some might be back in the reprint of the paper newsletters.

I think I gained 1/2 mph or something by changing my HS angle.

-Bryan
 
RV-6 with 200 HP IO360 angle valve with 3-blade composite prop

Unless there is some hidden weight somewhere in the back of your ship, it is definitely not tail heavy.
My 6.9i sports a lighter engine, and an -8 tail... and my trim, and elevator, are absolutely neutral in cruise.

Very good pointers by blaplante
 
That's normal. It'll be more pronounced as you load the baggage area.

With the elevator deflecting down, you're unloading the tail. Reducing the downforce and reducing the overall load the wing has to carry. That'll make the airplane slightly faster. You could accomplish the same thing by changing the incidence relationship of the horizontal stab and wing, but then you're probably going to run out of nose-up elevator authority with a forward CG and full flaps.
 
Just to expand on this a bit... The position of the elevator horn doesn't equate to the tail "lifting" in cruise. Your tail is always pulling down in level flight.

Where was the CG relative to the aft limit? That's what will tell you if you were tail heavy.
 
In cruise flight yesterday, I looked back at the horizontal stab and noticed the elevator horns were defected UP 1/2" above the stab. Is this 'normal' for a -6?

There have been many threads on the subject. This is common across most of the RV models and designed in per "rvbuilder2002" (Scott M) in Post #2 of the first thread linked below:

"... and a very slight amount of down elevator was specifically designed in by the designer (Van) and considered desirable. The slight down elevator improves pitch stability at the cost of a very slight amount of drag."



My previous RV-8 has a bit of down elevator as shown by the mass balance horns sticking up a bit in the photo below. My current RV-8 also does.

i-HRF2XJr-L.jpg
 
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Me Too

Our RV-6 runs toward the aft limit. As fas as Wt. & Bal. this airplane is almost the worst setup you could do. O-320, lightweight starter, Catto no-weightium propeller. At least we have a Landoll dampener which helps a bit. I don’t recall ever looking back at the tail in flight but I have a photo taken on a low pass that shows the elevator is deflected down a bit. But yeah, what everybody else says, the RV-6s run toward the aft CG limit. I ‘spect Van expected most of the -6s would have metal props. If it’s constant speed, so much the better. The lightweight starters hadn’t arrived yet. Anyway, we can go just outside the aft limit with minimum fuel, 2 FAA 170 pound people and 60 lbs. in the baggage box. Wife and I are aware of this and we probably pay more attention to loading than most pilots.
 
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I have a an angle valve in my -6 with Hartzell and the elevator horns are perfectly in trail at cruise, as is the trim tab. I set up the horizontal incidence per drawing. And with that engine, I'm pretty far forward CG-wise.
 
On the RV6 I once owned the elevator was also slightly nose up and it was very fast. 184 knot cruise. We took some weight out of the tail with a lightweight tailwheel and removal of a strobe power pack. It noticeably improved landing characteristics.
 
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