Neutral Stability - W & B

[Bad Sheila]

Going nuts trying to sort out Neutral Stability in my new RV6 (11 hrs).

Put the nose up or down and it just keeps going the same way.

It is either the wing incidence or AFT C.G. I bought it half completed with the wings already drilled and haven't got the equipment to measure the incidence yet. I am inclined to think it is the W & B after talking to Vans.

My W & B seems all screwed up because according to Vans, mine must be the lightest RV6 around. It weighs in at 982 lbs. It has 70 lbs on the tail instead of about 55 lbs (according to Vans?)

Specs:

WEIGHT: 982 lbs
C.G: 67.13
ARM: 65920
Fuel: 70
Pilot/Passenger: 87.4
Baggage: 117
Range: 68.7 to 76.8

AIRCRAFT
0-320 - Wooden Prop - Lightweight starter motor - EFIS (All electric) - unpainted.

Does anyone have a similar RV6 with a weight and W & B similar to mine?

Any suggestions would be greatly appreciated.

Thanks

Tony (The "Bad Sheila" is my plane, not me?????)

[PropMan]

Tony,
My -6 is 1015lbs(Aircraft Scales) with O360 and Wood Prop.I don't have a neutreal stability problem, but it is a bit light on the nose. 72lbs on the tail. If you need weight on the nose call Sam at www.sabermfg.com , he makes a crush plate just for this. I believe it's steel and is around 20lbs.

[Bad Sheila]

Thanks... he has a lot of good stuff that may fix the problem.

[PCHunt]

Another thing to check is control friction. Make sure that there is near zero friction in the pitch axis. Lube the bearings throughout, and make sure nothing is rubbing.

It doesn't take much friction around the neutral point to affect things.

[FLY6]

Tony, I too have an O-320 with a wooden prop in my RV6. I have steam gauges which add some weight up front. I don't have the numbers in front of me but my empty weight was 1062# and my tail weight I believe was 72#. I found when doing sample W & B that it was impossible to get a forward c of g but very easy to have a c of g too far aft.

I will be able to check the my numbers tomorrow if you want any more numbers.

Hope this lets you know if you are in the ball park, Al

[Mel]

That's pretty light. Mine weighed in at 992 before paint. Over 17+ years and several additions including paint, avionics, and ER fuel tanks, I'm now up to 1040 lbs.

[Snowflake]

Mine is 999lb. with metal FP prop. Bare metal, so no paint. 70 lb on the tail at my weigh-in a couple of months ago too. I believe the empty CG was 70.something, but I haven't got the paperwork with me right now to check.

[Bad Sheila]

It looks like my 70# at the TW seems pretty normal after several posts. Do any of you have the "neutral stability" problem?

If you don't then maybe my CG is OK and I need to look elsewhere, like my wing incidence.

For PCHunt: We had the problem you mentioned and fixed it with an new control stick mounting bracket that was drilled wrongly. We installed a new mounting bracket and control stick to fix the problem so that eliminated the problem you mentioned.

Thanks for all your input.

Tony
PS What is a "FP" prop?

[Andy Hill]

Bad Sheila...

I doubt 'Wing Incidence' is anything to do with it - it's not a critical setting, nor is the relationship between wing and tailplane incidence.

I would go for CG every time:

Basic..982 x 67.13 = 65922
Fuel...150 x 70.00 = 10500
Pilot..180 x 87.40 = 15732
Total..1312.00.......92154 = 70.24"

Pax....180 x 87.40 = 15732
Total..1492.00......107886 = 72.31"

Both CG figures look fine from what you give - however, the "dual" case is further aft?

Are the "problems" you are experiencing genuine handling issues with the aircraft? Or does it fly nicely, but when you try an academic stability test, only then is it an "issue"?

Subject to the aircraft being "safe/controllable to fly", I might suggest varying the CG e.g. add a passenger, or ballast, and see how it alters in terms of "feel" as well as the more formal test.

I do know someone who built an RV-6A, IO-320 and very light wooden prop, and he added a heavy flywheel, both for the wooden prop and the CG - and he has IO and a nosehweel over you - you have a tailwheel at a long arm he does not.

Andy

PS

PS What is a "FP" prop?

One that isn't "C/S" i.e. 'Fixed Pitch'

[jsharkey]

My tail wheel weight was 58 lb with the cockpit rails level and the tail raised. It is heavier with the wheel on the ground because the height of the main gear causes the cg to move aft as the tail drops - at least as far as the weight on the wheels is concerned.

Total weight was 1021 lb with YO-360-A1A, FP metal prop and no paint. There was also a 10 lb difference between left and right mains.

Jim Sharkey
RV-6 Phase 2