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  #11  
Old 08-14-2012, 06:02 AM
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LettersFromFlyoverCountry LettersFromFlyoverCountry is offline
 
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The heavy wing could be a number of things, including a twist in the horizontal stabilizer or misrigged flaps. As David suggested, first check how the ball is/isn't centered.

The HS is what it is, but get the flaps set right. Then consider dropping the heavy aileron. Take a small file and enlarge the holes a bit on the outboard hinge - effectively dropping the outboard edge of the aileron by thousandths. Fly, test, repeat. When you've got it right, lock it in by drilling a third hole and attaching a bolt or -- even better -- get a new bracket and drill for the new hole locations.

Also, check your elevators to be sure that they are even across the trailing edge. It's possible that they're a little "cockeyed" when drilling the bolt holes (mine are). You can always have the control horns welded and do that again.

You say your landing gear "appears" out of round. On both? You're sure it's not low tire pressure, right?
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Last edited by LettersFromFlyoverCountry : 08-14-2012 at 06:04 AM.
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  #12  
Old 08-14-2012, 06:30 AM
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Quote:
Originally Posted by flyenforfun View Post
My first issue is vibration. I can't seem to diagnose and fix this problem. I am having an overall airframe vibration when I fly. I can feel it when I put my hand on the arm rest, on the dash, on the canopy, and I can feel it in the stick. I had the prop dynamically balanced, which was a half inch out by the way, and it got better but the vib is still there. Ive checked for oil canning, I've checked the exhaust, Ive hit the brakes to make sure the tires werent spinning in the air. It seems to increase with higher rpm, but it is pretty much always there. I just can't figure it out.
I had a customer with a similar problem, we balanced his prop 3 or 4 times, he re-clocked it, etc etc.. He alway brought the plane over with the cowls off so I never noticed the wear mark on the upper cowl from the baffles contacting it. He re-worked the baffles to provide clearance and the problem went away! Bottom line is check to be sure nothing from the engine is contacting the airframe. Motor mounts can also transmit vibration to the airframe so check their condition as well or replace them if they are very old.

I assume the prop is good, a straightend or reworked prop can cause an aerodynamic inbalance
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  #13  
Old 08-14-2012, 06:32 AM
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Relative to the vibration - be sure none of the motor mounts are installed backwards. (Note the top and bottom are different.)

Relative to shimmy - can you get someone to video a takeoff or landing to get an idea what's going on? Also, the Van's tires, at least for me, weren't the greatest and it wouldn't be shocking if those were the source of the problem (even though I assume you balanced them). I since went with Desser monster retreads and they are fantastic. I don't envision ever using anything else.

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  #14  
Old 08-14-2012, 07:03 AM
yakdriver yakdriver is offline
 
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On the shimmy, do you have the red dot lined up with the valve stem on your tires? Also did you put the wood dampeners on the gear legs?
Now for the heavy wing is this a quickbuild kit from around 2005-6? If so look at the left aileron and see if it is sticking up above the wing skin at the outer end about 1/8" at the hinge line. If so and I would bet money it is, you need to adjust the end of the aileron down by elongating the hiles in the outer hinge bracket. Go to the Van's builder FAQs and read the wing heavy instructions. I'm surprised Vans didn't send you there in the first place. There has been 6 7s and 8s in this area that had the same problem. Mine had a pretty bad left roll but after adjusting the hinge it would fly wings level from cruise right down to stall speed.
On the engine clocking the prop will make a difference and I'm surprised the gut that did the balance didn't mention it. Did you balance the prop before you put it on? Is it new, used ,or freshly overhauled? Also as mentioned before any of the metal baffling or other parts of the engine touching the cowl will vibrate like crazy. Don
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  #15  
Old 08-14-2012, 07:09 AM
the4hens the4hens is offline
 
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One thing to check for the vibration is to remove the wheel pants and gear strut fairings. I had a vibration that turned out to be the left gear strut fluttering.

For the wing heavy condition, have you checked that the ailerons are mounted equally on either side. I had a condition where one aileron was mounted 1/4 inch lower than the other and it made a huge difference. I built my wings one at a time and didn't notice it until after I had installed the wings. I decided to do the first flight aware of the condition. After the first flight I purchased blank aileron attach brackets and redirill to correct the condition. I moved the left aileron up 1/4 and hand seamed the trailing edge a little and it flew straight.

For your ground shimmy, did you install stiffners on the gear legs?
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  #16  
Old 08-14-2012, 07:09 AM
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Quote:
Originally Posted by yakdriver View Post
On the shimmy, do you have the red dot lined up with the valve stem on your tires? Also did you put the wood dampeners on the gear legs?
Now for the heavy wing is this a quickbuild kit from around 2005-6? If so look at the left aileron and see if it is sticking up above the wing skin at the outer end about 1/8" at the hinge line. If so and I would bet money it is, you need to adjust the end of the aileron down by elongating the hiles in the outer hinge bracket. Go to the Van's builder FAQs and read the wing heavy instructions. I'm surprised Vans didn't send you there in the first place. There has been 6 7s and 8s in this area that had the same problem. Mine had a pretty bad left roll but after adjusting the hinge it would fly wings level from cruise right down to stall speed.
On the engine clocking the prop will make a difference and I'm surprised the gut that did the balance didn't mention it. Did you balance the prop before you put it on? Is it new, used ,or freshly overhauled? Also as mentioned before any of the metal baffling or other parts of the engine touching the cowl will vibrate like crazy. Don
The RV-8 has never used wood stiffeners on the gear, stiffeners are only for round leg RVs.

I would not reclock a prop that has been dynamically balanced. Seems to me that would throw the balance out of whack since the balance weights are clocked for a particular prop clocking.

While you are checking stuff be sure you give the exhaust hangers a good look to make sure the stacks aren't touching the airframe during flight.
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  #17  
Old 08-14-2012, 07:36 AM
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I remember your post about heavy wing a few months ago. Your symptoms were almost exactly as I had. Hold the stick neutral and all was well, flew straight, ball centered, ailerons in trail.... but relax my grip on the stick and immediate roll to the left when the ailerons deflected. The faster I went the worse it got.
I checked the aileron placement and sure enough one side outboard was above the wing skin maybe 1/8"(don't recall exact number). Dropping the hinge was the ticket. I could finally relax and go faster. This revealed another, actually a new problem. When I was over 200mph and tap the stick left or right, the plane would start to oscillate in roll and was unstable getting worse with each cycle. Controls were very sensitive from 200 up, I squeezed both ailerons a tiny amount and made things much better and stable.
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  #18  
Old 08-14-2012, 07:50 AM
Strasnuts Strasnuts is offline
 
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My RV-10 has a slight vibration to it. I dynamically balanced mine and it helped a little too. I have a different engine than most with a heavier crank and dampers. I tried a lot of things but what helped most was calling Lord mounts and speaking with an engineer. I ended up changing out two of my mounts. I know if any FWF is touching the engine (including new stiff baffling) it can cause vibration, like mentioned earlier. Mine has become better with time or maybe I'm used to it. I noticed other RV's shake too and maybe I'm more critical on my own plane.

I did a test by flying up to VNE and seeing if it made the shake worse. It actually got better from possibly the pressure of air on the control surface. This made me feel a lot better and helped me realize it was the engine/prop not the airframe. You should be able to do high speed/RPM and low speed/RPM to see what is vibrating. You don't necessarily need to kill the engine.

I always heard lower tire pressure is better for wheel vibration. Van's states it somewhere too. I ended up glassing in wood stiffeners on my 10 to help and it did. Balancing tires and wheel pants didn't help.

Make sure you read the FAQ's on Van's site on heavy wing. It has a list of priorities and it helped me through my slight heavy wing.
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Last edited by Strasnuts : 08-14-2012 at 07:55 AM. Reason: Added text
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  #19  
Old 08-14-2012, 08:13 AM
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flyenforfun flyenforfun is offline
 
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Quote:
Originally Posted by LettersFromFlyoverCountry View Post
The heavy wing could be a number of things, including a twist in the horizontal stabilizer or misrigged flaps. As David suggested, first check how the ball is/isn't centered.

The HS is what it is, but get the flaps set right. Then consider dropping the heavy aileron. Take a small file and enlarge the holes a bit on the outboard hinge - effectively dropping the outboard edge of the aileron by thousandths. Fly, test, repeat. When you've got it right, lock it in by drilling a third hole and attaching a bolt or -- even better -- get a new bracket and drill for the new hole locations.

Also, check your elevators to be sure that they are even across the trailing edge. It's possible that they're a little "cockeyed" when drilling the bolt holes (mine are). You can always have the control horns welded and do that again.

You say your landing gear "appears" out of round. On both? You're sure it's not low tire pressure, right?
Alrighty time to catch up.

The ball is always centered. Pretty sure the flaps are rigged right, but I am going to look into dropping the heavy aileron. I am confused as to what hole these Vans instructions are telling you to elongate. Not the one with the bearing in it right? Also, how do you guys determine if your aileron is 1/8th higher than the skin, that seems like a difficult thing to measure.

What I mean by out of round is when I jacked the tire up in the air, i spun it by hand, watched the top of the tire, and I could see the tread surface moving up and down.

What tire pressures should I be running on the Vans tubes and tires?
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  #20  
Old 08-14-2012, 08:15 AM
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Quote:
Originally Posted by Walt View Post
I had a customer with a similar problem, we balanced his prop 3 or 4 times, he re-clocked it, etc etc.. He alway brought the plane over with the cowls off so I never noticed the wear mark on the upper cowl from the baffles contacting it. He re-worked the baffles to provide clearance and the problem went away! Bottom line is check to be sure nothing from the engine is contacting the airframe. Motor mounts can also transmit vibration to the airframe so check their condition as well or replace them if they are very old.

I assume the prop is good, a straightend or reworked prop can cause an aerodynamic inbalance
This will be the very next thing I check. I haven't noticed anything touching but I havent looked either. Prop is a brand new sensenich, balanced and tracks straight. Motor mounts are new with the kit, 30 hours on them, and installed per the planes. Can motor mounts be too tight? I used a torque when I installed them, but read after some people suggest just bottoming them out then installing the cotter pin.
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