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Discouraging issues, looking for input

flyenforfun

Well Known Member
I wanted to get some input on some issues I am having on my RV that have been really troubling me. I have an RV-8, O-360, Sensenich FP prop, 30 hours on the plane, prop, and engine so far.

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.

My second issue is landing gear shimmy. When landing and taking off, the entire plane shakes until I either slow down on the ground or hit the brakes in the air. I've jacked the plane up and spun the wheels and they appear to be out of round. Its hard to believe that both of my tires from vans are bad, but so far I am thinking this is my problem. I don't think my toe in and out is wrong, but I haven't checked since I initially installed the gear. Should I change the tires and see if that solves my problem? And that leads me to another question, can anyone recommend a wing jack?

My third issue which is the most frustrating and discouraging is my heavy wing. I've checked everything that the document from vans recommends (incidence, rigging, ect) and that all seems fine. I've talked to vans and they had my squeeze down the aileron of the light wing. That made the heavy thing at least trimmable, but now my right aileron has a significantly thinner trailing edge than my left aileron, I can't sqeeze it anymore, and I still have a heavy wing. The heavy wing goes away at low speed, but as I speed up, the left wing gets heavier and heavier and it takes almost fill right aileron trim to get rid of it. Any other suggestions?

Thanks for reading and thanks for any help. I'm still searching for the RV grin but it's hard to find it with all these issues. -Matt
 
Matt,

My first suggestion would be to find someone local with rv experience, and let them take a look. Another good option would be to find an experinced EAA tech counselor. Sometimes a second set of eyes can see the obvious. I would recommend having them check the rigging and critical measurements for wing incidence, tail dimensions, gear dimensions, and anything else that might cause a heavy wing.

I also wonder if a couple of your issues are related. Vibration may be the engine, but might also be airframe induced. Its possible you are getting airflow seperation somewhere which could impact both wing level and vibration. Seperation on the ailerons would be the most logical explanation. I would also look really hard at any deviations from the plans especially if they might disrupt airflow somehow (i assume you are using stock landing gear).

One test you could run if comfortable would be to shut down the engine briefly, and see if your vibration disappears. This would at least isolate the vibration issue.

With regards to the shimmy, remeasure eveything, and see if you can borrow a set of wheels (rims and tires) from a local builder that does not need them yet. Another option would be to have the wheels balanced. I suspect you have a landing gear problem rather than two bad tires.

Aaron
 
I wanted to get some input on some issues I am having on my RV that have been really troubling me. I have an RV-8, O-360, Sensenich FP prop, 30 hours on the plane, prop, and engine so far.

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.

My second issue is landing gear shimmy. When landing and taking off, the entire plane shakes until I either slow down on the ground or hit the brakes in the air. I've jacked the plane up and spun the wheels and they appear to be out of round. Its hard to believe that both of my tires from vans are bad, but so far I am thinking this is my problem. I don't think my toe in and out is wrong, but I haven't checked since I initially installed the gear. Should I change the tires and see if that solves my problem? And that leads me to another question, can anyone recommend a wing jack?

My third issue which is the most frustrating and discouraging is my heavy wing. I've checked everything that the document from vans recommends (incidence, rigging, ect) and that all seems fine. I've talked to vans and they had my squeeze down the aileron of the light wing. That made the heavy thing at least trimmable, but now my right aileron has a significantly thinner trailing edge than my left aileron, I can't sqeeze it anymore, and I still have a heavy wing. The heavy wing goes away at low speed, but as I speed up, the left wing gets heavier and heavier and it takes almost fill right aileron trim to get rid of it. Any other suggestions?

Thanks for reading and thanks for any help. I'm still searching for the RV grin but it's hard to find it with all these issues. -Matt

Starting from the top - the vibration may well be with the engine/prop combination and something you'll have to live with. Metal props are heavy and the rotating mass along with an engine that may have parts not well balanced makes for vibration. I've felt it in production airplanes, not so much with experiments turning a light weight wood or composit prop. The truth of the matter is, Lycoming engines do not have finely tuned internal parts. They have certain tolerances that could be tighter but it would cost more money. Some engines do vibrate more than others and some have counter weights to control vibration depending on the prop.

Wheel shimmy could be a matter of tire pressure. I've had least trouble running with 45 psi, most trouble with 30 or 35 psi.

The heavy left wing is an aerodynamic unbalance. (brilliant deduction, Einstein) Are the flaps rigged similar to each other? Maybe that left flap needs to be adjusted just a bit lower than it is. Another factor is VS off set. Is the ball centered at say, 130 KIAS? Does centering the ball at any speed make a difference?

These are annoying issues for sure - here's hoping some smarter people than me will come up with other possible fixes.
 
Alan at Antisplat can take care of your shimmy / out of round problem. Cross that off your worry list at least. Search this forum or look in the advertisers for his contact info.
Erich
 
Matt,

My first suggestion would be to find someone local with rv experience, and let them take a look. Another good option would be to find an experinced EAA tech counselor. Sometimes a second set of eyes can see the obvious. I would recommend having them check the rigging and critical measurements for wing incidence, tail dimensions, gear dimensions, and anything else that might cause a heavy wing.

I also wonder if a couple of your issues are related. Vibration may be the engine, but might also be airframe induced. Its possible you are getting airflow seperation somewhere which could impact both wing level and vibration. Seperation on the ailerons would be the most logical explanation. I would also look really hard at any deviations from the plans especially if they might disrupt airflow somehow (i assume you are using stock landing gear).

One test you could run if comfortable would be to shut down the engine briefly, and see if your vibration disappears. This would at least isolate the vibration issue.

With regards to the shimmy, remeasure eveything, and see if you can borrow a set of wheels (rims and tires) from a local builder that does not need them yet. Another option would be to have the wheels balanced. I suspect you have a landing gear problem rather than two bad tires.

Aaron

I may try the engine shutdown test, climb high above my home airport and shut it down. It's going to take guts, but im getting desperate. Wont the prop still spin? If its caused by the prop rotating, will the vibration reduce enough to be able to isolate it?

I am also going to check wheel alignment as best i can without buying two wing jacks.
 
Starting from the top - the vibration may well be with the engine/prop combination and something you'll have to live with. Metal props are heavy and the rotating mass along with an engine that may have parts not well balanced makes for vibration. I've felt it in production airplanes, not so much with experiments turning a light weight wood or composit prop. The truth of the matter is, Lycoming engines do not have finely tuned internal parts. They have certain tolerances that could be tighter but it would cost more money. Some engines do vibrate more than others and some have counter weights to control vibration depending on the prop.

Wheel shimmy could be a matter of tire pressure. I've had least trouble running with 45 psi, most trouble with 30 or 35 psi.

The heavy left wing is an aerodynamic unbalance. (brilliant deduction, Einstein) Are the flaps rigged similar to each other? Maybe that left flap needs to be adjusted just a bit lower than it is. Another factor is VS off set. Is the ball centered at say, 130 KIAS? Does centering the ball at any speed make a difference?

These are annoying issues for sure - here's hoping some smarter people than me will come up with other possible fixes.

1. I'd hate to have to live with this vibration. Would prop clocking make a difference? Changing it would undo my dynamic balance, but would prop clocking matter since ive had the dynamic balance done?

2. I didn't know the tires could run at 45 psi. Whats the max? I've been running around 35-37 psi

3. I've checked rigging multiple times as best as I could. Ball is centered at all speeds.
 
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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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
 
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.

Dan
 
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
 
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?
 
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.
 
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.
 
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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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?
 
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.
 
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.

Dan

Motor mounts are installed correctly as long as the plans are correct. A video would be hard at our airport. If I lift the gear and spin the tires by hand and watch the top of the tread I can see the rubber moving up and down. Do you suggest these tires for a taildragger?
 
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

Red dot is lined up with the stem.

Not a quick build but I am gonig to check aileron height again.

Didnt think clocking would matter after a dynamic balance, and its a new prop balanced by sensenich. Checking the baffling tonight.
 
Prop tracking?

Have you checked the prop tracking? Both tips should pass pretty dang close to an index as you turn the prop by hand.
Also have you checked the nose wheel castor angle?

Tim
 
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?

I have flown with and without all of the gear leg fairings, no change.

Checking the ailerons tonight although I am not sure how to accurately measure this. Which aileron bracket is purchased blank? The one with the bearing in it or the white powdercoated ones?
 
I had the prop dynamically balanced, which was a half inch out by the way,.... -Matt

Matt, do you mean that the tracking of the prop blades differed by a half inch? If so, this is a significant deviation. It should be close to zero. How was it fixed and how does it track now?
 
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.

Exhaust hangars are good and tight and no witness marks on the airframe from the stacks. Thanks though.
 
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.

This is looking more and more like my next step, but how exactly did you check the placement? What hinge did you elongate to drop the aileron?
 
Have you checked the prop tracking? Both tips should pass pretty dang close to an index as you turn the prop by hand.
Also have you checked the nose wheel castor angle?

Tim

Tracking was checked when I has the dynamic balance done, it was perfect. My RV is a taildragger.
 
Matt, do you mean that the tracking of the prop blades differed by a half inch? If so, this is a significant deviation. It should be close to zero. How was it fixed and how does it track now?

No, tracking was fine. He said the balance was a half inch out which Im pretty sure means the center of rotation was deviating .5 inches.
 
This is looking more and more like my next step, but how exactly did you check the placement? What hinge did you elongate to drop the aileron?

It's the outboard hinge where it's bolted to the aileron. You remove the bolts and elongate the hole so that the outboard end of the aileron drops slightly. And by SLIGHTLY, we mean thousandths of an inch at a time. Yes, it will take time and testing, but you don't want to go for broke and just open up the hole, file off a bunch and slap it back on. These are very fine adjustments.

Do check the elevator alignment, though and see if that's a big contributor here first.

Also, I can't speak to an RV-8, on my RV-7A, all tires are at 40 psi.
 
Elevator and flaps are close to centerline so have less impact than screwed up ailerons. Any chance your wing tips are an issue?
 
Just talked to Joe Blank, he said to lower my tire pressures down to about 25 psi.

Yes, start at 25PSI (per Construction Manual), fly/test, increase PSI until it begins to shimmy again, then back it off a PSI or so. For the Aero Classic tires this seems to be the relative sweet spot. Any more pressure and you will definitely get some action. The lower pressure allows energy to be scrubbed off reducing vibration. Other tire brands will require another 'test' to see what pressure range they will tolerate. Verify or balance the tire sets...

Get another exerienced RV'r or Tech Counselor over to review your FWF installation. Take them for a ride and demonstrate what you are seeing. Your vibration (from what you described on the phone) appears to be RPM related (i.e. engine). It could be something as simple as a rub or component interference, loose exhaust, FAB hitting the cowl scoop, baffles hitting the cowl, etc. Recheck engine mount bolt torque values. (I've seen 'em loosen up during Phase 1 & 2!) :eek: Keep looking until you find it...
 
Yes, start at 25PSI (per Construction Manual), fly/test, increase PSI until it begins to shimmy again, then back it off a PSI or so. For the Aero Classic tires this seems to be the relative sweet spot. Any more pressure and you will definitely get some action. The lower pressure allows energy to be scrubbed off reducing vibration. Other tire brands will require another 'test' to see what pressure range they will tolerate. Verify or balance the tire sets...

Get another exerienced RV'r or Tech Counselor over to review your FWF installation. Take them for a ride and demonstrate what you are seeing. Your vibration (from what you described on the phone) appears to be RPM related (i.e. engine). It could be something as simple as a rub or component interference, loose exhaust, FAB hitting the cowl scoop, baffles hitting the cowl, etc. Recheck engine mount bolt torque values. (I've seen 'em loosen up during Phase 1 & 2!) :eek: Keep looking until you find it...

Awesome, I love having specific things to go check.

Do you know the engine mount torque off hand?
 
Is the vibration more pronounced in your feet while resting on the floor below the rudder pedals? At higher speeds I can certainly feel more vibe from the exhaust on the exit ramp. I added a small "bump" as some like to call it and the vibe is gone.
 
Is the vibration more pronounced in your feet while resting on the floor below the rudder pedals? At higher speeds I can certainly feel more vibe from the exhaust on the exit ramp. I added a small "bump" as some like to call it and the vibe is gone.

I can feel the vib everywhere about the same.. stick, floor, canopy, skin, etc
 
RV-8 Vibrations

Do you have any felt or foam rubber in between your rear canopy skirt and the turtledeck?

We had an awful vibration in the RV-8 we finished in 2010 and it turned out to be the rear canopy skirt rubbing on the turtledeck. It sounded like and felt like the whole empenage was about to come off the plane in flight. You could feel and hear it throughout the entire plane. I added some foam rubber weatherstrip to the underside of the rear canopy skirt and the vibration disappeared. The spiraling slipstream coming off the prop shakes the whole canopy assembly around.
 
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Do you have any felt or foam rubber in between your rear canopy skirt and the turtledeck?

We had an awful vibration in the RV-8 we finished in 2010 and it turned out to be the rear canopy skirt rubbing on the turtledeck. It sounded like and felt like the whole empenage was about to come off the plane in flight. You could feel and hear it throughout the entire plane. I added some foam rubber weatherstrip to the underside of the rear canopy skirt and the vibration disappeared. The spiraling slipstream coming off the prop shakes the whole canopy assembly around.

I had tried some weather stripping but never got to fly with it because it prevented me from fully closing the canopy. I have to find some foam that collapses better.
 
Awesome, I love having specific things to go check.

Do you know the engine mount torque off hand?

Regarding the torque on the motor mounts, it really wouldn't make a difference. The preload on the rubbers is determined by the length of the metal sleeve in the center. Once the hardware bottoms out you're good. Obviously proper torque is good for other reasons, but it's not gonna affect the way the mount does it's job.
 
Check

For 'play' in the controls - possibly as simple as a loose bolt at the bottom of one of the sticks. Best of luck - you'll find it.:cool:
 
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I have a small update. I have found a possible source of my vibration. I have found a couple of places inside the upper cowl where the metal baffling has been contacting the fiberglass. I am not sure if its all the time or only on start up when the engine shakes the most, but I am going to alleviate the interferences and fly again. I am really hoping this solves my problem.
 
I was wondering if anyone could give me some guidance as to how to measure the height of my ailerons and what dimension I am looking for. Just looking at my outboard aileron hinges, the position of the aileron does not appear to be higher than the wing, maybe slightly but I'm not sure just from eyeballing it.
 
Neutralize the ailerons, even clamping them to the retracted flaps. Then take a steel rule and stand it on edge overlapping the aileron. The wing skin is slightly curved but you can tell easily if the aileron is sitting above the wing profile. Also will show if it is sitting below the profile. Compare to the opposite side hinge points.

i'll look for a pic...I thinkI took one
 
Neutralize the ailerons, even clamping them to the retracted flaps. Then take a steel rule and stand it on edge overlapping the aileron. The wing skin is slightly curved but you can tell easily if the aileron is sitting above the wing profile. Also will show if it is sitting below the profile. Compare to the opposite side hinge points.

i'll look for a pic...I thinkI took one

I'd love to see that pic. I have a heavy right wing. I need to check flap positions, as well as aileron hinge positions.

Is it possible for RV-4 flaps to have:

1) The same degree down position when measured with a protractor relative to the top of the wing

2) But a different degree position when retracted, relative to the bottom of the wing?

Should the bottoms of the flaps be in line with the bottom of the wings?

Thanks,
 
Is it possible for RV-4 flaps to have:

1) The same degree down position when measured with a protractor relative to the top of the wing

2) But a different degree position when retracted, relative to the bottom of the wing?

Yes. The flap actuator rod connects to a builder-fabricated plate on the inboard end of the flap. If the hole on this plate is not the same distance from the hinge line on both flaps you would get assymmetrical flap travel.
 
Yes. The flap actuator rod connects to a builder-fabricated plate on the inboard end of the flap. If the hole on this plate is not the same distance from the hinge line on both flaps you would get assymmetrical flap travel.

Thanks, Steve. I purchased my plane. After I purchased it I checked the full down flap position, measuring from the top of the wing, and adjusted both flaps to the same degree measurement. Now the left flap TE is about 1/4" lower than the right, which could account for some, or all, of the heavy right wing.

I'm concerned that if I adjust the flap up to lighten the load on the right wing, then when the flaps are down they will be asymmetrical, causing roll issues in the pattern.

I'll check the hole location as you mentioned, and also the aileron hinge locations as mentioned in the other responses.
 
wing skin to aileron check pic

photobucket-7921-1345060962625.jpg
 
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