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  #1  
Old 08-13-2012, 06:46 PM
flyenforfun's Avatar
flyenforfun flyenforfun is offline
 
Join Date: Aug 2009
Location: Wilmington DE
Posts: 323
Default Discouraging issues, looking for input

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
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RV-8 - N861MM
Wilmington, DE
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  #2  
Old 08-13-2012, 07:25 PM
AaronG AaronG is offline
 
Join Date: Sep 2009
Location: Hartford, CT
Posts: 104
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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
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  #3  
Old 08-13-2012, 07:35 PM
David-aviator David-aviator is offline
 
Join Date: Feb 2005
Location: Chesterfield, Missouri
Posts: 4,514
Default

Quote:
Originally Posted by flyenforfun View Post
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.
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  #4  
Old 08-13-2012, 08:50 PM
6 Gun 6 Gun is offline
 
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Posts: 846
Default Vib

Try moving prop about 30 degress and see if it makes a difference.
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  #5  
Old 08-13-2012, 09:13 PM
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Ron Lee Ron Lee is offline
 
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Posts: 3,275
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Out of round or out of balance tires are not good. Replace or balance as required.
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  #6  
Old 08-13-2012, 09:19 PM
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erich weaver erich weaver is offline
 
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Location: santa barbara, CA
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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
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  #7  
Old 08-14-2012, 05:52 AM
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flyenforfun flyenforfun is offline
 
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Location: Wilmington DE
Posts: 323
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Quote:
Originally Posted by AaronG View Post
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.
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RV-8 - N861MM
Wilmington, DE
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  #8  
Old 08-14-2012, 05:55 AM
flyenforfun's Avatar
flyenforfun flyenforfun is offline
 
Join Date: Aug 2009
Location: Wilmington DE
Posts: 323
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Quote:
Originally Posted by David-aviator View Post
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.
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RV-8 - N861MM
Wilmington, DE
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  #9  
Old 08-14-2012, 05:56 AM
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flyenforfun flyenforfun is offline
 
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Quote:
Originally Posted by 6 Gun View Post
Try moving prop about 30 degress and see if it makes a difference.
Even though I've had a dynamic balance done?
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Matt Giordano Sr. and Jr.
RV-8 - N861MM
Wilmington, DE
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  #10  
Old 08-14-2012, 05:57 AM
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flyenforfun flyenforfun is offline
 
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Quote:
Originally Posted by Ron Lee View Post
Out of round or out of balance tires are not good. Replace or balance as required.
Can you suggest a tire for an RV8? Mitch Lock, the eat coast vans rep, suggest Goodyear Flight Custom IIIs.
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RV-8 - N861MM
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