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Tandem Rotor Helis Vertol Chinook > Blade Flutter
 
 
minuteman42
Heliman
Location: Stockton, CA USofA

My Posts This: Topic  Forum		Am trying to get and "old CH-46" in the air and everytime I get
ready to break ground, the aft rotor blades start fluttering wildly
out of control. I, of course, dump pitch immediately, so can not see a cause. I have checked, double checked, installed all new
servos, completely re-rigged all the controls. HELP

tandem rotor nut
09-14-2009 05:14 AM
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Phoenix NOTAR
Heliman
Location: State College, PA USA

My Posts This: Topic  Forum		Please take a picture of your set up (without body if possible), and maybe we can see if there is something to cause this problem

Sandy
09-14-2009 05:28 PM
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Turbinator
Senior Heliman
Location: Nanticoke, PA

My Posts This: Topic  Forum		DO you have heads spinning the proper direction for the way the blades are installed (all it takes is to have the belt twisted the wrong way)? Front should be CW, back CCW. Blades on backwards will cause mega flutter when pitch is introduced!!
09-14-2009 05:40 PM
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minuteman42
Heliman
Location: Stockton, CA USofA

My Posts This: Topic  Forum		Blade Flutter

NOTAR
Belt is on correctly, blades are mounted correctly, everything is turning correctly.
Here are a couple pictures of the control setup from each side,



tandem rotor nut
09-16-2009 04:48 AM
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Phoenix NOTAR
Heliman
Location: State College, PA USA

My Posts This: Topic  Forum		Minuteman,

I agree that the set up looks OK. But it looks like you are using standard blades. This heli must use blades with a lot (a real lot) of leading edge tip weight. This may be causing some of the issue.

Also check the phasing of the rear mast swashplate and make sure that with a blade at 90 degrees to the length of the body you get no movment with a roll input.

Also check that the bearing in the blade grips are very smooth even when you are pulling out on them with a lot of force.

Just an FYI, I re-positioned the front link to the rear swashplate all the way back on the lower bellcrank so that it applies a minimum amount of "elevator" input to the rear swashplate when the swashplate rises and lowers.In other words the rear swash plate should only tilt for roll and yaw, as well as rise and lower level during elevator and collective inputs. This was suggested to me by Hirobo many years ago, and it helped make the heli a little less sensitive to pitching up in forward flight or when climbing.

Sandy
09-16-2009 01:54 PM
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minuteman42
Heliman
Location: Stockton, CA USofA

My Posts This: Topic  Forum		Sandy

Thanks for the input. I will check it out further asap. the
blades are carbon fiber, shorter than original, but with a wider cord.
This bird was purchased second hand, but I did have it hovering
right after I bought it.

tandem rotor nut
09-16-2009 11:49 PM
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Rodend
Heliman
Location: P Town,OR.

My Posts This: Topic  Forum		Hey what about rotor Phasing ? not sure about a r/c but the real thing we put the blades 10 & 2 what this means is the FWD is at the 2 and the AFT is at 10 viewing from the top so one blade grip is at 2 and one is at 10 we call this rotor Phasing in the full scale Hope this helps


Jim
09-17-2009 12:07 AM
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airplanejunkie
Heliman
Location: Riverview, Mi.

My Posts This: Topic  Forum		Please check the blade covering for rips and loose covering. A carefull heat shrink job may solve your issue. Thanks, Dave
09-17-2009 10:03 AM
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krashtagain
Key Veteran
Location: ohio

My Posts This: Topic  Forum
Quote 
Please check the blade covering for rips and loose covering.



Quote 
Sandy

Thanks for the input. I will check it out further asap. the
blades are carbon fiber, shorter than original, but with a wider cord.
This bird was purchased second hand, but I did have it hovering
right after I bought it.

If you're not living on the edge you're just taking up space !
09-17-2009 01:20 PM
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Phoenix NOTAR
Heliman
Location: State College, PA USA

My Posts This: Topic  Forum		Minuteman,

It may be a longshot, but there is something else for you to check.

My Vertol is also 20+ years old and I had the original flat top blade grips. I was having problems with the tracking going in and out, as well as shaking in the landing gear. I found that 3 of the blade grips had cracks in them from the bolt hole to the tip. I think that since all of the grips cracked at about the same time, it may be due to their age.

If your blade grips are also original, you should check them carefully for cracks. I think if they are cracked, it could cause the flutter that you are experiencing.

Sandy
09-18-2009 12:27 AM
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minuteman42
Heliman
Location: Stockton, CA USofA

My Posts This: Topic  Forum		Thanks for the input guys, I haven't been able to do anything with it, these past few days, but I will check out the suggestions you have made.

Thanks, Al

tandem rotor nut
09-22-2009 03:31 AM
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Tandem Rotor Helis Vertol Chinook > Blade Flutter
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