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  #121  
Old 05-29-2011, 10:54 AM
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chepburn chepburn is offline
 
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Quote:
Originally Posted by Bob Kuykendall View Post
The intent of mass balancing is to reduce or eliminate the amount of surface deflection you get when you shake or wiggle the hinge axis in a variety of ways. The orientation of the axis of rotation is immaterial, and gravity is immaterial.

In a 100% mass-balanced surface, wiggling or shaking the hinge axis results in no rotation of the control surface around the hinge axis. That is what you want for flutter resistance. It prevents feedback reactions in which shaking the hinge axis results in control surface deflection, and the deflection results in an amplification of the shaking.


Thanks, Bob K.
Bob,
I agree with you...I was trying to make the point (badly) that the usual method we use to balance our control surfaces (in the horizontal plane) would not be correct for the vertical stab. Vans has designed the rudder mass balance to be different by 2.5 kg. So, I was trying to say that they did that for a reason...mainly the ones you describe.
Thanks for the clarification.
Chris
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  #122  
Old 05-29-2011, 06:18 PM
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frazitl frazitl is offline
 
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Default Rudder balance weight.

Wow!, Chris. If it takes 2.5KG to balance the rudder (or thereabouts), then balancing is not a good option. The structure needs to be strong enough and stiff enough to handle any weight added.

Rereading the Kitplanes articles, it is apparent the partial balancing might actually make a flutter situation worse! Partial balancing apparently can change the natural frequency of the rudder moving it into a dangerous range. Just as adding some weight to partially balance a control surface can make things worse, adding additional weight to the unbalanced (aft) side (extra heavy paint, rudder trim servo systems, etc.) could make the system more prone or less prone to flutter over the normal operating speed range. What sounds like unusually heavy paint and filler in the current situation might be better, and might be worse.

So we are back to Vne it seems. Our Vans aircraft are proven quantities when flown within the proven flight envelope. Outside that envelope we are conducting an entirely new set of (potentially very dangerous) experiments with MANY interrelated variables. Not for me...
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  #123  
Old 05-30-2011, 10:44 PM
johnny stick johnny stick is offline
 
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Default Mass balancing

So we are all talking about mass balancing the control surfaces to prolong the speed at which flutter occurs. A long time ago, i heard a rumor that the some air force bomber's control surfaces where over balanced; seems that the CG was ahead of the hinge line for better resistance to flutter. Does any of the experts out there have a sense for this, and will over balancing help a RV type of aircraft ?
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  #124  
Old 05-31-2011, 11:34 AM
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chepburn chepburn is offline
 
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Quote:
Originally Posted by johnny stick View Post
So we are all talking about mass balancing the control surfaces to prolong the speed at which flutter occurs. A long time ago, i heard a rumor that the some air force bomber's control surfaces where over balanced; seems that the CG was ahead of the hinge line for better resistance to flutter. Does any of the experts out there have a sense for this, and will over balancing help a RV type of aircraft ?
Please dont interpret the discussion so far as an intention to change anything with any control surface mass balance.

It was suggested here that we try to balance the rudder after paint, but, the rudder is NOT mass balanced in the same way as the aileron and elevator....so that would be a bad idea.

We are NOT suggesting changing anything with ANY control surface. DO NOT change any mass balance outside of what is recommended in the plans on any control without contacting Vans.

The current design works as intended through the designed operating speed envelope.
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  #125  
Old 05-31-2011, 02:40 PM
SvingenB SvingenB is offline
 
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Quote:
Originally Posted by frazitl View Post
So we are back to Vne it seems. Our Vans aircraft are proven quantities when flown within the proven flight envelope. Outside that envelope we are conducting an entirely new set of (potentially very dangerous) experiments with MANY interrelated variables. Not for me...
Exactly my thoughts. My condolences to his family. Just read through this thread and the report. The structure and strength of the airplane is relative to the airspeed (the forces are a direct result of the airspeed). The faster you fly, the weaker the airplane gets in relative terms. Past Vne the airplane is not an airplane any more, it's just an assembly of flimsy aluminium sheets with no structural rigidity, stability or strength. Exactly what happens beyond Vne is therefore only of academic interest and any analysis will be speculative at best.

It is therefore rather puzzling reading the report and the "analysis" of the structural failures. The pilot conducted aerobatic while exceeding the max weight limit at a speed way past Vne. That is all there is to it.
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  #126  
Old 05-31-2011, 03:41 PM
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Curiosity questions please.....

The RV-7 design originally used same VS and rudder as the RV-8?

Later the rudder was changed for one with more area and a riveted wedge trailing edge?

Are the current RV8 and RV7 rudder balance weights the same lead block?
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  #127  
Old 05-31-2011, 04:38 PM
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LifeofReiley LifeofReiley is offline
 
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Default Here's what...

Van's Website states:

I have not had time to research plans...

Counterweights for optional 0.020 Skins, RV-6/6A, Early RV-7/7A,
RV-8/8A, All Rudders
E-614-020 more info $15.40

Counterweights for 0.020 Skins, Late Model RV-7/7A and RV-8/8A.
E-714 more info $19.00

Many have read WAY to deep into my comments on this thread and I guess thats OK. Balancing FLYING surfaces is pretty clear in the plans. Many aircraft I've looked at plan for a little heavy on the down side of the elevator to allow for paint and balancing. IMHO, the down side method works pretty darn well.



Quote:
Originally Posted by DanH View Post
Curiosity questions please.....

The RV-7 design originally used same VS and rudder as the RV-8?

Later the rudder was changed for one with more area and a riveted wedge trailing edge?

Are the current RV8 and RV7 rudder balance weights the same lead block?
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  #128  
Old 06-01-2011, 12:43 AM
jrs14855 jrs14855 is offline
 
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Default balance

Apples to oranges BUT-I fly Twin and single engine Cessnas-NONE have the elevators balanced 100%. They are all quite tail heavy. I never investigated rudder balance. I will try to remember to look at maintenence manuals. I have looked at maintenence manuals for A36 Bonanza and Baron 58. The Baron has a trim tab on one aileron and the balance tolerance for the aileron with the tab is slightly different than the balance for the opposite aileron. Years ago a friend with a Midget Mustang I had to overbalance the ailerons. I don't think he had a fully developed flutter but the ailerons were moving around and the fix was 125% balance. Having survived aileron flutter on an early homebuilt I can say without question flutter can be induced by wake turbulence in close formation.
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  #129  
Old 06-01-2011, 05:42 AM
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Default

Quote:
Originally Posted by DanH View Post
Curiosity questions please.....

The RV-7 design originally used same VS and rudder as the RV-8?

Later the rudder was changed for one with more area and a riveted wedge trailing edge?

Are the current RV8 and RV7 rudder balance weights the same lead block?
Yes. The "new rudder kits" that Van shipped to customers did not contain the lead weight (and several other parts). Those parts had to be scavenged from the old rudder.
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  #130  
Old 06-01-2011, 07:34 AM
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DanH DanH is online now
 
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Quote:
Originally Posted by SvingenB View Post
Exactly what happens beyond Vne is therefore only of academic interest and any analysis will be speculative at best.
Dr. Svingen, I'm shocked...."only of academic interest"?

Kidding aside, interest in some quarters is more than academic. The racers are an obvious example, as are those who routinely fly high (the long fast descent) and those working on efficiency. It is useful to know what physical factors lessen the flutter margin so they can be avoided, even for those who are diligent about observing the manufacturer's VNE. Pilots make mistakes. Airframes with more margin (flutter, structural strength, etc) bring them home.
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Last edited by DanH : 06-01-2011 at 07:44 AM.
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