The Murphy Builders Site

G'day.

Help please.

I am now fitting the fibreglass tip to the rudder. Does the rudder tip have a lead weight as do the elevator tips?

Regards

Ian Donaldson

No weights in the rudder Ian
Drew
At 12:18 AM 2/26/01 +0800, you wrote:

G'day. Help please. rudder. Does the rudder tip have a lead weight
as do the elevator tips? Regards Ian Donaldson

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Hi Ian

I believe there are weights in the rudder tip. Though it has been quite
awhile since I looked at this.

Any other thoughts on this someone?

Brian #328R

-----Original Message-----
From: murphy-rebel@dcsol.com [mailto:murphy-rebel@dcsol.com]On Behalf Of
Drew and Jan
Sent: Wednesday, February 28, 2001 5:24 PM
To: murphy-rebel@dcsol.com
Subject: Re: Rudder tip


No weights in the rudder Ian
Drew
At 12:18 AM 2/26/01 +0800, you wrote:

G'day. Help please. rudder. Does the rudder tip have a lead weight
as do the elevator tips? Regards Ian Donaldson

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There are no weights in my rudder tips.





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Hi Ian;

No the rudder does not have a lead weight in it. The elevators do in order to reduce stick pressure.

REBEL 505

Aren't the weights there to prevent flutter? If this is the case, it is a little curious that the rudder does not have one? It may have no bearing on this but all three (maybe 5) surfaces on Cessnas are weighted.

-----Original Message-----
From: carol51 <carol51@attcanada.ca (carol51@attcanada.ca)>
To: murphy-rebel@dcsol.com (murphy-rebel@dcsol.com) <murphy-rebel@dcsol.com (murphy-rebel@dcsol.com)>
Date: March 3, 2001 10:54 PM
Subject: Re: Rudder tip


Hi Ian;

No the rudder does not have a lead weight in it. The elevators do in order to reduce stick pressure.

REBEL 505

Hi Peter
The stock rudder must not need a weight to protect against flutter. It
might be wise to ask MAM about some weight in there though if you add
extra items to the trailing edge of the rudder such as a white nav
light.
Ken




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To: <murphy-rebel@dcsol.com>
From: Bob Patterson <apat@istar.ca>
Subject: Re: Rudder tip


Hi !

I think there are a few reasons why there's no weight in the
rudder horn:

The rudder is hinged vertically, so gravity pulling downward on
the horn would not help counterbalance the rudder weight in any way.
I suspect that a counterweight would need a VERY substantial mass to
dampen the rudder on the basis of mass only, as opposed to weight
affected by gravity, as on the elevator horns. The aerodynamic
balance provided by the horn must be enough to prevent flutter on
the rudder, which has considerably less area & mass than the elevators.

The rudder horn is there just to aerodynamically balance the
rudder and lighten the control forces needed. (I flew the original
Rebel before the horns were added to the rudder & elevator - trust
me, it's much nicer WITH them ! )

.....bobp

PS
I completely agree with Ken - ALL builders should ALWAYS
check with the factory if you are making ANY significant change
to the aircraft, especially control surfaces !! They really
WILL appreciate the consideration !

----------------------------------orig.--------------------------------
At 08:51 AM 3/4/01 -0800, you wrote:

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Hi Peter
The stock rudder must not need a weight to protect against flutter. It
might be wise to ask MAM about some weight in there though if you add
extra items to the trailing edge of the rudder such as a white nav
light.
Ken

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I thought the main purpose of counter weights in the elevators, or any
control service, were to prevent flutter. Although they may reduce stick
force too.
Bruce G



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Don't know if it helps, or even applies to Murphy products, but I once
encountered aerodynamic flutter in a Rand Robinson KR-2 during a high speed
dive, and the only flutter I detected was in the elevator. (Stick shaking
fore and aft rapidly). I won't bore you with the details of how I ended up
in that situation, but it had something to do with trying to teach oneself
aerobatics with no prior instruction. Bad idea. I was momentarily 60 mph
(indicated) beyond the redline by the way. Apparently, even experimental
kit manufacturers know the concept of adding a safety factor to stress and
airspeed calculations. The rudder was unbalanced and smooth as glass at
that airspeed.

Mike Kimball

-----Original Message-----
From: murphy-rebel@dcsol.com [mailto:murphy-rebel@dcsol.com]On Behalf Of
Legeorgen@cs.com
Sent: Sunday, March 04, 2001 9:48 PM
To: murphy-rebel@dcsol.com
Subject: Re: Rudder tip


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I thought the main purpose of counter weights in the elevators, or any
control service, were to prevent flutter. Although they may reduce stick
force too.
Bruce G
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Flutter flutter and flutter is my understanding.
Ken

Legeorgen@cs.com wrote:

I thought the main purpose of counter weights in the elevators, or any
control service, were to prevent flutter. Although they may reduce stick
force too.
Bruce G

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Hi

I don't believe flutter has anything to do with which way the hinge line
goes. It is the aerodynamic loads which have to be taken care off. At
speed the gravity loads would be insignificant compared to the flight loads.

Brian #328R

-----Original Message-----
From: murphy-rebel@dcsol.com [mailto:murphy-rebel@dcsol.com]On Behalf Of
APAT@ISTAR.CA
Sent: Sunday, March 04, 2001 7:29 PM
To: murphy-rebel@dcsol.com
Subject: Re: Rudder tip


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To: <murphy-rebel@dcsol.com>
From: Bob Patterson <apat@istar.ca>
Subject: Re: Rudder tip


Hi !

I think there are a few reasons why there's no weight in the
rudder horn:

The rudder is hinged vertically, so gravity pulling downward on
the horn would not help counterbalance the rudder weight in any way.
I suspect that a counterweight would need a VERY substantial mass to
dampen the rudder on the basis of mass only, as opposed to weight
affected by gravity, as on the elevator horns. The aerodynamic
balance provided by the horn must be enough to prevent flutter on
the rudder, which has considerably less area & mass than the elevators.

The rudder horn is there just to aerodynamically balance the
rudder and lighten the control forces needed. (I flew the original
Rebel before the horns were added to the rudder & elevator - trust
me, it's much nicer WITH them ! )

.....bobp

PS
I completely agree with Ken - ALL builders should ALWAYS
check with the factory if you are making ANY significant change
to the aircraft, especially control surfaces !! They really
WILL appreciate the consideration !

----------------------------------orig.--------------------------------
At 08:51 AM 3/4/01 -0800, you wrote:

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Hi Peter
The stock rudder must not need a weight to protect against flutter. It
might be wise to ask MAM about some weight in there though if you add
extra items to the trailing edge of the rudder such as a white nav
light.
Ken

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Hi There

The weights are definitely there to reduce flutter. I am reasonably sure that the rudder would need one as well as the elevators as the design in similar.

Comments?

Brian #328R

-----Original Message-----
From: murphy-rebel@dcsol.com [mailto:murphy-rebel@dcsol.com]On Behalf Of Peter Cowan/Lexi Cameron
Sent: Sunday, March 04, 2001 7:39 AM
To: murphy-rebel@dcsol.com
Subject: Re: Rudder tip


Aren't the weights there to prevent flutter? If this is the case, it is a little curious that the rudder does not have one? It may have no bearing on this but all three (maybe 5) surfaces on Cessnas are weighted.

-----Original Message-----
From: carol51 <carol51@attcanada.ca (carol51@attcanada.ca)>
To: murphy-rebel@dcsol.com (murphy-rebel@dcsol.com) <murphy-rebel@dcsol.com (murphy-rebel@dcsol.com)>
Date: March 3, 2001 10:54 PM
Subject: Re: Rudder tip


Hi Ian;

No the rudder does not have a lead weight in it. The elevators do in order to reduce stick pressure.

REBEL 505

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To: <murphy-rebel@dcsol.com>
From: Bob Patterson <apat@istar.ca>
Subject: Re: Rudder tip


Hi Bruce !

You're right about the weights - it's the horns that help
with air loads. The weights could be just a streamlined lump of lead
on a rod, like the Tiger Moth and others.

Weights are mostly effective with elevators and ailerons, as they
are both hinged horizontally - so the weight can balance the weight of
the control surface, reducing the risk of flutter. The aerodynamic
balance of the horns can also help control the flutter tendencies,
but often the horns are enlarged to lighten control forces. (Like
the 'spades' on the ailerons of many aerobatic aircraft)

If the horns are too large, you can get 'control snatch',
where a small movement causes the horn to grab more air and try
to move the control surface a lot farther and faster than you
wanted !! The shape of the horns can be a factor, too - ideally,
they should have rounded leading edges, and, as on the Pitts
and Mustang ailerons, can work best if built <thicker> than the
wing or stab., so air flows over them constantly and stays attached,
as they are deflected. (I used to think they should be thinner than
the wing, for less drag - WRONG !! A Pitts driver explained that
thinner ailerons and elevator horns would cause the airflow to separate
at the gap, causing drag, and making the ailerons much less
effective, too.... )

Times like this I wish I could just sketch airflow ... ;-)

.....bobp

------------------------------orig.------------------------------------
At 01:47 AM 3/5/01 EST, you wrote:

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I thought the main purpose of counter weights in the elevators, or any
control service, were to prevent flutter. Although they may reduce stick
force too.
Bruce G
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Hi Brian

I believe the flex (and twist) properties of the structure that a
control surface is attached to is a very important part of flutter. It
is possible that the attachment method of the vertical fin vs. the stab
is sufficiently different that an added weight is not needed in the
rudder. Happily there are enough Rebels flying to confirm that the
weight is not needed on a stock rudder.

Similar situation with ailerons. Some ailerons need a mass balance
because of wing flex properties but the stock fabric covered Rebel
aileron doesn't at normal speeds. Change the construction method of the
wing though and troubles could arise.

There are other factors as well but I think that is the most likely
explanation.

Ken

ps - as an unrelated tidbit that has nothing to do with a Rebel - I have
even read of situations where the aileron became a trim tab for the
wing. ie up aileron twisted the wing enough to make the wing go up. Bad
day!

Hi There
The weights are definitely there to reduce flutter. I am reasonably sure that the rudder would need

one as well as the elevators as the design in similar.
Comments?
Brian #328R




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