The Murphy Builders Site

From: "Jones, Michael" <MJones@hatch.ca>
Reply-To: <rebel-builders@dcsol.com>
To: "'rebel-builders@dcsol.com'" <rebel-builders@dcsol.com>
Subject: RE: Tip rib
Date: Mon, 11 Apr 2005 12:01:15 -0400

jesse

you should not do the tips out of ply, they are balanced for a
reason,flutter maybe, you will have to rebalance them now as you are adding
allot of extra weight, be careful may cause serious design problems

mike#007

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com]On Behalf Of
Jesse Jenks
Sent: Monday, April 11, 2005 11:53 AM
To: rebel-builders@dcsol.com
Subject: Tip rib


After much thought I decided to make my tip ribs out of 1/4" plywood or
similar. I will make them the full length of the tip, and glue in with
epoxy

fillets on the inside, and glass cloth wrapped around the outside. I was
looking at the way the alum. leading edge fits into the tip (or doesn't fit
actually), and how the curve of the tip L.E. doesn't match that of the
vertical/horizontal stab, and decided to make everything fit and look good
I

was going to be doing some epoxy work anyway so why not just make the whole
tip with composite materials which are more workable. This will allow me to
easily mount the counterweights on the inside of the tips as well.
The only problem I can see is changing the balance of the tips by adding a
little more weight forward of the hinge line. This will be slightly offset
by making the rib extend all the way back to the T.E.
I am very comfortable working with epoxy/wood/glass.
Any thoughts/comments?
Thanks.
Jesse





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From: "Jones, Michael" <MJones@hatch.ca>
Reply-To: <rebel-builders@dcsol.com>
To: "'rebel-builders@dcsol.com'" <rebel-builders@dcsol.com>
Subject: RE: Tip rib
Date: Mon, 11 Apr 2005 12:01:15 -0400

jesse

you should not do the tips out of ply, they are balanced for a
reason,flutter maybe, you will have to rebalance them now as you are adding
allot of extra weight, be careful may cause serious design problems

mike#007

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com]On Behalf Of
Jesse Jenks
Sent: Monday, April 11, 2005 11:53 AM
To: rebel-builders@dcsol.com
Subject: Tip rib


After much thought I decided to make my tip ribs out of 1/4" plywood or
similar. I will make them the full length of the tip, and glue in with
epoxy

fillets on the inside, and glass cloth wrapped around the outside. I was
looking at the way the alum. leading edge fits into the tip (or doesn't fit
actually), and how the curve of the tip L.E. doesn't match that of the
vertical/horizontal stab, and decided to make everything fit and look good
I

was going to be doing some epoxy work anyway so why not just make the whole
tip with composite materials which are more workable. This will allow me to
easily mount the counterweights on the inside of the tips as well.
The only problem I can see is changing the balance of the tips by adding a
little more weight forward of the hinge line. This will be slightly offset
by making the rib extend all the way back to the T.E.
I am very comfortable working with epoxy/wood/glass.
Any thoughts/comments?
Thanks.
Jesse





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copy or take any action with respect to it.

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HATCH immediately via mailto:MailAdmin@hatch.ca.



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Mike,
Thanks for the comment. I think I could figure out how to end up with the
same ballance, by weighing the parts for the original setup, then cutting
off some of the led to arrive at the original amount of weight in the

suspect that the Fife tips I'm using are quite a bit lighter than the

tips as well. Also, it seems like it would be better to have a bit more
counterweight than a bit less, but I'm no expert for sure. My point is

if getting the counterweight exactly right is a major concern, then I

I can do that. Does anyone know what MAM says about % of counterweight in
the elevators for the Rebel? I remember some discussion about that.
Thanks again
Jesse

From: Ken <klehman@albedo.net>
Reply-To: <rebel-builders@dcsol.com>
To: rebel-builders@dcsol.com
Subject: Re: Tip rib
Date: Tue, 12 Apr 2005 09:11:35 -0400

Jesse

I agree with Mike that this is extra work for minimal gain however we
are all guilty of that ;)

Yes you can't really have too much counter weight. You don't want too
little. If anything you want extra counterweight to allow for any extra
material that you add behind the elevator hinge point. So ideally you'd
measure the stock moment arm of the tip and make sure you have a similar
amount of moment arm. In reality I doubt if it is very critical but that
will keep you on the safe side as far as I know.

Also make sure you don't create any traps (figuratively and literally)
such as could the plywood absorb moisture and freeze or trap water or
ice back there at the aft part of the tip - that could cause problems
(upset the balance and lead to flutter) and that sort of thing has
killed pilots.

Ken

Jesse Jenks wrote:

Mike,
Thanks for the comment. I think I could figure out how to end up with

the

same ballance, by weighing the parts for the original setup, then

cutting

off some of the led to arrive at the original amount of weight in the

tip. I

suspect that the Fife tips I'm using are quite a bit lighter than the

Murphy

tips as well. Also, it seems like it would be better to have a bit more
counterweight than a bit less, but I'm no expert for sure. My point is

that

if getting the counterweight exactly right is a major concern, then I

think

I can do that. Does anyone know what MAM says about % of counterweight

in

the elevators for the Rebel? I remember some discussion about that.
Thanks again
Jesse

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Thanks Ken,
I would seal the ply in epoxy, and make sure there is a way for moisture to
drain from the enclosure. I read Bingelis on mass balancing last night. He
sais 100% or more is best. The standard MAM setup seems less than 100%. Also
as I remember the trim system is optional, but the manual doesn't say (I
think) to adjust the counterweight for what must be quite a big difference
in weight aft of the hinge line. Has anyone actually ballanced to 100%? I
wonder how much lead it would take. Another interesting point from Bingelis
was a quote from some FAA bulletin saying the actual balance weight should
be mounted to take something like 24G. In case it does flutter I guess. I
think the fiberglass tip would rip off at 24G in flutter mode (whipping up
and down). That's another reason to beef it up. What got me started on the
whole thing though was that the nose profile of the tip doesn't match the
profile of the stabs. It doesn't look great, but more importantly the L.E.
rib doesn't fit properly in the tip. At first I was thinking I would use
thickened epoxy between the rib and the inside of the tip to fill the voids
caused by the mismatch, let it harden then rivet. This is still not a bad
idea I think, because if you just rivet it as is then something has to give.
Probably the fiberglass. Then I thought I wanted to re contour the profile
on the outside of the tip L.E. to better match the stab. With those 2
operations, it didn't make much sense to be using aluminum and rivets. I
think it would actually be less work to just make the rib out of ply and
epoxy/glass it in.
Jesse

Jesse
I didn't have to adjust mine but I do remember Dave saying that the tip
could be narrowed to change the leading edge curve angle (contour?). ie
if you are looking down vertically at the tip, you can cut some off the
open edge (reduce the span of the stab). That results in a shorter tip
in the forward to aft direction as the tip effectively slides onto the
elevator farther.
It doesn't sound like that is your contour issue though??. Things can be
a fair way from perfect and still be virtually unnoticeable by someone
else with a less critical eye, but by all means do what you think is
best and easiest for you. Regardless of what you do they are going to
look better than the stock tips I think.

100% mass balancing is great for an untested product but not really
necessary if the structure is flight tested OK and kept below Vne. I
think you can be certain that there is sufficient counterweight there
for the stock construction and normal speeds. That's the advantage of a
tested and well proven design. You are doing the right thing by doing
your homework before making changes. Also I think the Fife tip is
already stronger than the stock tip as far as I can tell so no worries
there.

Ken

Jesse Jenks wrote:

Thanks Ken,
I would seal the ply in epoxy, and make sure there is a way for moisture

to

drain from the enclosure. I read Bingelis on mass balancing last night.

He

sais 100% or more is best. The standard MAM setup seems less than 100%.

Also

as I remember the trim system is optional, but the manual doesn't say (I
think) to adjust the counterweight for what must be quite a big

difference

in weight aft of the hinge line. Has anyone actually ballanced to 100%? I
wonder how much lead it would take. Another interesting point from

Bingelis

was a quote from some FAA bulletin saying the actual balance weight

should

be mounted to take something like 24G. In case it does flutter I guess. I
think the fiberglass tip would rip off at 24G in flutter mode (whipping

up

and down). That's another reason to beef it up. What got me started on

the

whole thing though was that the nose profile of the tip doesn't match the
profile of the stabs. It doesn't look great, but more importantly the

L.E.

rib doesn't fit properly in the tip. At first I was thinking I would use
thickened epoxy between the rib and the inside of the tip to fill the

voids

caused by the mismatch, let it harden then rivet. This is still not a bad
idea I think, because if you just rivet it as is then something has to

give.

Probably the fiberglass. Then I thought I wanted to re contour the

profile

on the outside of the tip L.E. to better match the stab. With those 2
operations, it didn't make much sense to be using aluminum and rivets. I
think it would actually be less work to just make the rib out of ply and
epoxy/glass it in.
Jesse

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