Rebel Questions

[scott.hibbs]

Bob, can you clarify the CG limits? I have been
going by the Murphy website which says Forward:
(+10.85") Aft: 18.10"). If that is wrong, I need
to know. Right now my calculated CG is between
10.5 & 16.5 (the airplane is not finished, these
numbers are educated guesses.

Scott

(My CofG is at 8.1" aft of datum - these days, MAM suggests 12")
This is one reason several builders have chosen to use the Scott 3200
tailwheel - it adds a few pounds 'way back there. ;-)



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[Bob Patterson]

Hi Scott !

The C of G range has changed over the years - if in doubt, always
=========== ------
ask Murphy for the latest recommendations. My understanding was that
=== ====== ------------------------------
they <prefer> something around 12" as forward position ...

The original range was about 7.5" to 22", if I recall - that
was the <theoretical> range for the airfoil. Several years of flying
has suggested that 10" - 12" is a better idea forward, and about 18-
19" aft ..... but those are only suggestions.

Sounds like you are in the right range ! In any case, the
Rebel flies very nicely at 8" forward and 21" rear, with no great
control problems !!

.....bobp


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[Wayne G. O'Shea]

Scott, to "strain" a little more "mud" out of the equation, don't confuse
EMPTY C of G, with flying configuration C of G. Bob's XWI has an EMPTY C of
G of 8.1 inches and it flies just lovely (I have a <slightly> biased
opinion, but it does!!!). I know it can even be landed tail wheel first, as
I have done it a few times! Keep in mind that EVERYTHING that you load into
(or onto, ie: paint) a Rebel moves the C of G backwards. Pilot sits about 15
to 16 inches aft of datum. Fuel is around 24 inches aft (not 18" like some
of the older literature shows),etc. etc. I think the factory is recommending
a FLYING C of G of 12.8" now to get optimum cruise speed. I'm not in that
big of a hurray to go anywhere that 2 or 3 MPH is going to matter.

Murphy moved the theoretical forward limit for the 4415 airfoil from 7.7" to
a suggested 10.85" about the same time they started supplying their own
manufacture JDM wheels and brakes. It may have more to do with the
possibility of nosing the thing over, than the aircraft's flying
characteristics!!!!

Don't worry, yours will work out fine unless you have plans for a 75 pound
constant speed prop or something!

Wayne G. O'Shea
www.irishfield.on.ca


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[klehman]

FWIW bulletin 071095rb and a subsequent undated letter from MAM all
refer to a recommended forward flying limit of 10.85" which is the
latest info that I have seen from MAM.

Ken

scott.hibbs@dcsol.com wrote:

Bob, can you clarify the CG limits? I have been
going by the Murphy website which says Forward:
(+10.85") Aft: 18.10"). If that is wrong, I need
to know. Right now my calculated CG is between
10.5 & 16.5 (the airplane is not finished, these
numbers are educated guesses.

Scott

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[Bob Patterson]

Thanks Ken !

You're always there with the correct answers ! I'm afraid,
as Wayne said, that I "muddied" things a bit by mixing in a suggested
"flying" C of G of about 12", with the recommended "empty" C of G
of 10.85" !!

......bobp


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[brian amendala]

Rick- you definitely should add some weight in the rear to bring your CG to
atleast 10 inches aft of datum. There is a reason that 10-17 inches is the
acceptable CG. While too forward a CG is not as bad as too aft- it still
could be a problem for you some day as you will not be able to arrest your
descent when you need it most- upon landing....Brian

From: "Rick Harper" <rjwh@ozemail.com.au>
Reply-To: <murphy-rebel@dcsol.com>
To: murphy-rebel@dcsol.com
Subject: Rebel Questions
Date: Sun, 17 Jun 2001 09:39:54 +1000

G'day to All from sunny but COLD OZ!

I'm a happy vegemite again.....we're back in the air, with a few more
hours under our wings.
I fitted Wayne's firewall mods and have the new oil cooler in place :-)

I have a few questions which I'm hoping some of you long time flyers can
help us out with.

We have an 0-235 Lycoming with a standard firewall...IE: NOT shortened.
I also took good notice of Bob and Wayne and we have 28' of UP elevator on
tap.

The C of G range as advised by MAM is 276 mm to 459 mm aft of the Datum
Line.

Our EMPTY C of G is 197 mm ( nearly 8 " ) aft of the datum line (front of
the wing / gear leg)

After doing several loading charts...I came to the realisation that it is
virtually impossible to get
the Rebel out of its C of G range...the only real limiting factor here
being the all up MTOW of
1650 Lbs (750 Kgs)........do you guys agree with this ?

With just "little ol' me" , 130 Kgs (just under 290 lbs) and a half a tank
of gas ..120 Lts / 30 US gallons (we went out one more rib with the tank
and have 240 litres space !)...I seem to run out
of FLARE ...SUDDENLY.......at the last second !?!....(which is probably
just under 40 knots ..
with no flaps)

Is this normal Rebel stuff ?...........
or should I perhaps stick 5 to 10 lbs of weight down in the tail to move my
empty C of G
back a bit ?................( I'm thinking this might help the last few
seconds of roundout / flare )


Also, could someone out there offer some advice on the engine side of
things :

As I said before , we have an 0-235 Lycoming ..which I rebuilt myself (
marine engineer )
I fitted new "J" model pistons ( the 9.7:1 variety )...and cylinders
..."cleaned up" the ports a
fair bit (got rid of the dags and misalignments in the castings etc , fully
balanced the engine
throughout..propeller extension as well , made up a 2" stainless crossover
exhaust system
and replaced one magneto with one of Klaus Xavier's LSE crank fired
ignition systems...which
is supposed to give a 4% boost to the power as well........all in all, I'm
expecting this sucker
to put out 130 H.P. without having done any major mod's.

I'm getting 2200 - 2300 STATIC full power RPM and flat out in straight and
level flight she
hits 2500ish RPM.....and with no reflex on the flaperons is hitting around
100 knots .....
(it's rather hard to tell at this point as its been BLOODY WINDY here every
day since we've
been back in the air)

Do these figures sound about right to you guys...or should I be repitching
the Warp Drive
to get more RPM ?....


The plane flys beautifully and is an absolute joy.....can't wait to take
up the list of people
on my "waiting list" :-)


Rick & Wendy Harper
541 R....FLYING !

_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com




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[brian amendala]

Bob, are you saying you use FULL flaperons on takeoff? I have only about 8
takeoffs so far and havew found that no flaps seems to work as good as 10 or
20 degrees. The Rebel just leaps off with no flaps. What kind of performance
do you get when you use full flaps? I know most Cessnas recommend only 10
degrees at takeoff. I would have thought there would be wy to much drag at
full flaps. Mine is amphibious and I wonder what I will use on
floats.....Thanks....Brian
Also, I have gotten the engine to come down to 430 Fahrenheit, but I have
tried everything I can think of and can't get it to go lower. My spinner is
1/4 inch in front of my cowl and I have tried all kinds of exits and cut the
top of the inlet 1 inch and niothing seems to be working. I was thinking I
should build the other cowl as I have the SPEED COWL. Please tell me what it
costs....Thanks again....Brian



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[Rick and Cathy Ford]

Brian

Did you try opening up the hot air exit point.
Apparently there should be a larger exit opening than intake opening as hot
air expands.
I think the proper ratio is around 3:1, but that's not too feasible with the
speed cowl.
I'm running typically 250 to 350 deg. but that on wheels.

Just a thought Brian.

Rick Ford


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[Rick Harper]

G'day from the Land of OZ !

Tony Bingellis (and most builders) recommend Inlet / Outlet port AIR RATIOS
in engine cowls as 2:3 That is 50 inches of cross sectional area IN has to
have
75 inches of cross sectional area OUT.

We used the Aircraft Spruce Thorp T18 nosebowl...looks much the same as
the factory "speed cowl" , but it's a nose bowl ONLY.
We then made the cowl itself in 6061-T6 sheet with two overcentre latches
on each side....it opens up in two seconds and looks like a model T Ford !

We have EXCELLENT accessibility on both sides of the engine and you get
to see everything in two seconds flat :-)

Rick & Wendy
541R


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[Mike Kimball]

Cool! So what nosebowl do I need for a Super Rebel cowl? How did you curve
the aluminum sides to fit? What's on the bottom?

Mike Kimball
SR#044


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[klehman]

Rick and Wendy

Sounds like a nice installation. Are there photos of your cowl anywhere?
I do have the small photo of your great looking machine that you sent us
all back in March, but can't see much cowling detail. Also did you find
any streamlined overcenter latches that were affordable, or did you use
the large external ones?

Ken



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[brian amendala]

Hi Rick, I have been thinking of changing the cowl to an aluminum one. Where
do I get the drawings on how to build it. Thanks.....Brian

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[Rick Harper]

G'day Mike !

I made the whole front end up myself....off the top of my head as I
went......don't even have drawings....sorry :-(
I would rather suspect that the same Thorp T18 nose bowl from Aircraft
Spruce would also do you Super Rebel....but then there is the problem of
making the rest of the cowl.

Gotta admit the bottom section was difficult...I made a variable cowl flap
arrangement
so I could vary the amount of outgoing air...and hopefully reduce the
cooling drag a bit.
Don't think I'd bother doing it again :-(

I can send you some pic's....but I think you'd be better off designing
something yourself... I'm not sure my version is "the best" way to do it .

Rick & Wendy Harper




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[Rick Harper]

G'day Ken !

The latches were from a "squirrel" helicopter...(French)...our local
aviation wrecker picked them up cheap from a company going bust...we paid
$20 each latch..(the guy
at the wreckers said that they normally sold for over $300 each !!!)

Just a case of being "Johny on the spot" I think

I can't send you much in the way of pic's to do with the cowl....I sent lots
of photos down
to our SAAA ( like the EAA) headquarters so the could do a magazine article
on our baby........I don't think the pic's are going to show you much
anyway....and there's no
"drawings"...I made it all off the top of my head as I went along

I used the engine to hold the nose bowl by bolting two round bits of ply on
either side
of the flat nose bit to the end of the crank...then built up a flat top
piece with 1" folded
down edges...then made the lower wraps at the same time....All this "held"
the
cowl in place. I then made the "bonnet" sides by bending .025" sheet around
the light pole outside our house with my bare hands until I got the shape I
wanted.

Then I made up the bottom of the cowl to pivot on a hinge at the
front...thereby making
it a variable air outlet design at the back......sound complicated ...but it
wasn't
all that hard....(I think ).

Rick & Wendy


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[klehman]

Hi Rick

Not sure if you intended to send those photos to the entire list but
thank you very much. A good looking cowl and airplane! One of the nicest
cowls that I have seen. I believe you about the $300. recessed airplane
latches. There are some reasonably priced commercial latches around
that I will check out, but they are not recessed.

thanks again
Ken



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