Weight and Balance

Rebflyer · Post by **Rebflyer** » Fri Feb 17, 2012 9:22 pm

Thanks Walter,
I'll do some comparsions. Curt N97MR

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allsure · Post by **allsure** » Fri Feb 17, 2012 9:37 pm

G'day

I am about to try and do the weight and balance calculations for my Rebel, but have found some anomalies.

The construction manual gives limits of +12" & +19.7" whereas the flight operations manual gives +7.7" & +19.7"

What is correct?

What is everyone else using?

Thanks and regards

Ian Donaldson

Bob Patterson · Post by **Bob Patterson** » Fri Feb 17, 2012 9:37 pm

Hi Ian !

I think the 12" / 19.7" are the latest suggestions -
as I recall, the original (theoretical) limits were about
7.7 / 22 ". The factory have suggested the later numbers for
better handling .... (most Rebels end up about 12" anyway,
with pilot and a bit of fuel)

There are several Rebels flying with O-320's with the
'unmoved' firewall position, with forward empty CG's about 8 - 9",
and I have no problems flying mine that way. It's pretty hard to
load a Rebel back to 19.7" without going over gross, so that's
unlikely to be a problem ! ;-)

You're lucky - we can't fly ours without submitting
weight & balances before getting a permit !

.....bobp

----------------------------------orig.---------------------------------
At 09:28 AM 12/24/01 +1100, you wrote:

G'day

I am about to try and do the weight and balance calculations for my Rebel,

but have found some anomalies.

The construction manual gives limits of +12" & +19.7" whereas the flight

operations manual gives +7.7" & +19.7"

What is correct?

What is everyone else using?

Thanks and regards

Ian Donaldson
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<META content="text/html; charset=windows-1252" http-equiv=Content-Type>
<META content="MSHTML 5.00.2919.6307" name=GENERATOR>
<STYLE></STYLE>
</HEAD>
<BODY bgColor=#ffffff>
<DIV><FONT size=2>    </FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=2>G'day</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=2>I am about to try and do the weight and balance calculations
for my Rebel, but have found some anomalies.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=2>The construction manual gives limits of +12" & +19.7"
whereas the flight operations manual gives +7.7" & 

+19.7"</FONT></DIV>

<DIV> </DIV>
<DIV><FONT size=2> What is correct?</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=2>What is everyone else using?</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=2>Thanks and regards</FONT></DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV><FONT size=2>Ian Donaldson</FONT></DIV></BODY></HTML>

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allsure · Post by **allsure** » Fri Feb 17, 2012 9:37 pm

G'day Bob

Thanks for your reply.

I will run with the later numbers as you suggest.

We have to submit a weight and balance with the final inspection, but that
is a way off yet.

You know the old saying. 90% done. 90% yet to do!

Regards and thanks

Ian Donaldson

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Charles Bailey · Post by **Charles Bailey** » Fri Feb 17, 2012 9:37 pm

Lan,
Just to add more confussion, this is the MAM Tech Bulletin in Part:
I have flown my Rebel at 10.5 with no problems, a little up trim is required.
Technical Bulletin 041096rb
April 10, 1996
Chilliwack, British Columbia
Attention: Rebel Builders and Pilots
Subject: Murphy Rebel Center Of Gravity Calculations Contact: Technical Services
Murphy Aircraft Mfg. Ltd.
Ph. 604-792-5855
Fax. 604-792-7006
e-mail murtech@murphyair.com (murtech@murphyair.com) Recently there has been some concern among builders who apparently did not receive Bulletin #071095RB or the attached Rebel Weight and Balance information. The bulletin refers to the increase in allowable gross weight when operating on floats. This limit was raised by 5%, resulting in a limit of 1520 lb. for the 1450 lb Rebels and 1730 lb. for the 1650 lb models.
At the same time, after extended testing of the Rebel in a number of different configurations, there was a change in the recommended forward CG limit. The theoretical limits for the 4415 airfoil are between 12 and 30% of the Mean Aerodynamic Chord (MAC), h owever the recommendation for the forward limits has been changed to 20% (approx. +10.85" from datum).
The forward limit on the other hand, according to theory is 12%. In practice however it has been found that 20% is the more desirable forward limit for a number of reasons. This recommendation is based on hundreds of flight hours and feedback from Rebel bu ilders. It has been found that in most cases, airplanes flying forward of 20% tend to be somewhat nose-heavy or at least lacking slightly in up elevator authority. In addition to this, the airplane simply performs better, the closer the CG is to aft. This res ults in better cruise, better climb and generally a more enjoyable airplane to fly. Although some airplanes are flying at CG locations forward of 20% without problem or complaint and are considered safe, it was decided to make 20% the recommended forward limi t.
The aft limit has been tested to 33% and 32% was therefore selected as the aft limit. The recommended limits therefore are as follows:
Forward: 20% MAC (+10.85")
Aft: 32% MAC (+18.10")
Important: although the empty weight CG location may be outside of the limit, the important thing is that the CG location for different loading cases does not violate the limits. The reason for doing an empty weight center of gravity measurement as you do when you perform the weight and balance is so that you can accurately calculate the CG location for any loading case. Usually the most critical loading cases are usually the most likely forward and aft CG locations when loaded.
Chuck Bailey

Rebel 176

N225PC

From: "allsure"
Reply-To:
To: murphy-rebel@dcsol.com
Subject: Weight and balance
Date: Mon, 24 Dec 2001 09:28:04 +1100

G'day

I am about to try and do the weight and balance calculations for my Rebel, but have found some anomalies.

The construction manual gives limits of +12" & +19.7" whereas the flight operations manual gives +7.7" & +19.7"

What is correct?

What is everyone else using?

Thanks and regards

Ian Donaldson

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allsure · Post by **allsure** » Fri Feb 17, 2012 9:37 pm

G'day Charles

Thanx for the Technical Bulletin.

Makes for interesting reading.

I really don't know just where my Rebel will come out at, but it seems that it will be a forgiving aircraft.

Regards

Ian

Bob Patterson · Post by **Bob Patterson** » Fri Feb 17, 2012 9:37 pm

Hi Ian !

It sounds like 10.85" fwd and 18.1" aft are the limits to go
with - in the FLYING configuration (with crew & fuel aboard).

Don't be alarmed if your empty CG works out to be much further
aft than 10.85" <IF> you have a Rotax 912 - this is normal. With the
lighter engine, the CG is farther back, and one challenge can be
getting it far enough forward to allow full baggage. It is very
difficult to get over about 1550 lb. and still avoid that aft limit.
(Maybe that's why the factory recommends 1450 lb for the 912 Rebels ..) ;-)

.....bobp

------------------------------------orig.-------------------------------
At 01:29 PM 12/24/01 +1100, you wrote:

G'day Charles

Thanx for the Technical Bulletin.

Makes for interesting reading.

I really don't know just where my Rebel will come out at, but it seems that

it will be a forgiving aircraft.

Regards

Ian
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<BODY bgColor=#ffffff>
<DIV><FONT size=2>G'day Charles</FONT></DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV><FONT size=2>Thanx for the Technical Bulletin.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=2>Makes for interesting reading.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=2>I really don't know just where my Rebel will come out at,

but

it seems that it will be a forgiving aircraft.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=2>Regards </FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=2>Ian</FONT></DIV></BODY></HTML>

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Rick Harper · Post by **Rick Harper** » Fri Feb 17, 2012 9:37 pm

G'day Ian ....(Rick here)

It WILL fly at 7.7"....but it doesn't flare well...it kinda floats & floats & floats & floats and then DROPS
(no ability to round out at the last second )...it's the "theoretical forward limit"
In practice 10 to 11 " seems to be a preferred forward limit (it DOES land nicer !)

Merry Chrissy !

Rick & Wendy

----- Original Message -----
From: allsure (allsure@iprimus.com.au)
To: murphy-rebel@dcsol.com (murphy-rebel@dcsol.com)
Sent: Monday, 24 December 2001 9:28
Subject: Weight and balance

G'day

I am about to try and do the weight and balance calculations for my Rebel, but have found some anomalies.

The construction manual gives limits of +12" & +19.7" whereas the flight operations manual gives +7.7" & +19.7"

What is correct?

What is everyone else using?

Thanks and regards

Ian Donaldson

Wayne G. O'Shea · Post by **Wayne G. O'Shea** » Fri Feb 17, 2012 9:37 pm

Ian, FYI the 912 Rebel that I did, and sold, had an empty weight of 649
pounds and an empty C of G of 12.68". It did not have the rear floor in the
tail cone, nor was it painted. Basic panel, the seats upholstered and a 2
blade wood GSC prop.

Regards and a Merry Christmas to you and yours (and everyone on the list),
Wayne G. O'Shea
www.irishfield.on.ca

----- Original Message -----
From: "Bob Patterson" <bob.patterson@canrem.com>
To: <murphy-rebel@dcsol.com>
Sent: Sunday, December 23, 2001 10:36 PM
Subject: Re: Weight and balance

Hi Ian !

It sounds like 10.85" fwd and 18.1" aft are the limits to go
with - in the FLYING configuration (with crew & fuel aboard).

Don't be alarmed if your empty CG works out to be much further
aft than 10.85" <IF> you have a Rotax 912 - this is normal. With the
lighter engine, the CG is farther back, and one challenge can be
getting it far enough forward to allow full baggage. It is very
difficult to get over about 1550 lb. and still avoid that aft limit.
(Maybe that's why the factory recommends 1450 lb for the 912 Rebels ..)

;-)

.....bobp

------------------------------------orig.-------------------------------
At 01:29 PM 12/24/01 +1100, you wrote:
G'day Charles

Thanx for the Technical Bulletin.

Makes for interesting reading.

I really don't know just where my Rebel will come out at, but it seems

that

it will be a forgiving aircraft.
Regards

Ian
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<META content="text/html; charset=windows-1252" http-equiv=Content-Type>
<META content="MSHTML 5.00.2919.6307" name=GENERATOR>
<STYLE></STYLE>
</HEAD>
<BODY bgColor=#ffffff>
<DIV><FONT size=2>G'day Charles</FONT></DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV><FONT size=2>Thanx for the Technical Bulletin.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=2>Makes for interesting reading.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=2>I really don't know just where my Rebel will come out

at,

but
it seems that it will be a forgiving aircraft.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=2>Regards </FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=2>Ian</FONT></DIV></BODY></HTML>

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rickhm · Post by **rickhm** » Sat Feb 18, 2012 9:40 am

There was a spreadsheet for calculating weight and balance on a SR2500/3500 before the archive was lost. ANyone out there have a copy?

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Scott Aldrich · Post by **Scott Aldrich** » Sat Feb 18, 2012 9:40 am

Rick, not sure which sheet was out there but I just sent you a copy of the
one the Shotwell's made. It is custom for their empty wt and baggage space
arms but easily changed.

Also note they used the main wheel as the zero datum instead of the wing
leading edge like Murphy. Hence their zero datum is 1.5 inches farther
forward and makes the CG range 1.5 inches farther back (10.5 to 21.9
compared to MAM's 9.0 to 20.4), which I am sure you know is the same
physical location. I only mention it as I remember someone saying there was
two different min and max cg ranges published when they are really the same
(15 to 34% MAC)just different datums.

Scott
Moose 174

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of
rickhm@comcast.net
Sent: Monday, November 08, 2004 1:50 PM
To: rebel-builders@dcsol.com
Subject: Weight and Balance

There was a spreadsheet for calculating weight and balance on a SR2500/3500
before the archive was lost. ANyone out there have a copy?

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Rickhm at home · Post by **Rickhm at home** » Sat Feb 18, 2012 9:40 am

Many thanks..... I was about to generate it from scratch! THX

Rick

-----Original Message-----
From: Scott Aldrich [SMTP:sa@mwutah.com]
Sent: Monday, November 08, 2004 2:41 PM
To: rebel-builders@dcsol.com
Subject: RE: Weight and Balance

Rick, not sure which sheet was out there but I just sent you a copy of the
one the Shotwell's made. It is custom for their empty wt and baggage space
arms but easily changed.

Also note they used the main wheel as the zero datum instead of the wing
leading edge like Murphy. Hence their zero datum is 1.5 inches farther
forward and makes the CG range 1.5 inches farther back (10.5 to 21.9
compared to MAM's 9.0 to 20.4), which I am sure you know is the same
physical location. I only mention it as I remember someone saying there was
two different min and max cg ranges published when they are really the same
(15 to 34% MAC)just different datums.

Scott
Moose 174

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of
rickhm@comcast.net
Sent: Monday, November 08, 2004 1:50 PM
To: rebel-builders@dcsol.com
Subject: Weight and Balance

There was a spreadsheet for calculating weight and balance on a SR2500/3500
before the archive was lost. ANyone out there have a copy?

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Don Boardman · Post by **Don Boardman** » Sat Feb 18, 2012 9:40 am

Hi Scott,

I wouldn't mind having a copy.

Thanks, Don B.
DBoardm3@twcny.rr.com

From: Rickhm at home <rickhm@comcast.net>
Reply-To: rebel-builders@dcsol.com
Date: Tue, 09 Nov 2004 21:03:08 -0700
To: "'rebel-builders@dcsol.com'" <rebel-builders@dcsol.com>
Subject: RE: Weight and Balance

Many thanks..... I was about to generate it from scratch! THX

Rick

-----Original Message-----
From: Scott Aldrich [SMTP:sa@mwutah.com]
Sent: Monday, November 08, 2004 2:41 PM
To: rebel-builders@dcsol.com
Subject: RE: Weight and Balance

Rick, not sure which sheet was out there but I just sent you a copy of the
one the Shotwell's made. It is custom for their empty wt and baggage space
arms but easily changed.

Also note they used the main wheel as the zero datum instead of the wing
leading edge like Murphy. Hence their zero datum is 1.5 inches farther
forward and makes the CG range 1.5 inches farther back (10.5 to 21.9
compared to MAM's 9.0 to 20.4), which I am sure you know is the same
physical location. I only mention it as I remember someone saying there was
two different min and max cg ranges published when they are really the same
(15 to 34% MAC)just different datums.

Scott
Moose 174

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of
rickhm@comcast.net
Sent: Monday, November 08, 2004 1:50 PM
To: rebel-builders@dcsol.com
Subject: Weight and Balance

There was a spreadsheet for calculating weight and balance on a SR2500/3500
before the archive was lost. ANyone out there have a copy?

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Rickhm at home · Post by **Rickhm at home** » Sat Feb 18, 2012 9:40 am

All,

Attached is the spreadsheet that I evolved from what Scott gave me. I
don't have the engine hung or wings on, so there is some work to be done
yet! NOTE: This is slightly different than what Murphy sends out. The CG
range is measured from a different reference point. See below for details.

-----Original Message-----
From: Don Boardman [SMTP:dboardm3@twcny.rr.com]
Sent: Tuesday, November 09, 2004 9:27 PM
To: rebel-builders@dcsol.com
Subject: Re: Weight and Balance

Hi Scott,

I wouldn't mind having a copy.

Thanks, Don B.
DBoardm3@twcny.rr.com

From: Rickhm at home <rickhm@comcast.net>
Reply-To: rebel-builders@dcsol.com
Date: Tue, 09 Nov 2004 21:03:08 -0700
To: "'rebel-builders@dcsol.com'" <rebel-builders@dcsol.com>
Subject: RE: Weight and Balance

Many thanks..... I was about to generate it from scratch! THX

Rick

-----Original Message-----
From: Scott Aldrich [SMTP:sa@mwutah.com]
Sent: Monday, November 08, 2004 2:41 PM
To: rebel-builders@dcsol.com
Subject: RE: Weight and Balance

Rick, not sure which sheet was out there but I just sent you a copy of

the

one the Shotwell's made. It is custom for their empty wt and baggage

space

arms but easily changed.

Also note they used the main wheel as the zero datum instead of the wing
leading edge like Murphy. Hence their zero datum is 1.5 inches farther
forward and makes the CG range 1.5 inches farther back (10.5 to 21.9
compared to MAM's 9.0 to 20.4), which I am sure you know is the same
physical location. I only mention it as I remember someone saying there

was

two different min and max cg ranges published when they are really the

same

(15 to 34% MAC)just different datums.

Scott
Moose 174

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of
rickhm@comcast.net
Sent: Monday, November 08, 2004 1:50 PM
To: rebel-builders@dcsol.com
Subject: Weight and Balance

There was a spreadsheet for calculating weight and balance on a

SR2500/3500

before the archive was lost. ANyone out there have a copy?

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rickhm · Post by **rickhm** » Sat Feb 18, 2012 9:40 am

This message contains attachment 2 of 2.
See message 32344 for further information

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