[rebel-builders] SR Manual errors in weight and balance
Posted: Sun Feb 19, 2012 11:13 am
I used different moment arms than published on the Rebel as well. Things
like the average c of g of an average pilot, or the average c of g of
typical baggage, are little more than guesses for the paperwork. Even
the fuel moment may only be valid with full tanks and level attitude
which is not particularly accurate for landing a tail dragger with 1/4
tanks and fuel back against the bulkhead. No one questioned the moment
arm numbers I used but fortunately I don't believe they are published on
MAM's website. Our Canadian authorities have been known to quote
weights from MAM's website though. I guess the bureaucracy provides
safety value in some cases but it also usually dumbs things down and
stifles innovation somewhat...
Ken
Mike Kimball wrote:
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like the average c of g of an average pilot, or the average c of g of
typical baggage, are little more than guesses for the paperwork. Even
the fuel moment may only be valid with full tanks and level attitude
which is not particularly accurate for landing a tail dragger with 1/4
tanks and fuel back against the bulkhead. No one questioned the moment
arm numbers I used but fortunately I don't believe they are published on
MAM's website. Our Canadian authorities have been known to quote
weights from MAM's website though. I guess the bureaucracy provides
safety value in some cases but it also usually dumbs things down and
stifles innovation somewhat...
Ken
Mike Kimball wrote:
I know no-one would take position locations from the builder's manual weight
and balance section as gospel without double checking yourself but check
this out.
Builder's Manual
Pilot and passenger - 16
Fuel - 30
Rear Passengers - 46
Baggage - 49
My Measurements
Pilot and passenger - 24
Fuel - 30 (hard to determine so I'll go along with their number for this)
Rear Passengers - 65
Baggage - 86
They have the baggage only three inches behind the location of the rear
passengers for crying out loud. There's also a math error in one of their
moment calculations. I do have the rear passenger seats at the rearmost
point on the tracks but I can't see how you can get 46 inches aft of the
main gear leg. My measurement for baggage is to the middle of the baggage
area.
I think it's funny that the 30 inch separation between front and rear seats
is pretty close to the typical separation on airliners. In reality on a
Super Rebel, with the front seats in position to operate the controls and
the rear seats all the way back (why not after all) there is a much nicer 41
inches of separation. This also puts the rear seat passengers in just the
right spot to look out their window and use the horizontal channel on the
side walls as an arm rest.
In case anyone cares, for the center of my rear baggage area (two bay
extension) I get 124 inches. My battery and ELT are at the rear of that
baggage area helping to compensate for my heavy engine. Also, in case
anyone is interested, I came in at a hefty 1844 pounds and 7.6 inch CG
empty. That's nose heavy ahead of the forward limit by 2.1 inches but when
I add a little fuel and myself the CG comes into range. Add anything else
and it just gets better and better. Solo with light fuel (say 15 gallons
total) and no baggage puts the CG almost an inch behind the forward limit
which is pushing it so it's best to fly with more fuel and something in the
baggage area.
Mike
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