Thom Riddle
Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)
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 Posted: Sat Dec 09, 2006 6:37 am Post subject: Empty weight and C.G. LocationEmpty weight and C.G. Location |
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Hugh,
The maximum legal weight for an LSA in the USA that is not equipped for
water operations is 1,320 lb. Equipped for water operations, the max is
1,430 lb. BUT each manufacturer can specify any MTOW for their aircraft
at those weights or lower. The Fantasy Air USA website shows the MTOW
at 1,232 lb. I did some calculations on change in Vs1 based on MTOW of
1,232 lb. vs. 1,146 lb. At MTOW of 1,232 lb. the Vs1 is just within the
legal limit of LSA stall speed which is 45 knots. That is probably
(just and educated guess) the reason they chose 1,232 lb. for the MTOW
for LSA category, since a MTOW of higher than that would have
disqualified it by virtue of the higher stall speed.
As I said, the airplane handles fine at over 1200 lb. But the load
limit at 1,232 lb. must be factored downward from the +4g/-2g numbers
that were determined at 1,144 lb. Positive flight loads of 4 g at 1,146
lb. would equate to 4 x 1146 = 4,584 lb. Thus at 1,232 lb, a total
flight load of 4,584 would be equivalent to a 3.72g load limit at 1,232
lb. (4584/1232=3.72). Do similar math for the negative load limits.
These numbers are still very close to the required minimum load limits
for standard category aircraft like Cessnas (+3.8g).
There are other factors that should be considered when the designers
calculate a MTOW, including the forces on the landing gear,
particularly during landing operations. This may be one of the reasons
they increased the dimensions of the main landing gear since the early
design to accommodate the heavier MTOW in LSA category.
Also, the CG limit range is between 25% and 35% of mean aerodynamic
chord (MAC) which is 44" on the Allegro 2000. 25% of 44" is 11" for the
forward limit and 35% of 44" is 15.4" for the aft limit. The location
of the empty weight CG has no real significance, as long as the CG is
within this range when in operation. CG range in light aircraft rarely
exceeds 5" from fore to aft limit and the Allegro 2000 limit range is
4.4" (15.4-11), so that is a normal CG range. Unless you go way way
over the baggage limitation, it is difficult for typical American sized
pilots and passengers to get out of CG range in the Allegro as long as
you do not exceed the MTOW of 1,232 lb.
Attached is an Excel spreadsheet of my our W&B. You can modify this to
suit your airplane. You may notice that the location of the baggage arm
on my spreadsheet is further back than what the factory gives us. My
numbers are from measuring to center of the baggage area not the
bulkhead just behind the seats. Please use your own numbers as this is
for our airplane only.
If for some reason the file is not attached (have had troubles with the
attachment process) and you want a copy of my spreadsheet, email me
directly.
Thom in Buffalo
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_________________
Thom Riddle
Buffalo, NY (9G0)
Don't worry about old age... it doesn't last very long.
- Anonymous |
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