Thom Riddle
Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)
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 Posted: Mon Feb 13, 2006 6:00 am Post subject: Limit Load Ratings and their effects |
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Paul at Aero-Siam brought to my attention something that should probably be posted here about Limit Load ratings. The Allegro is rated at 4.0+ and 2.0- Gs at a flying weight of 520 kg or 1,146 lb. In the USA, the Allegros have a gross weight limit of 1,232 lb. so the pilot/operator must be aware that if flying above the 1,146 lb. Limit Load Rating weight the actual limit loads must be adjusted downward for the additional weight.
At 1,232 lb. the flying weight is 7.5% heavier than the rated Limit Load weight of 1,146 lb. The ACTUAL LIMIT LOADS for the Allegro flying at 1,232 lb. will be 3.7+ / 1.9- Gs, not the 4.0+/2.0- in the Allegro documentation. These numbers are derived by dividing the 4.0 and 2.0 by 1.075, the increased weight factor.
ALSO, be aware that the LANDING GEAR may be designed for a MTOW of 1,146 lb. and operating at 1,232 lb. should be done with caution, particularly in landing operations, to avoid undue stress in the landing gear and associated components. A hard landing at 1,146 lb. may be sustainable but the same rough landing at 1,232 lb. might cause cracks or failure of the landing gear.
The Stall Speeds are also affected by flying weight but not by the same factor. The Allegro manual says the Calibrated Airspeeds at stall for the three flap positions were taken at 1,146 lb., as follows:
FLAP 0 43 knots or 49.5 mph
FLAP 1 39 knots or 44.9 mph
FLAP 2 35 knots or 40.3 mph
Since LIFT is a function of the square of airspeed the increase in weight to 1,232 lb. (7.5% increase) does not affect the stall speed by this amount. It affects it by the square root of this increase, 1.075^.5 = 1.037
The Calibrated airspeeds at 1,232 lb. should be as follows:
FLAP 0 44.59 knots or 51.3 mph
FLAP 1 40.44 knots or 46.5 mph
FLAP 2 36.30 knots or 41.7 mph
Thom in Buffalo
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