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Howdy again,
After reading NTSB reports that attribute the cause of the accident to exceeding the airplane's maximum takeoff weight, I began wondering about the effects of an overweight takeoff within C.G. limits. Specifically, what would I have to do differently when flying an airplane that's heavier than what the POH specifies. I am not supporting the practice, of course, so let it be purely educational. Corrections, additions, and comments welcome. I would start by considering the increase in weight as comparable to an increase in load factor. Hence, all your aoa-related speeds would increase by the square root of the load factor. Vs, Vx, Vy, Vglide, etc. would all increase. Va would also go up. Now, by virtue of rotation speed being a function of stall speed, I conjecture you'd have to liftoff at a faster airspeed which would equate to a longer takeoff roll. Then, after pitching for your faster Vy airspeed, you'd notice a decrease in climb rate at full power due to the increased power requirement. During cruise, you'd notice a reduced cruise speed and an increase in stall speed. At approach to landing, should you bump up your approach speed, you'll find yourself sinking faster when chopping off the power even though your glideslope will remain the same. Since your stall speed is invariably higher, you'll eat up more runway when landing. So to sum up: Takeoff: higher takeoff distance, higher rotation speed. Climbout: lower climb rate at higher Vy speed, same angle of climb for obstacle clearance at higher Vx speed. Should Vx not be flown faster, a poorer angle of climb would result, making obstable clearance doubtful. *I may be wrong here* I am not sure if the max. angle of climb is constant regardless of weight...my calculations don't show so...could someone clarify? Cruise/Maneuvering: lower cruise speed, higher maneuvering speed, higher clean stall speed. Approach to maintain glideslope & descent profile: higher approach speed, higher sink rate for a given power setting. Higher dirty stall speed. Landing: higher landing distance Question (1 of 2): Seems to me that flying "overweight" is possible if you're aware of the performance reductions. So why do you read so many NTSB reports with probable causes listed as "overweight takeoff, exceeded performance limitations"? As you slowly pull the yoke to rotate, wouldn't a pilot *realize* through control forces, feel, gut feeling that something is wrong? Question (2 of 2): When considering accidents due to exceeding maximum takeoff weight, do the majority occur during takeoff? If so, is it typically due to not reaching proper liftoff airspeed for that increased weight, stalling, and spinning to the ground? Would this scenario be consistent with failure to set the flaps/slats to their takeoff value? Alex |
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