4 ms·

Why don't they automatically measure the actual airplane weight with sensors instead of doing this weird estimation? Based on the article, it seems like they o

by devit 5y ago

Why don't they automatically measure the actual airplane weight with sensors instead of doing this weird estimation? Based on the article, it seems like they only use that to determine how much engine thrust is needed for takeoff, so it doesn't seem they need to know the weight in advance.

Someone1234 5y ago
Cost. We have the technology to weigh aircraft. But they'd either be onboard, and thus safety critical and subject to a lot of abuse (being inline with the landing gear presumably), or they could be on the ground/at the airport, which means every airport in the world needs them, and they need to be compatible with every aircraft's footprint (i.e. huge or highly adjustable). Plus the time cost/queuing for getting weighed. Then adding fuel after (since fuel is based somewhat on weight).
- Cthulhu_ 5y ago
  Plus it's infeasible to retrofit all planes in service now (going back 30 years or so? I vaguely recall that planes are kept in service for that long) with weight measuring systems. But that's probably the issue here as well, compatibility with software systems going back 30, probably more years.
  - devit 5y ago
    What about a simple software dynamic control system with an accelerometer then? Basically you apply some thrust to the engine and look at the resulting acceleration with an accelerometer. Knowing the remaining length of the runway one can compute the acceleration that produces takeoff velocity at the end of the runway minus a safety margin, and then change engine thrust by the ratio between that desired acceleration and the measured acceleration. The remaining length of the runway can be computed by knowing the total length, initial position and integrating the accelerometer data, or by using GPS knowing the coordinates of the runway ends. This also automatically handles factors like wind, variable friction on the runway and miscalibrated engine thrust.

by devit 5y ago

Someone1234 5y ago

Cost. We have the technology to weigh aircraft. But they'd either be onboard, and thus safety critical and subject to a lot of abuse (being inline with the landing gear presumably), or they could be on the ground/at the airport, which means every airport in the world needs them, and they need to be compatible with every aircraft's footprint (i.e. huge or highly adjustable). Plus the time cost/queuing for getting weighed. Then adding fuel after (since fuel is based somewhat on weight).

Cthulhu_ 5y ago
Plus it's infeasible to retrofit all planes in service now (going back 30 years or so? I vaguely recall that planes are kept in service for that long) with weight measuring systems. But that's probably the issue here as well, compatibility with software systems going back 30, probably more years.
- devit 5y ago
  What about a simple software dynamic control system with an accelerometer then? Basically you apply some thrust to the engine and look at the resulting acceleration with an accelerometer. Knowing the remaining length of the runway one can compute the acceleration that produces takeoff velocity at the end of the runway minus a safety margin, and then change engine thrust by the ratio between that desired acceleration and the measured acceleration. The remaining length of the runway can be computed by knowing the total length, initial position and integrating the accelerometer data, or by using GPS knowing the coordinates of the runway ends. This also automatically handles factors like wind, variable friction on the runway and miscalibrated engine thrust.