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Electric aircrafts and most drones have simple powertrains, and their weight does not vary along the flight. After reviewing this thread I assume that:

MTOW = Empty weight (batteries incl) + max payload ?

I have reviewed some drone specs, and sometimes the numbers match, others don´t. Am I missing something?

Air Canada 001
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zaumo
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    At least conceptually, an electric aircraft might have optional batteries that could be installed or not depending on the required range. Those wouldn't quite be "payload," nor would they be "empty weight" either. A long-range mission on such an aircraft might use max batteries & be able to carry less payload weight than a shorter flight than only needed the installed batteries. In either case, takeoff weight would be limited by max certified takeoff weight, unless performance becomes more limiting (high altitude field, hot weather, short runway, etc). – Ralph J Apr 17 '20 at 21:07
  • https://en.m.wikipedia.org/wiki/Operating_empty_weight – user3528438 Apr 17 '20 at 23:01

2 Answers2

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A maximum payload may be specified to be less than tested MTOW minus empty weight in some cases, as a precaution against conditions that may reduce MTOW -- which depends on strip elevation, barometer, and temperature.

The thinner (higher and hotter) the air, the less a given amount of power can lift, in the case of a quad-copter or similar aircraft, or the longer it will take to reach takeoff speed and the slower climb will be, in the case of a conventional winged drone (electric or otherwise, though at least electric motors don't lose power with altitude). Responsible drone manufacturers may (and should) specify a maximum payload spec that will keep gross weight below the least MTOW for foreseeable conditions.

There may also be cases where, for one reason or another, payload is based on testing conditions different from your flight configuration -- for instance, if you're using a heavier battery pack than the one used for testing, you'll have less margin below MTOW than the test condition. Payload limits may also be specified below MTOW minus empty weight for reasons of center of mass location, payload restraint limitations, or other engineering reasons.

Zeiss Ikon
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  • So it sounds like you're saying that the end result is, Max Takeoff Weight is unreachable if all other limits are met. In transport aircraft, the reverse is always the case: MTOW is not only reachable but could be exceeded (i.e. max fuel+max cargo+max pac) - thus MTOW places a limitation on the operation, and it must be observed. Along with many other limitations, such as performance requirements (which themselves may keep you well below the certified MTOW in a hot, high altitude case). – Ralph J Apr 17 '20 at 20:59
  • @RalphJ At this time, there are no all-electric transport aircraft. The question spoke about electric aircraft and drones. For drones, especially, payload specification may be specifically nerfed to avoid exceeding MTOW, because manufacturers hate having to explain to "users" that their drone won't take off today with the same load it lifted last Sunday, because it's too hot out. – Zeiss Ikon Apr 17 '20 at 22:59
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There is a difference between MTOW and the actual weight of the aircraft and payload. MTOW, or Maximum Take/off Weight, is the amount of weight the aircraft is certified to carry on takeoff. 99.99% of the time, the actual weight of the aircraft and payload is lower than the MTOW. But I think you know this. I think what you meant was does the MTOW include the empty weight, or is it just maximum payload.

In that case, yes, MTOW does include both the MAXIMUM payload and the EMPTY WEIGHT of the aircraft (including electric).

Air Canada 001
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    How does your answer change in the case of an electric aircraft vs a conventional aircraft? That's the point of the question. – Ralph J Apr 17 '20 at 21:01
  • Oh didn't read it properly. But I don't think it changes much, does it? – Air Canada 001 Apr 19 '20 at 14:38
  • @AirCanada001 This answers a different question... I'm inclined not to delete in the event you can edit it to address the specifics of electric aircraft. – Therac Apr 19 '20 at 18:38