Watts per lbs

 

The 1903 Wright Flyer was 605 lbs without the pilot.  It flew on 12 hp.  If we use 750 watts per hp that is 9000 watts.   If we say 195 lbs for pilot the total weight is 800 lbs.   So 9000 watts/800lbs is  11.25 watts/lb. 

 

The Wright Brothers estimated that a 1 lb crow expended 7.68 watts to fly.   In a comment to that article someone says they made a 2 lbs solar airplane that only needed 18 watts to stay in the air, so 9 watts/lb.   We would like to be able to do that.


The guidlines for rc airplanes say:

  • Less than 50W/lb - very lightweight / low wing loading slow flyer.
  • 50 to 80 W/lb - light powered gliders, basic park flyers and trainers, classic biplanes and vintage ('Old Timer') type planes.
  • 80 to 120 W/lb - general sport flying and basic/intermediate aerobatics. Many scale (eg warbirds) planes suit this power band.
  • 120 to 180W/lb - more serious aerobatics, pattern flying, 3D and scale EDF jets.
  • 180 to 200+W/lb - faster jets and anything that requires cloud-punching power!

 

Part of the trouble with under 50W/lb planes is taking off.  Cruising at less than that is not so bad.   We are thinking that a supercapacitor can help with takeoff and then the solar power for cruising.

We are thinking of a peak solar of about 90 watts.  Anguilla is about 18 degrees North of the Equator.  When flying level, in direct sun, at 9am we might get 50 watts (should be nice online calculator for this but did not find it yet).     

We hope to be around 2 lbs, so if we can have an efficient airplane we should be ok for power.  To stay up all day could take some cloud dodging, but that seems like it might be fun.   Efficiency is very important. 

I think a good way to think about power requirements is the formula:

    power = speed * weight / efficiency

We want to increase efficiency, reduce weight, and we will at least start with low speed.    If we have plenty of power we can go faster. 





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