# Does the weight of a pilot exponentially affect the necessary weight of man-powered aircraft?

The MIT Daedalus, a man-powered craft, weighed about 31kg. This will be significantly lighter than its pilot during its record setting trip, though I can't confirm his exact weight. Still, this raises the question: If the pilot had been half the weight, would you be able to safely reduce the Daedalus weight by more than half (aka: exponentially instead of linearly)?

Since smaller birds seem to have an advantage over larger ones, I would assume it'd be easier to achieve flight with a smaller pilot.

Note that the pilot is not half weight due to being malnourished or lacking musculature. The half weight was meant as an easy example. If someone has an example for a 20% lighter pilot, that should be useful.

• Are you familiar with surface to volume ratio as it applies to scaling? Commented Aug 14, 2022 at 19:39
• Is this about getting airborne, or flying the distance between Crete and Santorini? Scaling up lets distances shrink and vice versa. Commented Aug 14, 2022 at 23:42

While the weight of the pilot of the Daedalus 88, Kanellos Kanellopoulos, is unknown/hard to find...I would posit that an adult male 1/2 his weight would lack the musculature to power the thing.

Going by other world class cyclists weight (Greg LeMond, Lance Armstrong, Eddy Merckx) 150-160lbs (68-72kg)....a 35kg human would absolutely lack the power to drive that thing, no matter how little it weighs.

Additionally, the airframe has to be strong enough to handle the thrust and torsion. Not just the weight of the pilot.

I expect if they could have built a 16kg airframe strong enough, they would have.

• Shotaro Iribe weighed 60kg, and he was a national champion. Eri Yonamine is 50kg. 12yo Gurdev Thakur managed 45km over hills in under three hours, which is fairly impressive when the record for most distance cycled in one hour is only 55km. So if the cyclist was half the weight due to lack of muscle mass, and not due to smaller general size, this would be correct. But it doesn't actually answer the question.
– Nail
Commented Aug 14, 2022 at 19:09
• Is it possible to answer this comparing hill climbing vs flat races? If a smaller human has a power to weight advantage this should show up as a shift in body weight of winners over flat races where presumably power to frontal area/drag is more important. Commented Aug 15, 2022 at 8:14

This would make sense in the aviation world by considering the pilot as an engine. We would need to know the feasible output of the engine vs the all-up weight of the aircraft.

Weight differential of the pilots would be small enough to limit aircraft modifications to perhaps an extra wing panel. G limits for these delicate man-powered aircraft are low.

The real difference is how much drag is saved with a lighter pilot vs how much less thrust the smaller pilot can provide. Rearranging the lift equation shows lift is proportional to Area.

Area = Lift/(density×Coefficient×Velocity$$^2$$)

Then compare Drag of reduced wing area to thrust output of the smaller pilot. It may turn out the larger pilot, or engine, will be better.

• The engine weight vs power comparison is spot on! Commented Aug 14, 2022 at 23:16
• I think a human generates like a quarter a horsepower? We could go with that estimate, and say the half-weight pilot generates 1/8th HP. We could have them weigh 40kg and 80kg.
– Nail
Commented Aug 15, 2022 at 5:38
• @Nail really looking at thrust here. A large slow prop is very efficient, as is a slow aircraft with large wings for lifting. Interestingly, with a larger pilot, Mass = Pilot + Airplane will have a higher % pilot. I would find the pounds of drag to fly (based on glide ratio), and consider a Daedalus built for two! Commented Aug 15, 2022 at 15:25