Minimum hp needed for powered flight?

I understand an answer to this question presupposes a myriad of technical specifications (such as drag coefficient, area of wing, wing design, friction and drag on propellors, etc.) but I essentially am looking for a general figure or even just some insight to this. I'm currently building a plane in my friends backyard and have begun wondering about building another one weighing around 273 pounds dry. For this plane, I am toying with the idea of using two 66cc 2 stroke engines that are sold very cheap as parts of a motorized bicycle kit, and two small propellors. I've read these motors put out around 1.5-2 horsepower each, but can be safely tuned to make around 4-5 (for a total of 10). Do you think this amount of power would be sufficient for powered flight given the weight of the craft? (Plus 34 pounds of fuel and 140 pound me, and maybe a 35 pound ballistic parachute). Ive read before that around 20 hp is the minimum for safe powered flight, but have no idea how this was calculated. If anyone has insight on this (or where to buy very cheap propellors) it would be much appreciated

Zaphod Beeblebrox

For something with around 400-500 pounds gross weight, IF you had sufficient wing area, about the minimum would be 25hp for sustained flight near sea level in cool temperatures. For safe performance margin you should have about 35hp. Besides that, you'd need an engine that could swing large, efficient propellers at a low rpm around 1,500) . Without a gear-reduction drive, those little engines you are looking at wouldn't work at all and they don't develop nearly enough power and a propeller won't work at the high rpm where they operate at full power.. In other words, you're dreaming and you need to learn the basics of aircraft engineering and design.


No, not much of a chance I'd say - shooting from the hip. It all depends on the glide ratio you can achieve, given the competing factors of wing length/surface area, overall aerodynamics and gross weight. If you know the glide ratio and gross weight, you can make a straight forward determination of required power to achieve a particular minimum rate of climb (essential if you are self-launching from a runway). An enigne under 100 cc seems extremely feeble for the weight. I once calculated an 18 hp motor to provide 200 ft/min climb of a sailplane with a 25 in 1 glide ratio. This, of course, is a very efficient design and the weight of the sailplane was probably about the weight you are anticipating. You can convert the weight and descent, at a particular glide ratio, into a negative power. This determines the power required to maintain level flight. Then you add to this power to provide an acceptable rate of climb. It is an interesting problem to puzzle over.

thomas f

I have read that bumblebees can achieve powered flight for less than 1/1000th hp.