What is the lift to empty weight ratio of some popular modern helicopters?
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4$\begingroup$ This question cannot be answered as it is. It's too broad for one thing, and you are asking for people's opinions rather than facts. Plus, I don't have any idea what you are actually asking. $\endgroup$ – GdD Oct 1 '17 at 19:09
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$\begingroup$ Your question about pros and cons is mostly a legal and financial one, not an aviation one. We might be able to help with technical issues for your prototype, though, if you have any specific questions. $\endgroup$ – Pondlife Oct 1 '17 at 22:38
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$\begingroup$ I have edited my question. Thank you. $\endgroup$ – David Walden Oct 2 '17 at 12:53
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1$\begingroup$ I have edited your question further to really focus on the aviation part of the question, making it more likely you get a good answer. You can rollback my edit if you disagree. $\endgroup$ – Sanchises Oct 2 '17 at 14:10
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3$\begingroup$ Popular according to whom? Popular for what purpose? $\endgroup$ – user Oct 7 '17 at 21:25
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From Prouty: Helicopter Performance, Stability and Control: the example helicopter that is referenced throughout the book, to illustrate the equations used and computations made.
The rotor thrust T is a function of blade geometry and number of blades. The blade is just a rotating wing and maximum thrust is a function of the lift coefficient $C_l$ of the blade profile. Rotor thrust is also a function of rotor disc area and number of blades.
The example helicopter has the following characteristics:
- Design gross weight = 20,000 lb
- Minimum operating weight = 10,700 lb
- Main rotor radius = 30 ft
- Blade geometry: chord = 2 ft, airfoil = NACA0012, 4 blades
The average lift coefficient of the blade is computed on page 18 as $C_l$ = 0.52 at sea level, for the design gross weight. NACA 0012 has a maximum $C_l$ of 1.2, which makes the maximum rotor thrust at sea level:
$$ T_{max} = 20,000 * 1.2 / 0.52 = 46,153 lb $$
So maximum lift divided by minimum operating weight is 46,153/10,700 = 4.3
Since NACA0012 and 0015 can still be found in many helicopters, this would be the general order of magnitude for popular type helicopters. A max lift/empty weight of about 4. Further variations are due to disk loading: higher disk loading means a higher $C_l$ to lift off.
