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# Formula to determine thrust using area, torque, pitch, etc?

## Formula to determine thrust using area, torque, pitch, etc?

(OP)
I'm a computer geek with an idea, but I'm a bit lost as to implementation and need the formulas to work with.

I'm trying to design a variable-pitch dual blade VTOL.  I can 'do the math' if I know what the input for the problem is.  The way I see it, I have to design the blades based on the engine and adjust the pitch from zero (no thrust) to x degrees (maximum thrust) at y RPM and z torque (or efficiency), but I have no idea what the formula is for diameter, width, speed, area, torque, etc...  I expect the blades to be straight, as opposed to curved, recurved or anything like that - the math for that is way too hairy.  This is a straight thrust vector problem, applying the thrust straight down and I'm not planning on using rotation of pitch for forward propulsion as with a helicopter.  It's not something I studied in engineering dynamics.

I have a gross vehicle weight in mind, but can adjust it as needed depending on materials used, engine needed, and a few other items.  But I need to do the math before I start the design so I know what kind of specifications for the powerplant and rotors I'll need for various weights in the design.  Aerodynamic flow is actually not much of a consideration.  It ain't gonna be a fast craft (about 100-150 MPH tops)

Oh, and does anyone know the thrust to weight ratio for a straight ascending line at, say, 250 and 500 feet per minute may be?  I don't expect the crafct to go higher than, say 10,000 feet, and I can deal with air density changes once I know where they go in the formula.

Can anyone help?  Thanks in advance!

### RE: Formula to determine thrust using area, torque, pitch, etc?

Its not cook-book, there are infinite variables, and even the experts get it almost right sometimes.
I would suggest Rotary Wing Aerodynamics, by Stepnewski and Keys, Dover publications, as a good basic discussion.  But designing blades is one tough job, structurally and aerodynamically.  It is a critical structure, in a whirling centrifugal field, with dynamic stability concerns, attachment structural concerns, structural modes, dynamic oscillations, and the like to make it complex.  Plan to pack a lunch, it is an all-day job.

### RE: Formula to determine thrust using area, torque, pitch, etc?

nlappos hit the nail on the head. In addition to the publication he suggests....Read pubs by Ray Prouty or try to contact him via email...I think he writes for Rotor&Wing again.

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