=SUZUKI G13=

-3-blade 1.7m propeller =180 kG thrust

-2*2-blade 1.7 m CR propellers=230 kG...

https://www.dropbox.com/s/ky1z5jc9g3srohq/Dym - zwolnione tempo.mp4?dl=0

Maybe static thrust can be improved this way, but a bigger simple prop could do it too. Now static thrust and dynamic thrust are two different animals.

You can do all sorts of things to make more thrust statically, even hover. Look at the human powered helicopters out there. Huge rotors, one human making about 1 hp can get them to just barely hover in ground effect for a few seconds.

Just because you can make big thrust statically does not mean that that this thrust increase will hold up as you pick up some speed. Once you are moving at flight speeds, thrust is absolutely limited to the inverse of airspeed, and the following equation fits the world really well:

HP*eff*550 ft-lb/sec = F*V

which solves to

Thrust possible = HP*eff*(550 ft-lb/s)/V

Where HP is your horsepower at the prop flange,

eff is your propellor efficiency which varies but will be around 85% and never reaches unity,

550 ft-lb/s is the work of 1 hp, so turns hp in to terms of thrust and speed,

V is velocity in Ft/s;

Once you are going flight level speeds, the thrust you can make with the prop goes down inversely with speed. Yeah, if you make V small, the equation says you can make awesome thrust statically, but another relationship (with its own equations limits you too:

mdot*dV = Thrust

1/2*mdot*dV^2 = HP*eff*550 ft-lb/s

where mdot is the mass flow of air per second through the prop, and dV is the change in velocity imparted. Statically, dV is the speed of the air through the prop and mdot is the mass density of air. If your prop got you the same dV everywhere through the disc (it does not so you can not do this well, but it gives us an upper bound), mdot = rho*dV*PI()*Dp^2/4 where rho is the mass density of air, dV is the same as befor and Dp is prop diameter. Substituting, we find that:

(rho*dV^3*PI()*Dp^2)/8 = HP*eff*550 ft-lb/s

Solving for V and D...

dV^3*Dp^2 = (8*HP*eff*550)/(rho*PI())

Then assuming a Dp to get the V limit

dV^3 = (8*HP*eff*550)/(rho*PI()*Dp^2)

Take the cube root of that last equation and you can compute thrust based upon prop diameter and horsepower... Once you have done that, there are practical limits on prop blade size and how much prop 1 hp can drag around in a circle, which then drives gearing, etc.

I ran you guys a quick spreadsheet. All of this is off the top of my head, so I may have missed something in computation of the exact numbers, but all of the concepts are there. Big thing is that statically, you can get huge thrust by using big props (or rotors), but to fly anywhere, you also need dynamic propulsion. Pursuit of static thrust can get in the way of dynamic propulsion. Props end up being compromises based upon what you are doing. If you are running slalom courses or drag races from a standstill in an airboat, by all means, grab all the thrust the rules will allow. But if you want your airplane to go places, you might find other stuff to be important.

Billski