BSDGuy

I've noticed that Motocalc says that the propeller is "stalled" with some high pitch combinations.

Anyone care to go into this? It seems that adding pitch doesn't add thrust when this happens but it adds thrust "in flight".

Motocalc will show that after gaining airspeed the rpm's will DROP, and then climb again.

I'm curious about this phenomenon, and what it means to us when picking props, etc...

Steve Lewin

I think the Motcalc help for this explains it pretty well. It basically means that prop doesn't work well until the plane gets up sufficient speed. Typically that translates into poor take-off or needing a bungee or real hard hand-launch to get going.

Steve

BSDGuy

It only shows it stalled for the first 3-4 mph, and plenty of thrust.

I have a motor/gear/prop combo that motocalc says is propeller stalled while static, but it makes plenty of thrust. I was just wondering what the terms mean and what the theory is. I'm a technical junkie, and like knowing all the details

aeropenguin

My Feedback: (1)

it is when the propeller is not moving air back (which makes the plane go forward, since you are pushing off of the air) but it is either going SO fast at too many RPM's, or it has so much pitch that it is just beating the air like a mixer for smoothies
the plane will not move anywhere, since it is beating the air rather than slicing through it. Of course, you will get moving, just that it will take a lot longer to get started. With a square prop (5x5, 9x9, etc) you will have to nusge the plane, or toss it really hard, or even bungee it so it has speed, and the prop begins slicing the air again, and giving thrust. Once this happens, the prop will give a lot more thrust, and that is why the "in-flight" thrust gets bigger, but the static thrust (when the combo is not moving, such as a bench test, or during hovering) gets smaller.

Well, hope that helps!
-Michael

Steve Lewin

I know what you mean, I like to learn stuff too, even if it is of no practical use so....

A propeller is very similar to a wing, It has an airfoil, angle of attack etc. It just happens to rotate throught the air rather than going straight through. "Stall" means exactly the same for the prop airfoil as it does for a wing airfoil. Basically it's not delivering the maximum lift (or in this case thrust) because the flow over the airfoil is breaking up. With the plane moving, the air approaching the prop is "angled" and so allows the flow to smooth back out and lift/thrust gets back to the correct maximum value.

That's a horribly oversimplified version but if you want to get into the real theory have a look at Martin Hepperle's wonderful site http://www.mh-aerotools.de/airfoils/index.htm It has a specific section on Propeller design including static thrust. But be prepared for some reasonably complex mathematics to really understand what's happening.

Steve

e-bird

Like some else said motorcalc at what speed the stall last
if you presist in useing that prop let the bird get a little airspeed
then no more stall. CU