Like a lot of things it’s a matter of balance. Static thrust is useful knowledge.
So is torque
Both are more useful as part of a series of information.
Perhaps a 50,000 hp engine that turns 25 RPM Doesn’t sound very useful.
But if that’s turning an appropriately sized and pitched propeller on a large ship it becomes a thing of beauty.
Yes, going to a coarser pitch would load up the prop more and allow you to use more of the engine's available HP (by not exceeding redline). But you mention that your concern was in getting more HP for high altitude takeoffs, and under those conditions it would seem that choosing a longer prop (rather than more pitch on a prop of the same length) would be a better way to use the available HP at redline to get more takeoff thrust. Compared to increasing the pitch, increasing the diameter will move more air during the low-speed takeoff roll and your blades will be un-stalled earlier, which will increase the prop's efficiency.Here’s a prop pitch question as it relates to altitude. I have a Rotax 914 (turbo) with a ground adjustable prop. I am happy with the takeoff, climb, and cruise performance with the current pitch setting. However, I recently did some high altitude takeoffs and discovered the engine would exceed redline at full throttle. Would increasing the prop pitch allow full throttle without over speeding max rpm? Low speed thrust is important too so I would not want to go too coarse. Thoughts?
Wow huge engine with a operating range of 22-120 rpm
With a caveat. The twist ratio is still a compromise for efficiency at multiple speeds no matter what the pretty cartoons that show the CS prop efficiency curves riding over the crests of a series of fixed pitch prop efficiencies show.This is why the constant-speed propeller is the best form of propeller propulsion. Its pitch changes to get the best efficiency for any speed and power setting.
Yes, a really good CS prop would have more pitch change at the tips than at the roots. Pretty hard to achieve without an awful lot of mechanisms inside the prop, and the blade would have to be either really flexible, or in numerous sections. An engineering nightmare.With a caveat. The twist ratio is still a compromise for efficiency at multiple speeds no matter what the pretty cartoons that show the CS prop efficiency curves riding over the crests of a series of fixed pitch prop efficiencies show.
A CS prop that accommodates from takeoff through, say, 180 knots will likely slow down an airplane designed for the same engine and 260 mph, although the faster plane might break ground a bit sooner with the slower compromise CS prop. The distribution of AOA changes with forward speed, with more of the blade further away from optimal AOA as speed rises for a prop designed for lower speed performance, similar to higher speed compromises giving up low airspeed performance.
Considerable effort was put into aeroelastic blade effects to eak out higher airspeed performance. The idea was to design a prop with the right response to flex at high pitch/high airspeed to gain a few to several extra percent prop efficiency when it would normally fall off. It was successful, and there are NASA tech briefs on this from the 80's. I still don't know why the efforts never really went anywhere.
How about this....get the straight and level full power red line airspeed.....Put the airplane in a wind tunnel, (take the propeller off ?) and measure the drag at that airspeed, calculate the force/thrust/hp from those measurements?hp of an airplane propeller/engine combination
-If a person is using static thrust in order to know the HP of an engine, he would be much better off to measure it using a calibrated test club using the Eiffel method. Costs less than a fish scale.So is there any real number that can corelate with one of the 3-4 formula found on different topic ? As a real plane with a 'fish scale' at the tail will give quite the real number.
I think you misunderstood Dan... he's saying it IS torque x rpm.
If we want to know the thrust at airspeeds up to about 70 mph, we could put the prop, engine, and stand on a flatbed trailer and measure the pull it can produce while going 70 mph. Then, add to it the aero drag from the engine, stand, etc as appropriate (or, build a streamlined cowling and call the drag equal to the aircraft's scrubbing drag in the propwash).How about this....get the straight and level full power red line airspeed.....Put the airplane in a wind tunnel, (take the propeller off ?) and measure the drag at that airspeed, calculate the force/thrust/hp from those measurements?
P=U*I ...simple power measuremant, aspatially DC !THP/BHP equals propeller efficiency.