# static thrust vs. prop RPM data?

edit: question was too long, and is actually simple, so I removed unneccesary description

Background:

There are many questions here about:

• propeller efficiency
• changes to thrust when it is dynamic
• calculating the prop thrust for a given power
• etc.

(Equation binding prop thrust, velocity and power)

(Units for prop thrust equations)

(Calculating thrust and required prop size for given engine power)

(Software for prop thrust and required power)

(Prop thrust equation taking into account number of blades)

(Prop efficiency of modern light sport aircraft)

(Correct formula for prop efficiency)

(Engine power vs. prop thrust for a 3-blade 14" prop)

But I would like to find more examples of measured static thrust made by a propeller.

So, if possible, please post some figures or some link with any data on measured static thrust on an aircraft with a piston engine.

Thanks

(example in photo below)

• Thrust per HP will be somewhat higher if using a constant speed prop, closer to 4+ lbs/hp static. Apr 29 at 15:24
• Excellent remark I will edit that in the question. thanks! Apr 29 at 15:26
• Thrust depends primarily on five factors: prop diameter, prop speed, prop pitch, airspeed and horsepower. Ignoring four to focus only on horsepower isn't going to work, which is why it is hard to find the simple chart you want. Other factors like solidity also start to matter depending on disc loading and altitude, which drives density of air. You are probably best off looking at multiple specific cases to see how thrust changes with variation of one or two factors, like your Cessna chart. Apr 29 at 17:53
• Dynamic thrust, ofcourse, is a different matter, and altitude/density/airspeed etc are important for those calculations. These can be derived once static thrust is known. However all this is irrelevant to this question, as here the aim is to find examples of all three parameters measured, not calculated. There is no ignoring any factors as there is no focus on HP. The focus is on looking at data where RPM + Thrust (static, ofcourse......... as only this can be measured unless the whole airplane is in the wind tunnel) + kW (or HP) which can be easily inferred from RPM because torque is known... Apr 29 at 18:37
• but thanks for the comment let me edit that into the question so it will be more clear what is sought Apr 29 at 18:39

Let's first clear up some nomenclature about "power".

Power into the system, or throttle, or rate of fuel consumption is one meaning. Power as Force × Velocity is another, also known as mV$$^2$$/s. These can be linked as potential energy/second fuel burn = Thrust × Velocity = Drag × Velocity (at steady state or constant Velocity.

More simply put Thrust = Drag

So, you can work this problem theoretically through calculation of form and induced drag for a given airframe in a range of speeds. But, it is still difficult to calculate oweing to effects of "prop blast", which can affect both lift and form drag.

There is a wealth of data out there for various airframe/engine/prop combinations, which through years of testing have shown what is optimal, but it is really like trying to hit a moving target to develop a "Rosetta Stone" formula because of drag, weight, and desired speed range at what altitude all factor in.

But static test data would not be where I would start, as the relationship of prop pitch, RPMs, and airspeed is crucial. All your Cessna 150 data is showing is that the prop AoA on the bench seems to be more efficient as RPMs increase.

More meaningful data might be airspeed vs RPMs in flight. Thrust could be estimated from drag calculations, but in reality how the plane performs at a given throttle setting is what counts.

An approximation of drag at various airspeeds could be achieved by plotting angle of descent in a power-off glide.

glide ratio × mass = approximate Thrust at that airspeed

Discounting effects of changes in the airstream from turning props, this yields thrust requirement for level flight, which could then be compared to RPMs required for level flight at that airspeed.

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So, attaching two props with bicycle chains and sprockets to a Belphagor turbine might improve thrust efficiency. I believe Kuznetsov knows this.

• thanks for this answer. You hit the nail on the head with the glide ratio! It is the fundamental cause of why I posted this question. Knowing the D/L gives the thrust required for an airspeed, but the issue here is that it concerns a specified airframe. Apr 29 at 23:22
• So, in contrast to that, I am not looking to know what thrust is required, and then being able to calculate everything deduced from that (prop rpm, engine kW, etc). What I am very interested to see is, for example, what sort of thrust would be at 2000 RPM for an engine which provides 150 kgF of static thrust at 3000 RPM with an output of 60 kW...? So, regardless of airframe Apr 29 at 23:27
• Also, by "power" i mean the power output on the engine's main shaft, the torque it produces at a given RPM. Apr 29 at 23:34
• so, by "engine power" I mean what it usually means (engine output at the prop shaft) and not the potential energy of the fuel etc Apr 29 at 23:35
• @ivanantuns well, you could work with the theoretical prop airfoil "lift" (thrust) at a given rpm. Even if pitch was not variable, AoA for a given relative wind could yield a theoretical thrust, but, when in doubt, overdesign it and test it safely please. Note that prop RPM is also a function of prop drag. I would stay away from static data. Apr 29 at 23:49