Well I thought the concept of energy IN- and "where does it go", was not THAT obscure.
You apparantly think I don't understand pitch/diameter etc., relationships
I do
the example I noted simply was to show that power in must somehow go someplace and the use of an electric motor which easily shows measurable power inputs, was a basic example .
The motor absorbed power so the thrust scale can do nothing else but record the motor load. as thrust.
the shape of the prop , is not important . The thrust is simply the only way the motor can express the work it is doing
aside from heat loss.and this was not an issue.
The test stand easily shows this to be true.
I did not use a flywheel and look at the load of accelerating it
just slowly brought up the various props to a predetermined power input and read scale loads.
Apparantly I am wasting my time on this and will end my involvement .

Dick,
I understand that you've performed lot of measurements with your test stand, but I wonder whether you've interpreted them right.

Thrust is only a force that is part of the prop's output Power equation, the other part is how much the air is accelerated by the prop, which may be simplified by referring to the prop's Pitch speed as follows:

Prop's output Power = Constant * Thrust * Pitch speed.

Different props (even belonging to the same mfr) have different Constants, which depend on the shape, area and profile of their blades as well as how flexible they are.

Further, props with P/D ratio equal or higher than 0.6 will stall at static condition (as when using your test stand) resulting in erroneous thrust results.
Props with high P/D ratio become inefficient at low forward speed, as when during the take-off and/or climbing. These props also unload much less the motor in flight than props with low P/D ratio.

The power goes to produce thrust AND to accelerate the air (apart from the losses).

So, a prop with a large diameter doesn't need to accelerate the air as much as a prop with a smaller diameter to produce the same thrust.

you missed the whole point -
put in 50 watts you get a 50 watt result - the prop used does NOT matter - I know that other stuff that's all basic.
It is a matter of conservation of energy
once the load draws 50 watts the scale will read the same
we are measuring LOAD!

If you disregard the losses you may assume that you'll get 50W out when you put 50W in, yet the output power is never thrust only. Prop Output Power = Thrust *times* Constant *times* Pitch speed…

For example:
APC E 12x6 produces about 18.5oz thrust and absorbs about 50W (at 4400 RPM - pitch speed 25 mph)
APC E 8x4 produces about 16.3oz thrust and absorbs about 50W (at 8300 RPM - pitch speed 31.4 mph)

The power input is about the same but they have different thrusts and pitch speeds.

The bigger the difference in prop sizes the bigger the difference in thrust for a given power.

However, if you compare props with only slightly different sizes, you might not get such a distinct difference in thrust due to their constants, so a slightly smaller prop might produce the same or even slightly more thrust than the slightly bigger one at the same power...

For example:
APC SF 10x4.7 produces about 21.3oz thrust and absorbs about 50W (at 5650 RPM - pitch speed 21 mph).
It gives more thrust than APC E 12x6 despite it is smaller in diameter (but it has a wider blade shape and thus different constant).

Welcome aboard
This is what I noted from the first - that if efficiencies are 100%, then the amount of thrust on the static test will be the same , that is the same input will yeild the same thrust. irrespective of the prop used By the way I did not ue anybody's charts
I measured the results.
Once more - I TEST this stuff -I don't go by textbook/published info. Pitch speeds etc., are not relevant in this test .
and the test results were a surprise to me
as on acouple of trials - I put TWO props on the motor crossed to make a 4 blade and the results again the same.
Obviously - the rpm was far different but the power in, to thrust output remained the same.
You really ought to try this stuff

However, you should not disregard the motor's different efficiencies with different props.
If you use the same motor while comparing props, you have to adjust the throttle in order to get the same input power with different props.
This will put the motor working at different efficiencies, which may vary from 85 to 50% resulting in big differences between power in to motor /power out to prop, which may further distort your comparisons.

Noi that is not so
I used electric motor and the efficiency varience was not that kind of extreme change. Present brussless technology is quite good.
Bottom line -I put in 50 watts and got back 10 ounces of thrust, for example .
The props used meant little.
power input in watts was simply changed to power output measured in ounces.
IF the motor efficiency was bad , heat would have changed because the 50 watts had to go somewhere
If your guesswork were correct - the 50 watts would have been redistributed to say more heat and less thrust BUT the numbers relationship remained very similar which meant that once the prop (whatever it's shape) produced a load on the motor , sufficient to absorb 50 watts input - the result was 10 ounces on the gram scale.
What is so strange about that?
You apparantly are thinking of engines and throttle settings which are wildly different in power to rpm.
Electric motors are far more predictable.
remember -I never discussed rpm - only the load necessary to absorb 50 watts (the example I used )
I could have put on a drag brake and absorbed 50 watts but I was looking ONLY at power in, relative to measured load. The load being expressed in thrust.

Ok I have beat this to death

Dick,
Could you tell us the actual prop types and sizes you have used that produced always the same 10oz thrust with 50W input?

Maybe you could convice helicopter manufacturers that the blades of their helicopters are way oversized, since they could get the same thrust no matter the prop size...

I must say -you missed the entire point of the test
Tho in your favor I must say that your misunderstanding is 100%.

You might be right, but I guess I'm not the only one here who misunderstood the results of your test.

Nevertheless, my question is fair.
Telling us the actual prop types and sizes you've used would greatly clarify these muddy waters.
Oh, perhaps you don't want to disclose too much of your "secret"...

No secret .
But I will leave you with a clue.
I was only measuring load to power input relationships
Load was expressed in thrust
input in watts .
Rpm was not a consideration
If that doesn't clarify it you might consider signing up for some more engineering classes.

Couple of ignorant questions/comments: CrateCruncher, I don't exactly understand Ei +V/(V + v). Does V = accelerated velocity, and v = external velocity? If so, then on a static stand where v = 0, Ei = 1, not 0 as you said.

AdamOne, you had a statement about both creating thrust AND accelerate the air. F=MA, where F is thrust, M is the mass of air, and A is the acceleration of the mass of air, isn't it? I don't see how you can treat thrust and accelerating air separately. I agree with your point that you can get the same, or more, thrust by using a larger disc area and accelerating a larger mass of air less.

Hi Jim,
I should have better defined big V and little v. Big "V" would be the airstream velocity relative to the airplane and little "v" would be the accelerated prop wash immediately downstream from the prop relative also to the airplane. I lifted the relation from Simon's book "Model Aircraft Aerodynamics", page 184. He derives it from the more common power ratio. I like to use Simon's work whenever possible because it is the most widely read among RC "thinkers".

Your observation is correct regarding thrust as a force.
The thrust produced is equal to the sum of all the lift components of the blades sections in the direction of flight.

However, as the prop rotates, there's not only an acceleration of the air in the opposite direction of the flight BUT also a rotational velocity of the air that remains in the prop wake (prop wash), which means that Thrust=MA is only the force needed to send the air straight backwards but further force is needed to give the rotational velocity to the air.
Now if we also put the prop drag in the equation, it's easy to realize that different prop types and shapes result in different thrusts for the same input power.

And there might be a way for a do-it-yourself-at-home scientist to measure some of this.

There are airspeed measuring devices that're dead cheap that've just come on the market. They're basically pitot tubes with a chip we can stick somewhere on our airplane. Forget the airplane and setup a rig like the D.Hanson one. It's going to provide some info for us. And there is a way to make a not so cheap wind tunnel setup. This part needs some shopping to work for us. I know the fans exist, just don't know the cost or source. You'll need one bigger than the props you're going to test. The fan needs to be variable speed. Nothing much more as to accuracy or whatever, because the pitots are going to provide the data we need to control both the big fan and the little one (the prop we're testing).

We setup the D.H. rig with an array of airspeed measuring devices downwind. We setup the fan upwind and on the same centerline of the D.H. rig. Turn on the fan and start playing. Ok, start being scientific.

There are a number of ways the data can be gathered but they basically rely on our control of the airspeed and what we do with the differing speeds we see from the pitots. And of course what we do with the prop/engine.

Just one possible test would be to compare a number of different props of the same dia/pitch. When a prop is at it's top speed, the slipstream approaches the airspeed. We got pitots in the slipstream and in the airstream. Those readouts let us adjust the airstream until the slipstream matches. We're at or near that prop's top speed. Read the tach on the prop, the wattmeter and whatever else you want. Run some tests on the similar props you got and then shift over and compare some supposedly similar motors.

Is it going to be good enough for NASA? Nah, but it'll be a darn sight better than what we got now.

That's an interesting idea for someone with the spare time and premises to build and do the research.
It would be dynamic tests as opposed to D. Hanson's static tests.

Go for it!

Yup, and it'd work for glow and gas as well. But I believe there would be far less capability since those type engines don't have such a cheap and readily available gauge of their input power.

The setup would go as far as the builder/users understanding of the limitations and requirements and interpretation would allow.

I let this thread get away from me so I'll sort of catch up.

I always found that for engine use if the engine is able to reach the correct RPM then the issue seems to be more about how well the prop works. Of all the props I've used only APC seems to have a leg up on turning power into airspeed. I've seen this on both my engine powered models in all cases but one and definetly on electric motors. The one time I noticed something outside of this was with the Master Airscrew 4 stroke series where their prop worked on my Barnstormer biplane as well as the equivalent APC but looked more "scale" like so I stayed with it.

In testing a heap of props on electric motors I always found that the APC's worked CONSISTENTLY well. The new scimitar Masters worked sporadically well. Going back to my buddy that resurrected Y&O props he found that APC props use a pitch reduction from just outboard of the widest point to the tip so they in effect have some washout in the tips and the main working area is the middle half of each blade. The washed out tips in this case would be there to help with reducing the tip section's load and thus the tip vortex strength. And when these tip vortices are reduced you have less drag. So that's power that the main working portion can use to turn into thrust..... at least that's what we surmised in discussions on this washout aspect.

Width does have some part to play but not directly towards performance. Those BY&O re-release props found great favour with the control line stunt guys. I believe it was because the wide blades worked better in the diving portions of the maneuvers as airbrakes. So while a wider blade may not produce more speed performance it may have advantages to specific styles of flying.

In playing with clunky wooden props on electric motors I also found that too thick reduces performance. But oddly enough not by as much as you'd think. Take Zinger wood props for example. Have you ever seen such a crude hunk o' timber in all your life? Thinning samples of these and shapeing them better produced gains in both current reduction and thrust increase all at the same time. But only to the tune of maybe 10 to 15%. Mind you with the old school electrics that counted for a lot when the weights were so high. So if some is good then too much is just right, correct? Thinning the Zinger clubs even more and adding a hint of undercamber actually promoted the airfoil to stall rather than give better performance. This ran counter to my work with rubber power but then the reynolds numbers of electric motor gear drives were still far removed from the much slower rubber model props. We could actually hear the "fluffle" sound of the prop running in a stalled condition on the ground. Mind you some of these that were not too extreme did actually test out well in the air with what appeared to be slightly better climb performance and the feeling that they got slightly longer flying times per pack. The "definite maybe's" being due to the small gains and obvious difficutly in using flight testing with inconsistent flying styles to test for something this small. Again the increase would be in the single digit % value range so any gains are lost during actual flying if you're actually trying to get hard measurements.

In electric motor testing I found that wider just added drag to the motor with no obvious increases in thrust. However going TOO narrow also added drag and resulted in less thrust all at the same time. We tested only one prop in this manner to make it more narrow. Again a modified Zinger that was modified to what we found to be optimum and then we cut and reshaped the blades to be around 3/4 the original chord. Hardly definitive I know but enough to turn us away from that avenue.

I was truly shocked though at the small range from worst to best. We found that the APC's were the best during our electric testing and the Zingers the worst with Top Flites and MA's being in the middle. Also for the slower turning the prop the more advantage there is to be had by making the blades thinner and including a hint of undercamber. But go too far on this and it will bite you. But for this aspect we are only talking about much slower turning props like used on electric assist gliders and the like.

I'm actually amazed that the GWS props and the thin electric APC props work so well and yet are so thin. I can only chalk it down to the very low, for a prop, reynolds numbers and the relatively fine pitch used on the fun fly models.

Yes the brands of props have some WIDE differences
Ireqork some prop to see what does what
both for low speed flying and fast flying
(th motly pile of props shown are some I regularly sue.
The large ones are on 50/40 cc gas engines The pitch and diameter are NOT predictable as to performance as you note. In some cases they are surprises!
My test on watts to thrust was an entirely different matter which I guess escaped some - at least one -
The 10/10 is a good prop for about 800+watts in a slippery airframe
but on 800 watts the 14x7 is far better for 3D - all pretty std stuff. For dynamic testing -I go straight to the model - and skip the cogitating .
The tiny GWS are extremely good -better than APC slo-fly as they have almost zero flutter/vibration .
I am no good at math-so I just fly and use what works the best.

Taken from a different forum and the topic wasn't even close.............

Let's see. The MAS was probably wider, and thicker, and heavier, and was considered by that poster (as many fans of another mfg often do) as a "non performer" prop.

I love this hobby.

Nothin wrong with the MAS- much of the theory on blades -for our uses , is so much malarky. just make em strong enough and some angle to em
the " lifting wing cross section "bit , is pretty much usless on many applications. Except for the stiffness it imparts.
As those who fly em have seen-

Yep. It's all about the testing to see which works. Back when I flew some .15 diesel control line combat the hot prop of the day was the white nylon Tornado 8x6. But the prop didn't really come into its prime until it had been boiled for 1/2 an hour to "temper" the nylon so it wouldn't break on the first crash and then to thump it in a few times so it was bent back at a jaunty angle and THEN it would really let the engine work.

Of course all of this sort if means this thread is really out of context within the "Aerodynamics" forum where it's all about the theory of making this stuff better.

Is there a better prop design waiting to be discovered? Likely there is. Will it be head and shoulders above the present optimum? Not a hope. A few %? Yeah, there's probably a little room. What'll it take to get there? Likely about 50-50 computational study and practical cut and try. The computational part suffers to some extent when dealing with our unique sizes and the aerodynamic issues. The best issue would be to study what we have now and then model the computational stuff until we obtain the same results as in real life. Only then once it has been calibrated in this manner can we alter the blade shapes and airfoils and study the results. Even then if the shapes change radically then you'd need cut and try to check out the computational results.

As always when you're doing this stuff it comes down to GIGO.... Garbage In = Garbage Out

APC has to date the best approach
way back when Landing products started doing these injected props - I got a package in the mail
- try these - let us know etc..
In very short order thru feedback there were more and more props sizes available in very incremental sizes and shapes
The users fed back info to APC- they in turn made a "new "prop which then went thru another iteration etc..
No hocus Pocus - just logical proven mods
I believe they had the ability to quickly generate computerized mods an put the results directly into a mold .
Today this is commonplace in some industries
and APC did it right
make the mod then proove it in use .
In my pic of props ,note that one carbon fibre prop, has curved forward tips
This very narrow thin prop loads the engine far in excess of what one would suspect by looking at it.
To further surprise the prop is quiet and yet goes very fast -If you have the power to turn it. The reason for it was to offer a quieter prop in the air - yet another science .

DaRock, do you have a link to those pitots on the net? I wonder if you could just attach two pitots on the plane (one in the propwash, one in the undisturbed airstream) and get real time data in-flight?

I wish I had an on-board tachometer also. Anyone hear of someone offering one of those?

Haven't seen them on the internet.

Saw the ads for speed (pitot) and a couple other function devices in the back pages of Model Aviation. They were inexpensive.

Where and how you use them will determine the quality of your data. Ooops, best to say that as the validity of your data.

Truth is, placing them in the suggested "open air windtunnel" I hypothesized should be quite easy to do to gather valid info. (Why? Because we're looking for comparative readings, not pure ones, and we understand the limitations of our "tunnel" and allow for it.) However, placing a pitot on an airplane, actually placing it attached anywhere NEAR the sucker, is quite an undertaking to get honest readings. And the idea is that reading is supposed to be an accurate one of the pure value.

I think the acceptance of their "information" as accurate is going to rely on the lack of understanding of most of our modeling buddies.