Hi Louis !

Here's some links to wind tunnel data of various RC propellers :
- UIUC prop database, large database (APC, Graupner, GWS, MAS, Aeronaut, etc.),
- Merchant, Wichita State University, 2004 (pdf) : APC 12x12E ; APC 16x12E ; MAS 16x8x3,
- Moffitt, Bradley, Parekh and Mavris, Georgia Institute of Technology, (Wichita's wind tunnel) (pdf) : Bolly 22x20CF ; APC 16x12E,
- Brezina, Wright State University 2010 (pdf) : various small propellers (<6 in), APC, Graupner and GWS,

The UIUC database shows the propeller coefficients Ct and Cp, but also the geometry of some propellers. That can help understand the difficulty to predict propeller performance from diameter and pitch only.

Recently, they (Deters, Ananda, Selig) published a paper about Reynolds effects on the performance of small-scale propellers. It also shows the variation of twist distribution between some specimens of the same species (here for a GWS 5x4.3) leading to huge static Ct and Cp variations. This adds to the difficulty. There may also be variations of blade shape inside one family (for example, large APC thin electric props are thinner than the smaller ones).

Bonsoir,

I thought of a way to read the UIUC data, without being too complicated or requiring huge computations.

If one can measure static thrust and the corresponding rpm, and so the corresponding pitch speed.

On the 1st picture below, there is a typical propeller polar, with Ct (thrust coefficient) vs J (advance ratio J = v/nD).

The red arrow shows how the static thrust is related to Ct, and the green arrow shows how the pitch speed is related to J (and P/D ratio). Of course, this supposes there is no "unloading" which is not correct, but it isn't very important.

More important is the shape of the thrust curve.

You can make a graph with thrust / speed. Then the static thrust and the pitch speed are landmarks to help you draw the thrust curve, like on the 2nd picture.

This last one shows an APC 10x5E vs GWS 10x6DD, with very similar results, and the different way of understanding pitch. APC sees the pitch as the geometric pitch (angle of the chord line, from the leading edge to the trailing edge of the blade) while GWS seems to see the pitch as pitch speed = zero thrust speed (I think in fact they just measure the angle from under the blade, which is a bit less than at the chord line, and it simply happens that it nearly leads to pitch speed = zero thrust speed).

Hi
APC performances data seems "in construction"
I hope that the tables could be available soon
Louis
I have edited my post #15, concerning the APC 7x5 E

great thread. how about a little discussion about materials? i specifically would like to know what advantages beechwood props have for 3D planes.

Hi
The aerodynamics is not depending of the material (wood or nylon or CF)
But the cost .. yes
CF is allowing a design more thin (less prop drag under rotation speed)
The behaviour in case of crash or collision is different (wood vs CF)
Difficult to answer to that general question.
Louis

Originally Posted by Fourdan

Hi
The aerodynamics is not depending of the material (wood or nylon or CF)
But the cost .. yes
CF is allowing a design more thin (less prop drag under rotation speed)
The behaviour in case of crash or collision is different (wood vs CF)
Difficult to answer to that general question.
Louis

I agree, most want to know what is better before to spend their pennies. The only problem is, what's good for me is good for you? Only testing! And to test, you have to buy or borrow from someone who has. Just my opinion!

Hi
Opinion of some french and friends hobbyists (big RC planes) :
Wood props have a better (service/cost) ratio
CF is rather expensive.
But some guys prefer to buy expensive items.
Louis

Big CF props can be quite expensive, especially if you buy the better quality European made CF props.

But the cheaper Chinese CF props are a pretty good buy now that they are down to as little as $2 or $3 or so. I think at those prices the reduced breakage offsets the higher cost.

Lot of examples here:

http://www.funtobuyonline.com/rc-pro....html?limit=40

And they are thinner, stronger, amd can be taken to higher RPM than their plastic counterparts.

I really like the flat hub or "T Style" CF props, those have a very low profile mounting and seem to work very well in my testing.

I have started buying most of my props on eBay, I am finding lower prices on some of the same items I was getting from overseas and/or getting quicker delivery from U.S. based dealers in some cases.

Jack

Louis,

What are you doing about the different iterations of the 'same' APC props.
They have changed a lot over the years and there is no way to tell which iteration you have besides measuring the hubs.

The screen captures are from apcprop.com.
The one with the .34 in Hub Thickness is from Aug. 2009
The one with the Hub Thickness: 0.45 in. is from the 3rd of this month.

I have both and they definitely are not the same, nor have the same 'constants'.

I forgot to mention the prop. It is the APC 12x8E thin electric. There is no change on the package nor the prop itself.

I used the Internet Wayback Machine to get the screen capture from 2009. I actually found several others and can see the progression through the 6 captures I have for this same prop.

Hi Ken,

I've noticed variations in blade thickness of some APC 8x6TE.

And there is probably variations of blades shape, especially pitch distribution, from one specimen to another (see my previous post).

So it is clear that performance measurements must be taken with care. I don't think though that it means we can't trust them at all.

hey, could someone answer a simple question for me.

I am currently running 9x4.7 gemfan props on my 1200kv NTM's for my quadcopter.
I want to upgrade to HQ Carbon Composite propellers from this site.

(http://www.floatship.co.uk/props.html?make=50&size=5)

They have 9x4.5 and 9x5" propellers. Could somebody tell me is there really much difference in performance between these 2 propellers and should i go for the 9x4.5 if i am running 9x4.7 at the minute?

So in conclusion, My question is, Whats the diff between 9x4.5 and 9x5

Thanks for any help, All appreciated.

The props at the link are carbon filled plastic props, they will be a little stiffer and heavier than all plastic props and probably about the same weight at a "real" CF prop (the carbon twill cloth is visible in the laminate).

If you 9 x 4.7's are not overheating the motor now, fly those and check them for heat. If they get too warm (if you cannot keep a finger in contact with the base plate of the motor on landing immediately after landing) back off on the throttle a little and you'll be OK. Dropping back to 3/4 throttle or so from full throttle makes a big difference in the heat being generated in the motor.

Jack

Here is a new type of prop that I am testing:

ApachePilot/Kline-Fogelman Propeller Testing - www.rcgroups.com/forums/showthread.php?t=2294656

That is the only one in the world as far as I know and I don't think we have more than gotten started with the testing...

So we are not claiming a breakthrough or anything yet, just discussing it...

Jack

how it should be a variable pitch propeller for electric motors?

ok now I say to you what I have done