University of Illinois Propeller Data

[Delta Foxtrot]

I was looking for some APC prop geometry to run through some performance prediction code and found a very useful web site:**LINK**

This contains wind tunnel test data for a large range of model aircraft propellers and will be very useful when looking at performance trades if you are technically minded. There is an AIAA paper which describes the testing and analysis of this data.

I thought it worth posting in case it has not been posted before. It may be of use to a small minority of aeromodellers with an aero engineering background.

Regards

David

[Biggles' Elder Brother - Moderator]

Very interesting David. Good stuff. It would be even more interesting if they had included Xoar and Zinger etc to see if their claims for greater efficiency (as justification for higher cost) actually withstood the glaring harsh light of experiment!

BEB

[FunnyFlyer]

Hi folks,

What will make this work for me is if you could provide a steer to what good looks like - what is the real world implication?

For example:

If I look at the plots for various props of same size and pitch - what are the different plots telling me?

What is Eta, Ct and Tp?

[Erfolg]

Yes, well, hmm.

I had thought that the performance of a propeller would be related to the revs in turned at. Although never quite being able to articulate the suspicion in numeric terms. Thinking that the Re number would change with speed. I had also thought that as the model advance, that the effective AoA would alter. I still do no know that this is true. The graphs do however seem to indicate a link with revs.

I have a number of questions, the first is, the wind tunnel correction factor quoted, is to be applied to what, or has it been applied?

My other issue is that if performance is related to revs, all the revs are a lot lower than the vast majority of my models, typically revolving at 10, 000, with one model at 21,000 revs.

I await a verbal tongue lashing with trepidation.

[Delta Foxtrot]

I only found this data today and have not had a lot of time to read through the AIAA paper which describes the experimental data and the corrections, but I can offer a few comments which might help you get some value from the data.

The data is characterised by three non-dimensional groups Ct (thrust coefficient), Cp (power coefficient) and Efficiency vs J (advance ratio). In theory all fixed pitch propellers which are scaled to different diameters, but have the chord and pitch distributions scaled accordingly and are tested at the same reynolds and mach number will give the same characteristics when Ct, and efficiency are plotted against J. This will also require that surface roughness / chord and untwist are also kept the same.

The variation in some of the data for a given prop will be due to variation in Reynolds number and untwist. It is a pity that the data doesn't extend to higher rpms, but for our purposes I am sure that eyeball extrapolation of the data to these speeds will not result in large errors for fag packet sums.

This data can be used by modellers to do some useful fag packet calcs. For example we can estimate the uninstalled propeller thrust statically and at different flight speeds for a range of propeller diameters and pitch to assess the potential benefits of changing props.

I will post an example calc, which may help in a little while.

david

[Delta Foxtrot]

Example calcs as promised starting with some definitions:

J = V / ( n x D )

Ct = T / ( air_density x n^2 x D^4)

Cp = P / ( air_density x n^3 x D^5)

eta = efficiency = useful propulsive power / power input = TV/P = J x Ct / Cp

where:

T - Thrust

V - Flight speed

n - propeller revs / sec

D - propeller diameter

P - power input

^2 - raise to the power 2 etc.

air density at sea level standard day conditions = 1.225 kg/m3

I am interested in prop selection for my Tucano fitted with a motor running at 10,000 rpm. Looking at the APC E 10 x 7 propeller I can estimate thrust and power consumption. Just as an example let us look at the advance ratio for peak efficiency 60% for J = 0.5.

V = J x n x D = 0.5 x (10,000 / 60) x 10 = 833.3 in/sec = 21.2 m/s = 47.3 mph.

Ct = 0.06

T = 0.06 x 1.225 x (10,000 / 60)^2 x (10/39.37)^4 = 8.498 Newtons = 1.9 lbf

P = T x V / eta = 8.498 x 21.2 / 0.6 = 300.3 watts.

This is a bit of a random example, but would could repeat the calcs for a static conditon or max design speed for different prop diameters and pitches to see what the changes in thrust and power requirements would be.

I did this a little hurriedly so apologies if there any errors, but hope it helps someone get value from the data.

regards

David

[Delta Foxtrot]

Another obvious use would be to compare all props of the same diameter and pitch at some critical flight case to see how much efficiency variation there is.

You could also compare static thrusts

David

[Erfolg]

The vast majority of modellers will find the process ponderous, particularly when all they want to know is an answer.

I guess the big issue, is what is that question or questions they want answering.

One way of improving access would be to construct either a data base (probably relational) or a spreadsheet with a fixed table and inputs which generate the answer (do the maths).

As the data stands, it seems of hand to be of limited use, although there appears to be plenty of it.

[Delta Foxtrot]

Posted by Erfolg on 10/01/2013 19:59:07:

The vast majority of modellers will find the process ponderous, particularly when all they want to know is an answer.

I guess the big issue, is what is that question or questions they want answering.

One way of improving access would be to construct either a data base (probably relational) or a spreadsheet with a fixed table and inputs which generate the answer (do the maths).

As the data stands, it seems of hand to be of limited use, although there appears to be plenty of it.

In order to exploit the data you require a tecnical engineering background and a knowledge of propeller aerodynamics, however the data is certainly very useful to people with the right skills to exploit this, some of these will be modellers.

I agree with you that it could be made a lot more accessible to modellers if it were incorporated into a spreadsheet or an propeller program, but for now I just wanted to make it know that this data is available. If a few people find it useful in its present form, job done.

Regards

David

[FunnyFlyer]

David,

Thanks very much for the very detailed explanation and calcs - I'll digest later!

[yomgui]

Hi !

I was just passing by and I saw there is here some interst for the UIUC database.

I'm developping a spreadsheet that can read those data :

**LINK**

It also has data from other sources.

Of course, I'm also interested by comments on the spreadsheet, which is a bit complex.

Thanks.

Guillaume

[cymaz]

Great subject and it's is usually the first question that's asked when you buy an engine, isn't it ? What's the best prop?? I for one look at the makers recommendations and buy that and also a larger diameter and finer pitch as an experiment. Sometimes it works and sometimes it doesn't. TBH I have never done the maths. I see what it's like in the air as all the calculations have been done for me by the engine maker on the back of the instructions.
Es