I have two concerns at this stage in my test program:

1. Particularly with the APC 12x7 static thrust curve, clearly there are measurement errors. I have three options; either leave the data as is (the underlying theoretical curve is reasonably obvious), repeat the measurements one or more times, or think up further techniques to reduce measurement error.

2. There is variation, of course, of temperature and ambient atmospheric pressure between the various curves as they were measured on different dates. Strictly speaking, to combine the thrust curves in one chart is invalid for this reason. Can anyone think up a way of normalising the curves for differing temperature and pressure? Or will the differences in thrust/RPM be insignificant within the bands of temperature and pressure that I am experiencing - we are now moving into winter and it is getting colder.

I intend to provide similar data in addition for APC 12x8, 13x6, 13x7, 13x8 props.

Can anyone offer advice? (I know I should be flying)

Best wishes
Mike

Mike,


Why waste your time on something that was already done, by another member of this forum?

Please go to PĂ© Reivers [link=http://mvvs.nl/prop-power-calculator.xls]PropPower calculation spreadsheet[/link].

It is really accurate and you can either use it on the the site, or download it (freely) to your PC (if you have an electronic spreadsheet program, such as MS Excel).


And as to thrust; it is not a function of the engine and thus cannot be calculated for an engine; but for the specific prop, the model's drag, the forward speed, the ambient conditions and the RPM only...

Thanks very much Dar Zeelon. The spread sheet is very good and something I had hoped to find. But remember my values are measured, not calculated. So it is of value for me to compare the two.

For instance, Pe Reivers' sheet gives a prop thrust of 3.78 kg at 11820 RPM, APC 12x6, OS 65LA. My measurement for the same is 3.87 kg.

There are lots of benefits for me at least to do my measurements. I must say again: I am very pleased indeed to have a copy of that spread sheet.

Mike

If you want to go all the way, you need to correct my sheet for "pressure head = atmospheric pressure" , but also for moisture content " is lack of oxigen, (sort of, depending on temperature, it gets too complicated with temperature changes).
Dar has pointed out to me he differences between prop makes and sizes. You can juggle prop factors to get good results, and you also can input atmospheric pressure in my spread sheet, even up to water density or more.
I see no way to carry this any further without departing from practical use too much.
measured data are welcome; thanks for that. I wil use them.

Actually I don't see too much at issue with your data, it might vary a little bit but not so much that it makes your measurements invalid.
If you want to normalize the data the best way is to make the measurements over and over until you have a statistically significant sample and then average the measurements.

PĂ©

Do you have any data of the new Graupner Propellers? the ones that look like the APCs?

Saludos,

Jorge

No I don't, but maybe others have?

I would like to collect some data for you, but I don't even have a tacho, nor a fish scale to collect the data...
I have a 13x6, but nothing to compare.... soon I'll get some of the square tip Graupners and I'll compare them... Should I expect that the old ones are better for a 4 stroker?