I have noticed that allot of people on this site and Supercub.org test allot of props for thrust, speed, and RPMs, so they get the best performance. This can get pretty pricey so why not just use some good old math.
So since I am on vacation this week and the weather is bad, I totally geeked out today and made a spread sheet (BROKE OUT THE OLD COLLEGE BOOKS) to calculate speed, thrust, tip speed, airflow over the top speed, and horsepower.

My issue is I don’t think I can upload an Excel spread sheet for you folks to play with, if anyone knows how please let me know, otherwise here is a screen shot.

Now before you all start picking away at it, it is just a DOE (design of experiment).
So for instance Speed, is the theoretical speed the propeller (not the aircraft) can go at the given RPM, and horsepower is also at the given RPM and is just an estimate that I would say is only accurate to about +/- 6-8%.
Anyways it can be fun to fiddle with, and from some data I have found online the thrust numbers are pretty accurate until the tips approach supersonic. I have placed an "IF" statement in the equation to lower the efficiency as the airflow over the tips reaches Mach 1.

here is a working link
http://spreadsheets.google.com/ccc?key= ... DOVE&hl=en

holy crap I only graduated high school cuz they didnt want me back.

Nice work using Google Docs to make it public.

Ummmm....I was told there wouldn't be any math. Or was it Meth.

So, I have vacation this week. I think I'll break out the quantum physics books and do a little light reading. Maybe cure cancer while I'm at it. Holy crap Zane.

Seriously though, that is kind of cool. If looking at excel sheets didn't make my brain hurt, I might actually play around with it.

Only type in the yellow cells I forgot to protect the other cells.

I like the goal seek function in excel
You say for instance I want 100mph and 400 lbs of thrust with 150hp and it will adjust the prop dimensions for you.
This is the kind of crap I do for a living.

Thats good stuff. I just repitched my prop to a climb prop (this was an after thought while i had the prop off). I dont have any good numbers for the original pitch. It would have been interesting to compare with your spread sheet.

Here's an online Java calculator for prop performance if you really, really want to get geeky:

http://www.mh-aerotools.de/airfoils/javaprop.htm

tom

Wow!! This thread is way to crazy for me . Good thing I have a constant speed prop.

HOLY SHIT! Are we all sharing the same spreadsheet or do I have a gost on my computer?

Small Tail Caddy wrote:HOLY SHIT! Are we all sharing the same spreadsheet or do I have a gost on my computer?

Did it change before your very eyes without you hitting any keys?

1SeventyZ wrote:

Small Tail Caddy wrote:HOLY SHIT! Are we all sharing the same spreadsheet or do I have a gost on my computer?

Did it change before your very eyes without you hitting any keys?

Sure did, is it a full moon?

After looking at http://www.mh-aerotools.de/airfoils/javaprop.htm I guess I should have added a cell for the number of blades.
Oh well I guess it is a work in progress, I hope you find it usefull.

Isn't there a song titled "To much time on your hands"

I like the Stones version better
Time is on my side, yes it is

That was interesting although it is not totally accurate. I have a Lycoming 0-360 CIA (rated @ 180 hp at 2700 rpm with a stock engine) with a 90" pitched at 32 propeller, 10-1 pistons, custom exhaust. I pulled an average of 805 on 3 static pulls at sea level on a cool day at an rpm of 2450 which is all it will turn. I would guess that would put the horsepower around 160-165 at that rpm, if I could get the full 2700 rpm I would guess my engine puts out around 190-195. I cruise at 95 mph at sea level at 2500 rpm in an Experimental Maule. I think there is a lot more to propeller performance then can be accurately calculated with math. I am not an engineer but I would guess the design of the blade, the material the blade is made from, etc. I think there is a lot of trial and error to get to the end design from the little tweaking that I have done with them it is not just a simple formula. I still found it interesting, thanks for posting it.

Greg

Yep Greg I assume a standard blade cord for all dimensions so like I said in the original post it is just a D.O.E.

Are your sure that your tach. is 100% accurate?
90/32 prop @ 2400RPM (just 50 revs different)
180 hp
802 static thrust
at 73mph

Yes, hand held Digital tach checked at the time matched the airplane tach