Prop constants???

[IloveFLIGHT!]

How does one calculate the constants of a given prop? I would like to do simulations of torque required for a given rpm? There are many programs out there that will do a motor test for the props and motors in thier own database. But how do you figure out the constants for DIY? I am mostly talking about APC E , APC Slowfly and APC Sport series props. Any help is greatly appreciated! Thanks Chris

[Jurgen Heilig]

How does one calculate the constants of a given prop? I would like to do simulations of torque required for a given rpm? There are many programs out there that will do a motor test for the props and motors in thier own database. But how do you figure out the constants for DIY? I am mostly talking about APC E , APC Slowfly and APC Sport series props. Any help is greatly appreciated! Thanks Chris

What you need is the n100 figure for a given prop (rpm at 100W).

As W is pretty much proportional to rpm^3, you can calculate lower or higher figures from there. But beware, the prop must not be stalled and there can be fairly big tolerances even from prop to prop of the same manufacturer.

:) Jürgen

[hul]

online: http://www.badcock.net/cgi-bin/powertrain/propconst.cgi
offline: http://www.badcock.net/EffXL/EffXL.zip

Hans

[IloveFLIGHT!]

Thanks guys. Chris

[peterangus]

You don't calculate prop constants.

You obtain them from tests.

Related links:
www.rcgroups.com/forums/showthread.php?t=296125
www.peterangus.pwp.blueyonder.co.uk/out_power.htm

[vintage1]

Indeed. they should come with data sheets that say so may watts per RPM cubed or somesuch..;)

Or someone with a dyno rig should plot power versus RPM for every prop ever made ;)

Oh, and whilst at it, thrust versus RPM and airspeed..

Oh..and they can kiss my.. :censored: as well.

Whilst in the scenario of unlikely things that should definitely be done. By someone else ;)

[peterangus]

The constants in the link are provided for users of the Hyperion Emeter.

But the Emeter is not essential --- a pocket calculator will do.

aircraft-world.com/prod_datasheets/hp/emeter/hp-propconstants.htm

[peterangus]

One of these days-------------the constant will be moulded or printed on the prop, as the diameter and pitch are.

And we might even get an accurate zero-thrust pitch, rather than some vague nominal value.