Ed Anderson wrote:

----- Original Message ----- From: "Ernest Christley" <echristley@nc.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Monday, September 11, 2006 9:02 AM
Subject: [FlyRotary] Re: It runs!

Al Gietzen wrote:

I'd say get a prop load on there, and adjust mixture, get some readout of
what's going on.  I don't think you necessarily want the thing spinning over
6000 on first startup anyway.

Way ta' go, Bob.  Several people have given the advice to put a load on the engine, but if you're buying parts as you progress (like me) you may not have a prop yet.  A 4ft section of wooden fence post will make a nice, disposable load though.

Good idea, Ernest.  However, without an airfoil cut into the fence post, its not going to impose much load - some resistance for sure, as it spins through the air, some additional inertia - but little load - compared to a prop.

Ed

I took a while to respond, because at one time I had and email that laid out some equations for calculating the amount of  power that a square piece of wood would absorb at different RPM.  Some French guy had worked it out.  The idea was that you would guess at what power you thought you'd get, make up a 'fence post' and run it.  Use the results to get a better idea of what the real Hp is and cut another 'fence post'.  I've since changed computers and I haven't been able to find that nugget.

As for throwing a chunk of fencepost as some else alluded to, as long as treated wood is avoided and some effort is expended not to select from the seconds bin, any wood that a fence post is likely to be made from will be more than strong enough for a propeller.