Propeller Balancing

On Dec 16, 4:16 am, Stealth Pilot
wrote:
a well made newbie prop can deliver exactly the same performance as a
professionally carved prop. after all they were newbies once themselves.

I'd be willing to bet that the prop I have--a Colin Walker
unit, uncertified, built by a guy who probably got his start building
one for himself, is MORE efficient than, say, a Sensenich. The builder
of my prop used a more cambered airfoil that pulls better than a
Sensenich, he milled off the leading edge and built it up with hard
urethane and shaped it so that it's a seamless, lightweight abrasion
protection much better than Sensenich's crude riveted-on brass leading
edge that disrupts airflow and can harbor moisture under it, and so
on.

here is a trick for sizing the prop. make it an inch overlength.
in straight and level flight you should not be able to hit redline
with full throttle.
trim 5mm from each end and rebalance and refinish.
fly it again and the top rpm will be slightly higher.
when the revs come just up to redline rpm with full throttle your prop
is the correct size.

I shortened mine from 76" to 72" to get more RPM on takeoff,
and lost performance in all regimes. I wish I could put those tips
back on. It used to cruise at a speed and RPM that indicated zero or
slightly negative slip, believe it or not. Not anymore. Now it slips a
little. Don Downie, an old homebuilder of note, said that long props
would do that.

Dan

Hi

I tryed to replay to this when I was in Thailand but it did not get here.

Cutting 4 inch off is like reduce pitch by 8" when come to power needed.

if diameter is right (depending of what you want) the relative pitch and propeller pitch at 75% r. is about the same, for a standard purpose pitched prop. at the flat botom that is.

A little negative alpha on a CLIMB prop, and little positive alpha on a CRUISE prop.

A speed prop will have maybe 2 degree of positive alpha.

this also depends on the thickness of blade, a thinner/ less camber will need more alpha, and a thicker less alpha. and it also depends on the blade aspect ratio.

You can trade diameter for pitch, in most cases 1 inch diameter for 2 inch pitch.

and it differ 2" in pitch between each of the 4 purpose props, CLIMB, STANDARD, CRUISE and SPEED.

Jan Carlsson
www.jcpropellerdesign.com



here is a trick for sizing the prop. make it an inch overlength.
in straight and level flight you should not be able to hit redline
with full throttle.
trim 5mm from each end and rebalance and refinish.
fly it again and the top rpm will be slightly higher.
when the revs come just up to redline rpm with full throttle your prop
is the correct size.

I shortened mine from 76" to 72" to get more RPM on takeoff,
and lost performance in all regimes. I wish I could put those tips
back on. It used to cruise at a speed and RPM that indicated zero or
slightly negative slip, believe it or not. Not anymore. Now it slips a
little. Don Downie, an old homebuilder of note, said that long props
would do that.

Dan[/quote]