For a base line.......
76" diameter Ivo prop. These are the magnum series,, not my paddle blades.
3076 prop rpm.... Motor turning 4400 rpm
35 degrees f
695 mph tip speed. .936 mach.
Plane still pulling strong up to 4500 motor rpm.
http://www.pponk.com/HTML%20PAGES/propcalc.html
Prop is not that noisy either. Motor makes more noise.
http://www.youtube.com/watch?v=AOF6eT6FRmY
Been running this way for 400 hours and blades look good.
Ben Haas
www.haaspowerair.com
To: flyrotary@lancaironline.net
Date: Mon, 1 Nov 2010 11:49:04 -0700
From: wdleonard@gmail.com
Subject: [FlyRotary] How fast is it safe to turn a Prop. Opinion Poll
So I am getting a little more bold with my new turbo. On the way home today I decided to open it up a little bit. At 8500' and MAP around 34", I was at 6700 RPM and 201 KTAS (about 3060 RPM at the prop with the tips doing 860fps). Temps still less than 160, plenty of throttle left. I just couldn't accept turning the prop any faster, not knowing what the limit really is.
My prop is a 64" diameter (pretty short) Catto (wood/composite) with a number of nicks in the leading edge and has not been dynamical balanced to date.
I talked to Craig Catto about the issue and what he told me completely makes sense, but is utterly unhelpful in setting my racing redline. He said that I could turn it as fast as I want, but the risk of separating the prop. increases as I go faster. I just depends on too many factors.
I realize the the final number is going to depend on my risk tolerance and how much I really want to post some big numbers in a race. But it is hard for me to balance that without better understand or the factors on the prop, hence, the opinion poll, on various factors..
I have heard that it is important to keep the prop tips under 900 fps, while others say it is not a factor. Is there some important number for the max tip speed? Is it a safety issue or an efficiency issue?
Most of my nicks in the paint and composite layer are in the outer 1/3 of the prop. Are these a big deal for safety? Efficiency?
If I were to run the engine at 7000 RPM that would give me 3225 at the prop, tips doing 900 FPS an an aircraft speed of around 209 kts (240mph). This seems pretty reasonable to me as an upper limit, but it is scary a little.
But what about 8000RPM at the engine (if I have the power to get there)? With a cleaned up and balanced prop, that would be almost 3700 RPM at the prop, tips doing 1020fps, aircraft going something less than 240kts (275 mph). Stupid though? Or give it a try and see how close to those numbers I can get?
Any issues with the gear-box going that fast, other factors I am not considering?
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