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62" Prop
Max HP @ 7200 RPM
Pulleys 7.75":3.75" = 2.07 Reduction = 7200 RPM Engine : 3478 RPM Prop
3478 RPM x 62" Prop = 286.7 m/s tip speed (http://www.tasonline.co.za/toolbox/pump/powtip.htm)
287 m/s / 340 m/s (mach) = 0.84 mach
Do these numbers make sense.. I am deathly afraid of this thing blowing apart on me.
I would check with the prop manufacturer, most are only good to 3100 and most efficient at around 2700-2800.
Whoa whoa whoa.
I thought max efficiency came with having a tip speed of Mach 0.9
This prop came off a Rotax 582 @ 6200 RPM @ 62" Prop = 195 M/S Tip Speed = Mach 0.61
Is this what I should be shooting for?
This changes everything...
Forgive me as I'm a bit under the weather with the flu but I'll try to make some sense. That mach figure is to keep the tips from resonating/buzzing. All props are not created equal so a blanket number for optimum tip speed would be impossible. Some props are made to pull a load, some for speed, etc.
Each prop design has a different operating rpm as far as efficiency but most are around that 2700-2700 mark. after that they lose push or cavitate like a water prop. Spinning them faster does no good. You need to research the specific prop you are using to decide what rpm range is needed. This is also prop model specific.
Maybe Ted will post up and clear this up a bit for you. I just can't make my brain get there with this bug.