Milling heli rotor blade

[daddyhobby]

Hi guys, I am newbie to cnc machining be it metal or wood. I am in the progress of sourcing stuff to build my first CNC for milling alu and wood. I had in my mind to make wooden rotor blade. I am not sure how it should be run....length wise or fr leading edge to trailing edge? Next is the end mill to use...what dia is able to do the job? The blade is appx 20cm long and 2cm in width.

Thanks in advance

Mike

[Ken_Shea]

I would run it lengthwise, seems this would be much quicker then running it front to back as this would require constant z motion to accommodate the chord.

You would want to use a ball nose cutter probably around 1/4" and adjust the step over to get the smooth blend.

Ken

[ballendo]

Hello,

I'd rough it out lengthwise, for the reason Ken mentions; then finish it across the chord, because that's the way the air will go

Ideally I'd use a final finishing pass at 45 to the chord. The effect of these three passes will make it much easier for you to finish manually to the exact profile of the airfoil. (where unintended "bumps" or "ridges" are NOT a good thing!)

Ballendo

P.S. Use as large a radius ballcutter as you can for the finish passes...

[daddyhobby]

Cool, thanks guys for the info, now I will go find more info on ball nose cutter.

Thanks

Mike

[mike hide]

Originally Posted by daddyhobby Cool, thanks guys for the info, now I will go find more info on ball nose cutter. Thanks Mike

I was thinking but doesn't the aerofoil vary along the length of the blade .I think the blade tip speed on a real helicopter is supersonic whereas the inboard section is a relativley low speed profile . perhaps on models though it might be less important...mike hide

[Ken_Shea]

Mike,
Some of the hi-tech (real) helicopters are using variable chord / pitch but likely the RC are still using fully symmetrical blades.

Tip speed on real helicopters is still the main factor limiting the maximum forward speed. Called retreating blade stall.

Ken

[mike hide]

Originally Posted by Ken_Shea Mike, Some of the hi-tech (real) helicopters are using variable chord / pitch but likely the RC are still using fully symmetrical blades. Tip speed on real helicopters is still the main factor limiting the maximum forward speed. Called retreating blade stall. Ken

I worked on a rigid rotor proposal at Calac in the 80s, never got built though.If I recallthe retreating blade stall limits forward speed to around 190or so .....mike hide

[Ken_Shea]

Retreating blade stall is as you say, about 190 knots or MPH , not sure but it is exciting when you enter it , climes toward the moon, not really all that catastrophic though, just lower the collective !.

Got lots of hours in a small helicoptor, still have it, although have not flown it in over 20 years, long story, Lord willing, it is still in my plans to fly it again.


Ken