Swept Blades?

[helipaddy]

Just watching the Sportscopter video on setting up their blades


http://www.youtube.com/watch?v=uGNKSacy_4c

at around 2:20 he say the blades are swept back relative to the teeter bolt or am I hearing thing wrong?

I thought the blades when perfectly set up, should be balanced and in line with each other and set exactly at 90 degrees to the Teeter bolt.

Maybe Im picking things up wrong

Master Roda, maybe you can put a thick Irishman straight!

Thanks
Paddy

[bones]

Yep both blades swept back is correct, both then need to be still over the centre of the block.
A good video, well done

[Master Roda]

Paddy,

No problem...I'm a quarter Irish myself :)

Mark is correct. However, in our adjustable pitch hub bar, you don't need to worry about this step. The way it works allows it to move in lead/lag on it's own.

[C. Beaty]

Sweepback provides reverse delta-3 coupling; an upflapping blade has its angle of attack increased.
59112

But in this case, the unstable flap-pitch coupling apparently is not enough to do any harm.

[helipaddy]

Thanks Jon,
Why are the blades swept back? is this normal on all gyro rotor blades. does it impart a particular quality to the performance of the blades?

thanks
Paddy

Chuck. you got the post in as I was typing. I figured that it was reverse Delta3 but cant figure out why you would want this.

what advantage has sweep back, compared to a set of parallel blades?

Paddy

[C. Beaty]

There is no physical advantage to sweep, Paddy. Any perceived advantage lies entirely within the mind of the beholder.

[helipaddy]

Thanks Chuck,

Sort of like "beauty is in the mind of the beerholder"!

Id like to know what the percieved advantage is with sport rotors swept versus unswept. Im sure they have flown and tested both.

Paddy

[Master Roda]

Paddy,

If you take a close look at the differences between our fixed pitch bar and the adjustable pitch bar, you will get a better idea of how and why.

I will be posting a video on the website regarding this. While the sweep may not be critical, the suspension system we use is.

[Passin' Thru]

My "perception" was that it would provide a bit of pitch - cone coupling? This would tend to reduce the pitch in high "G" loading, any advantages of that would be pure speculation on my part.

[C. Beaty]

There is an advantage to pitch-cone coupling, Pete, arising in this case from twisting the hub bar.

An increase of load, upward gust or whatnot, pulls pitch and increases rotor rpm above its normal increase. That tends to tilt the rotor forward, keeping it headed into the relative wind and improving angle of attack stability. Just like lowering collective on a helicopter causes a nose down pitch response.

Noseheavy rotorblades such as used on a Magni can do the same thing.

[Passin' Thru]

There is an advantage to pitch-cone coupling, Pete, arising in this case from twisting the hub bar.

An increase of load, upward gust or whatnot, pulls pitch and increases rotor rpm above its normal increase. That tends to tilt the rotor forward, keeping it headed into the relative wind and improving angle of attack stability. Just like lowering collective on a helicopter causes a nose down pitch response.

Noseheavy rotorblades such as used on a Magni can do the same thing.

Thanks Chuck. Those were precisely my thoughts, but I was not really sure if any other factors entered into the equation.
.

[RotoPlane]

Noseheavy rotorblades such as used on a Magni can do the same thing.

The blades I will be making soon, will have their root grip centers right at 26% of the airfoil chord. The CG however will be at 24% of chord. Because these grips have lead/lag hinges, I believe the spinning blades will tend to angle aft until the CG aligns with the static AC ~26%. Do you Chuck, see a problem with that?