Location of actuator disk for optimal efficiency 1

[Intermesher]

I am interested in knowing if locating a body ahead of an actuator disk or behind an actuator disk has any effect on the aerodynamic efficiency. This body would have a 3D-teardrop shape and additional items, which would contribute to drag, are not considered.

A sketch and additional comments are located at

http://www.unicopter.com/1538.html#Optimal_Efficiency

Thanks;

Dave

 

[MikeHalloran]

I give up: What is an "actuator disk"?



Mike Halloran
Pembroke Pines, FL, USA

 

[evelrod]

Mike, try...

http://www.afm.dtu.dk/Publications/PHD/RobertMikkelsen2003.pdf

I got interested in the Palm Springs 'wind farm' a while back and found this. It's a little too tech for what I was after, but check out Chapter 2, page 6.

Rod

 

[MikeHalloran]

Ah. Thanks, Rod.



Mike Halloran
Pembroke Pines, FL, USA

 

[MikeHalloran]

Uh, Dave, you appear to be trying to optimize the design of a rotorcraft model that has been simplified too far to be realizable.

E.g., worrying about the interaction of the actuator disk and the streamlined body without considering appendages.

E.g. declaring that a rotorcraft lacks wings. It does have wings, they happen to be rotating, and stable operation requires counteracting the torque required to rotate them by some means that usually involves appendages.

It might be more productive to model a rotorcraft that has actually flown, and attempt to deduce the compromises that influenced its geometry.



Mike Halloran
Pembroke Pines, FL, USA

 

[Intermesher]

Mike,

Thanks for your valid points.

I agree that the appendages will have an effect on the optimum placement of the propeller. However, it will be interesting to have an understanding of the basic fluid dynamics, in respect to the location of an aerodynamic object on the centerline of the flow.

This page shows a reasonably clean application where the propeller could be located in front or behind the 'fuselage'

http://www.unicopter.com/1512.html.

It is intended that the rotors will incorporate the Advancing Blade Concept and this means that during high-speed flight these rotors will be providing very little thrust over the fuselage. In addition, it is hoped that the spars to the rotorhubs will generate little turbulence.

Dave

 

[rb1957]

the links say that this was tried on an An2 ... a quick yahoo search didn't quickly lead to anything ... any pics ?

so level of common sense suggests hanging a body in front (or behind) of a prop doesn't help much, 'cause no-one does it. spinners are typically as small as possible, again suggesting that sticking something ahead of the prop doesn't help.

 

[evelrod]

rb1957
If you need a pic of the Antonov, just do a Google of 'Antonov 2'...it's a very popular aircraft, worldwide.
If you would like to see one up close and personal, there is at least two (one red and one yellow) near you... try the Planes of Fame Museum in Chino, CA. You might even score a ride.

Rod

 

[MikeHalloran]

If you put the prop at the front, you can at least hope to discharge a parachutist in forward flight without killing him.

The slipstream itself won't be lethal. The Flettner FL-282 and the Kaman K-225 were both pretty slow, because of all the machinery stuck out in the wind. Both of those machines had vertical stabilizers; I suspect your machine will need one too.

I don't understand your math about the tip speed and air speed adding to something less than the air speed.


K-225

http://www.nasm.si.edu/research/aero/aircraft/kamen_k225.htm

FL-282

http://www.fiddlersgreen.net/AC/aircraft/Flettner-282/flettner.php

AN-2

http://www.seqair.com/Other/UnFalco/UnFalco.html

http://www.warbirdalley.com/an2.htm

Mike Halloran
Pembroke Pines, FL, USA

 

[Intermesher]

Mike,

"I don't understand your math about the tip speed and air speed adding to something less than the air speed."

Newer faster helicopters will require that the rotational speed of the rotor(s) be reduced. This is because the tip of the advancing blade must be below Mach1. This results in the tip of the retreating blade operating in a low airspeed.

At mu=1 the retreating tip at 270-deg azimuth is in zero velocity and the retreating blade is totally in reverse velocity. The helicopter in the previous link has these retreating blades over the fuselage.


The Flettner FL-282 was actually quite fast for its day. It was 18 mph faster than the later Sikorsky R-4B. Kaman created the belief that the intermeshing configuration was slow configuration when he developed his synchropter for a different market from that of Sikorsky.

He is a picture of an 'aerodynamic' FL-282

http://www.unicopter.com/Flettner-GermanBook3.jpg

Dave

 

[rb1957]

everod, thx for the hint (mind you i posted that i searched yahoo and got tons of hits, and looked at some and saw a conventional biplane, and i thought that maybe the OP had a special plane in mind, but wth)

 

[evelrod]

rb1957
Drive over and take a look at the An2. I think you will find it anything but 'conventional'. Ck out all of Antonov aircraft...I don't think they know what 'conventional' means!

Rod