Any advantage of a one blade prop?

[helipaddy]

YouTube - Einblattpropeller (http://www.youtube.com/watch?v=6VwYHwvx6eU)

[C. Beaty]

Single blade props were patented in the US in the 1930s (the Tidd patents).

The problem is that the single blade takes most of the torque and tries to rotate the engine in a circle; a prop with two blades develops a couple. An additional counterweight at 90º can eliminate the circular motion imparted to the crankshaft but only works for fixed torque inputs.

One of Sikorsky’s Russian engineers (Eugene Gluraheff) did developmental work on a one blade tail rotor with a sliding 90º counterweight in the 1950s.

I know from hands on experience that one blade main rotors don’t work on gyros for altogether different reasons. The single rotor blade responds normally to cyclic inputs but the counterweight tends to remain in place, throwing everything violently out of track until it catches up.

[WaspAir]

I've seen counterbalanced one-blade props used on motorgliders with a retracting engine that folds down behind the cockpit. If stopped in the proper position, it makes a more compact package to pivot and drop into the fuselage bay. It wasn't chosen for aerodynamic or weight concerns in that application.

[helipaddy]

Thanks, It looked like a bit more complexity than needed to me. I wonder what that muffler will do to the exhaust timing for the 2-stroke too. The main gear looks real springy in this vid:

YouTube - Gyrocopter Probelauf mit Einblattpropeller (http://www.youtube.com/watch?v=KyHD_wTezio)

[C. Beaty]

The reason for one bladed props is that with a skewed teeter hinge providing pitch-cone coupling, constant speed operation is possible.

Stuff often doesn’t work out the way we hope.

“The inherent perversity of inanimate objects.”

[Earthboundmisft]

:smokin:The prop aside, I dig that airframe. Very clean...

[Wiplash]

That blade looked like it teetered or something.

Between 0.14 and 0.30 seconds of the first video he seemed to be flexing the blade but it didn't flex back. What's up with that?


Doh!

I know better than to not read Chucks posts thoroughly. He answered my question in the 5th post...

[birdy]

I want one.:)
A single teetering prop would be more efficiant and o so quiet, with no gyroscopic forces on the frame.
Wunder how i get in contact with this bloke?

[C. Beaty]

Birdy, you know how much I hate to rain on your parade but before you lay your money on the table for one of those one blade props, there are a couple of things you ought to consider.

Myth #1: A single blade is more efficient because it’s not in the wake of its mate.

Consider that in forward flight the helices from each blade are separated by the amount each blade screws itself forward with each revolution. We’re interested in forward flight; not pulling tree stumps.

Myth #2: Blade area.

Propeller blade loading is just as important as rotorblade loading. The necessary blade area can’t be obtained with a single blade.

You may have noticed that some gas turbine aircraft have props with as many as 6 blades, sometimes more. Perhaps no one informed Boeing or Airbus that so many blades were inefficient?

As for the vibration problems, imagine you’re tightening a nut with a long extension shaft on your wrench. If you use a T handle wrench, you apply a balanced couple to the extension shaft and it stays pretty much as you placed it.

Then imagine you’re using a ratchet handle; simply pulling on the handle causes it to fall over unless you brace the head of the wrench. That's the situation with a single blade prop; the engine is the head of the ratchet handle and the torque applied to the blade causes the engine to be pulled in a circle. As mentioned previously, for a single value of torque, the tendency of the engine to be pulled in a circle can be can be eliminated by an additional counterweight at 90º.

Here’s an experiment you can perform for yourself.

I believe you’re flying a 2-blade, teetering rotor on your gyro. Pretend one of the blades is the counterweight and set it for zero lift pitch. How do you think it will fly?

Actually, it would fly OK if you only did zero airspeed vertical descents with the lifting blade slightly overbalanced to compensate for the fact that the rotor thrust vector has a circular motion. But with any edgewise motion, it would rattle your eyeballs. And you’re not applying torque to the rotor.

[Rotor Rooter]

There is quite a bit of Internet information on "single blade propeller".

The single rotor has also be used successively in helicopters, but its limitations show up as the forward speed increases.


Most, if not all, of mankind's discoveries over the past 100,000 years are simply extensions of nature's discoveries over the past 1,000,000,000 years.

To my knowledge, the only example of a rotating airfoil in nature is the maple seed. It is interesting to consider that it only flies in the axial direction. Could this be the fundamental reason why rotorcraft are limited in their forward speeds?
http://www.unicopter.com/Think.gif


Dave

[birdy]

All good points CB.
But,
Myth #1: A single blade is more efficient because it’s not in the wake of its mate.
Considering most of my airtime, and 'max efficiancy' work is at low or min AS, and most of the noise i hear is the growl of each blade hitn the other blades distubance, ill be better off there. [ in IOW, im pulln stumps more often than just flyn from a to b.]

Myth #2: Blade area.
So your sayn a single blade of the same radius and more than the combined chord of 3 skinnys wont do?

Perhaps no one informed Boeing or Airbus that so many blades were inefficient?
I woulda thought it had more to do with practicality.
To harness the power of the turbine youd need blades thatd be too long to not hit the ground. So they just use more shorter ones. No? [ theres a bloke over ere with a 200 hp marine donk in his gyro, and only room for sumthn like a 68" prop, so he needs 6 skinnys to hold back the 200 nags]

As for the vibration problems...................
Id considered this a few years ago wen i first enquired bout teetering props.
Yes, you only have one blade pushn from one point of the disc at any one time. [ one airodynamic thrust]
But, the counter weight isnt just balancing the opposit mass of the blade. It also balances the thrust.
The thrust of the blade forces the counter weight backwards. But the weight dont want to spin there, it wants to rotate on a plain thats at 90* to the axis, and perpendicular to the teeter point.
IOW, it wants to be slung streight out. [ where it would be if the blade wasnt forcing it backwards.]
This 'want' counters the thrust equaly of the opposing blade.

How do you think it will fly?
Id say orrite, solong as it could feather so's to not produce any lift at any speed.
If your rite, why didnt ol mates engine get ripped off the machine?

[C. Beaty]

As you may know, Birdy, Hughes helicopter blades come in a set of three.

I lost two of them when the wire running the electric fuel pump on my gyro chose to vibrate itself in half over the Gulf of Mexico, leaving me with one perfectly good blade.

Having the urge to fly and having just one blade, the obvious thing to do is to build a one blade counterweighted rotor. Which I did, making up a streamlined counterweight from steel sheet poured full of lead.

Autorotation appeared normal on the ground except the whole machine would start shaking whenever the stick was moved. Stick still, it was glass smooth. Stick moved very slowly, shake was tolerable until the rotor caught up with the stick at which point, glass smoothness returned.

I very gingerly began my takeoff run and managed to get daylight under the wheels but it didn’t seem to very practical; being unable to move the stick at a normal rate.

My friend Gary, a much better pilot than I, wanted to have a go. I told him that he’d have to be careful and avoid rapid stick movement.

Gary got the rotor started but stirred the stick around and lost the neutral point. The thing began hopping and flipped over without ever having left the ground.

A rotor, as you know, is a giant gyroscope. The one blade follows the stick at a normal rate but the counterweight tends to remain in its orbit, being pulled out of orbit by the blade. Until the counterweight catches up, everything is grossly out of track.
***
One of the attractions of one blade rotors is that collective pitch change doesn’t require a bearing stack loaded by several tons of centrifugal force. Both blade and counterweight can be rotated together for collective change.

With that in mind and despite my unpleasant experience with one blade main rotors, when I began building a helicopter a year or so later, I chose a one blade tail rotor.

I assembled a tail rotor test stand powered by a 10-hp electric motor arranged so as to enable torque (and power) to the rotor to be measured.

The tail rotor naturally vibrated because of the unbalanced torque; the blade tries to stand still and let the tail rotor gearbox rotate around the blade. This can be balanced by another counterweight at 90º but it only works for one level of torque; any change of collective and the vibration returns. A sliding 90º counterweight seemed even less attractive than feathering bearings designed to resist centrifugal force.
***
One blade props look attractive because they can easily be given constant speed behavior. A skewed teeter hinge arranged to increase pitch when coning angle decreases bestows constant speed characteristics.

There was a flurry of these things in the 1930s; one was even type certificated on Cubs. But all were abandoned because of the intractable vibration problem.

[C. Beaty]

Here’s a link to one of the 1930s one blade propellers:

http://docs.google.com/viewer?a=v&q=cache:gWSKlwLrcXoJ:www.ultraligero.net/Cursos/varios/helice_de_una_pala.pdf+one+blade+propeller&hl=en&gl=us&pid=bl&srcid=ADGEESjVSzFd5AlIDKzSiJYDJ_ahHt-LuBNmyXmKUPG6qrIFH8VAcnaK_xloZwQ26P_S0D2qbvlfcIca5 glVu7iVP4LFH-2gyG7-sL5W9QzmAZ-ilp7hxLe5MLsJra2v3k9C7AMmRL1T&sig=AHIEtbQmxz9E-rkuAiFb88hqhW8z6pdszA

The author of this article claims it’s dynamically balanced but it’s not; otherwise, we’d see nothing else. Not only is the problem of torque unaddressed but blade CG and counterweight CG don’t lie on a single plane:

[Rotor Rooter]

Chuck,

I looked into the possibility of a single blade rotor (http://www.unicopter.com/0036.html) thinking that the dead counterweight could be replaced by something useful. From recollection, there appeared to be no significant problem as long as there was only axial flight. This appears to be in agreement with your 'hand-on' cyclic stick activity.

The propeller experiences only axial flight. But, it has been mentioned that the problem with the single blade propeller is that of ground clearance, due to its longer length.


Dave

[RotoPlane]

Your post #13 drawing is correct for the prop you noted Chuck, but I wonder how it would act with the counterweight angling up from the teeter-hinge so that its CG was in line with the blades CG, at a normal coning angle. Better yet having the counterweight and the blade CG's scissored so that they are in always in CF alignment regardless of coning angle. Just a thought.

[C. Beaty]

You might have something there, Ed. With skewed teeter hinge providing sufficient pitch-cone (AKA delta-3) coupling to make the prop a constant speed device, a fixed bend in the counterweight might work. The coning angle would be greater without the deconing effect of the counterweight but so what?

Now put your powers of deduction to work on solving the torque problem.

[RotoPlane]

Heheh....I don't do torque problems Chuck....so I'm trying to eliminate all torque effects....and that includes no one bladed anything ;).

[birdy]

a fixed bend in the counterweight might work
Cant see how.
Like a gyros thrustline, it never changes from the line of the prop hub, no matter where you mount it to the frame.


Which I did, making up a streamlined counterweight from steel sheet poured full of lead.
Your rite, i didnt think of the assymetrical cyclic bit.
Maybe, instead of just a streamlined blob for a counterweight, you had a very wide chord, short CW, set abit further out, so it too can airodynamicaly follow the cyclic commands??
The forward speed would be limited to how far out the CW was from the hub, coz itd be cyclicly ineffective wen the AS had the stalled area of the disc reach the CW.