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  #16  
Old 11-22-2004, 02:22 PM
Al_Hammer Al_Hammer is offline
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If you are looking to improve efficiency, I suspect that number of blades won't have as much effect as going to a full time partial power drive on the rotor.
Supplying up to 15HP to the rotor allows it to fly at a reduced angle of attack, thus reducing drag considerably. Any more than about 15Hp and torque is a problem.
See **** DeGraw's DeBird gyro for an example.

(guess I can't type the word D*** without being censored, that's funny)
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  #17  
Old 11-22-2004, 02:29 PM
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2 vs 4 Blade - would love to see that on a new tractor gyro....My helo experience (UH1 to HH60G) would bear out that the 4 blade is the way to go...MUCH smoother in the 'Hawk compared to the Huey.....'Course it is much more complex, but look at all those Pitcairns back in the day - they were by and large 4 blade rotors.....
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  #18  
Old 11-22-2004, 04:32 PM
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Quote:
Originally Posted by Al_Hammer
If you are looking to improve efficiency, I suspect that number of blades won't have as much effect as going to a full time partial power drive on the rotor.
Supplying up to 15HP to the rotor allows it to fly at a reduced angle of attack, thus reducing drag considerably. Any more than about 15Hp and torque is a problem.
See **** DeGraw's DeBird gyro for an example.

(guess I can't type the word D*** without being censored, that's funny)
Testing: **** **** **** ****

Damn, you're right. s**t f**k... and my father-in-law's name is ****. This s**ks.
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  #19  
Old 11-22-2004, 04:55 PM
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Quote:
Originally Posted by jolly467
2 vs 4 Blade - would love to see that on a new tractor gyro....My helo experience (UH1 to HH60G) would bear out that the 4 blade is the way to go...MUCH smoother in the 'Hawk compared to the Huey.....'Course it is much more complex, but look at all those Pitcairns back in the day - they were by and large 4 blade rotors.....
Hi Jolly, i hope i will see it on a tractor I want to build next year...
thanks
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  #20  
Old 11-22-2004, 05:21 PM
skyguynca skyguynca is offline
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the 4 blade was my discussion on another thread where we were sorting out the lead/lag hinge so that we could still use the teetering head stacked to keep it simple. I am still using that on my 2 place I am building over the winter. I am also planning on using partial power on it. Having a second small light engine to provide it with a shaft drive with sprag clutch to the head. I have most of the drawings done and should start construction in December...right now I am still painting my 172 so my hangar is full.
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  #21  
Old 11-22-2004, 05:48 PM
Al_Hammer Al_Hammer is offline
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Isn't the lead lag hinge going to act like a solid connection when it is under load?
The blades can lead and lag just fine if they are "sped up" or "slowed down" by coriolis forces, but in the case of the 4 bladed rotor, the hub of one rotor is being twisted from the center by the movement of the other rotor. I'm not explaining it very well, but, basically any hinge is not going to swing freely when loaded with 7000 lbs or whatever the CF force is. It might make more sense to simply allow the teeter bolt some freedom of movement by using a soft mount for the bushings.
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  #22  
Old 11-22-2004, 06:04 PM
skyguynca skyguynca is offline
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the hinge should move and the movement only has to be a small amount. others have tried the 4 blades with stacked teeter heads and developed cracks in the trailing edge of the blade near the blade attachment point. This hinge should eliviate that problem. Really not much different than the attachment hinge on 3 three bladed head like used on the CH-47. A pin thru a hole in the grip. True it uses a bearing but the bushings should provide enough bearing surface and movement. This will allow the blades to speed up and slow down without transfering the twisting load to the hub and trying to twist the two teeter heads should be taken care of. I don't know if I would want to try and make a teeter bolt in a slot that moves, seems like that would set up some serious vibrations.
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  #23  
Old 11-22-2004, 06:17 PM
Al_Hammer Al_Hammer is offline
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There's an important difference between a double teetering 4 blade system and a 3 bladed or 4 bladed fully articulated system.
The blades in the double teetering rotor are not really speeding up and slowing down as they do in a 3 bladed system, just as they don't in a 2 bladed underslung teetering rotor.
The source of the cracking may be(my speculation) that the hub is forced to slow down and speed up due to the cardan joint/hookes joint effect as we discussed on another thread. You are then trying to turn the hub against the force of centrifugal force of the blades trying to hold it stiff. It's like trying to turn your wrist when you are spinning a weigh on a string. The greater the CF, the harder it is to turn your wrist, even if you have a lead lag hinge , its still stiff. C. Beaty made some comments on the 2 per rev thread that backs up my position on this.
I don't think you will induce vibration by having a soft teeter mount because its not a driven system.(well you did say partial power, so that's not totally correct)I'm not criticising the design, just trying to establish if that hinge will do what you want.
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  #24  
Old 11-22-2004, 07:29 PM
skyguynca skyguynca is offline
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me too..........I am looking for a fix. Bensen did it originally but I can not find any more data from his work, he mainly dropped it because it was supposed to be a twin engine also but the single engine ops was not what he expected. Magni is flying one now also but they are very tight with any data at all concerning their stuff.
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  #25  
Old 11-22-2004, 08:10 PM
Al_Hammer Al_Hammer is offline
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Right, there isn't much info out there. . . Good luck in your quest.
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  #26  
Old 11-22-2004, 08:30 PM
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Al/Brian,

I deleted Mr. DeGraws first name from the censorship list.
Soyy, I didn't think of that when I made the list!
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  #27  
Old 11-22-2004, 09:10 PM
skyguynca skyguynca is offline
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Thanks Al, I am determined to do it. Not just for me but if it works the drawings will be free to everyone.
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  #28  
Old 11-22-2004, 09:51 PM
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David , as some one said to me : GET BUSY !
good luck ! and keep posting.
cheers
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  #29  
Old 12-02-2004, 02:17 PM
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In Norm’s old forum I asked why we need lead-lag hinges for more-than-two bladed systems and not for our present 2-bladed systems. I knew that lead-lag hinges can be very dangerous. See http://www.fwcvhpa.org/fw/ground.htm or http://safecopter.arc.nasa.gov/Pages..._Resonance.pdf

At that time I wrongfully thought that the Coriolis effect have something to do with it. (Coriolis have to do with the rotation of the earth. That causes water to spin in your bath outlet and winds to blow in rotation from high to low pressure. Cierva used this myth to fool his competition! — Chuck Beaty wrote: The Coriolis hoax, ....Was perpetrated by Cierva to bamboozle his competitors.

To have a Coriolis torque, you must have radial movement of mass in a rotating system. The commonest example is to stand at the center of a carousel and walk toward the rim. Your body, as it gains kinetic energy, exerts a torque opposing the rotation of the carousel
.)


Al Hammer was quick to point our the fallacy of my thinking: “It is not Coriolis, but rather hookes joint effect that causes a cyclic speed variation in the rotorhead” (Sorry Al you goofed earlier in this thread by saying “The blades can lead and lag just fine if they are "sped up" or "slowed down" by coriolis forces,”)

To understand what is going on, the following is important:
1. “The blades move in a single plane(the blue plane in the diagram attached), but the plane is tilted with respect to the rotorhead and ring gear.” (Al Hammer, emphasis mine)
The blades neither speed up/slow down in RPM (angular velocity) with respect to their own axis of rotation, nor do they climb and descend like a circular roller coaster. Both such behaviours would require the application of large forces at various points in their orbit. (Doug Riley)
These two gentlemen, rightfully observed that:
a) The blades do not accelerate or slow down.
b) They do not climb or descend out of the single plane in which they turn.
Al gave this diagrammatically in attachment 1.

2. Blades are coned. If all the blades are coned in the same angle with respect to the spindle, no problem with leading and lagging would have existed. Chuck Beaty have shown that, in order to compensate for the different wind velocities that the advancing and retreating blades experience, but in order to still carry equal load, the plane in which they move goes op on the one side and down on the other. This reduces or increases the angle of attack. (Type “Flap, flap, flap” into your search engine to find Chuck’s article.)

One blade will therefore be at a larger angle in respect to the axis of the rotorhead than the other. – something like my over-inflated diagram in attachment 2. While A and B are exactly the same length, the radii of a and b in regards to the axis differ. If both are turning at the same speed (as Doug Riley rightfully said above) then a, having a shorter radius, wants to turn quicker around the axes. A wants to lead and B is lagging. 180 degrees later B will be leading and A lagging!
Paul Plack describes this: "When the figure skater raises her arms over her head and reduces the radius of her body, her spin RPM increases, despite the fact that the attachment points for her arms are overslung above her body's CG. While less esthetically pleasing for the judges, she could put her arms straight down at her sides, and the same thing would happen...”3. To compensate for this leading and lagging, someone (at Bell) invented undersling. Al Hammer again gives a clear explanation: “If you look at the attached diagram it can be seen that no matter how the coned rotor tilts , a point on the rotor will always be at a constant radius from the teeter bolt or center of rotation if the undersling is correct.” His diagram is attached as the third attachment.

Again Al Hammer rightfully observed: "If the hub bar were not underslung (teeter bolt in the hub bar) we would certainly need lead lag hinges."

4. Lead-lag hinges have been suggested in this forum. For the problems associated with them, I really think that they are a very bad solution for a not-so-bad problem.


Ask me to write a long intro for a short question!!
Multi - bladed systems often come up in our conversations. They may enhance our machines. (See my first posting)

Now: to you who are smarter than I: Have anyone tried a system with undersling such as in the last attachment? – NOT on paper, but in real life!

Jim
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  #30  
Old 12-02-2004, 03:57 PM
Al_Hammer Al_Hammer is offline
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Jim,

its always good to see my name in italics, I think
I used the term "coriolis" above, mainly to avoid a lengthier disccussion (and to bamboozle my competitors..)
The blades do move relative to the lead lag hinge and that's the main thing. In a 2 bladed, underslung rotor, they do not lead and lag.
The logical step that some people would take is to use lead lag hinges to eliminate the stresses in the double rotor(4 bladed).
Unfortunately, they won't work for that, I don't think, as I tried to point out earlier.

I have no idea if anyone has used a system like in the drawing.
The L shape in the blade seems like it would be problematic.
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