My 1970s helicopter

C. Beaty

Gold Supporter
I stumbled across this photo of my 1970s helicopter; hingeless rotor with semi-floating hub, Canadian Kohler 440cc snowmobile engine and curved tail rotor driveshaft.

It hovers with the left skid low because left cyclic is required to resist tail rotor thrust and rotor hub is connected to the driveshaft via a stiff “U” joint made from Chevrolet engine mounts.

The tail rotor driveshaft ran at ~5,000 rpm, well above critical speed and if not curved, would have required support bearings every couple of feet to keep it stable.

helicopter.JPG
 
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C. Beaty

Gold Supporter
Blew the engine because it didn’t take kindly to running with a vertical crankshaft and the remains are in a barn growing cobwebs.

Outboard engines, designed for vertical operation, have serrations on the connecting rod big ends that enables an oil film to form between big end and crank cheeks. The Kohler had no such provisions.
 

jm-urbani

Junior Member
was it a 4 stroke engine ?
I am asking this because If remember well the mosquito articat engine ( 2 stroke) was mounted vertically , and believe me it worked perfect
 

jm-urbani

Junior Member
was it a 4 stroke engine ?
I am asking this because If remember well the mosquito artic-cat engine ( 2 stroke) we had in our Hangar was mounted vertically , and believe me it worked perfect
 

C. Beaty

Gold Supporter
My Kohler engine was 2-stroke as were most outboard boat engines at the time which were designed for vertical crankshaft operation.

For vertical engines, the weight of the connecting rod is supported by rubbing surfaces between it and the crank cheeks so some provision must be made for forming an oil film. This is normally provided by grooves or serrations on the big end which creates a wedging action for the oil. The Kohler engine had no grooves on the connecting rod.

The connecting rod roller bearing on my engne overheated and the rollers looked like pieces of bread dough that had been rolled between the hands.

But the actual cause of failure is all a matter of conjecture on my part.
 

Jean Claude

Junior Member
Chuck,
I wonder why this rotor is not more used by the industrial manufacturers of helicopters: not hinge not drag dampers, not ground resonance.
Very judicious too, the curved tail rotor driveshaft
 

C. Beaty

Gold Supporter
JC, as you and I know, birds’ wings flap but rotor blades don’t; it is only an illusion. Unfortunately, too many helicopter engineers have a fixation on rotor “flapping.” The technical literature is confusing.

As far as I know, the first helicopter rotor without flap or drag hinges was the Doblhoff WNF342 built in Austria during WWII. The next was the Doman LZ-5 built in the US in the 1950s.

Your plank on a rope is an excellent illustration of non-flapping; would you post the link to it again?

https://en.wikipedia.org/wiki/Doblhoff_WNF_342


https://en.wikipedia.org/wiki/Doman_LZ-5
 

bryancobb

Junior Member
No Title

Chuck and JC. You guys are smart. But every helicopter pilot IN THE WORLD is taught that rotor blades flap, feather, and hunt as aerodynamic forces change during flight. Flap may not be the best word selection but that fact does not mean the phenomena is an illusion. Call it "compensating" or whatever you`d like... or just get on board with the rest of the world and quit swimming upstream.

You two know SOMETHING must passively happen in the rotor to "fly the disk" to the proper tilt the disk needs, to make the aircraft do what the pilot wants it to do. For example, in straight-and-level flight the disk(s) have a significant 3:00/9:00 lateral tilt so that it is not perpendicular to the rotation axis. As you know, amount of lateral tilt varies with airspeed. This automatic, passive tilting of the disk is what is referred to as "flapping." I agree that compensation would be a more accurate term to use but it is not an illusion. On the H-21 in straight-and-level flight below, you can clearly see the opposite compensation or flapping because one rotor turns clockwise and one turns counterclockwise.
 

Attachments

C. Beaty

Gold Supporter
When you twirl a rock on a string, does it flap? Does it speed up and slow down? Not if you view the rock from the axis of its rotational plane but if viewed along the line of your forearm or wrist, it appears to.

Jack up the front end of your front wheel car, start the wheels spinning, put in a steering angle and view the wheel along the axis of its drive-shaft. With the wheel spinning at an angle to its drive shaft, the valve stem moves nearer and farther away from the viewer, therefore it’s flapping. And naturally, since it’s flapping, Coriolis enters the picture so it must speed up and slow down.

A rotor, like all masses in motion, must follow Newton’s laws of notion. And it’s no different from a rock on a string.

Viewed along the axis of the rotor tip plane, a blade moves with uniform motion, neither flapping nor speeding up or slowing down.

Lead-lag hinges and flap hinges are a kinematic rather than dynamic necessity that permit the rotor to run at an angle to its driveshaft.

With rotor blades rigidly connected to their hub with only feathering bearings and with the hub connected to the drive train via a “U” joint, there is no necessity for flap-drag hinges.
 

C. Beaty

Gold Supporter
from Gessow and Meyers: Aerodynamics of the Helicopter:

"On the other hand, an observer viewing the rotor from above, standing on, and rotating with, the control axis is utterly unaware that anything unusual is occurring. From his point of view. there is no flapping, no cyclic-pitch change, no cause of any sort for the blades to move in the plane of rotation. It is not odd, then, that he finds that there is no in-plane motion with respect to the plane of the tips. Apparently, then, the existence of this in-plane motion depends on the axis of reference used. With respect to the shaft axis, the blades move toward and away from each other as they rotate, while with respect to the tip-path plane axis no in-plane motion occurs."

This statement is for a hovering helicopter that is a bit noseheavy where the rotor is running at an angle to its driveshaft.
 

bryancobb

Junior Member
OK Chuck, I`m seeing the reason for your illusion viewpoint. However my 2-blade, semi-rigid, pre-coned, underslung rotor see-saws several degrees about the teter bearings about 1100 times per minute to minimize vibrations and compensate for dissymmetry of lift and we really need to call that action SOMETHING don`t we?
 

C. Beaty

Gold Supporter
Of course a seesaw rotor seesaws about the teeter pivot. With a 2 blade rotor, a single hinge suffices as a universal joint. Replace the rotor with a barbell equipped with a teeter pin at its center; install it on your rotorhead and it behaves just like a rotor would in a vacuum. Spin it up and it remains fixed in space but the Earth rotates your airframe at 15 degrees/hour, meaning it would hit the teeter stops long before an hour was up. When the barbell runs at an angle to the rotorhead axis is it flapping? Well, yes in the same sense that your rotor is flapping.

Viewed from the barbell’s real axis of rotation, it is not.

JC had a video of a plank on a rope that brought clarity to this flapping confusion.
 

C. Beaty

Gold Supporter
Thanks, Alan; JC’s video should bring clarity to nearly everyone; the plank behaves exactly the same as a see-saw rotor in forward flight.

It should be obvious that the plank is rotating at a uniform rate about its own axis and in a physical sense, is not flapping nor is it speeding up or slowing down as it rotates. The crotch in the suspension rope applies cyclic pitch to the plank and if it was a 2x8 rather than a length of ~square timber, aerodynamic force would bring it into alignment with the rope axis.
 

phantom

Newbie
C. Beaty;n1128598 said:
My Kohler engine was 2-stroke as were most outboard boat engines at the time which were designed for vertical crankshaft operation.

For vertical engines, the weight of the connecting rod is supported by rubbing surfaces between it and the crank cheeks so some provision must be made for forming an oil film. This is normally provided by grooves or serrations on the big end which creates a wedging action for the oil. The Kohler engine had no grooves on the connecting rod.

The connecting rod roller bearing on my engne overheated and the rollers looked like pieces of bread dough that had been rolled between the hands.

But the actual cause of failure is all a matter of conjecture on my part.
The only reason I think something happened to your engine to cause this other than being mounted vertically is that these engines and others that are similar ran hundreds of hours in hovercraft mounted vertically without having a problem.
 

C. Beaty

Gold Supporter
Norm, I base my conjecture on the fact that a rod bearing seized up and the rod broke in half. But it could have been any number of things.

I purchased this engine direct from Kohler as an OEM and it came without carburetors or exhaust system. I used OMC outboard carburetors that could have been too lean. I should have taken more time without rushing to get it in the air in time for a Bensen Days flyin.

Whatever the case, the Kohler was one of the nicest engines, including Rotax that I'’ve ever seen; hard chrome plating on cylinders and very lightweight.

But without exhaust system, it probably wasn'’t over 25 hp and the poor thing was running all out.

For those who don'’t know, Norm lives at the outer edge on the habitable world with polar bears and perhaps an Eskimo or two. So stay warm, Norm.
 
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C. Beaty

Gold Supporter
That’s OK JC. The copy of your video clip on Youtube works fine.

Alan, did you save a copy of JC’s original and repost it on Youtube?

Whatever the case, thanks to both of you.
 
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