Vibrations or u-joint wear

[Duke W.]

PS

The math may be over some heads, but look at the graph of output shaft speed variation versus constant input speed over 2pi, which is one complete revolution.

http://www.gwb-essen.de/fahrzeugbau/english/seite_20.html

Also, preferred designs are shown, which is the point Roy was illustrating - that the input angle should be the same as the output angle for a shaft with a Hooke joint at each end as in an automotive drive shaft. If your car has an annoying driveline vibration that can be traced to different output/input angles of the driveshaft to the transmissions/axle, raising or lowering the rear of the transmission by shimming the mount may bring the angles close enough to eliminate the vibration.

If the output/input angles are exactly the same, the driveshaft will have a slight sinosoidal component, but it will be cancelled by an equal angle into the drive pinion, so there should be no vibration transmitted through the drivetrain. Some difference in angle is acceptable, but at some point it may cause a noticeable vibration especially if the engine or trans mounts have "sagged" or the rear of the car has been raised or dropped to a significantly different than OE ride height.

Design engineers verify that driveshaft angles are within what is considered to be acceptable limits with layout drawings, but if components like motor/trans mounts degrade and alter driveline angles, or if the car is modified, angles may end up outside acceptable limits, which can cause annoying vibrations or even end up breaking something.

Duke

[John H.]

Re: Ha! Duke & Michael

Roy -

Actually, in normal operation, the entire disc area swept by a helicopter rotor blade contributes lift (although the advancing blade side of the disc makes a greater contribution than the retreating blade side does). This is true until the forward speed gets to the point where the retreating blade "stalls" due to insufficient relative airflow; when that occurs, the helicopter rolls over and creates a smoking hole in the ground.

[Roy B.]

Re: Ha! Duke & Michael

(Helicopter rotor blade contributes lift)
Yes! When pulling the collective stick
Moving in any other direction "joy stick" you use %50 of the rotors

And I hope this discussion on the drive shaft helped any one????

[Dennis C.]

John H. has the chopper info correct... *NM*

[Dick W.]

Re: Ha! Duke & Michael, My Head Hurts! *NM*

[Michael H.]

Mine too.......

I haven't even thought about any of this stuff for 30 years. Ran into a lot of cobb webs searching in the back corners of the brain. Hope I didn't do any more damage.

[Duke W.]

Re: Ha! Duke & Michael

"And I hope this discussion on the drive shaft helped any one????"

Yeah, it helped the "Village Idiot for the Day" (me) clean out some brain cobwebs!

Duke

[Michael H.]

Re: Ha! Duke & Michael

Good thing every village has it's own idiot because that's my job here in my village.

Duke, you are definitely among the most knowledgeable and informative posters here on this board and I always enjoy reading your posts. Thanks for taking the time.

[Duke W.]

Re: Ha! Duke & Michael

My occasional screwups help remind me that one can never know enough or remember all of what we've learned (and should remember) over a lifetime.

Duke

[Joe R.]

Re: Ha! Duke & Michael

Roy:

As far as I can tell, the bottom line of all the technical discussion is that the procedure you recommended in your original post (matching but complimentary angles) is in fact the correct approach.

[mike cobine]

Re: Ha! Duke & Michael

Yes and no.

If one side or another contributed more lift, the silly thing would flip over. This is why there is a semi-complicated method of adjusting the pitch of each wing. Sick Horsey used a squash plate. Bell used another design. So the lift is equal everywhere for level flight. For banking or aircraft pitch, lift becomes unequal in controlled amounts to reposition the craft.

They are actually wings, not blades. Wings are lifting bodies, and the vehicle is correctly known as a rotary wing aircraft. Blades are on fans, and try to push or pull air, like propellors and turbines, although many propellors and turbine blades are a wing-like design. A helicopter doesn't fly by pushing air (although from the noise and the wake over water you'd think so) but by creating lift, just like an airplane.

Lift is determined by speed through the air and the difference of the upper pressure and lower pressure on the wing created by that speed and the shape and pitch of the wing.

Thus helicopters are upper-limited in horizontal speed that exceeds the ability of the retreating wing to compensate by pitch.

For example, wing rotation speed of 300 mph. Horizontal flight speed of 100 mph. The advancing wing at 90 degrees to the flight direction is 300 + 100 = 400 mph. The retreating wing at 90 degrees to the flight direction is 300 - 100 = 200 mph. This means you need a lot of additional pitch to achieve the same amount of lift on the retreating wings as the advancing wings.

At 300 mph horizontal speed, it is impossible to get any pitch to work. Advancing = 300 + 300 = 600. Retreating = 300 - 300 = 0.

Of course, the stall of the wing is much sooner than zero speed and you hit an effective no-lift situation well before that 300 mph speed.

And this is the much simplied version. The long version convinces you Igor was on drugs when he came up with this. It was all mechanical, before computers or any electronics.

Add 7 wings, two jet engines, the desire to bank for turns, adjust the pitch of the aircraft, flex of the wings, and so on and it gets really complicated fast.

[John H.]

Re: Ha! Duke & Michael

Yup - I depended on Igor and his swashplates and gyroscopic precession-compensated cyclic controls for about 4400 hours; flew several of them into the ground (under fire) in other than the approved manner, but I'm still around to jabber about it Next we'll have a seminar on blade tracking, tail rotor harmonics, "splitting the needles", autorotations, and using crushed walnut shells in the field instead of hot-section overhauls

[John Walker]

Re: Ha! Duke & Michael

John, I am involved in helicopters as well, in fact I still fly the S-64 (Skycrane) and your basic explanation was very, very close. Good job and thank's for your service. John

[John H.]

Re: Ha! Duke & Michael

John -

That's a BIG bird! Most of my hours were in UH-1B gunships. Somewhere buried in my files in the basement is a tongue-in-cheek paper I picked up back in '63 at Wolters or Rucker entitled "Why Helicopters Can't Fly", that was absolutely hilarious (except for students nearing the 8-hour mark who still couldn't hold a 3-foot hover); gotta dig it out one of these days.

[John Walker]

Re: Ha! Duke & Michael

John, I have time in Uh-1E/L's Uh-1h's 212's 407's and Hu500's and of course the 54/64's. I really enjoy the work and the flying. I also was trained in the US Army but missed Vietnam by one month.(I turned 18 in May of 73). We now have a 1973 coupe with a 454 crate moter and 700r4 with 3.70 rearend and it is the most fun to drive car I have ever owned. This board is the source of so much information and education I have trouble at times comprehending all the help. Thanks again. John