Paul, I received 2 copies of Contact! #89 from Mr. Morgan. Just wondering if
you received anything, I can mail you a copy, and or scan some pages.



C. Smith

Not yet. I'll check the mail tomorrow.

I got the article and the Installation Handbook from Mr. Morgan. Thank you Mr. Morgan. Very interesting idea. They used my annular clutch throw out slave cylinder invention invented in 1971 now widely used on most auto transmission cars to change the pitch of the blades. There is a serious error in the dwg of the device  that will confuse most people. I'll have to redraw it to clarify but it has to do with the allowable travel of the annular slave cylinder. Here is a modified sketch.

They use a PWM electric motor to provide the oil pressure to change the prop blade pitch. It is not necessary to do this with a leak free system. You could mount a long travel, small diameter cylinder behind the instrument panel and change the pitch merely by pushing in the piston  rod with a knob on it. It would look just like the pitch control on a C182. There is a European designed variable pitch prop that does it this way. Super simple. Just like a clutch master cylinder in a car. That would save a lot of money. However you would not have the automatically controlled constant speed feature. That requires the PWM electric motor or a conventional prop govenor.

Paul Lamar

Hi Paul,

A couple of notes, I am not familiar with the device you referred to as being invented in 1971.  This evolved from a rack and gear system.  As to the long cylinder behind the instrument panel,  Been done. Two issues. #1, you don't have enough strength to adjust the system during operation, and without a HUGE mechanical advantage you don't have the precision available.  The blade's travel is very little during operation.

Larry

I got the 6,478,542 patent number from the hand book you sent me Larry. It is on the second page. It was patented in 2002. Yes I know you don't use the rack and pinion to change the pitch of the blades. You use a very common and almost standard spool to do that job. The blade travel force depends on the axis of rotation position relative to the blade cord so I don't have a blade drawing to go on. For example if the blade rotation axis is on the 1/4 cord point of the blade the force to rotate the blade will be a minimum. The force and travel is also a function of the distance of the pin from the axis. Again I don't have a dwg to determine that.

The force available from the control cylinder mounted behind the instrument panel depends on the diameter of the piston used. My guess is 100 psi is needed to change the pitch on most hydraulic props. If the average person can push 20 pounds the area of the control piston would have to be .2 square inches. .2 square inches  / 3.1416 = the radius squared or .0638 inches. The square root of which is 0.252. Therefor the control piston would only need to be about  .5 inches in diameter. The travel or distance needed has been discussed above. The mechanical advantage is five to one so a five inch change in the master cylinder or control knob will move the spool one inch which should be more than enough to change the pitch throughout the entire range.

Here are some pictures of the European prop that uses this method of control.

BTW What is the correct second patent number?

Paul Lamar