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An answer, hopefully

Posted by Christer on Tue Feb 05, 2002 09:33:04 AM

In reply top Wow....... a contra-rotating prop version.. Some questions ? posted by Michel Lemieux on Tue Feb 05, 2002 08:39:42 AM

You?re correct that the unwanted effects of a single propeller are eliminated;

there?s more than torque which make the aircraft roll in the opposite direction of propeller rotation, in the case of a Griffon Spit to the right;

there is the slip stream which hits the fin from one side which in this case makes the aircraft yaw to the right;

in the climb at high angles of attack the downwards going blade gets an increased pitch whereas the upwards going blade gets a decreased pitch which, again, yaws the Griffon Spit to the right;

these three effects combined are commonly known as torque.

Then there is the precession but, for me it would take too many words, so I?ll leave that for the experts to explain.

The front propeller in the contra propeller assembly is the master to which pitch control is transferred from the pilots lever in the cockpit. Pitch is transferred from the front propeller to the rear by means of a bearing, which IIRC is called a translation bearing. If this should fail, which has happened on several occasions, the rear propeller goes into coarse pitch and is rendered useless providing nothing but drag. The front propeller has to do all the pulling, against the will of the rear one, and full power has to be applied to even fly at minimum speed!
(I believe that at least one of the visitors to this forum has personal experience of the proverbial s**t hitting the fan)

HTH,
Christer

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