Tilting propellers
Thread Starter
Joined: Mar 2015
Posts: 138
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From: Off the map
Tilting propellers
Hello guys,
I stumbled on a very interesting design about a STOL aircraft: the Dornier Do-29:
https://en.wikipedia.org/wiki/Dornier_Do_29
I really like the setup but I was wondering how do you transmit the power from the engine to the prop.
I thought about a universal coupling, but I read on a manufacturer website that such joints are limited to small angles, whereas in this case the shafts can (theoretically) rotate up to 90 degrees. Wiki reports of successful testings of up to 60 degrees, which isn't that small.
So, how did they do it?
Thanks!
I stumbled on a very interesting design about a STOL aircraft: the Dornier Do-29:
https://en.wikipedia.org/wiki/Dornier_Do_29
I really like the setup but I was wondering how do you transmit the power from the engine to the prop.
I thought about a universal coupling, but I read on a manufacturer website that such joints are limited to small angles, whereas in this case the shafts can (theoretically) rotate up to 90 degrees. Wiki reports of successful testings of up to 60 degrees, which isn't that small.
So, how did they do it?
Thanks!
Joined: Feb 2009
Posts: 2,826
Likes: 110
From: Virginia
"Universal" joints -- the kind with a U at the end of each shaft and a cross-shaped piece connecting them, don't work well at large angles. "Constant velocity" joints, which are made in a number of different configurations, work at larger angles. I don't know whether that's what was used in the Dornier, or whether 90 degrees is possible with them.
Joined: Apr 2008
Posts: 387
Likes: 8
From: UK
Yep, almost certainly helical cut bevel gears, one on the output shaft of the engine, an larger idler perpendicular to the engine shaft whose axis of rotation is on the axis of tilt, and the third on the input to the prop shaft. The wiki article describes the engines as "geared", and that ratio could be incorporated into the bevel gears.
If the props were cross coupled then there may also have been some sort of clutch mechanism on the engines' output. Depends if the cross coupling was to ensure that both props had the exact same power input, or also to make an engine failure more survivable (in which case you'd want to be able to disengage the failed engine). Given that it was an experimental aircraft such niceties may have been left for production designs.
If the props were cross coupled then there may also have been some sort of clutch mechanism on the engines' output. Depends if the cross coupling was to ensure that both props had the exact same power input, or also to make an engine failure more survivable (in which case you'd want to be able to disengage the failed engine). Given that it was an experimental aircraft such niceties may have been left for production designs.
