I was just watching this video...

Restoration and startup of a Wright 1820 Cyclone

...and it got me thinking: a propeller shoves back air, and this creates a forward force on the prop. The prop attached to a shaft, and the prop is tugging on the shaft. Both the shaft and the prop are rotating.

The airframe on the other hand is (relatively) stationary. Yet the airframe depends on the rotating prop to pull it in the desired direction of trust.

This means there is an interface somewhere, between the rotating shaft and the rest of the engine, and that interface transfers all the thrust of the propshaft to the engine, and then the engine in turn transfers that force to the air frame.

That to me sounds like the mother of all bearings! What does such a bearing look like?! Or is there some other mechanical principle/device in play?

  • 1
    $\begingroup$ Your car has equally impressive thrust bearings, what do you think turns the car when you round a sharp corner? $\endgroup$ Sep 11, 2018 at 19:25

1 Answer 1


The engine mount is an important component that transfers the prop thrust to the airframe. It's clearly visible in this photograph of a fast and powerful plane, a Bf109. Of course, bearings transfer thrust between the rotating and static parts. That is common to all engine-propelled vehicles, ships, cars, planes... The main thrust load, in the picture showing the turbofan, is taken by the tapered roller bearings.

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  • $\begingroup$ Also, it would be nice to highlight the engine mount and bearing locations - not everyone is familiar enough with what's under the hood to instantly recognize it... $\endgroup$
    – FreeMan
    Sep 11, 2018 at 11:29
  • $\begingroup$ @FreeMan Well the engine mount even I can see here; it is the light grey-green frame that is "hugging" the big black engine block. But what I was wondering (I have edited the post to clarify) is how the prop transfers trust to the stationary parts of the engine. $\endgroup$
    – MichaelK
    Sep 11, 2018 at 11:32
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    $\begingroup$ The tapered roller bearings, as answered above already. The shaft pulls forward on the inner bearing housing, the rollers transfer the pulling to the outer bearing housing which push the engine/airframe forward. The rollers let the two parts move independently. More on the bearings here en.wikipedia.org/wiki/Tapered_roller_bearing $\endgroup$
    – CrossRoads
    Sep 11, 2018 at 12:20
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    $\begingroup$ Cars are different from planes and ships, and don't need (as much) taper in the bearings - at every stage from crankshaft to road contact, it's pure torque. But propeller-driven machines need that thrust bearing in order to provide transfer of axial thrust along the shaft. $\endgroup$ Sep 11, 2018 at 16:58
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    $\begingroup$ @TobySpeight - When a car rounds a corner, there are great sideways forces acting upon the wheels (along the axle), which must be transferred to the chassis somehow. $\endgroup$
    – Rainer P.
    Sep 12, 2018 at 20:12

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