How does a propeller remain attached to the engine? I know there is a gearbox and/or some other mechanism that transmit the movement but is there any security mechanism that avoids it from completely detaching from the main engine? There is a huge amount of forces acting on that tiny spot where the propeller is attached to the engine, especially on turboprops, and this is where my question comes from.

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    $\begingroup$ Do “sufficiently strong bolts” count as “security mechanism”? I am not really sure what you expect here. $\endgroup$
    – Jan Hudec
    Commented May 24, 2015 at 19:27
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    $\begingroup$ Now consider a helicopter rotor. The forces are even greater, as is the importance of keeping it attached. For that reason, the nut on top is sometimes called "Jesus nut". $\endgroup$ Commented May 24, 2015 at 20:13
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    $\begingroup$ I agree with the previous comments. Propellers don't fly off. Therefore the materials used are more than strong enough. What are you asking for? $\endgroup$
    – Simon
    Commented May 24, 2015 at 20:37
  • $\begingroup$ Answer is good. If its bolts and nuts and they are over engineered then I can understand. Even though there still would be a component of human error. $\endgroup$ Commented May 25, 2015 at 5:10

1 Answer 1


Nuts. Technically nuts and bolts.

If you look at pictures of propeller hubs (google "propeller hub") you'll see that the individual prop blades are held onto the prop hub by nuts and bolts holding the hub halves together. Or for wooden props they're bolted directly onto the hub.

If you then take the hub apart, you'll see that the hub is attached to the shaft using nuts and bolts.

I sometimes see people asking why aircraft engineers specify very expensive nuts and bolts for certain parts of the aircraft when a cheaper part can handle an equivalent load. Your question is exactly the reason - it's better to over-engineer certain parts like the prop assembly than have the prop accidentally fly off during flight.

  • $\begingroup$ Wouldn't the nuts and bolts also be safety-wired together to prevent them from accidentally unscrewing from vibration? $\endgroup$
    – FreeMan
    Commented May 25, 2015 at 16:24
  • $\begingroup$ I think you will find that the nuts and bolts will be threaded in the reverse manner to the force imparted on their. Hence they will be forced tighter if there is any play. $\endgroup$
    – jCisco
    Commented Oct 5, 2015 at 12:56

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