This question doesn't relate to the actual speed of the aircraft, but of the blades themselves. I have heard helicopters had problems of this happening if the rotors spin too fast it can break the sound barrier, so could this happen to a turboprop?

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    $\begingroup$ A minor edit. If there is one thing that annoys helicopter pilots more than calling them "choppers", it's calling their rotors "wings" ;) $\endgroup$ – Simon Aug 11 '15 at 17:13
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    $\begingroup$ @Simon And, yet, it's technically correct, no? Hence the terms "rotary-wing" vs. "fixed-wing." $\endgroup$ – reirab Aug 11 '15 at 18:10
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    $\begingroup$ The category of aircraft is correctly "rotorcraft", Rotary wing is an expression which is widely used, but the rotors are never called wings. $\endgroup$ – Simon Aug 11 '15 at 18:36
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    $\begingroup$ Fun fact (related to turbofans rather than -props): the very loud humming noise you hear on take-off inside a jetliner is in fact due to the fan blades breaking the sound barrier. $\endgroup$ – Sanchises Oct 5 '15 at 17:58

Can it happen: Yes

Does it happen: Generally no

As a matter of the pure physics propeller tips can go supersonic and some times do. There is at least one case of this being done by design on the XF-84H which was built to be one of the fastest propeller planes.

enter image description here

The main issue it faced was the noise generated by its supersonic prop. It is considered one of the loudest aircraft ever made as its prop was supersonic even at idle speeds. Due to the shock waves generated by breaking the sound barrier great care is often taken to ensure that propellers don't go supersonic.

  • $\begingroup$ Quoth Wikipedia: "...[the propeller blades produced] a continuous visible sonic boom that radiated laterally from the propellers for hundreds of yards. The shock wave was actually powerful enough to knock a man down; an unfortunate crew chief who was inside a nearby C-47 was severely incapacitated during a 30-minute ground run. Coupled with the already considerable noise from the subsonic aspect of the propeller and the T40's dual turbine sections, the aircraft was notorious for inducing severe nausea and headaches among ground crews." (1) $\endgroup$ – Vikki - formerly Sean May 4 '18 at 21:39
  • $\begingroup$ "In one report, a Republic engineer suffered a seizure after close range exposure to the shock waves emanating from a powered-up XF-84H. The pervasive noise also severely disrupted operations in the Edwards AFB control tower by risking vibration damage to sensitive components and forcing air traffic personnel to communicate with the XF-84H's crew on the flight line by light signals. After numerous complaints, the Air Force Flight Test Center directed Republic to tow the aircraft out on Rogers Dry Lake, far from the flight line, before running up its engine." (2) $\endgroup$ – Vikki - formerly Sean May 4 '18 at 21:40

It seems sometimes happens on the Tupolev Tu-95 "Bear" long-range strategic bomber. According to various sources like this (the first result from a Google search), the tip of the propeller goes transonic while turning at full rpm with a decrease in performances and a severe increase in noise.

The Tu-95 has straight blades, like many old turboprop aircrafts:

Bear's propellers

To partially overcome this problem, modern turboprops use "scimitar" blades, like the one on the C-130J:

C-130J propellers

In the same way a swept wing is more efficient at high speed in comparison to a straight wing, at high tip speed, a scimitar blade is more efficient than a straight blade.


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