Supersonic propellor tips?

[ronnie3585]

Im looking to find oout exactly what happens when propellor tips reach supersonic speeds. After reading books and asking other pilots the only answer I can get is that "bad stuff happens", but no real concise answer.

I presume the shockwave produced from breaking the sound barrier might cause damage to the prop or aircraft itself?

[wombat13]

Ronnie, try google. There is a lot of info on this.

[treadigraph]

The ear splitting rasping noise Harvards and Stearmen and similar types sometimes make is the prop tips going supersonic - I've always believed that pilots try to avoid it causing bad PR around airports rather than because anything catastrophic will eventually happen.

Harvards were banned from Biggin Hill in the 1980s because of the noise.

[rusty_y2k2]

"Revolutions per minute: For the same propeller diameter, the blade tips travel faster and faster as the rotational speed increases. Eventually, the blade tips become supersonic where shock waves form, drag increases substantially, and efficiency plummets."

http://www.aerospaceweb.org/question...on/q0039.shtml

I haven't come across anything about damage in particular.

[GANNET FAN]

Originally Posted by ronnie3585

Im looking to find oout exactly what happens when propellor tips reach supersonic speeds. After reading books and asking other pilots the only answer I can get is that "bad stuff happens", but no real concise answer.

I presume the shockwave produced from breaking the sound barrier might cause damage to the prop or aircraft itself?

Am I right in thinking that the Grumman Avenger propeller tips on max take off power used to achieve supersonic speeds??

[Shaggy Sheep Driver]

I don't think the tips need to actually go supersonic. Prop bladesa are lifting surfaces like wings, so they will first encounter compressability problems, then local superonic airflow due the speeding up of air over the cambered surface.

End result is mach stall - the blade ceases to produce lift (thrust) on the transonic bits, and so looses efficiency.

SSD

[treadigraph]

Originally Posted by GANNET FAN

Am I right in thinking that the Grumman Avenger propeller tips on max take off power used to achieve supersonic speeds??

Well, at Flying Legends one year, two Avengers flew past with a Catalina - one was audibly mis-behaving power/pitch-wise and my money was on the Avenger NOT flown by Tony Haigh-Thomas! Sounded magnificent though, rather like one of those 1930s flying movies...