Tu-95 Bear propeller velocity
 

I was watching a documentary on the mighty Tu-95 and it was mentioned that the propeller speed at the tips are supersonic.

Is this correct? I have heard propeller and rotor tips go briefly supersonic; for example on T-6 Harvards. However I always believed that this was highly inefficient and one of the factors limiting the top speed of propeller aircraft.

Please enlighten me...

KDY

Let´s see... the propeller diameter on the NK12 engine is 5,6m, which gives a radius of 17,6m. Now if the book I read is correct, the props run at 750rpm during cruise, this would make the tips of the engines run at 220m/sec. This is only the velocity along the circumference, so the vector of the arriving air has to be added to this as well. Without further calculation - at cruising altitude this easily should be supersonic.

You could certainly hear the beast inside a pressurised cockpit through a bonedome from a good few hundred yards away, so it sure was noisy.

Just to point out a typo: it's a circumference of 17.6m actually.

Not being a pedant, it's just than on first quick read it stroke me as a pretty big prop :ok:

Don`t know where you get the radius to be greater than the diameter! however,a TAS of 400kts at 35000` would give a tip speed of 990 ft/sec/301 m/s,and a local SoS 994 ft/sec/301 m/s..

Dang... yes, of course I mean the circumference, not some magically increased radius.

The inefficiency question seems the interesting bit here. Anyone...?

Supersonic tip speeds are not a fatal show stopper. They increase noise quite a bit. Maybe that explains the characteristic noise of the Bear.
A propeller blade is like a wing: it produces lift and induced drag. Like a normal wing it has a critical Mach number. If it approaches that Mach number or exceeds it, the drag increases dramatically. So the overall prop efficiency goes south. However, the tip of the propeller blade only contributes its part, the majority of thrust is produced more inward.

Actually, there was an aircraft with a "supersonic" propeller. It is supposed to be the noisiest aircraft ever!
Republic XF-84H - Wikipedia, the free encyclopedia

A hopefully 'not too bad' picture of the props on the Bear-F at Kiev Aviation Museum.

http://i170.photobucket.com/albums/u...z/IMG_1098.jpg

I once had the pleasure of arriving at the designated Lat/Long in a TriStar tanker to dispense fuel to the (chasing) Phantoms. Having broke cloud we spotted the Bear D and took chase. My skipper was an ex Phantom driver who had previous experience of chasing these mighty propliners; anyway, we caught up with the Bear and formated off his right wing. Whilst waiting for the 'interceptors' we crossed beneath the Bear to formate on the left wing-tip... the noise from those propellors were akin to someone throwing pebbles on top of our fuselage... shock-waves from those supersonic tips!

The Phantoms arrived some ten-minutes later; took a drink, and escorted the Bear well to the north of the Shetland Isles.

A great day out!

Sadly, the skipper who I flew with on that day is no longer with us; 'Bumps' Rowley... top bloke; RIP Bumps.

TriStar? Who mentioned the mighty TriStar?

Awaiting 411A...

TCF

- did you know he has supersonic tips?

Re contra rotating props. Depending on tip speeds, wouldn't there be a fair amount of blade/vortex interaction contributing to the overall noise produced? Similar to helo 'blade slap' i.e. as with the Chinook.

I would reckon the shock patterns would be a challenge to model:)

Regarding the efficiency question, I wonder whether this was part of the design brief?

Perhaps the props were designed so that they were relatively efficient for take-off and initial climb, using the full span of the blades, but once the aircraft was established in high level cruise, the tips were calculated to go supersonic and reduce the effective diameter of the props?