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Tu-20/95/142 Bear: The fastest prop-driven aircraft.

Appearance of Tu-95 at July 1955 Aviation Display at Tushino put western observers at a loss. A combination of propellers and swept wing and tail surfaces seemed to be inappropriate and early analysis of Bear's performance resulted in unrealistically downplayed bomber's performance. Western experiments with supersonic propellers flown on XF-84H and XF-88B have shown considerable loss in performance of the high-rotating propeller when tips were reaching supersonic speeds.

First DoD estimates shown that Bear was not capable of exceeding 400 mph with range of 7,800 miles. Appearance of Tu-114 (demilitarized version of bomber with slightly greater fuselage diameter) force DoD to review its numbers on Bear: 460 mph and max. range of 6,000 miles. In April of 1960 Tu-114D set a speed-with-load record at average of over 545 mph round 5,000 miles.

In 1975 the figure for range changed to 7,800 miles and currently it is believed to be 9,200 miles with 25,000 lb load. Level speed was admitted to be 570 mph (Mach 0.82) at 25,000 ft and 520 mph (Mach 0.785) at 41,000 ft. Cruising speed of Tu-95 is 442 mph (Mach 0.67). Later versions with more powerful engines have higher performance.

Gallery of Russian Aerospace Weapons published in March issue of Air Force Magazine gives following numbers for Tu-95MS:

Performance
Max. speed at 25,000 ft 575 mph, at S/L 404 mph, nominal cruising speed 442 mph, ceiling 39,370 ft, combat radius with 25,000 lb payload 3,975 miles, with one in-flight refueling 5,155 miles.

It is rumored that Bear is known to be able to out accelerate contemporary western interceptors. This hard to believe fact can be accounted by use of variable-pitch propellers of NK-12M turboprops. Modern jets need to use afterburners to keep up with accelerating Bear. In fact, one of the photo showing Panavia Toronado using reheat on one of the engines while pursuing this remarkable bomber.

Presumably, Bear holds an unofficial speed record for a prop-driven aircraft.

...And here is what left of Bears at Engels Heavy Bomber Base in Russia. The US government has provided US$150 million under the Nunn-Lugar Threat Reduction.

 

From: toro@inforamp.net (Thomas Rodriguez)
Newsgroups: rec.aviation.military
Subject: Re: Tu-95 (Was Loudest Aircraft)
Date: Tue, 29 Aug 1995 16:09:39

In article (40srnn$9r7@hopper.acm.org) garyh@acm.org (Gary Hine) writes:

>I have no personal experience with this one, but on the Discovery
>series "Wings of the Red Star" there was an episode about the TU-95
>Bear that claimed it was one of the loudest aircraft ever made. It's a
>situation like that experimental F-84 alluded to in an earlier post -
>times eight ! (Four engines, each with two four-bladed counterrotating
>propellers with supersonic tips.) They claimed it was so loud that
>fighters sent to intercept it could not fly close formation for long
>because of the noise.  Any fighter jocks out there who actually
>intercepted one of these care to comment ?

Gary, 

The Tu-95 propellers  reach transonic speeds (in the order of M1.05) when it 
flies at its maximum speed (M0.83) and when it flies at max. cruising speed 
above 11 000 metres (36 000 ft). The rest of the time they are subsonic 
despite their large diameter (5.6m , 18ft 4in). This is due to their very low
constant rotational speed, which is around 800 rpm( "plus/minus one mile") 8:}D
This can be observed in all Tu-95 in-flight pictures. In most of them even the 
de-icing boots can be clearly seen. In static conditions the tips reach about 
M0.74.

Those tips are in fact supersonic airfoils (1952/3 vintage. Remember this 
aircraft was shown in public for the first time in 1955), very thin and with a 
sharply diminishing chord that reduces to zero at the apex.

One interesting feature of these coaxial props is that they are mechanically 
independent. One can rotate them together in any direction or counter-rotate 
them in any direction too. All of this with the small fingers. Each propeller 
is driven by its own free-turbine (four stages each, if my memory does not 
betray me.) The counter-rotation is achieved gasodynamicaly by the flux 
turning the rotors in opposite directions.

They must be noisy at M1.0, but these a/c normally cruise at slow speeds 
(740 kmh for 12 000 km range) or a bit less for their 16 patrol flights.  
Under these circumstances intercepting pilots will not hear anything but their 
own engines I think.  If the Tu-95 pilot had enough fuel to play around flying 
at high speeds to annoy the intercepting pilots, I cannot imagine his crew 
consenting easily to that.  A noise loud enough to keep away helmet wearing 
intercepting pilots, flying in noisy cockpits, should be so intense that the 
poor people inside the bomber, wearing their flimsy leather helmets and 
sitting in their not too-well sound-proofed cubicles would simply go crazy.

In fact these propellers produce a rather agreeable deeop hum.  Years ago I 
flew [was flown :-) ] during 14 hrs in a Tu-114, the passenger version of the 
Tu-95 and the sound of the engines was not loud (by Soviet standards, anyway). 
A Bristol Britannia - the "Whispering Giant" - it was not, but it was less     
noisy than the An-24, for example.  The engines were derated from 14 750hp to 
only 12 750ehp (+ or -), but the props were the same and the speeds not that 
much slower.

(BTW, many helicopter main rotors and tail rotors reach transonic tip speeds)

These aircraft - the Tu-95 and Tu-114- are, IMHO, really fascinating from an 
aerodynamic and engineering point of view.  Technically the 114 was imposing.
As a transport aircraft it was very efficient (220 seats in 1959) ; as a 
passenger plane it was rather spartan, offering the comfort of the previous 
generation of western aircraft.

I hope I am at least 50% right.  8:-) D


As my $0.02 addition, I think the loudest a/c lies among the SR-71, the MiG-25 
and the Tu-160 when they take-off at max.gross weight, with full afterburners ,
in a heavily overcast cold winter day. I have never heard them, so I am only 
guessing. 

Thomas Rodriguez
toro@inforamp.net

From:	IN%"mbovanko@orlando.loral.com"  "Mark Bovankovich"
To:	IN%"agretch@OPIE.BGSU.EDU"
CC:	
Subj:	Tu-20/95/142 Comments

Alexei:
   
I just couldn't help visiting your interesting web page again this 
morning.  In scrolling through your FAQs again, I came across some 
comments (by Thomas Rodriguez again) about the Tu-95 that I thought 
needed clarification.  For your and your readers' edification:
   
------------------------------------------------------------------------
   
Thomas Rodriguez made some good responses to Gary Hine's comments and 
questions about the Tu-20/95/142 Bear.  Some quick clarifications:
   
Propellor Tip Speed and Noise -
   
I have spoken with several F-15, F-16 and F-106 pilots who have 
intercepted Bears.  They all said that they could clearly hear the noise 
of the Tu's props over the sound of their own engine(s), even with their 
helmets on.  Thomas' comments about the tip speed are all valid; 
however, he apparently missed the fact that the propeller blade itself 
need not be travelling at supersonic speed in order to generate shock 
waves.  When the tip velocity approaches high subsonic Mach numbers, the 
local velocity over the blades becomes supersonic, and shockwaves are 
generated.  Even supersonic airfoils have this characteristic behavior.  
The exact Mach number at which shockwaves will appear is dependent on 
airfoil and angle-of-attack.
   
Bear Acceleration -
   
The accounts of Bears out-accelerating western jet fighters are true, 
but only in the case of Tornado F.3 intercepts.  This is more a measure 
of the Tornado's weaknesses at high altitude than the Bear's exceptional 
capabilities.  The Tornado's high wing-loading and engines optimized for 
low altitude make it a slug in the high altitude, subsonic regime.  This 
performance failing is well known throughout NATO, but Gulf War 
experiences and recent accounts of Bear intercepts have brought the 
deficiency to public light.  The Bear is powerful, fast and efficient 
for a subsonic bomber, but most fighters will leave it in the dust 
without the mere flicker of an AB plume.


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