Explaining the high speed of the Tu-95

[charleybarley]

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The book examines the design operating process, principles of control and operational characteristics of jet engines of various types used in civil aviation...

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How the Bear flew at such high speeds for a propeller-driven aircraft has been a mystery from what I have read.

I'm not sure whether the information in this 1969 Soviet publication goes any way to explaining it, eg Fig. 21.3 shows optimum split between propeller power and jet thrust occurring at M 0.9.

 

[Tony Williams]

No answer to your question, but I do recall reading an account by a crewman of a Nimrod which accidentally found itself following a Tu-95 and tried to overhaul it. The Tu-95 pilot saw them coming, put the hammer down and disappeared into the distance.

 

[Archibald]

48 000 hp and swept wings - it helps a lot !

 

[kitnut617]

The engines were 15,000 shp weren't they ?

I was reading up on the TP400 engines on the A400M the other day, it said that the 11,000 shp engines combined with the 8-blade propellers installed, produced 25,000 lb of thrust, so 100,000 lbs total. I would imagine with 15,000 shp and the same number of blades per engine and prop diameters being close to the same, it should produce some pretty good numbers --

 

[Archibald]

Damn it yes, the NK-12 started at "only" 12 000 hp and soon upgraded to 15000 hp - so that's 60 000 hp, total !

The A400M is a transport, a fatty compared to a pencil-shaped, slim Tu-95... not sure if the wings are swept, too ? In fact it is closer from an An-22...

 

[charleybarley]

It was more the propeller side of things I was thinking of, eg how it converted 12 000 hp into the required propeller plus jet thrust and still had good fuel consumption. The experts of the day said it couldn't be done because at its cruising speed, very high for a prop-driven a/c, the compressibility losses on the propeller would be too high.

The Soviet document I referred to seems to say that with a contemporary (US translation) propeller and the optimum split of an engines power between the prop and jet nozzle it would all work ok at Mach 0.9.

I was just a bit excited because I thought I might have found a bit of Soviet documentation that said the Bears high speed (for a prop-driven a/c) was actually no big deal despite US opinion at the time.

 

[Ray]

I have a friend who flew F-8 Crusaders in the U.S. Navy. There is a rather infamous photo of him flying off the port wing of a Tu-95. He told me that he only flew there for a short period of time because the sound was so intense that it would have made him ill if he had hung around.

 

[Archibald]

Somewhat like the turboprop F-84H Thunderscreech !! It drove its unfortunate pilot(s) completely sick only with its noise alone.

 

[Basil]

Somewhat like the turboprop F-84H Thunderscreech !! It drove its unfortunate pilot(s) completely sick only with its noise alone.

... not its pilot but some of the ground crew, especially if standing plane to the propeller arc.

 

[Archibald]

I thought it affected the pilot, too ?! I'll check my sources.

 

[Basil]

The Kuznetsov turboprop engine of the Tu-95 had a somewhat different propulsion split than western turboprops of today where (today) most of the power is routed to the propeller gearbox to obtain the highest propulsive efficieny in the typical speed region between 500 and 600 km/h.
Designed and built by a team of German/Austrian ex-Junkers and -BMW specialists under the lead of Junker's Ferdinand Brandner (as prisoners of war), the engine of the Tu-95 has a much higher propulsion split towards the exhaust gas stream (jet exhaust) which can reach 50% of the total power output (depending on flight altitude). This is a main reason for obtaining such high speeds with a prop. The propellers of the Tu-95 were not designed to go supersonic although the tips can reach slight supersonic speed during periods of high flight speeds (vector of forward flight speed and propeller rotating speed).

During the 1950s a soviet design bureau was working on pure supersonic propellers for the Tu-95 but this was not adopted.

Btw the Soviets had even higher speed turboprops in their mind ...

https://www.secretprojects.co.uk/threads/tupolev-108-composite-bomber-developments.33751/

 

[charleybarley]

Thank you for that Basil.

 

[charleybarley]

The proportion propeller to jet is adjusted by nozzle area. Turboprops have fixed nozzles and performance is ok at TO and cruise with a fixed nozzle.
The tu95 cruise performance excelled (higher speed, good fuel consumption relative to others)
As it also had a fixed nozzle does that mean it was inferior (poor fuel consumption) at low speeds? ie with fixed nozzle it couldn't be good at both extremes.

Any thoughts?

 

[Basil]

The proportion of propulsion split between propeller and jet exhaust of a turboprop engine is fixed during its design phase primarily via the turbine layout (the NK-12 did not have a free power turbine) when you have to decide how much power will be extracted from the gas stream to power the propeller (via the reduction gear box) and how much power "is left" in the hot gas stream to provide the additional jet thrust. As mentioned above in case of the Kuznetsov engine (as of the german turboprop developments by BMW, Junkers and Heinkel) the energy left in the gas stream was higher than what is typical today, which is good for combat aircraft speeds but of course does not help for a very low sfc at lower flight speeds. However for the late 1950s the NK-12 had a rather good sfc of 225 g/kWh during cruise.

 

[Bcintruder]

I thought it affected the pilot, too ?! I'll check my sources.

The HUGE electromagnetic radiation from the EA6B Prowler jammers known to make sterile the entire aircrew’s CAJONES! Aircrew wore gold-deposited helmet visors to protect their eyes from E radiation.

In my own seat, the A6E Intruder, many a time I left my ground radar switch “on” after sighting it in on the target range beside the taxiway. I’d quickly get the message- ground crew rapidly flapping their arms to get my attention! Seems that they could feel the heat of the radar beam roasting their “Tesla-cles”, each time it rotated past them::::

 

[Archibald]

"Cojones" but I got the message.

MiG-25 (or was it MiG-31 ?) radar was rumored to fry rabbits standing too close from the runway.

 

[PlanesPictures]

"During the 1950s a soviet design bureau was working on pure supersonic propellers for the Tu-95 but this was not adopted." - Tu-108?

 

[Basil]

The HUGE electromagnetic radiation from the EA6B Prowler jammers known to make sterile the entire aircrew’s CAJONES! Aircrew wore gold-deposited helmet visors to protect their eyes from E radiation.

In my own seat, the A6E Intruder, many a time I left my ground radar switch “on” after sighting it in on the target range beside the taxiway. I’d quickly get the message- ground crew rapidly flapping their arms to get my attention! Seems that they could feel the heat of the radar beam roasting their “Tesla-cles”, each time it rotated past them::::

The topic is the noise of the prop and its effect.
Nevertheless, interesting.

 

[Basil]

"During the 1950s a soviet design bureau was working on pure supersonic propellers for the Tu-95 but this was not adopted." - Tu-108?

As mentioned above, there is already a thread about the Tupolev "Aircraft 108" (not: Tu-108) and a sub-thread in it about the propulsion of the "108" -

https://www.secretprojects.co.uk/threads/tupolev-108-composite-bomber-developments.33751/

The Aircraft 108 with its transonic layout would certainly have needed transsonic or probably supersonic propeller profiles. The soviet propeller design buero Schdanow had supersonic popellers in design / construction work. I have no info if they were tested. Their thickness was 4% and they had a "double wedge" profile (?).

 

[Scott Kenny]

I have a friend who flew F-8 Crusaders in the U.S. Navy. There is a rather infamous photo of him flying off the port wing of a Tu-95. He told me that he only flew there for a short period of time because the sound was so intense that it would have made him ill if he had hung around.

I'd believe it.

I was working in the aft baggage bay of a 727 while they were running the hydraulics, after about half an hour I staggered out and told the boss to find me a different spot to work until they stopped running the hyd pumps. They were just slightly out of phase with each other, so they'd really pulse hard in your ears about every 1/2-3/4 second...

 

[Scott Kenny]

The proportion of propulsion split between propeller and jet exhaust of a turboprop engine is fixed during its design phase primarily via the turbine layout (the NK-12 did not have a free power turbine) when you have to decide how much power will be extracted from the gas stream to power the propeller (via the reduction gear box) and how much power "is left" in the hot gas stream to provide the additional jet thrust. As mentioned above in case of the Kuznetsov engine (as of the german turboprop developments by BMW, Junkers and Heinkel) the energy left in the gas stream was higher than what is typical today, which is good for combat aircraft speeds but of course does not help for a very low sfc at lower flight speeds. However for the late 1950s the NK-12 had a rather good sfc of 225 g/kWh during cruise.

You know, it's starting to sound like the big NK-12s should really be called 1st Generation Propfans, not so much a turboprop.

Which gets me wondering about higher-blade-count props for the beast... props with a prime number of blades seem to be best in terms of minimizing vibrations outside of one specific frequency. So I'm picturing 13 blades on one prop and 11 on the other.

 

[Archibald]

I'd believe it.

I was working in the aft baggage bay of a 727 while they were running the hydraulics, after about half an hour I staggered out and told the boss to find me a different spot to work until they stopped running the hyd pumps. They were just slightly out of phase with each other, so they'd really pulse hard in your ears about every 1/2-3/4 second...

I was once a passenger on a MD-80 series short haul jetliner, and on a smallish spanish airport we boarded it through the rear stairs: the one between the jet engines and the APU. Can still remember the defeaning noise, must have been the APU (no way it would be the jet engines !)
Not exactly a pleasant experience !