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Thread: Seeking info on Tu-95 propellers

  1. #1
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    Seeking info on Tu-95 propellers

    Upon watching some YouTube videos of Russia's venerable Tupolev Tu-95 "Bear" turboprop bomber, it is apparent that the two propellers of each counter-rotating pair are not perfectly synchronized at all times, as they would be if geared together. The variations in the relative motion can be seen in these video clips.
    https://www.youtube.com/watch?v=SKkyINrSWik
    https://www.youtube.com/watch?v=q-2dfEc70gU
    I think I remember reading somewhere that the props are driven by separate power turbines on concentric shafts, but so far I am unable to find anything online to confirm it. A Wiki article, which I realize may or may not be reliable, simply says the compressor and the props are driven by a 5-stage power turbine. The irregularities are most apparent when starting the engines and in that second video when they feathered #2. The appear well synchronized in normal cruising, but that could be accomplished with a synchrophaser device.

    If anyone has better "Google-fu" then I do, your contributions would be most welcome.

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    Have you inquired at the USAF Historical Center at Maxwell Air Base? They might have intelligence studies on our friend the Bear.

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    The Tu-95 engines have a single power shaft; the props are driven by a gearbox. There are two ways to do that: use a differential to drive both props with the same torque and match RPM by adjusting pitch, or driving both at the same RPM and matching torque by adjusting pitch. The Tupelov’s engines probably use the former, which can’t respond to transients, unless it’s an optical illusion

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    Quote Originally Posted by Noisy Rhysling View Post
    Have you inquired at the USAF Historical Center at Maxwell Air Base? They might have intelligence studies on our friend the Bear.
    NASA may, too. When Aeroflot flew the passenger derivative, some of the people I worked with tried to get some information out of the flight crew, probably with beer and vodka, but US beer was bad and they didn’t like our vodka

    Information about American English usage here and here. Floating point issues? Please read this before posting.

    How do things fly? This explains it all.

    Actually they can't: "Heavier-than-air flying machines are impossible." - Lord Kelvin, president, Royal Society, 1895.



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    Thanks, swampyankee. It appears to me that a differential gearset is the answer. Perhaps it reduces the stress and strain if something goes wrong with the propeller pitch control and introduces unwanted torque into the system.

    With "differential" as an added key word, I found this:

    http://aspeckt.unitbv.ro/jspui/bitst...1193/1/771.pdf

    It is hard to read, because the text looks like a rough machine translation from Romanian, but I get the general idea.

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    A Bear overflew my cruiser back in 1982, just west of NORK. He was about 100 feet off the deck. It was nighttime and we could see the crews' faces from their panel lights. Very ... stimulating. I wonder if they felt the same, given that they were flying over a cruiser that could ripple fire (redacted) AA missiles in (redacted) seconds.

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    I've seen dozens of the damn things. My birds were escorting them away from our carrier constantly once we were west of the Straits of Malacca, (Indonesia).

    And if they were carrying external stores, e.i. armed, they weren't allowed within 100 miles of the carrier.

    The Bear in the top video doesn't have the tear drop shaped acrylic blisters on the tail that I'm used to. Sort of makes it look "third rate" without them. Like they couldn't maintain them.

    When was that filmed?
    Time wasted having fun is not time wasted - Lennon
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    Bears were the reason I had to learn to sleep on a greasy flightdeck and not care. (Covering the Alert Five's)

    So I know about them.

    Chief, that's lower than they could bank without dipping a wingtip into the ocean.
    Time wasted having fun is not time wasted - Lennon
    (John, not the other one.)

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    Quote Originally Posted by BigDon View Post
    Bears were the reason I had to learn to sleep on a greasy flightdeck and not care. (Covering the Alert Five's)

    So I know about them.

    Chief, that's lower than they could bank without dipping a wingtip into the ocean.
    Yeah, they were committed to that flight path. Doing a favor for the Kims, I think. Not really sincere, if you know what I mean.

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    The Kims? In the early 80's Bears were flown out of Hanoi.

    So it would have been for good ol' Uncle Ho.
    Time wasted having fun is not time wasted - Lennon
    (John, not the other one.)

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    Quote Originally Posted by BigDon View Post
    The Kims? In the early 80's Bears were flown out of Hanoi.

    So it would have been for good ol' Uncle Ho.
    Did they have big red stars on them?

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    Of course, I don't believe Russia exported the Bear. I could be wrong about that though.
    Time wasted having fun is not time wasted - Lennon
    (John, not the other one.)

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    You know what you don't see about the Bear? How tough it is. It's a flying battleship. That's a stainless steel airplane. And still the fastest propeller driven aircraft.

    My aircrews would tell us it would take nearly an entire 600 round drum of 20mm warshot to bring one down if you had to gun it.
    Time wasted having fun is not time wasted - Lennon
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    I hear that the guys who crashed landed in Siberian are now Heroes of the Soviet Union.

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    Somehow I just noticed you stated your cruiser was off the coast of North Korea.

    Sorry for questioning you.
    Time wasted having fun is not time wasted - Lennon
    (John, not the other one.)

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    Quote Originally Posted by BigDon View Post
    Somehow I just noticed you stated your cruiser was off the coast of North Korea.

    Sorry for questioning you.
    No prob. I'm working with one eye while taking oxycontin. I'm hapys it fits on the page.

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    Quote Originally Posted by BigDon View Post
    Of course, I don't believe Russia exported the Bear. I could be wrong about that though.
    Kinda sorta? The Indian navy recently retired their Tu-142 versions.

    And for BigDon and NoisyRhysling - are these planes as noisy as their reputation says>

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    Quote Originally Posted by ngc3314 View Post
    Kinda sorta? The Indian navy recently retired their Tu-142 versions.

    And for BigDon and NoisyRhysling - are these planes as noisy as their reputation says>
    Flying train wrecks.

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    In the video clips my musician ears tell me the props are spinning about 750 rpm. At cruising speed of over 500 mph that would have the tips around Mach 1 or a little over, which would make them plenty noisy. It also reduces efficiency, so I am guessing that the designers made a tradeoff between running them that way and trying to get the same thrust with different blades and/or a higher blade angle of attack at lower rpm.

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    I too found the blade pitch surprisingly high and the fact that they seem to be variable interesting. I assume the strobescopic slow motion corresponds to very high altitude and/or very powerful engine torque. It would ensure an increased blade interaction domain.
    Last edited by a1call; 2017-Oct-07 at 07:42 PM.

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    In my case we have a different issue. The air above an aircraft carrier's flightdeck is considered American airspace. With all the honors and protections due. The goal of the Bears in a lot of cases is to try and buzz the flightdeck. The goal of the fighters is to not let that happen. It's considered a "fail" if the Bears do.

    You herd these sons of unwed mothers by flying over their wingtips. This prevents them from turning.

    So whenever these things were close enough for me to see with the Mark I eyeball the flightdeck was already in a furious state of activity, preventing me from hearing anything but the thrum of the launch cycle.
    Time wasted having fun is not time wasted - Lennon
    (John, not the other one.)

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    Chief, have you every seen one of these do a hard bank at low altitude?

    As you keep seeing more and more wing surface become visible you get this unreal "clown car" sensation. And this was after being in aviation for a number of years already. Fully banked and right off the ocean they looked too big to be real.
    Time wasted having fun is not time wasted - Lennon
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  23. #23
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    Quote Originally Posted by a1call View Post
    I too found the blade pitch surprisingly high and the fact that they seem to be variable interesting. I assume the strobescopic slow motion corresponds to very high altitude and/or very powerful engine torque. It would ensure an increased blade interaction domain.
    No, the stroboscopic slo-mo corresponds to the matching or lack thereof of the propeller speed and the shutter frequency of the motion picture camera. If the prop spins exactly 12 times per second and the camera is working at 24 frames per second, the prop will appear stationary, with blur that depends on the shutter speed for each frame. If the prop is slightly faster it will appear to rotate slowly direct. If slightly slower it will appear to rotate slowly retrograde. If the two counter-rotating props are going exactly the same speed, the blades will coincide at a fixed position angle. If they are running at slightly different speeds that angle will vary.

    These strobe effects hold whether it is a 14,000 hp engine spinning a pair of 18 ft props or a 1/10 hp motor spinning a small household fan at the same angular velocity.

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    I'm blown away by the camera's shutter speed. Virtually no blur or
    distortion of the propellers at all. And the video streamed perfectly
    on my connection which typically gives jerky video.

    -- Jeff, in Minneapolis
    http://www.FreeMars.org/jeff/

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  25. #25
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    On some videos the blades appear bent. That is caused by a focal plane shutter or by an electronic scanning action that performs the same function.

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    According to this, the Tu-95 is second only to the Republic XF-84H in noise. The latter's propellers generated a continuous supersonic boom even idling on the ground that could do real damage.
    Last edited by wd40; 2017-Oct-07 at 10:48 PM.

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    Quote Originally Posted by BigDon View Post
    Chief, have you every seen one of these do a hard bank at low altitude?

    As you keep seeing more and more wing surface become visible you get this unreal "clown car" sensation. And this was after being in aviation for a number of years already. Fully banked and right off the ocean they looked too big to be real.
    Not really low, but I saw six of them do an "[language]" turn once in the Bering Sea. They were looking for one of our carriers. They found four. They were a bit perplexed, perhaps even distraught. Our fighters were on the deck opposite side of the formation and swarmed up and at 'em, just to show some love.
    Last edited by slang; 2017-Oct-13 at 07:43 PM. Reason: language

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    Quote Originally Posted by Hornblower View Post
    No, the stroboscopic slo-mo corresponds to the matching or lack thereof of the propeller speed and the shutter frequency of the motion picture camera. If the prop spins exactly 12 times per second and the camera is working at 24 frames per second, the prop will appear stationary, with blur that depends on the shutter speed for each frame. If the prop is slightly faster it will appear to rotate slowly direct. If slightly slower it will appear to rotate slowly retrograde. If the two counter-rotating props are going exactly the same speed, the blades will coincide at a fixed position angle. If they are running at slightly different speeds that angle will vary.

    These strobe effects hold whether it is a 14,000 hp engine spinning a pair of 18 ft props or a 1/10 hp motor spinning a small household fan at the same angular velocity.
    I was referring to your reference to "Angle of Attack" and not pitch of the sound. Having the airfoil almost parallel to the direction of the travel of the plane is unusual. I assume it's to increase the of the interaction of the blade in thin atmosphere. Corrections and insights are welcome.

  29. #29
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    Quote Originally Posted by a1call View Post
    I was referring to your reference to "Angle of Attack" and not pitch of the sound.
    That is what I understood you to be saying in your first sentence. It was the second sentence that had be scratching my head. You appeared to be asserting some sort of relation between the strobe effect and high altitude and/or engine torque. I don't know what you intended but what came out was non sequitur.
    Having the airfoil almost parallel to the direction of the travel of the plane is unusual. I assume it's to increase the of the interaction of the blade in thin atmosphere. Corrections and insights are welcome.
    The plane is moving forward so fast that the outer part of the blade needs to be inclined upwards of 50 degrees to make a positive angle of attack and generate thrust. The blade is twisted so that the pitch angle is even higher toward the hub, to compensate for the lower speed around the hub at that short radius. That's why the inner part is nearly parallel to the direction of travel. The outer part is harder to see because of the blur we get even with that high speed shutter. When the prop was feathered the inner part was turned past 90 degrees while the twist kept the outer part under 90, thus giving near zero net windmilling torque.

  30. #30
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    Addendum: I am guessing that the feathering and subsequent restart was part of their training in dealing with in-flight engine failures.

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