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Turbofan Powered E-2 Hawkeye

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  • Turbofan Powered E-2 Hawkeye

    One of the many random things rattling around my head: development costs aside, would the E-2 Hawkeye and C-2 Greyhound be more capable aircraft (given their roles) if they were equipped with turbofan engines (specifically TF34s) instead of T56 turboprops?

    Pros: increased thrust, higher speeds, higher altitude flight, maintenance commonality (formerly with the S-3 Viking), less vibration and crew fatigue.

    Cons: Less endurance.

    I've heard an E-2 pilot state that he wished the Hawkeye would have had turbofan engines, primarily to reduce vibration in the cabin and therefore fatigue in crew members. I suppose when the E-2 was developed, turboprops maximized endurance. I would imagine these days, the faster transit time turbofans would enable would be a big plus for both the E-2 and C-2.

    I'm not sure if turbofan powered aircraft are harder to bring aboard the boat (with turbofans being less responsive to throttle adjustments)? The S-3 never seemed to have a problem and the A-3 Skywarrior was a large, carrier capable, jet powered aircraft.

    It appears that at some point, Grumman / Northrup Grumman did propose an E-2X Hawkeye and C-2 Greyhound 21 models that were equipped with TF34 turbofan engines.

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    Last edited by JA Boomer; 31 Aug 21,, 20:31.

  • #2
    2 big reasons why they stick with turboprops....less maintenance and as you mentioned, greater endurance.

    It is critical to have availability kept very high...there are only 4 War Hummers in a CAW. And the C-2s need endurance and reliability to be able to support the CVG all the way to just past the Blue Water Ops line.

    So while the War Hoover was a great weapon, the turboprop makes more sense for Fleet ops.
    “Loyalty to country ALWAYS. Loyalty to government, when it deserves it.”
    Mark Twain

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    • #3
      Originally posted by Albany Rifles View Post
      2 big reasons why they stick with turboprops....less maintenance and as you mentioned, greater endurance.
      I do wonder how much less maintenance time/money is spent on the T56 (being sole turboprop powerplant on the boat) vs the high-bypass TF34s. I wouldn't have thought much difference.

      Originally posted by Albany Rifles View Post
      It is critical to have availability kept very high...there are only 4 War Hummers in a CAW. And the C-2s need endurance and reliability to be able to support the CVG all the way to just past the Blue Water Ops line.
      I'm not sure the range of the C-2 would be effected. Speed increase may cancel out endurance reduction?

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      • #4
        The T56 has fewer moving parts than the TF-34. By definition it will then require less maintenance. Also I believe it is smaller so replacement engines take up less space on the COD.

        Turbo prop is more fuel efficient...that equals more flying time and therefore longer range.

        I am pretty sure the airframe PMs looked at those as a consideration but stuck with the turboprop.

        Sometimes the decision is based on being able to keep repair parts flowing. One company going out of business can cripple and entire airframe fleet.
        “Loyalty to country ALWAYS. Loyalty to government, when it deserves it.”
        Mark Twain

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        • #5
          Originally posted by Albany Rifles View Post
          The T56 has fewer moving parts than the TF-34. By definition it will then require less maintenance. Also I believe it is smaller so replacement engines take up less space on the COD.
          Is that correct? Why would a turboprop have fewer moving parts than a comparable turbofan? The turbofan does not need the gearbox which is used to drive the propeller in the turboprop. The number of compressor and turbine stages in the two engines seem similar. As for the size, the T56 is longer and a bit heavier but has half the diameter (not counting the prop).

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          • #6
            Originally posted by Albany Rifles View Post
            Turbo prop is more fuel efficient...that equals more flying time and therefore longer range.
            At first I didn't buy this, quite frankly I thought the increase in speed would cancel out the increase in fuel burn in a turbofan powered aircraft vs a turboprop, and the two would have comparable range and fuel efficiency (the turboprop will always have more endurance).

            After comparing specific fuel consumption, range, speed, thrust, and horsepower my eyes went crossed. I thought of a better way to quickly examine this. The Dornier 328 - the only aircraft that I am aware of that can be equipped with either turboprop or turbofan powerplants.

            https://328.eu/wp-content/uploads/20...-turboprop.pdf
            https://328.eu/wp-content/uploads/20...0-lightjet.pdf

            These datasheets show that a turboprop powered Dornier 328-100 will consume 516 lbs (18.4%) less fuel than the turbofan powered 328-300JET (which is the same size) when transporting 32 passengers over 500 nm.

            I'm a believer now.

            Originally posted by Albany Rifles View Post
            I am pretty sure the airframe PMs looked at those as a consideration but stuck with the turboprop.
            Very interesting, although the development cost of changing engine types had to be a factor.
            Last edited by JA Boomer; 03 Sep 21,, 01:22.

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            • #7
              Originally posted by Firestorm View Post
              Is that correct? Why would a turboprop have fewer moving parts than a comparable turbofan? The turbofan does not need the gearbox which is used to drive the propeller in the turboprop. The number of compressor and turbine stages in the two engines seem similar. As for the size, the T56 is longer and a bit heavier but has half the diameter (not counting the prop).
              From the text books:

              Turboprops extract virtually all of the kinetic energy and a larger portion of the thermal energy via expansion turbines to drive the propeller, while turbofans utilize an expansion nozzle to create high speed exhaust (thrust) A turbo prop produces 2%-3% of total thrust output all the work is done by the gearbox and prop. A turbofan produces it thrust by the nozzles at the rear of turbofans act to reduce the volume of air leaving the back of the engine, which increases its velocity. This increase in velocity is the source of thrust. the goal is to turn relatively high pressure, low velocity exhaust into high velocity, low pressure exhaust. That requires engineering and parts.

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              • #8
                Originally posted by Albany Rifles View Post
                The T56 has fewer moving parts than the TF-34. By definition it will then require less maintenance. Also I believe it is smaller so replacement engines take up less space on the COD.

                Turbo prop is more fuel efficient...that equals more flying time and therefore longer range.

                I am pretty sure the airframe PMs looked at those as a consideration but stuck with the turboprop.

                Sometimes the decision is based on being able to keep repair parts flowing. One company going out of business can cripple and entire airframe fleet.
                I don't think any TF--34 powered aircraft is still being produced. The T56 is on the E-3 and C-130 aircraft still in production. P-3, C-2 still use it. It's quieter than a RR Dart.

                You would know better than I. New engine requires testing engine and complete airframe. New training and logistic trail. It won't be ready for service for a while.

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                • #9
                  My source was from a buddy of mine who is the Product Manager (Commander) for repair parts and replacement engines for USN/USMC common fixed wing aircraft. I wrote him and he provided the info. Unfortunately, it is an extrapolation of data and I cannot share directly. He did say it was all openly available but from what he gave I cannot share. We went to several Defense Acquisition University courses together.
                  “Loyalty to country ALWAYS. Loyalty to government, when it deserves it.”
                  Mark Twain

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                  • #10
                    I suppose the Navy couldn't have been all that concerned about COD speed, having selected the (slower) CMV-22 Osprey to replace the Greyhound.

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                    • #11
                      Originally posted by JA Boomer View Post
                      I suppose the Navy couldn't have been all that concerned about COD speed, having selected the (slower) CMV-22 Osprey to replace the Greyhound.
                      They Osprey has decent range, pretty good speed and has the bonus of being able to land on almost all US/USNS vessels. This means items meant for an UNREP vessel can go straight to the vessel and not cross deck from the CVN and then to the UNREP ship.

                      But going to your original point....

                      The turboprop for the C2/E2 made sense since they were old established airframes with a lot of institutional knowledge, assured part supply and a good, reliable airframe. It was likely not economically worthwhile to switch to a turbofan, especially whne the thought for the CMV-22 was already in their sites. And the SVM-22 replaces the CH-46 & C2 with a single airframe.

                      “Loyalty to country ALWAYS. Loyalty to government, when it deserves it.”
                      Mark Twain

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