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2019 F-35 News and Discussion

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  • TomcatViP
    Rank 5 Registered User
    • Nov 2011
    • 6108

    smaller diameter doesn't lead it to being tiny.

    Add a third stream to the F-135: In order to fit inside an F-35, the core diameter has to be reduced by two time the depth of the added stream... Hence smaller. Having inherently more cooling air makes also the core able to run hotter, hence at a better efficiency rate to the benefit of its IR signature (mil. engines).

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    • TomcatViP
      Rank 5 Registered User
      • Nov 2011
      • 6108

      Another thing smaller and gigantic:
      The Bee just got a queen

      Attached Files
      Last edited by TomcatViP; 10th August 2019, 16:09.

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      • XB-70
        Rank 4 Registered User
        • May 2018
        • 350

        Where are you getting the factor of two from? The amount will depend on how much airflow they are planning to divert with the third stream and at what pressure. I don't know if either has been decided yet.

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        • TomcatViP
          Rank 5 Registered User
          • Nov 2011
          • 6108

          Let's say that we have initially a diameter of 1
          Add 0.1 at each diametral extremities (the thickness of the added stream) and the new diameter become 1+ 2x0.1

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          • halloweene
            Rank 5 Registered User
            • Jan 2012
            • 4351

            Anther legal issue for helmet...

            https://patentdocs.typepad.com/files/order-17.pdf

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            • halloweene
              Rank 5 Registered User
              • Jan 2012
              • 4351

              Originally posted by TomcatViP View Post
              Let's say that we have initially a diameter of 1
              Add 0.1 at each diametral extremities (the thickness of the added stream) and the new diameter become 1+ 2x0.1
              Air intakes are desined for the enhanced air flow? (genuine question)

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              • XB-70
                Rank 4 Registered User
                • May 2018
                • 350

                halloweene - The airflow in the intakes doesn't appreciably change. You could change it, if there is opportunities for further enhancement and internal tolerances within the structure of the plane and such support it. But it doesn't have to. Having the third stream just changes bypass airflow.

                TomcatViP - That doesn't get you a reduction of a factor of two but I'll take that as a good initial approx.. They will probably reduce the internal volume of the engine core (to get their high pressure ratio) by a slight amount though - like how I first proposed - instead of bumping up the external diameter of the engine (and intake). So, since pressure is a factor it could be slightly more than that. We're talking small changes though...no need for the drastic difference in the size between the fan and the core seen in airliners because that third stream is compressed and so gives a very high bypass flow. And that means the engine will be very efficient because the fan can run at its optimum speed simultaneously with the LP and HP spools - which cannot happen with the big airliner engines without coupling the fan through reduction gears.
                Last edited by XB-70; 15th August 2019, 12:01.

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                • halloweene
                  Rank 5 Registered User
                  • Jan 2012
                  • 4351

                  Another genuine question : won't a triple flow enhance too much the engine weight? Apparently weight tolerances are quite low on F-35

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                  • TomcatViP
                    Rank 5 Registered User
                    • Nov 2011
                    • 6108

                    We are looking at a safe margin of +- 9t of ordinance to implement any modification...

                    Also, third stream will generate power that could be used on cooling (beyond their inherent participation to insuling the hot section) leaving the extra amount of fuel that has to be kept for that to a bare minimum. This will open op birds to some weight savings, opening room for the new propulsion system.

                    Last edited by TomcatViP; 15th August 2019, 15:01.

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                    • djcross
                      Rank 5 Registered User
                      • Jan 2000
                      • 5456

                      Originally posted by halloweene View Post
                      Another genuine question : won't a triple flow enhance too much the engine weight? Apparently weight tolerances are quite low on F-35
                      There are several parameters which are key contributors of an airplane's predefined performance baseline (aerodynamics, propulsion and mission profile are the contributors with greatest impact). Weight affects aerodynamics by requiring more angle of attack to provide lift as weight increases. And increased angle of attack drives induced drag which negatively impacts range, speed and acceleration (typical performance baseline requirements). Designers use the weight growth curve to assure weight stays under control and the performance baseline is achieved, all other key contributors remaining constant. "All other key contributors remaining constant" is the catch. Adding 3rd stream propulsion performance is not constant with respect to current F135 performance. This allows the design team to re-balance the design to achieve the airplane's predefined performance. Improved propulsion performance may offset the weight increase. If a great benefit to airplane's performance can be achieved, the predefined performance goals will likely be altered, e.g. combat radius increase.

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                      • TomcatViP
                        Rank 5 Registered User
                        • Nov 2011
                        • 6108

                        What are we looking at for 3rd stream, 250kg?
                        It's marginal. Think also that the reduced core section will generate more weight savings than the increase brings in. We might end with an even result

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                        • XB-70
                          Rank 4 Registered User
                          • May 2018
                          • 350

                          Originally posted by TomcatViP View Post
                          What are we looking at for 3rd stream, 250kg?
                          It's marginal. Think also that the reduced core section will generate more weight savings than the increase brings in. We might end with an even result
                          That definitely could happen. The third stream is relatively low temp. You could build the necessary structure out of CFRP. The core section is where your dense nickel based alloys are. Even small reductions there counts for a lot with regards to weight.

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                          • moon_light
                            Rank 5 Registered User
                            • May 2012
                            • 1033

                            Originally posted by halloweene View Post
                            Another genuine question : won't a triple flow enhance too much the engine weight? Apparently weight tolerances are quite low on F-35
                            what is the tolerances?

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