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F-5 engine upgrade?

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    #21
    Engines

    Oh, I didn't realize the F125 in the Ching-Kuo was that much larger. Guess that won't work then. Sounded good at least. Well, what about GE taking the J-85 and updating it to more modern standards. Surely modern technology can help produce an almost identical engine with more power and better fuel efficiency. Now that I think about it, the J-85 is really a wonder of technology. Also, why did the USAF never put the J-85 in their very large fleet of T-37 Tweet jet trainers. The A-37 Dragonfly was fitted with them. Are they too powerful for the airframe of the T-37?
    Fox-4!

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      #22
      RE: F-5C/D & engine specs

      Scooter,

      I agree that it sounds like a good idea, with the relatively large numbers of Tiger II's still in service, with many of them going through various stages of systems upgrades. But, I still think that if it made sense from a economical/performance standpoint in relation to the cost of doing it, that one of the several companies involved with F-5 upgrades would have pushed it. I doubt we have thought up something here that the upgraders have overlooked, given that they are all working hard to get any perceived advantage over their competitors for these contracts. I don't know much about engines, but I doubt that in this case it will be possible to get a drastic amount of increased performance out of a similar sized engine to the J85. This may be possible, and if it is I agree it should be considered. A major structural change to accept a larger engine/engines may be too costly in return for the added capability it would give or for the amount of time some of the F-5 operators intend to keep the F-5 operational. Good question, but I still doubt that we are breaking new ground with this question.

      Mike

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        #23
        RE: F-5C/D & engine specs

        You maybe right. I have often wondered why a engine upgrade was not done with the F-5 (J-85)? That said, it doesn't mean its not possible. Even if you believe the argument that the J-85 cannot be improved on. What about aircraft like the Mig-21? Many still in service and being up graded as we speak. The Mig-21 may only be around for another 10-15 years but, the T-38 should be around til about 2040! I may not be around that long?
        F-35 Lightning II

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          #24
          RE: F-5C/D & engine specs

          "What about aircraft like the Mig-21? Many still in service and being up graded as we speak."

          Not with new engines though Scooter. The various upgrade programmes for the Mig-21, e.g. Mig-21-2000, Lancer etc involve avionics and life extension developments. For the F-5 this is by far the better (and cheaper) path with minimal risk. Elbit systems from Israel offer a fairly good package which includes Multi-mode Fire Control Radar, Structural Modifications for new aerodynamic capabilities, the EW suite, HOTAS operation and head-out flight.

          Regards, Glenn.

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            #25
            RE: F-5C/D & engine specs

            Can somebody answer this..what about an m-88 or EJ-200 or TU RB199 with the afterburner removed? The engine length would be reduced , diametere would be 1 larger engine vs 2 smaller ones and weight would add a few hundred pounds but greater thrust.Also without afterburner , fuel consumption for a given thrust would be lower.Speed?I'm not sure..perhaps somebody could answer that.Is there a difference between an engine with say 4000lb wet thrust and 4000lb dry?

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              #26
              RE: F-5C/D & engine specs

              the exhaust velocity is much different, translating to a huge difference in transonic performance.
              Country::US of A

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                #27
                RE: F-5C/D & engine specs

                Glenn- As always your point is well taken. However the point that I was trying to make. If, you are upgrading aircraft with extensive avionics (i.e. Mig-21, F-4,etc.)for just 10-15 year. Wouldn't an engine upgrade be in order for a aircraft with one expected to last 20 to 25 years? (up to 40 in the T-38!)
                F-35 Lightning II

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                  #28
                  RE: F-5C/D & engine specs

                  Scooter,

                  Yes, if the right engine can be found or even arranged for the upgrade. If not, then an overhaul would be the next best thing. Trying to modify a larger engine to fit a smaller body is undoubtedly going to cost more than you think and make the upgrade financially ineffective.

                  Regards, Glenn.

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                    #29
                    RE: F-5C/D & engine specs

                    The last time I heard they were doing anything on a j85 engine, they were trying to design a new nozzle to increase the efficiency of the j85's. i don't agree on removing the two j85's and putting a bigger one since it would require new structural body work to fit the bigger engine.. and it costs money. Many of the countries who uses the f-5's probably had a lot of experience with the j85's about 13,500 of these engines have been delivered..

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                      #30
                      RE: F-5 engine upgrade?

                      i think a weapons upgrade would be better. like bvr missles.

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                        #31
                        RE: F-5 engine upgrade?

                        it alredy can take the aim-7 sparrow and as it can take aim-9 sidewinder then the aim-120 amraam in the same rail

                        rabie :9

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                          #32
                          I understand this is a very old thread but it is still just as relevant today as 15 years ago. The Rolls Royce Turbomeca Adour MK 951/F405 has a 22 inch diameter vs the J-85-21 diameter of 19 inches I believe. I know that the nacelles in the type II-E/F were redesigned to fit the -21 over the prior J85s. The original was 17" diameter and I couldn't find the numbers on the 21. The length of J-85-21 is 52" with a 60" nozzle/afterburner section. 112" total length. Mk951 is 114" total length. These engines put out 8000 pounds of DRY thrust vs the 5000 of the last J85 variant at full military with flame on
                          It's a 3 inch difference (1.5 inches a side) and the length will fit At 2" longer. The largest issue is weight. The j85-21 is maybe 700 pounds with afterburner and the mk951 is 1784 pounds. That's a 2000 pound difference. This could be the nail in the coffin for the swap. I am not sure if wiki numbers are accurate. The length listed doesn't include the huge afterburner section I haven't seen any specification on that. The Mk951's would be like adding a third engine with full afterburners. Brand new model full FADEC. Over 50% thrust increase would make the F5 an absolute rocket ship. The engines are heavier Moderators I apologize for revising an old thread but I've spent days searching for anything on this with the turbomeca derivative. They are the closest I've found in months of searching dimensions. Any help/ideas/thoughts appreciated

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                            #33
                            The only replacement for a J85 is really another J85. It's a remarkable little engine. Perhaps only the Viper comes close.

                            J85-21 has an inlet diameter of 21"

                            As you note, the Adour is in a whole different weight class plus that weight is all distributed along the 114" of the main casing ( rather than concentrated in the forward 52" casing of the J85 ). Even if it was possible to squeeze that into the airframe it would so massively ruin the CoG that it would be unflyable.

                            Back in the mid-1970s GE were developing the successor YJ97 on contract to the USAF; 24.4" diameter, 109.5" long with afterburner, weight 694lb, thrust 5,270lb dry and ~8,000lb augmented.
                            Last edited by Cherry Ripe; 7th December 2017, 09:32.

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                              #34
                              I don't know how modern construction couldn't improve a 1960's design when ceramics and composites could drop weights and raise maximum pressures and temperatures to gain a modest 20% improvement on the dry thrust alone. The J85 isn't magic.

                              The truth is the centrifugal turbofans are simpler and cheaper to produce at that scale. There wouldn't be a commercial product to sell, so there is no profit in accomplishing this boost of performance. The larger engines are the market.

                              The funny thing is, the volume of space for a J85 used in the F-5 is actually mostly the wet section.

                              Last edited by MadRat; 8th December 2017, 07:55.
                              Go Huskers!

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                                #35
                                Or you could put a single modern engine in the F-5 and call it a F-20....oh wait.....

                                Agree that diameter and weight make a Adour swap out impossible. Amazing how much power the J85 generates for its size.

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                                  #36
                                  There is one western engine I think that could make an interesting prospect for replacing J85s, that is Turbomeca's Larzac. It's quite small, inlet is basically the same size as a J85(per Wiki, might be wrong), weighs around 290-300 kg. In the alpha jet it makes 14 kN, but there was a higher powered FADEC version with close to 17 kN, dry, that was proposed as an upgrade. Adding an afterburning section should not be a major problem and should see it developing close to 30 kN of thrust. It would still weigh slightly more than a pair of J85s, but would offer better SFC and more thrust.

                                  But, J85s are cheap and plentiful and still supported by GE and they do work.
                                  George Costanza: It became very clear to me sitting out there today that every decision I've made in my entire life has been wrong. My life is the complete opposite of everything I want it to be. Every instinct I have, in every aspect of life, be it something to wear, something to eat - it's all been wrong.

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                                    #37
                                    Guys dont be so fixated to specific size dimensions and stats like weight if you are gonna find a replacement engine. Air mass flow is the real limiting factor.

                                    Nasa links
                                    Mass Flow Rate
                                    https://www.grc.nasa.gov/www/k-12/airplane/mflow.html
                                    General Thrust Equation
                                    https://www.grc.nasa.gov/www/k-12/airplane/thrsteq.html

                                    Engine thrust is dictated by the Air Mass Flow. In reality this translates to the relation of inlet and outlet dimensions. For example consider the difference between F-5A and F-E. F-5E's J85 had higher thrust but also required a larger airflow. The difference in requirement was not so large that the inlet redesigned was deemed sufficeint and the airframe could be (largly) left as is. However for the F-5G/F-20 the air mass flow was so large that not only the inlet but also the fuselage had to be redesigned. Airliners usually have their engines in a poded configuration outside the fuselage or wings which makes it relativly easy to replace/upgrade an engine.

                                    There is little economic sense in investing a lot of money and time in redesigning and reengineering/modifying an old and used airframe. A drop in replacement makes more sense. But then your new engine has to have the same dimensions and air mass flow as your old engine. So whats the point in replacing an engine which is already optimised for your specific airframe?

                                    That is why there are so very few fighter engine replacements around to talk about.

                                    \\Dan
                                    Last edited by Z1pp0; 16th December 2017, 12:08.
                                    Latencia Profecionalis

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                                      #38
                                      The J85 used on the USAF had a flameholder redesign and a parts reduction that saves money. That kind of upgrade can probably take place with major headaches. I'd be very surprised the blades couldn't take some kind of drop-in replacement. The turbines in a jet (e.g. axial-flow and centrifugal designs) are easy enough to upgrade something from the 1960's by taking advantage of current materials and production methods. A redesign of the F100 to add technology from the F119 went very smooth. They only sought tweaks that didn't change the design wholesale and ended up with dramatic decreases in spool-up time and similar increases with specific thrust. If the USAF had a considerable fleet and wanted the improvements then they would get done.
                                      Go Huskers!

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                                        #39
                                        Romania liked the idea of the Larzac... https://www.rumaniamilitary.ro/alr-p...-usor-elvetian

                                        Go Huskers!

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