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  • #16
    Re: Rare Bear question

    Originally posted by Rigby View Post
    Great thread, but not sure of the "betrayal of trust" statement. If I understand it correctly, all, or at least most, of the modifications that were done by the "old" crew have been removed. Since the original mods don't exist anymore, and I am pretty sure there is not going to be another racer that would use them, what is the harm in letting those of us who are interested in the modifications learn more about them?
    If you had spent half your life developing systems that were light-years beyond anyone else in the field and had developed and fostered the professional relationships to make sure everything was done right would you want to give away that information to anyone who wandered by?

    Would be like publishing the SR-71 plans and development on the internet. Airplane is retired but why let the Iranians have the info.

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    • #17
      Re: Rare Bear question

      Originally posted by omalley1537 View Post
      My understanding is that in lieu of essentially straight pipes for every cylinder (which is what I understand stock to be, please correct me if not).
      *stock* would not be quite the correct term, as the stock Bearcat also utilized a paired/scavenged exhaust setup. This is especially beneficial for cylinders that are farthest away from the exit trough and thus requiring a longer pipe. The scavenging effect just helps things along with regards to efficient elimination of exhaust gasses. Two of the cylinders were not paired in the previous setup, but those were also the two cylinders on either side closest to the exit hole so would not benefit as much.

      I believe *stock* was in reference to the stock Sea Fury setup the Ezel's were used to doing... which have an individual pipe for each cylinder.

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      • #18
        Re: Rare Bear question

        There had always been a problem with the exhaust blowing out on the Lyle-era setup due to the firewall (er... "diaphragm") being in the original stock position even though a much larger engine was installed. This made for some extremely tight plumbing and the "bondo" incident was partly due to this, since the cowling had been battered towards the backside from successive exhaust breeches.

        Cornell went on to tackle this problem by moving the firewall back to make more room for the exhaust. in the process, they built-up a new longer cowl. This may have had an effect on the airflow through the engine in itself, though to what extent I can only speculate. I'm guessing the real difference in airflow was caused by reshaping the exhaust outlet or plugging another hole somewhere. Sort of a balancing act as you want to eliminate cooling drag as much as possible while keeping the engine within operating parameters. The heat from the exhaust actually helps to pump air through the exit trough and keep it moving through the system. My guess is they made this exit a little too small during the re-work... unless the "desired effect" was to go ahead and let the cylinders cook!

        Exhibit A: (right after the Cornell firewall mod and exhaust re-work)
        Attached Files
        Last edited by RichH; 09-22-2014, 10:48 AM.

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        • #19
          Re: Rare Bear question

          Actually the outlets were too big.........
          Interesting bit of Trivia:
          Curtis-Wright set the Redline CHT on a 3350 at 500f..........For 30 Min
          Per a retired engineer they were ran in excess of 525f for much longer with no ill effects.
          ADI and mixture have a considerable effect on the CHT.

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          • #20
            Re: Rare Bear question

            Chris:
            Apparently I didn't quite make myself clear. I was not asking for complete engineering diagrams, drawings and all specifications, just some GENERAL information. We have seen some of the top Merlin builders talk about different rods, fingers, etc. when building up the racing Merlin engines. I was just asking for some general information. Sorry if I ruffled your feathers a bit.

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            • #21
              Re: Rare Bear question

              Originally posted by Rigby View Post
              Chris:
              Apparently I didn't quite make myself clear. I was not asking for complete engineering diagrams, drawings and all specifications, just some GENERAL information. We have seen some of the top Merlin builders talk about different rods, fingers, etc. when building up the racing Merlin engines. I was just asking for some general information. Sorry if I ruffled your feathers a bit.
              Lol no feathers ruffled(= Just don't feel it is my place to say anything about the secret squirrel stuff.

              Comment


              • #22
                Re: Rare Bear question

                While we're asking questions about the Bear - what was the deal with wet sanding the prop in the pits? It looked like it mostly took the shine off of it; I didn't see any witness marks to indicate high or low spots.

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                • #23
                  Re: Rare Bear question

                  Originally posted by AAFO_WSagar View Post
                  OK, I'm strictly from the same position as you.

                  As I understand it.....

                  BIG QUALIFICATION!

                  This is hearsay!

                  The "BEAR" exhaust was a complicated, hard to understand beast...
                  Actually... as I have described and illustrated, there is *nothing* complicated about the previous exhaust at all. Though "artwork" is a valid description. This is what completely baffles me as to why they threw the baby out with the bath water. Not only did they lose the effect of scavenging, but now they had to use up even more of an already cramped area with all those pipes...
                  Last edited by RichH; 09-22-2014, 10:12 PM.

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                  • #24
                    Re: Rare Bear question

                    Originally posted by L.E.D. View Post
                    While we're asking questions about the Bear - what was the deal with wet sanding the prop in the pits? It looked like it mostly took the shine off of it; I didn't see any witness marks to indicate high or low spots.
                    Wet sanding a painted prop gives the surface more bite.

                    It's an 'old' Bear trick from the fast days.

                    Comment


                    • #25
                      Re: Rare Bear question

                      To answer the first question, Yes we would like to make everything perfect out of the gate, but not so in Air Racing.
                      Rod Lewis is very patient guy, and wants results, as we all do. The Bear has been around, the course many times and
                      things have changed on the airframe and engine over the years. Speaking for any racer crew, it takes time to workout the details, especially if the track you run on is only open once maybe twice a year for a few hours for testing. We have had to take the last few years on the track to learn about the setup, and are making more improvements for next year.
                      Sorry if my replies are slow, Im not available all the time.
                      GO Bear!

                      Comment


                      • #26
                        Re: Rare Bear question

                        Welcome on board, great first post.

                        Nice to hear from team Lewis and crew.

                        Comment


                        • #27
                          Re: Rare Bear question

                          Originally posted by ChrisMX105 View Post
                          Actually the outlets were too big.........
                          Interesting bit of Trivia:
                          Curtis-Wright set the Redline CHT on a 3350 at 500f..........For 30 Min
                          Per a retired engineer they were ran in excess of 525f for much longer with no ill effects.
                          ADI and mixture have a considerable effect on the CHT.
                          A word on that, if I may.

                          The strategy on achieving "big power" thru running air-cooled cylinders at the ragged edge of detonation temps may have had some validity, but in practice (as demonstrated) it was someone's yet unproven theory that for whatever reason failed miserably in execution. It seems there was a very fine line of parameters to make it all happen, any slight deviation of which would have the potential to cause BIG troubles. Being that close to the edge, you are also more subject to issues of un-even cooling, or even what the ambient temperature on the day might be.

                          So a retired engineer is emphatic that CHT's are good at 500+ for 30+ minutes (likely under lab conditions). For the duration of a race that seems fine, but at what cost to longevity? Ancillary equipment?? As someone insists, why on earth were the heads subject to warpage at LOW power settings??? Excessive heat is rarely that tenable.

                          You cite that in 2012, the Bear qual'd at 491 with 1100HP on tap. Where was all that power on Sunday?? For the duration of the program since the cowl was modded, I can't remember any heat race where the Bear wasn't having to throttle back (other than when it was having to run a more or less "stock" engine).

                          You can go ahead and call me a non-engineer and break out your slide rule with your theories on thermodynamics, but I would counter that all of this is pointless when the "Shelton-era braintrust" didn't seem to have any issues making decent power... WITHOUT resorting to a BBQ!

                          Comment


                          • #28
                            Re: Rare Bear question

                            I will have to say that the cylinders we pulled off from the 2012, and the rest after 2013 were not in good condition due to heat expansion. Wright paid more attention to cruise settings than other thresholds. Looking at the parts after a race is the only real data we can generate to find the extremes. Would like to be able to destroy a few old cores to find some parameters, but to few parts to be playing that game.
                            GO Bear!

                            Comment


                            • #29
                              Re: Rare Bear question

                              Hey Chad thanks for replying on this board. I was wondering about the intake that is now on bear the first time I saw it I asked someone on the crew if the intake was big enough and if the motor would get enough air I was told it was more than enough. Just curious from the rumors on line about low manifold pressure. Thanks Rich

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                              • #30
                                Re: Rare Bear question

                                It's ok, Everybody says that it's to small. The basic scoop design on navy aircraft was sized for optimum airflow at full power at takeoff. This was to insure well armored and fueled aircraft could depart a carrier deck effectively. Other industries practiced this to shorten takeoff rolls. So if your racing it's not about takeoff it's the top end. We wanted a scoop that gave us all we needed at 500 Mph and above. More air coming in the intake than what is was needed starts to pile up and boil back out the front causing drag. Drag is bad. The engine can only take in what the blower can move past it. If you pile up the air the blower won't move it till the next vein comes around. This pressure builds up to the scoop, then boils out. This is not problem causing through power settings except if your top end speed is more important than takeoff roll. We worked with John MacGuire of Lockheed Skunkworks, Ft Worth, which worked on Dreadnought and the Supercorsair in their beginnings.

                                MP.. Our manifold Pressure Is comparable to previous telemetry and flight video data with 2012. We expected to achieve more as we usually do with over the top scoop. We discovered this year during the engine rebuild room for improvment, but did not have time to make corrections.
                                GO Bear!

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