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Strega Questions: Can It Be True??

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  • #46
    Re: Strega Questions: Can It Be True??

    Well the experts answered the Top Fuel motor stuff alot better than I could. I know much more about your basic car engine.

    As for fuel cars many of you probably know the Force's daughter ran last year in Top Alcohol Dragster, but not with a blower car, but a A/FD, which has no supercharger, and runs 100% nitro, while the blown cars run alcohol. The blower guys cried again this year, so NHRA is limiting the nitro to 96% in TAD next year. The sound these cars make without the blowers on nitro is really cool.

    Someone mentioned that they don't start the cars on nitro, this is true. Watching an A/FD car warm up is very interesting. They start it with a tiny detachable tank of alcohol. While on the alcohol the motor sounds like your basic hot motor, but man when they pull that tank off and go to 100% nitro, the motor just shakes, and spits and pops, it's pretty damn cool. Right now the national record is 5.11, not bad for no supercharger. If NHRA would just leave them alone we may see an unblown dragster run in the 4's!!

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    • #47
      Re: Strega Questions: Can It Be True??

      supersonic props (i.e. xf-84h, f-88, etc.)
      From what I have read the noise from the XF-84H was enough to make ground crews nauseous. You think the Stead neighbors complain NOW....
      Maybe a surplus TU-95 NK-12 attached to a Sea Fury with BIG tanks.
      Oops, no turboprops, but what a sound!

      Leo
      Leo Smiley - Graphics and Fine Arts
      airplanenutleo@gmail.com
      thetreasuredpeacock.etsy.com

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      • #48
        Re: Strega Questions: Can It Be True??

        leo, i'm not sure that all of that deafening and nauseating sound was coming from the prop itself. i mean they also tried the same concept on the xf-88 and as far as i know it didn't have the same effect.

        as for the tu-95's props, you'd have to cut those props down quite a bit to fit them to a sea fury. and i think they were designed for not much over 2000 rpms. (anyone know how to calculate tip speeds of a single 8' prop blade at 1500-2000 rpm?
        heh heh alriiiight

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        • #49
          Re: Strega Questions: Can It Be True??

          Sorry Matt, I agree with Leo, I think I remember reading where it was the props because they went supersonic. Ill have to check though. I could easily be wrong.
          Jarrod

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          • #50
            Re: Strega Questions: Can It Be True??

            And don't forget the severe gyroscopic forces a bigger/heavier prop produces-I refer to John Penney's comparison of the heavy 3 vs. lighter 4-blader on Rare Bear. Making a 4 blade "paddle wheeler" I think is out of the question as it would make the plane unflyable.

            Ron Henning
            Ron Henning

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            • #51
              Re: Strega Questions: Can It Be True??

              Originally posted by matt
              leo, i'm not sure that all of that deafening and nauseating sound was coming from the prop itself. i mean they also tried the same concept on the xf-88 and as far as i know it didn't have the same effect.

              as for the tu-95's props, you'd have to cut those props down quite a bit to fit them to a sea fury. and i think they were designed for not much over 2000 rpms. (anyone know how to calculate tip speeds of a single 8' prop blade at 1500-2000 rpm?
              Well, lessee. Tip speed for an 8' blade at 2000 rpm, when the plane is chocked on the test stand = (2*pi*r*2000*60)/5280 = 1142.4 mph. Supersonic!

              At 1500 rpm it's still 856.8 mph.

              What I don't know how to judge is the effect due to the fact that in flight, the prop blade's advancing through the air at 400+ mph at the same time the tip's going around in circles at mach 1-point-something. I suppose if the effective angle of attack of the blade at the tip is zero it's equivalent to the static case, but in that case the prop's not doing much useful work, so I dunno, really.

              I'm just making it up as I go along...
              SteveZ

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              • #52
                Re:Tip Speed

                Matt:

                Assuming:
                8 Foot Diameter prop
                500 mph
                5,000 foot altitude

                Chart gives
                1500 RPM ~ M .88 Propeller Tip Speed
                2000 RPM ~ M 1.05 Propeller Tip Speed

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                • #53
                  Re: Strega Questions: Can It Be True??

                  Ah, but Matt specified an 8' blade, which discounting hub diameter gives a 16' diameter prop: a real monster. You want to run the numbers again?
                  SteveZ

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                  • #54
                    Re: Strega Questions: Can It Be True??

                    kilo, i said 8' feet for a reason, i wanted the tip speed of one prop blade 8 feet in the air, to my understanding the full span of the tu-95's prop is something like 16'3" and i thought both blades might screw up the calculation so i asked for a single blade estimate.

                    right ron, i *think* as these planes get faster and faster (especially with the potential of the newer designs) we may need to look more closely at supersonic props to go much faster than these new designs are planning to.
                    heh heh alriiiight

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                    • #55
                      Re: Strega Questions: Can It Be True??

                      Originally posted by matt
                      kilo, i said 8' feet for a reason, i wanted the tip speed of one prop blade 8 feet in the air, to my understanding the full span of the tu-95's prop is something like 16'3" and i thought both blades might screw up the calculation so i asked for a single blade estimate.
                      Right, Matt: that's what I thought you meant, so I based my static calculation on a prop with a radius (i.e., blade length) of 8'. Jay used a diameter of 8', giving a blade length of 4' in his example. But he seems to have taken into consideration the forward speed of the airframe, whereas I didn't, so I asked if he would run his numbers again.

                      I suppose if you do a simple vector addition of two orthogonal vectors you'll get a usable result, so let me try again. At 500 mph the airframe is moving at 733.33 fps (which at 5000' MSL on a standard days is .668 Mach), while at 1500 rpm the tips of a 16' diameter prop are moving at 1256.64 fps, orthogonally to the progress of the airframe.

                      The vector sum of 733.3 and 1256.6 gives a tip speed of about 1455 fps, relative to the airmass through which the plane is flying. That's 992 mph or, at 5000' MSL on a standard day, about 1.326 Mach.
                      SteveZ

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                      • #56
                        Re: Strega Questions: Can It Be True??

                        This got way OT, but fun and informative, nonetheless!
                        Rutan Long EZ, N-LONG
                        World Speed Record Holder

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                        • #57
                          Re: Strega Questions: Can It Be True??

                          Standard prop rpm for T-56 engines is 1020. Rare Bear runs about 1100 prop rpm.
                          Ron Henning

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                          • #58
                            Re: Strega Questions: Can It Be True??

                            are you sure about that ron? i thought it was quite a bit higher than that?
                            heh heh alriiiight

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                            • #59
                              TU-95

                              To clarify the TU-95 question check website below.



                              The Tu-95 propellers reach transonic speeds (in the order of M1.05) when it flies at its maximum speed (M0.83) above 11 000 metres (36 000 ft). The rest of the time they are subsonic despite their large diameter (5.6m , 18ft 4in) due to their turning around 800 rpm.

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                              • #60
                                Re: Strega Questions: Can It Be True??

                                Matt:

                                Just to be sure, I got out my old pilot manual for the Convair 580. I have about 1400 hours as a captain in it. And yes, the prop RPM for the Allison 501-D13 engine driving the Aeroproducts A6441FN-606A prop is 1020. Nominal engine RPM is 13820 with a 13.54:1 reduction ratio.

                                While standing around the "Bear Cave" last Sept., eavesdropping on Bill Hickle's explanation of many issues including the prop change, I was stupid enough (since I thought they ran a lot higher prop rpm) to say, regarding the 3-blade (although the Navy P-3 runs a different prop the engine is basically the same as the CV-580 so the prop must turn the same rpm) that the 3 blade was only designed to run 1020, and Bill said "well, that's about what we run". Later, I can't remember the source, someone said it was "around 1100".

                                I was surprised too, but surely there HAS to be an old A-1, DC-7, Lockheed 1049/1649 driver (or B-29 as the Bear has the same gear ratio) driver who would really know the answer first hand.
                                Ron Henning

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