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Re: Josh Tschirhart--questions on your scale model

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  • Josh T
    ... He even zip-tied the piston tube to the upper motor. This is why I wish there was more time to look at and discuss this stuff at NARAM after scale day. In
    Message 1 of 15 , Aug 15, 2005
      Steve wrote:

      > How do you get the fine balance between the piston tube gripping the
      > upper stage tightly enough to allow the piston to expand yet loosely
      > enough to ensure separation at staging? Mike's Astrobee used pistons,
      > and staging just blew the next stage off without lighting the motor.
      He even zip-tied the piston tube to the upper motor.

      This is why I wish there was more time to look at and discuss this
      stuff at NARAM after scale day.

      In my own use of earlier versions of this pistoning system, I did not
      have any trouble igniting the upperstage motor. I did, however, have
      trouble getting the chute out, mainly due to too much friction-- both
      in the piston assembly itself and between the chute and the booster
      tube inner wall.

      Did Mike's piston have the standard vent holes beneath the upperstage
      nozzle?

      My system had two 1/4" vent holes as well as two Apogee PT-6's coming
      down to the bottom of my chute compartment so that the gas won't escape
      until the compartment is fully deployed. Incomplete deployment (i.e.
      chute getting stuck) at the Mick Wilkins meet (and one earlier test
      flight) did not prevent upperstage ignition. The gases must have had
      enough room to vent within my piston assembly without having to escape,
      but I think the initial holes were still necessary. The friction of
      the pistoning action was very minimal, as I had a homemade tube
      telescoping over a standard BT-5. The friction of the 2nd stage motor
      into the stuffer tube (top of piston) and the stage coupler up into the
      bottom of the 2nd stage was pretty much standard. My main concern was
      blowing out the booster motor (this happened in a 2002 test flight).
      In future models (both scale and boilerplate) I think a motor hook
      would be extra helpful.

      The problem with this particular system (revelation of the chute
      compartment beginning no more than an inch below the upper nozzle
      causes the inside of the telescoping tube to get burned by the 2nd
      stage motor. Future versions would probably work better by pistoning
      out of the rear of the model (similar to some FAI scale altitude
      methods--more on that another time) or even at a lower body break (like
      in front of the booster fins of a Javelin). That way the pistoning
      tube can move backwards rather than forward, and direct exhaust damage
      will be prevented (at least for the moving piston parts).

      Something about this latest version used at NARAM... instead of a
      chute, I used two opposing streamers so that if they deployed before
      upperstage ignition, they would cause equal drag on both sides of the
      model and not "kink-over" the trajectory.

      I can upload a scan of the design later if you all would like to see it.

      Josh T.
    • Steve Humphrey
      ... No, which could well be the design flaw; but he didn t add vents because we worried that with vents there d be no pressure to activate the piston.
      Message 2 of 15 , Aug 15, 2005
        Josh T wrote:
        > Did Mike's piston have the standard vent holes beneath the upperstage
        > nozzle?

        No, which could well be the design flaw; but he didn't add vents because
        we worried that with vents there'd be no pressure to activate the
        piston. Obviously he didn't test this (or any other) method ....

        > My system had two 1/4" vent holes as well as two Apogee PT-6's coming
        > down to the bottom of my chute compartment so that the gas won't escape
        > until the compartment is fully deployed.

        I'm not understanding this. I assume the 1/4" tubes direct the gases
        down past the parachute ... but how do they delay the gas escape until
        after deployment? And where does the gas escape, once it can?

        > Incomplete deployment (i.e.
        > chute getting stuck) at the Mick Wilkins meet (and one earlier test
        > flight) did not prevent upperstage ignition.

        Perhaps this is the problem we were trying to avoid--the vents bled off
        the pressure before the piston could move?

        Steve Humphrey
      • Josh and Jess Tschirhart
        Well, depending on the design, the piston would deploy either before ignition or after. In Bob Biedron s gold medal Nike Apache (S5B at the WSMC), the chute
        Message 3 of 15 , Aug 15, 2005
          Well, depending on the design, the piston would deploy either before
          ignition or after. In Bob Biedron's gold medal Nike Apache (S5B at the
          WSMC), the chute piston was not able to deploy until after ignition. In my
          design, it may deploy beforehand (but not necessarily). At the very least,
          a design that doesn't fully deploy with the booster motor's gases should be
          pressurized enough by the 2nd stage exhaust to fully extend the piston
          (otherwise how could a normal "vented" booster even separate after
          ignition?). The vent holes should then not be a problem in this system. In
          my system (without going into too much detail) the 1/4" tubes lead the
          vented gases down past the streamers to below the piston's lowest centering
          ring, so that the gases don't fully reach the outside air until the piston
          is almost fully extended. The gases then escape from between the top of the
          booster body and the bottom ring of the piston/chute compartment.

          But if the system deploys fully before ignition, and unless the chute is
          packed a certain way, it could theoretically inflate and jerk the model out
          of its intended flight path (this happened to me on my earliest test
          flight). That's why I used two opposing streamers in the N-47 booster to
          create equal drag on both sides of the model, since I had no time to test
          the parachute-packing theory.

          >> Perhaps this is the problem we were trying to avoid--the vents bled off
          > >the pressure before the piston could move?

          The vents are apparently necessary for successful gap staging. Booster
          motor pressure is not the best source for piston deployment if you want full
          deployment before staging, but once the 2nd stage motor lights you should
          have the pressure you need to complete the deployment-- assuming that the
          friction of the stage coupling is greater than the overall friction of the
          piston/recovery system coming out of the booster (it's very important to get
          a good slip fit--so loose that the booster and piston will separate under
          their own weight if possible). The problem in the two flights that had
          incomplete deployment was twofold: 1) the piston compartment did not slide
          smoothly enough, and 2) the chute package was a bit too big (tight) for the
          compartment. But that didn't prevent staging.

          So I learned several things that would not be obvious:

          1) Vent holes below a motor may be sufficient for gap-staging ignition even
          if the gases are not fully vented to the outside of the airframe, but merely
          into the space between the outer airframe and the stuffer tube (the
          important thing is to vent the stuffer itself). Note: I don't totally
          trust this concept for future stage design. I still plan to try to vent to
          the outside as much as possible. Nevertheless, the Biedron Nike booster
          piston mentioned above vents only to the airframe inner space and not to the
          outside of the model.

          2) Positive retention of the booster motor is important (at least friction
          fit the heck out of it). Otherwise, you might blow the booster motor out of
          its mount at 2nd stage ignition and toast your booster. This has happened
          to me on about three occasions with either piston or non-piston models. It
          happened to Jess once with her Iris model.

          Josh T.
        • Josh T
          Steve, Something I thought of after replying last night... The pistoning recovery systems I ve been talking about should not be confused with the type of
          Message 4 of 15 , Aug 16, 2005
            Steve,

            Something I thought of after replying last night...

            The pistoning recovery systems I've been talking about should not be
            confused with the type of piston launchers that rocketeers use, so
            maybe "pistoning" is not the best word for it. My version probably
            does not aid much in terms of velocity of the upper stage, but only
            serves as a mechanical recovery system deployment method.

            But thinking in terms of traditional pistons, I can now see why you
            were wary of vent holes, as obviously we do not put vent holes in the
            pressurized compartment of our piston launchers. In my case (as
            stated in the other reply) the friction of the motor/coupler fit must
            be greater than the friction of the pistoning action of the recovery
            compartment.

            So I would not expect to be able to combine gap staging with true
            launch-type piston (aiding in gaining speed and/or altitude) because
            of the need for vent holes below the upper motor; I think this should
            only be done with electrical staging methods so as to seal the
            traditionally-built piston tube (I'm still planning on this very
            thing with my unfinished Saturn model).

            Josh T.
          • mmcreynlds@aol.com
            In a message dated 8/15/2005 10:50:55 AM Pacific Daylight Time, ... Looks like less than an hour s drive from the airport at Nashville. Would be fun, assuming
            Message 5 of 15 , Aug 16, 2005
              In a message dated 8/15/2005 10:50:55 AM Pacific Daylight Time,
              dalewindsor@... writes:

              > Who would attend an all Sport Scale (including F/F), say in Manchester,
              > TN in the Spring or Fall?

              Looks like less than an hour's drive from the airport at Nashville.
              Would be fun, assuming it wasn't on a "name" weekend or I was
              otherwise able to use frequent flyer miles, though American seems
              determined to see that it will never happen.

              Marc McReynolds




              [Non-text portions of this message have been removed]
            • Len Bryan
              Hello All, I ve been trying to help a fellow Canadian rocketeer find data on the Aerobee 150A. Specifically, he is looking for photos and scale data from the
              Message 6 of 15 , Jan 28, 2007
                Hello All,

                I've been trying to help a fellow Canadian rocketeer find data on the
                Aerobee 150A.
                Specifically, he is looking for photos and scale data from the actual
                rocket.

                Any assistance would be appreciated.

                Thanks!

                Len Bryan
                CAR S620 L3
              • Scheevel, Mark
                These aren t particularly interesting for scale purposes (I don t think they provide any dimensional information that isn t already available in RotW), but
                Message 7 of 15 , Jan 28, 2007
                  These aren't particularly interesting for scale purposes (I don't think
                  they provide any dimensional information that isn't already available in
                  RotW), but they're interesting if you're curious about the rocket
                  itself:

                  http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19640013111_1964013
                  111.pdf
                  http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19660085129_1966085
                  129.pdf

                  It's also interesting that Barrowman's dissertation used the 150A as one
                  of the subjects:

                  http://www.vtsrp.org.vt.edu/Reference%20AIAA%20and%20NASA%20Papers/D&C/2
                  0010047838_2001074887.pdf

                  Once upon a time I stumbled across some online photographs of a 150A
                  that showed good levels of detail, but I wasn't smart enough to bookmark
                  them, and I've been unable to locate them again. They're probably still
                  out there, so keep looking.

                  Mark Scheevel

                  -----Original Message-----
                  From: scaleroc@yahoogroups.com [mailto:scaleroc@yahoogroups.com] On
                  Behalf Of Len Bryan
                  Sent: Sunday, January 28, 2007 12:59 PM
                  To: scaleroc@yahoogroups.com
                  Subject: [Scaleroc] Aerobee 150A

                  Hello All,

                  I've been trying to help a fellow Canadian rocketeer find data on the
                  Aerobee 150A.
                  Specifically, he is looking for photos and scale data from the actual
                  rocket.

                  Any assistance would be appreciated.

                  Thanks!

                  Len Bryan
                  CAR S620 L3




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