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RE: Aero stability test result

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  • Arthur Middleton
    ... Gyro effects make bikes more stable when travelling faster. A simple vector diagram will show that the apparent side wind is reduced by forward speed,
    Message 1 of 5 , Jan 1, 2004
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      > At 14:28 31/12/03, Arthur Middleton wrote:
      > >Interestingly, my estimation that higher speed makes for
      > higher cross
      > >wind stability is borne out. This is of course because the head wind
      > >component of the apparent wind is much bigger than the side wind
      > >component
      > --------------------------------------------------------------
      > ----------
      >
      > I suspect that the more aerodynamic the bike, the less true
      > this is, if at all:
      > - an un-aerodynamic bike (very rough, no smooth flow over
      > it) may well
      > generate most side thrust in a pure cross wind - ie, 90 deg
      > apparent wind
      > angle;
      > - however an aerodynamic bike (smooth flow, so relevant to
      > a brick as
      > well as an aerofoil) will generate most side thrust at small
      > angles of
      > attack and high wind speeds - ie, an apparent wind angle just
      > off 0 deg.
      >
      > I think the benefit of speed is that the bike is mechanically
      > more stable
      > the faster it goes (is this true?), so a given side force
      > will have most
      > effect on the rider at low speeds. Certainly my Gold Wing required
      > highly-developed buttock-clenching muscles at low speed in
      > big cross winds.
      >
      > Andrew

      Gyro effects make bikes more stable when travelling faster.

      A simple vector diagram will show that the apparent side wind is reduced
      by forward speed, irrespective of any gyro stability. A 30 mph wind is
      quite strong, whereas my average speed on a cross country trip is about
      45mph, so I am almost all the time travelling much faster forwards than
      the cross wind at its worst is blowing sideways. This is one reason why
      I think the HPV models are not generally applicable (in terms of
      magnitudes of effects). [The other is the mass difference and mass
      distribution is very different between vehicle types, though there is
      presumably a range of lightweight powered STV's that will be closer to
      HPV's.]

      The 'sailing close to the wind' analogy is what leads me to think that
      the tail is helpful in steering the bike into the wind.

      My experience of uprights is that bikes with large windscreens are badly
      affected by cross winds. Without, they are less affected. GPZ FF (with
      tail fairing and front fairing) is much less affected than either.
      Overall height must be a factor, but I don't know how big the effect is.
      GPZ FF is lower than an upright. Ecomobile is high, though, and has a
      large side area, but from reports is OK in cross winds (Blez?). When you
      (Andrew) get the ComforTMAX tail fitted, you can tell us what you
      discover. Any more progress?

      What is the big scooter experience like in strong cross winds? Most have
      big, high screens and low tails, and small wheels (less gyro effect).

      Arthur.
    • Bob Wreford
      ... Most have ... effect). My 400 Burgman seems subjectively to be so low that cross winds do not send it off course. However I do drive like a granny!! The
      Message 2 of 5 , Jan 1, 2004
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        --- In feet_forward@yahoogroups.com, "Arthur Middleton"
        <artmidd@e...> wrote:
        >> What is the big scooter experience like in strong cross winds?
        Most have
        > big, high screens and low tails, and small wheels (less gyro
        effect).

        My 400 Burgman seems subjectively to be so low that cross winds do
        not send it off course.

        However I do drive like a granny!!

        The 900 Triumph has massive weight to stick it to the ground but does
        blow me around in a crosswind, actually I am buffeted around by the
        breeze off the screen even in still conditions, enough to make my
        shoulders ache anyway.
      • David Scott
        I can t say as my burger is particularly stable in crosswinds, probably because of the big screen and despite my weight. The coast which has an even bigger
        Message 3 of 5 , Jan 1, 2004
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          I can't say as my burger is particularly stable in crosswinds, probably
          because of the big screen and despite my weight. The coast which has an
          even bigger screen is OK but it's kerb weight is about 640 pounds which
          might explain something, less "sail effect".

          David.

          Bob Wreford wrote:

          >My 400 Burgman seems subjectively to be so low that cross winds do
          >not send it off course.
          >
          >However I do drive like a granny!!
          >
          >The 900 Triumph has massive weight to stick it to the ground but does
          >blow me around in a crosswind, actually I am buffeted around by the
          >breeze off the screen even in still conditions, enough to make my
          >shoulders ache anyway.
          >
          >
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