RE: Aero stability test result
- View Source
> At 14:28 31/12/03, Arthur Middleton wrote:Gyro effects make bikes more stable when travelling faster.
> >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
> 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
> - 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.
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
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).
- View Source--- In email@example.com, "Arthur Middleton"
>> What is the big scooter experience like in strong cross winds?Most have
> big, high screens and low tails, and small wheels (less gyroeffect).
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.
- View SourceI 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".
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.