Just a thought, I don't think a fin on the rear of the bike is the solution
as if the aerodynamic forces push the front boom to the side a fin on the
rear of the bike won't correct it.
Cheers Daryl
From: Øivind Grønli <oivind@xxxxxxxxx> Reply-To: python@xxxxxxxxxxxxx To: <python@xxxxxxxxxxxxx> Subject: [python] Re: some thoughts Date: Thu, 13 Oct 2005 22:01:09 +0200
Hi all,
I've been following the discussion for a couple of days. I am thinking about
building a Python, and in my opinion the only real drawback of the design is
the poor stability when coasting at high speed. So I want to find a
solution.
Regarding the tailfin, Dirk Jan, are you sure it couldn't work? Since the pivot point is between the front and the rear wheel, a force trying to straighten up the rear wheel would also indirectly try to straighten up the front wheel, shouldn't it? If so, one could either place the fin far enough behind the rider to avoid the turbulence or place it right behind the rear wheel, but lifted up above the turbulence from the rider.
Oivind -----Opprinnelig melding----- Fra: python-bounce@xxxxxxxxxxxxx [mailto:python-bounce@xxxxxxxxxxxxx]På; vegne av Dirk Jan Luiting Sendt: 13. oktober 2005 20:52 Til: python@xxxxxxxxxxxxx Emne: [python] Re: some thoughts
Hi,
During my student coarse aeroplane building i got some info on aerodynamics.
the thing with cigar-shaped objects is that they tend to turn sideways. its easy to understand, visualise a cigar shaped object moving lengthwise through air. the air stops at the tip and creates statical air pressure. this is also the case at the back of the cigar where there is a similar pressure.
when the cigar turns a bit at an angle to the airstream, the pressure area at the front and backend will shift accordingly, creating a moment on the body, trying to turn it even more.
thats the problem with which those hpv people have to deal in these streamlined hulls.
the obvious solution there is to add a tailfinn, which will create a correcting moment to the destabilising moment from the cigar shaped object described before.
in case of the python bikes, there is not directly such an obvious solution.
here the destabilising moment works directly on the steering front, so a fin on the back of the bike would do no good.
maybe some vertical fin in front of the bike, steering in the counter direction of the pivot, to get some correcting moment on the frontpart at high speeds, compensating aerodynamic forces. one could do that with some wires attached to the backend, in their turn attached to the fin so it counterturns slightly more than the center pivot.
its of absolutely no use to use a backfin on the back part.
1. it will be in the turbulence of the rider, thus rendering it useless.
2. stabalising the back of the bike will probably even make things worse,
as the front wants to turn and the back dont.
i could think of other solutions like extending the front part of the bike, over the riders head to the back, behind the pivot point. (like a stiff fishing rod with a vertical fin attached) that would also work, as log as the backfin doesnt get caughtup in the riders drag.
//Dirk Jan
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