A paradoxical thought experiment
in [Motorcycles]
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From: Beav on 8 Jul 2010 19:07 "J. Clarke" <jclarke.usenet(a)cox.net> wrote in message news:i14ghs02nvi(a)news5.newsguy.com... > On 7/8/2010 4:26 AM, TOG(a)Toil wrote: >> On 8 July, 08:16, Twibil<nowayjo...(a)gmail.com> wrote: >>> On Jul 7, 10:53 pm, totallydeadmail...(a)yahoo.co.uk (The Older >>> >>> Gentleman) wrote: >>> >>>> The US built an experimental lifting body, yes. It crashed. >>> >>> The US has built and flown a number of different lifting body aircraft >>> featuring various configuations. >> >> I'm sure the US has, but that was the only one I could remember. I >> suppose you could say that the Northrop whatever-it-was and the B2 >> bomber are lifting bodies of a kind. > > Nope, they're flying wings, the opposite of a lifting body. By the way, > the B2 is a "Northrop whatever-it-was", sixth in the line of > development--there was the small prototype, a 1/3 scale development mule, > the propeller driven bomber, the rocket fighter, the jet bomber, then a > long hiatus, then the B2. But people have been flying RC lawnmowers (based on the lifting body principle) for years. Put a big enough engine into a big enough lawn mower and you could even carry the grass catcher full of people. -- Beav
From: Twibil on 8 Jul 2010 20:16 On Jul 8, 12:50 pm, "S'mee" <stevenkei...(a)hotmail.com> wrote: > > > > In real life, on real roads, a riderless bike will fall over rather > > quickly. > > No it wont. Try it. Even a small nudge is enough to start a bike leaning one way or the other, and after that it's just a matter of time.
From: Twibil on 8 Jul 2010 20:29 On Jul 8, 2:15 pm, "Vito" <v...(a)cfl.rr.com> wrote: > > > > Note: Left to it's own devices, a non-sidecar bike will fall right > > over. And this is equally true whether said bike is moving or at rest. > > > It's only the kickstand when at rest, or the rider's constant > > corrections when moving, that keep it upright. > > You're joking? I've seen bikes buck their rider off then proceed to the > next corner just fine on their own. I assume you have too. Sigh. Yes, a bike at speed is dynamically stable. But only until (A) some input such as road camber upsets that stability and starts the bike leaning towards one side or another, or (B) the bike hits something. In the real world, neither thing ever takes very long to occur because the slower the bike is going the less stability it has, and the faster it's going the more quickly it's likely to laminate itself to an immovable object.
From: S'mee on 8 Jul 2010 20:30 On Jul 8, 3:26 pm, sean_q_ <nos...(a)no.spam> wrote: > S'mee wrote: > > Not true, not true at all. Below a given speed it can fall over. BUT > > past that threshold (about where countersteering takes over) > > Gyroscopic precession and gyroscopic forces would prove you wrong. > > I think the gyro effect is insignificant below very high speeds. > As another thought experiment consider a bicycle with wheels > of negligible mass (ie near-zero rotational inetria). > > The bike still steers and handles normally due to the usual > steering geometry (self-centering front wheel because of > the trail's caster effect) etc. > > SQ that to! almost forgot that bit and yeah aaamof I have seen a riderless bicycle going down the street until it slowed down and the lack of the front wheel acting as gyroscope let the front wheel flop over and then the whole bike.
From: S'mee on 8 Jul 2010 20:30
On Jul 8, 6:29 pm, Twibil <nowayjo...(a)gmail.com> wrote: > On Jul 8, 2:15 pm, "Vito" <v...(a)cfl.rr.com> wrote: > > > > > > Note: Left to it's own devices, a non-sidecar bike will fall right > > > over. And this is equally true whether said bike is moving or at rest.. > > > > It's only the kickstand when at rest, or the rider's constant > > > corrections when moving, that keep it upright. > > > You're joking? I've seen bikes buck their rider off then proceed to the > > next corner just fine on their own. I assume you have too. > > Sigh. > > Yes, a bike at speed is dynamically stable. But only until (A) some > input such as road camber upsets that stability and starts the bike > leaning towards one side or another, or (B) the bike hits something. > > In the real world, neither thing ever takes very long to occur because > the slower the bike is going the less stability it has, and the faster > it's going the more quickly it's likely to laminate itself to an > immovable object. You are just not correct. |