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Old 04-20-2008, 07:55 PM   #11 (permalink)
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A highly streamlined object drafting another highly streamlined object will actually cause drag to increase for both. Drafting only works when large areas of separation exist (i.e. blunt bodies). Well faired bicycle tires are probably approaching airfoil drag values.

I would suspect the reason for using one large wheel is lower weight (less suspension components), lower rolling resistance, and its use as a flywheel to smooth out pulses from the rider.

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Old 04-20-2008, 09:47 PM   #12 (permalink)
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Quote:
Originally Posted by trebuchet03 View Post
Otto,

Small wheels have a higher rolling resistance - at least traditionally...
I always thought that too, until I saw a street luge contest on TV.

Those tiny skateboard wheels would, being so small, seemingly have high rolling resistance. OTOH, they'd have very low wind resistance. The bottom line, though, is those street luges go like bats out of hell.

So, I got to wondering if such might not have application on an HPV, esp. since they may offer considerable flexibility in design parameters.
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Old 04-20-2008, 11:08 PM   #13 (permalink)
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Quote:
Originally Posted by Otto View Post
I always thought that too, until I saw a street luge contest on TV.

Those tiny skateboard wheels would, being so small, seemingly have high rolling resistance. OTOH, they'd have very low wind resistance. The bottom line, though, is those street luges go like bats out of hell.

So, I got to wondering if such might not have application on an HPV, esp. since they may offer considerable flexibility in design parameters.
Hrmm... that's a pretty good observation.... worth looking into methinks....

To take a semi-educated guess.... It's a super hard material - so it doesn't deflect as much. The reason smaller tires are generally higher in RR is due to the amount of deflection the rubber must conform to for the contact patch....

You probably won't get much in the way of side loading traction on wee wheels (which is fine for luge methinks)..... Something tells me you can't use just one wheel to turn either....

But, generally, guys that want to go fast use super high pressure tires -so there's not too much in the way of suspension....

Then again...
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Old 04-21-2008, 11:44 AM   #14 (permalink)
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Quote:
Originally Posted by trebuchet03 View Post
Hrmm... that's a pretty good observation.... worth looking into methinks....

To take a semi-educated guess.... It's a super hard material - so it doesn't deflect as much. The reason smaller tires are generally higher in RR is due to the amount of deflection the rubber must conform to for the contact patch....

You probably won't get much in the way of side loading traction on wee wheels (which is fine for luge methinks)..... Something tells me you can't use just one wheel to turn either....

But, generally, guys that want to go fast use super high pressure tires -so there's not too much in the way of suspension....

Then again...
Alex Strojnik discussed the tandem small wheel idea in his Laminar Aircraft Design trilogy, then built it into his S-2 motorglider, which has less drag with two tandem wheels than a typical sailplane with just one. He reasoned that much of the rolling resistance is from the wheel dropping into small holes or depressions, then having to compress as it came up the other side of the pothole, with consequent unwanted vertical motion and drag. With tandem wheels, though, he says the ride is much smoother, since rather than dropping into the hole, the front wheel goes over since it's held up by the back wheel, which in turn goes over the hole since the front wheel is by now past the hole. In other words, just like Roller Blades, which wheels have durometer hardness ~85-90. Anyway, Strojnik put the brakes on his rear wheel, so if braking too hard the rear wheel lifts off and loses braking power before the plane can nose over, a very handy feature for short field landings.

On an HPV streamliner, one can imagine small tandem front wheels, with one fixed and the other castering, both on a short well-faired truck mounted on a streamlined stalk below the pod nose. That way, you'd get good steering without needing to bugger the flow around the front wheel and the big hole it typically needs (like World's Fastest Indian fairing).

Street luges first caught my attention in a car mag article ~20 years ago--some luger challenged a Corvette to race to the bottom of Mullholland Drive or somesuch steep and windy road in S. California. The Corvette guy thought he was nuts, the luge having no engine. Luge also had CG about 4" off the pavement, and won the race with top speed ~80 mph. The Vette could not match luge speed in curves, and rolling resistance of those skateboard wheels was apparently pretty low, maintaining high overall speed.

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