Rotating wheel drag

In article said:

It is known that the disc wheel has less resistance than a 3-spokes wheel (while moving for
example at 30km/h). If the wheel is inside a body (for example fairing) the wheel rotate at the
same speed, but air is not flowing around the wheel. Only "rotational-frictional" drag counts.
Which is now the wheel with less resistance? How can man approximately compute it?

Thanks.

An interesting question. The best answer that I can give is that the fastest HPV records are set
with disc wheels, and they have given some thought to this stuff:

fortebikes.comDiablo.htmOpen ↗

Note especially the section where they talk about how wheel covers, inside the fully-faired bike,
made a considerable difference in the efficiency of the vehicle.

--
Ryan Cousineau, [email hidden] sfu.ca~rcousineOpen ↗ President, Fabrizio Mazzoleni Fan Club

[email hidden] (SR) wrote in message news:<[email hidden]>...

Quoted message said:

It is known that the disc wheel has less resistance than a 3-spokes wheel (while moving for
example at 30km/h). If the wheel is inside a body (for example fairing) the wheel rotate at the
same speed, but air is not flowing around the wheel. Only "rotational-frictional" drag counts.
Which is now the wheel with less resistance? How can man approximately compute it?

Thanks.

You should put that question to Matt Weaver: speed101.comspeed101.comOpen ↗
. He's built several streamlined HPV's with the wheels inside fairings *and* with the wheels sealed
in separate tight-fitting enclosures. He's pretty generous with advice.

I wouldn't attempt an answer to your question without a windtunnel or computational fluid dynamics
experts or both.

Jeff

Quoted message said:

Only "rotational-frictional" drag counts.

I believe a spoked wheel has the lower rotational aero friction.

There are two types of aero drag. Form drag and profile drag. One is the skin effect of viscous air
sliding along the surface. Disc wheel, more surface. One is the pressure drag effect of air
collapsing along a negative pressure gradient behing a moving object. Spoked wheel, less surface,
but now the new gradient.

These two can be optimized if you know conditions and relations precisely. One might come out with
seven spokes, for instance.

Might.

One or the other might already be the winner.

Yours,

Doug Goncz (at aol dot com) Replikon Research, Seven Corners, VA

1100 original posts at: groups.google.comgroupsOpen ↗