On 9 Jul, 18:21, wrote:
On Jul 8, 9:52 wrote:



On 6 Jul, 11:15, Boltar wrote:

On 6 Jul, 11:05, Adrian wrote:

Don't forget that the engine is basically just being used as a generator,
therefore can run at optimum revs for the specific output - there's no
requirement for any kind of useful rev range or torque curve.

True , and I suppose that will mitigate it somewhat. However
ultimately that engine will produce less power than a normal bus
engine so when relying on the engine alone its going to be slower
compared to the normal engine running at optimum gearing.

B2003

You might be right for an outer suburban bus route, or one going from
town to town. However, a bus in London will probably average about
15mph. Hypothesising a little, if a 6 litre engine can deliver 60mph,
a 1.5 litre engine should deliver 15mph. The battery is being used as
an accumulator so average speed determined average power requirement.

On the flat, and assuming your drag is mainly air resistance power
required to maintain a constant speed goes up as cube of speed.

So if we assume that a 1.5 ltr engine can deliver 1/4 the power of a 6
litre engine then the 1.5 ltr engine should be able to maintain a
speed of about 38mph if the 6ltr engine can maintain 60mph.

It's why there isn't a huge difference between the best in the world
cyclists and a reasonable club cyclist in average speed.

IIRC, a 90 year old has done a 25mile time trial in just under an hour
(so lets say 25mph). Saturday, the fastest rider managed a 5 mile time
trial in just under 9 minutes (lets say 34mph)

But Cancellara, all else being equal, was delivering 2.5x the power
that that 90 year old was managing.

Yesterday David Millar managed the first hour at 30mph. That's still
70% more power of that 90 year old for just a 20% increase in speed.

Tim.

I broadly agree though I doubt if the main force for an inner city bus
is air resistance. Partly because of the cube law you refer to, at low
speeds air resistance is not so important.

For a traditional bus, most of the energy from the motor will end up
in the brakes, so regenerative braking is very important, though its a
long way off 100% efficient.