Power/Weight ratio of a horse

A million candlepower light can only be used in one place at once where as the candles could be used in a million different places.

I've got a 2 million candle power torch and the batteries don't last a whole long time...

-- James

You're right.

What I dont really understand though, is how are torque and horsepower related?

On the How Stuff Works website, it states that...You can easily convert torque to horsepower by multiplying torque by rpm/5,252.

If that was the case, then on torque/power output graphs from dynos, the lines would always cross at 5250 rpm, whereas clearly, they do not.

Pete

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Clearly they should!

I build dynos and write the software.... Mine all do!

If not somethings very wrong!

Grab a copy from my site here and take a look, lots of run data included.

There a useful "convert" program on there too.

Yep.

Er, they clearly DO !

If not, then the dyno/reading is broken !

If they're both graduated onto the same scale they should, but often they aren't, often having a torque scale on one side and a power scale on t'other.

-- James

Makes the torque curve look nice and fat.

For Kw/Nm it is even easier P = T * n (rads/sec = revs*2*Pi). Power in Watts so its usual to use P = T * revs * 2 * Pi / 1000 to get power in Kw.

-- Peter Hill Spamtrap reply domain as per NNTP-Posting-Host in header Can of worms - what every fisherman wants. Can of worms - what every PC owner gets!

The saxo and nova boyz would have been much happier if they had used one of those miniture ponys style breeds, they would have had over 100bpp* then :-D

*Bpp = Brake Pony Power!

Ah, but. One Hp was originally supposed to be the power a steam engine would need to have to replace a horse, when lifting loads out of mine shafts. Since the steam engine is naturally more efficient at that sort of task, 1 Hp is actually significantly less than the power one horse can produce. IIRC, 1 average horse produces about 2.5 Hp (e.g. when galloping uphill). A well trained race horse produces up to ~10 Hp during sprints.

Indeed. Horses make pretty crappy engines :-)

Aye. The kW is a more sensible unit, and Nm is more sensible than lb-ft, but we're lumbered with these antiquated units for a good few decades yet, I'd reckon.

bandwidth well spent ;)

I am so bored of nova/saxo jokes.

NO. There is no difference in efficiency of a steam engine or horse on a capstan driving a mill or pulling a sack up a shaft over a pulley. When winding a rope up a shaft the capstan would have a pawl and ratchet to ensure that if the horse lost it's footing or dropped dead the load would be locked in place until a new horse could be put to the wheel.

As you say that's short term but if you want it to work all day and still be alive for the next day you won't get more than 0.6hp out of the beast. If you had looked at one of my other posts you would see a mechanical horse power was actually 2/3 better than a horse on a capstan over a working day. This meant that a mill owner got the same work from a steam engine with 3hp as he would with 5 live horses. So the mechanical horse power is a very good worker.

When they worked a horse above 0.6hp it took a lot of expensive care and maintenance. About every 5 to 15 miles along the old mail coach routes you will find a place where they changed the horses over. Lots still exist as roadside pubs, though some have been pulled down and replaced by modern service stations. The horses that had been taken off had to be fed, watered, rubbed down etc. The 4 horses would have been worked at about 1 1/2 hp for a hour. At the end of a day with 8 changes of horse (32 horses giving 6bhp for 8 hours) they only gave

1/3 the amount of work each as a team working at 0.6hp would if worked all day.

macadamised roads made a startling difference, journey fromCambridge to London which in 1750 had taken two days, only took 7hours by 1820. Coaches could now be built lighter and were known totravel at the alarming speeds of 10 miles per hour includingstoppages. Stage lengths were from 5 to 15 miles depending on the typeof country but it only took one to two minutes for a coach to changehorses on the road.

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Ah but what is the 'brake' in BHP

The 2CV (two horses) has about 29BHP in original form so BHP is obviously different to HP

Probably to make cars sound better. So an escort cossie has about 14hp but over 200bhp?

help!

i think its how they measure it today, using a flywheel and putting a braking force on it and measuring the resistance, anyway someone told me that :)

YES. There is. The mechanical properties of horses are non-ideal - it takes a certain amount of energy for the horse to move unloaded. Secondly, the horse moves in 'lunges', and both the horse and the lifting mechanism have non linear losses and the net effect is a drop in efficiency. Neither of these apply to the steam engine.

i.e. the steam engine is more efficient.

both Hp and BHp = 746 watts. The difference is in the way they are measured - Hp is a measure the ability of the engine to do work, be it accelerating a mass or lifting a weight or whatever. BHp is the measure of the amount of power the engine does when you stop it speeding up, e.g on a dyno; you set the engine to a particular speed and then stop it accelerating by 'braking' it and you measure the torque that the engine is producing at that speed, which gives you the BHp of the engine at that speed.

Because it takes power for an engine to accelerate itself, the measured Hp of an accelerating engine will be _slightly_ less than the BHp, but usually by a miniscule amount, unless the external loading is very small.

I dunno what the 2cv really referred to, but it wasn't the actual engine power.

Heh. Nope.

Suck on your towel.

It's a tax thing.

Once upon a time, tax on cars was levied on the basis of "horsepower", but instead of being measured for a given engine, the tax gatherers based it on engine bore.

So, you would calculate "horsepower" using the bore squared times the number of cylinders and divided by 2.5, for example an F1 engine with a 3.5 inch bore and ten cylinders would deliver:

3.5^2 * 10 / 2.5 = 49 horse power.

Not a lot, for what might have a 3.5 inch stroke and displace 5.5 litres, revving up to 18,000 rpm. ;)

I dunno what the 2cv had, but I can well believe it was a stroked engine and had a narrow bore, and with its small engine that may well be around 2 hp, except that I worked it out nearer eight when I tried. Maybe due to mixing up diameter and radius but the explanation doesn't depend on that.

Note that this ignores stroke and hence isn't too closely related to capacity as such, also it led kinda inevitably to the overly long stroke engines of the

20's and 30's, which had quite a lot of displacement and grunt, but couldn't rev to save their lives.

And since engine manufacturers spent so much time optimising engines to get around the tax, it had some direct consequences for military aircraft which had engines designed by people focused on making excessively long stroke engines instead of trying to get maximum power for weight, or decent fuel efficiency, and didn't mind a ridiculously big and heavy block, etc, etc. Basically, it's the usual story with tax and subsequent avoiding of it.

The French used the British RAC / Treasury tax rules to name a French car? I doubt the French taxation system for cars ever has been the same as ours. Though if the EU gets it's way ...

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How the heck do you measure the efficiency of a horse? KJ/s Work out / KJ/s oats in?

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