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nakman
08-13-2009, 10:58 AM
I never knew they were mathematically related.. :o I just scanned a page from a handbook to send to the XYL with whom I'd like to QSO (little hamspeak) and noticed on the other page the horsepower calculation... interesting.

HP = (Torque*RPM)/5252

here's the sheet....

rover67
08-13-2009, 12:11 PM
Yup. Dynos measure torque and RPM and calculate The HP.

Red_Chili
08-13-2009, 01:28 PM
The whole idea of 'horse' power is kinda amusing if you think about it.

Question: how was the 5252 derived, what does it represent?

nakman
08-13-2009, 01:46 PM
same as pi, or Avagadro's number, some dude just proved it out one day and it stuck!

DaveInDenver
08-13-2009, 03:12 PM
Question: how was the 5252 derived, what does it represent?
Do you really wanna know? It's got to do with James Watt and his original observations. He noted that a horse could do 22,000 lbf-ft of work per minute, so he claimed that his engine could reliably do one better, it would do 33,000 lbf-ft without getting tired like a horse. That is moving 150 lbf over 220 feet in 1 minute. If you apply that 150 lbf to an arbitrary 1 foot moment you'll have 150 lbf-ft. That 1 foot circle will have a circumference of 1 * 2 *pi = 6.28 feet. Turning 220 feet/min on a circle of 6.28 ft gives an RPM of about 35. So to convert 1 HP you take 150 lbf-ft * 35 RPM / 1 HP = 5250. The engineering definition of horsepower is more clear I think.

HP = torque (lbf-ft) * 2 * pi * RPM (revs per min) / 33,000 (lbf * ft/min)

So, Nak is right, 5252 is basically there just because Watt used 33,000 lbf-ft to describe how much work his engine could do. If he'd have claimed his invention could do more, the number would have been different.

subzali
08-13-2009, 03:21 PM
I can understand why metric people make fun of american units. But hey they make more sense in my mind so I'll roll with it :D - It doesn't compute in my mind that an engine can produce kilowatts of power - that sounds like electricity to me :confused:

(and BTW metric units are just as arbitrary, you should look up the "official" definition of a meter sometime)

(but I do like the story of James Watt and his horse - heard that in college :D)

DaveInDenver
08-13-2009, 03:25 PM
I can understand why metric people make fun of american units.
Hey, Watt was a Scotsman, that ain't no 'Merican silliness.

subzali
08-13-2009, 04:06 PM
oops - forgot that part :o

oh well, bonafide proof that metric units are arbitrary! :p:

Red_Chili
08-13-2009, 05:34 PM
Hey, Watt was a Scotsman, that ain't no 'Merican silliness.
If he had had a Morgan horse the benchmark would've doubled. But then, he never woulda tangled with 'Merican silliness, would he? Ha!

http://upload.wikimedia.org/wikipedia/commons/thumb/4/49/American_Morgan_Horse.jpg/250px-American_Morgan_Horse.jpg
A Morgan resembling Figure, the first Morgan, and rider attired as Justin Morgan would've been in the 1790s. 950 lbs. of horsepower and could outrun a Thoroughbred (and much smarter... though that is a lowish standard :lmao:). Used in the Pony Express, as mounts in the Civil War (both sides but mostly Yankee), and a Morgan-Mustang mix named Comanche was the sole US Cavalry survivor of Custer's mishap.

'Merican silliness indeed. Good thing the Welsh got melted in the melting pot. Along with the Irish.
:cheers:

14250

leiniesred
08-13-2009, 06:01 PM
Custer's horse is on display at the University of Kansas Natural History Museum.
At least it was in 1995 or so.
I think a dog limped back from the last stand too.

Beater
08-14-2009, 07:09 AM
dave, you are a geek.








and I mean that with all the love I can muster...

DaveInDenver
08-14-2009, 09:42 AM
Custer's horse is on display at the University of Kansas Natural History Museum.
That horse is named Comanche and wasn't actually Custer's, but rather another officer named Capt. Myles Keogh. Comanche was at the Battle of Little Big Horse and did survive it (the legend says he was the only horse, which isn't really true). Comanche was badly injured in the battle but still did not leave Capt. Keogh (who died), sitting by his side until the Army came to Little Big Horn. Something else about Capt. Keogh, he was the only solider not scalped by the Sioux and Cheyenne after the battle, although no one knows why.

Beater
08-14-2009, 10:29 AM
That horse is named Comanche and wasn't actually Custer's, but rather another officer named Capt. Myles Keogh. Comanche was at the Battle of Little Big Horse and did survive it (the legend says he was the only horse, which isn't really true). Comanche was badly injured in the battle but still did not leave Capt. Keogh (who died), sitting by his side until the Army came to Little Big Horn. Something else about Capt. Keogh, he was the only solider not scalped by the Sioux and Cheyenne after the battle, although no one knows why.

jeez - see post 11 again....


lol

Cheeseman
08-14-2009, 02:43 PM
Torque and Horespower. An article on Indy cars years ago spells it out very simply.

Torque gets you off the line. Horsepower keeps you at full speed.

As for the formulas, just don't forget them for the Physics test.
________
Bdsm Video (http://www.****tube.com/categories/8/bdsm/videos/1)

subzali
08-14-2009, 02:56 PM
Dave, it's cavalry.

Rzeppa
08-14-2009, 11:05 PM
What I've always had issues with is that a HP is around seven and some hundred watts. So I buy a 5.5 horse air compressor. How the Frack are you you gonna pull the kinda juice out of a 117VAC x 15 or 18 amp breaker out of a wall outlet???

Even given that startup is WAY over run amperage, I remain convinced that 'merican marketing is, shall we say, optimistic?

DaveInDenver
08-15-2009, 07:21 AM
What I've always had issues with is that a HP is around seven and some hundred watts. So I buy a 5.5 horse air compressor. How the Frack are you you gonna pull the kinda juice out of a 117VAC x 15 or 18 amp breaker out of a wall outlet???

Even given that startup is WAY over run amperage, I remain convinced that 'merican marketing is, shall we say, optimistic?
It's possible (although maybe not likely) that the compressor is a 5.5 HP compressor. That does not mean you are going to get 5.5 HP of work from that compressor on a standard single pole household branch, which like you say can deliver at most 1800 W or maybe 2400 W (1 HP is 746 W). Obviously potential power delivered is only 2.4 HP on a 15 A branch before any line loss, motor efficiency and heat loss and frictional piston loss. You would be doing well to get 2 HP of work on any compressor at 120V/15A. But on a 220/50 branch with a better motor (probably higher speed) that compressor could be capable of 5.5 HP.

A rule of thumb is that it takes 0.375 HP per CFM at 100 psi (so a typical branch will support about 5 CFM at 100 psi at 2 HP). A 5.5 HP compressor at 100 psi would deliver a volume of about 16 CFM. So basically your compressor might do that at, I dunno, 3600 RPM. But you are running it on light duty 120 V motor at 1800 RPM (just example numbers), then you are only using half it's rated capacity at most before any losses. Remember back to your thermodynamics, work can be defined as the integral of pressure and differential volume and so doubling the RPM of that same compressor would in effect double it's work.

So the sticker claim is that it's a 5.5 HP unit is possible with a high speed motor on your welder circuit. It might even do that much work for a couple of seconds before meltdown, too. Longevity is not achieved with any super high speed compressor, particularly these oil-less wonders. So being rated to 5.5 HP actually means that in normal infrequent use at a lower (maybe much derated) speed it won't burn up... Those real 2-stage compressors come as small as 5 or 6 HP sizes, but that is done at like 750 RPM and can be continuous duty (they'll have bores or/and strokes twice or three times as big as our cheapie oil-less things). Just the same you'll never get 5 HP on a 120V line, though. Even the best compressor will still only deliver ~5 CFM at any decent working pressure on a 1800 W branch.

Rzeppa
08-15-2009, 06:10 PM
So the sticker claim is that it's a 5.5 HP unit is possible with a high speed motor on your welder circuit. <snip> Just the same you'll never get 5 HP on a 120V line, though.

That was kinda my point - I was being a little (okay a lot) facetious :rolleyes:

My guess for these marketing claims is that they do a TDS (time domain spectrograph) and take the peak amperage draw right at startup, multiply it by whatever the line voltage is (probably supplied by a huge bus bar) and say "hey lookiee here! we got us 4104 watts on this here sucker!! 31.08 Amps at 132 volts (10% high for the specs). Yee haaw, we just beat out our competitor's claim!!!"

Of course as soon as the motor spins up it's probably only drawing 5 amps and it's really around 600W and less than 1 HP. But who cares, if you can put that peak in your claims, right?

:D

(FWIW, utilities shoot for 117VAC at the outlet after line losses; mine measured numbers generally run between 112 and 118VAC depending on both source and loading)

DaveInDenver
08-15-2009, 09:39 PM
FWIW, utilities shoot for 117VAC at the outlet after line losses
Most utility companies will guarantee a service entry min of 114/228Vrms and a max of 126/252Vrms to residential customers, based on a nominal 120/240 service. They usually don't consider a sag or swell under 5% abnormal unless persistent.

Red_Chili
08-16-2009, 12:14 AM
That horse is named Comanche and wasn't actually Custer's, but rather another officer named Capt. Myles Keogh. Comanche was at the Battle of Little Big Horse and did survive it (the legend says he was the only horse, which isn't really true). Comanche was badly injured in the battle but still did not leave Capt. Keogh (who died), sitting by his side until the Army came to Little Big Horn. Something else about Capt. Keogh, he was the only solider not scalped by the Sioux and Cheyenne after the battle, although no one knows why.
Yeah I meant Custer's by extension, i.e. in his command.

I can imagine the Sioux and Cheyenne took note of the horse's behavior and loyalty and that weighed in their decision that maybe taking a scalp from Keogh would have been dishonorable. Dunno.

I do know that if you spend enough time with people and animals you learn to weigh the animal's opinions a bit more than people's.

DaveInDenver
08-16-2009, 06:27 AM
Yeah I meant Custer's by extension, i.e. in his command.

I can imagine the Sioux and Cheyenne took note of the horse's behavior and loyalty and that weighed in their decision that maybe taking a scalp from Keogh would have been dishonorable. Dunno.

I do know that if you spend enough time with people and animals you learn to weigh the animal's opinions a bit more than people's.
Your guess is as good as anyone's. Some speculate that Capt. Keogh died heroically and impressed the warriors as a man worthy of respect. Just one of those great unknowns.