Torque or HP?

[LVjetboy]

More thoughts about torque. Can't remember now who posted "torque is work" but torque is not work...even though both torque and work have the same units. Work requires force moved through a distance. Torque does not. How can they be the same thing?
Just because torque is a force applied at a distance doesn't mean that force is applied with any motion through a distance. And just because combustion engines apply torque with rotation doesn't mean the term "torque" implies rotation...or work. Torque and work represent two different things. As do torque and power.
jer

[LVjetboy]

"Did you miss the part about "flying and aviation bore me?" It's mostly because it's full of arrogant stuffed shirts that have this idea that they're smarter than everyone else. The eletists because they "fly"
I won't argue the arrogant pilot thing. Seen plenty of that. Never the less, why use a personality trait you consider the majority of pilots have as a reason for aviation boring you? With your love for the zoom factor and things mechanical and performance which I share. I doubt flying a fighter or high performance airplane would "bore" you. Or even flying that Blackhawk. Not talking sail planes or sail boats here. Either way, I find your comment "flying bores you" as a bit disingenuous. I've never flown a glider, maybe they are truly boring.
I probably have a few more hours than you, some of it I suppose boring...most not. I flew for a living for 17+ years. And flying for a living not always as exciting as flying for fun. Yet to me and many others I'm sure, the subject of flying and aviation still would never be classified as boring. Although this forum's not about flying, I thought Tom's example good for a different angle on the topic of power vs. torque.
jer

[LVjetboy]

"Mazda Rotary. Different animal, BUT, makes as much as 50% mkore power than Lycoming...at a much higher RPM. Why wouldn't it pull harder? So what? It won't last nearly as long, has to work twice as hard"
To me, the subject of this thread, "Torque or HP?" not so much reliability or how long can you make the engine last or what's best for gas mileage, etc. Rather...what drives performance? I'm guessing that's what momudder had in mind with his first post as well as many who've ask the torque vs hp question in the past. Once you understand what drives performance, you can tweek the answer with reliablility and economy issues if you like.
But first you gotta know what drives performance.
jer

[steelcomp]

"Did you miss the part about "flying and aviation bore me?" It's mostly because it's full of arrogant stuffed shirts that have this idea that they're smarter than everyone else. The eletists because they "fly"
I won't argue the arrogant pilot thing. Seen plenty of that. Never the less, why use a personality trait you consider the majority of pilots have as a reason for aviation boring you? With your love for the zoom factor and things mechanical and performance which I share. I doubt flying a fighter or high performance airplane would "bore" you. Or even flying that Blackhawk. Not talking sail planes or sail boats here. Either way, I find your comment "flying bores you" as a bit disingenuous. I've never flown a glider, maybe they are truly boring.
I probably have a few more hours than you, some of it I suppose boring...most not. I flew for a living for 17+ years. And flying for a living not always as exciting as flying for fun. Yet to me and many others I'm sure, the subject of flying and aviation still would never be classified as boring. Although this forum's not about flying, I thought Tom's example good for a different angle on the topic of power vs. torque.
jer
You're right, Jer...I'm busted. There's more to it that the fact that it "bores" me. Boaring...not really. Never had more fun that my ride in a P51, or my hours in the Blackhawk. Gliders were a special time. Other issues, indeed, although I truely do get tired of the eletist attitude. Sorry to get off topic. :coffeycup

[steelcomp]

I'd agree Tom. Physics doesn't change with application, neither does the understanding of power and torque. And examples like you gave from different applications still illustrate the same principle...power is key to performance. Even though different applications often lead to a unique power plant and drive choice for best performance.
Btw, I also run a prop...a duoprop.
http://members.cox.net/lvjetboy/StarPanel.jpg
Not your fastest boat yet what little performance it has? Still all about power...
http://members.cox.net/lvjetboy/Cruiser.jpg
"The reason I don't have a bayliner is because my ego wouldn't stand for it. Life would probably be much easier, and boating actually enjoyable, but then I wouldn't have all this "fun" here on the bords, now would I. I'm like every other swingin dick out there with a hot boat. It makes my blood rush when I stand on the loud pedal, and I hear the music of open headers and feel the rush of acceleration that'e really never enough for me."
Since you mentioned Steel, allow me to go off-topic a bit too. Your ego may actually survive the bayliner (or searay...same company now) just fine. Yes, boating maybe a bit easier. At least less dependant on water conditions and temperature. Or how long you stay out.
If you buy a cruiser I think you'll find it nearly as enjoyable as the jet...in a different way. And you'd like it too. Adds a whole different dimension to boating enjoyment, just not the same level. Even though one can't replace the other, both have value.
That said if I had to pick, the jet'd win of course.
jer
Maybe you missed the part where my ego admitted that life would probably be easier and boating more enjoyable...(in a more relaxed way) I may be fiesty, but I'm not stupid! :coffeycup

[kojac]

{Quote "Not sure what you mean by "both graphs" but let me explain a bit. Duane's B dyno numbers refer to dyno run B. He also sent me run A which had a similar trend but varied by about +/- 6 ft-lbs either side of that trend. That gives an approximate error band or idea of test repeatability...for the somewhat closely controlled dyno test conditions, btw."
Jer,
By both graphs I meant Duane's B dyno run and your lake torque plotted graph.
{Quote "You are correct, my adjusted lake torque for run B never exceeds 700 ft-lbs. The way I adjusted his run B dyno torque to lake torque means I'm estimating at the lake he has about 75 ft-lbs less torque than "corrected torque" on the dyno. I wouldn't be surprise if that true. Yet the curve shape or trend will likely stay the same...or close to it. Mostly shifted down not so much sidewards. If you're interested we can talk more about that point. If I missed your point let me know."
Thanks,
NOW That brings up another one. How did you arrive at your estimate regarding the 75 ft-lbs less torque? Do you have a standard torque/rpm curve for impellers?
Duane's dyno sheet estimated lake hp estimated lake torque
horsepower torque
5400rpm 786 764.5 "AA" 710 76hp less 690ft# 74 dif
5900rpm 847 754 "A" 753 84hp less 680ft# 74dif
6300 898 748 "B" 815 83hp less 672ft# 72dif
6600 902 729 "c" impeller not plotted
After looking at Duane's dyno sheets I would have guessed that the "B" impeller should have given the best results. I wonder what kind of boat he was testing? hull design? weight? The speed wasn't that particularly impressive with the "A"turning 5900 rpm's Considering that I have a fairly heavy tunnell that turned that speed with a berkley "B" impeller at 5900rpm's. Aggressor's "A" impeller being equal to a berkley "AA"?
Maybe something else was going on with the pump or real different water conditions during the test?
A lot to think about.
Thanks,
kojac

[steelcomp]

Jer...I was also wondering about the lake hp correction factor you use.
Also, is there a cross over point where two different impellers offer the same performance at their respective rpm's? For example...is there an rpm for a B that will give the same result as an A (obviously at a different rpm) AFA output?
Thanks, Jer.

[LVjetboy]

"How did you arrive at your estimate regarding the 75 ft-lbs less torque? Do you have a standard torque/rpm curve for impellers?"
I estimated adjusted power and torque by first calculating the power required to turn an Aggressor AA to his tested full throttle 5400 rpm (= 709 hp) Then I calculated a power modifier or multiplication factor that adjusts his dyno tested power at 5400 rpm to lake power. So 709/786 = 0.9020, where 786 was engine dyno corrected power output at 5400 and 709 is Aggressor AA impeller required power input to turn 5400 (at the lake.) My thought is a multiplication factor works better over a wide rpm range than a simple subtraction factor.
Finally I multiplied 0.9020 by all his corrected dyno test power data points to get lake power numbers. So the two curves will be nearly identical in shape, just adjusted downwards to lake conditions.
As I've posted, I could've calibrated using his A or B full throttle rpm... and got similar but slightly different results. Differences most likely because of test accuracy (was true full throttle rpm 5400 or 5420 or 5435?) and the fact we don't have exact impeller pump curves for any mfg let alone Aggressor...especially at that power level? Extrapolating sketchy Berkeley data then adjusting to Aggressor's claimed (but not extensively tested?) one cut size up rule-of-thumb, not the best accuracy? Not to mention impeller detailing affects on loading rpm. Duane indicated all impeller cuts were factory and race preped by him.
All that aside, when I matched his dyno power curve to lake conditions this way, other impeller cut tested full throttle rpm results matched fairly close, usually within 50 rpms. That seems to indicate I'm in the right ballpark.
As for, "do I have standard torque/rpm curves for impeller cuts?" Indirectly yes. Since I have the standard power/rpm curves I can back out torque/rpm curves using the equation relating torque and power. That's what you see in the torque plot above. I only showed that to illustrate a point about torque, not to imply that plot's useful for impeller matching. The reason pump impeller curves are typically shown in power/rpm not torque is because that format makes most sense for performance... even if you're talking a wheat farm irrigation system. :yuk: Sad but true.
"I wonder what kind of boat he was testing? hull design? weight? The speed wasn't that particularly impressive with the "A" turning 5900 rpm's"
I think it's 21 ft. His lake boat and I'm sure he could fill you in on hull design and weight. He mentioned at some point but forget now. Must be that brain wasting disease.
jer

[LVjetboy]

"...I truely do get tired of the eletist attitude."
Maybe just fighter and blackhawk pilots.
The O-clubs I spent time at (Nellis for one) had mostly fighter just a few helicopter pilots. Helicopter pilots seem more down-to-earth. I was a minority. Back then there were strippers in the club. It was crazy. Life was good...but times change.
Much later, watching top gun and the bar scene I turned to my wife and said, yep, that's the fighter ego...hollywood captured it perfectly...in a pg way. Now I'm 10 years retired and blue collar...airlines. Even now, I run across a SWA airlines pilot or two with "the attitude."
jer

[LVjetboy]

"Jer...I was also wondering about the lake hp correction factor you use."
See above. If I'd known the density altitude, I could've adjusted Duane's corrected dyno power to lake conditions that way too. Those results should match with full throttle rpm reported.
"Also, is there a cross over point where two different impellers offer the same performance at their respective rpm's? For example...is there an rpm for a B that will give the same result as an A (obviously at a different rpm) AFA output?"
Yes. But that answer deserves a bit more than I can post now. More later.
jer