Posted by NCWayne on July 25, 2010 at 12:21:28 from (173.188.168.49):
Just read the replies to my post about my 55. There was alot being thrown around about aerodynamic drag vs HP vs whatever and Trucker40 was taking alot of heat for talking about gearing. Why is it so hard to understand that speed is just as much a product of the gearing as it is of HP, drag, or anything else just as Trucker was saying.
Example my service truck weights nearly 32000 lbs has Series 50 Detroit putting out 275 HP backed by a MD3060P Allison auomatic with 6 speeds. 1-3 are geared, 4th is direct drive, and 5 and 6 are both OD. Now based on the HP and aerodynamis's are everything theories with only 275 HP my truck shouldn't be able to go over maybe 15 MPH as it is nothing but a big, heavy, rectangluar brick. Thing is I've actually had it running 90 on the interstate when I first got it and wanted to see what it would do. Typically, on a long stretch running 75 in 6th gear the engine is only turning around 1700 RPM, and below 60 it won't get out of 5th and again stays around 1700. With the OD the engine is allowed to turn slower as not as much HP is needed to keep the load moving as it is to get it moving initially. That's why drag cars need SO many HP, not so much so they can "go fast", but rather so they can "go fast as quickly as possible". Take that same drag car and put a really high ratio rear end in it and HP or not that car isn't going to "go fast" as quickly as it did with the lower gear ratio. In that instance you sacrifice speed for time. Basically it's all a product of speed vs time and that is what HP is. One HP is the ability to move 33,000 lbs per minute just as much as it is the ability to move 1lb in 33,000 minutes. Drag car equals 33,000 lbs in one minute, weedeater motor equals 1lb in 33,000 minutes. Both examples equal out to one HP developed.
Like Trucker said it's not the HP or the drag that gives or limits top end as much as it is the gearing. If HP and aerodymnamic drag and weight were the limiting factors, again I'd be lucky to get my truck to 15 MPH on a downhill run, with a tailwind.
Stepping outside of the box a little here since I work on equipment for a living. I work on alof of older cranes set up as draglines. Take something like an old Northwest with a inline 6 cylinder Murphy diesel. The model engines they used run in those machines run in the 1000 cu in range but only put out in the neighborhood of 175 HP at 1200 RPM. Based on the HP is the limiting factor theory 175 HP is next to nothing so it shouldn't be able to do much if any work. That said with the gearing those 175 HP go through they are capable of both pulling in and simultaniously picking up a 4 cu yard drag bucket along with the material in it while at the same time swinging the house of the machine and 80-100 feet of boom all at the same time. When moving the machine those same 175 HP have no problem walking around a machine, both up and downhill, that weights over 100,000 lbs. Given the HP is the limiting factor theory those machines shouldn't even be able to move but they do, and it's all because of the gearing.
Granted Trucker used some really extreem examples but as you can see in my examples they might not be as extreem as some people think. I mean 275 HP pushing around 32,000 lbs at 90 MPH, 175 HP moving around over 100,000 lbs, neither should be possible given all of the naysayers but each instance is not only possible but proven each and every day. Would I put a 5 HP Briggs in my service truck, no, would I put it in a crane, no,it just wouldn't be practical, but given the proper gearing can it be done????You bet it can.
Now if anyone want's to see a good example of how gearing actually works and what it can do, go to Discovery Place in Charlotte, NC. They have a setup where you turn a little handle and the machine is crushing a galvanized metal trash can... length wise, not on it's side.... As you spin the dial with one finger they have a big micrometer setup on the press headso you can see it is actually moving. I forget how many turn's of the dial it takes to move the press head .001 but it is alot. Now who'd of thought you could crush a galvanized trash can by spinning a dial with one finger? Thing is it can and does happen and it's all because of gearing....
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