Second thoughts about the nuke program

[crusemm]

8x the amount of fuel to go 60mph vs. 30mph? ...If what you said was true, then I could get over 200mpg out of my Subaru by dropping my speed to 30mph.

This is in fact true, all other aspects being equal.  If you look at the advice for fuel conservation, one of the biggest things they say is to drive at the slowest speed you safely can, along with gentle acceleration and deceleration (yes, I know deceleration is -Acceleration).  One of the big reasons for the push to 55 mph back in the 70's and 80's was not safety like everyone was told, it was fuel conservation.  I'm not sure of the exact #'s, but off the top of my head I remember that they figured that limiting speed to 55 mph would cut national fuel consumption by a third (which was a huge concern back then).  It was not until 10-15 years later when gasoline was cheap again (relatively) that states started lifting speed limits.

[bradley535]

This is in fact true, all other aspects being equal.  If you look at the advice for fuel conservation, one of the biggest things they say is to drive at the slowest speed you safely can, along with gentle acceleration and deceleration (yes, I know deceleration is -Acceleration).  One of the big reasons for the push to 55 mph back in the 70's and 80's was not safety like everyone was told, it was fuel conservation.  I'm not sure of the exact #'s, but off the top of my head I remember that they figured that limiting speed to 55 mph would cut national fuel consumption by a third (which was a huge concern back then).  It was not until 10-15 years later when gasoline was cheap again (relatively) that states started lifting speed limits.

You failed to follow my advice of actually going out and looking at the graphs, and your post is a result of this. For one thing, you are talking about engine efficiencies of those made ~35-years ago. For another, a fuel consumption of 2/3 is VASTLY different than a fuel consumption of 1/8. For a third, those graphs I asked you to look at before posting would have shown the result of ~2/3 between 45 and 70mph (I would guess the difference of speed to efficiency is a result of those 35-years of engineering improvements). Those graphs will show you that fuel efficiency does drop off at higher speeds, but they will also show that the efficiency is not an exponential of speed. As a matter of fact, fuel consuption is most efficient at ~45mph for an average 4-door; however, the change to 60mph barely changes the fuel consumption per mile, and definitely doesn't change it by over 2x per hour, as would be required if you define efficiency as fuel consumption per unit time and kept with the 8x per doubling. If you had looked at those graphs, you would see that your post is actually agreeing with them.

Now I am certain that if you look at those graphs really closely then you can find a singular place where doubling the speed does cause fuel consumption to rise by 8x; but this will be at the very height of engine output and an event, not a constant that can be traced from every point along the engine's efficiency/output.

[deltarho]

Okay folks,
 
Homework for tonight: Using the Mechanical Energy Balance Equation, prove how much more or less energy it takes to go from 30 mph to 60 mph. Assumptions: uniform acceleration and friction is negligible. Show all work.

[deltarho]

There's no Applaud/Smite thingy that tells who did what to who...is there?

[Motown homey]

There's no Applaud/Smite thingy that tells who did what to who...is there?

There is.

http://www.nukeworker.com/forum/karmalog.shtml

[deltarho]

Oops!

[RDTroja]

Oops!

Hint: If you applaud after smiting, only the applaud counts... and vice-versa.

[spekkio]

I'm off to take my ASVAB and MEPS this coming Monday and am having second thoughts about the nuke program. I still want to enlist in the Navy even if it's not as a NUKE. I love math and science but I'm not exactly mechanically oriented, although I'm sure i could learn. The military websites have such vague job descriptions I was hoping some people on this site could help with some ideas as to what i might like doing in the Navy.

I think you have the wrong idea about what the Navy is about.

The Navy is an operational force. If you're looking for a job where you sit and crunch numbers all day, the Navy probably isn't going to be your deal. If you can do basic algebra and maybe a little trig, you can do pretty much any job in the Navy.

As far as being mechanically inclined, the Navy will teach you the skills you need to be successful in your rating. From there, it's up to your own work ethic to refine those skills. They may come easier to some people, but it's nothing that you can't overcome with some hard work.

Having said that, this thread can now return to arguing over whatever the hell it was you are all talking about. By the way, you fuel efficiency guys are ignoring the elephant in the room: time the engine is running. Engines burn fuel as a function of both speed and time, which is why car engines are most efficient in the 50-60 mph range...you get from A to B in the intersection between the time and velocity curves...anyone who took college calculus can probably remember doing optimization problems like these. So while BZ is correct that going faster will always use more fuel (although I'm not convinced on 8x as much being universal, unless you're claiming that somehow all vehicles have the same drag constant, gear ratios, and such), getting from A to B faster will result in using less fuel. Below the sweet spot, time dominates...above the sweet spot, speed dominates.

I did look up the graphs, and all of them seem to peak at two spots: 30 and 60 mph. Between those, the graphs tend to dip somewhat.

However, on graphs of fuel economy vs. engine RPM, the graphs are consistently most efficient in the 2-3000 RPM spot for most models.

[adrianI]

I wasn't mechanically inclined at all when I joined the Navy. As others have said the Navy will teach you whatever you need to learn. As far as the job goes it depends what nuke rate you become. If you have questions as to what life will be like as either PM me. One other thing to say, if you really aren't sure what that you want to join the Navy you can still say NO.