Re: [Phys-l] slow news day?

[Paul Nord <Paul.Nord@valpo.edu>]

BC,

Planes have an hour meter.  It's a little like an odometer that runs off the tachometer rather than the speedometer.  An "hour" is defined here as one hour at a certain rpm.  If the engine is turning a little slower, an "hour" will be a longer than a real hour.

Conversion to mileage is also tricky.  You can control your air speed but a headwind or tailwind can change your groundspeed a lot.

It's a good little vector addition problem.  And it's always made me think that cars should also have an hour meter.  If you do a lot of slow city driving or a lot of idling you're suppose to change your oil more often.  Knowing how many revolutions the engine has turned since the last oil change would be a better measure than the odometer.

Paul


On Jun 23, 2011, at 9:42 PM, Bernard Cleyet wrote:

> On 2011, Jun 23, , at 18:48, brian whatcott wrote:
>
> > Then there's another case:
> > I was talking to a fellow last week  who keeps an ex-Chinese primary 
> > trainer. He's had it for fifteen years.   It will go 180 mph compared to 
> > the modest 100 mph my old Cessna will do. Rugged and reliable (pneumatic 
> > everything!)
> > But it costs 18 gallons of mogas per hour, compared to my 5.5 gals/hr.
> >
> > I might easily have picked these numbers out of the air to illustrate 
> > the square law of energy versus speed in airplanes - but I didn't. More 
> > speed really does cost disproportionately 
>
>
> More data please.   Not valid to fit two points of air speed and gallon/mile to a quadratic.   
>
> Bryan!
>
> Your Cessna doesn't have a gallons/mile gauge like my Prius?
>
>
> bc wonders, What are their respective Reynolds' numbers?
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