Those high school math classes finally pay off for me. At last a practical
application!
Thanks for the formula, I'm chasing for the calculator now.
Bob
----------
> From: JOHN SEIDTS <john@astory.com>
> To: ROBERT GALLAGHER <hooterdog@worldnet.att.net>
> Subject: Re: [MV] Vehicle gradability
> Date: Tuesday, March 17, 1998 4:49 AM
>
> OH BOY, PHYSICS!
> Gradability can be calculated accurately by the trial and error method
> "Hey, Joe, was that 35 or 36 percent before the Autocar crashed?"
>
> Or you can calculate it in the following way.
>
> The truck is rated at a maximum braking horsepower. This is a quantity
of
> force which can be translated into the exact amount of force a vehicle
can
> apply along its axis of travel. This force has to overcome a few other
> forces. It must overcome friction from a travelling surface, and if on
an
> angle, must overcome the force of gravity, not to mention all the
> frictional forces between components on the driveline. Without deriving
an
> equation too complex, the average MV-er can roughly determine the
departure
> angle with the following formula and a calculator with the arcsine
> function.
>
> A. Calculate weight of truck(in kilos) x 9.8 meters/second squared
>
> B. Calculate the average acceleration of your truck. Start at rest in
> your truck, and have someone time you going to any point in km/h and how
> long it takes to get there. For example, start at a stop sign, and time
> how long it takes you to get to 35 km/hr. Divide this by the number of
> seconds it takes you to reach the speed. This is your average
> acceleration, in Km/hr. Convert it to m/s by multiplying by 3600 and
> dividing by 1000. Multiply by the mass of your truck in kilos.
>
> C. Divide A by B. This ratio is the rough ratio of the force of gravity
> exerted on your truck which doesn't let you go up the hill, and the total
> force your truck can exert. In order to find the angle where your truck
> will be stopped by gravity, enter this number into the calculator, and
hit
> the arcsine button. This will be the button with sin and a little -1
> superscript next to it. This is the angle of the hill which your truck
> cannot negotiate. It should be able to negotiate any angle less than
that.
>
>
>
> john@astory.com
> http://www.astory.com
>
> ----------
> > From: ROBERT GALLAGHER <hooterdog@worldnet.att.net>
> > To: mil-veh@skylee.com
> > Subject: [MV] Vehicle gradability
> > Date: Tuesday, March 17, 1998 3:22 AM
> >
> > Honorable Keepers of the List,
> >
> > Ok here's a long and confusing question. I hope the experts can help
or
> > curiosity may kill this cat.
> >
> > Q: How is Maximum Gradability of a vehicle computed?
> >
> > Many MV books, such as TM 9-2800, list a vehicle's maximum gradability,
> ie
> > maximum grade the vehicle can climb. Gradability is given in percent
of
> > slope. I understand how to convert "degree of angle" to "percent of
> > slope". But is every vehicle actually tested to see how steep an angle
> > (slope percentage) it can climb? Is the test performed at rated load
or
> > empty?
> >
> > I suspect there is a formula for figuring this, but what is it? Or is
> each
> > vehicle in fact tested? Or does someone make a "best guess" for each
> > vehicle?
> >
> > Some examples from TM9-2800:
> >
> > * CCKWs listed as 65% regardless of wheelbase or body style EXCEPT the
> 750
> > gal tanker listed as 84% .
> >
> > * Chevy 1 ton 4x2 truck listed at 66% but Dodge WC51 4x4 listed as only
> > 60%.
> >
> > *Car, Light Sedan, 5 passenger, 4x2 made it to 38% while the enormous
> > Autocar U-8144-T 5-6 ton ponton tractor could only muster 30%. CAT
D6
> > made only 36%, that's less than the staff car!!
> >
> > *And of course the M-29 Weasel made standard at 100%. MB pulled 60%.
> >
> > Jane's Military Vehicles and Logistics 91-92 lists:
> >
> > * Hummer 60%, M35A2 60%, M54 50%, M52 77%, M715 58%, M38 65%,
> > M38A1 69%, M151 60%and M37 68%.
> >
> > If there is a formula, it must be based on weight vs horsepower.
That's
> > the only way I can figure the General's staff car is going to pull a
> > steeper grade than the SeaBee's D6 Cat. But is traction a factor? Is
> 4x4
> > vs 4x2 factored in? Wheels vs tracks?
> >
> > Comments or gradability formula gladly accepted and shared:
> >
> > Thanks and Aloha from sunny Honolulu,
> >
> > Bob
> >
> >
> >
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