Subject: Re: Drafting effect behind trailers
From: "David E. Pearce Jr."
Date: Fri, 10 Jan 1997 08:10:19 -0700
Robert C. Jacobson Sr. wrote:
>
> Anyone know where I can find some info on cars "drafting" behind
> tractor trailers? I want to know what effect it has on drag (ie
> MPG), and how close you'd have to be to get any benefit from it.
>
> -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
> Robert Jacobson teridon@glue.umd.edu
> BS, Aeronautical Engineering Univ. of Md., College Park
> Flight Ops. Team - SOlar Heliospheric Observatory (SOHO)
Back in 1981, I had a 1981 Mazda GLC. On the flats around Wichita Ks. it
got 30-35 mpg. On a drive from Wichita to D.C. I got consistantly 30-35
mpg except for one leg from St. Louis to Indianapolis where I found a
smei going at the same speed I was. I stayed pretty much one to one and
one half car length behind him for much of the leg. On that leg I got 44
mpg. The leg before I got around 35 mpg and the leg after I got 35 mpg.
On other trips, I have stayed about 5 car lengths behind and did not see
an appreciable change in gas mileage.
I seem to remember some studies in the mid 70's in some journals (I
don't remember which, possibly ASME or some other transportation type
journal) that dealt with truck drag and drafting. I also remember
hearing stories about trucks convoying and trading leads every 50 miles
in order to maximize gas mileage (diesel) for all the trucks.
David Pearce
BS Aerospace and Ocean Engineering- VA Tech
Staff Engineer
Lockheed Martin Astronautics
Subject: Re: Formation of water drops on solid surfaces
From: sorame@lerc.nasa.gov (Enrique Rame)
Date: Fri, 10 Jan 1997 09:41:47 -0400
In article <19961216020500.VAA21983@ladder01.news.aol.com>,
jorje11@aol.com (Jorje11) wrote:
> I'm looking for information on the formation of water droplets on vertical
> surfaces and on ceilings. Interested in factors that control drop size
> before they fall. Would appreciate any pointers. Thanks, George Rice, San
> Antonio, TX.
There's a maximum drop size for each Bond Number and contact angle. This
maximum size represents the largest volume of fluid that can exist in a
stable static capillary configuration. Beyond this volume, the capillary
surface is unstable and the drop breaks off.
The Bond Number is the dimensionless ratio of:
density*g*(radius of wetted area)^2 / surface tension
A godd reference is a paper by Boucher and Evans: Proc. Roy. Soc. London
A, vol. 346, pp 349-374 (1975)
-enrique
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