Date: Sun, 18 May 2008 01:21:59 -0500
Reply-To: John Rodgers <inua@CHARTER.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: John Rodgers <inua@CHARTER.NET>
Subject: Re: Belly Pans for speed or MPG
In-Reply-To: <00c101c8b8a5$fe291900$6401a8c0@DJZL7KF1>
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Scott Daniel - Shazam wrote:
> Yes, but vortex generators might help a vanagon - lower the stall speed if
> nothing else.
>
> It's 14.7 to one isn't it ?
>
Can't really remeber for sure. Haven't thought of it for a long time.
But is fixed and cannot be changed. We are stuck with it as long as we
are using gasoline. It is of course, different for other fuels.
> You are right, speed costs fuel.
> I say a vanagon is a 60 to 65 mph 'sporty almost-truck van.'
> Built for that cruise speed range, max.
> Much above any speed like 60 , fuel consumption goes up dramatically
>
I think you are optimistic. If you peg a Vanagon at 55 mph, I think you
will find you will get the best MPG available for that vehicle. Just IMHO.
> Drag increases as the cube of speed, right ?
>
Factors affecting Lift and Drag in airplanes are:
The shape of the airfoil
The square of the velocity (or true airspeed)—V^2 .
The density of the air—.
Vanagons travel so slow relative to airplanes that there is not much
concern for most of these factors except perhaps the velocity -V2 and
it's relashon to horsepower. The shape for purposes of lift are moot,
since we don't want to livft the vehicle from the ground. However, a
lifting surface MIGHT mage the vehicle lighter in weight at speed, thus
requiring less horsepower thus making for lower horsepower and therefor
greater fuel efficiency. (mpg) But all this is a guess and would
required a lot of testing for proof of concept.
For further reading here is a good link:
http://www.allstar.fiu.edu/AERO/lift_drag.htm
Regards,
John Rodgers
88 GL Driver
> Scott
> Aviation nut
> www.turbovans.com
>
> -----Original Message-----
> From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
> John Rodgers
> Sent: Saturday, May 17, 2008 9:59 PM
> To: vanagon@GERRY.VANAGON.COM
> Subject: Re: Belly Pans for speed or MPG
>
> Hmmmmm. This is a toughy. Everyone wants more speed, better fuel mileage
> for their vans. It ain't going to happen - at least to any degree making
> the cost and effort worth while.
>
> As every pilot is trained to know - slow it down, extend the range -
> increase the speed and get there faster, burn more fuel. Simple fact of
> life in a pilots world. It's the physics, and you cannot get around it.
> The faster you go, the more aerodynamic resistance encountered (drag) so
> what is the only thing that can be done? Increase the horsepower to
> overcome the drag. Heeey! - Look at me - I'm going Faaaster! Heeeey!
> Look at my gas tank needle - it's going Faaaaster! - towards the empty
> mark!!!! So if you increase the horsepower, you are increasing the
> amount of energy required and that fuel consumption goes way up. But
> now the barn door flys, but the fuel bill is horrendous.
>
> You see - you can make a barn door fly - If you have enough horsepower
> to overcome the drag. But increased horsepower requires increased fuel
> consumption to generate that extra horsepower. No matter what we do,
> we cannot get around that stoichiometric relationship of fuel to air of
> 12/1 - 12 pounds of air to one pound of fuel to release the energy of
> the fuel. (or is is 15/1 - can't remember - brain cells getting old)
>
> Enter the Vanagon Barn Door. It flys along nicely at 55 mph on a little
> horsepower - designed to deal with the aerodynamics of a box shape. To
> increase the speed of the box it is simple - increase the
> horsepower........ OOPs! more horses means more oats, so open the wallet
> a little wider please - buy more of the $4/ gallon oats to .feed all
> those extra horses who are required drag that un-aerodynamic barn door
> faster.
>
> There is no way to win this battle. In Airplanes you deal with
> lift-to-drag ratios. Lift is generated by speed which increases the drag
> which requires more horsepower which requires more oats. The only place
> yo can win is in the realm of aerodynamic efficiency. It is with that
> issue that aircraft engineers spend thousands of man hours and millions
> of dollars on, to get small improvements. Every little bit counts,
> especially when an airplane is going to be around for a lot of years.
> Small gains mean a lot of money when you are talking millions. But for
> an out of date, no longer manufactured barn door like the Vanagon, the
> time, effort and expense aren't going to be worth it IMHO. .
>
> Dr. Porsche had it right. The Van - given it's tasks, it's shape and
> aerodynamic inefficiencies, is perfectly mated to an engine that will
> push it along at 55 mph all day long nonstop, mile after mile after
> mile, relatively maintenance free, at optimum fuel efficiency. Get above
> that, and fuel efficiency drops dramatically.
>
> So what to do?
>
> Drive for the way the machine was designed. Slow it down to 55 mph and
> get that maximum fuel efficiency. It was not designed to drive on super
> highways and keep up with the high performance automobiles
>
> When I had my engine in the old '88 Pomgranite rebuilt, it was done
> locally by a guy who I think must have worked on the very first VW
> aircooled engine in the US, and every model since - you know, one of
> those grand old guru's you love to find still working. in an old shop
> somewhere. Not much they don't know about VW engines. - particularly the
> flat 4's. He cautioned me - don't try to keep up with the traffic on the
> interstates and the freeways and expressway's. It's not built for it.
> But drive it right - it will last 200,000 miles plus with no trouble. I
> have tried to follow his advice. I've 100,000 on that engine now, and it
> is going strong with virtually NO direct engine related problems.
> Accessories, yes - alternators, hydraulic pump, water pump - some
> problems, but not with the engine itself.
>
> My $0.02,
>
> John Rodgers
> 88 GL Driver
>
>
> Chris S wrote:
>
>> Has anyone ever fitted full belly pans under their Vanagon for increased
>> aerodynamic efficiency? There's a lot under there that snags airflow and
>> causes unnecessary drag. I'm contemplating installing galvanized sheets
>> under the van and some in front. With 82hp every bit helps while going 75
>> mph.
>>
>> Here are pics of the underside to help visualize:
>>
>> http://i16.photobucket.com/albums/b7/misterpolak/Hershey/25.jpg
>> http://i16.photobucket.com/albums/b7/misterpolak/Hershey/26.jpg
>>
>>
>> Any engineering thoughts? How would you do it?
>>
>> Chris S.
>>
>>
>>
>>
>
>
>
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