Date: Sun, 12 Apr 2009 21:17:01 -0500
Reply-To: John Rodgers <inua@CHARTER.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: John Rodgers <inua@CHARTER.NET>
Subject: Re: Only ONE drive wheel?
In-Reply-To: <024801c9bbc9$952f5ea0$6401a8c0@PROSPERITY>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Scott,
Very good description and insight into what happens with the standard
differential.
Viva la Posi-trac!!!
Nice "Tip's and Trick's" on how to get a "poor man's limited slip
differential". It's akin to letting some air out of the tires to drive
off a sandy beach or get out of your home garage when to save money at
home you switched to bigger rims and tires only to discover you can't
get out of your garage any more, or perhaps to go under a really low bridge.
To expand on the aircraft propeller thing - whether single or
multi-engine aircraft type - the crankshaft is for the most part
horizontal to the ground or the earths surface plane in aircraft with
tricycle landing gear. On tail-draggers there is another element
involved which I won't mention here. In the tri-gear machines the blade
angle on a propeller is the same on all blades, and all rotate in the
same plane - 90 degrees to the crankshaft - and 90 degrees to the
relative plane of the earths surface. However, when the pilot rotates
the nose of the airplane skyward, the angle of the propeller and the
crankshaft changes relative to the earths plane. Given that most modern
American made aircraft engines rotate to the right as seen from the
pilots seat, the propeller blade on the right will be going down while
blades on the left will be going up. Because of the change in the angle
relative to the ground, the propeller blade on the right going down
takes a much bigger bite of the air, than the blade on the left coming
up. This produces much greater thrust on the right than the left, and
the airplane tries hard to turn left all through the climb to altitude.
The pilot is trained to overcome this and kept the airplane under
directional control, but it adds an additional load on him to take care
of the airplane. Additionally, the left turning tendency also tends to
drive the right wing forward faster, allowing the left wing to drop back
relative to the path of flight. The result is increased lift on the
right wing, and reduced lift on the left wing. With more lift on the
right wing and less on the left, the airplane has a tendency to roll to
the left. So there you have it. Left turning, and left rolling, all of
which a pilot is trained to control very precisely. But it can make for
some interesting moments under certain conditions. But it makes a pilots
life interesting to say the least. It is said that a pilots flying life
is filled with thousands of hours of relative boredom, interspersed with
moments of sheer terror!!! I'm here to tell you it is so true, so true!
Engines, crankshafts, torque, left wheels lifting, right wheel getting a
better bite on the ground, rotating propellers getting a bigger bite on
the right and less on the other ---- it's all got it's similarities -
and it all derived from the same physics. Vanagons and airplanes - who
would have thought there could be such similarities.
Regards.
John Rodgers
88 GL Driver
Scott Daniel - Turbovans wrote:
> what you experienced is perfectly normal.
> let's see.........
> the differential in the rear end drives both wheels evenly............
> as long as the van is going straight, and there is equal and good
> traction
> for each rear wheel.
>
> so it drives both rear wheels..........but either rear wheel is free
> to turn
> more revolutions ( like the outside wheel would in a turn ) or just plan
> spin.
>
> saying that the right rear is 'the driven wheel' .......
> is not true in the hardest sense of the term.
> What is true, I believe is .........
> due to the direction of engine rotation ( especially true in a front
> engine
> rear drive car ) ....engine and drivetrain torque tends to lift one rear
> wheel, and push the other rear wheel downwards.
>
> yeah........just thinking about in my head - consider a front engine rear
> drive car .......engine rotates clockwise when viewed from the front
> of the
> engine ......or counterclockwise viewed from the driver's seat. Viewed
> from the driver's seat, the body of the car is trying to rotate opposite
> the direction of crankshaft rotation .........thus the left rear wheel is
> lifted slightly and the right rear is driven into the pavement more.
>
> this affect is also observable in single engine propeller aircraft,
> and in
> single prop boats too. The body of the vehicle tries to twist in the
> opposite direction of crankshaft rotation, and in a car that tends to
> drive
> one side of the vehicle more into the pavement. It's quite observable in
> big trucks too .......they really tilt when the jump on the gas
> ...........the tractor part with no trailer attached .........with all
> that
> torque the cab really wants to tilt under a heavy right foot on the go
> pedal.
>
> here's a trick......
> the 'poor man's limited slip rear differential ' ...........when you're
> stuck from one wheel spinning..............put the parking brake on half
> way, or even a little more.
> the idea is that by making the resistance to turning of both driven
> wheels
> roughly the same, drive will be transferred to both wheels, including the
> one not touching the ground, or slipping on ice etc.
> Scott
> www.turbovans.com
>
>
> ----- Original Message -----
> From: "Brian Doss" <doss88wkndr@ZOOMINTERNET.NET>
> To: <vanagon@GERRY.VANAGON.COM>
> Sent: Sunday, April 12, 2009 5:28 PM
> Subject: Only ONE drive wheel?
>
>
> I have an '88 GL with a manual transmission. I got it stuck backing
> into an
> uneven driveway yesterday. Just so happened that I was in a saddle on a
> hillside, with just enough torsion on the bus to lift the left rear wheel
> off the ground - and presto - no go. The left wheel spun happily in
> forward
> or reverse. What I can't understand is that I thought the right wheel was
> driven as well - why did it not receive any power? Does this mean
> something
> is wrong with my transmission?
>
> Thanks for any insight on the matter
>
>
> Brian Doss
> Butler, PA
> '88 Weekender, Queequeg
>
>
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