I am please that this topic has got aus-soaring going, and thinking.
The real message is : when driving, if the road is wet, icy, snow
covered, or you have just passed the 'spin' advisory sign, consider:
TURN THE CRUISE CONTROL OFF!
My mid 90's Ford Owners Manual [at page 71 states] "Warning! To avoid
the possibility on loss of control, the cruise control should not be
used .... On winding, slippery or unsealed roads." The maintenance
manual [page 229 section 15 states "The electronic [cruise] control
module receives a signal from the speedometer and activates an electric
motor .... [that] adjusts the throttle position via the control cable to
maintain the preset speed." So initially speed is measured by the
speedometer [and this is connected to a 'speed sensor' tied to tailshaft
speed] and there is some time constant or lag as below.
In any event, in a rear wheel-drive car there is high risk that cruise
control will provide heaps of excess power [in my case change down two
gears @ 90 kph] spin rear wheels, fishtail and probably spin if the
cruise control cannot be disengaged.
I know later cars have traction control that is more sophisticated
[check Porsche 911 etc but I don't have those]
but in older family cars cruise control selected can lead to TOTAL LOSS
OF CONTROL.
I have been there, done that, spun out of control, off the wet road at
90 kph. I now wonder at horrific 4WD accidents that have killed many:
did they have cruise control selected? [How would you prove either]
But the message I want to leave is: when driving, if the road is wet,
dirt, or you have just passed the yellow 'spin' advisory diamond sign,
consider: TURN THE CRUISE CONTROL OFF!
Now I will return to some gliding, noting the above message as I drive
to the airfield.
Regards,
Alan Wilson
Canberra.
PS. As ever there are those who shoot the messenger, some who add value,
and .......... But I am thankful for those who even took the time to
read.
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of John
Giddy
Sent: Friday, 5 May 2006 3:53 PM
To: Discussion of issues relating to Soaring in Australia.
Subject: Re: [Aus-soaring] FW: Safety issue in the car when it'sraining
-please read this! [Switch Cruise Control OFF]
There is an effect which I notice in the (not very good) cruise control
on my car: When going up a hill, it obviously opens the throttle to
provide more power. When it reaches the top of the hill, the time
constant in the system is such that the throttle doesn't close early
enough, and the car accelerates over the top of the hill, and then
maintains the higher speed for part of the down slope until the drag
exceeds the gravity force, and slows the car to the set speed again. If
the car was driving at some set speed, with the throttle setting
suitable to overcome the losses at that speed, and then the wheels all
start spinning due to aquaplaning, in my car, the engine revs would rise
swiftly, as there is no longer any resistance to the torque. After the
slow time constant expires, the revs will come back to the set amount,
but in the meantime, the conditions as described in the derided posting
occur.
I agree that this behaviour is not what one should expect, but I suspect
that a long time constant has been chosen to achieve a stable system,
using the "dominant pole" approach.
I don't know how many cruise controls are like mine. My previous car had
a much better system, which didn't have the same problem to any
noticeable extent.
John G.
David & Glenys Sharples wrote:
What garbage this is, so in the wet the wheels spin up they say, the
wheel speed is what controls the car speed and with cruise control
engaged the wheel (or tailshaft) speed is constant thus giving a
constant speed whether going up or down hill. If we hit a slippery
road
and the wheels remain at the same RPM (which they will in cruise
control) the car actually slows down due to the slip. For it to
remain
at a constant speed not controlled by wheel speed it would need to
have
a GPS system that measured the car speed. Nothing on the car can
measure
velocity, it can only measure wheel speed. Anyhow if the car were to
suddenly take off due to some unknown reason the immediate reaction is
to tip the brake which immediately disconnects the cruise control.
Try putting the car on a jack with the wheels off the ground and set
the
cruise at 60 K, that's where it will stay with the car not moving but
the wheels will be doing the RPM that will give 60 K if on the ground
(if not slipping)
Dave.
----- Original Message ----- From: "Derek Ruddock"
<[EMAIL PROTECTED]>
To: "Discussion of issues relating to Soaring in Australia."
<[email protected]>
Sent: Friday, May 05, 2006 1:58 PM
Subject: RE: [Aus-soaring] FW: Safety issue in the car when it's
raining
-please read this! [Switch Cruise Control OFF]
Typical of the nonsense that seems to propagate via the internet
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:aus-soaring- [EMAIL PROTECTED] On Behalf Of
Alan Wilson
Sent: Friday, 5 May 2006 1:32 PM
To: Aus Soaring
Subject: [Aus-soaring] FW: Safety issue in the car when it's raining
-please read
this! [Switch Cruise Control OFF]
NEVER KNEW THIS BEFORE ~ NEITHER DID I
A 36-year-old female had an accident several weeks ago and Totalled
her
car. A resident of Wollongong, NSW, she was travelling between
Wollongong & Sydney. It was raining, though not excessively,
when
her car suddenly began to hydroplane and literally flew through
the
air.
She was not seriously injured but very stunned at the sudden
occurrence!
When she explained to the policeman what had happened, he told
her something that every driver should know - NEVER DRIVE IN THE
RAIN WITH YOUR CRUISE CONTROL ON. She had thought she was being
cautious by setting the cruise control and maintaining a safe
consistent speed in the rain.
But the policeman told her that if the cruise control is on and your
car begins to hydroplane -- when your tyres lose contact with
the
pavement, your car will accelerate to a higher rate of speed and
you
take off like an airplane. She told the policeman that was
exactly
what had occurred.
[Actually I don't think that is the failure mode, the rear wheels
start
spinning, cruise control sensors on the front wheels read a slow
speed and pours on the power, and the rear wheels spin even more]
The policeman estimated her car was actually travelling through the
air
at 10 to 15 kms per hour faster than the speed set on the cruise
control.
The policeman said this warning should be listed, on the
driver's
seat sun-visor - NEVER USE THE CRUISE CONTROL WHEN THE PAVEMENT
IS
WET OR ICY, along with the airbag warning. We tell our
teenagers
to set the cruise control and drive a safe speed - but we don't
tell them to use the cruise control only when the road is dry.
The only person the accident victim found, who knew this
(besides the policeman), was a man who had had a similar accident,
totalled his car and sustained severe injuries.
If you send this to 15 people and only one of them doesn't know
about
this, then it was all worth it. You might have saved a life
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