Why Do Motorcycles Have Two Throttle Cables?

 

I was talking with a guy at work today ...

What exactly led to the situation today where nearly all motorcycles have
two throttle cables?

I understand what would happen with a stuck single cable and so on, but it
doesn't seem to be enough risk to justify the second cable.

Also, if the cable that closes the throttle fails (breaks), it seems like
the spring arrangement in the carb (I'm guessing that is where the spring
is) would conceal the fault and it would be silent until the cable that
opens the throttle also fails.  If so, that doesn't seem to bright?

 

Dnia 2008-09-04 David T. Ashley napisa³(a):

Not?  Well, it seems like enough reason to me.  But cables can get
tangled too, and then having a closing cable is fairly convenient.


On a dual cable arrangement this closing spring tends to be rather weak,
so you will probably notice that a bike hangs to revs for longer.  Once
I broke this plastic flange in throttle grip of my bike, so I tried to
get rid of one cable.  It didn't work.

--
Andrzej Rosa

 



Yes, and airplanes really only need one elevator cable for up elevator
because the airstream will blow the elevator back to neutral and you
really don't need down elevator, you can always throttle back to
descend...

 


You probably realize that you are right on.

In fact, in the traditional Cessna checklist for failed elevator control,
one trims the plane for level flight at a certain speed (forget what it is),
then uses the throttle to control descent.  It works just fine.

And, of course, if you have passengers in the plane--particularly passengers
who also hold airman ratings--there can be a lot more action and excitement
if something goes wrong.

I'm reminded of one story I heard where somebody was messing around and spun
a plane with two (pilot) passengers in the back seat, then had difficulty
recovering.  It ended up with a big love-fest in the front seats because the
two rear passengers flung themselves forward practially up against the
windscreen to shift the CG forward and aid recovery.  It normally helps with
the excitement factor if the passengers hold airman ratings, because then
they understand the gravity of the situation and tend to act decisively.

Personally, if I were in a light airplane (with at least one other pilot)
and the elevator failed in a way where it wasn't flapping in the breeze, it
would probably end up with one person kicking out the rear bulkhead so the
heavier person could move around to trim the plane.

An elevator flapping in the breeze (i.e. a broken control cable) is normally
a manageable annoyance.  The larger threat would be an elevator that somehow
mechanically stuck.  Fortunately, they are engineered not to do that ...

 



http://en.wikipedia.org/wiki/Alaska_Airlines_Flight_261