are "counter-rotating" and "contra-rotating" interchangeable terms?

I'm doing some research, trying to find information on airplanes with
counter-rotating props, but I'm getting a lot of junk hits from
articles that use "counter-rotating" when they should mean
"contra-rotating".

I was always taught that "contra-rotating" was when you had two sets of
blades spinning from the same hub, as in this: http://tinyurl.com/vxu9a
and "counter-rotating" meant two different engines on a twin, each
spinning in opposite directions, ala the Seneca and Twin Comanche.

But according to google, more than half of the instances of
"counter-rotating" are used to describe "contra-rotating". Are all
those people wrong, or is the term interchangeable?

(by the way, I'm trying to compile a list of counter-rotating twins, if
anyone knows of any that are not listed he
http://en.wikipedia.org/wiki/Counter...ing_propellers please post)

Yea,

The Wright Flyer.


Karl
"Curator" N185KG



"buttman" wrote in message
ups.com...
I'm doing some research, trying to find information on airplanes with
counter-rotating props, but I'm getting a lot of junk hits from
articles that use "counter-rotating" when they should mean
"contra-rotating".

I was always taught that "contra-rotating" was when you had two sets of
blades spinning from the same hub, as in this: http://tinyurl.com/vxu9a
and "counter-rotating" meant two different engines on a twin, each
spinning in opposite directions, ala the Seneca and Twin Comanche.

But according to google, more than half of the instances of
"counter-rotating" are used to describe "contra-rotating". Are all
those people wrong, or is the term interchangeable?

(by the way, I'm trying to compile a list of counter-rotating twins, if
anyone knows of any that are not listed he
http://en.wikipedia.org/wiki/Counter...ing_propellers please post)

Counter-rotating: prop tips rotate inboard

Contra-rotating: prop tips rotate outboard

Counter-rotating: you have to run to keep up with the cash register.
Contra-rotating: you have to run to keep up with the sales people.

Jose
--
"Never trust anything that can think for itself, if you can't see where
it keeps its brain." (chapter 10 of book 3 - Harry Potter).
for Email, make the obvious change in the address.

Counter rotating props are on two engine and shafts, they
rotate both clock and counter clockwise. On the P38 the
blades rotated away from the fuselage. Modern practice is
to have the blades rotate toward the fuselage and thus have
the lowest Vmc.

Contra-rotating is having two propellers on the same shaft
rotating in opposite directions to cancel torque effect and
gyroscopic forces.




"john smith" wrote in message
...
| Counter-rotating: prop tips rotate inboard
|
| Contra-rotating: prop tips rotate outboard

On Fri, 10 Nov 2006 23:21:53 -0600, Jim Macklin wrote:
On the P38 the blades rotated away from the fuselage.
Modern practice is to have the blades rotate toward
the fuselage and thus have the lowest Vmc.

Kind of depends upon your point of reference, doesn't it? No matter what,
the props are going to rotate towards the fuselage... It just depends upon
whether your point of reference is the top or the bottom of the fuselage...

P-factor and rotation is always, by convention, based on the
top blade moving downward.



"Grumman-581" wrote
in message
news | On Fri, 10 Nov 2006 23:21:53 -0600, Jim Macklin wrote:
| On the P38 the blades rotated away from the fuselage.
| Modern practice is to have the blades rotate toward
| the fuselage and thus have the lowest Vmc.
|
| Kind of depends upon your point of reference, doesn't it?
No matter what,
| the props are going to rotate towards the fuselage... It
just depends upon
| whether your point of reference is the top or the bottom
of the fuselage...
|

"Jim Macklin" wrote in message
...
P-factor and rotation is always, by convention, based on the
top blade moving downward.


I can't think of a situation where the top blade would move any direction
but down. ;-)

The most common rotation pattern in modern twins is for the top blade(s) to
rotate towards the fuselage.

KB