Whats the deal with counter-rotating props?

Hello,

We're looking into a twin and the Twin Comanche is on our list. I know
that the later models have the counter rotating props -- although i
don't know too much about what this means, other than its "better".

We fly a mooney now and thus I don't worry about the prop -- as long as
it keeps spinning.

Is there a web site that gives a good explanation as to why I want CR
props. There are hundreds of the earlier model Twin Comanches flying
without the CR props --- so what does someone with 300 hours single
engine time need to worry about? What actually goes wrong? And when
it does, what happens? I hear "critical engine" but it means very
little to me.

I like to fly and try to be very careful when I do fly... but I don't
follow too much aviation stuff other than how it affects me -- so I'm
not exactly a "buff", hence the above questions which may seem obvious
to many.

Why are we looking at a Twin Comanche? Because its a twin, safer for
IFR flight (perhaps this is only preceived), plus we live on the east
coast on an island so we're flying over water quite a bit. Also this
plane has decent speed and is an "economical" twin. We rarely fly with
4 people, so we don't need any more seats than 4.

Any help or links to help would be appreciated.

Thanks,

Dico

Think about what you do with your right foot during takeoff.

"Dico" wrote in message
oups.com...
Hello,

We're looking into a twin and the Twin Comanche is on our list. I know
that the later models have the counter rotating props -- although i
don't know too much about what this means, other than its "better".
Thanks,

Dico

On Sun, 29 Jan 2006 04:17:23 GMT, "Michael Ware" wrote:


"Dico" wrote in message
oups.com...

We're looking into a twin and the Twin Comanche is on our list. I know
that the later models have the counter rotating props -- although i
don't know too much about what this means, other than its "better".
Thanks,

Think about what you do with your right foot during takeoff.

Most trigear pilots are scratching themselves behind the right ear. :-)

Ron Wanttaja

I push the rudder with my right foot. This doesn't really answer my
questions though. Like I said, I'm not a "buff" and don't know much
about twins.

-Dico

that's right. i am trying to get you to think why you have to do this,
therefore leading to the reasons why you might want counter-rotating props.

"Dico" wrote in message
oups.com...
I push the rudder with my right foot. This doesn't really answer my
questions though. Like I said, I'm not a "buff" and don't know much
about twins.

-Dico

So with counter rotating props I won't have the plane want to go left?
Or I'd really have to hammer down the right rudder? Even worse if one
engine quit, I could be screwed? And I'm guessing the critical engine
comes into play here. Although I'm not sure if the critical engine
means its the good one (its critical you keep it) or the bad one (its
critical if you lose it)....

-Dico

"Dico" wrote in message
oups.com...
So with counter rotating props I won't have the plane want to go left?
Or I'd really have to hammer down the right rudder? Even worse if one
engine quit, I could be screwed? And I'm guessing the critical engine
comes into play here. Although I'm not sure if the critical engine
means its the good one (its critical you keep it) or the bad one (its
critical if you lose it)....

-Dico


Try Googling "minimum controllable airspeed"

Gerry

"Dico" wrote in message
oups.com...
So with counter rotating props I won't have the plane want to go left?

Correct. Not when they are both running, anyway!

Or I'd really have to hammer down the right rudder? Even worse if one
engine quit, I could be screwed? And I'm guessing the critical engine
comes into play here. Although I'm not sure if the critical engine
means its the good one (its critical you keep it) or the bad one (its
critical if you lose it)....

check this out.

http://avstop.com/Technical/twins.htm

Remember, too, that with a twin (except for planes like a Cessna 337) the
engines are not on the centerline of the fuselage, they are offset a few
feet.


-Dico

think of the thrust line of the propeller
and for the smart guy that mentioned right foot for take off.. that's some
thrust but also P-factor

without counter rotating propellers,
consider downward arc of prop has more thrust, left engine, downward prop is
next to fuselage, right engine it is on the right side of that engine and
farther from fuselage, if the left (critical) engine fails then all that
thrust is way out on the right side moment arm causing yaw, and if real
slow, roll factors to deal with.

counter rotating propeller means the right engine the propeller rotates
counter clockwise, moving that thrust line closer to the fuselage, (now same
on both sides) and reduces the yaw action in the event of either engine
failing.. thus negating the "critical engine" factor.

You need to pick up and read a good multi engine training manual.. something
by Kershner

BT

"Dico" wrote in message
oups.com...
Hello,

We're looking into a twin and the Twin Comanche is on our list. I know
that the later models have the counter rotating props -- although i
don't know too much about what this means, other than its "better".

We fly a mooney now and thus I don't worry about the prop -- as long as
it keeps spinning.

Is there a web site that gives a good explanation as to why I want CR
props. There are hundreds of the earlier model Twin Comanches flying
without the CR props --- so what does someone with 300 hours single
engine time need to worry about? What actually goes wrong? And when
it does, what happens? I hear "critical engine" but it means very
little to me.

I like to fly and try to be very careful when I do fly... but I don't
follow too much aviation stuff other than how it affects me -- so I'm
not exactly a "buff", hence the above questions which may seem obvious
to many.

Why are we looking at a Twin Comanche? Because its a twin, safer for
IFR flight (perhaps this is only preceived), plus we live on the east
coast on an island so we're flying over water quite a bit. Also this
plane has decent speed and is an "economical" twin. We rarely fly with
4 people, so we don't need any more seats than 4.

Any help or links to help would be appreciated.

Thanks,

Dico

MORE critical if you loose it

consider the single engine service ceiling of most light twin aircraft, and
where you would be flying it

IIRC the SE service ceiling of a Twin Comanche is about 3800MSL (Density
Altitude), or below the ground level of most places out here in the mid
west.

The second engine, on failure of the first engine, will only lead you to a
landing location, not necessarily of your choosing.

BT

"Dico" wrote in message
oups.com...
So with counter rotating props I won't have the plane want to go left?
Or I'd really have to hammer down the right rudder? Even worse if one
engine quit, I could be screwed? And I'm guessing the critical engine
comes into play here. Although I'm not sure if the critical engine
means its the good one (its critical you keep it) or the bad one (its
critical if you lose it)....

-Dico