Michael,
You only left out one part: when a pilot does learn to fly the
PA30 and stay ahead of it, it's a blast to fly!! (especially the turbo'd
model)

-----Original Message-----
From: Michael ]
Posted At: Monday, January 30, 2006 11:54 AM
Posted To: rec.aviation.owning
Conversation: Whats the deal with counter-rotating props?
Subject: Whats the deal with counter-rotating props?

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".

You've gotten a lot of uninformed opinions here. I started countering
them, and after the first post decided it would be better to put it
all
in one place. I have over 900 hours in Twin Comanches of various
flavors (including the CR), I've instructed in them, and I've worked
on
them. Having said that, here's what you're dealing with.

There are exactly two things a counter-rotating prop does for you in
flight.

First, it relieves you of the necessity of applying right rudder on
takeoff or climb.

Second, it allows you to fly at a slightly lower airspeed in the event
the left engine fails without rolling over - which boils down to being
able to fly not just much too slow, but much, much too slow. The
reality of the situation is that the PA-30 should never be flying at
less than 90 mph unless
(a) the runway is made and you are decelerating in preparation for the
flare, in which case power is near-idle and an engine failure is
irrelevant,
(b) you are in ground effect accelerating after takeoff, in which case
an engine failure calls for an immediate idling of the throttles and a
touchdown straight ahead, or
(c) you are at a safe altitude doing training.

The downside is you get an engine where the prop, prop governor,
magnetos, alternator, vacuum pump, fuel pump, oil pump, and tach
adapter are nonstandard, and thus rarely stocked. On top of that,
some
of those parts are used only on that one engine (the counter-rotating
IO-320) which is used on only that one airplane (the PA-30CR or PA-39)
which hasn't been made in decades and of which relatively few were
made. The impact on maintenance is spectacular.

The reason Piper modified the original PA-30 (in many ways - they
added
control linkages, stall strips, and finally the counter-rotating
props)
was to make it a more docile trainer. They didn't succeed. If you
buy
the plane, make sure you find an experienced Twin Comanche instructor
to train you. No amount of time in Seminoles, Duchesses, Apaches,
Geronimos, or similar trainers prepares someone to fly a PA-30. I've
seen what happens when someone who just took an MEI ride in a Duchess
gets into a PA-30 - he can't hold on to the tail. You rarely see
PA-30's as trainers anymore, and for good reason. When MEI's with
50-100 hours multi time tried to teach in them, the carnage was
spectacular.

You do not need an STC to convert a straight PA-30 to CR. There is a
service bulletin from Piper for the conversion. All you need to do is
buy the parts and convert the engine by simple parts replacement.
That
won't be cheap either.

With the low altitudes and cool weather of the East coast, the service
ceiling of the PA-30 is quite high enought (5800ft density altitude at
gross). Contrary to popular opinion, the PA-30 will fly just fine on
one engine, even at gross. BTDT.

Most of the PA-30's out there now have been modified to reduce Vmc.
The popular mod is the rudder fin (Knots-2-U and Robertson make them)
which improves lateral stability and reduces Vmc.

The real Vmc of a PA-30 without CR props is 80 mph. That's what was
designed in and verified by flight test at Swearingen. However, that
assumes you do everything right. Relatively small errors in technique
can raise that. This was fixed by raising the Vmc marking on the ASI
and in the AFM to 90 mph by AD (no changes were made to the airframe).

If you want more info, just ask

Michael