Just a thought, and I don?t know why. But with the renisis side
  porting, or peripheral porting. It wouldn?t be very hard at all
  to make a  rotary engine run the opposite direction if a person
  needed it to. I wonder why I care?

  Bob M.

  You are probably thinking of a twin.

  It will run backwards but the internal cooling would be all screwed
  up :)

  Paul Lamar


  It would work perfectly in a parallel universe.
  jd

Paul,
With a few of us working on billet machined side housings (with steel
inserts), the  cooling pattern and bolt patterns could be mirrored and
the
rotor housings mounted rotated 180. This would give a reverse rotation
rotary that had identical performance, both hp and cooling. Other
stuff like
the oil and water pumps would have to be reworked for rotation, but very
doable.
This would provide a great twin set up.
Larry

We might even sell one :)

Then we will have to deal with the law of unintended consequences.

I think we are twenty or thirty years ahead of our time here.
Perhaps when I have my 100th birthday party.

First we must get 100,000 rotaries flying :)


Paul Lamar

Why wouldn't it be easier to beef up the e-shaft and use the other end
of the engine  for power output?

Victor

Much cheaper and more likely to work.
The required modifications are extensive but not nearly as bad as running
the engine in the other direction. A new front cover would
need to be designed and built as well.

Paul Lamar

Pardon my ignorance, but wouldn't it be easier to regear the
PSRU/redrive to have have each turning in different directions for a
twin. We are already using them and Tracy's current redrive already turn
different directions biu with different reduction ratios.

Chris Barber


I would posit that counter rotation of props has little to do with the
safety of a given twin engine aircraft.  If you had an airplane that
otherwise was nice, and wanted to make it a bit nicer, making separate
left and right engines would make sense. Otherwise, I don't think it's
worth the effort.

A few interesting tidbits..  The P38 lightning props turn the wrong way.
Both engines are "critical." Done for gunnery accuracy somehow.

Some models of Piper twins came both with and without counter rotating
engines.

Twin safety depends on training.  And overall performance.  The way the
engines turn only sort of effects how close the blue line is to VS0.


</GROUCH

;)

Matt-

Gunnery accuracy was one reason, gyroscopic effects in turns will be
zeroed out in this way,  but there will also be a small aerodynamic
efficiency increase by doing counter rotating props, that have classic
wing mounted engines.

In war machines, they utilized this feature to squeeze a few more Knots
out of those aircrafts, as mentioned P-38, but also others, like the
Mosquito, and a few others had it.

An application like in a Piper twin, the effects would probably not be
too big, and the reason some had it and some don't, is probably because
of the availability of counter rotating engines, so I guess they
figured...what the heck, it does something....and did it....... if they
didn't have counter rotating engines in stock....I guess they said it
again....what the heck...and did it with two same rotating engines....,
but in critical applications like racers, and war machines ( at least
back in those days when they all had propellers) , and in very slick
aircrafts,  it is a desirable feature.

By reasons I have not fully understood, the effects is more pronounced
in two engine, than in four engine propeller aircrafts, thus even if
some four engine aircrafts had it, it is less common in that application.

Roger
I'm not sure if I'm missing something here in this discussion, but the
reason for counter-rotating props on a twin (as I was taught many years
ago) is safety.  It eliminates the critical engine scenario.  Critical
engine is the one which, if failed, creates the biggest problem for the
pilot.  It could be something as basic as the engine driving the only
hydraulic pump or the only generator.  However, apart from components,
the thrust created with only one engine running is brutal on
aerodynamics.  That engine is trying to pull the aircraft around in a
circle.  To compensate, the pilot jams in a bunch of opposite rudder to
stop the turn.  What he really wants to do is bank the aircraft towards
the running engine (lean on the good engine).  By banking in towards the
running engine and applying rudder, the turning tendency is eliminated
but the aircraft is now sideslipping thru the air.  In cruise flight
there is usually enough rudder to keep things going straight, but on
takeoff with little rudder effectiveness, the aircraft could eventually
flip over on its back and crash.  Designers are required to come up with
a minimum airspeed that provides for enough rudder control to prevent an
engine failure crash on takeoff.  This speed is called Minimum Control
Airspeed or Vmc.  If the airplane's stall speed is less than Vmc, then
it's a dangerous place to be flying around just above stall but below
Vmc.  If an engine quits....you're upside down.  A really safe twin will
have stall and Vmc the same, or Vmc even lower than stall.  That
requires a really big tail, or engines mounted quite close to the
fuselage centerline.

When we think of torque, the normal clockwise propeller is trying to
torque the airframe counterclockwise while flying thru the air.  This is
most obvious during takeoff when engine torque is maximum and aileron
control is the least.  With the left engine of a twin trying to twist
the airplane into a left roll, this is a good thing if the right engine
has failed.  The pilot already wants to bank to the left.  However, if
both engines are normal rotation, then the right engine wants to also
twist the airplane into a left roll, a really bad thing if the left
engine has failed.  The pilot has to use even more aileron and rudder
(if he has any left).  Vmc is calculated with the worst scenario engine
failure, so the critical engine in this cast would be the left engine
failure.

Counter rotating props eliminate the "wrong" rolling tendency with a left
engine failure.  Left engine wants to roll the airplane to the left and
a right engine failure want to roll the airplane to the right.  Vmc is
not dependent on a critical engine.  Vmc is now a few knots
slower.......maybe even equal to or less than stall speed.   The
aircraft will experience a stall before it will ever flip over from
asymetric thrust.  That would make for a much safer aircraft.

Greg in Canada

Greg,



  Critical engine is an aerodynamic thing. When you lose one engine the
aircraft will slow down. If the aircraft slows down and the pilot wants to
maintain altitude, then he must increase his angle of attack. With a higher
angle of attack you get assymetric thrust off of the propellors because the
down going blade has a higher angle of attack as the upgoing balde. As a
result of this, the center of thrust moves to the right (down going side).
If your right engine fails the center of thrust on the left engine shifts
inboard, minimzing yaw (reduced arm) whereas if the left engine fails, the
center of thrust on the right engine shifts to the right thus increasing yaw
(increased arm). Therefore on most aircraft, with both engines rotating
clockwise the right engine is deemed the critical engine. Engine driven
accessories, or lack of them, can certainly make a pilots problem greater
but are not a determining factor in critical engine.

  It has been a while but I believe Vmc is primarily a yaw thing and is
the defined as the calibrated airspeed at which, when the critical engine is
suddenly made inoperative, it is possible to maintain control of the
airplane with that engine still inoperative, and thereafter maintain
straight flight at the same speed with an angle of bank of not more than 5
degrees. The method used to simulate critical engine failure must represent
the most critical mode of powerplant failure expected in service with
respect to controllability. The following are factors that effect the
controllability;



Density altitude
Critical engine inoperative
Bank - up to 5 degrees into operative engine
Landing gear retracted
Operative engine at max power

Weight at max
Aft CG
Cowl flaps open

Out of ground effect
Wind milling prop

John (also in Canada)