Whats the deal with counter-rotating props?

Thanks Jim

"Jim Burns" wrote in
:

One of my favorites is Bob Gardner's book The Complete Multi-Engine
Pilot. It's written in a very easy to read down to earth manner. The
Jeppesen Guided Flight Discovery, Multi Engine book is very complete,
but in my opinion hard to read due to the distracting pictures and
captions. Jim


Rob McDonald" wrote in message
...
What would you multi folks recommend as good "introductory" reading...

I suspect that our perception of the dangers are skewed by the fact that
the failures (i.e. "second engine took them to the crash site") are
reported in both the official records and the media, but we are less likely
to hear about successful outcomes like yours.

Rob


"Michael" wrote in
oups.com:

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

My experience differs. When the left (critical) engine of my Twin
Comanche failed (due to undetectable corrosion in the fuel servo) the
remaining engine took me to a normal landing at an airport. Had I
been in a single engine plane in the same situation, well, let's just
say I was over Arkansas and there was an avtive airmet for mountain
obscuration.

Michael

On the other hand, out here (central Ontario) most of the real estate does
not much exceed 1000' ASL. I have the Great Lakes on three sides and most
of the territory I fly over when going any distance is trees, rocks, and
small lakes - no emergency land sites, just crash sites. Even the 3800' SE
ceiling of the Twinkie with the Robertson STOL kit would be enough to
prevent an engine failure from ruining my day.

Rob


"BTIZ" wrote in
news:auyDf.54832$V.15854@fed1read04:

Out here, most airports are around 3000MSL, with terrain over 8000MSL
between them, add in the density altitude factor on a standard 100F or
higher day.. and that single engine is not going to be me to an
airport. BT

"Dico" wrote in message
oups.com...
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 would like to throw an interesting (if maybe false? I have no personal
experience or a cite.) factoid into this discussion.

I have read that the P38 Lightning was equipped with counter rotating props
that rotated in the opposite (down going blades on outboard side of engines)
from normal direction resulting in an aircraft with two critical engines and
much increased yaw force when either engine failed. This was done despite
control issues because it resulted in 15 knots extra top speed as compared
with CR props using typical configuration (down going blade on inboard side
of engines)

Someone more knowledgeable may be able to explain why.

Private wrote:
: I would like to throw an interesting (if maybe false? I have no personal
: experience or a cite.) factoid into this discussion.

: I have read that the P38 Lightning was equipped with counter rotating props
: that rotated in the opposite (down going blades on outboard side of engines)
: from normal direction resulting in an aircraft with two critical engines and
: much increased yaw force when either engine failed. This was done despite
: control issues because it resulted in 15 knots extra top speed as compared
: with CR props using typical configuration (down going blade on inboard side
: of engines)

: Someone more knowledgeable may be able to explain why.

Interesting. Perhaps less downward propwash on outboard ends of wings? Or
maybe propwash vorticies "lifting" the fuselage rather than "swatting it down?"

Just WAGs on my part.

-Cory


--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

Private wrote:
I have read that the P38 Lightning was equipped with counter rotating props
that rotated in the opposite (down going blades on outboard side of engines)
from normal direction resulting in an aircraft with two critical engines and
much increased yaw force when either engine failed.

This is definitely true, in the sense that the props did counter-rotate
opposite to what is now normal. However, the whole critical engine
thing is way overrated. Vmc is a control speed, not a performance
speed. It is quite a bit lower than Vyse, which is as slow as you ever
want to fly with anything close to full power (other than in a training
situation) whether you have an engine out or not. In other words, it's
really not a big deal, which is why it's rare to see counter-rotating
props in anything other than a trainer.

This was done despite
control issues because it resulted in 15 knots extra top speed as compared
with CR props using typical configuration (down going blade on inboard side
of engines)

That doesn't sound right. My understanding is that the reason was to
make the plane more maneuverable (using differential thrust for yaw).
Of course you could get the same effect by using a bigger rudder, but
that would mean more weight and drag, so maybe it boils down to the
same thing - a cleaner, lighter, and thus faster airframe with the same
maneuverability.

It is also my understanding that the extra maneuverability was rarely
used due to the complexity of engine management involved. Late in the
game, a prototype was built with single-lever engine controls. Richard
Bong, one of the most famous of the WWII aces, died test flying it when
an engine blew up.

Michael

"Michael" wrote in message
oups.com...
snip
Late in the game, a prototype was built with single-lever engine controls. Richard
Bong, one of the most famous of the WWII aces, died test flying it when
an engine blew up.

Michael

I thought he died in one of the first jets... perhaps a P-80?

Joe Schneider
8437R



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"JJS" jschneider@remove socks cebridge.net wrote in message
...

"Michael" wrote in message
oups.com...
snip
Late in the game, a prototype was built with single-lever engine
controls. Richard
Bong, one of the most famous of the WWII aces, died test flying it when
an engine blew up.

Michael

I thought he died in one of the first jets... perhaps a P-80?

Correct.

Fuel Pump failure (IIRC) which he did not know how to handle as he was too
much the "hot shot" pilot to read the operating manual.

Interestingly...both Bong and McConnell, the highest scoring aces in WW2 and
Korea, both died right at the respective wars end while test flying, both in
low altitude accidents.

I suspect that our perception of the dangers are skewed by the fact that
the failures (i.e. "second engine took them to the crash site") are
reported in both the official records and the media, but we are less likely
to hear about successful outcomes like yours.

Yes, that's part of it. My engine failure was under IFR, but while I
reported it to ATC, that was as far as it went. I requested priority
handling (not wanting to descend low over trees until I was closer to
the airport) but that was as far as it went. After a throrough
cleaning and flush of the fuel servo, I was back in action. There was
no accident or incident.

Engine failures do not figure heavily in the accident stats, but I've
noticed that this is because single engine pilots are noticeably more
conservative about flying in situations where an engine failure is
likely to kill you. I think nothing of making an overwater flight
dozens of miles from land, or a flight over rough terrain with
widespread low IFR. I do it routinely in the twin. I will do it in a
single, but only if I really need to make the flight.

Michael