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'[EE]:: Achtung Spitfire !!!'
The Griffon engine caused a number of accidental deaths for Spit pilots.
There are three factors which induce significant "unconventional" forces
on a propeller-driven plane that few 'civilians' know about. P-Factor,
Spiral Propwash, and Torque unwind....
Torque unwind is familiar to most of us, and is why a helicopter
requires a tail rotor.... but in prop planes it means that, for a
clockwise turning prop (from the pilot's perspective), the plane will
want to unwind in an anti-clockwise direction, making the plane want to
roll to the left. This requires right-aileron to counteract.
P-Factor (pitch factor) is significant when the plane has an attitude
that is not in line with it's direction of travel. like a plane on the
ground and during take-off where it's angle of attack is large. (i.e.
the nose is pointing up while the plane is traveling horizontally). This
causes the angle-of-attack of the propellor to be different on the
upward and downward sides of it's turn. A clockwise propeller will be
going down on the right, and up on the left. Because the right-hand side
bites in to more air (it's blade pitch is greater) the airspeed and
forces on the right side of the prop will be greater, the plane will
tend to turn (yaw) to the left, and will require right-rudder to counteract.
Spiral Propwash is best described with a diagram, but in essence the
prop imparts a spinning motion to the air. A clockwise turning prop will
cause the air behind it to have a clockwise twist (in proportion to the
torque applied to the air by the prop). The twisting air will have an
equal effect on both wings, and on the stabilizer (because the air
twists around the fuselage of the plane), and will cause a "rolling
effect" on those surfaces (pushing up on the left, and down on the right
surfaces...) (this effect partially negates the torque-unwind). The more
significant effect is on the tail fin. This is un-balanced because the
tail extends only upward from the fuse (there is no tail below the
plane). The effect of the twist is to push the tail to the right, (yaw
the plane to the left), and this needs to be corrected by applying right
rudder (like the P-factor).
All of these effects are most pronounced when the plane is at high
power, and low air-speed ... i.e. at take-off. But, just before the
wheels leave the ground, the rolling forces are not very effective
because the wheels *are on the ground*, and pilots have to immediately
counter the rolling motions when the wheels leave terra-firma. This has
to be an instinctive correction. The yawing forces will have to be
corrected on the runway though, to keep straight.
Still, a pilot who has spent many hours flying a spit with a
counter-clockwise prop (on the merlin engine), will have to un-learn a
lot of instincts to safely fly the Griffon engine....
A number of pilots learned the hard way.
Russell McMahon wrote:
> The Griffon engine caused a number of accidental deaths for Spit
That's the reason I was looking it up.
I told someone about Sir Tim Wallis crashing a MKXIV at the Wanaka air
show, and wanted to chek which Mk it was that he was flying. AFAIK he
was experienced in Spitfires BUT this was the first time he'd flown
the griffon engined MKXIV AND he did it in front of an airshow crowd.
He was very badly injured and very lucky to live.
|On 4/25/07, Rolf <rogers.com> wrote: learr
> The Griffon engine caused a number of accidental deaths for Spit pilots.
> There are three factors which induce significant "unconventional" forces
> on a propeller-driven plane that few 'civilians' know about. P-Factor,
> Spiral Propwash, and Torque unwind....
Your description of the factors involved are good, but you missed one.
There are *four* "turning" factors that affect most light
You forgot about gyroscopic precession. The tendency for a gyroscope
(propeller) to react to a force input by imparting a force 90 degrees
from the input force. Pulling back on the stick (yoke) for takeoff
imparts a vertical force on the prop which is turned in most aircraft
into a left yawing force.
During initial training in most typical aircraft with a prop that is
turning clockwise (as viewed from the pilot's seat), all four of these
forces are all introduced by the instructor as "left-turning
tendencies", and we all learn to stomp pretty aggressively on the
right rudder during the takeoff roll.
Later, after the pilot has a grasp of these fundamentals, the
instructor will discuss that that factors change significantly in an
aircraft with a counter-clockwise turning prop.
You're correct that pilots must think about and correct this "almost
automatic" foot movement when transitioning to different aircraft.
The counter-clockwise engine is but one example.
Long-time instructors working their way up the food chain to turbines
also have a tendency to push on that right rudder pedal automatically,
when it's not needed... which can be pretty entertaining to watch
until the person corrects their learned behavior.
In addition, multi-engine students learn about the "critical engine"
in aircraft with multiple props that turn the same way. In most twin
designs, one specific engine in a twin engine aircraft (usually the
right engine) will create more adverse effects on yaw and aircraft
controllability than the other.
Some twin-engine designs try to eliminate the "critical engine"
scenario by mounting counter-rotating engines on each wing.
Bottom line - it's up to the pilot to know and fly their aircraft.
On Wed, Apr 25, 2007 at 10:50:18AM -0600, Nate Duehr wrote:
> Some twin-engine designs try to eliminate the "critical engine"
> scenario by mounting counter-rotating engines on each wing.
Makes me think that in engine failure scenarios the poor pilot would
suddenly have to deal with all those pesky rotational induced effects...
right when he would rather think about something else.
|On 4/25/07, petertodd.ca < petepetertodd.ca> wrote: pete
> On Wed, Apr 25, 2007 at 10:50:18AM -0600, Nate Duehr wrote:
> > http://en.wikipedia.org/wiki/Critical_engine
> > Some twin-engine designs try to eliminate the "critical engine"
> > scenario by mounting counter-rotating engines on each wing.
> Makes me think that in engine failure scenarios the poor pilot would
> suddenly have to deal with all those pesky rotational induced effects...
> right when he would rather think about something else.
That's why you're trained NOT to think about anything else. :-)
Multi-engine pilots are drilled, then drilled, then drilled some more
on the emergency procedures for a dead engine, hopefully in the
specific aircraft type and aircraft they are flying.
"Dead foot, dead engine"... e.g. the foot that's not pushing on a
pedal is the side the engine's dead on... (you'd be amazed how may
accidents pilots have caused via shutdown/feather the OPERATING
Fly at MCA (minimum controllable airspeed) or faster (preferably
faster!) or you'll find yourself yawing dramatically or rolling upside
down in worst-case scenarios...
Attempt restart/relight if possible. If not possible, feather dead
engine propeller, etc...
All depends on the aircraft. Bigger aircraft have auto-feather systems, etc.
But generally, yes... an engine out in a light twin is a bigger
"emergency" than in a whiz-bang do-everything-for-the-pilot bigger
The morbid joke about light twins is: "What's the second engine for
in a light twin aircraft? To get you to the scene of the crash."
An engine failure in a light twin of the critical engine requires your
full uninterrupted attention, immediately.
And there has been more than a few that shut down the good engine. I
have experienced 3 complete single piston engine failures 2 due to
failed threaded cast iron cylinder to aluminum head joint failure, and
once where the mechanic who overhauled the engine (before I was part
owner) didn't replace 4 small bolts and 4 dowel pins that hold the main
(drives cam and mags) gear on the end of the crankshaft. All times made
it to a paved runway and landed safely. Quit flying a year ago, but that
wasn't the full reason. :)
And then there was DC-10 ?? the ran out of fuel over the Atlantic, and
just made it with zero to spare to the Azores. ~)
Nate Duehr wrote:
Not to mention the gimli glider..
> And then there was DC-10 ?? the ran out of fuel over the Atlantic, and
> just made it with zero to spare to the Azores. ~)
> Not to mention the gimli glider..
Shades of spacecraft to Mars.
Measure fuel by hand.
Calculate in litres.
Convert to US gallons.
Get it wrong.
There used to be an airforce base at Gimli.
We may just possibly be able to glide there from there. Maybe ... "
But there's more to it than that.
>> And then there was DC-10 ?? the ran out of fuel over the Atlantic,
>> just made it with zero to spare to the Azores. ~)
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