Who can trust this article?
He misidentifies one of the most famous and easily recognizable airplanes of ALL time :eek::D
He might as well call a P-51 a 'Jug'!

USMCFLYR

In all seriousness - good article. I always find Peter Garrison's articles to be informative.

Just my thoughts, but I do not think spiraling slipstream is a very big factor in left turning tendency. P-factor, torque and precession are bigger forces. The latter only shows up when there is a change in pitch rate. In terms of percents, something like 50/30/variable/10, with the last number being slipstream.

He probably had seen:

http://lockthewelderdotcom.files.wor.../hellcat-2.jpg

PW - please repost. The picture didn't come through.

USMCFLYR

Isn't torque only an issue due to bearing friction (and that's compensated for with engine mounting usually) and when accelerating/deccelerating the prop? I know the size of the prop and the power behind it can have a big effect obviously. Maybe it's just me, but when I took off in conventional twins by going full power, then brake release, it never seemed to take off to the left nearly as much as if I went full power while rolling.

try this USMC http://lockthewelderdotcom.files.wor.../hellcat-2.jpg

I like the other one better :D, but yeah - your probably right.

USMCFLYR

I would think bearing friction is a trivial quantity. You can turn an engine with your bare hands, compression and all- there isn't a lot of friction there.

Torque is not dependent on rate of RPM change like gyroscopic precession is. P-51s and other high displacement engines may produce a lot of torque, but it is constant for a given RPM, disc load etc.

PHAK (Pilots Handbook of Aeronautical knowledge) mentions that since airplane wheels are small and often a bit low on air, high torque engines compress the left wheel on takeoff roll (conventional twins, single engines) making ground friction on the left a significant left turning factor.

In cruise torque shows up as a constant roll force, which is as you mention is countered by engine angle and aerodynamic design tweaks. High torque engines on slow airplanes produce a lot of residual roll. Roll of course is a turning function in airplanes. Stand in front of Caravan for example, and notice the angle of the engine is noticeably to the right.

http://i284.photobucket.com/albums/l...os/caravan.png

In piper meridians the engine is mounted 1-2 degrees to the right. I have also seen the soot stains on those, as well as on TBM's and King Airs, Cheyennes, etc

Slipstream, with regards to high powered military single engine propeller aircraft, in particular the navy fleet, was a critical design consideration. Being most critical at low speed and high power, such as landing on a carrier.

It's not a theory; we know it to exist. Here's a quote from a design book written in the late 40s:

On the flight instructor level, aerodynamics for naval aviators chapter on direction stability and control covers the subject well. Noting that slipstream rotation and/or spin recovery are the typical critical criteria placed on rudder control in a single. Though I suspect they too are referring to high powered singles used for carrier landings.

--

FWIW, this is how I teach it:

Torque: A left rolling tendency, not yawing, that is the result of the airplane reacting to the spinning propeller. It's effects are small enough to be ignored unless viewed at full power and at, or very near, stall speed.

Gyroscopic Precession: A left turning tendency during the days where tail draggers ruled the fleet. In todays tricycle aircraft it too can be ignored. Though I depict it visually using a stick, held vertically, to represent the propeller/yoke, having the student grab the top with one hand and bottom with the other, and then push on the top/pull the bottom. We then rotate the stick/propeller 90 degrees and see the right side is pushed forward, left back -- a left yaw. (This is the classic raising of the tail in a tail dragger aircraft)

Slipstream and P-factor: This is what we contend with during takeoff roll and departure climb out. At cruise design corrects for them or our legs would get quite tired.

P-factor is of no factor until we leave the ground and the fuselage has an angle of attack to the relative wind. Slipstream is what requires use of the rudder during the takeoff roll. In flight a combination of these two require rudder corrections during full power climbs, go arounds, or any other high powered low speed flight.

--

You may notice the particular interest I've put into mentioning when a pilot must contend with these conditions. That is because it is my position that we are not trying to teach the pilot a complete theory behind these 4 conditions. Instead, we try to show them enough to 1) not be confused/scared and 2) understand and accept their existence.

Once their existence is accepted it will be of far greater value to have a complete understanding of when these conditions require particular attention and input from them. And that is during takeoff roll, climbs, go arounds, and any other slow speed and high power condition.