Pitch Yaw Coupling & Metal Blade Props

I have flown many, many different types of tailwheel aircraft over many decades, often giving hands-off dual from the right 

(or rear) seat on my first flight on type, and here’s something really valuable I’ve learned.

You can tell a LOT about how an airplane flies - and this is really noticeable for tailwheel or aerobatics - simply by looking

at the prop before you get it in.  Are the blades metal, or wooden/composite?  This makes a HUGE difference because

of something called “moment of inertia”.  If you’re an engineer, math or physics guy, it’s calculated as the integral radius

squared dm.  

If you’re a normal person, what you need to know is that the mass of the metal blades can impose quite a load on the crankshaft, 

and can greatly affect how the aircraft flies.  Wooden or composite blades weigh a lot less and have vastly reduced effect 

in this regard.  My personal observation is that the nose feels “loose” and this is subjectively very pleasing to me, in terms of

my ability to easily maneuver the aircraft.

This particular effect is not noticeable in straight and level flight - it is ONLY noticeable during pitching and yawing.

What you need to know as a pilot, is that if you have a metal blade prop, if you raise the tail on takeoff, the nose is going

to yaw left, and if you lower the tail on landing, the nose is going to yaw right.  This is called pitch-yaw coupling and is

caused by gyroscopic precession of the prop, which is probably going to be familiar to you if you ride a motorcycle … it’s

called “push steering” or “counter steering” in that world.  Fundamentally, when a force is applied perpendicularly to a

spinning disc (like an aircraft propeller) the force appears to act 90 degrees lagging the direction of rotation.  

With a Lycoming or Continental or Franklin aircraft engine, the prop rotates clockwise when viewed from behind.  So when 

you raise the tail on takeoff of a taildragger, you are basically pushing at the TOP of the prop “disc” and the resulting gyroscopic 

force appears to push on the RIGHT side of the prop disc, resulting in a yaw to the LEFT.  As your primarily instructor told you 

more than once: “Right Rudder!”   :-)  

This is in fact one of the very few things you really need to know about, before you fly say a Beech 18 with TWO three-blade metal 

props.  When you raise the tail, the nose will swing left and full right rudder won’t do much at that slow speed.  Don’t use brake 

on takeoff, even if you are an airline pilot taking off in a 787 at Munich (VN34).  What you do, is momentarily rotate your right wrist 

clockwise on the throttles, and use differential power to stay straight until your airspeed increases and the rudders gain effectiveness.

You need to do this instinctively, and this is why pilots should solo on tailwheel aircraft - they learn to automatically control yaw, 

from day one, without even thinking about it.  Differential power should not be foreign to piston twin engine pilots - this is how piston

twins are turned during taxiing.  Please don’t use just the brakes!

So. When you raise the nose for landing, you are pushing on the BOTTOM of the prop disc and the resulting 90 degree delayed

force appears to be pushing on the LEFT side of the side (with western piston aircraft engines) resulting in a yaw to the RIGHT.

Hundreds of times, as a tailwheel instructor with a metal blade prop, I have sat in the right seat and watched the student get 

“behind” the aircraft (the cause of many aircraft accidents) on final and flare - correctly - at the last second to the three point 

attitude.  He thinks he salvaged the delayed flare, but unfortunately the rapid nose pitch up, yaws the aircraft right and we 

touch down in a 5 degree crab and off we go to the side of the runway.  Unfortunately you cannot tell a student to simply 

“think faster” - he is pedaling as fast as he can.  Practice is required.  Lots of it.  I tell people, my landings got better after

the first ten thousand.

Tangential Pro Tip:  Always touch a taildragger down, aligned perfectly with its direction of travel.  If you do so, the aircraft

(if the landing gear isn’t bent from a previous ground-loop) will move straight down the runway with no input from the pilot.

It’s not stable by any means, like a broom balanced vertically on top of your finger, but in the absence of any perturbations,

it will continue to stay there, even rolling down the runway at very high speed.   If you land a taildragger in a crab, you have 

created a directional problem which you need to immediately solve with quick feet on the rudder pedals.  I should mention 

this is true for only dry pavement or concrete, where the tires have lots of traction.  It is far easier to land a taildragger on 

grass or snow or ice or gravel for this reason.  Oddly this is never mentioned.

This has implications for a wheel landing in a taildragger.  With a metal blade prop, the tail must be lowered very slowly 

afterwards to allow you to control the resulting yaw to the right, with your feet.  If you have a strong crosswind from the right, 

the combination of the two can cause an expensive (ground-loop) problem.  But if you have a wooden or composite blade 

prop, you can raise or lower the tail during takeoff and landing, with impunity.  And I know that, just from looking at the front 

of the aircraft before I climbed in.  N.B.  my Beech 18 “checkout” consisted of one of my best friends, Freddy Cabanas telling

me all I need to know to fly a Beech 18 was (1) lock the tailwheel on takeoff, and (2) have a good left brake.

Back to pitch-yaw coupling.  This is also seen during aerobatics.  Above, we have seen where pitching creates yaw.  In

aerobatics when we quickly yaw an airplane, we get a resulting pitch, with a metal blade prop.  If we do a hammerhead and 

apply left rudder at the top of the vertical line to pivot, the force we are applying to the RIGHT side of the spinning prop disc 

appears to push on the BOTTOM of the disc, pitching the nose UP.  If this is not corrected for, we pitch onto our backs during

the pivot to the left, and we enter the prettiest inverted spin at the top of the hammerhead.  The contest people call this the 

“hammerspin”, it is so common.  Again, with a wooden or composite blade prop, this effect is greatly reduced and minimal 

(or no) forward stick needs to be applied during the pivot to keep the aircraft vertical.

Note that during aerobatics, the pitching and yawing during tail slides, torque rolls, tumbles and aggressive spins can

be so powerful, over time it will break the crankshaft and it will depart the aircraft in flight.  Again, this is generally ONLY

seen with metal blade props.  Wooden and composite blade props are much, much easier on your crankshaft, if you want

to fly these violent aerobatic maneuvers.  Oddly there is no regulatory or manufacturer paper on this, so caveat emptor.

One last thing I should mention: pitch-yaw coupling is also a function of engine (prop) RPM.  The faster the prop spins, the

more pitch-yaw coupling you will observe.   The slower the prop rotates, the less pitch-yaw coupling you will observe.  Because 

I am extraordinarily lazy, in a hammerhead pivot I will pull the throttle back from full to half after I apply full left rudder and the 

pivot begins.  Once the aircraft comes off vertical, the engine knows where the surface of the planet is and it will try to go to 

it, nicely establishing your vertical downline all by itself.  Also, your pivot radius is noticeably tighter with the reduced power, 

something I learned after doing hundreds of formation hammerheads - me reducing the power, and my father Tim not reducing 

the power.  A tighter pivot is aesthetically pleasing and makes better smoke, in my opinion. 

Here’s something I’ve learned over the decades of doing aerobatics:  at slow speeds - like nearly zero at the top of the vertical

line for a hammerhead - the effects of the wildly spinning prop - torque, slipstream, etc - completely overpowers the totally 

ineffective flight controls, which don’t do anything at zero airspeed.  The tail wags the dog.  So reducing power when you are 

in this condition, makes your life much easier.  Like instinctively learning to control yaw, learning to automatically reduce power 

in unusual attitudes (and trailing the flight controls) is very useful.  It really helps your spin recovery.

—

acboyd@gmail.com  Oct 2026