Right turning tendencies

LifeAsBen

LifeAsBen

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LifeAsBen
While I was being grilled in prep for my CFI checkride this question came up: do tailwheel airplanes have the same turning tendencies as tricycle gear plane? To which I said, hmmmmmm. IDK

So, after a bunch of research here's what I think I've discovered. There's not a lot of info to be found when you google "right turning tendencies" so I'm wondering if others can validate this:

First, to keep things simple I'm only speaking about what occurs at or close to rotation (pitch change) and clockwise spinning props (as viewed from the cockpit).

When raising the empennage of a tailwheel a pilot pushes forward on the stick which requires the top of the spinning disk (aka the prop) to "pull" the rear of the plane up. But due to gyroscopic precession this force is deflected 90 degrees to the right which creates a left yaw motion.

Here's where it gets interesting, in a tricycle gear airplane when the pilot pulls back the empennage is forced down and the front of the nose of the airplane pivots up. This requires the bottom of the spinning disk (aka prop) to "pull" the nose up around the CG. But due to gyroscopic precession this force is deflected 90 degrees to the left creating a RIGHT yawing motion.

Am I right?
 
[By no means an expert]

I think the left turning tendency doesn't care where the third wheel is. A tailwheel plane is on two wheels before it gets to rotation speed and from there it's the same, RIGHT RUDDER while at high power and high AoA.

Won't be the first time I'm wrong, though.
 
LifeAsBen said:
While I was being grilled in prep for my CFI checkride this question came up: do tailwheel airplanes have the same turning tendencies as tricycle gear plane? To which I said, hmmmmmm. IDK

So, after a bunch of research here's what I think I've discovered. There's not a lot of info to be found when you google "right turning tendencies" so I'm wondering if others can validate this:

First, to keep things simple I'm only speaking about what occurs at or close to rotation (pitch change) and clockwise spinning props (as viewed from the cockpit).

When raising the empennage of a tailwheel a pilot pushes forward on the stick which requires the top of the spinning disk (aka the prop) to "pull" the rear of the plane up. But due to gyroscopic precession this force is deflected 90 degrees to the right which creates a left yaw motion.

Here's where it gets interesting, in a tricycle gear airplane when the pilot pulls back the empennage is forced down and the front of the nose of the airplane pivots up. This requires the bottom of the spinning disk (aka prop) to "pull" the nose up around the CG. But due to gyroscopic precession this force is deflected 90 degrees to the left creating a RIGHT yawing motion.

Am I right?
Click to expand...
You are right...keep in mind that raising the nose on a taildragger creates the same right yawing motion that it does on the nosedragger.

so the answer to the question in your oral prep is “yes”.
 
LifeAsBen said:
When raising the empennage of a tailwheel a pilot pushes forward on the stick which requires the top of the spinning disk (aka the prop) to "pull" the rear of the plane up. But due to gyroscopic precession this force is deflected 90 degrees to the right which creates a left yaw motion.

Here's where it gets interesting, in a tricycle gear airplane when the pilot pulls back the empennage is forced down and the front of the nose of the airplane pivots up. This requires the bottom of the spinning disk (aka prop) to "pull" the nose up around the CG. But due to gyroscopic precession this force is deflected 90 degrees to the left creating a RIGHT yawing motion.

Am I right?
Click to expand...

Yes.

I think gyroscopic precession yawing to the left is more apparent in taildraggers, since the tail is often lifted more rapidly than the nose is lifted in a nosewheel when it rotates. The latter, in theory would cause a right yaw.

Anecdote: I learned to fly tailwheel in a Cub and later bought and flew a Citabria. Due to my tailwheel “expertise”, I was hired to ferry a Cessna cropduster - an AgTruck or AgHusky I think. With a single seat, no way to be checked out. On my first takeoff I raised the tail with the same authority I used in the Cub and Citabria, and nearly ran off the left side of the runway due to the gyroscopic precession - with 300+ hp about triple what I was used to. That taught me to be more “gingerly” when raising the tail going forward.
 
LifeAsBen said:
While I was being grilled in prep for my CFI checkride this question came up: do tailwheel airplanes have the same turning tendencies as tricycle gear plane? To which I said, hmmmmmm. IDK

So, after a bunch of research here's what I think I've discovered. There's not a lot of info to be found when you google "right turning tendencies" so I'm wondering if others can validate this:

First, to keep things simple I'm only speaking about what occurs at or close to rotation (pitch change) and clockwise spinning props (as viewed from the cockpit).

When raising the empennage of a tailwheel a pilot pushes forward on the stick which requires the top of the spinning disk (aka the prop) to "pull" the rear of the plane up. But due to gyroscopic precession this force is deflected 90 degrees to the right which creates a left yaw motion.

Here's where it gets interesting, in a tricycle gear airplane when the pilot pulls back the empennage is forced down and the front of the nose of the airplane pivots up. This requires the bottom of the spinning disk (aka prop) to "pull" the nose up around the CG. But due to gyroscopic precession this force is deflected 90 degrees to the left creating a RIGHT yawing motion.

Am I right?
Click to expand...

Yup. The initial nose down force gives some left turn tendency. Although you wouldn’t do it, same thing would happen in a trike if the nose gear would allow enough ‘compression’ to let the nose down much. Of course maybe followed by a complete cessation of gyroscopic precession as the runway brings the prop to a sudden halt
 
A) It depends on which way the motor spins (there are several that spin the "other" way). And B) unless you are driving something really big, it doesn't matter. Just keep it straight. I don't recall ever noticing a tendency to go one way or the other when the tail comes up.
 
That's why I always teach it as "turning tendancies", not necessarily directional. You are progressing from rote learning to understanding why.
 
OP is right, but don't worry too much about it unless you're in a Mustang, Corsair, or such.
 
Capt. Geoffrey Thorpe said:
A) It depends on which way the motor spins (there are several that spin the "other" way). And B) unless you are driving something really big, it doesn't matter. Just keep it straight. I don't recall ever noticing a tendency to go one way or the other when the tail comes up.
Click to expand...

Yulp ... I have one of them wrong way spinning engines. Roll the power on smoothly and gently lift the tail. It behaves pretty well ...
 
LifeAsBen said:
While I was being grilled in prep for my CFI checkride this question came up: do tailwheel airplanes have the same turning tendencies as tricycle gear plane? To which I said, hmmmmmm. IDK

So, after a bunch of research here's what I think I've discovered. There's not a lot of info to be found when you google "right turning tendencies" so I'm wondering if others can validate this:

First, to keep things simple I'm only speaking about what occurs at or close to rotation (pitch change) and clockwise spinning props (as viewed from the cockpit).

When raising the empennage of a tailwheel a pilot pushes forward on the stick which requires the top of the spinning disk (aka the prop) to "pull" the rear of the plane up. But due to gyroscopic precession this force is deflected 90 degrees to the right which creates a left yaw motion.

Here's where it gets interesting, in a tricycle gear airplane when the pilot pulls back the empennage is forced down and the front of the nose of the airplane pivots up. This requires the bottom of the spinning disk (aka prop) to "pull" the nose up around the CG. But due to gyroscopic precession this force is deflected 90 degrees to the left creating a RIGHT yawing motion.

Am I right?
Click to expand...

The answer to the question isn't a rote "yes" or "no response", to which an applicant has a 50% chance of getting correct. The answer is for the applicant to demonstrate comprehensive knowledge of the subject.

"Turning tendencies" may reflect the major difference in a tailwheel aircraft, where the CG is located behind the main wheels where, if disturbed from moving in a straight line it will continue to move off that straight line. That's the opposite of a nose wheel airplane where the CG is in front of the main wheels and if disturbed away from moving straight ahead, will return to that straight ahead direction. That's why tailwheel aircraft ground loop and nose wheel aircraft do not. Once the CG of a tailwheel aircraft gets outside the path of the main gear there usually won't be enough rudder to bring it back, and application of brake will just make it worse. In fact, you are usually past the point of no return long *before* the CG gets outside the main wheel track. In that case, the only thing that might save it is an application of power to increase rudder authority. The downside is that you'll also be dealing with torque that will either help or hurt you at that point.

On the other hand "turning tendencies" might refer to "torque", "precession", "P factor" (asymmetric disc effect, or slipstream effects.

1) Torque is torque regardless of tailwheel or nose wheel configuration.

2) Precession has been covered in prior posts, but the key thing to remember is that when you displace a spinning disc in one direction it will respond in the same direction 90 degrees later in the direction of rotation and the opposite direction 90 degrees earlier in the direction of the rotation. In other words, If you have a bicycle tire spinning clockwise on an axle in front of you and you tilt that axle so that the top of the tire moves forward, the axle will turn to the left.

You get the same result when you lift the tail of a tailwheel aircraft with a clockwise rotating propeller and the aircraft will yaw left. When you rotate on take off, the top of the propeller disk is moved backwards and the aircraft will yaw right.

In a nose wheel aircraft, you don't lift the tail, so you don't get the initial left yaw response, but you still get the right yaw if you rotate on take off.

In flight however, you'll get the same response regardless of landing gear configuration, and you need to be aware that the effects occur on all phases of flight, not just on take-off. For example, Sean Tucker does a double hammer head in this video:


The first rotation is done with rudder, but look carefully as he starts the second rotation. The aircraft is yawing left in the hammer head, and precession from that left yaw makes the aircraft want to pitch nose "down" (relative to the fuselage, not the ground) and for a double hammer head when the pilot runs out of yaw from the rudder, he stops correcting that nose down pitch tendency with up elevator and instead pushes forward on the stick so the aircraft pitches about 20 degrees "nose down" (about when it goes vertical the second time in the video). The propeller disc rotating at high rpm is displaced forward (using prop wash over the elevator to get the input energy to move the disc), and the resulting precession then converts that 20 degree pitch displacement into more left yaw to help the propwash on the rudder push nose around through another 180 degrees around to a vertical downline.

3) P Factor or asymmetric disc loading is also more noticeable in a tailwheel aircraft. When the tailwheel is on the runway the fuselage and the propeller disc are angled upward. That means the descending blade on the right hand side of the disc (when viewed by a pilot behind the propeller) has a greater angle of attack, and thus produces more lift/thrust on the right side of the propeller disc. The result is that the center of lift for the propeller is not at the propeller hub but rather several inches out toward the right hand side of the propeller disc. That asymmetric loading then creates left yaw. You don't have the same effect on the runway in a tricycle gear aircraft.

However, once again in flight you have identical effects regardless of gear type. For example in a high power, high angle of attack, climb, you'll have the same P factor in tailwheel or tricycle gear aircraft and at low airspeeds with less airflow over the vertical fin and rudder the effect will be very noticeable.

4) Slipstream effect, where the prop wash spirals around the fuselage and impacts the upper left hand side of the vertical fin and rudder is the same regardless of gear configuration. The most visible evidence I see of this in an aircraft with a narrow gear track is the increased number of bugs stuck to the inside of the left hand gear and wheel pant where they are thrown by the prop wash. You'll have almost none on the inside of the right wheel pant or gear.

That's what you need to be able to convey in the oral exam, but more importantly to students.

-----

And please, please, please DO NOT get your CFI, then spend 5 to 10 hours in a tailwheel aircraft getting a tailwheel endorsement and hang out a shingle as a "tailwheel instructor". There are far too many of those incompetents sitting at the peak of "Mount Stupid" on the Dunning-Kruger effect graph teaching pilots how to be really bad tailwheel pilots.

If you want to get a tailwheel endorsement so you can give a flight review in a pilot's own tailwheel aircraft and count it as PIC time, that's fine. But get a few hundred hours (actually flying, not just instructing) in a tailwheel aircraft before you decide you know enough to teach pilots how to fly one.
 
Larry Vrooman said:
The aircraft is yawing left in the hammer head, and precession from that left yaw makes the aircraft want to pitch nose "down" (relative to the fuselage, not the ground) and for a double hammer head when the pilot runs out of yaw from the rudder, he stops correcting that nose down pitch tendency with up elevator and instead pushes forward on the stick so the aircraft pitches about 20 degrees "nose down" (about when it goes vertical the second time in the video).
Click to expand...

You've got that backwards BTW, unless Sean was flying a Russian radial motor. With Lycomings, left yaw produces gyroscopic precession in pitch toward the canopy, or nose "up". That's why you use forward stick during a hammerhead to control the gyro effect that is trying to pitch you onto your back. The double hammerhead doesn't rely on a lot of gyroscopic force though, since they actually work better with light composite props than with metal props, even though the metal prop has a lot more gyro force.
 
RoscoeT said:
That's why you use forward stick during a hammerhead to control the gyro effect that is trying to pitch you onto your back.
Click to expand...

I’ve only done, and taught, very basic aerobatics. But I thought the forward stick in a hammerhead was due to the outside wing traveling faster than the inside wing. But I might be wrong - it’s been a long time.

If it’s precession causing the need for forward stick, would that not only apply in one direction? To the left if my mental model is processing correctly.
 
Gyroscopic precession: when you raise the nose, the nose feels a pull to the right. When you lower the nose, the nose feels a pull to the left. Same for both tailwheel and nosewheel.

On a nosewheel takeoff, you only get the *first* one. Now, gyroscopic precession is the weakest of the four turning tendencies, so you might not notice it amongst the others which all pull the other way on takeoff (to the left), and you'll just need right rudder for the whole ordeal.
On a tailwheel takeoff, you start with the nose already up, so first you lower the nose on the roll, and then raise it again. So you get the second one, and then the first one, during the takeoff. If you're like me, you'll feel this as a general sense of the airplane seemingly having a crazy mind of its own and needing to dance on the rudder a lot.
 
FastEddieB said:
I’ve only done, and taught, very basic aerobatics. But I thought the forward stick in a hammerhead was due to the outside wing traveling faster than the inside wing. But I might be wrong - it’s been a long time.

If it’s precession causing the need for forward stick, would that not only apply in one direction? To the left if my mental model is processing correctly.
Click to expand...

A couple fallacies in what you've stated. I'll address the "outside wing traveling faster" secondly. There are forces on two axes that attempt to move the airplane off the plane of the pivot and disrupt the figure - that is a pitching force toward the canopy and also a rolling force opposed to the prop rotation. The pitching force is a gyroscopic reaction of the pivot (yaw) input. Yaw the prop disc left, and you will get precession on the pitch axis toward the canopy, assuming the prop turns like a Lycoming. This is reversed for a Russian radial engine. This requires forward stick to control. Likewise, all tailwheel pilots know that if you pitch the prop disc forward abruptly on takeoff that there is gyro precession in yaw toward the left. It's all the same effect. You can even visualize rotating the airplane 90 degrees for any given movement of the prop disc, and get the same result.

During the hammerhead pivot, you also must apply aileron in the direction opposite the rudder pivot input. This is purely to keep the airplane from rolling off plane due to propeller torque. There is a widespread misconception that you must apply aileron because the "outside wing traveling faster" produces more lift. A proper hammerhead is done from a perfectly vertical attitude (zero lift axis). This means zero AOA. If AOA is zero, neither wing is producing lift no matter how much faster one may be moving than the other. If you did a hammerhead from a positive AOA, there would be a slight lift imbalance, but it would be very small considering how slowly the wings are actually moving. Gliders do hammerheads and have extremely long wings. Guess what, they require ZERO aileron input during the hammer because it's done at zero AOA and there is no propeller trying to torque the pivot. And they require no forward stick to control gyroscopic precession either, again because there is no propeller. ;)
 
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Thanks everyone for taking the time to reply. This has been very helpful!

@Larry Vrooman noted, will not hang out a shingle as tailwheel CFI. Already a real pilot, er tailwheel pilot :)
 
LifeAsBen said:
...due to gyroscopic precession this force is deflected 90 degrees to the left creating a RIGHT yawing motion.
Am I right?
Click to expand...

Yes, you are correct. Though the actual left-turning tendencies of the other 3 factors more than cancel out that slight right-turning tendency felt on single-engine, tricycle gear airplanes. Here's a great video that explains it perfectly. (go to 7:22 in)

 
Larry Vrooman said:
2) Precession has been covered in prior posts, but the key thing to remember is that when you displace a spinning disc in one direction it will respond in the same direction 90 degrees later in the direction of rotation and the opposite direction 90 degrees earlier in the direction of the rotation. In other words, If you have a bicycle tire spinning clockwise on an axle in front of you and you tilt that axle so that the top of the tire moves forward, the axle will turn to the left.

You get the same result when you lift the tail of a tailwheel aircraft with a clockwise rotating propeller and the aircraft will yaw left. When you rotate on take off, the top of the propeller disk is moved backwards and the aircraft will yaw right.

In a nose wheel aircraft, you don't lift the tail, so you don't get the initial left yaw response, but you still get the right yaw if you rotate on take off.
Click to expand...

This.

And no, when you lift the tail in a tailwheel aircraft the top of the prop does NOT pull the tail up. The angle of the elevator causes lift on the horizontal stab/elevator to left the tail.
 
I don’t think about it. I just let my feet take care of it.

My 180 is nearly 300hp, on the ground it sits at 13 degrees nose up. Like I said I don’t think about it, but I swear I need more right rudder when I bring the tail up. It’s coming up like 6 feet
 
Wagondriver said:
I don’t think about it. I just let my feet take care of it.

My 180 is nearly 300hp, on the ground it sits at 13 degrees nose up. Like I said I don’t think about it, but I swear I need more right rudder when I bring the tail up. It’s coming up like 6 feet
Click to expand...
Yup. Normal. There will be a bit of a swerve to the left if the prop is big and heavy and fast enough, and if the tail comes up quick enough. The prop acts as if it was pushed forward on the top of its arc, so it reacts as if it was pushed forward 90° to that, in the direction of rotation, or the right side of the arc, and it will try to turn the airplane to the left.

That's only one of the left-turning forces. There are three more. First, in a taildragger, especially, the prop's downgoing blade is at a higher AoA in the three-point attitude, placing the center of thrust off to the right a bit and pulling the nose left. Second, the propeller torque reaction, through the engine and mount, tries to twist the fuselage to the left, placing more weight on the left wheel and adding some drag there. Third, the propeller slipstream, due to the prop blades' high AoA, is twisting around the fuselage, especially at low forward speeds, and it strikes the fin on the left side and pushes it right. Nose goes left.

Lifting the nose to start flying will pull right, but that is usually a minimal angle change and we have so much right rudder in that we really don't notice it.
 
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There is a great discussion of this in the book The Compleat Taildragger Pilot Chapter 5 Takeoff’s, Torque—Revisited. It includes several graphs of the different forces as they change over the course of takeoff, and a comparison with tricycle gear. As a bonus there is an in depth discussion of P-factor in an appendix with lots of fun math and geometry.
 
Bottom line is you move the stick or the rudder or the throttle you gotta also move all of them again to get the nose to go where you want it to go. And then there's the wind, you can't write a book about this stuff or explain it with formulas. You just have to get in the airplane and fly it.
 
Wagondriver said:
I don’t think about it. I just let my feet take care of it.

My 180 is nearly 300hp, on the ground it sits at 13 degrees nose up. Like I said I don’t think about it, but I swear I need more right rudder when I bring the tail up. It’s coming up like 6 feet
Click to expand...

I would go back to whoever did you tailwheel training and ask for a refund. That should have been covered in your training.

YES, you will need more right rudder when you lift the tail. And the faster you lift the tail, the more right rudder you will need.
 
Pinecone said:
I would go back to whoever did you tailwheel training and ask for a refund. That should have been covered in your training.

YES, you will need more right rudder when you lift the tail. And the faster you lift the tail, the more right rudder you will need.
Click to expand...
Lighten up Francis.

He's just saying how most of us who have been flying tailwheels for a long time approach it - we don't sit there and THINK about what to do - we apply whatever correction is necessary.
 
I agree with you comment.

But the post I was replying to stated he THOUGHT he was experiencing it. And yes, he is, and that is a point in learning to fly a tailwheel aircraft. That there is a big change in rudder input when you raise the tail.
 
Pinecone said:
I would go back to whoever did you tailwheel training and ask for a refund. That should have been covered in your training.

YES, you will need more right rudder when you lift the tail. And the faster you lift the tail, the more right rudder you will need.
Click to expand...
Seriously?
Left turning tendencies were covered. However, the refund would be small, I was signed off in 1.8 hours. I was “the best student I’ve ever had”. I bought the 180 with a total time of 160 or so, started backcountry shortly after that. I hardly think a “refund” is due. the statement was partially in jest as someone’s post says they needed left rudder upon raising the tail.
 

NTSB:
"Analysis
The private pilot was taking off in the float plane from the lake's west waterway. The airplane
was on step, gaining airspeed, and the takeoff run seemed normal to the pilot. The airplane was
nearing takeoff speed, and proceeding directly down the waterway, when it encountered a right
quartering tailwind gust that lifted up the right wing and float. The airplane veered to the left
toward a steep bank, and the pilot was unable to correct the deviation with the rudder. He did
not feel that he could reduce power as he would slam into the bank. The airplane lifted off, but
the float collided with the top of the bank. The airplane cartwheeled about 160 degrees to the
left before coming to rest on its right side. It sustained substantial damage to the wings,
fuselage, and floats. The pilot reported that there were no mechanical malfunctions or failures.
Reported wind at the airport approximately 3 minutes after the accident was from 020 degrees
magnetic at 3 knots, with no recorded gusts.
Probable Cause and Findings
The National Transportation Safety Board determines the probable cause(s) of this accident to be:
The pilot’s failure to maintain directional control during takeoff."

You can see the float lift at 34 seconds in the video...
 
When the float lifted you can see the plane turn to the pilot's left. Don't understand why he wasn't further to the right during the take-off run ...
 
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