Cross-Controlling the Airplane

[M20F-1968]

I was reading the final report on the Minnesota crash and read the reports on the belief that the pilot was steering the airplane by rudder only.  

This led me to think of the times that we intentionally cross-control the airplane,  such as landing in a crosswind.   The only time  I intentionally cross-control is when I'm landing in a crosswind.   Speed brakes take care of any need to slip the airplane to lose altitude.  

 does anyone have any information about how far away from a problem we are by cross-controlling the airplane to land in 20 knot or better 90° crosswind?

John Breda

[201er]

Cross control in and of itself isn't a problem at all. It aggravates a stall and likely turns it into a spin. But if you maintain sufficient angle of attack, it won't stall. And when you begin flaring cross controlled in a strong crosswind, you're right over the ground so a stall is usually called a landing at that point.

Just be careful about wind gusts because those kinds of winds are often gusty. That can get you unexpectedly. Carry extra speed to combat wind gusts.

[midlifeflyer]

22 minutes ago, 201er said:

Cross control in and of itself isn't a problem at all. It aggravates a stall and likely turns it into a spin. But if you maintain sufficient angle of attack, it won't stall. And when you begin flaring cross controlled in a strong crosswind, you're right over the ground so a stall is usually called a landing at that point.

Just be careful about wind gusts because those kinds of winds are often gusty. That can get you unexpectedly. Carry extra speed to combat wind gusts.

Well, that pretty much covers it. 

[Ragsf15e]

I think the Minnesota crash just highlighted that cross control in imc might be disorienting, exacerbate small attitude disturbances, and could easily end up in a spiral dive or even spin (if you stall as well, but that’s a whole other thing).

As @201er  said, there’s no reason not to cross control in a crosswind landing or slip the aircraft in accordance with the poh (some have limitations with flaps down).

[Old Pilot]

Sounds like some people could use some taildragger time.

 

[carusoam]

8 hours ago, Old Pilot said:

Sounds like some people could use some taildragger time.

 

It also sounds like people can use some glider time as well…

Oops… that comes from aviation 102…

More training and experience will make you a better pilot…

Let’s say you are a tail dragger pilot…and you come to MS…

What would the high performance pilot get from Tail Dragger time?

(Hoping to boost Old Pilots post a count a bit…)

Best regards,

-a-

[carusoam]

let’s discuss when we cross control things intentionally…

1) Dumping excess energy, when we don’t have speed brakes…

2) When we transition from nose into the wind on final approach to aligned with the runway’s centerline, during a strong cross wind…

 

Avoiding a cross controlled stall is very important…

3) In the first case keep the nose low while balancing rudder with aileron inputs… 

4) In the second case the cross controlling is only occurring close to the ground, a transition from weather vaning to a slip is only a few moments long…

5) There aren’t many reasons to have an extended approach with cross controlled inputs… we used to carry a slip from miles away… this exposed us to a nose level, cross-controlled situation, that can turn dangerous as airspeed can bleed off faster than expected…

 

What’s really important…

6) How we enter and exit the cross controlled situation…

7) These aren’t full, fast, snap inputs… smooth and slow are the order of the day…

8) Don’t let your feet slip off the pedals…

9) When near the stall speed, we can induce one wing to stall by hitting the rudders full and quickly…

10) the relative speed of the wing tips is interesting, one speeds up, the other slows down…

11) The slow tip may fall below stall speed as the airflow gets disrupted…

12) What is the stall speed of the plane if it is in a bank, but not pulling Gs, like in a slip..?

13) Oddly, the accident that initiated this discussion… discusses using rudder only to adjust heading to stay on the VOR/ILS path… this is a technique used for a couple of degrees adjustment, not steering the plane around the sky… on scale, not off scale…

Using automation to keep things coordinated, or hand flying and keeping things coordinated… are both good ideas…

Having the plane stall on approach in IMC…  must have lost significant airspeed before the rudder use exacerbated the following spin…pull.. wings depart… sadness.

 

 

This gets more important the closer to the traffic pattern we are… as we are getting closer to stall speeds as we get closer.

PP thoughts only, not a CFI…

full respect for the lost airmen is intended… in case I missed something while typing…

Best regards,

-a-

 

[A64Pilot]

Tail dragger time teaches you what to do with your feet, runway alignment is critical with a tail wheel airplane, nose wheel aircraft allow you to be sloppy, so most get sloppy.

I explain tailwheels like this.

Next time you’re at the Supermarket take the shopping cart and pull it from the front. See how stable it is, how it follows your hand with no problem? 

This is a nose wheel aircraft, engine is pulling from the very front, steering wheel right behind the engine and the larger fixed wheels in the rear.

Now pull it backwards from the handle, engine is still in the front, but what’s changed is the big fixed wheels are right behind the engine and the small steering wheels are in the rear.

How stable is it now?

Tail wheels are called conventional gear because they came first. Tailwheel aircraft are lighter, simpler, usually faster and require less maintenance and can handle significantly rougher landing areas, often harder to see straight ahead when taxiing but require greater skill and more attention when on the ground.

What they do however is hone your rudder skills, keeping things in line becomes second nature, you sense better when the tail isn’t exactly behind you, because a landing without the tail precisely aligned can get sporty, fast. You can’t use the trim ball of course for runway alignment because it’s just a level. All you have is your senses, no instrument can help, pure stick and rudder skill.

The worst pilots to teach tailwheel to are Military fighter pilots, apparently they don’t use their feet much at all, no P factor etc. even the two engine fighters are actually center line thrust or maybe the computer controls trim I don’t know, but a simple tail wheel eats their lunch.

[A64Pilot]

Did the accident airplane stall and spin?

I thought he got into a graveyard spiral?

[midlifeflyer]

A taildragger definitely teaches alignment and rudder use. I pretty much suck at tailwheel (perishable skill) but I have incorporated a number of things from my tailwheel excursions when I teach slips and crosswind landings, proper alignment using rudder being #1. 

But I don't think tailwheel time is an absolute necessity here. The biggest problem I see is the one I think is reflected in the beginning of this thread - a basic fear of slips. Overcoming that can be done in any airplane.

BTW, #2 is not neutralizing the controls on touchdown - I explain that crosswind accidents don't happen in the air.

[carusoam]

45 minutes ago, A64Pilot said:

Did the accident airplane stall and spin?

I thought he got into a graveyard spiral?

I probably mis-described what occurred…

There was a spiral… as 1980 graciously posted the WAAS data from the last few miles of the flight…

And the wings would not have folded if they were stalled…  (how maneuvering speed gets defined)

 

What could cause the graveyard spiral in this case?

 

If you fall asleep while flying a Mooney with the wing leveler off…

the plane will gently lower the wing with a heavier fuel load in it… (depending on how big the fuel imbalance is)

as the wing dips, the plane starts turning towards the lowered wing…

as the turn continues… the wing goes lower, and the turn tightens…

 

as the turn tightens, the vertical lift, becomes more horizontal, and altitude is being lost at an accelerating pace…

 

But, being asleep is required for this to occur…as described above.

 

PP question only, not casting aspersions on the il-fated pilot…

Best regards,

-a-

 

[A64Pilot]

The cause of a graveyard spiral is from the inner ear, once you enter a constant rate turn the inner ear fluid returns to stasis, that is you perceive the constant rate turn as no turn at all, so if you stop the turn, you sense you have entered a spiral going in the other direction and will roll back into the turn, it is an increasing rate though, hence “Graveyard spiral”

Of course you can develop some very high speeds and G forces in a spiral, get into one and recovery has to be gentle or you will over G, add in the ground rush and anyone would over G. If you don’t roll wings level and only pull back on the Yoke, the spiral wraps up and you WILL over G

In flight testing to increase the main spar life limit from 29,000 hours to I believe 60,000 hours in the H-80 Thrush I had to pull 3.5G’s sustained for some number of seconds 5 or 10? as we had strain gauges on the spar, to do that at 10,500 lbs gross weight on an airplane with a 4,800 empty weight only way I could do that was in a spiral, stall speed at that weight and G load was right at VNE. It took a couple thousand feet to recover and two or three turns without over stressing the airframe.

If I only had 1,000 ft or less there would have been no chance, even if you pull it to idle

[A64Pilot]

Copied from Wikipedia

”The pilot mistakenly believes they are flying with the wings level, but with a descent indicated on the altimeter and vertical speed indicator. This usually leads to the pilot attempting to climb by pulling back on the control yoke. In a banking turn, however, the airplane is at an angle and will be scribing a large circle in the sky. Pulling back on the control yoke has the effect of tightening that circle and causing the airplane to lose altitude at an increasing rate, like water swirling in a drain or funnel. An increasing component of the lift being generated by the wings is directed sideways by the bank angle, not only pushing the airplane "upward" into the turn, but reducing the amount of lift which is holding the airplane up. At that point the aircraft is describing a descending circle or spiral, with a flight path that again resembles being in a funnel. In the ever-tightening, descending spiral the aircraft eventually exits the base of the clouds and/or hits the ground.^[1]”

[carusoam]

Hence the well taught…

Trust your instruments!!!

It must suck when you can’t trust your instruments in IMC… 

It is a bit discomforting when your eyes and inner ears are in disagreement…

Suddenly, two AIs isn’t enough… a third would be required for the tie breaker…

Best regards,

-a-

[Pinecone]

2 hours ago, A64Pilot said:

The worst pilots to teach tailwheel to are Military fighter pilots, apparently they don’t use their feet much at all, no P factor etc. even the two engine fighters are actually center line thrust or maybe the computer controls trim I don’t know, but a simple tail wheel eats their lunch.

Some military jets have yaw dampers, but most all airlines do.

The closest I got to a "student" killing me while I was instructing with a 24,000 hour 747 Captain.  He needed to get some where, an instead of getting checked out in our 150, he just had an XC lesson.

Dusk take off, he throws the power to it, and we turn 45 degrees to the left and head for the trees.  I quickly got a bunch of right rudder and barely keep us on the narrow paved runway.  Same thing on the return flight, but I was expecting it this time.  
 

It is amazing how much the nose will swing on a lowly 150 if there is NO feet on the rudder.

[Fly Boomer]

20 hours ago, Old Pilot said:

Sounds like some people could use some taildragger time.

 

Amen, brother.  Although, I'm trying to tamp down my old technique of coming in high and then slipping the brains out of the airplane.  A long time ago, I was taught 800-foot close-in pattern, chop power when abeam intended touchdown.  Worked okay in a couple of M20Es but in the M20K I asked Bob Kromer (test pilot) if it was okay.  His answer was "maybe, but I wouldn't do it".  'Nuff said.

[carusoam]

If you get the chance to see a Bob Kromer presentation… Do it!!!

He gave a great presentation at a Mooney Summit a couple of years ago…. 
 

Giving great insight on climbing out after T/O… Best speeds to use in case turning back, engine out, is needed/wanted…

Bob really knows Mooneys!!!

 

I bought my M20C right after he wrote a few pages about the M20C in the MapaLog….

It was a great what to look for, and how you know the M20C is right for you… when buying an M20C…, from an engineer’s point of view…

Printed late in 1999?

Best regards,

-a-

[M20F-1968]

Calculating the stall speed in a cross-controlled condition is a more complex equation than simply adjusting the stall speed for landing weight.

Can someone share the math?

In uncoordinated flight, it would seem that the stall speed at each wing tip might be different.  The angled linear cross-section of the wing seen by the wind at any point is much the same, but the functional area across the wing length is different (one side using more of the tip and one side using more of the root) This math is above my pay grade.

Do these hypothetical (or real) concerns minimize when you apply the rudder opposite to the aileron to line up with the runway (assuming the wind is lined up with the runway)?  Again, the math is above my pay grade.  

Any insights?

John Breda

[carusoam]

1 minute ago, M20F-1968 said:

Calculating the stall speed in a cross-controlled condition is a more complex equation than simply adjusting the stall speed for landing weight.

Can someone share the math?

In uncoordinated flight, it would seem that the stall speed at each wing tip might be different.  The angled linear cross-section of the wing seen by the wind at any point is much the same, but the functional area across the wing length is different (one side using more of the tip and one side using more of the root) This math is above my pay grade.

Do these hypothetical (or real) concerns minimize when you apply the rudder opposite to the aileron to line up with the runway (assuming the wind is lined up with the runway)?  Again, the math is above my pay grade.  

Any insights?

John Breda

Some People I would invite for that discussion…. @donkaye @midlifeflyer @KSMooniac

a collection of great CFIIs and an engineer…

Best regards,

-a-

[KSMooniac]

21 minutes ago, M20F-1968 said:

Calculating the stall speed in a cross-controlled condition is a more complex equation than simply adjusting the stall speed for landing weight.

Can someone share the math?

In uncoordinated flight, it would seem that the stall speed at each wing tip might be different.  The angled linear cross-section of the wing seen by the wind at any point is much the same, but the functional area across the wing length is different (one side using more of the tip and one side using more of the root) This math is above my pay grade.

Do these hypothetical (or real) concerns minimize when you apply the rudder opposite to the aileron to line up with the runway (assuming the wind is lined up with the runway)?  Again, the math is above my pay grade.  

Any insights?

John Breda

Very much above my skill level as well, and I even took (and got an A) Aircraft Stability and Control in college.   You're very much correct in your assumptions, and I have no idea how one could calculate such a stall speed, absent a LOT of wind tunnel and/or flight test data to build some curves.  Not only is the local angle of attack different for each wing due to aileron deflections, if you have any yawing movement, you'll have different local velocities at each wing tip (like a helicopter rotor in forward flight).  In a static steady-state slip, you might have a better chance at getting there, but you'll still need a lot of data as far as I can tell.  Traditionally, calculating a stall speed in straight-and-level flight is pretty simple, provided you have a correct lift curve and know the precise weight.  With an asymmetric lift distribution across the wing, none of that is valid any longer.

As @201er pointed out, it's best to stall in such a condition only during the actual touchdown!  I concur completely. 

[Fly Boomer]

46 minutes ago, carusoam said:

If you get the chance to see a Bob Kromer presentation… Do it!!!

He gave a great presentation at a Mooney Summit a couple of years ago…

I met him maybe a couple of years ago at a MooneyMax conference.  When Bob talked, people listened.  Reminded me of the EF Hutton commercial "When E.F. Hutton talks, people listen”.

[Ragsf15e]

33 minutes ago, M20F-1968 said:

Calculating the stall speed in a cross-controlled condition is a more complex equation than simply adjusting the stall speed for landing weight.

Can someone share the math?

In uncoordinated flight, it would seem that the stall speed at each wing tip might be different.  The angled linear cross-section of the wing seen by the wind at any point is much the same, but the functional area across the wing length is different (one side using more of the tip and one side using more of the root) This math is above my pay grade.

Do these hypothetical (or real) concerns minimize when you apply the rudder opposite to the aileron to line up with the runway (assuming the wind is lined up with the runway)?  Again, the math is above my pay grade.  

Any insights?

John Breda

Go out and stall it in a slip.  Oh wait, did I say that?!  Yes, take a cfi if you want, do it at 8,000’, sure, but try it.  Both left and right.  I’m not saying spin it, but you can recover at the buffet or at the break and not spin.  You will gain a lot of knowledge about what it will take to actually stall in a slip.  It takes effort.

Release back pressure, opposite rudder.  You will end nose low, but won’t spin.  
 

Flame suit on.

[KSMooniac]

Thinking about John's question a bit more, perhaps there is an academic way to get close to calculating a stall speed in a slip/cross-controlled orientation using handbook data.  If the airfoils are known across the span, AND you have lift curves for each airfoil with aileron (and perhaps flap) deflections, you could build a spreadsheet by discretizing the wing into smaller chunks (say 6" wide strips) going from tip to tip to calculate a lift distribution.  Sum the total lift, and when it drops below the weight...you'll have a stall.  This would be a fun problem for an engineering student that has more time than I do.    This method would have to neglect any dynamic effects and likely assume normal/perpendicular airflow relative to the wing span, which isn't entirely true either in a slip, but it might get close.

[carusoam]

2 minutes ago, KSMooniac said:

Thinking about John's question a bit more, perhaps there is an academic way to get close to calculating a stall speed in a slip/cross-controlled orientation using handbook data.  If the airfoils are known across the span, AND you have lift curves for each airfoil with aileron (and perhaps flap) deflections, you could build a spreadsheet by discretizing the wing into smaller chunks (say 6" wide strips) going from tip to tip to calculate a lift distribution.  Sum the total lift, and when it drops below the weight...you'll have a stall.  This would be a fun problem for an engineering student that has more time than I do.    This method would have to neglect any dynamic effects and likely assume normal/perpendicular airflow relative to the wing span, which isn't entirely true either in a slip, but it might get close.

That would require somebody that knows math and aviation at the college level…

Let’s see if @aviatoreb would know anyone with insight on that subject…. (Mathematics of stall speeds during a slip…?)

Best regards,

-a-

[A64Pilot]

2 hours ago, M20F-1968 said:

Calculating the stall speed in a cross-controlled condition is a more complex equation than simply adjusting the stall speed for landing weight.

Can someone share the math?

In uncoordinated flight, it would seem that the stall speed at each wing tip might be different.  The angled linear cross-section of the wing seen by the wind at any point is much the same, but the functional area across the wing length is different (one side using more of the tip and one side using more of the root) This math is above my pay grade.

Do these hypothetical (or real) concerns minimize when you apply the rudder opposite to the aileron to line up with the runway (assuming the wind is lined up with the runway)?  Again, the math is above my pay grade.  

Any insights?

John Breda

Yes the downwind wing will stall first.

But here’s the thing, I don’t know about you but if memory serves in a crosswind landing until very short final the ball is centered, aircraft isn’t of course, but I don’t cross control until about the landing flare time. If you want to slip all the way down just keep speed up a little.

In doing Certification test flights on the Thrush, one thing I had to check for was “rudder lock”

http://heli-air.net/2016/02/25/rudder-lock-and-dorsal-fins/

The Thrush, like most tailwheel airplanes has an unusually large rudder, so much so that at 1.2VSO you can actually get the airplane so sideways that the rudder will lock into position, that is to say that all rudder pressure disappears and you can take your feet off of the pedals and the rudder will stick at full deflection. On the Thrush an opposite push will unlock it and normal rudder pressure is back. You basically stall the rudder.

The FAA determined that although she will lock, that’s it’s so far uncoordinated that it will never get there in any normal flight.

The 550, we had to put a Dorsal fin on because it locked bad due to its increased frontal area.

I mean honest to God it was just like doing a lateral hover in a helicopter it was so sideways at 1.2 VSO and she didn’t stall, this was at empty weight by the way.

Point is that while I know of no simple way to compute stall speed in a cross control, apparently it doesn’t go up as much as say G loads take it. From memory 2G raises stall speed by 1.4. So if level unaccelerated stall occurs at 60, then at 2G’s it’s 84.