Landing in Crosswinds

 

Landing an aircraft is a precision maneuver we all must master before soloing – and continue that mastery throughout our flying careers.   The concept is to have the aircraft run out of flying airspeed just as the wheels are skimming the landing surface.   If this were easy, we wouldn’t find lots of books, articles and discussions of it.

 

I want to focus on crosswind landings since every landing is a crosswind landing.  In a few cases the crosswind component of the wind is so small as to have almost no effect – the ‘down the runway’ conditions.   The instructors look for days like this to have a student pilot execute his or her first solo flight.    We do this because landings are easier in these conditions.

 

To get very pedantic, the landing starts with the arrival at the Initial Point of the landing pattern.   While the entry, downwind and base segments of the pattern have a strong effect on the success of the ensuing landing, we are going to focus on the final segment of landing, from rollout of the base-to-final turn to the actual landing and rollout.

 

Start right

 

If we start ‘final’ in the right position at the right altitude at the correct airspeed and attitude, our chance of making a good landing is much improved.  So what are the measures of these ‘right’ attributes for gliders?   The right position is on the extended centerline of the runway.   The right altitude depends on the wind conditions at the time, but I like to position the aircraft ‘on the glideslope’ 150-300 feet AGL at 1000-2000 feet from the aiming point {Note: these figures are estimates.  We don’t look at the altimeter once we have passed the aiming point on downwind, do we?}.  The airspeed is 1.5 * Vso plus a factor for the wind conditions at the time.   We have set a standard of 55 kts for the Blaniks and the Lark on a typical day.   This is a little higher than the 1.5 * Vso, but it provides an added margin of safety above the stall.

 

So what happens if you roll out onto final and are ‘out of the box’?  The easy answer is ‘get back in’.  The practical answer is to make appropriate corrections to get back into position and stabilized well before the roundout point.  If you are only a ‘little bit’ out, small corrections are called for.   If you are a lot out, it will take big corrections and it is important to be reasonably aggressive in getting back into position early.   If you are still making big corrections close to the ground, the odds of a good landing are very small and the chance for damage or even injury or death are increased.

 

So to get back on track, let’s assume we are ‘in the box’ and there is a non-trivial crosswind.  The crosswind will immediately try to push the aircraft off the aircraft centerline.  So besides handling the glideslope using the spoilers (and maybe even a slip), we have to handle this tendency to depart from the centerline of the runway.

 

Two methods: crab and slip

 

There are two different methods for getting to roundout without straying from the centerline: the crab method and the side slip method.   The interesting fact is at roundout they both end up in the forward slip method.

 

Crab

 

In the crab method, we crab the aircraft into the wind to cancel the sidewind component’s effect.  So in essence we are looking out the side window at the runway and flying wings level down the glideslope.   The greater the crosswind, the greater the angle between the aircraft’s axis and the centerline of the runway.    This would be fine all the way to the ground, except that the landing gear takes a real beating when the aircraft lands sideways, the downwind wing has a tendency to slam down and this is a fine way to damage a perfectly good aircraft.

 

A side note that Frank can confirm is that the B-52 had crosswind gear.  The pilot flew the final approach in a crab. The aircrew adjusted the gear to be aligned with the runway. The crab was carried all the way to touchdown and the airplane landed not aligned with the runway.

 

Back on track,   the crab is a maneuver we do all the time.   We crab to maintain course during a crosscountry.   We crab on downwind to maintain appropriate spacing from the runway.   The crab is not a challenge in itself, the challenge is transitioning out of the crab and into alignment with the runway.  Since this occurs during roundout, the pilot is pretty busy at this point and this is one more additional task.

 

Slip

 

The side slip is the other mechanism for maintaining position on the centerline.    {Editorial comment:  the terms forward and side when applied to slips is very confusing and adds no information.  I personally think they are backward and I avoid their use.}  This is a crosscontrol maneuver and we all feel uncomfortable in crosscontrolled situations, at least we should!    Repeat after me, “if I stall the aircraft in a cross controlled configuration, I am asking for a spin.”

 

One of the good things about using side slips on windy days is that we are  also increasing our airspeed to provide a margin against gusts and windsheer so we are flying the approach at a speed well above stall.  

 

Mechanically, we point the aircraft down the centerline of the runway with the rudder and lower the upwind wing with the ailerons just enough to cancel the effects of the crosswind.   We carry this configuration all the way to touchdown.  The trick is to keep the functions of the controls in mind.   We use the rudder to point the aircraft, to keep its longitudinal axis  aligned with the runway centerline.   We use the ailerons to adjust the angle of bank to counteract the crosswind.    It is surprising how little bank is required to compensate for a substantial crosswind component.  As with every other aspect of flying, small gentle control movements are most effective.  Also we have to remember that ailerons induce adverse yaw, so large aileron movements will require compensatory rudder movements.

 

RUDDER: point the aircraft

AILERONS: set angle of bank to keep the aircraft on the runway centerline

 

If we fall into the mistake of trying to counteract the crosswind with the rudder, we will not only fail, but we  will also use up valuable time and altitude.

 

We have to remember difference in control effectiveness with respect to the task at hand.  The job of the rudder is to maintain alignment and  the responsiveness of the aircraft to the rudder is very good, a little push and the nose of the aircraft moves at once.   On the other hand, countering the sideways push of the crosswind is a integrating function.   The aircraft is very responsive to aileron deflections, but it takes a while for the effect of the changed angle of bank to affect the sidewise motion of the aircraft. 

 

If we are landing in a left crosswind and find ourselves to the right of the centerline, we increase our angle of bank to the left.  We must not only stop drifting to the  right, but begin moving left so we can realign ourselves with the centerline.  Accomplishing this realignment will require more bank than we would need to simply maintain the correct position.   Once we realign ourselves with the centerline of the runway, we decrease the angle of bank to just the amount needed to hold that  position.   This is a trial and error  process:   Set the angle of bank, watch for the effect, assess, make an adjustment, watch for the effect, assess, make an adjustment, watch for the effect..and so on.

 

Painting it on

 

The final portion of the landing using either the crab or the sideslip is really a sideslip.  If we are using a crab on approach, as we roundout we transition to a sideslip.  We use the rudder to align the aircraft’s longitudinal axis with the runway and the ailerons to lower the upwind wing  to counteract the crosswind push.

 

It is very important that the aircraft’s longitudinal axis be aligned with its velocity vector when the main gear  touches down.   Ideally, the aircraft’s velocity vector, its longitudinal axis and the runway centerline are all aligned.   However, we can land slightly across the runway, but we want the aircraft’s velocity vector and its longitudinal axis aligned perfectly at touchdown.  Fortunately the responsiveness  of the aircraft to rudder input makes achieving this alignment relatively easy.

 

So we grease the aircraft onto the runway and voila! we’re done.  Not so fast, buster!   We’re still rolling at about 40kts and we still have a crosswind blowing on the vertical stabilizer.   Whether we have done a wheel landing or a full stall landing,  it is very important to get the tailwheel down (OK, this is not so for the Grob 103 and the Genesis 2, both ‘nosedraggers’), but for the majority of the aircraft we fly, we will be much better off with the tailwheel on the ground helping us to fight the crosswind.

 

Keeping the upwind wing lowered into the wind slightly makes the rollout significantly safer and easier.   If the wind gets under the upwind wing, we have potentially lost control of the aircraft and may end up in a ground loop or worse.  The rudder still works on the ground and we’ll use ‘downwind’ rudder to keep the aircraft from weathercocking into the wind.   While it may be ‘cool looking’ to roll up to the flight line, we are better off controlling the aircraft and bringing it smartly to a smooth controlled stop.  As our speed bleeds off the relative wind across the control surfaces decreases and the controls lose their effectiveness.  That’s why we’ll see even the best pilots veer at the end of their landing rolls.

 

If you are rusty on your crosswind techniques, get with an instructor on a crosswind day and shoot a few landings.  Making good, safe landings is not an option.

 

Another good exercise for practice is to fly your aircraft perpendicular to the prevailing in a slip with spoilers deployed, maintaining alignment with a feature on the ground.   This may appear stupid…we’ll be burning up hard earned altitude at a prodigious rate.   Duh.   There are two times when this is useful.  The first is at the end of a great soaring day when you arrive back at GHSA with a couple of thousand feet to burn off.   This is a technique for getting down and improving your skill at the same time.   The other time is on a weak day when you are working on your thermaling technique.   After you have ridden a thermal or two to the top,  use this to get back down to the altitude where the thermal is inconsistent, hard to center and frustrating.   It will make a better glider pilot of you.

 

The Last Word

 

As with all aspects of flying, pilot judgment plays an enormous role in the overall safety of the flight.   Judging the TLAR during the pattern, judging the wind drift, judging how much extra airspeed to carry on a gusty day…   The biggest judgment is whether to fly or not.   On the first flying day of the year when there is a significant crosswind, the right judgment might be to wax the wings or hangar fly at the operations shed.   Or, grab an instructor and a two place and brush up on your skills.

 

If we undertake a flight in conditions  at the edge of our ability to perform, we are taking the first step in the error chain that can lead to further compromises that drive us into a position where the best possible result is a badly botched landing.   Converting this bad decision into a good one is not difficult if we consider the ultimate risks involved.   One really bright aviatior once said, “It is far better to be down here wishing we were up there, than to be up there wishing we were down here.”