Coping with significant crosswind

[facthunter]

We are talking real figures here. I would always see it relating to a max crosswind COMPONENT, and you are taught to calculate that, for any particular wind.

 

I guess once the figure is in the book it applies, but if you arrive somewhere and the component is over the specified figure you MAY have to land. We ALL know that we should take enough fuel for an alternate where the forecast wind is above the component allowed, but forecasts are not infallable.

 

The main thing is not to muck it up. If you bend the plane, you are not only out of pocket, you might get hurt , seriously, even.

 

You can always be unlucky and encounter a gust that is beyond the ability of you and/or the plane to handle even when things look easy.

 

You may not want to land at the recommended crosswind limit because you are not happy to do it at that time and place. ( The wind may be gusting , or the runway may have water on it).

 

You may elect to regularly land a plane you are very familiar with at over the book x/wind limit, as you have found that the stipulsted limit appears to be " conservative". but you take a extra risk where insurance cover might be affected, and you are relying on your experience and skill being equal to the task

 

Some pilot had to make an assessment of what speed would be appropriate for perhaps the "average" pilot to handle safely, and there would be a requirement for that to be "demonstrated". This is a judgement not a calculation, like the Max AUW (structural) or the indicated stall speed at a certain weight and CofG, which are precise determinable figures. A crosswind limit is not really like that. More judgement is required in applying it. Nev

 

 

[kaz3g]

Merv I agree there would be nothing measurable to be gained by sitting on one corner of a 1000m strip and aiming for the other corner. Instead the intent would be to sit on one corner and aim off the side of the strip part way down.

Kaz it sounds like the real limit for you was taxiing with the cross wind not landing with it ;)

Just for the record, what I described was a landing at Mildura after coming from Broken Hill. The wind picked up from the north-west along the way and was significantly more than forecast being some 25-30 knots ie a x-wind component of more than 20 knots. My Auster has a demonstrated max of 9 knots (it has the "big" rudder) and was designed in the days of all over airfields.

 

The sealed part of Rwy 18-36 at Mildura is 30 metres wide. It has a well maintained grass strip at least as wide again either side of the sealed runway and all of it is within the markers. By taking an angle into wind across the whole width I landed with a ground speed of around 15-20 knots and had an actual ground run of not much more than 100 feet. I was certainly down to normal taxi speed as I entered the sealed section. My alternate, Wentworth, with an 18 metre wide 17-35 was less of a proposition.

 

After touching down I continued at that cross-angle until I got to the east-west taxiway A (the first exit) when the real trouble occured and the starboard wing wanted to lift while the tail wanted to swing to port even though I was partially sheltered by the airport infrastructure at this stage. Auster brakes are mechanical and not real good.

 

I certainly wouldn't take off in those conditions but I think it perfectly reasonable to use what airstrip there is to effect a safe arrival rather than have a white line fixation and come to grief.

 

Oh, and white lines are there to help those who can't fix on anything else to keep them straight. People who routinely fly TW aircraft off grass generally don't have that sort of assistance and learn to do without

 

kaz

 

 

[turboplanner]

The original Handling Notes for the Airtourer that Victa posted, and the original DCA Flight Manual for the Airtourer, stated 20 Knots demonstrated and there are a number of pilots, myself, included (and at night for good measure), who would include safe operations (ie no accident) at excess 20 Knots.

During my training, the instructor of the day, taking time off from reading up on theory for his CPL course decided to show me how to do a crosswind landing, the only one I was asked to do in the PPL syllabus.

 

He congratulated me on a smooth landing in the Cherokee adding "we were well over the maximum component of the aircraft"

 

And so I was released to fly and take up passengers.

 

Then I learnt all about gusts, variable winds, wind shear etc.

 

My point here is, yes you may be able to demonstrate it now and again, but if you want to promote it you have to be careful of what inexperienced pilots are absorbing as acceptable practice in ALL conditions.

 

Not having a go at you Narremman, but your post was a good example to talk about what some of the other "unconventional" pilots are preaching.

 

 

[David Isaac]

Getting an aircraft down into wind in extreme circumstances is only part of the solution as Kaz has pointed out. Her method in the Mildura example was and is perfectly acceptable given the extreme circumstances and no other options available. I would have done the same thing in something like an Auster with its great STOL performance. Whats more there was nothing illegal about her action under the circumstances she found herself.

 

But as Kaz said, getting down was not the problem, taxing crosswind in the Auster was a big problem. The tendency of tail wheel aircraft to weathercock into wind when taxiing can literally have you ground looping at taxi speed several times to get you where you want to go, hence the term Kaz used 'zig zag' back to the parking area. In extreme circumstances you may have to let the aircraft swing right through 360 degrees using the momentum of the swing to point the aircraft where you want it to go and then try again (it really helps if onlookers can assist by wing walking the aircraft as you taxi). Unless you have had experience in taxiing tail wheel aircraft in twitchy wind conditions it is all theory. As Kaz said she would not attempt to takeoff in those conditions but she was caught in unforecast high winds and had to land; and it can happen.

 

Back in the early 80s when considerably younger, I was flying a C172 from Boonah to Warnervale with a couple of mates and the forecast was reasonable; not long past Coffs Harbour and the tower called me to warn me with a 'Sigmet' for moderate to severe turbulence for the Central Coast area and a message from my CFI ... "Do NOT attempt to land at Warnervale ... I repeat do NOT attempt to land at Warnervale". With that the controller offered to find me an alternate into wind landing ground and promptly came back with a suggestion to land at Maitland (Rutherford) and that he had gained permission for me to do so. (These guys are fantastic help in time of need).

 

I remember landing into 026 at Maitland with full flap and full power on final in the 172 and I swear when we touched down we rolled barely 100ft and stopped. That was all well and good and a wake up call, so we taxied up the strip and turned left into the taxiway beside runway 023 back to the club house ... that was when all the fun began, and this was in a tricycle undercarriage not a tail wheel aircarft. The wind kept picking up the starboard wing and I had to keep swinging into wind using power, rudder brakes ailerons and elevators to keep the bloody thing stable. I remember it well, it was a good lesson, I must have swung into wind at least 10 times while we crawled up that taxiway before I got to the refuel area at Rutherford. We only had to wait about an hour for the wind to drop sufficient to return to Warnervale, where even that landing was a hoot into 020 with a brisk westerly.

 

Yeah ... we know ... you shouldn't be there in the first place ... but this is what happens when you are ...

 

 

[eightyknots]

Why do you think they paint a centerline on the runway? If we find ourselvs taking off in a wind that is so strong we need to do silly things like that, then we are asking for trouble. Directional control is the issue. Angling across a runway is not going to change the angle very much. I'm not gunna do the maths, but say you have a 1000 meter strip and it's 50 Meters wide, the angle you are creating would not be significant enough (IMHO) to change the crosswind compOnent very much . What it will do is reduce your safety margin by having less room to handle it should directional control become difficult. Runways to be certified must fit certain cryieria with regards to splay areas and runoff ( lateral) areas ......

 

The preceeding two posts come from two very experienced and respected instructors. Their posts give credence to that old adage: "there are no wrong actions, but certain different actions."As a comparative aviation layperson, one thing that I have observed in nearly 40 years of flying are that not all aircraft are not the same, and not all pilots are not created equal.

Here is a "lateral thinking" solution to the crosswind isssue. Instead of using the length of the runway, this pilot (in the first of three takeoffs) uses the width of the runway. This is only an option for STOL aircraft, no doubt:

 

 

 

[motzartmerv]

Lol thanx 80, that's what we have been discussing.:) nice vid . Xheers

 

 

[turboplanner]

I'll admit my trigonometry is rusty, but using Motz's hypothetical runway of 1000 metres length x 50 metres width:

 

If the crosswind component is 90 degrees to the strip, and you opt to roll diagonally from one side to the other into the wind, you'll only have changed the crosswind component by 3 degrees to 87 degrees in exchange for the being less than optimum from the side of the runway for 2/3 of the runway.

 

Doesn't look like a good risk/reward ratio to me

 

 

[motzartmerv]

Thanx tubz. Was hoping someone would do the maths. Pretty Obvious it's a pointless procedure. ;)

 

 

[David Isaac]

Guys,

 

Really ... get out of the theory basket ... It is only pointless if you were planning on using the whole bloody 1,000 metres ... who would need to do that?

 

If you are flying an aircraft that has reasonable STOL performance and there is a wide runway such as what Kaz described above, and a stiff crosswind, there would be considerable advantage at an angle if you only need a 100 or so metres to take off.

 

Work it out, if there is a stiff crosswind, turning into wind significantly increases the headwind component, which significantly reduces the takeoff run. Potteroo described this in an earlier post. It is a significant advantage in STOL types and there are plenty out there with STOL type performance ... perhaps not a good idea with a Jab mind you.

 

 

[turboplanner]

Ah, you caught me, couldn't be bothered calculating a theoretical roll to takeoff,

 

 

[naremman]

This thread, together with one other discussion on the site prompted me to reach for my copy of Cliff Tait's "Water Under my Wings". This is a veritable treasure trove for flying skills, honed by many years of delivering single engined aircraft from New Zealand, that includes in excess of 100 Tasman Sea crossings, all before the GPS.

 

Cliff devotes a whole chapter to weather.

 

One gem that I picked up was a simple means of calculating crosswind components mentally:

 

If the wind is 30 degrees from the centreline you have 90% of the wind strength as a headwind component, and the crosswind component will be 50% of the wind strength.

 

45 degrees will be 70% for headwind, and the crosswind will be 70% of the wind strength.

 

60 degress from the centreline will be 50% of the wind for the headwind component, and start loading the rudder up cos you will be getting 90% of the wind strength as a crosswind.

 

A fair number of us operate from uncontrolled airstrips where it is up to us determine the wind conditions from windsocks, windmills, trees, dust, smoke etc.

 

Just how accurately do we process this information when we overfly an airstrip and apply it to our approach and landing?

 

I found the following par in Cliff's book:

 

"Generally rough weather is nothing to fear............ Pilot incapacity, not aircraft inability determine the outcome of most weather-related accidents."

 

 

[boingk]

Landed the flying schools Gazelle in a 20kt+ crosswind a few weeks ago while I was logging time for my RAA pilot certificate. I was very glad to be back on the ground, and my best advice would be:

 

• Don't panic - treat it as any other landing.
   
   
  
• Don't be afraid to use power to hold yourself into the wind, the throttle is as much a useful control as anything else.
   
   
  
• Do flare to the windward side of the centreline - straightening up and coming down you'll drift with the wind onto it.
   
   
  

 

 

As an aside, we can't always predict the weather 100%, but make sure you check the advisory before takeoff and again before any other flights that day. It'll forewarn you at the very least.

 

Cheers - boingk

 

 

[motzartmerv]

David. I understand your views and I know that they come from substantial experience, but I hope I can offer a contra view without you wanting to have me shot. Lol.

 

The problem I have with the cross runway takeoff ( I'm only talking about takeoff, not landing) is as follows.

 

I realize that an angle across the strip in a STOL aircraft would change the xwind/ headwind components. We have 2 bantams online with our school, and I could argue that they are as STOL as it gets. If the wind conditions present on the day were such that I had to tell a student or a pilot to cross the strip and aim for the edge of the runway 100 meters ahead, I would be mad. If the conditions were such then the bantams would remain hangard. I could just see myself in court attempting to explain how I came to be recommending the procedure. Perhaps I have tainted view as our strip is narrow with cattle fences close to the strip.

 

What if the pilot thinks to aim at the side of the runway 100 meters along, but infact needed 120 meters? What then? Does he boot the rudder and turn with the wind to align with the runway? Secondary effects are strong at low speed so up comes the windward wing.

 

What if the engine fails just after liftoff? The aeroplane is not within the splay of the runway? Land straight ahead into what?

 

What if the takeoff is dodgy and a settling back onto the ground occurs? How many times have we all seen that happen?

 

If winds were strong enough to need this procedure one could expect turbulence. In a light aeroplane which is much more under the influenc of wind gusts etc, room to move is a valuable life saving commodity.

 

There are rules regarding a pilot assessing a potential landing/ takeoff area. He must calculate splay areas, toda etc. Someone using the technique in question is essentially using a NEW runway and by law would be expected to assess the area for haZards etc. These questions would be asked by the courts should I ever send a pilot or student out to perform this move an he/ she ends up injured or worse.

 

I'm sorry I've gone on a bit here. But to simplify my point, if the winds were such that a STOL acft needed to do it, then perhaps discretion would be the better part of valor.

 

Respectfully

 

Cheeers

 

 

[turboplanner]

I think you are making some valid points here, from a big picture perspective.

 

Many of the airstrips I've seen posted on here are in fact very narrow, some with power lines over them, some with close tree lines, and a few you could only describe as one way strips being used both ways.

 

The old military airfields sometimes have enough grassed area with smooth transitions free of infrastructure which might allow diagonal take offs and landings to meet legal requirements, but that has to be researched before getting anywhere near hitting the throttle.

 

But as we see so often here, someone will come up with a procedure which requires a strict set of circumstances, but not mention them and then we have low hours pilots putting that in their tool kit - like the one a couple of posts up which assumes the weather report you get before you take off will produce the same conditions when you land.

 

 

[68volksy]

All the theory is well and good but I'd like to look at it from the view of why there is a crosswind maximum component on aircraft. In my understanding it comes down to the amount of crosswind the aircraft can handle in the air which is basically a combination of controls versus profile of the aircraft. There's also a great deal of thinking that goes into the side load on the undercarriage i'd imagine however. Talk to Piper pilots and they'll tell you how much they love their wide low undercarriage in a good crosswind. Basically i'd be more concerned with the damage being done to the aircraft when operating at max crosswind more than i'd be worried about anyones ability to takeoff or land the plane.

 

I think you can put any aircraft down with a 30 knot crosswind if you have to but you'd put no faith in the legs holding.

 

 

[motzartmerv]

I keep seeing this "theory" word. For some this whole discussion may be only theoretical, but from the standpoint of being responsible for issuing certificates, training to a defined syllabus and authorizing solo flights for students, I can assure you my views stem from the "practical".

 

I do have an open mind all beit conservative, and I'm happy to be told otherwise from a practical point of view.

 

Cheers

 

 

[turboplanner]

68 Volksy, I'll give you one reason why - when you run out of rudder authority even when you're bending the pedal tube.......and you start to become a helicopter

 

That sure gets your attention.

 

Only problem is even in the 21st Century we still don't have enough visual data to measure the wind component vs the max AC rating accurately, particularly with intermittent gusting conditions.

 

 

[Jabiru Phil]

I read somewhere a while ago about a method of determining X wind strength on final.

 

It went something like... 10 deg off centre line = 10 kn X wind.

 

Does anybody remember the formular?

 

Phil.

 

 

[turboplanner]

I've been doing Trigonometry all day and my head's spinning, but that sounds like one of those grandma recipe things which requires calibrated eyeballs.

 

 

[Jabiru Phil]

New

 

I've been doing Trigonometry all day and my head's spinning, but that sounds like one of those grandma recipe things which requires calibrated eyeballs.

 

Guess that I didn't explain myself.

 

You are on final and lined up with the centre line

 

You are crabbing 10 deg determined by the compass

 

determine the X wind by the 10 deg factor.

 

It was in a forum or book about a couple of years ago but don't remember the answer.

 

Could have been 1 deg = 2 knots or 1 deg = 1 knot.

 

Assuming you have a compss that is.

 

Phil

 

 

[turboplanner]

You'll have a compass and probably can sight the centreline, but what about the maths and what about the variations in gusts and wind directions.

 

 

[motzartmerv]

Yes and approach speed would change the maths aswel. Slower speed means effected more by the wind so bigger crab angle needed.. Can't see how it could work..

 

 

[68volksy]

I suppose my point was more that I don't see maximums as really all that relevant. I'd rather show a little respect for the machines that we use - there's no need to go trying to rip the undercarriage from the fuselage unless it's absolutely necessary. I don't think you can argue that being able to take a 13 knot crosswind comfortably is really that much more difficult than being able to take an 18 knot max crosswind - only difference is the strain you're putting on everything. There'll always be some who push the limits of their aircraft but to me that's akin to running your car down the freeway in 2nd gear bouncing off the rev limiter - it's technically below the maximum but there's not many who'd argue it's good for the engine.

 

 

[Jabiru Phil]

Yes, it was assuming 80 knots

 

 

[Zibi]

NewI've been doing Trigonometry all day and my head's spinning, but that sounds like one of those grandma recipe things which requires calibrated eyeballs.

 

Guess that I didn't explain myself.

 

You are on final and lined up with the centre line

 

You are crabbing 10 deg determined by the compass

 

determine the X wind by the 10 deg factor.

 

It was in a forum or book about a couple of years ago but don't remember the answer.

 

Could have been 1 deg = 2 knots or 1 deg = 1 knot.

 

Assuming you have a compss that is.

 

Phil

Just ran a quick calc on this one and what you're looking for is:

 

x/w comp = sin (angle in degrees) x IAS

 

Since for low angles (blow 10 deg) sin function is almost linear, you can replace the sin (angle) with 0.017 x angle.

 

So for a approach speed of 50 kt and angle of 10 deg you'd end up with something like: 0.017 x 10 x 50 = 8.7 kt cross wind component or rather 0.87 kt per one degree.

 

At 60 kt it's about 1 kt per degree.

 

At 75 kt it's about 1.3 kt per degree.

 

But as TP mentioned this only works in constant wind and at low angles.