On "maximum demonstrated crosswind capability"

[RFguy]

I have a question about what interpretation might be of this rather variable definition....

 

1) Is that the maximum crosswind for any pilot because of the finite  amount yaw the plane can develop at some airspeed ?

2) Is that the maximum for 'most pilots' of reasonable skill  (whatever that is ?!)

3) A  combination of both the above, in varying degrees .

 

How many aircraft run out of yaw (tail) ability at say their flapless landing speed (IE yaw ability limited) , and that becomes their "maximum demonstrated"

 

of course there are variables, like gusty and shearing versus  constant laminar flow X wind. Let's assume constant velocity , laminar homogenous air flow for the argument.

-glen

 

Edited September 22, 2020 by RFguy

[Roscoe]

The Jabiru J 170 Manual says that with average Pilot Technique, direct steady crosswinds of 14kts can be handled safely.

It also talks about variables such as gusts, terrain, and technique to use.

In some GA Flt Manuals, they talk about max demonstrated crosswind but these numbers are usually taken from test pilots under controlled conditions.

[SSCBD]

 

To me which I proceed on a  practical way, which is, it all depends on the exact time you are about to land. As you may get a gust which is way more than you can control to land so be ready for an instant go around, or you arrive at touchdown when the wind has dropped before the next gust. 

I have enough hours to understand what i am getting into - so be warned for new pilots it can all go wrong - especially in tail wheel aircraft which i have a lower risk for in cross wind limits.  

[Yenn]

This is exactly what it says. Maximum demonstrated crosswind.

Yhat means it is the highest cross wind speed that the plane has been demonstrated to handle.

It does not mean that you or I cand handle it in that wind, nor does it mean that is the highest possible wind speed it is possible to use. Just the highest speed someone has demonstrated,

[old man emu]

I would have thought that the value for Maximum Crosswind Capability would be a "never exceed" value, like Vne  and  engine "red line".

 

The value might have been demonstrated by a highly experienced test pilot, confirming the designer's calculations. However for the average joystick waggler, it is the boundary to a No Go zone. A prudent pilot would look at that figure and set a personal limit maybe 10% lower than the published value.

 

The whole matter of planting a crosswind landing is determined initially by calculating the crosswind component of the wind, and also the head wind component. It's a worthy exercise to look at the variables, headwind component and corresponding headwind component to see if a landing is indeed possible.

[kgwilson]

All of the POH manuals I have read quote the Maximum demonstrated crosswind component. 15 to 20 knots seems to be a common area. Mine is 15 knots and I have no problem handling that & if the windsock is correct even a bit more at times. With my low wing less than a metre off the ground in strong crosswinds a combination of crabbing & into wind wing down works well for me.

[RFguy]

thanks for the inputs. yeah I was just curious to whether it was what the test pilot came up with, or the limitation of rudder authority ?  (could have been both)  . might also make a difference I guess on which crosswind (left or right) , if there is any power on, prop wash etc yaw. I bet people develop better left or right X wind  skills also, like skiing or mountain bike cornering.

X winds next week. 🙂

Edited September 22, 2020 by RFguy

[planesmaker]

How to determine xwind from windsock? Not an accurate science. Next time your at a field ask around what pilots think the wind speed is from reading the windsock? Could be quite educational. 

[RFguy]

well the windsock will be velocity calibrated. (or should be). not just any old sock in the wind.  

Edited September 22, 2020 by RFguy

[Downunder]

I've landed far in excess of my max cross wind rating. Basically because I had to...

I don't think any excessive forces were put on the aircraft as I was landing and slowing down.

What I did find out is that at a certain (declining) speed at max rudder deflection you lose the ability to remain straight.

At this point I was well and truly in the landing "roll out" with the mains on the deck.....

Thinking quick, as I started to weather cock, I pushed the elevator forward putting the steerable nosewheel on the deck and "drove" the aircraft back straight as I slowed to taxi speed.  

 

 

[SSCBD]

1 hour ago, RFguy said:

well the windsock will be velocity calibrated. (or should be). not just any old sock in the wind.  

RF -You are being tooo rigid - For example Whitsunday airstrip has a windsock at each end of the runway. 

Many at time both show opposite  wind direction. 

You also get an idea of wind strength with a wind sock -BUT what about a gust after you checked the wind sock 15 seconds ago - strength now has changed. 

Edited September 22, 2020 by SSCBD

[RFguy]

good points SSCBD. 

Downunder, that's a good story. you found the rudder limits- they do exist of course. And really your comment is what my original question was all about.  The comments of others is useful -  that the demo Xwind speed is likely the upper percentile  of what you yourself might handle.... Might fly tmw. see what the wind does, otherwise it will be sunday, monday. - GLEN

Edited September 22, 2020 by RFguy

[ClintonB]

Buy or borrow a large enough paddock To land in all directions just like some of the WWII fields, takes all the hassle out of it.😁

[Old Koreelah]

13 minutes ago, ClintonB said:

Buy or borrow a large enough paddock To land in all directions just like some of the WWII fields, takes all the hassle out of it.😁

Some of our farmer pilots might tell you the cost in (lost revenue) of leaving a strip of paddock uncultivated Is considerable. 

Who can afford a whole paddock?

[IBob]

The Savannah manual gives max crosswind as 26kts (which is only just short of the quoted full flaps stall speed). I can confidently say I am not going anywhere near that in the foreseeable future, and given the STOL performance of the aircraft, have been advised to land in whatever direction suits me, regardless of strip orientation, if crosswinds seem excessive.

[RFguy]

I just read through the Savannah VG POH. a versatile aircraft !!!! Nice deep chord also (1320mm) .  great CG range.

except USA book W&B calculated in ... pounds*meters .  LOL  . talk about come to metric kicking and screaming.

 

Wow she can fly slow. better be careful when say getting out of your Savannah and into your Cirrus SR20...

 

 

 

[facthunter]

MAX demonstrated X wind is usually when the plane is certified initially and if it's high enough generally is not revisited by the manufacturer. These figures are only an indication of what a competent pilot might safely achieve. It will always say (in the handbook (if it's any good) THIS FIGURE may be further REDUCED for water on the runway and wind gusts etc IE conditions existing that reduce your chances of doing it safely and they also include pilot ability. There 2 (TWO) limitations to consider. The Planes, and YOURS. Nev

Edited September 23, 2020 by facthunter

[old man emu]

It is usual practice when laying out an airfield with set runways, to align the runways with the direction that the wind blows most of the time. In the NSW most main runways are aligned roughly 25/07 or thereabouts. You can check for your own State.

 

The average hourly wind speed in Sydney does not vary significantly over the course of a year. It keeps within about 0.5 kts of 6.75 kts 

https://weatherspark.com/y/144544/Average-Weather-in-Sydney-Australia-Year-Round

 

Of course there are months when the wind could blow the hide off an elephant, but the direction in those months does not change from the average. 

 

What sort of wind direction and speed would the wind have to produce a crosswind component of 15 kts on a runway heading of 240 degrees, if the seasonal wind direction varied between 210 and 270? 

 

 

[RFguy]

you asking me ? 210-240 = 30, sine 30 = 0.5, so 30 kts at 210 or 270 will produce 15 kts Xwind on 240.... I do complex math for a living...

just remember 22.5, 30,45,60 from a standard triangles.... as you probably wont know the  wind any better than that.

 

in practice, there will be a known std deviation from the runway, that might give you some probability stats to work with that might help with your understanding yours  chances based on your total load....

 

Most planned runways are yes designed to be friendly.

However I see many farm and bush strips are orientated  in the only way they could get them in. 

 

 

I liked IBob's comment- fly it in whichever direction suits me !

 

[RFguy]

WHich brings me to another point / question.

If windsocks are 100% erect at 15 kts, and a majority of light aircraft might be capable of 12-24 kts, the fact that it saturates means you don't have all the information.

IE it might indicate >=15 kts full X wind, which for example might be at your skill and your plane's limit.....  but you dont know if it is 15 kts or 150 kts... 

I guess you could overfly the runway and estimate the wind from the drift from one end to the other. (yeah yeah I know some EFIS just tell you) 

 

[facthunter]

It's usual for the wind's freestream velocity to drop off a bit near the surface and you get continuous feedback by your drift and slip applied on final as to whether it's dodgy or not and you are maintaining the extended runway centreline on approach. Your ground speed and drift angle will enable you to determine XW component. You can have a good memory formula if you work it out for your plane if you prefer to do things that way.

 A highwing allows lots of into wind down positioning but eventually the rudder will probably be limiting and the FUNdamental orifice's pucker factor. On very lengthy fuselages your (plane's) nose may be well into wind of centre, for centreline considerations. Killing all lift on the ground roll, with spoilers is a big help not available with U/L's. NEVER allow the upwind WING to lift above the other and you can PIN a tailwheel on the deck with forward stick, if you have enough prop clearance but eventually the tail will have to fall as you reduce speed and you have to control the planes tendency to weathercock into wind, (some how). A tricycle Light aircraft will probably wheelbarrow if you try the  same trick unless it's nosewheel is set high and it normally sits noticeably tail high with normal loads when on the ground. You don't want much of the planes weight on the nosewheel . Landing on one wheel works fine in small stuff, although it seems a lot of pilots resist the suggestion . Nev

Edited September 23, 2020 by facthunter
clarity

[IBob]

1 hour ago, RFguy said:

I liked IBob's comment- fly it in whichever direction suits me !

 

RFguy, I really should have given some context. Here it is:

I'm based in the Wairarapa in NZ, which is low traffic uncontrolled airspace with a lot of ag strips and the like. So you could say we have more latitude to perform nonstandard approaches and landings, should we have to, than in more highly trafficked areas.

Even so, I am reminded that the circuit can be a dangerous place: we had an in-circuit midair a year ago that killed two pilots.

Were I to be making a non standard approach (and I have never done so yet) I would be making it absolutely clear with multiple concise radio calls what I was doing.

In the meantime, I continue to practise my conventional crosswind landings, because mostly that is the safer thing for me to be doing.

 

As for the Savannah, the model now is the S, but the quoted max crosswind is the same at 26kts. I hope I never have to deal with anything like it: the difficulties would only start with the landing, the 'fun' then would be keeping it on the ground and more or less upright!

[RFguy]

Ibob, understood

 

Nev, you said " and you can PIN a tailwheel on the deck with forward stick,"

forward stick in the tail dragger to pin the tailwheel down ??????

Or do you mean you can hold the  traildragger mains hard on the ground with forward stick? that makes more sense, because you push the CoG  bias onto the mains.

Edited September 23, 2020 by RFguy

[IBob]

RFguy, one other important piece of context: the flight characteristics (very low touchdown speed) of the Savannah mean that in windy conditions there is minimal rollout, so far less likelihood of travelling any distance in the rough and ending up in a ditch. This is important, since what looks like clear flat ground from above can be anything but when you arrive on it.

I'm picking you will already have added this to the equation: clearly the best landing options depend greatly on what you are flying and where, as well as what the weather is doing.

 

[facthunter]

RF yes pin it on by nose down. There's a lot more to this. IF you brake fairly hard it will go on it's nose as you slow up when there's little air over the tail feathers. Older "SPEED" planes (30's) had small rudders and you had to get the steering from the well functioning tailwheel by holding the stick right back after a 3 point landing Nev