Crosswinds

[JKawai 7]

Did a couple of approaches into EGNS tonight with crosswinds ranging from 19-23kts. Probably too high (although did some very quick research online and I found the aircraft should be capable of this? Unless my sources are dodgy) - but both times on landing my aircraft veered off INTO the wind (not with it). 

Did some tests doing takeoffs in various degrees of crosswind, and I found that above about 15kts crosswind the aircraft veers off the runway into the wind rather than with it.

Anybody got any info on why this phenomenon may be, and what the crosswind limits are for this A/C? Is the wind hitting the tail and spinning the aircraft......??

I'm using ActiveSky P3D4. 

Edited August 1, 2018 by JKawai

[skelsey 765]

34 minutes ago, JKawai said:

Is the wind hitting the tail and spinning the aircraft......??

You got it. The fin is a great big sail on the back of the aeroplane with a long moment arm - the result is that on the ground all aircraft of conventional design will behave like a weathervane and try to turn nose in to the wind. 

In a small aircraft like the King Air I would probably do my best to get the nose pointing as straight down the runway as possible at touchdown - assuming you are approaching in the crab, as you get to the flare look at the end of the runway, use the rudder to smoothly (squeeze, don't kick!) bring the nose around so it is aligned with the centerline and at the same time smoothly feed in opposite aileron to lower the in-to-wind wing and thereby keep the aircraft tracking straight down the runway.

It should not be a hurried or violent manoeuvre - keep it smooth and progressive so that you can coordinate the aileron and rudder input - if you apply the rudder too quickly and/or do not apply sufficient aileron the aircraft will drift downwind, and if you do not apply enough rudder the aircraft will still be pointing in to the wind when you touch down and once the tyres grip the aeroplane will want to go where it is pointing - ie off the side of the runway! Touchdown should occur on the upwind main wheel first, then gently relax the aileron just a touch to lower the other main wheel - then finally fly the nose wheel down. 1, 2, 3.

Most important of all - don't stop flying the aeroplane at the moment of touchdown! You must hold the rudder and aileron in throughout the ground roll and in fact as the speed reduces the controls will become less effective so you will actually need more and more - ultimately ending up at taxi speed with full in-to-wind aileron and as much rudder as required to stay on the centerline.

Max demonstrated crosswind for the King Air seems to be 20 kt from what I can find in a brief search - so your conditions were certainly challenging.

Edited August 1, 2018 by skelsey

[BlueStar 323]

Simon,

Use the rudder to keep the nose pointed down the runway, and the ailerons to hold it on center line.  Max demonstrated crosswind doesn't mean it can't be landed with more than 20 knots of crosswind, it just means that is the maximum the test pilots used for cross winds as part of the certification.  I flew U-21s for a while in the military and 20 knots is not even close to the crosswind limit. 🙂

 

[Chock 17,769]

4 hours ago, JKawai said:

Anybody got any info on why this phenomenon may be, and what the crosswind limits are for this A/C? Is the wind hitting the tail and spinning the aircraft......??

You are correct, the phenomenon is known as 'weathercocking', i.e. your aeroplane's tail surface acts like a weather cock does on top of a church steeple. You will still be be blown off course in the direction of the wind as gusts hit the big slab side of your aeroplane, and the air mass you are moving through is of course moving over the land too, but the tail of the aeroplane is such a large surface area that it will cause a weathercocking effect. This is true for almost every aeroplane type to at least some degree, but it can be very pronounced with some aeroplanes, for example, you can imagine how much a large airliner or something like a B-52 is going to be affected by the phenomenon with a massive tailplane sticking up into a wind gradient. This is in fact why large aircraft are often only chocked on the mains when parked in high winds, so they can pivot a bit on the ground if the tailplane gets blown about rather than the wind imparting stress on the undercarriage and the airframe via the tailplane if they are rigidly in place with chocks on all of the undercarriage.

As also pointed out on this thread, when aeroplanes are certified, as part of that process, they have to demonstrate their crosswind capability so a suitable set of numbers can be determined for inclusion the aeroplane's operations manual. This is why you often see the term 'maximum demonstrated crosswind' in such manuals, but of course if the weather never gets bad enough to be able to demonstrate a seriously high crosswind landing capability during the certification process, that can affect what ends up going in the manual as the demonstrated crosswind limit and it's almost always the case that aeroplanes can handle more than what is in their manuals. This is because engineers and test pilots etc are always somewhat conservative in saying what the limiting figures will be for an aeroplane they are developing, just to be on the safe side, because whilst a very experienced test pilot might easily be able to land an aeroplane type in a severe crosswind, the manuals, and the limitations listed in them, are geared towards what an average pilot could be reasonably expected to do.

Edited August 2, 2018 by Chock

[JKawai 7]

Wow... I did not expect to go to bed last night and come back to find such a comprehensive and helpful set of replies as this, thank you so much everybody!

One other question - this touchdown sounds like quite an accurate manouvre, and I find on touchdown there are so many things to do (props full forward, rudder, opposite aileron, flare, retard throttles) that as you say, I often get a bit panicky (with practise this will reduce); however part of me is wondering what flight yoke you are using? I'm using Saitek, are you? (In other words, is such accuracy achievable with Saitek?)

Going to have a practise now of what you described, many thanks...

EDIT: Actually seems perfectly doable on the Saitek, and your suggestion of opposite aileron has really helped maintain perfect control... thanks for that!

Edited August 2, 2018 by JKawai

[Chock 17,769]

Keep in mind that you often have to make quite large control deflections on landing since there is less control authority when the airflow over the control surfaces is reduced at landing speeds, so that's one occasion where the subtlety and precision of really expensive controllers is not really needed quite so much.

In other words, yeah, a Saitek yoke is good enough to do the job. By way of example, take a look at the end of this video of a DC-3 landing (from about the 13 minute point) and observe how big the control wheel deflections are just to get it to do fairly subtle corrections. At higher speeds you'd be ripping the control surfaces off an aeroplane moving the yoke about like that, but at landing speeds you really do have to move it that much quite often:

 

Edited August 2, 2018 by Chock

[JKawai 7]

Yes! Funny you should say that because after watching many Youtube videos of landings, and also having heard about what you just described, as I cross the threshold that's what I'm usually doing, making macrocorrections which translate to very little. So here it's getting the balance of being accurate not panicky like skelsey says  but I suppose also being positive. 

Edited August 2, 2018 by JKawai

[skelsey 765]

7 hours ago, JKawai said:

Yes! Funny you should say that because after watching many Youtube videos of landings, and also having heard about what you just described, as I cross the threshold that's what I'm usually doing, making macrocorrections which translate to very little. So here it's getting the balance of being accurate not panicky like skelsey says  but I suppose also being positive. 

Exactly right -- smooth and progressive but positive is exactly what I like to see. Many fall foul of either being very rough with the aeroplane -- resulting in not just an uncomfortable ride but also inaccurate flying as such sharp, aggressive inputs tend to destabilise the aeroplane and it is very difficult to properly co-ordinate the other controls as well -- or, at the other extreme, are incredibly tentative and almost reluctant to move the controls at all, with the result that they end up being rather flown by the aeroplane instead of the other way around! 

The general rule in any aeroplane (but especially as you start going up in size and inertia) is to make all inputs smoothly and progressively and give the aeroplane a chance to respond. Even when making a large input you still want to do so in a smooth and progressive manner. Alan's video is one of the better demonstrations of that -- quite often (both in FS and in real life) one sees people making all sorts of rapid inputs, the sum result of which at best is virtually zero and at worst results in pilot-induced oscillation ("I say Bloggs, it's jolly bumpy isn't it?"... miraculously cured by taking hands off!). Less is often more (but, as I say, avoid sliding towards the 'tentative' end of the scale).

In answer to your question about hardware -- I am using the Saitek Cessna yoke and I find it provides more than adequate control resolution for all phases of flight (provided one's control sensitivities etc are correctly set).

8 hours ago, JKawai said:

I find on touchdown there are so many things to do (props full forward, rudder, opposite aileron, flare, retard throttles) that as you say, I often get a bit panicky (with practise this will reduce)

I'm not familiar with the King Air specifically so Wilhelm or someone else might have some thoughts here -- but in general terms I would set the props full fine with landing flap selection at the latest (possibly even a little earlier) which does at least get it out of the way a little earlier in the approach so it's one less thing to worry about in the flare!

As you say though, practice makes perfect and the more you do it the more comfortable it will become.

As you may have figured -- obviously for a crosswind takeoff it is effectively the same drill but reversed: typically one can start the takeoff roll with full aileron in to the wind, using rudder to keep straight and gradually reducing the aileron input as airspeed increases; at the point of liftoff one then smoothly transitions from this cross-controlled situation (i.e. a sideslip) to a crab by smoothly releasing the rudder and aileron inputs, turning the nose of the aircraft in to the wind in order to maintain the extended centreline in balanced flight (slip ball in the middle).

8 hours ago, JKawai said:

Actually seems perfectly doable on the Saitek, and your suggestion of opposite aileron has really helped maintain perfect control... thanks for that!

Glad it helped!

[JKawai 7]

Cheers Simon!