The wind knocked out of my sails today..

[Scoobster]

Today - I was flying into an airfield which is just on the edge of the North Atlantic Ocean.

The wind was 140/06/G 'Deep' (or what sounded like deep - not sure of the meaning in U.S Phraseology) - I went for runway 16 - based on the wind coming from 140 - but could not land the plane as I was getting bashed about a lot (Piper Warrior II).

Both approaches once the attitude was corrected the 'speed' crept up to 80 knots - keeping wings level was a challenge - attempted to crab into wind with aileron down and opposite rudder applied to keep the nose level with the center line - was also not happening today. A bad day at the office what seemed.

Haven't experienced these kind of winds back home in the UK -

1) The approach appeared flat each time I got the correct speed resulting in not being able to see the runway below me

2) Once the attitude was was corrected to see the runway- the speed crept up to 80-85 kts.

I called the go around and decided the 'know your limit rule applied' and left out of the circuit deflated - but alive. The ailerons on approach was also not maintaining wings level.

Not after a pat on the back or sympathy - but for extreme x-wind conditions I am just verifying that the following applies as was taught but perhaps this was too gusty for me at the moment which is why I canned the approach:

1) You crab into wind - in this case - towards 140 - SSE - aileron into wind and opposite rudder to keep the centre line.

I was happy with the call to abort and depart out of the circuit and had a bumpy ride back but it was a hair raising experience with that level of wind which changed to gusting - en route.

The U.S phraseology also appears to be non-ICAO standard such as 'Ill call your close left traffic' - instead of 'Ill call your crosswind' - Maybe it depends on the controller.

Scoobster

[piperboy84]

Sounds like a helluva rough ride you had there, well done !!

My method for xwind landing in gusty conditions at my home field (farm strip) is as follows:

1. Don't bother slowing down from cruise speed and basically fly a fast slightly wider patter with no flats all the way round to final while staying at pattern altitude.
2. Upon turning final crab into the wind ( side slipping this far out is too much work and it makes the pax woozy), ball park the glide slope start based on how the ground speed is looking.

3. Add half the gust factor or if you can't get an idea of what that is add 5mph to the airspeed.
4. With about 400 feet to go convert the crab to a side slip, verify you have the rudder authority to cancel all crab, if so continue landing with first notch of flaps at most, if you can't cancel crab with rudder you've got a healthy xwind so power in turn downwind and come back around and land across the runway.

Probably not for everyone but it works for me in the tail dragger will low xwind and short stopping capabilities.

[TowerDog]

.
1) You crab into wind - in this case - towards 140 - SSE - aileron into wind and opposite rudder to keep the centre line.


While crabbing into the wind your controls should be neutral, as in a coordinated flight.
As mentioned above, at 400' or whatever you prefer, lower the wing and use rudder to stay on centerline. Control glide path with power and stay 10-15 knots faster than usual, also less than full flaps.

Nothing in US phraseology about gusting deep.

[alex90]

I'll second Piperboy84,

Although I have a tendency, of slipping in from a bit further out just because I find it quite nice to start feeling the gusts (which normally) diminish as you get lower, allows you to know roughly how much rudder to put. The PA28s seem more happy when there is heavy x-wind when slipped rather than crabbed, especially when gusty.

I normally come in flapless (if runway length allows) as this would give me an easier ride. and I would normally come in at around 85kts in a warrior III. (remember that depending on your slip, and where your pitot is, you may either under-read or over-read).

I have found pax to be happier, when already really lumpy, to look straight ahead and seeing the runway in roughly the same place between the lumps, despite the discomfort of flying out of balance. (this only applies when already a really bumpy / lumpy day).

Good call on going around when not comfortable! I really appreciate to hear that! The last flight I took with BA, we landed at Gatwick (26) with 220/25G36 which admittedly is still within limits of an A320, despite being chucked around quite a bit, but we hit very hard the first time, well beyond the "chocolate boxes" as we were at about a 25 degree angle over those, and bounced 3 times on the runway before maximum braking and reverse thrust was applied. I would have much rather they had gone around to give it another go rather than risk their lives and our lives trying to "make it work". I think the above is knowing your aeroplane limit, and knowing your own personal limits as a pilot is also really really important. So congratulations there Scoobster! Very good decision making!

(by the way - to note - the pilots of air new zealand's A320 that we flew into Wellington from Auckland last August, was able to land runway 16 with 270/34G45, landing visually with a cloudbase at 1500' (flying the circuit which I recognised) much much smoother than the crew of the BA flight despite a rather short and very wet runway! So there is a lot to say about pilot currency, and pilot ability compared to just aeroplane limits).

Dont let this be anything other than a learning point, and remember that you did the right thing!

[Mungo Man]

Its been a while since I instructed on the Warrior but 80 kts sounds far too fast for approach in any wind conditions. At medium weights the plane stalls at under 50 kts. The POH says approach at 63 kts, slower for short field if appropriate. I found schools tended to push for 70 kts on final which only makes for deep touchdowns and long rollouts.

[Fly4Business]

A couple of questions and comments, trying not to be rude.

* What airfield was that, any special topography you were not familiar with?
* Did you feel well that day?
* 14006G?? for RW16 is only 20 degrees off and 06G is almost no wind at all for the cost, I would tend to say even far from x-wind, 24020G35 would be x-wind ;-) ...
* I prefer not so flat and steeper descent at gusty conditions to pass the turbulence faster.
* If attitude learned from windless conditions looked correct, it was wrong.
* Go around was the perfect decision, you did great!
* Did you stabilize approach on airspeed? If you don't see the runway it may have been correct for the ground speed.
* If speed increases when attitude corrected one of the two was wrong.
* The Warrior tends to like being slipped, although I prefer to crab in neutral and only push into alignment at a very late approach.

My resumé, you did everything perfectly well, but should consider doing some explicit x-wind exercises with a FI of your choice. Nothing wrong with training that for an hour or two.

[Pace]

Its been a while since I instructed on the Warrior but 80 kts sounds far too fast for approach in any wind conditions. At medium weights the plane stalls at under 50 kts. The POH says approach at 63 kts, slower for short field if appropriate. I found schools tended to push for 70 its on final which only makes for deep touchdowns and long rollouts

Hmm

Yes on calm days? In strong winds especially with windshear the normal rule of thumb is 1.3 Xs the stall in a given configuration plus half the gust factor.

I would question half the gust factor in all situations as you only know the gust figure at airport elevation 200 feet up on approach there maybe much stronger winds.

I have had occasions when I had seen plus and minus 25 KTS on IAS on approach. Ok not the sort of conditions most PPLs fly in but a consideration which needs to be taken into account on any gusting and windshear day.

Why should a higher than 1.3 Xs the stall in a given configuration make for a deep touchdown?

Surely thats a landing technique fault? 1.3 Xs the stall is purely a figure giving enough energy on a closed throttle to transition from a descent profile to a landing profile.
with an AOA indicator you could quite easily have a smaller margin while equally you could land using 1.4 or 1.5 etc.

We are conditioned to a traditional landing at or near the stall, holding off to touchdown near that.

In strong winds with gust and windshear the last thing you want in a strong crosswind is to be holding off

fly the aircraft onto the runway. Yes the speed will be higher but then if the headwind component is strong the landing run will be shorter and its a judgement on how limited the runway is and remember that landing an aircraft is not all about touchdown at the stall

Pace

[Genghis the Engineer]

I'm guessing you were flying a Warrior or 172?

Both of those the approach speed at MTOW is about 65 knots, plus or minus a bit depending upon model.

I'm also guessing you were lightweight - 1 POB, half tanks? So probably around 80% MTOW? That brings the approach speed down to about 58-60 knots.

The gust response in turbulence is calculated as TAS^2 / (wing loading x lift curve slope)

Let's just assume that TAS=IAS: it won't be, but you don't have any direct control over the relationship on a given day.

So, by (presumably) not trimming and controlling speed properly you allow speed up to 85 knots you've increased speed by a factor of 1.44, which squared is near as dammit 2.


So by having speeds that high, you've doubled the airframe response to turbulence. That would indeed give you something of a wild ride. Being too fast also means that the whole landing process lasts much longer whilst you get rid of all that

(Then throwing it away and going somewhere more benign was then excellent judgement, as is trying to learn from the event).



Incidentally, several people have repeated the common mantra of adding half the gust factor. I'm well aware that this is common advice, but I've come to believe that it's wrong - it doesn't work with the gust response equation I've quoted, and I've stopped using it myself for some years with no ill effects. Can anybody quote an authoratitative statement on this - preferably backup up by some maths and flight testing? I've yet to find one, and have come to conclude that - at least for our little aeroplanes - that it's just plain incorrect and seems to have just been made up by some FAA CFI one day and perpetuated.

G

[MrAverage]

At last someone I can agree with Pace.


Without wanting to start a thread drift, (and only referring here to nose wheel types) has anyone ever seen an airliner crabbing?


(I'm donning my bullet proof vest right now)

[Genghis the Engineer]

I don't fly airliners, but just searched for "airliner crabbed landing" on youtube, and found loads of examples.

G

[Pace]

Incidentally, several people have repeated the common mantra of adding half the gust factor. I'm well aware that this is common advice, but I've come to believe that it's wrong - it doesn't work with the gust response equation I've quoted, and I've stopped using it myself for some years with no ill effects. Can anybody quote an authoratitative statement on this - preferably backup up by some maths and flight testing? I've yet to find one, and have come to conclude that - at least for our little aeroplanes - that it's just plain incorrect and seems to have just been made up by some FAA CFI one day and perpetuated.

G I intend to agree with you but see it more of a statement that in windshear and gust conditions to need to carry more speed/energy above the stall speed how much depends on the shear conditions on the approach

I really have seen plus and minus 25 Kts on IAS. Ok In a Citation but taking that as an example the normal sort of VREF IS 105 KTS

You could fly the approach at VREF but we wouldn't normally! we hold 180 Kts, Gear at 5 miles coming back to 160 KTS until 3 miles then its full flap and depending on conditions aiming to be at VREF over the fence.

In that situation say holding VREF with plus and minus 25KTS You would be jumping from 80 KTS to 150 KTS not very clever
So IMO a gust factor has to be added but at 200 to 300 feet the wind maybe very different from the GIVEN wind at the surface and that has to be taken into account for what you add to VREF as well as headwind component and runway length

I landed in Ostend this week and we had a manageable 32 KTS 80 degrees off watched an AIRBUS landing behind us and he was well and truly crabbed down the approach

Pace

[MrAverage]

My mistake, what I meant to say was:


Has anyone ever seen an airliner not crabbing, i.e. using the wing down method.

[Genghis the Engineer]

That's an interesting question Pace.

Take the nominal 4 seat SEP - Vref=65, and let's say wind 25G36, which isn't all that unusual. If 65=1.3Vs, then Vs=50.

Into wind at a nominal 25 knots, keeping inertial groundspeed, then the airspeed will fluctuate from 65 to 76 knots, but shouldn't in theory go down.

Into wind at 36 which then drops to 25, it's more interesting. 65 will drop to 54 (briefly, the aeroplane will self recover speed due to static stability if this condition sustains and with the relatively low inertia of a light aeroplane speed will change much faster than in your Citation). That's certainly enough to get you into stall warning application.

The Citation with Vref=105, presumaby Vs ~ 105/1.3=80kIAS. So, not unlike my example above, +/- 25kIAS is nibbling the stall (and I suspect nibbling Vfe?), but with static stability sporting, rather than destructive.

All of which is very "fag packet" - one of these days I'd really like to take the time and some flying hours to try and study this properly.

G

[Genghis the Engineer]

Has anyone ever seen an airliner not crabbing, i.e. using the wing down method

Tristars used to land wing down IIRC.

G

[Pace]

G I would be interested to read your expert conclusions if you ever do that test )

I agree it is very Fag packet and probably more relevant to extreme condition flying.

All we have are runway surface winds and gusts readouts which as stated can be very different a few hundred feet up.

The other point to consider are bursts of air caused by terrain and localised which may even exceed the average approach gusts and shear.

Strangely this year has been many crosswind landings from my home base on top of a hill which experiences extreme down draughts to the landing at Ostend in fairly flat ground at sea level.

A few weeks ago I had to throw away an approach and divert with a strong crosswind but extreme shear and downdraught while at Ostend although the crosswind was strong the landing because of relatively smooth air was a piece of cake

Shear is far more demanding than crosswind itself and there is no formula other than to note and add the airspeed fluctuations to your VREF

[Danny42C]

piperboy84 (your #2),
...Sounds like a helluva rough ride you had there, well done !!......... Add half the gust factor or if you can't get an idea of what that is add 5mph to the airspeed...
We used to say: "Add five knots for the wife, and five for your Pension !"

Danny42C.

[Genghis the Engineer]

There's certainly no dispute that gusts, burble, windshear and the like exist and are a problem.

The dispute, in my mind - is exactly what to do about it. Usually the opinions of experienced pilots about what works are valuable, but equally there's often little science behind those opinions which means that they can occasionally be less than optimal.

There's never a shortage of research questions! One of these days. But in the meantime, I remain dubious about the "5 knots for the wife and kids" / "half the gust factor" thing, not least when the limited maths I have shows that flying faster increases the aeroplane's response to gusts.

G

[ETOPS]

Has anyone ever seen an airliner not crabbing

I flew Boeing 757s for 5 years in the 1990s. Crabbing or wing down were both approved and various crews had their preferred methods. As we were dual rated on the 767 (and could see both types in a working day) I restricted myself to crabbing as I didn't want the bill for a pod scrape on the '67 :uhoh:

The wingdown experts on the '57 used to achieve some alarming angles of bank, in very strong crosswinds, which I dealt with by closing my eyes :eek:

[Pace]

G can you explain in more detail what you mean by the graphs you have means that the control response increases with extra speed with gusts shear ?
I would think that was a good thing as obviously more speed means more control response and more available energy ?

On the day in question from the airport with severe windshear which a recently departed aircraft reported as such due to runway length I elected to add 10 Kts to VR and was glad I did as we experienced a severe wing drop soon after takeoff!

Whether FAA or the blasted EASA they must have used some technical detail in recommending 1/2 the gust factor for landing
Part of that will be more control authority
If you are recommending no speed increase over VREF regardless of conditions I am perplexed?
I would certainly not have liked to be a test pilot in the conditions I had with plus and minus 25 kts on the IAS flying the normal VREF
That would have put me at 80 KTS with less control authority! As I said not something I would like to try (( and hope to still remain flying in a straight winged Citation
My methods right or technically wrong have kept me safe in over 30 years flying

Pace

[Genghis the Engineer]

Getting a book off the shelf. Firstly my memory's crap - it's a V term, not a V^2 term as I claimed earlier.

Working in the normal plane, this shows in response to a sharp edged gust that the change in normal acceleration is...

delta_Nz = 0.5 x rho x V x (lift curve slope) x gust velocity / wing-loading.

(Intuitively, response will be much the same in the other axes.)

So high wing loading = low gust response, that we can all bear out with experience and just looking around at the world aircraft fleet. But...


The issue here is that whilst you're quite right and higher speed gives more control, that same higher speed gives the gust more to work with. Multiply aircraft speed by gust strength, and you get something linearly proportional to the aircraft's motion response.

So whilst the control authority should also improve - if it's adequate anyhow, you're giving yourself more to correct by flying at higher speeds. I know it's anti-intuitive, but the maths seems to work, and it seems to work also on the smaller aeroplanes I fly.

Regarding FAA and EASA - I've not yet seen any *science* from either justifying the "half gust" amendment to Vref. If I'm wrong - which is entirely possible and wouldn't be a first - I've not seen proof of it yet.

That you've not come a cropper using the method you have could mean one of a number of things. One is of course that I'm wrong - another is that there's enough margin in everything to mean that it doesn't matter as much as we think - another is that gust response and control authority scale about the same (which probably is true) that they pretty much cancel each other out.

G

[BEagle]

This nonsense of adding gust factor increments for light aircraft needs to be stamped out. It is totally unnecessary for low inertia, low wing-loading aircraft and the last thing you want to be doing in gusty conditions is fannying about in the flare because your approach speed was too high and the aeroplane is still flying whilst you move further from the trimmed approach speed and lose finesse as a result.

Unless the POH advocates a gust factor increment, just use the normal approach speed and ignore the BS spouted by pilots of larger aircraft trying to influence light aircraft flying with large aeroplane techniques.

There is ample fat built in to the POH speed for landing at the planned mass - no need for '5 knots for the wife and kids' or other garbage.

When I was HoT at an RF, I inherited a load of nonsense which included:

Flying the approach at POH +10
Adding 5 KIAS if 3 or more PoB (PA28)
Adding 1/3 gust factor above 15 kts


We reviewed the speeds and changed the checklists. As a result we had no more damaged nosewheels, no more drifts off the RW and students learned how to land more easily.

As for 'wing down', that's something weird and American - I never found it very pleasant to fly in such an unbalanced manner. So in everything I ever flew, I used the 'crab' technique - everything from the Chipmunk to the Vulcan to the Phantom to the VC10 to the PA28.

Use the 'point and power' technique, fly at the correct approach speed and 'de-crab' at the same rate as you flare - it's very simple.

And anyone advocating 'kicking the aircraft straight with rudder' deserves a good kicking themselves!

[piperboy84]

Use the 'point and power' technique, fly at the correct approach speed and 'de-crab' at the same rate as you flare - it's very simple.


Wouldn't de-crab during the flare make the aircraft drift? In a tail dragger that could be a problem.

[Genghis the Engineer]

I've found some types prefer crab, some wing-down, both techniques are fine.

The end of crab is effectively into wing down to land aligned with the runway anyhow, surely.

I do find it interesting that we've got a lot of quite experienced people, with some very different views on something that should ideally be pretty fundamental and universally agreed.

G

[BEagle]

Wouldn't de-crab during the flare make the aircraft drift? In a tail dragger that could be a problem.

Not if you time it correctly.

[Scoobster]

I didn't expect to start a debate about techniques.. but always good to hear from more experience.

I was trying to come down at 70 kts as taught and crab into wind.. and then should have straightened out at the last minute before touch down (had I have made it down).

Flying with an instructor here during the checkout - they teach - wing into wind, and keep the nose aligned with the rudder - which is side slip - but that clearly didn't work for me.

At a maximum back home in the UK in a strong wind - the instructor during my PPL said you should not be faster than 75 knots as the piper in a cross wind will land at 70kts if you keep the power on.

Reviewing my notes from yesterday the wind was 140/16 G **something** couldn't quite work out what the AWOS recorded message said..maybe my hearing or the thicker accent.

Anyway I'm glad I canned it and made it back in one piece to my base.

[Genghis the Engineer]

That is one of the joys of PPrune when it's working well.

What type were you flying? 70 seems high for most singles, particularly solo.

I'd suggest that numbers aside, you may not have had the aeroplane as well trimmed on approach as you needed it to be - if the speed was creeping up, assuming a serviceable aeroplane (I've known the occasional pitch trimmer that crept, but it's unusual, and not usually that fast) then the increase in speed can only be because either the aeroplane's not properly trimmed, or you're inadvertently pushing forwards on the yoke.

G

[Pace]

doing in gusty conditions is fannying about in the flare because your approach speed was too high and the aeroplane is still flying whilst you move further from the trimmed approach speed and lose finesse as a result.

But Beagle thats landing technique which is wrong I would suggest that in strong crosswind and gusting conditions the last thing you want to be doing is hanging around in the flare full stop.

Anyone with excess speed above the stall on landing who floats is indicative of landing technique being wrong.

In some conditions its better to fly it on

Pace

[Scoobster]

G - it was a PA 28 161 Warrior II.

Yes, I think a number of things were out of aligned hence the judgement call.

They did say to me the real learning comes after the PPL has been issued!

Thanks for all the replies!

[Genghis the Engineer]

Your go-around and divert was clearly spot-on.

Speedwise: Warrior II POH approach speed is 63 at MTOW. Solo at half tanks, probably about 59. Even with another 5kts "for the wife and kids" (which I'd not advocate) that's 64kts.

I'd suggest practicing working out, and trimming for, the book approach speeds. You should find it makes a big difference to both your stress levels and landings.

G

[Scoobster]

I had full tanks and I weigh about 121 lbs.

All a learning experience.

It scared the c**p outta me been shook like a rag doll but I learned from it to tell the tale.

Ta!

Scoobster

[Genghis the Engineer]

(Just in case you don't know - multiply the MTOW approach speed by the square root of [actual weight / MTOW] ).

I wish I weighed 121lb !

G

[dsc810]

I'm told "They" don't like you to 'wing down' an airliner
risk of dragging a wing mounted engine pod on the floor you see.

[Maoraigh1]

I prefer crab in a Pa28, but always sideslip in a DR1050. With the latter, I get over the runway, stir the controls as required to keep in middle of runway, aligned along it, until into-wind wheel touches. Then keep as straight as possible until speed is lost.
Not possible with a bumpy grass runway, where I would have to go elsewhere if I was losing control effectiveness as speed dropped.
I've tried holding off in a gusty crosswind, but as speed dropped, I was unable to maintain position and alignment, and went around.
If speed over ground seems low on approach, expect windsheer. Higher airspeed won't lead to landing far down the runway in that situation.
Just some controversial views of a basic PPL mainly flying a light taildragger.

[Pace]

G

Having thought about your post I have to say I am not clear on the science of what you are saying
I presume you are arguing that no extra speed should be added for gusts and windshear and Infact increasing speed is negative above 1.3 Xs the stall in a given configuration.

Turbulence windshear is not a condition confined to landing but obviously something which can be encountered at altitude and at cruise speed in the form of severe turbulence or inadvertent CB intrusion
Normally experiencing such turbulence means an instant reduction in speed to VA
We have to dissect two aspects here loss of control authority and danger of stall at two slow a speed and over stressing the airframe
It's a bit like a high powered speed boat crashing into waves or riding waves but aeroplanes don't float )

As stated I experienced airspeed leaps of plus and minus 25 KTS and it doesn't take much maths to work out the danger at being at a normal VREF

Turning to light GA Pistons I don't think the FAA or EASA would stipulate 50% of the gust factor added to VREF if they didn't have good reason to do so
Are you suggesting and I am not clear on this that at higher speed windshear has pronounced effect at higher speeds or that at higher speed there is risk of structural damage by holding a slightly higher speed than VREF

And in simple cause and effect terms as I am pretty thick )) I would be too scared to test that theory with a normal VREF and 25 KT plus and minus for real )

Pace

[Genghis the Engineer]

Turning to light GA Pistons I don't think the FAA or EASA would stipulate 50% of the gust factor added to VREF if they didn't have good reason to do so

Do they?

Can you give authoritative references?

G

[abgd]

Don't EASA stipulate that balloons should be landed into wind?

[andytug]

Don't EASA stipulate that balloons should be landed into wind?
Ah, but where on a balloon is the "front"?

[Genghis the Engineer]

It's the bit that's into wind, obviously.

G

[Mach Jump]

I do find it interesting that we've got a lot of quite experienced people, with some very different views on something that should ideally be pretty fundamental and universally agreed.

I often find that pilots who consistently handle crosswinds without difficulty are using the same technique, but describe it differently.

Successful pilots who say that they 'kick off the drift' or 'decrab', are almost invariably using these terms to describe the process of converting, in the flare, from a crabbed approach, (flying in balance with the aircraft heading somewhat into the wind to maintain the centreline) to a side slipping touchdown, where angle of bank (aileron) maintains the aircraft on the centreline, and yaw (rudder) maintains the runway heading.

I find that if you teach this technique for all landings, then dealing with crosswinds ceases to be a problem.

... is that there's enough margin in everything to mean that it doesn't matter as much as we think - another is that gust response and control authority scale about the same (which probably is true) that they pretty much cancel each other out.

I think you're right on both these points, Genghis. If people would just stick to the speeds in the POH, they would be generally better off than making up their own.


I think he 'speed' thing is a misunderstanding in two parts. There is the gust response/control response factor on the approach, but the more important for crosswind landings, is the touchdown speed.

The faster your touchdown speed, the less the drift for a given wind.

For instance, with a crosswind of 20kt an aircraft touching down at 20kt will have a very scary drift angle of 45 degrees, whereas, another aircraft touching down at 200kt would hardly notice a 20kt crosswind at all.

It follows, therefore, that the faster you touch down in any aircraft, the less effect any crosswind will have.

The problem with landing at higher speeds, is that it requires a lower nose attitude on landing. In the old days, this wasn't a huge problem, as the tailwheel aircraft of the time simply raised their tails, and did a 'wheeler landing'.

For modern tricycle types, this isn't an option, as 'flat' landings damage nose-wheels, and cause 'wheelbarrowing'. We have all seen the results of that. :=

There is, however, a way of landing such aircraft at higher speeds, whilst still maintaining the same landing attitude, and that is to reduce the flap setting.

A Warrior landing without flap, but in the same lading attitude as one landing with 3 notches, will touch down around 10-15kt faster. (Remember those flapless landings you last did during your PPL?) This will reduce the drift at touchdown considerably.

Note: You don't need to increase the approach speed beyond the normal flapless speed for this, so the landing distance should be no more than for a flapless landing.


MJ:ok:

[Pace]

G

Here you go as requested a link to an FAA article
You will also find a specific link within the article for using higher speeds with gusting winds

http://www.faa.gov/news/safety_briefing/2010/media/MarApr2010-FlyingByTheNumbers.pdf

Pace

[Genghis the Engineer]

Thanks - reading that opinion piece it links back to an FAA training document.

Going into that, it says...



To maintain good control, the approach in turbulent air with gusty crosswind may require the use of partial wing flaps. With less than full flaps, the airplane will be in a higher pitch attitude. Thus, it will require less of a pitch change to establish the landing attitude, and the touchdown will be at a higher airspeed to ensure more positive control. The speed should not be so excessive that the airplane will float past the desired landing area.

One procedure is to use the normal approach speed plus one-half of the wind gust factors. If the normal speed is 70 knots, and the wind gusts increase 15 knots, airspeed of 77 knots is appropriate. In any case, the air-speed and the amount of flaps should be as the airplane manufacturer recommends.

and later...

In the absence of the manufacturer’s recommended approach speed, a speed of not more than 1.3 Vso should be used. For example, in an airplane that stalls at 60 knots with power off, and flaps and landing gear extended, the approach speed should not be higher than 78 knots. In gusty air, no more than one-half the gust factor should be added. An excessive amount of airspeed could result in a touchdown too far from the runway threshold or an after-landing roll that exceeds the available landing area.

Not exactly a firm recommendation for the approach, and containing no clear arguments as to why. It's really just an acknowledgment that that opinion exists, and a firm witches warning not to add too much speed.

G

[Pace]

G

1.3 times the stall in a given configuration is just a number
It is a number worked out to give with a closed throttle and in normal conditions enough energy to transition from the descent profile to a higher drag landing profile as well as to allow you to make turns

In very strong winds and shear you need control authority which is speed related and with a closed throttle may not have enough energy to stop the aircraft either abruptly descending into the ground or stalling

That is where I see the half gust factor to give a slightly higher that 1.3 times the stall while not giving too much speed to make the average pilot float
It's a compromise figure
You could add the whole gust factor
Floating is pilot technique fault not so much speed

Pace

[Genghis the Engineer]

I find it interesting that they say "not more than" 1.3Vso - not that I disagree that it's just a number (okay, just a number that's common to most airworthiness standards). Some slippery aeroplanes - most motorgliders for example, 1.3Vso may well be too fast, whilst I've flown microlights where 1.5Vso is more likely to give you the handling you need in roundout and flare.

I also agree that not all conditions want closed throttle, although speed is certainly relevant to tendency to float - not *just* piloting technique.

G

[mary meagher]

Hey Scoobster, flying into an American airport on the edge of the Atlantic Ocean? I'm wondering about the surroundings of that airport....in a lot of US smaller airports, the trees keep on growing, unfortunately. And can provide severe disturbance to wind conditions when descending into a space that is more like a trench. Most rural airfields in the UK are set in relatively open farming areas, so less likely to experience these problems. The proximity of the ocean would more likely give steady winds....but nonetheless descending below tall treetop level nearly always has an interesting effect on light aircraft.

[Pace]

G

The tendency to float is purely that the wing is still flying
We look at landing as where the wing starts to stop flying and is also creating drag and sinks to the runway
That is not the only way to land
I placed a link in another thread to an AAIB report where a citation with control problems landed at 190 kts where the normal VREF was 105 KTS obviously a crazy example but he landed and stopped
Hence any float is pilot technique and in certain conditions it's better to fly it on
Put it down rather than holding off
The main problem is keeping the nose wheel clear and an aircraft with a large distance from nose to mains suits better

Pace

[Big Pistons Forever]

In a tricycle gear airplane the aircraft must touch down on the main wheels first. This means the aircraft must have a nose high attitude, which means the airspeed must be reasonable low. As a general rule of thumb 1.3 Vso allows a safe margin above stall yet gives a speed low enough excessive float while waiting for the aircraft to slow down to allow the requisite nose high landing attitude to be obtained before touchdown.

Excessive speed makes a balloon more likely in the initial flare pitch up, prolongs the float which makes it harder to counter the effects of the crosswind and in general just makes everything harder.

A bit of extra speed is not a bad idea on final but it must be washed off as you cross the fence so that you start the flare at the normal speed.

It is almost impossible to break a Pa 28 or C 150/172 if you hit main wheels first, even with descent rates as high as 500 feet min. However a nose wheel first hit will result in damage even at relatively low rates of descent. The nose wheel first hits are almost always a result of excessive speed as the aircraft will fly level in ground effect at a nose low attitude. At that point all it takes is the pilot trying to force the aircraft on with forward stick and you get yet another written off light aircraft

[Pace]

BPF

I think the Airbus will fly a groundspeed on auto and have a VREF plus 20 limitation on landing on suitable runways
VREF is a very important figure for landing as stopping distances are calculated from that and there is no way I am suggesting that you come flying at high speed down the runway but 50% of the gust factor is a tried and tested compromise where you have a headwind component.

There are times when you can hold off and times where its better firmly on the ground and in those situations flying it on is a better option and of course mains first
If you are flying something like a Citation the distance from the nose wheel to the mains is large meaning a tiny pitch change will bring the nose clear.

SEP an aircraft like a Saratoga will do well with a good distance from nose to mains but if its a short coupled aircraft with a tiny distance between nose and mains then keep to relatively calm conditions :E As its not a wind bird

Pace