Go Back  PPRuNe Forums > Non-Airline Forums > Private Flying
Reload this Page >

The wind knocked out of my sails today..

Private Flying LAA/BMAA/BGA/BPA The sheer pleasure of flight.

The wind knocked out of my sails today..

Old 11th Mar 2016, 23:47
  #1 (permalink)  
Thread Starter
 
Join Date: Sep 2005
Location: London
Posts: 326
The wind knocked out of my sails today..

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
Scoobster is offline  
Old 12th Mar 2016, 00:18
  #2 (permalink)  
 
Join Date: Aug 2005
Location: Glens o' Angus by way of LA
Age: 57
Posts: 1,975
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.
piperboy84 is offline  
Old 12th Mar 2016, 00:56
  #3 (permalink)  

SkyGod
 
Join Date: Aug 2000
Location: Ft. Lauderdale, Florida, USA
Age: 63
Posts: 1,486
.
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.
TowerDog is offline  
Old 12th Mar 2016, 01:01
  #4 (permalink)  
 
Join Date: Sep 2015
Location: London
Posts: 442
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!
alex90 is offline  
Old 12th Mar 2016, 05:44
  #5 (permalink)  
 
Join Date: Oct 2006
Location: UK
Posts: 357
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.
Mungo Man is offline  
Old 12th Mar 2016, 07:00
  #6 (permalink)  
 
Join Date: Feb 2016
Location: Greater London Area
Posts: 166
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.
Fly4Business is offline  
Old 12th Mar 2016, 09:20
  #7 (permalink)  
 
Join Date: Jan 2001
Location: In the boot of my car!
Posts: 5,999
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
Pace is offline  
Old 12th Mar 2016, 09:39
  #8 (permalink)  
 
Join Date: Feb 2000
Location: UK
Posts: 13,798
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
Genghis the Engineer is offline  
Old 12th Mar 2016, 09:46
  #9 (permalink)  
 
Join Date: Jan 2008
Location: Uxbridge
Posts: 722
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)
MrAverage is offline  
Old 12th Mar 2016, 10:06
  #10 (permalink)  
 
Join Date: Feb 2000
Location: UK
Posts: 13,798
I don't fly airliners, but just searched for "airliner crabbed landing" on youtube, and found loads of examples.

G
Genghis the Engineer is offline  
Old 12th Mar 2016, 10:13
  #11 (permalink)  
 
Join Date: Jan 2001
Location: In the boot of my car!
Posts: 5,999
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
Pace is offline  
Old 12th Mar 2016, 10:19
  #12 (permalink)  
 
Join Date: Jan 2008
Location: Uxbridge
Posts: 722
My mistake, what I meant to say was:


Has anyone ever seen an airliner not crabbing, i.e. using the wing down method.
MrAverage is offline  
Old 12th Mar 2016, 10:23
  #13 (permalink)  
 
Join Date: Feb 2000
Location: UK
Posts: 13,798
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 is offline  
Old 12th Mar 2016, 10:27
  #14 (permalink)  
 
Join Date: Feb 2000
Location: UK
Posts: 13,798
Has anyone ever seen an airliner not crabbing, i.e. using the wing down method
Tristars used to land wing down IIRC.

G
Genghis the Engineer is offline  
Old 12th Mar 2016, 10:42
  #15 (permalink)  
 
Join Date: Jan 2001
Location: In the boot of my car!
Posts: 5,999
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
Pace is offline  
Old 12th Mar 2016, 10:44
  #16 (permalink)  
Danny42C
Guest
 
Posts: n/a
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.
 
Old 12th Mar 2016, 10:58
  #17 (permalink)  
 
Join Date: Feb 2000
Location: UK
Posts: 13,798
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

Last edited by Genghis the Engineer; 12th Mar 2016 at 11:09.
Genghis the Engineer is offline  
Old 12th Mar 2016, 11:38
  #18 (permalink)  
 
Join Date: Apr 1999
Location: In front of a computer
Posts: 1,980
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

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
ETOPS is offline  
Old 12th Mar 2016, 12:06
  #19 (permalink)  
 
Join Date: Jan 2001
Location: In the boot of my car!
Posts: 5,999
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
Pace is offline  
Old 12th Mar 2016, 13:13
  #20 (permalink)  
 
Join Date: Feb 2000
Location: UK
Posts: 13,798
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
Genghis the Engineer is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.