stall warner on landing [Archive]

homeguard

9th Jun 2005, 17:38

You should land at the speed where the pilot still has effective controls beyond that which will be available at the stall all be it that the stall warner should be set to be activated between 5-12kts before the main wing stalls. On a normal landing it is unlikely that the stall warner is activated. Indeed for the aircraft CofA airtest a check is to note that it is NOT activated. I would imagine this particular Swiss Instructor is responsible for a lot of nose leg maintenance as in some types it will come crashing down unexspectedly as pitch authority is lost and no doubt will lead to some very tired main gear when the hold off is a touch too high.

As to the idea that a low slow approach produces a shorter landing is wrong although I know often taught. On an earlier thread a contributor proved the physics that the steeper an approach the shorter the landing distance. The correct approach speed is the most important element.

1McLay

10th Jun 2005, 06:52

On an earlier thread a contributor proved the physics that the steeper an approach the shorter the landing distance

yeah...very short when you have no forward speed to flare.
:ooh:

WrongWayCorrigan

10th Jun 2005, 06:57

To me, insisting on this is a total irrelevance, a focus on all the wrong things.

In a normal landing who cares if the stall warner sounds? Main thing is right place, right speed and in control.

A short field landing should involve a steep descent at a given airspeed over the nominal obstacle, minimum or no flare and braking to come to a halt within the shortest distance.

Poncing around just to get a stall warner going is i.m.h.o. totally daft.

Miserlou

10th Jun 2005, 19:03

A matter of definition regards short field landing' and 'short landing in a field'.

A short field landing is your strip technique assuming you have obstacles at the approach end. Thus, a steep approach is made to make use of as much of the field as possible, as close to the obstacle as possible.

A landing in a short field, known as a precautionary landing, assumes that you have selected a good field where the only unknown is the actual surface condition. Here you want the shortest possible ground roll at exactly the spot you have selected to touch down on.

Nothing wrong with requiring the stall warning to be activated at touchdown; it shows that the speed was controlled acurately and that isn't a bad thing to learn. Bearing in mind all landing data is based on the correct approach speed leading into the correct moment of power reduction and flare to the right attitude for touchdown.
Where there is little accuracy for the stall warning, I perhaps, wouldn't require it for every landing, it is a good indicator that the correct technique is being used.

You're never going to lose elevator authority at this point without a tailstrike first and that doesn't mean the nose will hit the ground that hard anyway.

The main gear is also much more able to cope with the strain.

I'd also like to take issue with the above method of short field landing. Minimum or no flare is v. bad advice. The key to a good short field landing (or any landing for that matter) is accurate speed control. Your technique implies that braking is the best way of stopping. It isn't if you have a taildragger, it isn't if you're on wet grass, and it isn't if you break the nose wheel which isn't designed for this treatment, and it isn't if you haven't got rid of all the lift the wings can produce (due to higher touchdown speed).
Once down you want to put as much weight on the mains as possible.

WrongWayCorrigan

13th Jun 2005, 08:48

I wasn't about to reply to this as clearly The Heart is nowhere near The Brain.

1. I'm not saying it's not a good thing to teach, but rather that it shouldn't be taught as the main priority.

2. No one is advocating driving aeroplanes into the ground and smashing up nosewheels. Really!

homeguard

13th Jun 2005, 10:38

wrongwaycorrigan

I don't think that you intended any such thing either. At some point some may wish as you have clearly intended to DEBATE on these threads and not simply argue a singular point of view.

A correctly flown approach dosn't need the added distraction of simply holding off and hanging on airborne until the stall warner is activated, which may be; a horn, light or even stick-shaker.

There are some commonly flown types different from say a Cessna that while a Flare in the old sense of the word may be executed perfectly they will very suddenly lose pitch authority such as the Piper Tomahawk and the Grumman AA5. A common fault with Tomahawk is that the nose will come down very firmly if held up too long and if any rudder input is maintained the wheel will make contact with the ground sideways on. Differently with the AA5 the nosewheel assembly is a simple U-shaped tube which on impact is a very effective spring. Any sudden impact will cause a very lively pitch skywards. As to the main gear even such dosile types as the Piper Cherokee series will, if held aloft too long, simply belly flop and whether the main gear/nose gear is tough or not, time will take its toll.

unfazed

13th Jun 2005, 15:50

Oh dear what a lot of differing "opinions" on a very simple subject

For the pedants out there

1 - Ever heard of 1.3 VSO

2 - Stall "warner" as an indication that you hit the right spot ! Not suggesting you hold off until you hear it (but you will if you get the speed right).

Stands back - expecting more trouble !

huckleberry58

13th Jun 2005, 18:28

For those 'pendants', 1.3Vs is a legal requirement to ensure pitch authority for the flare but you could conceiveably keep floating until you hear the stall warning on touchdown so I don't think you can use that argument for this question.
IMHO I think it's dangerous to land with the stall warning horn sounding for a normal landing. In a Cessna, the nose would be awful high, I would feel very uncomfortable and there would be a possibility of a tailstrike. For a short field landing I would accept it if it came on just prior to touchdown but of course there are other considerations regarding that technique. I would like to know what type of aircraft this Swiss chap flies.

Miserlou

13th Jun 2005, 20:51

I agree, Unfazed, I thought it was a simple subject too.

My precautionary landing technique was learnt in a Tiger Moth, no stall warner other than seeing the slats pop out. Three point attitude and held in the air with power until you reach the point you want to touchdown on. Close the throttle and a quick check on the stick to soften the actual touch and you're down and stopped in no time.

I did point out that stall warners vary in accuracy. There does seem to be some confusion as to where the aeroplane is at this point where the stall warner may or may not activate.

The approach should be flown, as stated at a figure close to 1.3 Vso but the throttle will be closed at a certain point and the aircraft flared to the landing attitude. Having closed the throttle and reduced the rate of descent you will find the speed has reduced. If you stall at 45 and have approached entered the flare at 60 you only have approximately 10 kts to the stall warning. And this at a height of an inch or so, not going to harm any undercarriage. That's not unreasonable, is it?

Not a requirement, as I have agreed, but certainly not unreasonable.

Corrigan, old boy, you'll have to explain what you mean by "little or no flare".

Sounds like driving it on to me and as I pointed out, there doesn't seem to be any good reason for it. Get 'em all the time at work, "Going low, on purpose.", "Speed high, on purpose."

"What purpose?" if I may enquire.

Huck,
Is it pedantic to fly an aircraft as it was designed to be flown and according to the data produced when the aircraft was tested?

Perhaps, you prefer to make up your own rules?

huckleberry58

14th Jun 2005, 07:51

Miserlou, I agree with you. Fly the aircraft as it is designed to be flown. But is it normal for the stall warning to come on during touchdown? I personally don't think so and I don't think it's designed to do so either. I've never heard it during a normal landing in a Cessna except on gusty days when it will come on intermittently. As for making up my own rules, no I don't.

unfazed

14th Jun 2005, 08:16

"I've never heard it during a normal landing in a Cessna" (stall warner)

Huck old chap you need to try harder !

Picture the scene somewhere in Blighty - mid summer - smell of grass cuttings and aviation oil - nil wind and only fairweather cu to colour the scene.....all enhanced further by the sound of the stall warner congratulating you on your textbook Cessna landing !!

Come on give it a try and loose some of that excess airspeed

:D :D

huckleberry58

14th Jun 2005, 08:34

Ahh, nice scene. But can I change the location to a place called Ardmore? I mentioned I've never heard it during a normal landing... didn't mention about my other less than 'normal' ones. Haha.

FlyingForFun

14th Jun 2005, 09:38

Forgive me for barging in so late in the discussion, but it seems to me that all the "Yes" and "No" answers must surely be wrong?

Different stall warners, as Miserlou has said, have different sensitivities. One C150 I fly has a stall warner which used to sometimes goes off just after the aircraft enters a clean power-off stall at altitude, for example. This was clearly a fault with the stall warner on that particular aircraft, but demonstrates that not all stall warners on any given type of aircraft will go off at the same point.

So now, if we were to say that the stall warner must go off prior to landing, we would be faced with a situation where we could carry out a landing in one aircraft which, according to our criteria, would be perfectly acceptable. Then we could move to another aircraft, with a very slightly less sensitive stall warner, and carry out an identical landing (I know that no two landings are the same.....), yet by our own criteria this identical landing would be a bad one because the stall warner is configured differently? What crap!

Likewise, if we were to say that the stall warner must not go off before landing, we would be faced with the same problem, where a landing which was perfectly acceptable in one aircraft might not be acceptable if the stall warner was slightly more sensitive.

What do I look for in a landing? I teach my students to try to not land the aircraft, but to keep it flying for as long as they possibly can. This is the way I always try to land the aircraft myself, too. When I do what I consider to be a "good" landing in a C150/152/172/PA28, I run out of lift just as the wheels touch the ground. The nose wheel does not come crashing down when this happens; it actually makes a nice smooth landing. I have never had a tail-strike using this method either; I can't see how you could get a tail-strike unless you had left the power on for the flare (or, as happens more often with students, for a bounce recovery). Sometimes the stall warner goes off for this type of landing, more often it doesn't. I have never run out of elevator authority on landing, I just run out of lift. In fact, I often demonstrate to my students that I still have some elevator authority whilst taxying - move the controls forwards and backwards at about 20kts, and watch the nose go up and down. (Or point the aircraft into a 20kt wind whilst stationary on the ground and try the same thing.)

However, what is far more important in my opinion is what you do with the controls after the aircraft has landed. Anyone who lets go of the controls column after the aircraft has landed does not go solo in my aircraft, because it is that which causes the nose to come crashing down onto the ground after the main wheels. Once the main wheels have touched the ground, keep the controls back. Once the nose-wheel has touched the ground, keep the controls back. Keep the controls back until you have reached taxy speed - and even then you should really be keeping the controls back too, unless you have a strong tail-wind, but I tend to be a little more lenient at taxy speeds because in the aircraft I fly it's not so critical.

FFF
-----------------

DFC

14th Jun 2005, 12:05

The stall speed is the minimum steady flight speed.

The stall warner is required to sound at some pre-determined speed above the stall.

If one runs out of elevator authority before reaching the stall speed, how can one stall the aircraft (1g) and demonstrate what the stall speed is?

If pilots are touching down close to the minimum flight speed then the stall warner should be sounding because holding the aircraft off at this speed will require an angle of atack close to the stall angle.

Perhaps if the speed is close to the stall at touchdown and the warner fails to sound then the stall warner is U/S and one must check to see if flight without the warner is permitted!

Best short landing figures are obtained from power off approach at the appropriate speed, flare, land and maximum braking. That is where Cessna get the numbers from.

Remember also that if one flares a bit quickly (more than 1g) than the stall speed will increase and not only will the stall happen at a higher speed (nose drop) but the warner will so at a higher speed also. This is also worth thinking about with regard to the nose wheel.

Regards,

DFC

Miserlou

14th Jun 2005, 20:20

So, we're all agreed then and can say without shadow of doubt or fear of contradiction, maybe!

FFF mentions a point which is particularly relevant when discussing the abuse of the undercarriage during landing.

Why do people give up flying the aircraft as soon as the main wheels are firmly planted?

Centaurus

16th Jun 2005, 13:01

The Cessna 172 POH has a table headed Landing Distance - Short Field. The speed used to attain the distances quoted is in fact the "normal" approach speed based on certification tests - ie 1.3 VS. The Boeing 737 "normal" approach speed for normal landings is the equivalent in principle to the Cessna figures.

In no case does the pilot deliberately reduce the approach speed below the stated "normal" approach speed as stated in the flight manuals (POH if you like). Therefore in reality the so called short field landing is always a normal landing speed and technique in order to attain the book landing distance figures.

During the war real short field landings required a certain speed reduction below the certification speed - usually 10% or even 20% lower. Landing on an aircraft carrier is an example of this where the approach is made at 1.1Vs instead of the normal 1.3Vs. (those figures are not necessarily correct but you get the idea, I hope). In those cases, it was slipstream provided by the propeller that kept the inboard wing area from stalling and if you chopped the power before the flare you would certainly fall out of the sky. Thus the true "short field" landing certainly required a powered approach "hanging on the prop" and of course as soon as the aircraft was flared the float would be minimal and the subsequent landing roll short. Just the sort of technique needed to land an aircraft into a field of unknown length but assuming the worst - very very short. Military trainee pilots were taught this technique until proved competent. These were not normal 1.3Vs landings that we know nowadays.

It wasn't until Flight Manuals were produced for civilian aircraft that certification requirements demanded a min speed of 1.3Vs for calculation of landing distances. Again there were probable exceptions to the method of stall speed calculation for purposes of landing speeds "over the fence".

All this boils down to there is no such thing as a short field landing where an approach speed significantly below the certification speed in the POH is routinely used. Thus if the POH speed is used correctly, then there will always be a float period to dissipate the speed (light aircraft such as Cessna types) before touch-down. That is because it is not the done thing to "plant" an aircraft on all three wheels at flying speed. There are obvious dangers to this - nose-wheel damage - bounce - and application of non-anti-skid brakes at relatively high ground speed.

If your instructor demands an approach at less than the POH recommended approach speed (1.3Vs) then it is both illegal and reckless. It is never done in a airliner or business jet, so why should it be done in a trainer?

FlyingForFun

16th Jun 2005, 13:10

Centaurus,

I have the manual for a 1981 Cessna F152 in front of me.

In section 4, under normal procedures, it describes the procedure for a "normal landing". The indicated airspeed, it suggests, should be "55 to 65 kts" with flaps down.

It then describes a "short field landing". Here, it suggests selecting 30 degrees of flaps, then a speed of "54 kts".

So yes, the speed for a short field landing should be between 1 and 11 kts slower than for a normal landing.

How this affects the issue of the stall warner, though, I'm not sure, because in either case the power is reduced to idle, and the aircraft is flared, and actually lands at the same speed.

FFF
----------------

Centaurus

16th Jun 2005, 13:48

Flying for Fun. You are quite right. I don't know the history of the C152 POH but it may be that the Cessna book suggests you can use any speed between 55k and 65 knots approach speed without causing any unusual aerodynamic effects. If however you wish to operate into a field that is on the minimum length to meet book figures, then 54 knots is the approach speed to use.

I earlier referred to the Boeing 737 approach speed. The term "Short Field Landing" is not mentioned. It mentions "normal" approach speeds and there are tables giving landing distances versus weights and varying flap settings. In contrast to your C152 POH, Boeing do not give a range of normal approach speeds. There is just one speed depending on various parameters.

I knew of one particular civil Examiner who was a former Navy Sea Fury pilot that in GFPT, PPL, and CPL flight tests, demanded that the student demonstrate a "short field landing " by flying the approach with the stall warning actuating intermittently (1.1Vs?) which was around 47 knots IAS in a Cessna 152. It was foolish and illegal, but in his opinion it was a true short field approach. In fact many flying schools in the Fifties and Sixties used this technique (sans stall warning devices in those days) as part and parcel of the PPL syllabus. This is because many instructors were trained in wartime and brought military techniques to the aero clubs and flying schools. Of course at those low approach speeds there was no float which was the point of the exercise!

Rather than call the 54 knot approach speed in your Cessna 152 a short field landing speed, perhaps it should be renamed "Minimum ground roll approach speed" In fact some years ago, the Australian CAA changed the Day VFR Syllabus section on landings from Short Field Landing, to Minimum Ground Roll landing. This recognised that the certificated 1.3Vs approach in a light aircraft would of necessity require a float period of some seconds in order to dissipate speed prior to touch-down just at the stall.

homeguard

16th Jun 2005, 14:51

Very good points have been made within this thread. In our school we do not use the term 'Short Field' at all. We prefer to refer to the maximum performance Take-off/Landing of the aircraft in accordance with the POH.

The term short-field is immotive and may infer that it is OK to approach and land on runways that are too short - albeit it can be done by a kind of cheating.

Miserlou

16th Jun 2005, 21:20

I think people are confusing what you teach a student with what you may need to know later when flying into short strips.

I have also flopped open an aircraft operation manual (Beaver) which states normal approach speed 80 mph.to 50'. The short landing speed is 75mph; and the rate of descent 'should not exceed 1040fpm at the flare position'.

It seems obvious that there is some discrepancy. Where the book may not say that the speed may be reduced below the approach speed, I'd like to ask Centuarus what he supposes happens to the airspeed when you close the throttle and reduce the pitch attitude.

Another book here on my shelf has some specifics for the ATR. Says that touchdown should be '5-10kts below the stabilized approach speed'.

So if you have made your approach at 1.3Vs (say 60kts) and reduce the power and flare, then the speed can be expected to be below 1.3VS. This reduction (5-10kts) may easily fall into the range of the stall warner.

homeguard

16th Jun 2005, 23:08

Ah!

We teach one thing and do another - dont think so!

Not wanting to be smart but this thread is about training and testing and in response to a qoute from a Swiss Instructor.

Your example incidently;

60kts x 1.3 = 78kts minus 10kts = 68kts
therefore touchdown would be 8kts above the speed expected at the stall and within the 5-12kts if the stall warning is set correctly, true.

However the stall warner is activated as a result of relative airflow not speed. Throughout the hold-off the pilot is concentrating on attitude reference the runway (main wheels first). Does it follow that the stall angle to RAF is achieved?

Arguements please

Miserlou

16th Jun 2005, 23:44

Approach speed for a 152 is '55-65kts' as quoted earlier. Let's just call it 60 (just to be in the middle of the acceptable speed range).

That figure is 1.3Vso which would make the stall speed about 46kts.
Still with me?
minus 5 equals 55, yes?

55 minus 46 equals 9.

So you only need to lose 5 knots to achieve the speed range which may trigger the stall warner (5-12kts).

And your example shows the same.

Until we can get angle of attack indicators in light aircraft, ASI's are the best alternative hence the reference to speed.

No, you are most certainly not being smart.

I don't understand the 'do one thing and teach another' part unless you mean between the old and new definition of precautionary landing.

huckleberry58

17th Jun 2005, 01:06

Anyone actually flown a C152?? The fully configured stall speed is the bottom of the white arc and the clean stall speed is the bottom of the green arc. They are 35kts and 40kts respectively. This can be found in the flight manual also. Even with the short field landing speed of 54kts, you are well above the 1.3Vs and will not hear the stall warning when landing.

Miserlou

17th Jun 2005, 11:46

The figures I have show it to be 43-48kts.

Your figures, which may well be the instrument markings, would put the stall speed of the 152 below that for a Super Cub (36-42kts).

This, I know not to be the case.

unfazed

17th Jun 2005, 15:08

Lots of conflicting data on approach speeds (normal or otherwise)

Lets not forget there is an approach - then a transition to the flare - and then the hold off while speed reduces. Some commentators seem to imply that an approach speed is maintained until contact with the ground.

I would suggest that the approach speed used is held until the flare and then speed bleeds off until we stall the aircraft (or just above the stall ) onto the ground.

Stall warner not required because the stall is an aerodynamic fact so don't get hung up on "stall warner"

I was interested to hear of the old military techniques for real short field landings which sound challenging.

;)

huckleberry58

17th Jun 2005, 17:11

Miserlou, you may be quoting KCAS whereas I am quoting KIAS.

Miserlou

17th Jun 2005, 17:58

Nope, specifically KIAS.

I still maintain that a 152 will stall before a Cub.

ProfChrisReed

17th Jun 2005, 20:25

I don't know if it's any help (I'm only a glider pilot and Basic Instructor), but when flying a new type I will stall it, note the stall speed, and then calculate 1.3 x Vs to give my minimum landing speed. Add half wind speed (more if gusty or wind shear is expected) and I'm there.

I certainly wouldn't rely on the handbook for this number, as Vs varies with pilot weight and seating position in a single seater glider, though I'd want to know this number in case of a launch failure.

But I gather that in powered a/c deliberate stallng to check this, plus handling, wing drop etc, is rare?

Genghis the Engineer

17th Jun 2005, 22:58

I'd caution you there Prof, many airspeed indicating systems in smaller aircraft (and I believe this is likely to include gliders) tend to underread somewhat just around the stall. So, an IAS of 1.3Vs(ind) may well be somewhat below a real 1.3Vs.

Dr.G

huckleberry58

18th Jun 2005, 07:35

Er... then what is the purpose of the bottom of the white and green arcs? Or for the top of the arcs, or for the yellow arc or red line...

FlyingForFun

18th Jun 2005, 15:10

Prof, I'm curious. Why do you add half the wind speed (more if gusty)? I've never heard of anyone adding extra knots to the approach speed because of a steady wind.

FFF
-------------

Miserlou

18th Jun 2005, 23:05

Approach speed correction to get you through the wind gradient safely.
Usually something like 'add 1/3 of headwind component or gust value in full but max 15 knots', or 'when wind speed exceeds 10kts add...'.

Centaurus

19th Jun 2005, 11:15

You have been copying the Boeing recommendations on flying jets about adding half the steady HW component and all the gust factor. That's fine if you want to float a long way, but it also says bleed off the half the HW component approaching touch-down.

The Boeing recommendation doesn't apply to propeller types due instant power response slipstream lift.

Miserlou

19th Jun 2005, 14:00

I first learnt the adding part of headwind component when I was 15. When operating a glider in strong wind conditions a correction was made to the approach speed and it worked exactly. As we reached the last 20' or so wind dropped dramtically and we were left at the correct height at the correct (normal) speed to land from. The extra 15 knots just disappeared. Had we been at the normal approach speed to begin with we would have stalled in from 10'.

FlyingForFun

19th Jun 2005, 18:41

Hmm, learn something new every day. I've flown small propellor-driven aircraft in lots of different wind conditions. I've often added a bit of speed if the wind was gusty (half the gust speed), but I've never added anything for the steady wind, and never had any controllability problems. As Centaurus mentions, as you encounter the wind gradient you just use power to maintain the desired flight-path - seems to work well enough for me.

Interested to hear that jets and gliders do it differently. I can see why this may be the case for jets (presumably because it takes longer to get a response from the thrust levers), but I'm confused about gliders, which seems to be where both Prof and Miserlou got the technique from. I've never flown a glider, but I would have thought that you'd get a pretty much instant response from the speed brakes, so adding extra speed for steady wind would be unnecessary???

FFF
-------------

Miserlou

19th Jun 2005, 20:12

You might get an instant response if you used them instantly but the cause for using them has to happen first. By the time the need for them occurs it may be too late. Hence, I noted that the extra speed vanished and we were left at the flare with exactly the correct speed.

The corrections are also applicable to turbo-props and I seem to remember having seen them in an SOP for single-engined pistons (commercial ops).

Not being a Boeing ace I cannot comment on the bleeding off of speed in the latter part of the approach but I haven't seen it anywhere else. The whole point of the exercise is having a safety margin that will not leave you 'velocitarily challenged' at the most crucial point in the flight, the transition from flight to ground, and the sudden loss of lift as the wind speed decreases at the surface.

It was not a factor of normal ops in gliders but only used in strong wind conditions.

ProfChrisReed

20th Jun 2005, 19:58

Flying for Fun wrote, about gliders adding half wind speed to cope with the wind gradient:

"as you encounter the wind gradient you just use power to maintain the desired flight-path - seems to work well enough for me."

Don't forget that in my glider I don't have that option - no power! The only way I can increase speed is to lower the nose, and my inertia over the ground means that it will take some seconds to regain the lost speed. At 50 feet, which is where the wind gradient tends to bite, this means the ground will arrive before I have enough speed to flare - not recommended.

To give some idea of the numbers involved, my 1968 glassfibre glider has a stall speed of about 35kt and a recommended nil wind landing speed of 45kt. If I land into a 20kt headwind, I could easily lose 10kt in the wind gradient, which I think makes my point. So I approach at 55kt, lose 10kt, and end up at 45kt which is where I wanted to be in the first place.

Putting the airbrakes away increases the lift from the wings and reduces drag, but not enough to get my 10kt back in time.

Onan the Clumsy

20th Jun 2005, 21:36

Don't forget that in my glider I don't have that option - no power! The only way I can increase speed is to lower the nose I've never had a problem using speed brakes for power. Come in with them half extended and if you need a little extra 'power' retract them as needed. I've never had a problem with inertia either. I'm not saying you're wrong, just that I don't necessarily do it your way.

As for the original idea behind this thread, I think it's counterproductive and a little dangerous. (plus I'd like to know if a stall warning system even works the same in ground effect). Teaching your students the importance of some single task is ok when they need a crutch to rely on, but pretty soon it becomes the wheelchair that they can't operate without. I think you'd be doing them a much greater service to teach them to actually fly the airplane, not rely on some piece of equipment that may or may not even work on the day.

DFC

21st Jun 2005, 11:35

As we reached the last 20' or so wind dropped dramtically

I don't think that we can call that any sort of steady wind.

Where I come from that is called windshear and should be reported as such.

The aircraft can be stalled at any airspeed - simply increase the angle of attack enough. The stall warner will activate to warn of the approaching stall. Thus the activation of the stall warner as an indication of correct touchdown speed is only correct in a 1g situation.

Regards,

DFC

homeguard

21st Jun 2005, 14:40

I cannot envisage that a wind gradiant has any bearing here for it has no bearing on air speed but ground speed.

Wind Shear is not a wind gradiant but a sudden change of wind velocity caused by a number of factors such as CB activity or resulting from surface conditions such as Trees, buildings and undulating ground when the winds are quite strong.

If there is a trick with gliders such that you can increase momentum, point at the target and then quickly lose airspeed for a precise touch down by deploying air brakes so be it but it is not to be advised by the application of flaps nor would i think it wise in a glider when spoilers are being used. Remember air brakes in most types (i'm loath to say all types - someone will prove me wrong) do not cause a pitching moment. Landing does not take place in relation to a ground speed BUT at an airspeed. Better to arrive at the runway at the correct airspeed to land rather than sit too fast floating for an undefined period at minimum control. Stall warners buzz flash or whatever at an angle of attack that they are set, as decribed by DFC.

WrongWayCorrigan

21st Jun 2005, 16:09

Corrigan, old boy

Miserlou!

I resemble that remark!!

Miserlou

22nd Jun 2005, 14:00

No offence meant, Mr Corrigan. ;-)

Homeguard,

The technique involves no change in configuration, If you'd like to imagine knowing that there is a wind shear with a headwind decrease of 50 knots you may be able to add 50 knots to your speed and still fly through without going below your uncorrected speed; you lose the 50 knots as soon as you hit the wind shear.

If you have a stiff breeze you know that there will be more friction at the surface than usual. The situation is exactly the same as a decreasing headwind, wind shear. The situation is exacerbated in a glider where the wings are often that much closer to the ground than a powered aircraft and the friction is greater.

There is no trickery involved.

DFC,
It may well be a steady wind. The friction increases the closer you get to the surface. The stronger the wind greater the effect and wind gradient.