The wind knocked out of my sails today..

[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 As its not a wind bird

Pace