Crosswind Landings... But airspeed?

Jmarc99 wrote:
After having read all the posts in the previous thread, no one said a word
about de right airspeed to keep along the final approach... whatever this is done
with a sideslip or crabbing.


Beware of flying indicated airspeed during a slipping approach. The
pitot/static system on some giders will give large indicated airspeed
errors when slipping. As an extreme example my ASW-19 read zero
airspeed in a full rudder slip, probably due to the nose pot pitot.
You need to know your glider and fly the appropriate attitude rather
than the ASI.

Andy

"Andy" wrote in message
oups.com...

Jmarc99 wrote:
After having read all the posts in the previous thread, no one said a
word
about de right airspeed to keep along the final approach... whatever
this is done
with a sideslip or crabbing.


Beware of flying indicated airspeed during a slipping approach. The
pitot/static system on some giders will give large indicated airspeed
errors when slipping. As an extreme example my ASW-19 read zero
airspeed in a full rudder slip, probably due to the nose pot pitot.
You need to know your glider and fly the appropriate attitude rather
than the ASI.

Andy


Sure Andy. I am pretty well aware about the false reading of the
indicated airspeed. I stick to visually have the right angle with horizon
at all time in order to get a steady right speed during base and final.

It seams that everybody miss the right question in this thread.. What
is the right airspeed to decide to get, when the wind is NOT perfectly
alligned with the runway?

When you have 15 knots wind, with gusts at 20...

at 0 degree with the runway , you'll calculate 1.3 Vs + 15, right ?
at 45 degree ... calculate 1.3 Vs + 15, right.. maybe ?
at 90 degree ... calculate 1.3 Vs + 15, right.. no ?
at 135 degree ... calculate 1.3 Vs + 15, no.. right.. maybe ?
at 180 degree (wind right from the back) ... calculate 1.3 Vs + 15, always?

or 1.3 Vs + 20 knots at all times, whatever the wind direction with
the runway ? Or only 1.3 Vs when the wind will be at the back during
the final ?

The questtion is.. WHAT IS THE CALCULATED SPEED
do you wish to get during the base and final, according with
the wind angle with the runway. Do you take care the gusts speed
or not in your calculation ?

Is anyone can answer that simple question?

jmarc..

Jmarc99 wrote:
When you have 15 knots wind, with gusts at 20...

at 0 degree with the runway , you'll calculate 1.3 Vs + 15, right ?
at 45 degree ... calculate 1.3 Vs + 15, right.. maybe ?
at 90 degree ... calculate 1.3 Vs + 15, right.. no ?
at 135 degree ... calculate 1.3 Vs + 15, no.. right.. maybe ?
at 180 degree (wind right from the back) ... calculate 1.3 Vs + 15, always?

or 1.3 Vs + 20 knots at all times, whatever the wind direction with
the runway ? Or only 1.3 Vs when the wind will be at the back during
the final ?

The questtion is.. WHAT IS THE CALCULATED SPEED
do you wish to get during the base and final, according with
the wind angle with the runway. Do you take care the gusts speed
or not in your calculation ?

I can tell you what I'd do in England (that's important, because in very
different conditions, such as hot country or mountains, I'd be asking
local pilots for advice).

1. Nil wind landing speed for an airfield or flat field is 1.3 Vs. 10 kt
more for landing uphill, even more for a steep slope.

2. Plus half estimated max wind speed (i.e. gusts, not the average,
because you're giving yourself a margin for the worst that can happen).
So if the wind is 15kt gusting 20kt I'd add 10kt. Adding all the wind
speed is too much for a field landing, giving you a closer view of the
far hedge than is comfortable. I don't have different landing speeds for
runways and fields because it would be too easy to use the wrong one
under pressure.

3. If the wind is cross, there's a useful rule of thumb to reduce it by
1/6 for every 10 degrees from 90 to get the headwind component. 90
degrees cross = 0/6 (i.e. no head wind), 60 degrees cross=3/6 (half head
wind), 30 degrees cross=6/6 (full head wind). So in our example, if the
wind is 15/20kt at 60 degrees I'll treat it as gusting 10kt headwind and
add 5 kt.

4. Finally, you may need to add a margin for expected wind shear,
curlover etc - here you need advice from local pilots. If you've got
yourself into the situation where you only have a bad field you will
need to compromise, in which case remember that undershooting at flying
speed is usually worse than running into the far hedge at a lower speed.

Where I fly the fields are big and there are few hills, so input from
those who fly in more challenging areas would be worth reading.

Chris Reed wrote:

1. ... 10 kt more for landing uphill, even more for a steep slope.
....
2. Plus half estimated max wind speed
....
3. If the wind is cross, there's a useful rule of thumb to reduce it by
1/6 for every 10 degrees from 90 to get the headwind component.

And when exactly are you going to calculate all this? :-P

I'm just doing normal approach speed plus 1/2 estimated wind, no matter
what direction (except tailwind, of course). Has always worked good
enough for me.

BTW: 5 kt for upslope is enough, even for steep slopes. But when the
field is long enough, 10 kn don't hurt, either.

Stefan

Stefan wrote:

And when exactly are you going to calculate all this? :-P

On downwind leg, and I won't do the full calculation. Something like 90
degrees= nil wind, 60 = half wind, 30=full headwind. In the example this
gives me +0, +5 or +10. Close enough.

If your glider floats well, like my Open Cirrus, then the extra few
knots is significant. If I land 10kt over the correct speed for the day,
I'll float more than twice as far after the roundout.

"Chris Reed" wrote in message
...
On downwind leg, and I won't do the full calculation. Something like 90
degrees= nil wind, 60 = half wind, 30=full headwind. In the example this
gives me +0, +5 or +10. Close enough.

If your glider floats well, like my Open Cirrus, then the extra few knots
is significant. If I land 10kt over the correct speed for the day, I'll
float more than twice as far after the roundout.

Hi Chris,
You wrote that something like 90 degrees= nil wind. So if someone
do a slip in the wind direction in order to sayt alligned with the runway
during the final leg, the pitch angle of the sailplane is somewhere greater
than supposed! In this case, with 90 degree wind, the sailplaine have
to travel a longer way through the air mass.

Though, the sailplane fly more faster than supposed, and the pilot
doesn't use much airbrake! Is that what effectively happen in that
wind condition?

Jmarc

Jmarc99 wrote:
You wrote that something like 90 degrees= nil wind. So if someone
do a slip in the wind direction in order to sayt alligned with the runway
during the final leg, the pitch angle of the sailplane is somewhere greater
than supposed! In this case, with 90 degree wind, the sailplaine have
to travel a longer way through the air mass.

Though, the sailplane fly more faster than supposed, and the pilot
doesn't use much airbrake! Is that what effectively happen in that
wind condition?

Jmarc


I'm not suer I understand the question properly.

My crosswind landing technique is to crab into wind, and then kick off
the drift after the roundout. This works fine for, say, a 10kt crosswind
at 90 degrees, and at that wind speed there's no real danger of wind shear.

However, if the wind is gusting 20kts or more at 90 degrees, that's
outside the demonstrated crosswind limits of my glider. Ideally, I
choose a better landing direction. If I had no choice (e.g. poor or late
field selection), then this would be one of those "interesting" landings
which test one's improvisational and piloting skills. I'd be using a
combination of crabbing and slipping, to give me less drift to kick
off,and I'd certainly add 10 kts or more to allow for gusts and wind
shear unless that seemed more dangerous than approaching at a slower speed.

I guess the point I was really trying to make is that if on every
landing you add extra speed for "safety", the result is that you never
learn to land with the minimum safe energy. This is a skill that I think
every XC pilot needs. However, in gusty or high winds, you have to allow
for the possibility of needing extra control authority or suddenly
losing 15kts airspeed through wind shear. So minimum safe energy
landings are for benign conditions.