Crosswind Landings... But airspeed?

"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.

"Chris Reed" wrote in message
...
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.

I also prefer crabing than slipping!
I also agree that a little wind, coming from any direction, can't produce
dangerous wind shear. No wind means no real effective change in the
wind speed or wind direction.


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.

No need for extra speed when there is no wind at all! I agree again
that is important to 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.

The real point to talk in this thread is "how much" speed to add to
the 1.3 Vstall speed, depending on the wind speed? Especially if
the wind come from a side or the back!

All pilots seams to say that only the heading portion of the wind
should be took in care, when choosing the landing (circuit) speed.

Is someone might agree that a 15-20 knots wind, at low altitude
(like the final leg) may produce windshear that may lower the
the relative airspeed, instead of increasing it, even when the
wind come frome the back?

This is the real question. I think that very experienced glider
pilots, lurkink in this newsgroup, might have someting very
interesting to say about that!

Sure, the good thing is to land upwind, anyway! But, is that
right to reduce the speed to only 1.3 Vstall when you realize,
when doing the base leg, you're going to land tailwind?

Thanks Chris, for your interest to this question!

Jmarc...

"Jmarc99" wrote in message
.. .

"Chris Reed" wrote in message
...
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.

I also prefer crabing than slipping!
I also agree that a little wind, coming from any direction, can't produce
dangerous wind shear. No wind means no real effective change in the
wind speed or wind direction.


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.

No need for extra speed when there is no wind at all! I agree again
that is important to 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.

The real point to talk in this thread is "how much" speed to add to
the 1.3 Vstall speed, depending on the wind speed? Especially if
the wind come from a side or the back!

All pilots seams to say that only the heading portion of the wind
should be took in care, when choosing the landing (circuit) speed.

Is someone might agree that a 15-20 knots wind, at low altitude
(like the final leg) may produce windshear that may lower the
the relative airspeed, instead of increasing it, even when the
wind come frome the back?

This is the real question. I think that very experienced glider
pilots, lurkink in this newsgroup, might have someting very
interesting to say about that!

Sure, the good thing is to land upwind, anyway! But, is that
right to reduce the speed to only 1.3 Vstall when you realize,
when doing the base leg, you're going to land tailwind?

Thanks Chris, for your interest to this question!

Jmarc..

One answer is based on understanding what the "reported wind" really means.
15kt gusting to 25 kt means that the average speed over time (I have
forgotten the exact time interval but about 30 to 60 sec) is 15kt. If peak
gusts are 25kt, then that means it can fall as low as 5kt on the average,
and for some moments can be 0kt. The gusts come from turbulence, and can
therefore come from *any* direction. The danger is not so much the 25kt gust
but the 5kt lull. Hence the advice to add the gust differential to the
approach speed. Some advise "half the wind plus half the gust
differential"--more or less the same result. What is needed is to remain
above stall speed until touchdown! Thankfully, the wind is much less very
close to the ground---3-4 ft (1 meter). My glider stalls at 38kt --1.3 Vs
is therefore ~ 50kt. So, with a "negative" (opposite direction) gust, I
would be very close to stall without the extra velocity.

As to the tailwind question---the wing only knows airspeed. But the landing
field does not move with the wind, so the ground speed is eventually
important. The pilot will be tempted to slow at this point as the ground
speed seems high. Then there is the loss of control issue then the glider is
rolling on the ground, but has little aerodynamic control due to low
airspeed. Finally there is a wind shear issue at about 200 ft. If you are
landing downwind, you will descend into a decreasing tailwind, and inertial
forces will give you an increase in airspeed. It is best to be on final
approach before descending into this shear, which BTW, always exists. It is
just the magnitude that varies. This is so speed adjustments can be made
without the complications of turning--i.e. raised stall speed, increased
workload, etc.

Sooner or later, you will have to slow down in order to land and stop. So
fly the "no wind" approach speed and add the gust differential, until it is
time to roundout and land. Use the brakes if the tailwind is leading to a
imminent loss of control.

Happy Landings
Hartley Falbaum
ASW27B KF USA

At 14:00 30 September 2005, Jmarc99 wrote:
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..

Given that the above calculation is made with regard
to the surface wind and that as far as the glider is
concerned until it touches down the direction of the
surface wind is of no consequence to the aircraft
(the relative airflow experienced by a flying glider
has no connection to the wind direction) I fail to
see why the question is being asked. The simple answer
is you have made the calculation based on the windspeed.
Why do you need to worry about your groundspeed once
you have touched down?

"Don Johnstone" wrote in
message ...
...
Given that the above calculation is made with regard
to the surface wind and that as far as the glider is
concerned until it touches down the direction of the
surface wind is of no consequence to the aircraft
(the relative airflow experienced by a flying glider
has no connection to the wind direction) I fail to
see why the question is being asked. The simple answer
is you have made the calculation based on the windspeed.
Why do you need to worry about your groundspeed once
you have touched down?

Hi Don,

Indeed, the real concern is not about groundspeed...! It's
about the right flying speed to get on the final leg, depending
to the wind direction.

The rule to calculate the airspeed is to increase it if the
wind direction is facing the aircraft, but the rule seams to
say that we shouldn't add anyting when the wind come the
back. Sure, we would not substract anyting to1.3 Vstall
in this case.

Should we add the same amount of knots to 1.3 Vstall,
regardless of the wind direction for every circuit legs?