Effect of rain on gliders in flight

Hi all,

Beginner student here again.

The weather during my last training session was overcast with ceiling
at 2,500 ft. Right after our last tow for the day to 2,000.....after
the release and a turn or two....it started to rain, perhaps for just
5-10 seconds. I could see the rain drops on the canopy and see them
pushed back by the relative wind.

My instructor made no mention of it and I forgot to ask about it post
landing.

What are the implications about getting rained on in flight?
Obviously, if the ceiling is 2500 and overcast, this is primarily a
"training day." How should a glider pilot react to rain? How does it
affect the control of the aircraft?

How does one fly safely in the event or threat of rain?

--Michael

Michael,

First, welcome to soaring. All of us were beginners once, and it's
great that you are asking questions. The things that come to mind with
rain:

Is there a possibility of lightning? If so, stay clear. Composite
ships are especially prone to lightning damage and I seem to remember
hearing of damage to the metal control linkages in one glider.

High performance gliders will suffer more loss of L/D in rain due to
their laminar flow airfoils -- which rain makes non-laminar flow, with
higher drag.

Will visibility stay VFR? Aside from seeing other traffic, is there
any danger of loss of spatial orientation?

A good general rule: If it feels dangerous, it probably is. At a
minimum, err on the side of believing that until you confirm
otherwise.

Martin

Rain on the wings will almost certainly increase the stall speed - by
how much depends on the particular airfoil. As a rule of thumb, older
wood & fabric or metal gliders suffer only a little degradation, early
glass (like my Open Cirrus) suffers quite a lot, newer glass suffers
something in between.

This means that if you are landing with wet wings you need a higher
approach speed to retain the same safety margin over the stall. Your
instructor will advise you (but maybe later in your training - now
you've got too much to think about just following the tow plane).

*Never* winch launch with wet wings, as this could lead to a stall and
spin off the wire. I wouldn't aerotow with anything more than mildly
damp wings either.

There is also an illusion caused by rain on the canopy that makes the
glider appear higher than it is - causing the pilot to flare higher
than normal. When you have rain on the windscreen, you should gently
fly it on; it is a surprise when you find that the height you expect
to touch the ground is not correct. Also, because you think you're
higher, you tend to fly a lower approach, so add a few feet for
obstacle clearance in rain.

There will also be a tendancy for the inside of the canopy to mist up
more, so open the vents.

What are the implications about getting rained on in flight?
Obviously, if the ceiling is 2500 and overcast, this is primarily a
"training day." How should a glider pilot react to rain? How does it
affect the control of the aircraft?

How does one fly safely in the event or threat of rain?

--Michael


Most of the time, light rain is not going to be troublesome with
training flights as long as the visibility is good. However, take it
from one who knows: Even light rain can be accompanied by an occasional
downburst or or unexpected wind shear. You don't have to be actually
caught in the downburst itself. A downburst near the field can result in
a very rapid change in wind direction (shear). Not good if it catches
you on landing or takeoff. I was getting checked out in a glass 2-seater
for the first time. An instructor and I were doing takeoffs and landing
in a Grob. A little light rain had started falling. Almost now wind.
Ceiling was probably around 2000' but we were only towing to 800-1000.
We were on the takeoff run on what was to be my last dual flight that
day. We had just lifted off behind the Maul tug and airspeed was
indicating about 70 (don't remember if it was knots or mph).
Unexpectedly, the Maul plopped back down onto the runway, then we did
the same. I glanced at the airspeed and it was reading 40! Then I
noticed the trees tops whipping around. We were too close to the end of
the runway at that point to abort and the Maul went up over the low
trees at the end and we went with him. We immediately started descending
into the valley and picked up some speed. We got rolled around pretty
violently. The Maul driver got it more-or-less back under control,
managed to start climbing, and expressed his surprise that we had not
broken the tow rope in the turbulence. As we turned back towards the
airport, things calmed down. We had been caught in a reversal of wind
direction, apparently due to a downburst off the approach end of the
field.

On Apr 26, 9:36*pm, Michael wrote:
Hi all,

Beginner student here again. *

The weather during my last training session was overcast with ceiling
at 2,500 ft. *Right after our last tow for the day to 2,000.....after
the release and a turn or two....it started to rain, perhaps for just
5-10 seconds. *I could see the rain drops on the canopy and see them
pushed back by the relative wind.

My instructor made no mention of it and I forgot to ask about it post
landing.

What are the implications about getting rained on in flight?
Obviously, if the ceiling is 2500 and overcast, this is primarily a
"training day." *How should a glider pilot react to rain? *How does it
affect the control of the aircraft?

How does one fly safely in the event or threat of rain?

--Michael

When wet, some airfoils, such as found on the Pic-20, can turn your
glider into a lawn dart... more like a hang glider than a slick glass
ship.... maybe 15:1. And, associated with some rain can be some
unpredictable and changing winds... strong down, strong up, headwind,
crosswind, downwind.

In my opinion, days that are overcast, and possibly rainy, should be
left to the ducks, not gliding... much less training gliding. We
might be eager to fly, and train, but haste can make waste... or
worse. Think safety. Fly safe.

19

Then again, if you are training in a 2-33, a little rain will probably
increase your performance by washing some of the bugs and dirt off!

Seriously, in a non-laminar wing (any metal trainer, pretty much),
especially if it hasn't been waxed recently (and who waxes a 2-33 or a
Lark!), light rain will have no aerodynamic effect. Biggest problem
will be reduced visibility through the canopy, and less braking action
if you land on grass.

Obviously, stay away from heavy rain showers or thunderstorms, but
pattern-bashing in a light, occasional drizzle beats watching birds
fly.

Good training, too.

Kirk

On Apr 27, 11:29*am, "
wrote:
Then again, if you are training in a 2-33, a little rain will probably
increase your performance by washing some of the bugs and dirt off!

Seriously, in a non-laminar wing (any metal trainer, pretty much),
especially if it hasn't been waxed recently (and who waxes a 2-33 or a
Lark!), light rain will have no aerodynamic effect. *Biggest problem
will be reduced visibility through the canopy, and less braking action
if you land on grass.

Obviously, stay away from heavy rain showers or thunderstorms, but
pattern-bashing in a light, occasional drizzle beats watching birds
fly.

Good training, too.

Kirk

Kirk beat me too it! When you have an ugly crinkled metal wing
bristling with rivets, a few raindrops are hardly going to matter from
an aerodynamic perspective.

The most important consideration is the type of cloud overhead
producing the rain. Out here in the US west, there's a good chance
it'll be a shower cloud or thunderstorm that may produce downdrafts
and lightning - things to worry about a lot more than a few raindrops.

If you are in western Europe where most of the rain comes from
stratiform clouds, it's not so bad. Heck - if you live in some of the
countries with the worst climate (Britain for example), flying in the
rain is a necessary skill!

Mike

I also did some of my initial training in a 2-33 in the rain.
Naturally a light steady rain with good visibility, not associated
with unstable air. One thing nobody has mentioned is the sound. Even a
light rain sounds like someone is throwing BB's at the canopy.

I've also had to deal with rain while out on course on a cross-country
flight, and my glider has the same airfoil as a PIK-20. I've
thermalled to cloudbase more than once in a steady rain from lake-
effect cumulus (with full water ballast). I've also had to ridge soar
through heavier rain that ran across the wing in sheets (the boundary
layer water flow was mostly laiminar, the airflow not so much). And I
used a rain street to run upwind and get home late in the day. But
I've also landed out just a few miles from home when a summer thermal
street overdeveloped and started raining on me. So there is a
performance hit from rain, but it does not necessarily mean the end of
your soaring day. In fact, one promising soaring day almost looked
like a bust, until we realized the rain over the airport was falling
from a massive wave cloud--we towed upwind out of the rain, and had an
amazing wave flight.

On Apr 27, 4:40*pm, Mike the Strike wrote:
On Apr 27, 11:29*am, "
wrote:





Then again, if you are training in a 2-33, a little rain will probably
increase your performance by washing some of the bugs and dirt off!

Seriously, in a non-laminar wing (any metal trainer, pretty much),
especially if it hasn't been waxed recently (and who waxes a 2-33 or a
Lark!), light rain will have no aerodynamic effect. *Biggest problem
will be reduced visibility through the canopy, and less braking action
if you land on grass.

Obviously, stay away from heavy rain showers or thunderstorms, but
pattern-bashing in a light, occasional drizzle beats watching birds
fly.

Good training, too.

Kirk

Kirk beat me too it! *When you have an ugly crinkled metal wing
bristling with rivets, a few raindrops are hardly going to matter from
an aerodynamic perspective.

The most important consideration is the type of cloud overhead
producing the rain. *Out here in the US west, there's a good chance
it'll be a shower cloud or thunderstorm that may produce downdrafts
and lightning - things to worry about a lot more than a few raindrops.

If you are in western Europe where most of the rain comes from
stratiform clouds, it's not so bad. *Heck - if you live in some of the
countries with the worst climate (Britain for example), flying in the
rain is a necessary skill!

Mike-

At 00:02 28 April 2009, wrote:
I also did some of my initial training in a 2-33 in the rain.
Naturally a light steady rain with good visibility, not associated
with unstable air. One thing nobody has mentioned is the sound. Even a
light rain sounds like someone is throwing BB's at the canopy.

I've also had to deal with rain while out on course on a cross-country
flight, and my glider has the same airfoil as a PIK-20. I've
thermalled to cloudbase more than once in a steady rain from lake-
effect cumulus (with full water ballast). I've also had to ridge soar
through heavier rain that ran across the wing in sheets (the boundary
layer water flow was mostly laiminar, the airflow not so much). And I
used a rain street to run upwind and get home late in the day. But
I've also landed out just a few miles from home when a summer thermal
street overdeveloped and started raining on me. So there is a
performance hit from rain, but it does not necessarily mean the end of
your soaring day. In fact, one promising soaring day almost looked
like a bust, until we realized the rain over the airport was falling
from a massive wave cloud--we towed upwind out of the rain, and had an
amazing wave flight.

On Apr 27, 4:40=A0pm, Mike the Strike wrote:
On Apr 27, 11:29=A0am, "
wrote:





Then again, if you are training in a 2-33, a little rain will
probably
increase your performance by washing some of the bugs and dirt off!

Seriously, in a non-laminar wing (any metal trainer, pretty much),
especially if it hasn't been waxed recently (and who waxes a 2-33 or
a
Lark!), light rain will have no aerodynamic effect. =A0Biggest
problem
will be reduced visibility through the canopy, and less braking
action
if you land on grass.

Obviously, stay away from heavy rain showers or thunderstorms, but
pattern-bashing in a light, occasional drizzle beats watching birds
fly.

Good training, too.

Kirk

Kirk beat me too it! =A0When you have an ugly crinkled metal wing
bristling with rivets, a few raindrops are hardly going to matter from
an aerodynamic perspective.

The most important consideration is the type of cloud overhead
producing the rain. =A0Out here in the US west, there's a good chance
it'll be a shower cloud or thunderstorm that may produce downdrafts
and lightning - things to worry about a lot more than a few raindrops.

If you are in western Europe where most of the rain comes from
stratiform clouds, it's not so bad. =A0Heck - if you live in some of
the
countries with the worst climate (Britain for example), flying in the
rain is a necessary skill!

Mike-

When you encounter precip you are likely to experience sink to one extent
or another because of the cooling effect of droplets or crystals that have
a relatively large surface area or just the natural effect of
precipitation entraining some local air as it descends. But as long as you
are dealing with the stable air type of precip--drizzle or flurries--its
unlikely to be noticeable