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Base to final, cross wind stall

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Base to final, cross wind stall

Old 10-28-2014, 03:07 AM
  #51  
BobbyMcGee
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For a brief moment, the earth stopped rotating at the time RCPete was turning final. That caused his plane to fall from the sky. It did not stall ... It simply fell from the sky.

I hope that answers the question, and we don't have to go through another 48 pages of the misconception of aerodynamic stalls. THERE IS NO SUCH THING AS AERODYNAMIC STALLS ... It's just a simple fact that the earth stops rotating from time to time. Then someone has to "reboot" the earth.

Last edited by BobbyMcGee; 10-28-2014 at 03:12 AM.
Old 10-28-2014, 03:28 AM
  #52  
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What force acted on the aircraft to cause its airspeed to drop from 60 to 40 during the turn?
The air slowed down!

On base leg the model was flying into a head wind of 20 mph.

As it turned onto final that 20 mph wind ACROSS the chord of the wing became a 20 mph wind blowing from tip to tip, not much help developing lift.

Ironically, as the plane turned from flying into the wind to flying across it, it may have actually gained more ground speed.

Think of it this way, if you had a model with quite a bit of wing incidence (say like a propeller trainer) flying steadily cross wind & then you turn it into
the wind what happens? It balloons up, because the speed of the air across the wing increases the lift. Of course we shove in some down elevator
so it doesn't balloon right up & stall.

If that same trainer is turned from cross wind to down wind it drops (apart from the usual tendency for a model to drop it's nose in turns) because until
it 'catches up' with moving mass of air the speed of the air across the wing has fallen. We shove in some up elevator to keep the nose up so it doesn't
pile into the ground which reduces the speed of the model relative to the moving mass of air even further. Hopefully the speed safety margin (airspeed
above stall speed) is great enough to keep the model flying until it catches up with the moving mass of air.

Otherwise: he who stalleth, falleth!

Jets are more a point & shoot device than a trainer so the effects of wind are less obvious but, if you're flying close to stall speed anyway, like on approach,
if you don't have a large enough airspeed safety margin down you go.

My opinion anyway, have a think about it. - John.
Old 10-28-2014, 04:04 AM
  #53  
Rob2160
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Originally Posted by Boomerang1
The air slowed down!

On base leg the model was flying into a head wind of 20 mph.

As it turned onto final that 20 mph wind ACROSS the chord of the wing became a 20 mph wind blowing from tip to tip, not much help developing lift.

Ironically, as the plane turned from flying into the wind to flying across it, it may have actually gained more ground speed.

Think of it this way, if you had a model with quite a bit of wing incidence (say like a propeller trainer) flying steadily cross wind & then you turn it into
the wind what happens? It balloons up, because the speed of the air across the wing increases the lift. Of course we shove in some down elevator
so it doesn't balloon right up & stall.

If that same trainer is turned from cross wind to down wind it drops (apart from the usual tendency for a model to drop it's nose in turns) because until
it 'catches up' with moving mass of air the speed of the air across the wing has fallen. We shove in some up elevator to keep the nose up so it doesn't
pile into the ground which reduces the speed of the model relative to the moving mass of air even further. Hopefully the speed safety margin (airspeed
above stall speed) is great enough to keep the model flying until it catches up with the moving mass of air.

Otherwise: he who stalleth, falleth!

Jets are more a point & shoot device than a trainer so the effects of wind are less obvious but, if you're flying close to stall speed anyway, like on approach,
if you don't have a large enough airspeed safety margin down you go.

My opinion anyway, have a think about it. - John.
I'll give you a scenario and following your logic above would like to hear your opinion.

Flying a Cessna 152 - cruise speed 100 Kts. at 1000 ft.

Stall Speed @ 1G (level flight) = 45 kts

There is a Steady (unchanging) wind of 60 knots blowing from the north.

The aircraft is flying north at 100 Kts airspeed, it then banks right to 30 degrees and completes a 360 turn back onto north. The pilot does not change altitude.

What is the Airspeed & Ground speed when facing...

North

East

South

West.

second part of my question - is it actually possible for this aircraft to complete a 360 degree turn under these conditions?

Last edited by Rob2160; 10-28-2014 at 04:07 AM.
Old 10-28-2014, 04:34 AM
  #54  
George
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Originally Posted by Rob2160
I'll give you a scenario and following your logic above would like to hear your opinion.

Flying a Cessna 152 - cruise speed 100 Kts. at 1000 ft.

Stall Speed @ 1G (level flight) = 45 kts

There is a Steady (unchanging) wind of 60 knots blowing from the north.

The aircraft is flying north at 100 Kts airspeed, it then banks right to 30 degrees and completes a 360 turn back onto north. The pilot does not change altitude.

What is the Airspeed & Ground speed when facing...

North

East

South

West.

second part of my question - is it actually possible for this aircraft to complete a 360 degree turn under these conditions?
This will be interesting!!
Old 10-28-2014, 04:38 AM
  #55  
bevar
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Pete,

Sorry Mate...but inputting all the aileron in the world will not alone make an airplane snap roll...at any speed. It snapped because you had too much elevator in for the airspeed you were flying at the moment it stalled.

I hope it was not Frankenstein...I just love what you did with that jet!

Boli
Old 10-28-2014, 05:06 AM
  #56  
Top_Gunn
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Think of it this way, if you had a model with quite a bit of wing incidence (say like a propeller trainer) flying steadily cross wind & then you turn it into
the wind what happens? It balloons up, because the speed of the air across the wing increases the lift. Of course we shove in some down elevator
so it doesn't balloon right up & stall.
I have a Kadet Seniorita with a small four-stroke engine. On days when there's a steady wind, I like to take it up high, fly upwind some, trim for a turn, set the transmitter down, and watch it fly spirals while drifting back downwind toward the field. It does not balloon at all (or drop at all) during these turns. If I give it a bunch of throttle, it will start to climb, because the airspeed has increased. But the airspeed doesn't increase just because you are turning. The reason some trainers "balloon up" when turning is that inexperienced pilots don't get off the elevator soon enough when they come out of the turn. This is particularly true when turning into the wind, because to make that turn look good from the ground, you have to bank more steeply than usual, and so you have to use more up elevator.

The plane is flying in a mass of moving air. So the "wind" doesn't "blow" along or across the wings. Get a ride in an open-cockpit biplane some day. You won't feel any wind, because the windscreen blocks the only relative wind the plane is subject to in coordinated flight: straight from the front. For more examples, google "downwind turn myth."

All of this assumes no gusts or wind shear.
Old 10-28-2014, 05:59 AM
  #57  
speedracerntrixie
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Al you are correct. The issue here is that we all pilot from the perspective of ground speed because that is the only visual reference we have. What I believe happened here is that while Pete was flying into the wind his perspective was that the model was at the appropriate airspeed. While turning to cross wind, the model maintained it's airspeed which means that the ground speed increased.. Pete saw that increase in groundspeed cause by the reduction of drag by no longer having a head wind. He instinctively pulled back to decrease the ground speed to the point of getting below minimum airspeed and stalled. I think we have all done this but someone with experience at flying slow would " feel " the controls getting mushy and increase throttle an/or ease off the elevator.
Old 10-28-2014, 05:59 AM
  #58  
invertmast
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Guys,
i hate to tell you this, but the wind at the surface can be significantly different than the wind at 100/200/300+ feet above the surface. If it is a direct crosswind into your face and 6mph on the surface it can at times be 180* completely different and higher or lower wind speeds or not change at all. "Micro climates" are very abundant due to the stuff on the ground.
My full time job entails operating a fullsize kingair at 300' agl (above ground level). There have been times where the winds are dead calm at an airport, but directly above that airport at 300' agl, the winds are blowing a hard 30+kts. I know this for fact because i have a $90k real time weather monitoring system on board.

So while our perception of what we think is happening on the ground based in the surface wind is one thing, the actual conditions have the possibility of being completely different where the airplane is.

Last edited by invertmast; 10-28-2014 at 06:19 AM.
Old 10-28-2014, 06:15 AM
  #59  
HoundDog
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The only thing that caused the plane to stall and crash was "PILOT ERROR" Just like the NTSB says about most (all) Stall Spin accidents ... "Failure to maintain flying speed". It is Pilot error if U don't realize that in a 20 MPH wind U have to compensate for the apparent speed of the aircraft Relative to the ground, no mater what direction the plane is relative to the wind.
Old 10-28-2014, 06:20 AM
  #60  
bevar
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On the jets I fly in the real world, we have what is called a wind vector arrow. It shows the wind direction and velocity derived from the FMCs real time.

While landing, below 800' I have seen the wind direction change a complete 360 degrees the last few hundred feet prior to touchdown. I think some here are way over thinking the problem as to what happened to Pete. None the less it is stimulating conversation and is quite helpful to the community at large because it does give all of us a better understanding of aerodynamics and how it relates to what we do at the flying field.

Cheers,

Boli

Last edited by bevar; 10-28-2014 at 06:23 AM.
Old 10-28-2014, 06:41 AM
  #61  
HoundDog
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Originally Posted by bevar
On the jets I fly in the real world, we have what is called a wind vector arrow. It shows the wind direction and velocity derived from the FMCs real time.

While landing, below 800' I have seen the wind direction change a complete 360 degrees the last few hundred feet prior to touchdown. I think some here are way over thinking the problem as to what happened to Pete. None the less it is stimulating conversation and is quite helpful to the community at large because it does give all of us a better understanding of aerodynamics and how it relates to what we do at the flying field.

Cheers,

Boli
I believe U ment 180 degrees, Correct
Old 10-28-2014, 06:42 AM
  #62  
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Lots of wisdom in the last five posts. RC pilots can easily mistake ground speed for airspeed, winds get squirrely near the ground (especially if they blow past trees or buildings), and RC pilots tend to want to make all turns have the same radius, no matter what the wind speed and direction. The moral of the story is keep your airspeed up down low. And when it's windy, keep it up more. And even more when turning from downwind to base and base to final, because that is where the stall-spin crashes occur.

Last edited by Top_Gunn; 10-28-2014 at 11:54 AM. Reason: correct count: didn't mean to leave anyone out.
Old 10-28-2014, 06:49 AM
  #63  
HoundDog
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Originally Posted by Top_Gunn
Lots of wisdom in the last four posts. RC pilots can easily mistake ground speed for airspeed, winds get squirrely near the ground (especially if they blow past trees or buildings), and RC pilots tend to want to make all turns have the same radius, no matter what the wind speed and direction. The moral of the story is keep your airspeed up down low. And when it's windy, keep it up more. And even more when turning from downwind to base and base to final, because that is where the stall-spin crashes occur.
Exactingly ... No truer words were ever spoken .... Airspeed, Airspeed, Airspeed.
The 3 most useless things in aviation are Altitude above U, Run Way behind U and Fuel in the Truck. To this I'd add
the Lack of Airspeed.
Old 10-28-2014, 07:12 AM
  #64  
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Invert, good points. When discussing IMAC spin entries I had told another pilot to keep the nose of the airplane pointed straight ahead with rudder. One guy jumped in and reminded me that the rules allow for 45 degrees of ' Weathervane " of which he was correct. However I explained is that the judges have no idea what the wind is doing 1,000 feet up so if it is calm at ground level they are going to want to see the maneuver flown as if in clam weather.
Old 10-28-2014, 07:12 AM
  #65  
Rob2160
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Originally Posted by bevar
On the jets I fly in the real world,
Cheers,

Boli
What do you fly? Is your sim training in the USA or elsewhere? The reason I ask is related to the information I posted on Stick position vs Angle of Attack which has been part of many Aerobatic rating syllabi in Australia for years (See below)

Bombardier also cover it during sim training in Montreal (I fly a GLEX) but I never saw it at Flight Safety Wichita when I was on the HS125.

From the Australian CASA Aerobatics CAAP. http://www.casa.gov.au/wcmswr/_asset.../ops/155_1.pdf

3.14 Stick Position And The Stall


3.14.1 An important aspect of both normal and aerobatic flight is the
relationship of the stick position to the angle of attack of a wing for a
specific flap setting or centre of gravity, in particular at the stall. The
fore and aft position of the control column determines the angle of the
aircraft's wings to the airflow. For example, the stick positions for
cruise, glide and the stall move progressively aft. Once the stick
position for the stall has been determined (and remembered), it can be
used as a measure of whether an aircraft's wing is stalled or not. If the
stick is forward of the 'stalled stick position', the aircraft will always
be in unstalled flight, regardless of aircraft attitude or airspeed.


3.14.2 Appreciation of this concept, and the ability to recognise and
apply stick position to achieve CLMAX (that is the point just before a
wing stalls) can increase awareness and enhance a pilot's confidence
and aircraft handling at this critical phase of flight.

That last point is also very useful for windshear recoveries when you need maximum climb performance.

Last edited by Rob2160; 10-28-2014 at 07:19 AM.
Old 10-28-2014, 07:21 AM
  #66  
dbsonic
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In high wind conditions there is a wind gradient that we typically fly through on final. The gradient is due to friction with the earths surface. This can be observed in smoke plumes and dust turned up by farming plows near the airport. Roughly 500 feet down to the ground you can often times see a 5 to 10 knot difference in headwind. Which means you can be robbed of 5-10 knots airspeed and is the main reason to carry extra airspeed in the base and final leg to ensure staying above stall on the flare and ensure good control in that phase of landing and rollout. I don't know how much this really matters in RC since the scale is quite different but it does exist for models as well in high wind conditions (where it would be most noticeable). Start throwing in obstacles around the airport, hangars, trees, mountains and the occasional t-storm microburst and a pilot can have a real handful of complex wind patterns!
Old 10-28-2014, 07:35 AM
  #67  
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Originally Posted by Rob2160
What do you fly? Is your sim training in the USA or elsewhere? The reason I ask is related to the information I posted on Stick position vs Angle of Attack which has been part of many Aerobatic rating syllabi in Australia for years (See below)

Bombardier also cover it during sim training in Montreal (I fly a GLEX) but I never saw it at Flight Safety Wichita when I was on the HS125.

From the Australian CASA Aerobatics CAAP. http://www.casa.gov.au/wcmswr/_asset.../ops/155_1.pdf

3.14 Stick Position And The Stall


3.14.1 An important aspect of both normal and aerobatic flight is the
relationship of the stick position to the angle of attack of a wing for a
specific flap setting or centre of gravity, in particular at the stall. The
fore and aft position of the control column determines the angle of the
aircraft's wings to the airflow. For example, the stick positions for
cruise, glide and the stall move progressively aft. Once the stick
position for the stall has been determined (and remembered), it can be
used as a measure of whether an aircraft's wing is stalled or not. If the
stick is forward of the 'stalled stick position', the aircraft will always
be in unstalled flight, regardless of aircraft attitude or airspeed.


3.14.2 Appreciation of this concept, and the ability to recognise and
apply stick position to achieve CLMAX (that is the point just before a
wing stalls) can increase awareness and enhance a pilot's confidence
and aircraft handling at this critical phase of flight.

That last point is also very useful for windshear recoveries when you need maximum climb performance.
There are subtle differences that can occur between models and full size aircraft due to the way the trim is employed. In full-size you tend to trim to maintain a stick position (although this may not be true in all cases). In a model, the stick position is maintained by a spring and the trim bypasses this and moves the control surface directly. Therefore, you could fly straight and level close to the stall and by moving the trim fully up the model will stall, but the elevator stick won't have moved. This can become a factor if using flight conditions as you could have a different trim setting in the landing configuration than in normal flight. You might not be able to tell simply from the stick position whether you are close to the stall or not.
Old 10-28-2014, 07:40 AM
  #68  
Rob2160
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Originally Posted by siclick33
There are subtle differences that can occur between models and full size aircraft due to the way the trim is employed. In full-size you tend to trim to maintain a stick position (although this may not be true in all cases). In a model, the stick position is maintained by a spring and the trim bypasses this and moves the control surface directly. Therefore, you could fly straight and level close to the stall and by moving the trim fully up the model will stall, but the elevator stick won't have moved. This can become a factor if using flight conditions as you could have a different trim setting in the landing configuration than in normal flight. You might not be able to tell simply from the stick position whether you are close to the stall or not.
Excellent point and I totally agree.

Personally I never touch the trims on my RC models after initial set up, but I agree for those who do, the exact stick position at the stall on an RC TX will change for the reasons you listed.

With the right radio, it could be programmed to "shift" the activation of the stall warning alert (as in my video) based on the flight condition and any trim adjustments.. That would actually be a good project. - I'll add it to the list..

Last edited by Rob2160; 10-28-2014 at 07:56 AM. Reason: typos - its 3am here.
Old 10-28-2014, 07:59 AM
  #69  
bevar
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HD,

No...360 degrees.

I have been landing before and had to go around at 200'AGL because the called winds of 100 at 8 changed to 180 at 49KTS...on a clear day. About 10 minutes later we landed and the winds were...100 at 7.

Boli

Originally Posted by HoundDog
I believe U ment 180 degrees, Correct
Old 10-28-2014, 08:05 AM
  #70  
bevar
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Rob,

B-757s and 767s currently. I also used to fly full scale airshows when younger and had an unlimited maneuver, any make and model zero altitude Aerobatic Waiver when I was 18 years old. I learned to fly in taildraggers from when I was a Pup...LOL.

Oh...I fly in the U.S. and all of it was done here.

Cheers,

Boli

PS...these creds don't make me better than anyone else...they just have allowed me to see more things that allow me to relate to what we do. My wife will still tell you that I am a dork however...LOL.


Originally Posted by Rob2160
What do you fly? Is your sim training in the USA or elsewhere? The reason I ask is related to the information I posted on Stick position vs Angle of Attack which has been part of many Aerobatic rating syllabi in Australia for years (See below)

Bombardier also cover it during sim training in Montreal (I fly a GLEX) but I never saw it at Flight Safety Wichita when I was on the HS125.

From the Australian CASA Aerobatics CAAP. http://www.casa.gov.au/wcmswr/_asset.../ops/155_1.pdf

3.14 Stick Position And The Stall


3.14.1 An important aspect of both normal and aerobatic flight is the
relationship of the stick position to the angle of attack of a wing for a
specific flap setting or centre of gravity, in particular at the stall. The
fore and aft position of the control column determines the angle of the
aircraft's wings to the airflow. For example, the stick positions for
cruise, glide and the stall move progressively aft. Once the stick
position for the stall has been determined (and remembered), it can be
used as a measure of whether an aircraft's wing is stalled or not. If the
stick is forward of the 'stalled stick position', the aircraft will always
be in unstalled flight, regardless of aircraft attitude or airspeed.


3.14.2 Appreciation of this concept, and the ability to recognise and
apply stick position to achieve CLMAX (that is the point just before a
wing stalls) can increase awareness and enhance a pilot's confidence
and aircraft handling at this critical phase of flight.

That last point is also very useful for windshear recoveries when you need maximum climb performance.

Last edited by bevar; 10-28-2014 at 08:15 AM.
Old 10-28-2014, 10:01 AM
  #71  
GOGGLES PIZANO
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I used to fly IMAC.....one important note to keep aware of is wind direction and wind speed..after a while it becomes second nature.one must be aware of this to fly consistent patterns. Really comes to point flying at new fields for the first time.new background references and terrains can throw the senses of perception off...let alone adrenaline or someone talking causing distraction. I found it useful to bring a well k own beater test plane to get my senses in order and loosen the fingers..get on point to fly.check for wind swirls...drafts around trees etc.we have a great hobby and its always a bummer when crash happens but much more important to analyse to learn from it.when we do and share as we are .....we all are better mentally equipped to operate high performance models....that are expensive and time consuming.thx.
Old 10-28-2014, 10:24 AM
  #72  
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Hello all, here a great article about all this : http://www.australianflying.com.au/n...-downwind-turn
;-)
Old 10-28-2014, 10:32 AM
  #73  
mr_matt
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YADWiTT

(Yet Another Down Wind Turn Thread)

Figured as much in post 4
Old 10-28-2014, 10:41 AM
  #74  
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Matt, I really didn’t want to create or feed such a monster; I just found this article by “educating myself” and thought that some of you may have interest in it…
Old 10-28-2014, 11:24 AM
  #75  
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I'll give you a scenario and following your logic above would like to hear your opinion.

Flying a Cessna 152 - cruise speed 100 Kts. at 1000 ft.

Stall Speed @ 1G (level flight) = 45 kts

There is a Steady (unchanging) wind of 60 knots blowing from the north.

The aircraft is flying north at 100 Kts airspeed, it then banks right to 30 degrees and completes a 360 turn back onto north. The pilot does not change altitude.

What is the Airspeed & Ground speed when facing...

North

East

South

West.

second part of my question - is it actually possible for this aircraft to complete a 360 degree turn under these conditions?
Hi Rob, yep I can see where you are coming from.

To answer the first half of your question:

Travelling north - AS -100kts, GS - 40 kts

east - AS - 100kts, GS - a bit tricky to calculate. Assuming you are going with the flow (pun intended!) & not cranking in full rudder & a heap of aileron trying
to maintain course (that's why we don't fly 152's in 60 kt winds!) and ignoring the fact that the ground speed is constantly changing through the turn, at the point
when the plane is pointing east the ground speed would be 100kts from west to east but the plane would also be drifting north to south at a speed of 60 kts
(the wind speed). The course over the ground would be an angle, NW to SE.

South - AS 100kts, GS - 160 kts

West - AS 100 kts, GS - same situation as east but drifting from NE to SW.

The second half of your question.

Yep, of course the plane could complete it's 360 deg turn although (and your from Sydney)
if you started the turn (assuming constant rate of turn) over Sydney CBD, you would finish
your turn over the airport as the plane would be drifting south.

BUT (it's a big but) that would be a gentle turn. A 30 deg bank in a full size aircraft is not a gentle turn, it's an I want to go over there now turn. (not quite a watch
the wings don't pull off turn though). In a TIGHT turn from into wind to cross wind I believe the airspeed would drop until the plane regains it's equilibrium (probably the first time I've typed that word) with the moving mass of air.

The plane is flying in a mass of moving air. So the "wind" doesn't "blow" along or across the wings. Get a ride in an open-cockpit biplane some day. You won't feel any wind, because the windscreen blocks the only relative wind the plane is subject to in coordinated flight: straight from the front. For more examples, google "downwind turn myth."
Al brings up a good point about the airflow being 'straight from the front'. The key words are coordinated flight. Full size gliders usually have a length of wool taped to the canopy.
It's not a Christmas decoration, it's there to tell the direction of airflow relative to the glider. The name of the game is to do a turn while keeping the wool pointing straight back along the canopy. It's difficult until you get the technique correct. Start hooking into careless turns & the airflow over the canopy (and the wings) will be anything but the right direction.

My last ride in an open cockpit biplane was an AgCat on floats. I think most of the wind was from the 450 HP Pratt & it was certainly coming from the front!

John.

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