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Old Aug 18, 2012, 02:07 PM
agnotology
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Upwind or downwind launch?

I understand the reasoning behind going downwind to find a thermal from a winch launch, but I'm beginning to think ALES may be different. With the ability to thermal search during the 30 second launch, and to go significant distance upwind under power, it seems like going upwind can be an advantage.

In moderate winds I can many times only work one thermal from an upwind position to make the time. If the drift isn't too strong, I end up high and downwind at the 6 or 7 minute mark, and then can penetrate back in time for the landing. If I go downwind in similar conditions, I usually have to leave the first thermal because of visibility, and penetrate back upwind to find more lift. I find this has a higher risk factor for me: finding the second thermal is not always easy.

In even stronger winds, I find an upwind thermal is even more valuable at the start of the flight.

I am still learning how to recognize weaker lift while under power, so my ability to read the air upwind may not be as good as a downwind thermal read.

I'm still trying to sort out the conditions when going upwind or downwind (or cross wind upwind and downwind) seem to be the optimum strategy. What are your experiences?

Kevin
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Old Aug 18, 2012, 02:18 PM
turn, turn, turn.
Athol, Massachusetts
Joined Oct 2005
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Unless you have a good read, flying upwind for thermals is really just a crapshoot.

One can skillfully get a read from the air that has moved by, all around them.... Then you can actually head for a thermal, instead of relying on luck, and simply reading your plane.
Although there's a lot to be said for reading your plane... it's just good to actually have a plan when you launch.... and lift is always downwind.
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Old Aug 18, 2012, 07:28 PM
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12 launches at the Nats, only one that went up wind because we had FF guys with streamers at 90 degrees to what our field streamers were saying. Worked perfectly.

There has been a thread on this in F3X thread, and the overwelming consensus was going downwind is a much higher payoff than up wind anyday. And if I absolutely have no call at all, then I go at 45 degrees to the wind one side or the other, but never directly upwind. When you go directly upwind it is a very bad use of energy versus any other option of to the side or downwind.

Marc
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Old Aug 18, 2012, 09:10 PM
agnotology
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Marc,

I certainly understand going downwind from a winch launch, particularly with a modern moulded full-house sailplane, but I'm still wondering if there isn't a difference using the upwind ranging capability of an ALES launch. I have been having very good success going upwind on windy days at maybe a 45 degree angle after an initial in-to-the wind leg.

How strong were the winds at the nationals? Do you think it would make a difference if you were flying a slower 3m spoiler glider without camber changing?

Perhaps I'll see the light when I finish my eSupra, and I have better penetration back into the wind. Right now getting downwind seems to seriously limit my options when the wind gets past a certain level, and voluntarily going that direction with the motor doesn't seem to work very well unless I have indication of a strong thermal. If I'm upwind I can afford to work lighter lift, and since I can get quite a long way upwind under power I find it buys me time and options.

Perhaps sailplanes with poor wind penetration in glide, but with good penetration under power would need different tactics? I just need a new glider!

Thanks,

Kevin
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Old Aug 18, 2012, 09:33 PM
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Maybe Kevin, but it goes back to reads. The only thing you know for sure is close upwind or downwind. Going upwind is a dice roll, but the Nats was low wind, but also I am flying movers too.

Marc
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Old Aug 18, 2012, 11:58 PM
Where is the lift?
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I go upwind almost every time especially if I'm flying my Radian vs my eSupra. The only exception is an obvious read that is very close or light wind with no penetration issues. Take that with a grain of salt though as I don't have experience flying against the very best...

Charlie
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Old Aug 19, 2012, 09:09 AM
turn, turn, turn.
Athol, Massachusetts
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I'm no stranger to up wind launches... At the last hand launch contest, I worked the upwind side almost the whole entire contest and was quite successful.

But I had reads....lots and lots of reads.

Also, sometimes flying down wind, you can let a feeder take you right into lift, with little loss of altitude.

That said, you need a plane with legs... if you're going to play that game.
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Old Aug 20, 2012, 07:19 AM
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Please clarify something for me.

Are you launching upwind with eveyone then turning downwind to find lift or are you launching downwind behind eveyone?

Thanks

Charlie
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Old Aug 20, 2012, 07:37 AM
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Depends Charlie, if the call is down wind and the winds is such I can go out the back way, maybe. One thing I have done was to head out back at a 90 degree to upwind and behind the line of pilots to be safe. But remember, in my book, I try to have my launch be where I can see the launch from the side if possible so I can nail the end of the launch. I want to hit the end of the launch with some energy to make a final altitude grab and control where I am going.

Marc
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Old Aug 20, 2012, 10:20 AM
turn, turn, turn.
Athol, Massachusetts
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Quote:
Originally Posted by cpc625 View Post
Please clarify something for me.

Are you launching upwind with eveyone then turning downwind to find lift or are you launching downwind behind eveyone?

Thanks

Charlie
At Polecat, I turned around opposite everyone, and launched.
It was not a last second thing, as I turned around well before the countdown.

A round or two later, half the field was doing it as well.
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Old Aug 20, 2012, 10:23 AM
turn, turn, turn.
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Originally Posted by OVSS Boss View Post
Depends Charlie, if the call is down wind and the winds is such I can go out the back way, maybe. One thing I have done was to head out back at a 90 degree to upwind and behind the line of pilots to be safe. But remember, in my book, I try to have my launch be where I can see the launch from the side if possible so I can nail the end of the launch. I want to hit the end of the launch with some energy to make a final altitude grab and control where I am going.

Marc
I'm flying a Topaz S... with 1000 watts on a spring loaded switch...a turn and burn is out of the question for me.

I would destroy the plane.
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Old Aug 20, 2012, 10:58 AM
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I have 300W and a Tragi, and can take any way possible aerodynamically. But also, you could back off the throttle curve and not fold the ship.

Marc
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Old Aug 20, 2012, 11:20 AM
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Quote:
Originally Posted by OVSS Boss View Post
I have 300W and a Tragi, and can take any way possible aerodynamically. But also, you could back off the throttle curve and not fold the ship.

Marc
Marc, I just upgraded my Xplorer 4.0 ST to a 1200 watt system and reduced the AUW to 83.5oz. Looks like the arms race is on. On a brighter note I am still flying my Maxa at 640 watts.
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Old Aug 20, 2012, 12:01 PM
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Supra, 68 oz, 450 watts. 1300 mah TP 65C battery, 18-20 seconds to 200 meters, about 275 ma per climb, separate flight pack battery. Why bother with more power?

JT
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Old Aug 20, 2012, 01:22 PM
agnotology
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I spent some time thinking about why motoring upwind on windy days seems to work better for me, hoping it wasn't entirely the feeling of safety. We have an airplane eating forest in the predominately downwind direction that adds to the excitement of being downwind. I did a bunch of Excel math with different glider polars and wind strengths. I used Dave Register's polars from RCSD, Feb 2004 as a starting point.

Much of what I gleaned is fairly obvious:

- The lift strength required to maintain a glide angle back to the field from downwind goes up with decreasing glider high speed performance.

- The effect of sink on the glide angle over the ground into the wind gets worse with decreasing glider high speed performance performance.

- The downwind range that will still allow making it back to the field to land from the cut-off altitude gets smaller with decreasing glider performance, and the extra altitude safety margin must be larger because of the greater effect of unexpected sink on the way back.

- If you can't climb fast enough to allow your glide angle into the wind to at least break even, then being downwind is a losing proposition. As the wind speed increases and glider high speed performance decreases, the break-even climb rate increases. It can easily get to 1m/sec (200ft/min) minimum usable climb rate in a 7m/sec (15mph) wind.

- All these changes are gradual as the glider performance is turned down, and the downwind ranging capability gets better with increasing glider performance.

One interesting thing I found is that flying too fast into headwind and sink has very little effect on the glide ratio over the ground. Flying too slow into a headwind and sink destroys the glide ratio over the ground. It seems getting the nose down when trying to come back into the wind is the way to go, except of course the flight time gets shorter as you push the speed past the real best glide over ground speed.

My reasonably modestly powered glider (600W, 62oz) can go near the limits of my vision diagonal/upwind in 30 seconds in any wind I have flown in so far. The 30 second limit means that I am likely less than 800m away. I should also be able to make it back to the field from 200m at 800m downwind if I get the nose down. I should be able to fly a bit longer path length under power going in the downwind quadrant, since my ground speed will be higher. But I can fly a much longer path length at min sink during the glide if I power upwind first. If the thermals are randomly distributed relative to the ground, then the chances of flying through one should be better with the upwind quadrant launch, and recognizing even light lift will be easier since you will be at flying at minimum sink. I am not that good at recognizing light lift during a high speed glide back towards me from a downwind position.

Another effect is that if I go downwind under power and do not contact the relatively strong lift I need to maintain a glide angle back to the field, I have to spend the rest of the flight in relatively high speed, high sink rate flight to make it back to the field. This makes for very short flight times. This is of course worse with lower performance gliders. If I go to the upwind quadrant under power and do not contact lift, I can still spend the rest of the flight at minimum sink and make it back to the field. I can also afford to work light lift or zero sink, because it is bringing me back towards the field. The flight time will be much longer.

We have been using 150m cut-off height, and that accentuates the advantages of going upwind under power even more than from 200m. The allowable downwind range shrinks quickly with low glider performance and lower start altitude.

All this means that with lower performing gliders, as the wind picks up, you must be very sure of a high climb rate read close-in to consider going downwind. If the climb rate (including the time you spend centring it) may be below the break-even rate or beyond your shrinking downwind range with increasing wind speed, going upwind under power may be your only option. Ensuring you have good speed under power would expand your upwind capability, and doesn't seem to take many watts.

I don't know what the odds of randomly flying into zero sink versus flying into a 1m/sec thermal are. I seem to find low climb rate/zero sink areas far more often than strong lift. The ability to work even light lift if you are upwind seems to be a major advantage.

It is much easier to penetrate into a thermal from the upwind side on a windy day. The air rising from near the ground has lower speed than the higher air due to ground friction and wind gradient with altitude, so a thermal column tends to be moving slower than the air it is rising into. This makes ridge lift on the front side, and turbulence and sink on the downwind side. If you don't fly into your expected thermal going downwind under power, getting into a core if you do find lift will be more difficult as you try to penetrate back upwind. From an upwind quadrant motor run, it should be easier to fly back into a thermal from an upwind coming downwind position.

The more confident you are of strong downwind reads, the better your glider performance, the more sense it makes to go downwind even as the wind gets stronger. The ability to power a long way upwind even with some lower performing gliders gives the upwind quadrant the advantages of being able to work weak lift and increases your chances to randomly find a thermal if you aren't very confident with a strong, close-in thermal read on a windy day. At the worst, if you are upwind you can fly minimum sink for the whole flight from upwind and salvage some points. Going to the downwind quadrant and not finding strong enough lift will result in a very short flight as you dive into the headwind.

ALES can be fundamentally different than pinging off a tow line. The option of getting a long way upwind provides the ability to search a larger area and work light lift even on a windy day and with gliders that don't have great high speed glide. This isn't possible from a winch launch. I think that many of the ideas developed around starting from a fixed location winch launch do not necessarily apply.

Big moulded gliders and thermal reading expertise would make the downwind quadrant more inviting. I need to work on my thermal reading skills from the ground, and get a glider with better performance to increase my ability to make use of the downwind quadrant.

Kevin
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