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![]() "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.. |
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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. |
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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 |
#4
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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. |
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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? |
#6
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![]() "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? |
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