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#21
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The Yellow Triangle
On Thursday, 18 February 2021 at 13:11:35 UTC, Eric Greenwell wrote:
Nicholas Kennedy wrote on 2/16/2021 4:56 PM: On many German gliders on the ASI is a yellow triangle. This Yelloe Triangle on my ASw 20 and my LS3a is the factory recommended approach airspeed. This speed is 49 knots. This has bothered me for a long time now, I think the factory did alot of pilots a disservice by putting this, to me anyway, very low number on there. On both the above gliders, the max speed, normal landing flap flaps down, is 86 knots. About 15 years ago my Gold Seal flight instructor Bob Faris, CX,indicated to me in his LS3 he planned on a much higher speed in the pattern, like 70-75 knots depending on conditions. I followed suit ever since. Since so many gliders have 49 knots for the Yellow Triangle, I think this might be a regulatory requirement, not a choice by the glider manufacturer. Perhaps gliders are required to have an approach speed no higher than 49 knots at a certain weight with the regulation required control authority. -- Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me) - "A Guide to Self-Launching Sailplane Operation" https://sites.google.com/site/motorg...ad-the-guide-1 In the EASA CS22 specification for ASI markings it includes "a yellow marking (triangle) for the lowest approach speed (at maximum weight without water ballast) *recommended by the manufacturer*". (My stars). As far as I can see there is neither a set value nor a formula for deriving it from e.g. stall speeds |
#22
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The Yellow Triangle
On Thursday, 18 February 2021 at 14:48:55 UTC, wrote:
On Thursday, 18 February 2021 at 13:11:35 UTC, Eric Greenwell wrote: Nicholas Kennedy wrote on 2/16/2021 4:56 PM: On many German gliders on the ASI is a yellow triangle. This Yelloe Triangle on my ASw 20 and my LS3a is the factory recommended approach airspeed. This speed is 49 knots. This has bothered me for a long time now, I think the factory did alot of pilots a disservice by putting this, to me anyway, very low number on there. On both the above gliders, the max speed, normal landing flap flaps down, is 86 knots. About 15 years ago my Gold Seal flight instructor Bob Faris, CX,indicated to me in his LS3 he planned on a much higher speed in the pattern, like 70-75 knots depending on conditions. I followed suit ever since. Since so many gliders have 49 knots for the Yellow Triangle, I think this might be a regulatory requirement, not a choice by the glider manufacturer. Perhaps gliders are required to have an approach speed no higher than 49 knots at a certain weight with the regulation required control authority. -- Eric Greenwell - Washington State, USA https://sites.google.com/site/motorg...ad-the-guide-1 In the EASA CS22 specification for ASI markings it includes "a yellow marking (triangle) for the lowest approach speed (at maximum weight without water ballast) *recommended by the manufacturer*". (My stars). As far as I can see there is neither a set value nor a formula for deriving it from e.g. stall speeds There's probably some approximation or rounding 49 and 54 knots might sound like precision to us, but these are 90 and 100 km/h. 86 kts is 160 km/h |
#23
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The Yellow Triangle
My D2B says 54 kts. The standard does not fix a given speed.
IN My SZD-55 says 56.7 kts/105 kph. CS 22.1545 Air-speed indicator (See AMC 22.1545) Each air-speed indicator must show the following markings: .... some deleted .... (e) a yellow marking (triangle) for the lowest approach speed (at maximum weight without water ballast) recommended by the manufacturer; 2D |
#24
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The Yellow Triangle
On Thursday, February 18, 2021 at 7:48:45 AM UTC-5, wrote:
There is margin at the yellow triangle. ASW-20B, landing flaps + full spoilers on final, spoilers held open all the way to wheel stopped. Touch down is tail first, landing roll 200', disk brake on hard but not rubbing nose in the dirt. https://www.youtube.com/watch?v=oBexl9GfKK0 T8 My feeling/training others....what does it feel like, what does it look like, what does it sound like....make it all seem correct...don't break the aircraft.... |
#25
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The Yellow Triangle
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#26
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The Yellow Triangle
On Thursday, February 18, 2021 at 7:48:45 AM UTC-5, wrote:
There is margin at the yellow triangle. ASW-20B, landing flaps + full spoilers on final, spoilers held open all the way to wheel stopped. Touch down is tail first, landing roll 200', disk brake on hard but not rubbing nose in the dirt. https://www.youtube.com/watch?v=oBexl9GfKK0 T8 There is plenty of margin, try putting a cover over your airspeed indicator for the entire flight, actually it will be in your best interest to see exactly how your ship flies. E9 did this to me back in the day and it taught me a thing or two. Number one is that fly by the seat of your pants, number two prepare yourself for the off field landing. We did this often and it was one of the best learning experiences that I ever had. |
#27
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The Yellow Triangle
On Thursday, February 18, 2021 at 6:32:19 PM UTC-5, wrote:
This is the problem I'm referring too: https://www.youtube.com/watch?v=use6PnxjO7s Nick T That sort of accident has nothing to do with speed on final approach. T8 |
#28
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The Yellow Triangle
On Thursday, February 18, 2021 at 7:12:31 PM UTC-6, wrote:
On Thursday, February 18, 2021 at 6:32:19 PM UTC-5, wrote: This is the problem I'm referring too: https://www.youtube.com/watch?v=use6PnxjO7s Nick T That sort of accident has nothing to do with speed on final approach. T8 Discussions at my club and at a FIRC prompted my research and writing a piece on my personal website. The link is below. I suspect or expect a few comments, as undoubtedly somebody will think I"m all wet. Mention of the huey is because that's what I know. http://www.unofficialuseonly.us/gelbe.html Brent, 7A , |
#29
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The Yellow Triangle
I suggest avoiding blanket statements like assertions that the yellow triangle is ALWAYS based on max unballasted weight. On my 1980 Ventus A, the yellow triangle is required by the flight manual to be at 62 knots based on max allowable weight (with full ballast) at 525 kg / 1157 lbs and landing flaps down, airbrakes retracted. Design rules have undoubtedly changed since then, but the POH is always the final authority.
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#30
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The Yellow Triangle
On Friday, February 19, 2021 at 11:38:02 AM UTC-5, bgrly wrote:
On Thursday, February 18, 2021 at 7:12:31 PM UTC-6, wrote: On Thursday, February 18, 2021 at 6:32:19 PM UTC-5, wrote: This is the problem I'm referring too: https://www.youtube.com/watch?v=use6PnxjO7s Nick T That sort of accident has nothing to do with speed on final approach. T8 Discussions at my club and at a FIRC prompted my research and writing a piece on my personal website. The link is below. I suspect or expect a few comments, as undoubtedly somebody will think I"m all wet. Mention of the huey is because that's what I know. http://www.unofficialuseonly.us/gelbe.html Brent, 7A , I have understood (though I can't give you a reference) the YT as marking the minimum recommended approach speed needed to complete the landing flare at max mass without water ballast in calm air. Modern gliders have a high rate of descent with airbrakes fully extended and gear down. The D2b flight manual status that the L/D in this configuration is approximately 5.8:1, which translates to a sink rate of roughly -10kts. In this condition you need enough airspeed to arrest the descent and flare. If the approach is too slow, the glider will mush and land heavily. The YT doesn't say anything per se about airspeed margin for wind gradient and gusts. A variety of approaches can be found in the literature on the subject of approach airspeed in windy conditions, e.g.: 1.3 Vso plus the full wind speed (Soaring Association of Canada Student handbook p61) http://www.sac.ca/index.php/en/docum...011-optim/file 1.5 Vso plus half the gust speed if not otherwise specified in the POH (FAA glider manual pp 7-23 and 7-25) https://www.faa.gov/regulations_poli...h-8083-13a.pdf 1.5 Vso plus half the wind plus all the gust (Soaring Safety Foundation). https://www.soaringsafety.org/public...6-airspeed.pdf They all give the same general advice, that is fly higher airspeed in windy and gusty conditions. I don't claim to know which exact formula which is best. Ian IN |
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