effte Posted April 3, 2011 Posted April 3, 2011 By 5 miles out from the runway you should be... If flying an airliner... :) (Or, granted, on the ILS) ----- Introduction to UTM/MGRS - Trying to get your head around what trim is, how it works and how to use it? - DCS helos vs the real world.
SFJackBauer Posted April 3, 2011 Posted April 3, 2011 The issue is the runway you are eating up as you are decelerating from 150 knots to 119 knots. He said he touchs down at 119 knots at 25% fuel, which seems fine.
BlueRidgeDx Posted April 3, 2011 Posted April 3, 2011 (edited) Although it works for me, I don't want to be missunderstood: I'm not saying my way of landing is "the bestest" just trying to show it works as well. No worries, I'm not here to judge. At the end of the day, DCS is an entertainment title and if you're enjoying it, that's all that matters. ...but did you check that increased weight really does increase stopping distance in game or is it just theoretical? No, I haven't had a chance to do that. Primarily because it's very difficult to accurately measure distance in the simulator. I hesitate to use in-game visual "yardsticks" like Runway Centerline Line Markings (RCLM), or other painted distance markers, since I can't independently verify that they are the correct size (my gut tells me they're not). Nontheless, as you're aware, in the real world, all other conditions being equal, an increase in gross weight will result in a longer landing distance. Additionally, anti-skid will provide a significant improvement in landing distance, especially on a wet or contaminated runway. There should also be a significant difference in landing distance when using Kenan's "universal" approach technique as opposed to the real procedure, primarily due to the excess float associated with carrying extra speed down final. Generaly speaking, you can count on a 20% increase in landing distance for each 10% above approach speed (Vref). However, if you intentionally hold the aircraft off the runway during the flare, it becomes a 30% increase in landing distance for each 5% above Vref... Take the following example for the A-10C: Example Conditions: Dry Runway Gross Weight - 30,000lb Calculated Approach Speed - 130kt Air Distance (50ft obstacle) - 1200ft + Landing Roll Distance - 1400ft = Actual Landing Distance - 2600ft Now, suppose we flew the approach and landing using Kenan's technique at 155kt, and instead of a firm touchdown, we hold it off looking to "grease it on": 155kt is an approximately 20% increase in approach speed, so... Actual Landing Distance - 5720ft I don't even want to contemplate what the numbers would be without anti-skid...typically, the penalty factor is 1.75, so landing distance at 155kt with an extended flare and no antiskid would be 10,010ft. Thats at sea level on a standard day! Edited April 3, 2011 by BlueRidgeDx "They've got us surrounded again - those poor bastards!" - Lt. Col. Creighton Abrams
Kenan Posted April 3, 2011 Posted April 3, 2011 Now, suppose we flew the approach and landing using Kenan's technique at 155kt I never said my touchdown speed is the same as my approach speed so your math is little off: 1. 25% of fuel, no payload, light as a feather, aproach speed 150-155 knts, touchdown at app. 119 kts. 2. 100% fuel, full payload, heavy as a pig, aproach speed 150-155 kts, touchdown at app. 143 kts. You will never run out of runway if you flare ie. if you engage the touchdown procedure on time (and drop throttle to idle BEFORE that). When I put my throttle to idle, I start loosing speed and energy hence the touchdown speed numbers I got above are not that really far from the RL values in the PDF you posted. Just pay attention to the bolded parts for an "empty" plane and the "fat" one. [sIGPIC][/sIGPIC] Commanding Officer of: 2nd Company 1st financial guard battalion "Mrcine" See our squads here and our . Croatian radio chat for DCS World
effte Posted April 3, 2011 Posted April 3, 2011 I never said my touchdown speed is the same as my approach speed so your math is little off: Either your procedure is... let us call it interesting, or there is a misunderstanding. I'll assume the latter, so let us try to clear it up. What speed do you have when crossing the runway threshold in your light aircraft example? 150 knots or 119 knots? Cheers, Fred ----- Introduction to UTM/MGRS - Trying to get your head around what trim is, how it works and how to use it? - DCS helos vs the real world.
BlueRidgeDx Posted April 3, 2011 Posted April 3, 2011 Hey Kenan, Like I said, I'm not going to tell you how to enjoy your simulator. But you are missing an important piece of the puzzle. As Fred is implying, it doesn't matter what your touchdown speed is. The fact that you cross the threshold nearly 25-30 knots fast means that you're floating excessively down the runway while bleeding off airspeed. That's hundreds, if not a thousand or more feet of runway that you could have used to stop the airplane. Not to be a wise-ass, but the airplane in the link below landed "on-speed" too; but as you can see, it didn't end too well. I know it's not a perfect 1:1 analogy, but the point remains the same. A high approach speed combined with the desire to achieve a soft landing results in excessive float, and depending on runway length remaining and aircraft gross weight, the remaining runway may not be sufficient. The proper way to do it is fly the approach speed and/or AoA indexer, and strive for a firm landing in the touchdown zone. "They've got us surrounded again - those poor bastards!" - Lt. Col. Creighton Abrams
Kenan Posted April 4, 2011 Posted April 4, 2011 ^^The example you posted is a bit drastic, I'm not THAT fast! :D Anyway, I understand what you're saying. I did study the PDF file you posted in the meantime and this time, adjusted my approach accordingly, doing the weight/approach speed calculations. Although running out of runway was never an issue for me, I did use up a lot more with my method and once I tried the RL way (the PDF info), I did realize I can stop a lot earlier even if slightly overshooting the skidmarks on touchdown. [sIGPIC][/sIGPIC] Commanding Officer of: 2nd Company 1st financial guard battalion "Mrcine" See our squads here and our . Croatian radio chat for DCS World
Kenan Posted April 4, 2011 Posted April 4, 2011 Either your procedure is... let us call it interesting, or there is a misunderstanding. I'll assume the latter, so let us try to clear it up. What speed do you have when crossing the runway threshold in your light aircraft example? 150 knots or 119 knots? Cheers, Fred I think I (finally) understand what you're saying: You're refering to a approach speed AND the treshold speed (once passing the runway treshold)? So, if the approach speed was say 130 kts, once I'm about to start passing the runway I should slow down to 120 kts and keep that speed value untill touchdown? [sIGPIC][/sIGPIC] Commanding Officer of: 2nd Company 1st financial guard battalion "Mrcine" See our squads here and our . Croatian radio chat for DCS World
BiPod Posted April 4, 2011 Posted April 4, 2011 Deja vu OK, I've partially repeated my tests with the release version (1.1.0.6) and found that not much has changed since the Beta. The anti-skid adds and extra 1000 feet to the stopping distance, and a light aircraft still takes longer to stop than a heavy aircraft. Having flaps down increases stopping time. Conditions: The aircraft was landed and allowed to settle while rolling. At exactly 120kts full wheel brakes were applied and the time to stop was recorded. Repeat results are shown separated with a comma. Distances are a rough estimate based on measuring from visual cues in the mission editor. My Point is, flying by the numbers may be a fun challenge, but you should not expect the sim to give the expected results. A more in-depth discussion can be found here: http://forums.eagle.ru/showthread.php?t=66217 Best stopping configuration: A/S Off! (but handling is negatively affected) Flaps Up! (Increases weight on wheels - less skidding?) Airbrakes Open Wheelbrakes approx 3/4 (assigned to joystick slider) This sim is still the best ever made! It's just not perfect. BiPod.
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