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#81
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Polar with spoilers extended?
bagmaker wrote:
I have to add my thinking, open to scrutiny. 1- whatever needs to be done to get the a/c to an acceptable landing position above and before the field needs to be done early, to minimise ground effects. (theoretically, if this is adhered to, the problems wouldnt eventuate, as the pilot would have noticed his/her extra altitude before arriving at final and modified the curcuit to suit.) Good point. No-one has mentioned using airbrakes on the base leg, or even the downwind leg. I often do this if the sink is less than I anticipated or I hit lift. Once a pilot has some experience it's really easy to see at this stage if you will be too high, and losing the excess height early makes the last part of base and the approach much easier than if you leave all the excess height to be lost in the approach. I recall that when being trained, I was told not to use airbrakes until I'd turned finals (though also that in post-solo training it was pointed out to me that I could now break this rule). Is it possible that we are too heavily conditioned not to use airbrakes before the final turn? In my Open Cirrus I'd rather turn finals a *little* too low, as if I fly the first part of the approach without brakes I'll soon intercept the approach funnel. Turning too high is always more difficult. Note that in a K8 the opposite is true - too low might not be fixable and losing height is easy (and often not optional!). One of the points which comes out clearly from this thread is that the answers are very glider-specific. So I guess my preferred answer is: 0. Lose the excess height before making the final turn, in whatever way works for you. [PS For those blessed with a tailchute, I can highly recommend practising opening the tailchute towards the end of the downwind leg. If you need it for a real field landing, the approach is too late - what if it fails to deploy? The feeling of despair as you are clearly too low is balanced by the elation when you realise that you will make the field after all. Anyone trying this will need to fly a curved path from end of downwind to touchdown, as a formal circuit is *far* too scary and will probably leave you short.] |
#82
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Polar with spoilers extended?
Bruce wrote:
This is the kind of rigid thinking that kills people. You can't be rigid enough when it comes to final approach speed. If you teach that the needle has to be ON the yellow triangle, what happens to the pilot when he suddenly notices the glider he is in doesn't have one. Yeah, yeah, yeah. I would expect from a glider pilot that he doesn't "suddenly" discover on short final that there isn't such a triangle, but that he familiarizes himself with the glider before the flight. If he doesn't, then many other things have gone wrong during his training. For every weight and configuration there is a stall speed. Of course. But the other poster proposed to slow down to the point where you get a steeper approach. For me, this is a *very* rigid no-no. I don't think that rigidness in this point kills people. I even tend to think the contrary. |
#83
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Duo Dive-brakes ( Polar with spoilers extended?)
Bill Daniels wrote:
I think the Duo's airbrakes are better than many people think. The Duo is a big heavy glider with lots of inertia. It doesn't like to change direction quickly. That includes its behavior on sudden airbrake deployment. You don't get a lot of sink right away. My first reaction was that the airbrakes were weak but a little more experience showed me that with a little patience, the brakes took effect and produced a respectable decent rate. The Duo just makes you plan ahead a little more than with a light single seater. In other words, the Duo "airbrakes" are not very effective. Lots of big, heavy, fast aircraft do have effective spoilers/speedbrakes/"airbrakes", or whatever you want to call them, that make the desired changes in speed/rate of descent promptly. Every car's acceleration from 35 to 65 for merging into Interstate highway traffic is adequate--if you are willing to wait for it. I learned to "plan ahead" when passing on two lane roads in my VW Beetles and early un-blown Corvairs. I know what planning ahead means and that is not "performance" as we like to think of it. The same goes for sailplane spoilers whose effects are not prompt, and rudders which are not effective enough to allow a good steep high descent-rate slip. Jack |
#84
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Duo Dive-brakes ( Polar with spoilers extended?)
BB wrote:
As fun as the high parasitic drag maneuver is, I wonder if anyone has ever actually used it in combat. Has anyone been so flustered and out of synch to get monstrously high in an off field landing, then had the presence of mind and skill left to dive to the ground at near VNE, aiming several hundreds of yards short of the intended small paddock with fence at the far end, and had it work? The mental attitude that gets to the problem seems incompatible with the attitude needed to pull this one off. In "combat"? In a Duo? There are a number of real combat stories about people keeping the speed high in damaged aircraft to get down out of the fight, through clouds, etc. to find a safer area for a forced landing or bailout--so as not to be hosed while under canopy, or to avoid setting up a big slow pattern that would make them a sitting duck--but I think that diverges from what you are asking. I don't think fighter pilots get a chance to practice engine out landings much, so yes, they adapt. The best adaptation is that for which the mental groundwork is laid _on_ the ground. Sailplane pilots have the incomparable advantage of doing their preparation on the ground _and_ in the air by planning and practicing both low- and high-energy approaches, as has been outlined here in previous postings by several contributors. Jack |
#85
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High on Final, Summary....
Tim Taylor wrote:
The situation: You are 70 miles from home over unfamiliar territory (read not sure of exact elevation of the terrain below, your altimeter is useless now). You have gone for a Cu over a dry lake bed and it doesn't work. You have selected a landing site in the lake bed that is about 350 feet long and 100 feet wide that looks safe to land. There are tree stumps and other object in other parts of the lakebed. There are no obstructions on the ends of the site so you can do a normal approach. The winds are 15 to 20mph out of the south so you are landing from the north to south. As you drop lower you make a rectangular pattern over the site checking for any missed obstacles. The downwind is fast with the tailwind, as you turn base you estimate you are 400 feet. Your adrenaline is pumping as you prepare for a fairly technical landing. You want to keep it close so that you don't end up short back into the wind and you turn base a little too soon. You are on short final about 350 feet, but about 100 feet over full spoilers decent. What do you do? Tim, We've already screwed up a bunch of things to get ourselves here, but then we may do that from time to time, so: S-turns. In this situation I want more time: to achieve the necessary descent while flying the ship in the way I most frequently fly it--this is not the time for something completely different--even though I can _probably_ do a "360" from that height with a "clean" wing. _Know_ what your configuration is. Gear? Spoilers? If there is any cross-wind, turn into the wind initially, using anything from a 45 to 120 degree turn depending on conditions, but I'll be more comfortable with 60 to 80 degrees; keep the touchdown area in sight; control speed carefully; do not hurry the process; continually assess drift, obstructions, and condition of roll-out space as your vantage point changes while crossing the extended runway centerline. Do not continue maneuvering below a safe altitude. The last 100 feet should look as normal as any you've ever done. If not you've been in too much of a hurry to get to the runway. Just relax and fly around until you get to where everything looks about right again--really, thats what we always do, isn't it? That's why we must be able fly the pattern very comfortably without reference to the altimeter. When airliners need more spacing on final approach, something similar to this method is surprisingly effective without disturbing the customers too much. One more note: if every approach we fly at our home field looks just the same as every other one, we may not be learning enough. Mix it up a little. Where I fly that's rarely a problem, though, and I think that's good for us in the long run. Jack |
#86
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Duo Dive-brakes ( Polar with spoilers extended?)
In article , J a c k wrote:
Bill Daniels wrote: I think the Duo's airbrakes are better than many people think. The Duo is a big heavy glider with lots of inertia. It doesn't like to change direction quickly. That includes its behavior on sudden airbrake deployment. You don't get a lot of sink right away. My first reaction was that the airbrakes were weak but a little more experience showed me that with a little patience, the brakes took effect and produced a respectable decent rate. The Duo just makes you plan ahead a little more than with a light single seater. In other words, the Duo "airbrakes" are not very effective. Lots of big, heavy, fast aircraft do have effective spoilers/speedbrakes/"airbrakes", or whatever you want to call them, that make the desired changes in speed/rate of descent promptly. The Duo's airbrakes are effective. I fly a DG1000 and Duo's a lot. The DG1000 airbrakes _feel_ much more effective than the Duo's, but they both work about the same. I've descended from the wave wingtip to wingtip with the DG1000 and a Duo, both with full brake, and they go down at the same rate. I'll be most interested in how the Duo X compares. -- Philip Plane _____ | ---------------( )--------------- Glider pilots have no visible means of support |
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