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#41
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Lancair crash at SnF
Shirl wrote:
WingFlaps wrote: I've also heard a lot of BS in this thread about not having good palces to put the plane. There is nearly always somewhere flat to put the plane within 90 degrees of the runway centerline -even a road. Malls have big parking lots! I don't know about where you live, but malls here have lots of light poles, concrete islands, park-and-rest benches and ... and ... vehicles everywhere. And having gone through it once, I'm no longer fooled by what *looks* "flat" at 500, or even 50 feet. This guy ended up in somebody's yard and missed all the suburban traffic last year. I drove through the neighborhood (about a mile from my house) to see if it's where I'd have landed. Hmm. http://www.nwcn.com/statenews/oregon....3a6a3952.html " FAIRVIEW, Ore. -- A pilot flying a small plane he had purchased just minutes earlier crash-landed in a dense suburban neighborhood near the Troutdale Airport Wednesday after the plane's engine quit. " |
#42
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Lancair crash at SnF
tman inv@lid wrote in
: Hold on while I try to correct some nits in what Bertie said and see what happens Bertie the Bunyip wrote: Nope, the wind is going to help you in almost every way if you're turning back. [ many good points supporting this assertion, but... ] also, your best LD speed is going to occur at a lower airspeed, Well, technically, your best LD speed is related to angle of attack, and not the groundspeed, so that won't change. Your best glide speed certainly will be less... OK, not the LD, you're right. but your best glide speed is realted to your ground speed. To take an extreme example to illustrate this point, imagine that your published best glide is 70 and you're trying to glide into a 70 knot headwind. You're going nowhere. Increase your speed and you will make headway. In the tailwind scenario, your best glide distance over the ground will be better at a lower speed than published. the stronger the wind, the lower the speed required until you arive at your min sink speed. There is no inertia involved in making a downwind turn. None. Here's why I wonder about that. Let's suppose 65 KAS before and after a 180 turn from a 10 KT headwind. OK, before the turn, your groundspeed is 55KTS and after the turn your groundspeed is 75KTS. Your intertial frame of reference is tied to the g/speed, not the a/speed. So -- the kinetic energy of the aircraft and contents is about 33% higher (75/55)^2. That energy is only going to come from one place with no power -- trading in altitude (potential energy) for kinetic energy. Nope, your inertial frame of reference owes nothing to the ground whatsoever. None. Zero, nil zilch zippo. You ar entirely a creature of the air and owe nothing to the ground whatsoever ( except in the vertical, of course) The earth simply isn't that important in the bigger scheme of things! If it were, you'd have trouble making left or right hand tunrs in your car.... Bertie |
#43
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Lancair crash at SnF
On Apr 24, 6:41 pm, tman inv@lid wrote:
Hold on while I try to correct some nits in what Bertie said and see what happens Bertie the Bunyip wrote: There is no inertia involved in making a downwind turn. None. Here's why I wonder about that. Let's suppose 65 KAS before and after a 180 turn from a 10 KT headwind. OK, before the turn, your groundspeed is 55KTS and after the turn your groundspeed is 75KTS. Your intertial frame of reference is tied to the g/speed, not the a/speed. So -- the kinetic energy of the aircraft and contents is about 33% higher (75/55)^2. That energy is only going to come from one place with no power -- trading in altitude (potential energy) for kinetic energy. See the previous post. There's a change in kinetic energy, but very, very little. Many people make the mistake of thinking that the earth has an effect on the airplane. It does, but only vertically, by gravity. Gravity has no horizontal Component. Like a gyroscope, which is rigid with respect to space and cares not one bit about the earth, the airplane's mass, as it moves in the horizontal, is affected only by its relationship to space and the air it flies in. That isn't to say that the earth isn't going to get in the way a little harder. Landing downwind, as with landing into the wind, involves transferring the weight from the wings to the wheels, and downwind means much more groundspeed and maybe loss of control as the roll continues at higher speed while the flight controls feel a decreasing airspeed, or maybe the airplane will run out of runway. Bang. We do illusions created by drift turns with students, usually in a strong wind and at around 500 feet, so that they can see that the ball stays centered in the turn while they get the visual impression that the airplane is skidding or slipping on the downwind and upwind sides of the turn. The airspeed does not change. Not so's you could read it. If we put the student under the hood and make him fly on instruments while we do this, he can't tell us when he's turning into the wind or out of it. Can't feel anything, can't see any performance changes on the gauges. Dan |
#44
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Lancair crash at SnF
gatt wrote in
news:ru6dnZlbZ5BGu4zVnZ2dnUVZ_qjinZ2d@integraonlin e: Dylan Smith wrote: We don't know it was an 'impossible turn'. We don't even know what altitude they were at, whether the engine was still developing power or not, or whether the plane caught fire, or ... there simply isn't enough information to Except we know they didn't make it. Assuming the pilot was reasonably proficient, that suggests the turn couldn't be made. No, it suggests that he probably wasn't prficient, but we don't know and are unlikely to ever know. There's always a min height that it can be performed from and only a lot of practice will tell you what that is for each departure. As i've said before, only proficiency in handling an airplane in this situation and a carefully thought out self briefing before the departure can give even a chance of success in the turnback manuever. Add in a bit of luck and you have it, but it's almost always safer to go straight ahead if at all possible. Bertie |
#45
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Lancair crash at SnF
On Apr 24, 6:41 pm, tman inv@lid wrote:
Here's why I wonder about that. Let's suppose 65 KAS before and after a 180 turn from a 10 KT headwind. OK, before the turn, your groundspeed is 55KTS and after the turn your groundspeed is 75KTS. Your intertial frame of reference is tied to the g/speed, not the a/speed. So -- the kinetic energy of the aircraft and contents is about 33% higher (75/55)^2. That energy is only going to come from one place with no power -- trading in altitude (potential energy) for kinetic energy. In your world, it's gonna be pretty hard for a sailplane to circle in a drifting thermal. In my world, it's not a problem. |
#46
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Lancair crash at SnF
gatt wrote in
news:T-Sdnb-eo8vLtIzVnZ2dnUVZ_tWtnZ2d@integraonline: Buttman wrote: On Thu, 24 Apr 2008 17:05:06 +0200, Stefan sayeth: Brian schrieb: Your right in that many aircraft it is possible. But the problem is it isn't possible for many pilots when the engine quits. It is not a maneuver that is routinly practiced. Now this problem could be solved. You're suggesting instructors practice engine failures with their students on takeoff? Oh boy, better hope Dudly doesn't see this... One way to practice this would be to establish a "runway altitude" at, say, 1000ft AGL, get the airplane into takeoff configuration on heading at that altitude over a road or something, simulate a failure at a specified altitude--say, 1,500 feet--and see what altitude you're at when you get back to your reciprocal heading. If it's above your starting altitude, you made it. Wind, density altitude and aircraft weight are significant variables. Of course, a proficient pilot will have considered all these variables as well as the terrain downrange before takeoff, so they already know what they will do if the engine quits at a specific altitude. On probably as many checkrides and flight reviews as not, the instructor has asked me what I will do if I lose power on takeoff so I already know where there transmission lines are, about how far it is to the lake, etc. -c More importantly, perhaps, is the fact that if you make nice gentle turns in an average lightplane, you simply won't make it. You have to make the turn at a very high angle of bank to have even a hope of making it in time. If you make it at say, 30 deg of bank at about 65 you're going to lose the guts of 800 feet just manuevering to line up with the runway if you fly the airplane accurately. You're going to be very low at the end of this manuever to say the least. The best way to do it is with a steep bank. Very steep. This will, of course, mean a high sink rate, but the time required to make the turn will be cut drastically and you'll be closer to the centerline when you've come about, so less time and alt wasted trying to get lined up. To do this you must be absolutely completely comfortable doing a steep power off turn at a reltively low airspeed when you do it. Not imagining you can do it based on experience doing steep turns with the power on, you have to be able to simultaneously offload the wing at a rate that won't get the nose too low as to get an excessive alt loss and make this drastic turn at the same time without stalling. All this while your brain has become akin to that of a lizard looking a rather big snake. IOW, you have to have practiced this and other aerobatic manuevers so that they are second nature. It can be done and it can be done in almost any airplane, but it requires a lot of practice, experience, careful planning and a lot of luck. Better to go straight ahead if you can. Bertie |
#47
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Lancair crash at SnF
In rec.aviation.student WingFlaps wrote:
On Apr 25, 3:12?am, Dylan Smith wrote: In gliders, every glider pilot is taught "the impossible turnback" from 200 feet (which, in the typical low performance training glider, is about equal to turning back at 600 feet in a C172). It's the L/D that makes it much harder in a typical powered plane. This means that all manouvers lose energy much faster. The turn back needs at least 2 turns as well as acceleration if there is any wind. You will note that nearly all the accidents are stall spins -a moments thought about the situation will make you realize why this is. The turns are made tight because there is not enough height/time for a lazy turn. Let's work some real numbers for a 172 at 500'. Say climb was a Vx 59 knots. The plane must first be accelerated to 65 for best glide. The pilot carries out some trouble checks say 10s. Calls on the radio =10 s and plans his return. Note that 20s have probably elapsed. The plane has already travelled ~0.4 miles and at a 10:1 glide ratio has lost 200' (assuming he did get it to best glide in the first place). Can he make 2 turns and land back -no way! It's worse than just the L/D difference would make you expect in a few ways. The glider's best glide speed is considerably lower. Typical best glide speeds are 50-55kts. Also, for best performance while doing a 180 you want to fly at min sink speed rather than best glide speed, which in a typical glider will put you down at 40-45kts. This speed difference has two effects, neither of them good. First, your sink rate will be considerably higher. At 10:1 and 65kts you're sinking at 650fpm. At 30:1 and 55kts you're sinking at under 200fpm. Second, a turn done at lower speed is smaller and faster, so you're spending more time at that 650fpm sink rate than the glider is spending at under 200fpm. Another speed-related effect is that the glider is taking off much faster than his best glide speed. A typical glider tow may be at 65kts. The extra speed is energy to be burned off in the turn. A modern medium-performance glider will come out of a 180-degree rope-break turn at the same altitude he started! In the Cessna in your example you have the opposite problem, you have to trade altitude for speed just to get *up* to best glide, and then you keep losing it at an extremely high rate. Rope breaks are also extremely obvious when they happen, so reaction time is essentially instantaneous. There are other glider launch emergencies which aren't so obvious, such as the tow plane losing power, where things can get more difficult. In the case of the piece-of-cake 200' rope break you'll have the controls deflected in less than a second from the event unless you really screwed up your pre-takeoff mental preparation. In conclusion: fly gliders, it's safer! More serious conclusion: these things are much easier in gliders because they're basically made for it. Don't carry it over to powered flight. -- Michael Ash Rogue Amoeba Software |
#48
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Lancair crash at SnF
WingFlaps wrote:
A Lancair crashed just moments after takeoff here in Mesa, Arizona, today, too. Plane was headed for California. There was smoke trailing from the plane on takeoff and controllers cleared them to turn back around and land. They tried -- they made the left turn but crashed into the orange orchard. Three fatalities, all in their late 20s. Sympathies and prayers to the families. When will pilots learn to stop trying to do the impossible turn... and go for a straight ahead landing on soemthing horizontal? I saw the local news report and the suggestion was that he hit where he did to avoid populated areas. A picture shown did suggest that straight ahead was problematic. Ron Lee |
#49
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Lancair crash at SnF
In rec.aviation.student tman inv@lid wrote:
Here's why I wonder about that. Let's suppose 65 KAS before and after a 180 turn from a 10 KT headwind. OK, before the turn, your groundspeed is 55KTS and after the turn your groundspeed is 75KTS. Your intertial frame of reference is tied to the g/speed, not the a/speed. So -- the kinetic energy of the aircraft and contents is about 33% higher (75/55)^2. That energy is only going to come from one place with no power -- trading in altitude (potential energy) for kinetic energy. This simply does not make any sense. Kinetic energy, like velocity, is a relative quantity. You cannot look at an object and say, "it has X joules of KE". You can only talk about KE relative to some frame of reference. Just like velocity. So forget about KE. It's in the same boat as velocity, so look at velocity. You make a turn and suddenly you gain a bunch of groundspeed. Where does the extra speed come from? It comes because you're maneuvering relative to a medium, the air, which is itself moving. Your KE relative to that medium is exactly the same as it was, so no energy has to come from anywhere. -- Michael Ash Rogue Amoeba Software |
#50
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Lancair crash at SnF
On Fri, 25 Apr 2008 01:27:52 +0000 (UTC), Bertie the Bunyip
wrote in : The best way to do it is with a steep bank. Very steep. The bank angle may be quantified: http://groups.google.com/group/rec.a...1d80a2e846a88b John T. Lowry Best turnaround bank angle phi (least altitude loss per angle turned through) for a gliding airplane is given by: cos(phi) = (sqrt(2)/2)*sqrt(1-k^2) where k = CD0/CLmax + CLmax/(pi*e*A) where CD0 is the parasite drag coefficient, CLmax is the maximum lift coefficient for the airplane's flaps configuration, e is the airplane efficiency factor, and A is the wing aspect ratio. I know most ng readers hate those darned formulas, but that's the way the world works. For GA propeller-driven airplanes, k is a small number (0.116 for a Cessna 172, flaps up) and so the best turnaround bank angle is very closely the 45 degrees cited by Rogers and, much earlier, by Langewiesche (Stick and Rudder, p. 358). For the above Cessna, for instance, it's 45.4 degrees. For a flamed-out jet fighter, however, things are considerably different. The formulas above, along with formulas for the banked stall speed, for banked gliding flight path angle, and for the minimum altitude loss in a 180-degree turn, can all be found in my recent book Performance of Light Aircraft, pp. 294-296. The following seven pages then treat the return-to-airport maneuver, rom start of the takeoff roll to contact with the runway or terrain, in excruciating detail. Including wind effects, the typical four-second hesitation when the engine stops, etc. John. -- John T. Lowry, PhD Flight Physics; Box 20919; Billings MT 59104 Voice: 406-248-2606 |
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