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#121
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At 14:48 01 September 2004, Chip Bearden wrote:
There's a somewhat separate question of what the right contents for the procedures and checklists should be! With apologies to pilots whose memories never fail even under stress, I'm one of those guys who does use a very detailed written checklist. Chewing gum isn't on it but things like food, drinking water, reading glasses, and landout jacket are. But I don't wait until I'm #1 on the takeoff line to use it. etcetera It's fun to scoff about obsessive/compulsive types reaching for their checklist and pencil during a spin recovery. But I'll continue to use my written checklist before every flight, as I noted in the safety talk I gave at this year's U.S. Standard Class Nationals. Chip Bearden At the World Gliding Championships many years ago, I crewed for a guy who presented my fellow crewman and I with a checklist containing 19 items regarding the setting up of the glider ready for him to fly. After about two days of practice we added two extra items. #0 get rid of pilot, #20 ensure pilot in glider before launching. We got on just fine after that (and it was always just how he wanted it). |
#122
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"Ian Johnston" wrote in message news:cCUlhtvFIYkV-pn2-uRi7CmzCveOr@localhost...
On Tue, 31 Aug 2004 18:19:55 UTC, (Tom Seim) wrote: : 2. An immediate check of each control linkage after hookup. Which I always get someone else to do. I have mixed feelings about this. Nobody knows your glider as well as you do (save, perhaps, by someone flying-or flown-the identical model). I certainly am not going to trust my life to someone who is unfamiliar with my glider. Additionally, flying a motorglider, I am often times the only one at the airport, so I have to do the complete assembly unaided. It wouldn't hurt to have someone else review the assembled glider after you had done all of your own checks, however. BTW: I check my Hottellier connections by simultaneously pressing on the release plunger and pulling on the rod. Of course, the connection has to be safetied first. I know of accidents where the connection was only part way on, passed a PCC, only to come off in (attempted) flight. Tom |
#123
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Bill,
Can't say I agree, but at least from my point of view, you are erring on the side of safety. Here is a simple argument that I have backed up with experiment in many types of gliders. An aircraft that is capable of spinning during a stall while aileron and rudder are held neutral (and within published cg limits) is inherently unsafe. This means that such a glider flown into a strong, turbulent wind gradient 50 feet above the ground is likely to autorotate. Since recovery from an insipient spin requires much more altitude than a straight ahead stall, there is a very good chance that such a glider would see very few flights before being retired. I have proven to myself many times that stalling a glider without abusing the controls results not in a spin but a spiral dive. While we can all point to experiences of having a wing drop and losing control in a stall, I doubt very seriously that any of us were holding coordinated controls throughout the stall break. It takes a very determined effort not to move the stick throughout the stall and self-recovery. Here's another argument. The vertical stabilizer provides a great deal of yaw stability, even at very low speeds. To start autorotation, you need a source of drag at the tip greater than the normal differential to be expected resulting from span effect in a turn. That we don't kill ourselves everytime the glider approaches stall is testament to the stability provided by the tail. That we occasionally do screw gliders into the ground makes me think that the cause lies more in the way we are applying the controls under stress than any inherent tendency of the glider snap into a spin at the least external provocation. Yes, outside factors can influence how the glider flies, but I think they do more damage by causing pilots to react in unacceptable ways. Go back and read through my reports on control use during stall in my Ventus. What it drives home in my mind is that spins are the result of control abuse. You're right, don't stall land you won't spin. But it's just as right to say that a stall needn't develop into a spin so long as the controls are not abused. |
#124
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I'd always assumed there were two factors in choosing a pattern speed.
First, safety, thus the +5 for turbulence. The other was to place the glider at best speed to fly. That way if you have to put the spoilers away, you are guaranteed to cover the maximum distance. If I recall, the simple formula for best speed was best l/d speed plus 1/2 the headwind. Don't recall the second ever being explained though. Just seemed to fit. |
#125
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Could be. I think the approach speed in my flight manual
is several knots below best L/D. I'll have to double-check. Of course at my home airport (Minden), there's hardly ever less than 15 knots of wind in the afternoon... ...egads, maybe I'm flying too slow!!! 9B At 18:24 01 September 2004, Chris Ocallaghan wrote: I'd always assumed there were two factors in choosing a pattern speed. First, safety, thus the +5 for turbulence. The other was to place the glider at best speed to fly. That way if you have to put the spoilers away, you are guaranteed to cover the maximum distance. If I recall, the simple formula for best speed was best l/d speed plus 1/2 the headwind. Don't recall the second ever being explained though. Just seemed to fit. |
#126
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"Chris OCallaghan" wrote in message om... I'd always assumed there were two factors in choosing a pattern speed. First, safety, thus the +5 for turbulence. The other was to place the glider at best speed to fly. That way if you have to put the spoilers away, you are guaranteed to cover the maximum distance. If I recall, the simple formula for best speed was best l/d speed plus 1/2 the headwind. Don't recall the second ever being explained though. Just seemed to fit. up to plus 15 knots is currently being taught around here gust fronts and micro bursts make 30-50knot gusts relatively common during summer afternoons here if there's over-development two years ago we had a member landout in 70+mph cold front winds roaring in from the north. in some places along the front the winds exceeded 90mph. the pilot got about 8 miles in 7000ft to a landing about 4 miles south of the gliderport. he stayed in the glider, flying it on the ground until someone walked out and phoned for help. at the time I was playing father/son softball with my boy scout troop about 30 miles southeast of the landout location. large chunks of trees started flying by almost immediately as the winds hit we knew the front was coming, but no clue of the strong conditions. we usually expect some dust, but this was very different frank whiteley colorado |
#127
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That's nonsense. Spin/autrotation is all about one wing (partially) stalled,
and the other not. It's not about drag. -- Bert Willing ASW20 "TW" "Chris OCallaghan" a écrit dans le message de m... Here's another argument. The vertical stabilizer provides a great deal of yaw stability, even at very low speeds. To start autorotation, you need a source of drag at the tip greater than the normal differential to be expected resulting from span effect in a turn. That we don't |
#128
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the simple formula for best speed was best l/d speed plus 1/2 the headwind. Don't recall the second ever being explained though. Just seemed to fit. Not a formula but a rule of thumb that's pretty close - judging by a number of polars I've looked at. The following article is very simplistic but was written for a student who had trouble grasping the concept of needing to stay upwind of the field in strong conditions: http://home.comcast.net/~verhulst/GB.../headwind.html Tony |
#129
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Uh, Bert, what happens when a wing stalls? Lift decreases... drag
increases. Something needs to start the spin. Could that be... a force? I suppose we could call it something other than drag. Gremlins maybe? Let's see, perhaps I can offer another explanation. Non-symmetrical, differential lift across the wingspan produces roll. Non-symmetrical, differential drag along the wingspan produces yaw (adverse yaw when actuating the ailerons, for example). The vertical stablizer and rudder are there to provide stability and yaw authority to counteract the aileron drag effect (as well as the destabilizing effect of the fuselage forward of the cg). If the stall (or partial stall) produced no drag, the glider would simply roll. There would be no yawing motion. And thus, no spin! (But lots of rolling.) Here's another way to think about it... if you had an infinitely large vertical stabilizer (that is, infinite directional stability), would it be possible to spin? Since the infinitely large tail would produce an infinitely large counterforce to any adverse yaw, then a spin is not possible. What's the practical substitute for an infinitely (or very) large vertical stabilizer? A moveable rudder. It's all about the flippers, man. And from a practical standpoint, spins are all about the drag. And even though a partially stalled wing will display adverse yaw with neutral control surfaces, so long as you don't move the flippers, the vertical stabilizer will keep you from spinning. As noted before, I prove this to myself with every modern model of glider I fly. But if you move those flippers in an uncoordinated fashion, baby, all bets are off! Piggott: "Drag from the badly stalled, falling wing, pulls the glider down into a steep spiral and the autorotation is speeded up." There's a graceful way out of your dilemma... we could discuss the torques brought into play by the rolling motion of a partially stalled wing. That will introduce a rotation about the yaw axis (the aerodynamicist's definition of autorotation), but you'll need to prove to me that it alone is sufficient to overpower the vertical stabilizer, even at very low airspeeds and relatively high rates of roll. Since the vast majority of modern aircraft need an additional yawing moment to enter a spin (pro rudder, counter aileron), it's going to be a tough sell. But I'd be interested to see you work through the problem. Maybe we'll both learn something new. "Bert Willing" wrote in message ... That's nonsense. Spin/autrotation is all about one wing (partially) stalled, and the other not. It's not about drag. -- Bert Willing ASW20 "TW" "Chris OCallaghan" a écrit dans le message de m... Here's another argument. The vertical stabilizer provides a great deal of yaw stability, even at very low speeds. To start autorotation, you need a source of drag at the tip greater than the normal differential to be expected resulting from span effect in a turn. That we don't |
#130
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BTW,
I thought I'd add that "autorotation" is why highly controllable, low stability aircraft can be spun with ailerons held into the direction of spin. If you can roll fast enough with stick well back, the resulting torque about the yaw access is sufficient to overpower a too small vertical stabilizer (in designs where stability is sacrificed for greater controlability). But this does not describe a modern, certified glider. And, after all, we're looking for practical knowledge we can take into the air. But I remain interested in whether you can demonstrate that rolling torque alone will make the glider spin. If it can't, then we can focus on other sources of adverse yaw that contribute to the autorotation. If it can, then we'd all best be looking for a new, safer passtime, like freeclimbing solo. But hey! I'm making your argument for you. Bert, this could really be fun. Fire away, please! |
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