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#1
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Or the corkscrew motion of an aileron roll must provide enough "outward"
(normal) force to counteract the downward force of gravity. I think I understand what you're saying, Hamish. It may depend on the airplane. An SNJ doesn't "corkscrew" very much. It would hardly be enough to provide positive G in excess of 1.0. The maneuver starts with a pullup... It does start with a slight pullup, but then then back-prssure on the stick is released, to produce what approximates a zero-G situation. (Don't you do that in an Aerobat?) I thnk the best description of an aileron roll is to call it a zero-G maneuver. Not *exactly* zero, to the tenth decimal place, but close to zero all the way around. and that pullup is never really lost I don't understand that. I need to use some right rudder after passing the half-way point of a left aileron roll, or I'll end up with the nose pointing down about 20 degrees. (unlike the slow roll, which can result in negative G's in many aircraft). I don't understand that, either. You're saying there are airplanes that can perform a slow roll without experiencing negative Gs? vince norris |
#2
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In article ,
vincent p. norris wrote: Or the corkscrew motion of an aileron roll must provide enough "outward" (normal) force to counteract the downward force of gravity. I think I understand what you're saying, Hamish. It may depend on the airplane. An SNJ doesn't "corkscrew" very much. It would hardly be enough to provide positive G in excess of 1.0. Well, the *whole point* of a textbook aileron roll is to maintain positive G's -- not 1+ G's, but *positive* -- all the way through the maneuver, regardless of whether you do it in a Pitts or a puny Aerobat (the Pitts is a lot more, erm, exciting in this respect :-)). The maneuver starts with a pullup... It does start with a slight pullup, but then then back-prssure on the stick is released, to produce what approximates a zero-G situation. (Don't you do that in an Aerobat?) The textbook aileron roll in an Aerobat starts with a shallow dive to 120 KIAS, then a smart pullup to 30 degrees pitch, then a quick simultaneous full-over on the ailerons and neutralization of the elevator until pullout. Apply rudder as appropriate... The Pitts is pretty much the same, but at least with the constant speed prop you don't have to spend so much time obsessing about the throttle. I thnk the best description of an aileron roll is to call it a zero-G maneuver. Not *exactly* zero, to the tenth decimal place, but close to zero all the way around. In no plane I've ever done an aileron roll in is the G force "close to zero all the way around". In fact, it's close to 2G's at two points in the maneuver (pullup and pullout), and it's probably around .5 to 1 G over the top. and that pullup is never really lost I don't understand that. I need to use some right rudder after passing the half-way point of a left aileron roll, or I'll end up with the nose pointing down about 20 degrees. Remember, half way around your altitude is still quite a bit higher than it was when you started the maneuver.... (unlike the slow roll, which can result in negative G's in many aircraft). I don't understand that, either. You're saying there are airplanes that can perform a slow roll without experiencing negative Gs? No I'm saying that true textbook slow rolls result in negative G's (and are nearly impossible in an Aerobat, but never mind...). Hamish |
#3
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An SNJ doesn't "corkscrew" very much. It would hardly be
enough to provide positive G in excess of 1.0. Well, the *whole point* of a textbook aileron roll is to maintain positive G's -- not 1+ G's, but *positive* -- all the way through the maneuver.... Sorry, I didn't express myself well. I meant "It would hardly be enough to provide positive G in excess of 1.0, enough to negate the negative 1 G caused by gravity, plus a bit more to make it a positive G maneuver." BTW, I looked again at a tape of Tex Johnston's rolls, going and coming. I cannot detect any "corkscrewing." regardless of whether you do it in a Pitts or a puny Aerobat (the Pitts is a lot more, erm, exciting in this respect :-)). I'm sure it is. I've had a little time in a friend's Starduster 2 but never had the pleasure of flying a Pitts. It does start with a slight pullup, but then then back-prssure on the stick is released, to produce what approximates a zero-G situation. (Don't you do that in an Aerobat?) The textbook aileron roll in an Aerobat starts with a shallow dive to 120 KIAS, then a smart pullup to 30 degrees pitch, then a quick simultaneous full-over on the ailerons and neutralization of the elevator until pullout. Apply rudder as appropriate... I would agree with that, except I neutralize the elevator THEN begin the roll. I don't think of the pullup as part of the maneurver, but as "preparation" for it. In fact, it's close to 2G's at two points in the maneuver (pullup and pullout), and it's probably around .5 to 1 G over the top. I don't think of the pullup as part of the maneurver, but as "preparation" for it. I don't pull up that sharply, and if I have to "pull out" at the end, I figure I didn't do it right. If by "over the top" you mean when 180 degrees inverted, I find that very hard to imagine, based solely on my experience. (I've never flown an airplane with a G-meter.) I don't hang on the seat belt, as in a slow roll, but I feel a bit "weightless." I don't seem to be pushing down (up?) on the seat very hard. Remember, half way around your altitude is still quite a bit higher than it was when you started the maneuver.... Yes, I think the airplane follows something like a "ballistic curve" during the maeuver. Certainly, it gets dang little vertical lift as it rolls past the 90 degree and 270 degree points. Despite the fact that the nose is pointed up slightly, the airplane is essentially "falling" and thus it, and whatever is in it, is experiencing zero Gs. (One G from gravity, counteracted by one G from the accelleration.) vince norris |
#4
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In article ,
vincent p. norris wrote: An SNJ doesn't "corkscrew" very much. It would hardly be enough to provide positive G in excess of 1.0. Well, the *whole point* of a textbook aileron roll is to maintain positive G's -- not 1+ G's, but *positive* -- all the way through the maneuver.... Sorry, I didn't express myself well. I meant "It would hardly be enough to provide positive G in excess of 1.0, enough to negate the negative 1 G caused by gravity, plus a bit more to make it a positive G maneuver." This is a little frustrating -- the standard aileron roll is done to cause continuous positive G's. That's an *aim* of aileron rolls. And the net G forces don't have to be more than 1, just enough to cause *net* positive G forces on the pilot 9and engine, etc.). That's the *definition* of a positive G maneuver. This started when you stated that aileron rolls don't cause positive G's all the way around, -- and that's just wrong, unless by "aileron roll" you mean something different from what the IAC, various texts, etc., all mean by the term. BTW, I looked again at a tape of Tex Johnston's rolls, going and coming. I cannot detect any "corkscrewing." I can't comment on that except to say the corkscrewing is not always obvious, especially from the ground... (I've never seen the videos, if you're talking about the Dash-80 "barrell roll"). regardless of whether you do it in a Pitts or a puny Aerobat (the Pitts is a lot more, erm, exciting in this respect :-)). I'm sure it is. I've had a little time in a friend's Starduster 2 but never had the pleasure of flying a Pitts. It does start with a slight pullup, but then then back-prssure on the stick is released, to produce what approximates a zero-G situation. (Don't you do that in an Aerobat?) The textbook aileron roll in an Aerobat starts with a shallow dive to 120 KIAS, then a smart pullup to 30 degrees pitch, then a quick simultaneous full-over on the ailerons and neutralization of the elevator until pullout. Apply rudder as appropriate... I would agree with that, except I neutralize the elevator THEN begin the roll. Well, I'm lucky if I can get it all done at the same time :-). I don't think of the pullup as part of the maneurver, but as "preparation" for it. It's a necessary part of achieving that ballistic corkscrew motion -- and (speaking from dumb experience) if you don't do the pullup properly, you can end up in something more akin to a split-S or a nasty dive off the end of the "roll", and / or a great deal of lost altitude. In fact, it's close to 2G's at two points in the maneuver (pullup and pullout), and it's probably around .5 to 1 G over the top. I don't think of the pullup as part of the maneurver, but as "preparation" for it. I don't pull up that sharply, and if I have to "pull out" at the end, I figure I didn't do it right. Well, the standard aileron roll typically has you pointing down at the ground at much the same pitch at the 360 degree point that you started the roll from (as a consequence of the corkscrew motion), so if you don't do the pullup, you find yourself gaining speed very rapidly... If by "over the top" you mean when 180 degrees inverted, I find that very hard to imagine, based solely on my experience. (I've never flown an airplane with a G-meter.) I don't hang on the seat belt, as in a slow roll, but I feel a bit "weightless." I don't seem to be pushing down (up?) on the seat very hard. For it to be a positive G maneuver, you don't have to be pushed down very hard. Most people probably think it's negative G's when in fact it's just reduced G's. Negative G's mean, yes, you're pressing up against the straps.... Remember, half way around your altitude is still quite a bit higher than it was when you started the maneuver.... Yes, I think the airplane follows something like a "ballistic curve" during the maeuver. Indeed -- the ballistic corkscrew curve is part of the definition of the aileron roll I gave from Szurovy and Goulian earlier in this thread. It's that motion that makes it a positive G maneuever. If, like me on a typical day, you screw up and use the elevator or rudder wrongly, you can certainly make it a negative G maneuver, but it stops being a real aileron roll at that point (and starts becoming a cause for quick roll-out-of-trouble action :-)). Certainly, it gets dang little vertical lift as it rolls past the 90 degree and 270 degree points. It's not really supposed to. Despite the fact that the nose is pointed up slightly, the airplane is essentially "falling" and thus it, and whatever is in it, is experiencing zero Gs. (One G from gravity, counteracted by one G from the accelleration.) No, the plane is experiencing *positive* G's in a decent aileron roll. It's already starting to dive off the top at this point. Or should be, if you're doing it right... Hamish |
#5
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Sorry, I didn't express myself well. I meant "It would hardly be
enough to provide positive G in excess of 1.0, enough to negate the negative 1 G caused by gravity, plus a bit more to make it a positive G maneuver." This is a little frustrating -- the standard aileron roll is done to cause continuous positive G's. That's an *aim* of aileron rolls. I'm not trying to frustrate you, Hamish, but I don't agree with that. I don't know if the aileron roll has any "purpose" or "aim" except to have a little fun, and perhaps impress people who don't know how easy and undemanding it is. It also puts minimum stress on the airplane. Although an aileron roll can be done well, or badly, it's not a precision maneuver. It wasn't even taught in navy flight training when I went through. We learned to do slow rolls and barrel rolls to very precise, very exacting, criteria, because it was *hard* to do them that well, for a young pilot, and thus they developed our stick-and-rudder skills. And the net G forces don't have to be more than 1, just enough to cause *net* positive G forces on the pilot 9and engine, etc.). That's the *definition* of a positive G maneuver. That's what I said, above. But if an airplane is in inverted flight, it takes at least 1.000001 positive Gs caused by acceleration to overcome the negative G caused by gravity and produce a G sum that is positive. This started when you stated that aileron rolls don't cause positive G's all the way around, IIRC, I responded to a posting that said it was a "one G" maneuver, which is what I disagreed with. Perhaps my memory is faulty on that score. I can't comment on that except to say the corkscrewing is not always obvious, especially from the ground... Seems to me that enough corkscrewing to produce at least 1 G of accelleration when the airplane is inverted would be noticeable. Think about what it takes to produce one G of acceleration in other maneuvers. (I've never seen the videos, if you're talking about the Dash-80 "barrell roll"). Yes, that's the one. I've read Tex Johnston's book, and know it is described there as a "barrel roll" and a "one G" maneuver. I strongly suspect that wording was provided by the "ghost writer" who thought it would sound impressive to the reading audience. Whether one accepts the definition of a barrel roll supplied by Bob Moore, a fellow naval aviator, or by, IIRC, "Big John," which is radically different, each one produces very noticeable "corkscrewing" and thus cannot be a one G maneuver. The textbook aileron roll in an Aerobat starts with a shallow dive to 120 KIAS, then a smart pullup to 30 degrees pitch, then a quick simultaneous full-over on the ailerons and neutralization of the elevator until pullout. Apply rudder as appropriate... I would agree with that, except I neutralize the elevator THEN begin the roll. Well, I'm lucky if I can get it all done at the same time :-). OK, I'll accept that; in any case, the stick is "unloaded" while the airplane is rolling. I don't think of the pullup as part of the maneurver, but as "preparation" for it. It's a necessary part of achieving that ballistic corkscrew motion -- In an Aerobat, I suppose it is necessary. In a more powerful airplane, it is not. For example, an airplane capable of a steep climb can nose over toward level flight and when his nose reaches the desired point above the horizon, do an aileron roll. In fact, he can do an aileron roll going straight up. Similarly, low-powered airplanes, including the SNJ, generally need to lower the nose to pick up a little speed to begin a loop. But that is not part of the maneuver; more pwerful airplanes can do a loop without lowering the nose, and it is perfectly correct loop. Indeed -- the ballistic corkscrew curve That sounds like a contradiction. As I understand it, "ballistic" refers to the trajectory of a shell after it leaves the muzzle of a cannon, say, and is affected (in theory) only by gravity but in actuality by air resistance, etc. It does not, so far as I know, "corkscrew." I believe the "Vomit Comet" describes a ballistic curve to produce a weightless condition for budding astronoauts. No corkscrewing is involved. Certainly, it gets dang little vertical lift as it rolls past the 90 degree and 270 degree points. It's not really supposed to. That's right. Despite the fact that the nose is pointed up slightly, the airplane is essentially "falling" and thus it, and whatever is in it, is experiencing zero Gs. (One G from gravity, counteracted by one G from the accelleration.) No, the plane is experiencing *positive* G's in a decent aileron roll. It's already starting to dive off the top at this point. Or should be, if you're doing it right... I'm afraid I disagree with that, too, Hamish. As I said eaarlier, if I end up in a dive, I conclude I did it wrong. I don't think we're ever going to agree about this, Hamish, so we might as well just agree to disagree. vince norris |
#6
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In article ,
vincent p. norris wrote: [...] And the net G forces don't have to be more than 1, just enough to cause *net* positive G forces on the pilot 9and engine, etc.). That's the *definition* of a positive G maneuver. That's what I said, above. But if an airplane is in inverted flight, it takes at least 1.000001 positive Gs caused by acceleration to overcome the negative G caused by gravity and produce a G sum that is positive. This started when you stated that aileron rolls don't cause positive G's all the way around, IIRC, I responded to a posting that said it was a "one G" maneuver, which is what I disagreed with. Perhaps my memory is faulty on that score. Erm, well, we can stop right there, because that's what the problem is... here's your article and my initial response (my stuff with the single ""): In article , vincent p. norris wrote: Not if you maintain positive G all the way around (as in aileron roll). You don't have positive G all the way around in an aileron roll. In a properly done aileron roll you certainly do... To maintain positive G, you need a barrel roll. Or an aileron roll. Were you thinking of a slow roll? And later in the thread I also explicitly asked whether you meant a "1G maneuver" rather than a "positive G" maneuver. In both cases you said no. Oh well. I think I kinda suspected this -- if you'd actually said it wasn't a *1 G* maneuver, I'd have agreed wholeheartedly. But to make the blanket statement that you don't have positive G all the way around in an aileron roll (or any aileron roll), well, that ain't right.... Hamish |
#7
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This started when you stated that aileron rolls don't cause positive G's
all the way around, IIRC, I responded to a posting that said it was a "one G" maneuver, which is what I disagreed with. Perhaps my memory is faulty on that score. Erm, well, we can stop right there, because that's what the problem is... here's your article and my initial response (my stuff with the single ""): In article , vincent p. norris wrote: Not if you maintain positive G all the way around (as in aileron roll). You don't have positive G all the way around in an aileron roll. I believe that's essentially true. As I said more recently, But if an airplane is in inverted flight, it takes at least 1.000001 positive Gs caused by acceleration to overcome the negative G caused by gravity and produce a G sum that is positive. And I said that I have serious doubt there is enough "corkscrewing" in the aileron rolls I've done, and seen others do, to produce more than about 1 G. Maybe a bit less. I would not suggest there are *noticeable* negative Gs, like a slow roll; as I said, I don't hang on my seat belt. I think that halfway through the roll, the airplane is *essentially* (i.e., for all practical purposes) in a zero-G condition. I tried to say that before, but perhaps I didn't say it well enough. For that matter, when I "unload" the stick to begin the roll, I am just about at zero Gs. I *attempt* to create a zero-G condition. I believe that is the correct procedure. I'm sure I can't produce exactly zero Gs every time, to several decimal places; no doubt I sometimes produce a slight negative-G condition, sometimes a slight positive-G condition. Apparently you do not agree with that. I'm not suggesting you ought to change the way you do aileron rolls, or think about them; I am simply saying what I believe to be the case. I've expressed my views several times, so I don't think there is much to be gained by my repeating them again. We can just agree to disagree. Oh well. I think I kinda suspected this -- if you'd actually said it wasn't a *1 G* maneuver, I'd have agreed wholeheartedly. I imagine you would have. On that subject: In a protracted discussion with a friend who is an aeronautical engineer prof, specializing in aerodynamics, a year or so, in reaction to an earlier thread on this newsgroup, we came to this conclusion: "There is no such thing as a one-G maneuver." An airplane flying straight and level, at constant speed, on a smooth-air day, experiences one positive G. ANY departure from that condition changes the G, either in amount, or direction, or both. Yet we often hear about "one G maneuvers." I think people use the term to any maneuver that does not produce *palpable* G forces on their bodies. In that peculiar, inaccurate, sense, I suppose I would agree with the statement that an aileron roll is a "one G maeuver." vince norris |
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