I did not understand it either and I have been an aeronautical engineer for Fifty years. The fact that when you bank the airplane the lift vector is broken down into a vertical componet and a horizontal componet with the horizontal componet causing the turn is sufficient. Anything more than that is pure crap.
Subject: Light-Sport Aircraft Yahoo group Re: What makes an airplane turn?
--- In mailto:Sport_Aircraft%40yahoogroups.com, "Jim Bair" <jimbair@...> wrote IN PART:
>
> Alex,
> What was the aeronautical training of the engineer you talked to?
Fair enough question, Jim. He's an electrical engineer, but a 3000 hour pilot who owns a RV and another high performance single engine the name of which escapes me. That said, while credentials are important, WHOever comes up with an explaintion it should be able to stand on its own, not JUST because a nominal expert says so.
>You just watched a video in which an airplane was banked left, and initially there was no turn, then the pilot started a turn to the right, and then the pilot did a turn to the left. <
Frankly, maybe I'm getting softbrained, but I found it hard to follow the video and its point. It flashed through my head that maybe the initial turn to the right was that "adverse yaw" I hear kicked around (and which I don't think I've ever noticed on our Skyranger LSA).
Maybe I should watch it again.
>
> I'm not sure what you mean when you say, "But if that (horizontal component of lift) were ALL that was going on when you bank left all that would happen would be the plane horizontally moving sideways to the left" because that IS all that's going on. That'ss what a level left turn is, nothing more than a horizontal turn to the left."<
I NOW think I get your point that if the plane in my picture were to from the pilot's perspective "only "slide to the left" while moving forward it WOULD indeed be _turning_ as its ground track would indeed be a curved path to the side of the bank.
Thank you for getting me to think about that.
What I was driving at and mistating (but got to later) was that "horizontal component of lift" doesn't explain the nose turning but itself.
What _I_ was driving at and didn't explain or understand clearly was this: That taking my understanding of physics and compoents of force (long time ago I WAS a physics major) from a horizontal compenent of force occurring (whether from a bank moving the lift vector away from straight upward or an airborn elephant colliding with the side of the plane) the plane should just start moving sidewards, nothing else, as if someone got outside the cockpit and pushed the plane to the left....IF nothing else was going on.
I would not, from THAT expect to see the normal sort of turn (nose turns to new headings too) that in fact I usually see if I lean the stick to one side.
So, as you allude, in addition since presumably in level flight just before the bank was initiated there was just enough vertical lift to balance gravity and now some of that is siphoned off (so to speak) into horizontal forces, if you don't apply more power to "replace" the vertical lift the plane will start sinking.
My point was unless there's something ELSE going on in the picture other than "the horizontal component of lift" in a bank what I would have expected to see as result of a bank to the left is my plane sliding down to the left -- with my nose pointed straight ahead exactly on the heading it was before I pushed the stick to the left. In that sense I was saying that the standard answer to "what makes a plane turn" given as "horizontal component of lift" is true, but was incomplete in that doesn't explain why, at least in my plane and the few others I've been at the controls of the nose turns too... even with no rudder applied.
> Then you ask, "The remaining question is "What turns the _nose_ of the plane to the left and keeps it turning?" That's easy. The horizontal component of lift. There has to be a vertical component of lift to counteract gravity. If the lift is tipped off vertical by banking the airplane, then there is now a horizontal component as well. That component pulls the airplane in the direction of the component. If you increase lift by pulling the stick back, the nose begins to climb, right? This is how a loop is done. Pull back on the stick, and the nose starts up and the plane goes around in a vertical circle. If you roll into a 90 deg angle of bank and do the same thing, you can make a loop in the horizontal. Of course, gravity is in the equation so we must counter that in some way, and some lift must remain in the vertical from somewhere. In my video, that lift was being provided mostly by the fuselage. <
OK. I think I got it now. Once banked left (let's say it's a 45-degree bank) I'm either going to be consiously or unconsiosly pulling up on the stick or applying power and now I'm so-to-speak "climbing to the left" with my nose trying to move 45-degrees upward. Makes sense.
I'm still a little puzzled though:
In reality in my plane (and the few others I've flown) if I bank left and don't apply power or pull the stick back the nose STILL does turn... What happens is that I go into a spiral descending turn.
I guess there's still sufficent lift component on the vertical axis of the plane to pull the nose around.
>...The plane does NOT move sideways and then weathervane into the wind and thus, turn...<
OK... that's not the full or even necessary explaination for the turn. Darn... I rather liked it.;-) But planes DO weathervane into the relative wind.
> So in your last sentence when you say "we all know you can turn an airplane by banking" then can you explain to me why it can happen that an airplane can be banked and a turn not occur? Or even be turned in the opposite direction from the bank? You just watched a video of an airplane doing exactly that. How do you explain it?<
I guess I miss that. Can't explain it unless I mouth off "adverse yaw" while not being certain I fully understand that.
See http://www.aeroexperiments.org/AEPaytwistedwind.shtml
Where it starts out saying --
---------------------------
The simplest explanation of adverse yaw goes something like this: "When an aircraft is rolling toward the right, the left wing is creating 'more lift' than the right wing. This means that the left wing is also creating 'more drag' than the right wing, so the aircraft's nose will tend to swing toward the left."
Here's the flaw in this "explanation": the left wing only creates more lift than the right wing while the roll rate (toward the right) is increasing rather than constant. Yet in any aircraft that experiences marked adverse yaw, the adverse yaw is quite evident even when the roll rate is constant rather than increasing.
To get a better understanding of adverse yaw, .......
---------------------------
and then goes on with diagrams and probably 1000 words of explaination.
Honestly (I'll have to try it again) but I seriously doubt I can bank my plane left without it starting a more-or-less ordinary, if sloppy, turn to the left. Unless I apply opposite rudder, in which case it's sliding to the left and its ground track is still, as I think you were trying to tell me, a turn to the left.
> So, the classic answer we give on the FAA test and asked by CFIs is not only acceptable, but complete. If it is incomplete, it is because you don't understand it.<
In my defense I would say "because I understood it incompletely" and suggest that some of those who just quickly answer "horizontal component of lift" understand it even less and haven't even asked themselves the question "yes, but what makes the nose turn." Most of those who I have asked _that_ have either not even understood my question or had to think a lot about it and come up with very different answers, or answers you would likely reject.
> I may redo the video because I wasn't pleased with the camera placement. I know the back of my head is quite attractive, but it wasn't supposed to be the main focus of the video.
From my point of view what I think you're trying to demonstrate might be easier to understand with, or supplemented by, an animation with labels and force vectors, and viewed from several different angles outside the plane.
Far easier for me to suggest that than for anyone to do it.
Thanks for getting me to think this through a bit clearer.
Alex
__._,_.___
No comments:
Post a Comment