Hi Jim,
I think we are saying the same thing, with a few sloppy wordings to make it interesting.
One thing you will notice is that your stick will be physically further forward in knife edge flight than in upright flight. This is due to the engine end being heavier than the tail end and needing some 'upness' for normal flight. This is also why you'd need to hold your nose up with rudder for level sideways flight. You then need to use even more nose up rudder so your fuselage and prop provide sufficient altitude control. If you kept your rudders neutral, your nose will be below the horizon since your nose is still heavier than your tail. All this presumes we are talking about prop aircraft that we can afford to fly and not F22's.
I do think of the up elevator as repositioning the (nose up) component of lift towards the front of the plane and down doing just the opposite. Perhaps this is the more "Bernoulli" version of thought than the "Newtonian" version where the tail is being pushed down on the giant teeter totter of life. To me when you tie the model string to the roof and have the string too far forward, the nose will always go up. To others when the heavy kid sits on the seesaw the other kids go flying. Same stuff just thought of differently.
Bill Watson
bill@sportpilot.info
From: Sport_Aircraft@yahoogroups.com [mailto:Sport_Aircraft@yahoogroups.com] On Behalf Of Jim Bair
Sent: Thursday, October 04, 2012 2:09 PM
To: Sport_Aircraft@yahoogroups.com
Subject: Re: Light-Sport Aircraft Yahoo group Re: What makes an airplane turn?
Hi Bill,
Your description of knife edge flight is spot on and is basically describing what I described as a loop in the horizontal, which as you say, results in a turn in the horizontal. However, when a roll is occurring, it doesn't really reposition the nose. The nose stays exactly on it's spot on the horizon. If we draw a bunch of little arrows vertically off the top of the wing to represent lift, moving the stick to the side (making an aileron input) rolls the airplane and points those little arrows in a new direction. Those little arrows also represent the lift vector, and where they are pointed is where the lift is pulling the airplane. If we are in level flight, the sum of the lift of the arrows up equals the pull of gravity down, or the weight of the plane.That's why I like to think of a loop as simply a turn in the vertical. It is curved flight, just like a turn in the horizontal is curved flight.
I think people think of straight and level flight as being "neutral" because it's level 1g flight. That is our basis, even though the wing is not at 0 deg AOA. I think of neutral as being a hands off trim setting, so it will be a new spot for every speed and CG condition. I think in your description you meant to say more elevator up, or more tail down, but other than that your description is perfect. I tend to think of the purpose of the extra elevator added in a turn as being added for extra vertical lift to make up for that lost by turning the lift vector in a horizontal direction, not to add lift to make us turn. However, the overall effect of adding up elevator certainly will help us turn faster, so I don't mean to quibble.
What I do think people should understand, and what I tried to demonstrate in the video, is that bank alone does not make an airplane turn. It must be creating lift. If you take an airplane to zero G, i.e., float it, and then roll the airplane while you are at zero G, you will discover it will roll just fine (actually better than normal) but it will not turn at all. You can skid the nose around with rudder, but that is illusory of a turn. When you release the rudder, the nose will come back to where it was before you pushed the pedal. It is LIFT that makes an airplane turn, and what is our control that controls lift?
Except in my video when part of the time when I was in knife edge I was sideways and using the rudder as the elevator and the fuselage as the wing as far as providing lift to counter gravity. However, when I wanted to turn in a circle horizontally (what we normally think of as a turn) I had to add elevator. When I was flying in knife edge flight, the wings were producing no lift, so there were no little arrows, and no turn occurs. As soon as I either pushed or pulled on the stick, then lift was generated and a turn started. If I was in a 90 deg AOB left and pushed forward, the turn would be right. If I pulled on the stick, it would be left. If I went back to "neutral", meaning zero lift, then the turn stops. And when I roll, the nose doesn't move.
Jim
From: Bill
Sent: Thursday, October 04, 2012 12:33 PM
Subject: Re: Light-Sport Aircraft Yahoo group Re: What makes an airplane turn?
My $.005
The horizontal component of lift will cause the plane to go sideways. The location of
the center of that lift will make it turn. Imagine knife edge flight for a bit. Pull
back on the stick and the nose rises. Push and the nose goes down. Since from the
nose's perspective, rising is turning when compared with the Earth, we call that a
turn. Same for nose down. That's why turning takes two inputs - one to reposition the
nose about our longitudinal axis (aileron), followed by one to give upness to the nose
from this new perspectice (elevator). All of one without the other doesn't turn.
Now for those who input ailerons and find it turns anyway, you are actually adding
elevator without knowing it. The heavy end of the airplane is up front. The elevator
actively pushes the tail down to achieve straight and level flight. This being called
neutral is misleading. When you roll the plane, you lose the vertical component of
lift and must replace it with more elevtor down or your nose will drop. This gives the
elevator input needed to turn, so the apparent failing premise doesn't actually fail
the criteria.
Bill Watson
mailto:bill%40part103.org
---------- Original Message -----------
From: "circicirci" <mailto:acensor%40fastmail.fm>
To: mailto:Sport_Aircraft%40yahoogroups.com
Sent: Thu, 04 Oct 2012 16:44:49 -0000
Subject: Light-Sport Aircraft Yahoo group Re: What makes an airplane turn?
> No question that the horizontal component of lift when plane is banked left is
> what starts moving the plane to the left.
>
> {And of course as we all know the plane WILL turn with no rudder applied (even
> if it's a lousy uncoordinated turn you CFI would frown on).}
>
> 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 and or sliding slipping downward to the right if
> insufficient vertical upward component were left. In other words, the classic
> answer we give on FAA written tests and when asked by CFIs ("the horizonatal
> component of lift in a bank is what makes the plane turn") is accepted but
incomplete.
>
> The remaining question is "What turns the _nose_ of the plane to the left and
> keeps it turning?"
>
> What is missing IMO in the often sophisticated explainations I see here an
> other places claiming to answer that remaining question is a clear credible
> answer to that question... .At least those answers have never been clear and
> credible to me.
>
> I finally got a clear and very simple answer to that one from one engineer
> that I paraphrase in my own words as follows:
>
> "OK, you bank left, and as you say the plane begins to move SIDEWARDS to the
> left from that horizontal component of lift. So now the plane almost
> immeadiatly has a relative-wind component coming against it from the left. In
> fact I should say 'almost immeadiatly' as you notice there's a slight delay
> between the time you bank and the nose starts turning left. As you know all
> planes 'weather vane' turning their nose into the wind even on the ground if
> nothing (such as brakes tie-downs, or chocks) stop them. That's because among
> other things there's that big vertical horizontal tail catching all that
> relative wind on its left side and being pushed to the right."
>
> So in a manner of speaking very nitpickingly banking left and left horizonatal
> component of lift doesn't make the plane _turn_ but initiates conditions (left
> horizontal slide and relative wind compenent coming from the left) that in
> turn makes the plane turn.
>
> As a practical matter of course we all know you can turn a plane left by
> banking, rudder, or of course coordinated use of both.
>
> My two cents.
>
> Alex
>
> --- In mailto:Sport_Aircraft%40yahoogroups.com, "Jim Bair" <jimbair@...> wrote:
> >
> > Is this the list where we had the discussion about what makes an airplane turn? I
think the original question was, What is the primary control used in turning an
aircraft?
> > I made a little video that attempts to answer that question.
http://www.youtube.com/watch?v=VbaexiBw7jg
> >
> > Jim
> >
------- End of Original Message -------
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