If a plane is in rising air, and has equilibrated in the mass of rising air,
it is in exactly the same state as if it were eqilibrated in neutral or
falling air. it is just moving forward the same in each mass of air from its
own perspective. So why should it tilt nose down from our perspective on the
ground?
Rodger
----- Original Message -----
From: "Ben Diss" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Cc: "Rodger Hamer" <[EMAIL PROTECTED]>; "Moved by the wind."
<[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>
Sent: Sunday, March 12, 2000 12:26 PM
Subject: Re: [RCSE] On Step
> This sounds a lot like the downwind turn argument. The way I envision
> this situation is the plane is in a steady state and enters a rising air
> mass. Once in the rising air mass, the steady state returns and the
> wing and stab don't know that they're rising. Thus, the airflow on the
> wing and stab remains the same, yet our observation is that the airplane
> goes faster and loses some AOA.
>
> Wait a sec. Are you saying that this effect only occurs during the
> transition into the rising air mass? If so, I think I see your point.
> The wing enters the thermal and goes up slightly because of the rising
> air. When the stab then follows and enters it is effected to a greater
> degree because of its comparably lower loading than the wing. Thus, the
> tail is unable to produce the same down force to balance the plane to
> maintain the same AOA it had in the prior air mass. If this is so, then
> it would be reasonable to conclude that given enough steady state flight
> in the rising air mass, the balance would return to the previous slow
> airspeed without need for trim.
>
> Have I got it now?
>
> -Ben
>
> Jill and Rick Brown wrote:
> >
> > There isn't any more or less up force on the wing or the stab. That is
> > correct. But the tail takes far less force to lift it than the wing due
> > to the fact that the wing is lifting nearly all the weight of the
> > plane. It's the same reason that a small deflection of the stab or
> > rudder affects the attitude of the plane. Because it take so little
> > force applied at the end of this monment arm (the tail).
> >
> > Ben Diss wrote:
> > >
> > > Not really. It doesn't make sense to me. Since the wing and stab are
> > > both in the same airmass, the effective AOA changes together and then
> > > stabilizes together. There isn't any more wind striking the stab then
> > > there is striking the wing.
> > >
> > > Maybe I missed something?
> > >
> > > -Ben
> > >
> > > Jill and Rick Brown wrote:
> > > >
> > > > You have got to be joking!
> > > > How does a weather vane work? It wants to point into the wind. The
tail
> > > > of a sailplane is essentially a weather vane. The sailplane is
pivoting
> > > > about the CG and the tailboom and stab form a moment arm. It doesn't
> > > > take much force on the tail to rotate it. If you need proof just
balance
> > > > the plane on it's GC and add a 1/2 oz of lead to the tail. Tail
Down!
> > > > The lift component is an upward force on this system and wants to
> > > > rotate the tail upward to some degree as it also starts to lift the
> > > > whole plane. Because it takes very little force to rotate the tail
up
> > > > or down this force gives a tail up/nose down attitude to the plane.
> > > >
> > > > Does this seem to make any sence to anyone?
> > > >
> > > > RB
> > > >
> > > > Rodger Hamer wrote:
> > > > >
> > > > > That is an answer that makes sense!
> > > > > Rodger
> > > > > ----- Original Message -----
> > > > > From: "Moved by the wind." <[EMAIL PROTECTED]>
> > > > > To: "Rodger Hamer" <[EMAIL PROTECTED]>
> > > > > Cc: <[EMAIL PROTECTED]>
> > > > > Sent: Sunday, March 12, 2000 9:52 AM
> > > > > Subject: Re: [RCSE] On Step
> > > > >
> > > > > >
> > > > > >
> > > > > > Rodger Hamer wrote:
> > > > > >
> > > > > > > Can somebody explain to me why when in good lift the tail
rises and
> > > > > the
> > > > > > > plane appears "on step"
> > > > > >
> > > > > > Seems like there's a lot of opinions on this. IMHO the opinions
above are
> > > > > wrong, so I'll add mine.
> > > > > >
> > > > > > The story starts with your plane is flying along level in still
air at an
> > > > > AOA of say 3*, and the fuse level, (unless it's an Hobie
> > > > > > Hawk). Now you have wisely steered the plane to lift, how does
the plane
> > > > > "see" this? With the upward component of lift the wing is
> > > > > > now flying into the air at an AOA of say 5*, but the plane is
trimmed to
> > > > > enter the air at 3*, so what happens now? The plane will
> > > > > > assume an AOA of 3* to the air, but that looks like it's -2* on
the fuse
> > > > > compared to ground. You're on the ground, so it looks like
> > > > > > the nose went down or the tail went up to you.
> > > > > >
> > > > > > Did I get it right?
> > > > > >
> > > > > > Rich B
> > > > > >
> > > > > >
> > > > >
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