Phantom flight

Cockpit Colin wrote:
One way to think of it (not too scientific) is that adding power just
adds more "juice" to the spin. The power vector rotates around, just
making the plane do whatever it's doing with that much more vigor.


I understand what you're trying to say, but I just can't get a handle on the
physics of it ...

OK, stream of consciousness here. Ignore any violations of the law(s of
physics).

A plane in a spin is yawing and rolling simultaneously. It is also at a
stalled angle of attack. What happens is that, as the AOA of a wing
increases, its drag always increases, but at a certain point its lift
decreases (near and past stall speed). So in a spin (to the left) the
left wing has a higher angle of attack, due to adding the downward
motion of the plane and the relative motion of the spin (steal kid's F-4
model, experiment), than the right. It has higher drag and less lift,
and so the plane rolls left and yaws left. You get spin.

To break the spin ususally you must break the yaw, which puts both wings
back into an equal amount of AOA condition. To break the yaw you need to
create a moment. The moment is created typically with rudder, and
sometimes helped by tricks with ailerons. The thrust would not help with
creating a moment.

So what would it do with more thrust? Well, if the nose was pointing
down, it'd make the plane fly "heavier" due to a downward component to
the thrust. That'd give you more spin.

As for the thought of having the thrust fly you away, if you watch how
fast planes spin, versus how fast they accelerate on takeoff with full
blower, you'd see that before it'd have chance to accelerate in one
direction it'd be pointing another, so to speak. Mathematically
speaking, say you wanted the plane to fly away to the east. Integrate
the component of thrust that points east over a half-rotation of spin
(less than a second?) and divide that by the mass of the plane to get a
delta velocity eastward over the half-rotation. Or something like that.
Small number which is immediately cancelled by other half-rotation. A
plane in a spin carves a slightly spiral trajectory. It'd make the
spiral a wee bit bigger. Not enough to matter.

That's my story (based on 200+ inverted spins in a Buckeye...thought
processes cloudy now), and I'm sticking to it.

Thanks for that. I was thinking mostly about flat / falling leaf spins, but
there are some definate "food for thought" in this regard in what you wrote.


"nafod40" wrote in message
...
Cockpit Colin wrote:
One way to think of it (not too scientific) is that adding power just
adds more "juice" to the spin. The power vector rotates around, just
making the plane do whatever it's doing with that much more vigor.


I understand what you're trying to say, but I just can't get a handle on
the
physics of it ...

OK, stream of consciousness here. Ignore any violations of the law(s of
physics).

A plane in a spin is yawing and rolling simultaneously. It is also at a
stalled angle of attack. What happens is that, as the AOA of a wing
increases, its drag always increases, but at a certain point its lift
decreases (near and past stall speed). So in a spin (to the left) the
left wing has a higher angle of attack, due to adding the downward
motion of the plane and the relative motion of the spin (steal kid's F-4
model, experiment), than the right. It has higher drag and less lift,
and so the plane rolls left and yaws left. You get spin.

To break the spin ususally you must break the yaw, which puts both wings
back into an equal amount of AOA condition. To break the yaw you need to
create a moment. The moment is created typically with rudder, and
sometimes helped by tricks with ailerons. The thrust would not help with
creating a moment.

So what would it do with more thrust? Well, if the nose was pointing
down, it'd make the plane fly "heavier" due to a downward component to
the thrust. That'd give you more spin.

As for the thought of having the thrust fly you away, if you watch how
fast planes spin, versus how fast they accelerate on takeoff with full
blower, you'd see that before it'd have chance to accelerate in one
direction it'd be pointing another, so to speak. Mathematically
speaking, say you wanted the plane to fly away to the east. Integrate
the component of thrust that points east over a half-rotation of spin
(less than a second?) and divide that by the mass of the plane to get a
delta velocity eastward over the half-rotation. Or something like that.
Small number which is immediately cancelled by other half-rotation. A
plane in a spin carves a slightly spiral trajectory. It'd make the
spiral a wee bit bigger. Not enough to matter.

That's my story (based on 200+ inverted spins in a Buckeye...thought
processes cloudy now), and I'm sticking to it.

I remember (dimly) the TAC crew who ran spin tests in the F4 back
around 1967 and then went around briefing crews. They came down to
Homestead while I was going throught the F4 RTU. They described the
flat spin and how finally they both ejected and neither ejection did
anything to force the nose down enough to break the spin. They also
said if the tail surfaces were about 8 feet further back from the wing
recovery from a flat spin would have been possible. As for ejection
sensations - FWIW a Martin-Baker H7 ejection isn't punishing at all.
the only odd effect I noticed is that the powerful upward push and
acceleration pulls your eyelids. As soon as the telescoping catapult
tubes parted the powder gases dissipated, that hard push stopped and
the lanyard-fired rocket took over. You can see again and you can hear
the rocket hissing away. (Helmet soaks up the real noise) Looking down
you can see the airplane apparently dropping below you - way below you
- and the hole you just came out of. The rocket quits and you're still
going up, maybe 250 feet above the airplane now. Then there's an
audible click as the drogue chute deploys followed by a sudden yank as
it fills and the seat is yanked up to coast butt-first into the
airstream. (we were only at about 215 IAS at 1500 when I initiated the
ejection sequence). One startling thing for me was that apparently
something was awry, perhaps because ISTR I was slightly canted to one
side) and the seat started to spin rapidly around the longitudinal
axis. I remember thinking "If I have to go manual now this will be
difficult . . ." thinking about manual seat separation and ripcord
pulling. The spin was rapid enough to be quite disorienting. But then
the main chute deployed and I was yanked firmly from the seat. It was
all very cool from then on - I landed in blowdown and second growth
following a hurricane about a dozen years before and the landing was so
well cushioned my feet were about a foot above the ground when I
stopped.
Of course the early seats were punishers before a) pilots started
getting back injuries and b) the physiologists and the seat designers
got together and observed some design limitations inherent in homo sap,
like 15 G was too brutal and 8G was okay. One comment - from the time
I pulled the D-ring until the seat fired seemed about five full
seconds. It didn't fire immediately and I started to look down to make
sure I had the handle - dumb thought! but then my mind said "Don't look
down - you'll hurt your back!" so I stayed erect and then the seat
fired. This seemed to take about 5 seconds - according to the Dash One
it's just 0.54 seconds from pull to fire. Shows how adrenalin speeds
up thought in 'combat mode'.
Walt BJ

wrote:

I remember (dimly) the TAC crew who ran spin tests in the F4 back
around 1967 and then went around briefing crews. They came down to
Homestead while I was going throught the F4 RTU. They described the
flat spin and how finally they both ejected and neither ejection did
anything to force the nose down enough to break the spin. They also
said if the tail surfaces were about 8 feet further back from the wing
recovery from a flat spin would have been possible. As for ejection
sensations - FWIW a Martin-Baker H7 ejection isn't punishing at all.
the only odd effect I noticed is that the powerful upward push and
acceleration pulls your eyelids. As soon as the telescoping catapult
tubes parted the powder gases dissipated, that hard push stopped and
the lanyard-fired rocket took over. You can see again and you can hear
the rocket hissing away. (Helmet soaks up the real noise) Looking down
you can see the airplane apparently dropping below you - way below you
- and the hole you just came out of. The rocket quits and you're still
going up, maybe 250 feet above the airplane now. Then there's an
audible click as the drogue chute deploys followed by a sudden yank as
it fills and the seat is yanked up to coast butt-first into the
airstream. (we were only at about 215 IAS at 1500 when I initiated the
ejection sequence). One startling thing for me was that apparently
something was awry, perhaps because ISTR I was slightly canted to one
side) and the seat started to spin rapidly around the longitudinal
axis. I remember thinking "If I have to go manual now this will be
difficult . . ." thinking about manual seat separation and ripcord
pulling. The spin was rapid enough to be quite disorienting. But then
the main chute deployed and I was yanked firmly from the seat. It was
all very cool from then on - I landed in blowdown and second growth
following a hurricane about a dozen years before and the landing was so
well cushioned my feet were about a foot above the ground when I
stopped.
Of course the early seats were punishers before a) pilots started
getting back injuries and b) the physiologists and the seat designers
got together and observed some design limitations inherent in homo sap,
like 15 G was too brutal and 8G was okay. One comment - from the time
I pulled the D-ring until the seat fired seemed about five full
seconds. It didn't fire immediately and I started to look down to make
sure I had the handle - dumb thought! but then my mind said "Don't look
down - you'll hurt your back!" so I stayed erect and then the seat
fired. This seemed to take about 5 seconds - according to the Dash One
it's just 0.54 seconds from pull to fire. Shows how adrenalin speeds
up thought in 'combat mode'.
Walt BJ

Damn!...very interesting...we need many more of these, told just
that way...a description that can be believed...you really should
write a book Walt, you have a knack of describing an event that
paints a vivid picture (and what's even better is totally
believable)
--

-Gord.
(use gordon in email)

Damn!...very interesting...we need many more of these, told just
that way...a description that can be believed...you really should
write a book Walt, you have a knack of describing an event that
paints a vivid picture (and what's even better is totally
believable)

Thanks Walt - and sign me up for my copy!

BTW - there is a good collection of ejection experiences at
www.ejectionsite.com


Damn!...very interesting...we need many more of these, told just
that way...a description that can be believed...you really should
write a book Walt, you have a knack of describing an event that
paints a vivid picture (and what's even better is totally
believable)
--

-Gord.
(use gordon in email)