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inverted spin recovery explanation



 
 
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  #1  
Old August 3rd 04, 10:49 AM
Alan Wood
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Default inverted spin recovery explanation

.... and don't forget to close the throttle :-)


"john smith" wrote in message
...
TD wrote:
Can someone help me and list the steps to recover from an incipient inverted
spin and fully developed inverted spin?


It doesn't matter whether you are inverted or upright.
If you are in a spin, step on the "HARD" rudder pedal, neutralize the stick.
When the rotation stops, the nose will be pointed down. Pull to the
nearest horizon. Speed will rapidly increase with the nose low, so don't
hesitate.



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  #2  
Old August 10th 04, 03:24 PM
Andrew Boyd
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Default

(Rick Macklem) wrote:

don't think for a nanosecond that anything you read will teach you
how to recover from inverted spins.


Well, yes, but it's really the visuals that tend to blow
beginner pilots away. The aircraft doesn't become emotionally
concerned because it's upside down - only the pilot does

In fact, I'd rather do an inverted spin any day, vs an upright
spin. Why? Because the rudder is in "clean air" in an inverted
spin.

The Pitts (in which I've recovered from hundreds of inverted spins)
can take up to TWO complete rotations to recover from an upright
spin. During that time, pilots can lose faith and get off the
correct rudder. However the Pitts will recover from an inverted
flat spin in ONE rotation, because the rudder is not being blanketed
by the rudder, as it is during an upright spin.

Three things you need to know about spins:

1) power is bad. Get off the power
2) stick is bad. Adverse yaw, rudder blanketing. Neutralize the
stick.
3) yaw is the problem. Fix it with rudder. I don't use the "heavy
pedal" trick, I just look across the nose. Works for me.

Give the above time to work. In a spin, you're going to be pumped,
and you're going to want to recover in a nanosecond. It doesn't work
that way. You have to give the correct inputs time to work.

As you can tell, I'm a Beggs-Mueller advocate. I'm sure you
can find aircraft types that it doesn't work in, but it sure
works well in the Pitts, which truth be known, has incredibly
docile stall/spin characteristics. Sure you can wind it up, but
it recovers just as easily as it gets into the spin. Many people
have managed to kill themselves in spins - I suspect they "froze",
which I have seen in students. This "deer-in-the-headlights" reaction
is not the optimal response to this situation.

One last comment: sometimes you will hear people talk about
the "rogue spin" they got into. Often these are beginner aerobatic
pilots, whom are perfecting the "hammerspin" which is best performed
with a metal prop.

Think about the control inputs for a hammerhead pivot: full left
rudder, full front right stick: those are perfect inputs for a
beautiful outside snap (generally only performed by Unlimited
category dot-pilots, and airshow pilots) which if performed on
the vertical downline, allows altitude to be exchanged for airspeed
which will keep that wonderful outside snap going - snaps stop when
you run out of airspeed (eg upline, buried stick).

As you might guess, I'm rather partial to outside snaps, because the
Pitts does them so well. Just like an inverted spin, the rudder is
in clean air. Outside snaps are great fun, just keep in mind your
-ve Va. One fun maneuver is a level 1/2 roll to inverted, then a push
up (half outside loop) then an outside 1/2 snap back to inverted at
the
top of the loop, then a nice pull for an inside loop downwards. Very
easy to do. It's a bit of a G-loc trap - don't do this for the first
time from the surface, because you may grey out a bit if you don't
grunt enthusiastically during the pull - but great fun nonetheless.

--
ATP www.pittspecials.com
  #3  
Old August 11th 04, 03:12 PM
Andrew Boyd
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Dudley Henriques wrote:

established your lower and top gate parameters with a
g/altitude/airspeed profile.


We're wandering off topic, but yes, the concept of a "gate"
is sorely underutilized in the civilian aerobatic world.

Most of the people into civilian aerobatics aren't really
very big into physics, which is a pity, because aerobatics
is really just applied physics. So what happens most of the
time is that people experiment, trial and error, and figure
out what works, and what doesn't, hopefully at a high enough
altitude to recover from any mistakes.

The gate is a wonderful - I would opine essential - tool of
the low-altitude aerobatic pilot. You can program an airplane
similarly to a computer: same inputs, same outputs.

Let's take a reverse outside half cuban eight, for example.

We start level, pull to the 45 up (I personally prefer a tad
steeper, say 55 deg, to reduce x-axis requirements) and my gate
for the push over the top is 1500 feet of altitude and 80 mph in
the Pitts.

The gate altitude is what determines whether or not I hit the ground,
and the entry airspeed determines the G I must pull to obtain the
desired radius, because the velocity squared factor in the lift
equation is cancelled
out the the velocity squared factor in the angular momentum equation
at the stalling AOA. Neat, eh?

I can enter the maneuver faster (90 mph works nicely), and obtain the
same
downward radius by pushing more G on the way down, but it's easier on
the hardware to minimize the negative G. I can push over slower than
80 mph but
I don't like it much - I'm on the edge of a negative stall as the nose
pitches down, which doesn't feel good if it's a bumpy day - turbulence
can cause you to exceed your stalling AOA and you can get into a
drag trap as Cd exponentially soars, which isn't so bad going down
except that Cl is reduced.

Now, thinking about the start of the maneuver, we have to be able to
have enough potential energy to obtain 1500 feet and 80 mph, which
means that
I'd like to see 160 mph of kinetic energy at 250 AGL before I pull up
to
the 55.

The above really isn't very complicated. A very nice, simple
maneuver which has you exiting inverted at 250 AGL. Great view.

We do it in wingtip-to-wingtip formation, which is great fun.

Keeping in mind that with a negative AOA the effect of bank is
reversed, which is a phenomenon which gets more apparent as the
negative G increases. This means that if the wingman gets too
close to the lead and absent-mindedly slightly spirals away from
the lead (a harmless enough adjustment during a positive G formation
maneuver such as a loop) the high pressure on the top of the wing
will cause the wingman to move *closer* to the lead. It's best
to start out doing this stuff with nose-to-tail clearance for
this reason, but that increases the power delta required between
the lead and the wing because of the geometry during the vertical
maneuvers.

What great fun, though!

--
ATP www.pittspecials.com
  #4  
Old August 11th 04, 03:50 PM
Dudley Henriques
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Default


"Andrew Boyd" wrote in message
om...
Dudley Henriques wrote:

established your lower and top gate parameters with a
g/altitude/airspeed profile.


We're wandering off topic, but yes, the concept of a "gate"
is sorely underutilized in the civilian aerobatic world.

Most of the people into civilian aerobatics aren't really
very big into physics, which is a pity, because aerobatics
is really just applied physics. So what happens most of the
time is that people experiment, trial and error, and figure
out what works, and what doesn't, hopefully at a high enough
altitude to recover from any mistakes.

The gate is a wonderful - I would opine essential - tool of
the low-altitude aerobatic pilot. You can program an airplane
similarly to a computer: same inputs, same outputs.

Let's take a reverse outside half cuban eight, for example.

We start level, pull to the 45 up (I personally prefer a tad
steeper, say 55 deg, to reduce x-axis requirements) and my gate
for the push over the top is 1500 feet of altitude and 80 mph in
the Pitts.

The gate altitude is what determines whether or not I hit the ground,
and the entry airspeed determines the G I must pull to obtain the
desired radius, because the velocity squared factor in the lift
equation is cancelled
out the the velocity squared factor in the angular momentum equation
at the stalling AOA. Neat, eh?

I can enter the maneuver faster (90 mph works nicely), and obtain the
same
downward radius by pushing more G on the way down, but it's easier on
the hardware to minimize the negative G. I can push over slower than
80 mph but
I don't like it much - I'm on the edge of a negative stall as the nose
pitches down, which doesn't feel good if it's a bumpy day - turbulence
can cause you to exceed your stalling AOA and you can get into a
drag trap as Cd exponentially soars, which isn't so bad going down
except that Cl is reduced.

Now, thinking about the start of the maneuver, we have to be able to
have enough potential energy to obtain 1500 feet and 80 mph, which
means that
I'd like to see 160 mph of kinetic energy at 250 AGL before I pull up
to
the 55.

The above really isn't very complicated. A very nice, simple
maneuver which has you exiting inverted at 250 AGL. Great view.

We do it in wingtip-to-wingtip formation, which is great fun.

Keeping in mind that with a negative AOA the effect of bank is
reversed, which is a phenomenon which gets more apparent as the
negative G increases. This means that if the wingman gets too
close to the lead and absent-mindedly slightly spirals away from
the lead (a harmless enough adjustment during a positive G formation
maneuver such as a loop) the high pressure on the top of the wing
will cause the wingman to move *closer* to the lead. It's best
to start out doing this stuff with nose-to-tail clearance for
this reason, but that increases the power delta required between
the lead and the wing because of the geometry during the vertical
maneuvers.

What great fun, though!

--
ATP www.pittspecials.com


See Aeroplane Monthly Feb. issue 2004 Article "Precision Decision" by
Col (now Gen) Des Barker. In it, Gen Barker covers fairly completely my
comments on the issues involved in high gating and it's effect on low
altitude vertical recoveries in the P51 Mustang. You might find the
article interesting.
Hope you guys are having a good season. I understand your dad was
Canadian Forces. Ask him if he knew Greg Bruneau. I flew the #10 bird as
a guest of the Snowbirds back in the 70's with Greg. Great guy, and a
wonderful team.
You two remind me of another father and son team from back when.
Don't know if you would remember Bill and Corkey Fornof. They put
together the first F8F civilian Bearcat team ever. Bill is gone now, but
Cork is still out there doing movies. Just emailed with him last week.
Doing fine!
All the best,

Dudley Henriques
International Fighter Pilots Fellowship
Commercial Pilot/ CFI Retired
For personal email, please
replace the at with what goes there and
take out the Z's please!
dhenriquesZatZearthZlinkZdotZnet


  #5  
Old August 12th 04, 04:01 AM
Jay Smith
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Default

Andrew, do you compensate for density altitude when you define your gates?

  #6  
Old August 12th 04, 07:13 PM
Andrew Boyd
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Jay Smith wrote:

Andrew, do you compensate for density altitude when you define your gates?


As a formation team, we are far more sensitive to density
altitude than solo performers, who are free to improvise
as they go along.

Some of our maneuvers - like our opening no-roll vertical eight,
which has an outside loop on the bottom and an inside loop on
the top - simply wouldn't be possible at say a 3,000 foot elevation
airport on a 100F day. We'd drop the top (slow, high AOA) inside
loop, and just do a vanilla outside loop instead, which is also
what we do for our low (not flat) show with low ceilings.

Frankly what bothers us mostly with higher density altitudes is
power loss. We try to deal with that by trading potential energy
for kinetic: for example, on a hot day we will plan to exit the
opening vertical eight at 400AGL instead of 250AGL and let the
nose drop to 250AGL before the push to the following outside cuban,
which I have to be very gentle over the top to avoid outside snapping
in close formation. Giving away the 150 feet of altitude also unloads
the wing and gives us another 10 mph entry speed for the outside
cuban, which is worth gold to me on wing over the top.

At higher density altitudes you will definitely see higher TAS
and larger radiuses, and if you're going to airshows under those
conditions, you will DEFINITELY want to pad your gate altitude.

I live way too far north, but can't stand to not fly during the
winter. When it's -20C (dunno what that is in F, probably below
zero) you wouldn't believe the aircraft performance: engine, prop
and wing all love that cold, thick air. I can get 2,000 feet of
vertical from the surface to the hhead kick in my stock S-2B, which
is simply not possible in summer.

P.S. Even though there's no heater, your toes don't get cold - just
pull some G, and they warm up just fine :-)

P.P.S. Apologies for being off-topic,

--
ATP www.pittspecials.com/images/oz_inv.jpg
  #7  
Old August 13th 04, 07:03 PM
Peter Ashwood-Smith C-GZRO
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Andrew, do you compensate for density altitude when you define your gates?

An interesting fact, which is not obvious to many folks, including
some aerobatic pilots (judging by the number of loop into the ground
accidents) is that the radius of any turn, up, down, sideways or
whatever, is a function of the square of TRUE airspeed, which is of
course a function of density altitude and calibrated airspeed.

So, if the density altitude increases your true airspeed by 5mph,
you get a 5mph^2 impact on your radius. This kind of change in radius
can ruin your day if you are playing down near the dirt.

This velocity^2 thing is also why the reverse cuban or loop down is
a real killer. If you start the pull with X knots too many, you will
use X^2 more radius for the 1/2 loop, throw in an increase in TAS of
say Y due to density altitude and you are into (X+Y)^2 more radius ...
not good. If you have not left margin either in terms of available G
or altitude you are either gonna high speed stall on the way down (and
hit the ground) or hit it on the arc.

This sort of question is on the ICAS exam now if I'm not mistaken.

Peter
  #8  
Old August 13th 04, 07:07 PM
john smith
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Peter Ashwood-Smith C-GZRO wrote:
Andrew, do you compensate for density altitude when you define your gates?


An interesting fact, which is not obvious to many folks, including
some aerobatic pilots (judging by the number of loop into the ground
accidents) is that the radius of any turn, up, down, sideways or
whatever, is a function of the square of TRUE airspeed, which is of
course a function of density altitude and calibrated airspeed.
So, if the density altitude increases your true airspeed by 5mph,
you get a 5mph^2 impact on your radius. This kind of change in radius
can ruin your day if you are playing down near the dirt.
This velocity^2 thing is also why the reverse cuban or loop down is
a real killer. If you start the pull with X knots too many, you will
use X^2 more radius for the 1/2 loop, throw in an increase in TAS of
say Y due to density altitude and you are into (X+Y)^2 more radius ...
not good. If you have not left margin either in terms of available G
or altitude you are either gonna high speed stall on the way down (and
hit the ground) or hit it on the arc.
This sort of question is on the ICAS exam now if I'm not mistaken.
Peter


Hence the reason I asked the question.
Thank you, Andrew and Peter.
The original ICAS/FAA ACE proposal required a PhD in Aeronautics and
computational fluid dynamics software to answer the questions.
Fortunatly, the program was changed and common sense prevailed.
Sadly, there are still many acro pilots out there who have no
understanding of how density altitude affects their flight and refuse to
be educated.

  #9  
Old August 16th 04, 12:48 AM
Pete...
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"Peter Ashwood-Smith C-GZRO" wrote in message
m...
Andrew, do you compensate for density altitude when you define your

gates?

An interesting fact, which is not obvious to many folks, including
some aerobatic pilots (judging by the number of loop into the ground
accidents) is that the radius of any turn, up, down, sideways or
whatever, is a function of the square of TRUE airspeed, which is of
course a function of density altitude and calibrated airspeed.

So, if the density altitude increases your true airspeed by 5mph,
you get a 5mph^2 impact on your radius. This kind of change in radius
can ruin your day if you are playing down near the dirt.

This velocity^2 thing is also why the reverse cuban or loop down is
a real killer. If you start the pull with X knots too many, you will
use X^2 more radius for the 1/2 loop, throw in an increase in TAS of
say Y due to density altitude and you are into (X+Y)^2 more radius ...
not good. If you have not left margin either in terms of available G
or altitude you are either gonna high speed stall on the way down (and
hit the ground) or hit it on the arc.

I think this may need a little more explaining even if only for my
understanding. I am very new to aerobatics.

So if I normally commence a loop at 100 knotts but get the entry speed wrong
and start at 105 knots then my loop (assume horizontal plane and constant
speed for simplicity) will be

New_Loop_Diameter=Old_Loop_Diameter x New_Speed ^2 / Old_Speed ^2
i.e. a factor of 1.103.

A bad entry of 15 knots over speed would have a factor of 1.323.
But a target speed of 200 but entry of 215 would have a factor of 1.156.

If my understanding is not correct then please explain why. I prefer to
understand the physics/maths before I attempt some of these manoeuvres.

Anyone care to formulate what happens when speed ( or "G") are not constant?

This sort of question is on the ICAS exam now if I'm not mistaken.

Peter



  #10  
Old August 16th 04, 07:42 PM
Andrew Boyd
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wrote:

So if I normally commence a loop at 100 knotts but get the
entry speed wrong and start at 105 knots ....

Anyone care to formulate what happens when speed ( or "G")
are not constant?


Your speed and G are NEVER constant during a loop. A
vertical maneuver is always low and fast, then high and slow,
then low and fast again, etc.

You continually convert your kinetic energy at the bottom,
to potential energy at the top, then back to kinetic energy
on the downline. A hhead (aka stall turn) is a perfect example
of this. You go straight up until you stop, then pivot, and
fly down and gain airspeed again.

Given a constant density altitude, additional entry speed
implies additional G to make the same radius, assuming you
fly at (or near) the stalling AOA which generates Clmax.

Think of it this way: given that you fly at Clmax:

1) the radius of the vertical maneuver is a function of the
aircraft stall speed (Vs), and

2) The G you must pull or push is a function of the entry speed.

Does that make sense? It's not completely true - it will not
withstand a rigorous proof, but practically speaking, it's
what you really need to know to yank and bank down low.

The t-bird F-16 (famous canopy pic) that dug a hole this year
doing a vanilla reverse inside 1/2 cuban-eight is a perfect
example of this: he blew his gate - he was 1000 feet low. It
didn't matter how much G he pulled, or what speed he flew, the
F-16 was simply not capable of that tight a radius.

However, the Pitts with it's lower stall speed would have been
easily capable of it - 1500 feet is plenty for me, because my
stall speed is roughly half of his.

This is worth repeating: for a gate at the top of a vertical
maneuver (with downwards energy vector) such as a split-s
or reverse cuban-eight:

1) the altitude determines whether or not you hit the ground
(your radius is a function of your true stall speed, which
in turn is a function of density altitude) and,

2) the entry speed determines how much G you will have to pull
(or push, if it's outside) to attain Clmax which results in
the minimum radius. Hopefully this G is less than ultimate load!

I am assuming that everybody reading this is familiar with
a fundamental equation of aerodynamics, which is crucial for
understanding aerobatics:

Vs(G) = sqrt(G) x Vs(1G)

There is a fundamental relationship between speed and how
much G you can fly. A wing stalls at the pretty much the
same AOA, which can be attained at a variety of airspeeds.

N.B. The above is easily derived from the lift equation.
I will do so for the lowly price of a beer

P.S. One doesn't need a Phd (piled higher and deeper) to
understand this stuff. It's mostly high school physics with
a smattering of first year college/university mechanics.
Remember all that crap about weightless ropes and frictionless
pulleys? :-) I had forgotten about it too, until years later
I ran across a brainless pulley, but that's another story :-)

P.P.S. Good luck trying to find an aerobatic instructor
who has both a solid practical background and an understanding
of the theory involved, and who can explain both. They are few
and far between!

--
ATP www.pittspecials.com
 




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