Scudrunners

Aerobatic aircraft have their fair share of accidents.  Ok, probably
more than their fair share.  Why is that?

First thing to realize that there are two different kinds of aerobatics:

1) recreational aerobatics at high altitude (includes contests, practices)
2) airshow aerobatics at low altitude

You would expect that given the hard lives that aerobatic aircraft live -
they see lots of G, lots of torsional G, often too much - that mechanical
failure would be the leading cause of aerobatic accidents, but somewhat
surprisingly, that's not the case.

The main reason for recreational aerobatic accidents is simply unrecovered
spins.  Inexperienced pilots accidentally enter spins at high altitude, and
ride it all the way into the ground.  They are slow to recognize the spin
entry, and quite often make control inputs that make the spin much worse.

Sadly, this is often with a passenger, that has moved the C of G aft, and
changed the spin characteristics of the aircraft. 

[img width=500 height=288][/img]

Or, the polar moment of inertia (see Art Scholl camera) makes the spin difficult
to stop.  Radius squared.

One thing you need to worry about is rudder blanketing.  This means that
an upright flat spin in a Pitts is very dangerous, which an inverted flat spin
is a pussycat because with all that rudder in clean air, you can easily stop
the yaw.

Spins are a weird little corner of aerobatics, and many so-called aerobatic
experts really don't know much about them.  It's important to realize that
spin behavior is very type-specific.  What works in one aircraft, might not
work in another.  My friend Freddy - dead now - almost died in a two seat
Pitts that he removed the big two-place canopy from, and that was enough
to alter the spin characteristics.  Beggs-Mueller all the way.

If pilots can't recover from spins entered at high altitude, the problem gets
a lot worse at low altitude.  Many new airshow pilots spin into the ground
because they simply haven't spent the time, to learn about their aircraft.

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That guy had an ATP and 23,000 hours.  Just not the right ones.

Occasionally aircraft do break.  My friend Joe Broeder died when he lost
a wing from a wooden taildragger, but it had been recently groundlooped,
dragging a wingtip.  Nothing to do with aerobatics.  My friend Bob Sterling
and his wife died when his C210 lost a wing.  TSB blamed it on turbulence,
but that's BS.  That aircraft had been previously written off, and had hidden
damage.  My friend Andy Philips died in his RV-7A when he exceeded Vne
and fluttered the rudder.  I guess that was aerobatics, but all the bondo aft
of the hinge line had more to do with that one.

Vicki Cruz died when she jammed a rudder pedal and spun into the ground.
She was quite short, and had some homebrew extensions like you would use
on a tricycle.  Obviously, you want to be very careful of any flight control
modifications.  Kathy Jaffe died when she put some lead in the back of her
single seat Pitts and spun it in.  Changed the C of G and polar moment of
inertia (again) and took a docile aircraft and made it a nasty one.

Pilots often don't use the right control inputs when they try to recover from
spins.  I used to give spin training, and tried to explain that aileron and elevator
were not good flight controls to use, during a spin.

I hope I don't have to explain to you, that you don't pick up a dropping wing
with aileron.  Adverse yaw.

But the elevator is similarly counter-intuitive.  Pulling back on the elevator,
which pilots unconciously do, increases the alpha of the stall, and you can
guess what that does.

But forward elevator can be quite dangerous, as well.  Putting the nose down
in an upright spin can reduce the radius of gyration, like a spinning ice skater
that pulls her arms in, and speeds up.  Also, forward stick can blanket what
tiny amount of rudder you have to oppose yaw, below the elevator.

Power can also be bad.  The effects of torque and gyroscopic precession
can be powerful at slow speeds - think of the tail wagging the dog.

It's important that pilots recognize spins ASAP, which always have tremendous
yaw.  Visually, it's quite something.

As a starting point, the recovery should involve power off, allowing the ailerons
and elevator to trail, and full opposite rudder against the yaw.  See Beggs-Muller
which works in some airplanes, and doesn't work in others.

Read the POH, and do what it says.  Really smart pilots wrote the spin recovery
sections.

Jesus, I didn't mean for this to become a spin diatribe, but that's a leading cause
of aerobatic accidents.

Other causes of aerobatic accidents?

A tiny fraction would be G-loc.  Generally an issue at low altitude and high speed
and high G.  Blue Angels.  The recovery in a slow, little airplane is pretty quick, but
is worsened by viagra/cialis as Ian Groom found out, trying to keep up with his
young wife.

Medical incapacitation isn't as much of a problem as you might think.  Plenty of
people vomit in aerobatic aircraft, but precious few have heart attacks.

A serious problem at low altitude, is pilots flying a downward looping maneuver
right into the ground.  This is not a problem for the recreational guys up high.

It's very simple.  If your vector is going to subtend the horizon by more than 45
degrees (ie worst case 90 degrees, straight down) you need to know enough
basic physics to calculate, and discipline to adhere to your top gate, which is
mostly a function of the aircraft stall speed and how thick the air is. 

The higher the stall speed and the thinner the air, the higher the top gate.

An example would be the Hawker Hunter over in England flown by a guy with
a lot of hours, but not much airshow pilot training.  No idea of what a top gate
was, despite all of his straight and level hours.

[img width=500 height=300]https://i.dailymail.co.uk/i/pix/2017/03 ... 119136.jpg[/img]

Your top gate is a minimum altitude (and max airspeed) required for a downward
looping maneuver.  You don't make the top gate, you don't go down.  It's that
simple.  Just continue into a wingover, get some more energy, come around,
and do it again.

There was an F-16 in Idaho that flew into the ground when he did a reverse
1/2 cuban eight with too low of an entry, because he couldn't zero the altimeter
above 3,000 feet, so he figured he'd do some mental arithmetic to get his top
gate.  He was 1,000 feet low, and he hit the ground.

So many lessons in that accident.  And a great picture.

[img width=500 height=325]https://upload.wikimedia.org/wikipedia/ ... irshow.jpg[/img]

Hard to follow that act.

Anyways, I hope some of this helps.  Lots of people have died, but oddly I am
still alive, which Ernie Gann would have something to say about!

I love aerobatics, almost as much as I like dogs, and I like dogs very much.
Almost as much as dogs love a day at Redondo Beach.

[img width=500 height=333]https://www.californiabeaches.com/wp-co ... 50x433.jpg[/img]

[img width=500 height=281][/img]

Aerobatics, when treated with respect, is tremendously educational and enjoyable.

If you treat aerobatics with contempt, it will kill you.  This does not make it bad,
merely that you should not treat aerobatics with contempt.

Similarly, I have rather a lot of very fast motorcycles.  If you treat them with respect,
you will learn a lot, and it's immensely enjoyable on a sunny day to ride a very fast
motorcycle.

[img width=500 height=221][/img]

If you treat them with contempt, they will quickly kill you - quite possibly in the first
corner.  This does not make very fast motorcycles bad - merely, that you should
not treat them with contempt.

I could mention firearms, ladders and power tools now, but hopefully you get the point.

It's an attitude thing.  Possibly generational, I don't know.  People have grown up
in Fisher-Price playpens with rounded corners, and they think the world is a gentle,
docile place.

What idiocy.  My father would have hurt me, if I had been that stupid.  Possibly that
makes him a Bad Personâ„¢ - ok, almost certainly - but oddly, I am still alive, when
so many others have gone.

[img width=500 height=333][/img]

[quote author=Colonel Sanders link=topic=10005.msg28691#msg28691 date=1567655269]
The higher the stall speed and the thinner the air, the higher the top gate.

Your top gate is a minimum altitude (and max airspeed) required for a downward
looping maneuver.
[img width=500 height=333][/img]
[/quote]

Colonel, what does "max airspeed" mean?  I've read Winkle Browns books where he mentions 'minimum' safe airspeeds to enter various manouvers, 'max airspeed' confuses me.  Also, could you go through how one determines what the minimum altitude is for the top gate for any given airplane?  I'm hoping to start some aerobatic training in a venerable 7ECA with a class 2 aero instructor.  Should be fun.

Gerry

Ok.  For simplicity, I have only mentioned the "top gate" at the top of a downward
looping maneuver.  In that instance, you are going to convert altitude into airspeed
so it behooves you to not enter it with excessive airspeed.  A good example of this
is a split-S from cruise.  Let's say you're straight and level at the top of the green
arc.  If you half-roll to inverted and pull to fly and half of a downward loop, your
airspeed is guaranteed to blow through Vne.  That hurts the airplane.

I think you might be thinking about the "entry gate".  Let's say you're at the surface,
over the runway at 80 mph.  Is it a good idea to pull and enter an inside loop?
Probably not.  As the nose comes up, your airspeed is likely to bleed off, even
with full throttle, and you will likely run out of airspeed on the vertical.

So, if you're going up, you want lots of airspeed to convert into altitude.

And if you're going down, you want low airspeed and lots of altitude, to
convert into airspeed.

From a high school physics standpoint, you convert kinetic energy to
potential energy, then back to kinetic energy again.

To figure out your top gate, dive to 2000 AGL so that you are at least
at the top of the green arc on the ASI and full throttle.  Pull +4G and
enter an inside loop.  Passing the vertical, lighten off the G to avoid
pinching the loop, and make it nice and round.  Inverted, note your
altitude at the top of the loop.  At that point, you can either continue
and fly the second half of the loop, or just let the nose drop to the
inverted 45 down, and 1/2 roll upright and pull from the 45 down
to level.

The difference between your entry altitude (2000 AGL) and at the
top of the normal, inside loop is the diameter of loop in that aircraft
[u]at that density altitude[/u].  I would suggest that you pad that diameter
by 20% to get your top gate.  Take some advice from Bob Hoover.

So, if you saw 3000 on the altimeter, inverted over the top of the
loop, your top gate is now (3000 - 2000) x 1.20 = 1200 feet above
your minimum altitude, which very well may be the surface.

Note that if you are Skip Stewart, you don't need to pad the top gate.



But if you're Skip Stewart, you aren't reading this.  Note that when
I am performing surface aerobatics in the Pitts S-2B at sea level
density altitude, and I enter a 1/2 reverse cuban-8 from the surface -
which the contest people say is utterly suicidal - after rolling inverted
on the 45 upline, if I patiently wait for 1300 on the altimeter - zeroed
at the surface - I know I can gently pull through and complete the
second half of a vanilla inside loop and exit safely at the surface,
with plenty of margin and nice low alpha and G which yields lots
of airspeed and hence energy for the next maneuver.

Thanks for the notes Colonel, makes perfect sense now.
G

[quote author=Colonel Sanders link=topic=10005.msg28696#msg28696 date=1567739380]
Ok.  For simplicity, I have only mentioned the "top gate" at the top of a downward
looping maneuver.  In that instance, you are going to convert altitude into airspeed
so it behooves you to not enter it with excessive airspeed.  A good example of this
is a split-S from cruise.  Let's say you're straight and level at the top of the green
arc.  If you half-roll to inverted and pull to fly and half of a downward loop, your
airspeed is guaranteed to blow through Vne.  That hurts the airplane.

[/quote]

I remember one of your older posts where you had a very convincing argument that altitude loss gets minimized when you pull the maximum Gs at maximum power in downward manoeuvres. I'm curious why that reasoning breaks down in this split s example.

Imagine 2 situations:

1) that you are at the top of the green arc at the beginning of the split S. You roll inverted max power and pull max G
2) you are barely above the stall speed at the beginning of the split S, you roll inverted and use power and G in whatever alternative way

Shouldn't 1) result in less altitude loss? In 1) you start with, let's say medium energy, you convert altitude into a little bit extra speed and then you fly at max G to convert as much of that energy as possible back into altitude.
In 2) you start with low energy, you need to build up the speed before you can pull significant Gs without stalling the plane and get out of the dive.

I don't advocate performing 1), as you will most likely overspeed the airplane, I just don't get *why* it doesn't work as I described.

[quote]altitude loss gets minimized when you pull the maximum Gs at maximum power[/quote]

Absolutely correct.  The missing piece to the above, is

"at Clmax, at the top left corner of the flight envelope."

[img width=500 height=333]https://www.uavnavigation.com/support/s ... dited2.jpg[/img]

You have to keep your speed down, and in a split-S from high speed cruise and full power,
you're probably going to gain even more speed as you descend.  Most people don't pull
enormous G at the start of that maneuver, which keeps the drag up and the speed under control.

[quote author=Colonel Sanders link=topic=10005.msg28701#msg28701 date=1567832066]
[quote]altitude loss gets minimized when you pull the maximum Gs at maximum power[/quote]

Absolutely correct.  The missing piece to the above, is

"at Clmax, at the top left corner of the flight envelope."

You have to keep your speed down, and in a split-S from high speed cruise and full power,
you're probably going to gain even more speed as you descend.  Most people don't pull
enormous G at the start of that maneuver, which keeps the drag up and the speed under control.
[/quote]

That actually makes sense, thanks!

About this:

[quote author=Colonel Sanders link=topic=10005.msg28701#msg28701 date=1567832066]
One thing you need to worry about is rudder blanketing.  This means that
an upright flat spin in a Pitts is very dangerous,
[/quote]

Do you mean "dangerous" as in: "you would lose more altitude than expected during recovery"
or "you could enter a flat spin you could never recover from".

I haven't read in any other material that flat spins in a pitts would be unrecovereable or more dangerous than in other types. If anything, the general consensus seems to be the plane will recover from any attitude you somehow put it in, assuming you know how.

Oh dear.  There's no one to teach spins in Canada any more, is there?

Please go see Bill Finegan if you're on the east coast, or Sean Tucker's
school if you're on the west coast.

Keeping in mind that spins are highly type specific ....

In the Pitts, up to [u]2 full rotations[/u] may be required to recover from an upright
flat spin, due to the tiny amount of rudder below the elevator.

However, an inverted flat spin in the Pitts can be stopped in 1/4 rotation.

While this might not seem very interesting, in real life, what happens is that
pilots lose the faith after applying the correct control inputs to recover from
the upright flat spin, because they don't seem to do anything.  Then, they
try something different, which can delay the already slow recovery.

Plenty of accidents, over the decades, from this.  Pilot think that upright spins
are safer than inverted spins.  No.

I'm trying to think of who in Canada might know something about this.  Maybe
Gerry Younger in Kitchener - he must be 90 now and retired - and perhaps Luke
in Steinbach, but I'm pretty sure he's flying a monoplane now.

[quote author=Colonel Sanders link=topic=10005.msg28704#msg28704 date=1567893281]


In the Pitts, up to [u]2 full rotations[/u] may be required to recover from an upright
flat spin, due to the tiny amount of rudder below the elevator.

[/quote]

Ah ok, yes, I've noticed that. Your initial post seemed to hint at bigger problems. Then again 2 full rotations could be a big issue at low level, but it's a bit of a non-event at hight altitude, just sit and wait.

In my experience, many pilots DO NOT sit and wait for the upright flat spin
to stop.  When they do not get an instant response - as they do inverted -
they think they aren't doing the right thing - which they are - and then they
try doing something else - something wrong - instead.

This is a very, very dangerous trap.  It's not the airplane that's the problem. 
It's just the way the airplane is.  It's the pilot that's the problem.  Pilots do
very dumb, bad shit, especially under pressure.  They often don't even
know they are doing bad shit.  Sometimes they just freeze (with bad
control inputs).  I call that "deer in the headlights" and in my experience
is the only time that a heavy metal fire extinguisher is of any use, in an
aerobatic aircraft.

I strongly recommend both of Mikey Goulian's books - Aerobatics and Advanced
Aerobatics - to anyone interested.  They an excellent ground school, and talk
about these sorts of considerations.

Again, spins are highly type-specific.  If you look at a modern monoplane - like
the MX2 - it has considerable rudder underneath the elevator.  This allows it to
quickly stop an upright flat spin.

[img width=500 height=333]http://airshowstuff.com/v4/wp-content/u ... axi-XL.jpg[/img]

Rob Holland scares the shit out of me, because he ends his airshow routine with
an upright flat spin to about 500 AGL on final and lands (and touches down and
does a roll and touches down again).  That's ok in an MX2.  Crazy in a Pitts.

Again, spins are highly type specific, and not very many people understand even
the basics about them, even supposed aerobatic "experts".

Even basic yaw seems to be something mysterious to today's pilots.  Look at the
King Air accidents in HI and TX.  Today's pilots seem to think that if they fly something
with a nosewheel, or something that burns kerosene, they don't need to know anything
about controlling yaw.  They wear white shirts with gold bars, and tell me how stupid
I am to fly a taildragger, and how they don't need to know how to use the rudder pedals.

Sometimes, I talk to dead people.  Well, they aren't dead when I talk to them.  But
they are, not too long after.



I am a 20th century pilot.  I do not understand why, in the 21st century, it is considered
unforgivable to [u]hurt someone's feelings[/u], but it's acceptable for them to die in a crash,
caused by their own incompetence and ignorance.  It is not considered acceptable
behavior in the 21st century to try to cure someone's incompetence and ignorance
because it might [u]hurt their feelings[/u].

This virtue-signalling world is bizarre.  And exceedingly intolerant of any opposing
viewpoints, in a frighteningly totalitarian manner.  The anger of these badly-behaved
children is quite something.