Approaching Much Too Fast

[triplese7en]

Colonel...

I should have worded my response better. What I meant to talk about is dividing the velocity vector of the aircraft into an x and y component—i.e., the speed of the airplane across the ground and directly towards the ground.

It's interesting you use an example of a glider and say to forget about the engine... because that doesn't apply in this situation! Yes, in a glider (without drag) you can easily solve a bunch of energy problems by using those equations and trading kinetic for potential and vice versa. However, in the real world there is drag which is constantly decreasing the energy of the aircraft—for a glider that means it will constantly descent in steady air and for an airplane that means the engine has to compensate for the drag.

In the case of an airplane in a steady (airspeed and VSI steady) descent, the potential energy is irrelevant for the purposes of a normal landing! It is now all about the kinetic energy of the airplane. It could be decreased by increasing the potential energy of the airplane but I'm sure you would never teach a student to do that on landing, Colonel. The normal way it is decreased is by reducing the power, and flaring which increases the AoA of the wings which increases drag. Then when contact is made with the earth, the tire friction and brakes will further reduce the kinetic energy in the x direction.

So yes, every object has potential energy when it has height above a particular reference surface but in this case it is irrelevant. It also has thermal and chemical energy while on approach but I'm not worried about those values either.

Edit: Kinetic energy becomes of interest especially when talking about approaching a runway with a tailwind. There will be a high rate of descent required due to the increased speed over the ground on approach. Due to this increased speed there is a tendency for the pilot to reduce the airspeed as they feel they're going too fast. This could be a big problem at anytime on the approach but particularly right before landing—the airplane may not have the required speed to flare enough to reduce the high rate of descent and may stall at that point, resulting in you crushing the plane onto the runway. In this case the potential energy values are all exactly the same as if the airplane was approaching with a 10 knot headwind, however, the airplane kinetic energy values are NOT the same! You could argue that change in potential energy is different (which is correct) but when dealing with motion of an object it's much more intuitive to work with kinetic energy.

[Colonel Sanders]

In the case of an airplane in a steady (airspeed and VSI steady) descent, the potential energy is irrelevant for the purposes of a normal landing! It is now all about the kinetic energy of the airplane.

Nope. It's all about having the correct total
energy of the airplane.

For example, if your airspeed is good, but you
are high, is everything ok? Nope - you have
too much energy. Even an Asiana pilot knows that.

You have to somehow decrease your energy
to the correct amount.

In the situation above (high and on speed) people
often pitch down to the correct glide path - and
now they are fast. They have converted their
potential energy to kinetic energy, but haven't
solved the problem of excessive energy on final.

Another scenario: low and fast. You have the
correct amount of total energy, but in the wrong
forms. All you have to do is pitch up to the correct
glide path, and your airspeed will decrease, and your
problem is solved.

I use the example of the glider, so people can
understand the basics - potential and kinetic
energy - before they try to comprehend more
advanced stuff.

Ever watch an airshow pilot fly? All he does, is
convert energy. At show center he is low and
fast (lots of kinetic energy, no potential energy)
and at the end of the box, he pitches vertical for
some kind of vertical reversal, at the top of which
he has zero airspeed, but plenty of height. He
has converted his total energy into nearly all
potential energy. Then he dives vertically for
the surface, converting all of his energy back
to speed, at show center. Back and forth he
goes - low and fast at the center, high and
slow during the reversals at the ends.

Once you understand that, you can then address
the drag of the aircraft, which is opposed by the
thrust, to maintain the total energy.

This really isn't hard to understand. I find it depressing
that so many people can't comprehend high
school physics.

[triplese7en]

Colonel, I understand that! I know how potential energy can get transformed to kinetic and vice versa.

Again... I was taking about a steady approach... on slope. I understand the high and fast, low and fast, low and slow, etc. situations. If you can't see what I mean I'll leave it at that then.

[Colonel Sanders]

You said:

every object has potential energy when it has height above a particular reference surface but in this case it is irrelevant.

My point is that potential energy is not irrelevant.

It's very important, actually. Let's say you arrive
at an airport, and join downwind 1000 feet high,
at the correct airspeed. Do you have a problem
or not? You seem to be implying that you don't.

You also seem to imply that there is some magical
virtue in being "steady". You could be coming in
tremendously high and fast, with a constant high
airspeed and descent rate, but life is not good.

[triplese7en]

Colonel, you seem insistent on fighting over this.

I'll tell you what I did say: for an airplane which is on slope and on speed with VSI and airspeed steady, potential energy is irrelevant! Let me just clarify again that the airplane is NOT high or low... it is ON SLOPE... it is NOT accelerating OR decelerating. Do you disagree with that?

[triplese7en]

Maybe a better way of thinking of this would be to put the height of the reference surface at the height of your INTENDED flight path. Being above the intended path means that you need to reduce the potential energy either by reducing power and letting drag do its job or by increasing kinetic energy by pushing the nose over. The opposite is true when you are below your intended flight path. But when you're on the intended flight path I'm only worried about kinetic energy.

"You could be coming in
tremendously high and fast, with a constant high
airspeed and descent rate, but life is not good."

I never said that. You'd have a very high kinetic energy and as I've already said, that would have to be dissipated prior to or during landing.

[triplese7en]

Going back and rereading what sidestick had written is making things clearer. When sidestick mentioned height, he/she was referring to being either too high, too low, or at the correct height. Which is also what you're referring to. I've never disagreed that being too high or too low is a problem. I think that's where the misunderstanding is. The first time I read sidestick's comment I had understood height to mean the height value in feet ASL/AGL on approach... which, by itself, is irrelevant!

[Colonel Sanders]

I pity the student pilots, trying to understand this thread.

I guess that's not important.

[triplese7en]

I pity them too.

[Colonel Sanders]

One thing I might try mentioning: a "steady" approach,
which might satisfy some various arbitrary religions, is
neither efficient or safe for that matter.

Once you develop some proficiency, there is great value
in learning how to fly a decelerating final. There is no
earthly reason that you should fly a single speed the
entire final leg.

For example, at a large airport, if you decide to fly a
five mile final in a 172 at 60 mph, well, you're going
to piss off a lot of people behind you.

If there was a crosswind in the above scenario, I suppose
to be "steady" you could fly the entire five mile final in
a sideslip, too. Personally I wouldn't recommend it.

I like to approach at 200 mph until very short final, then
rapidly decelerate to 120 mph for the touchdown. Efficient,
and fits well with other traffic. I suppose it's not "steady"
but gosh it works well.

[photofly]

I know how potential energy can get transformed to kinetic and vice versa.

Did you know how much?

9 feet, per knot, per 100 knots.

That is, if you're flying at 103 knots, and you raise the nose to slow to 98, you'll gain 45 feet in altitude. Or if you're 100 feet high flying at 100 knots and you dive 100 feet you'll pick up very close to 11 knots of speed.

I'll leave it to the experts to work out if that's KIAS, KTAS, or knots groundspeed.

[PilotDAR]

Once you develop some proficiency, there is great value
in learning how to fly a decelerating final. There is no
earthly reason that you should fly a single speed the
entire final leg.

For example, at a large airport, if you decide to fly a
five mile final in a 172 at 60 mph, well, you're going
to piss off a lot of people behind you.

Very much agreed. I fly into Muskoka many days a week for work. 6000 feet. Occasionally there is something fast behind me. In the 150, no problem flying a normal height approach, crossing the fence at 110 MPH, and having a steady deceleration and descent, and clearing neatly at the far end with no screeched brakes.

A steady approach can include a steady trend of deceleration, to end at the desired speed at altitude over the runway. I believe that some large jets fly approach segments, where configuration changes, and speed changes in stages along the approach. Other than the necessary flaps and gear, I opine that the segmented speed changes are actually a form of a non stabilized approach. Power and pitch changes, with retrimming, where alternatively, power and trim could just be set for a steady, and very stable deceleration the whole time. At most, the trend in speed change needs a tweak.

This really isn't hard to understand. I find it depressing
that so many people can't comprehend high
school physics.

Yeah, I vaguely remember potential and kinetic energy from high school physics, but that was 35 years ago. I do remember, however, from yesterday, correct energy management in an airplane. Yes, you can analytically disassemble the physics of an approach, and I agree that there's nothing wrong with that, as long as doing so does not prevent one from simply learning the feel and the art of flying the plane.

One day or another, you're going to be landing a plane with less than a full suite of reliable instruments, you may as well get used to the feel of it, 'cause numbers will be meaningless.

[Colonel Sanders]

No one has to believe what I say, about the
incredible importance of potential energy due
to the height of the aircraft.

Listen to what the master, Bob Hoover, says
and does:

http://www.youtube.com/watch?v=9ZBcapxGHjE

large jets

While a "stablized" approach - constant airspeed
and descent rate - might be motherhood and
apple pie for the lowest common denominator
of pilots flying jets, there is no earthly reason to
restrict yourself, and force yourself to fly a small
aircraft like a big aircraft.

At the risk of stating the obvious, small aircraft
and big aircraft are very different. For example,
while you might have to wear a white shirt and
four gold bars to fly a big aircraft, the small
aircraft does not require you to dress that way.

Similarly, the lack of mass of the small aircraft
allows you to do things that are simply not
possible with a big aircraft.

Case in point: rapid acceleration in an aerobatic
aircraft, from 200 mph to 120 mph on very short
final. You can't do that in a big aircraft.

But just because you can't do that in a big aircraft,
doesn't mean you have to fly a small aerobatic
aircraft like a Boeing. That would be silly and
extremely suboptimal, which is what everyone wants.

Why not take advantage of what a small airplane
can do, when you fly it?

I might mention, at the risk of being burned at the
stake by the religious zealots, that you don't have
to fly a stablized approach in a jet, either. It's just
safer for pilots with marginal skills.

[Colonel Sanders]

I might mention that in both the C421 and L39, I
do NOT fly a "stablized" approach, as is conventionally
defined.

In both aircraft, I set a constant power setting and
continuously increase drag in the last 1000 feet of
descent before touchdown to continually and smoothly
reduce airspeed to the desired value, right before
touchdown. But at no point is my approach ever
"stabilized".

My objective is to not be a "throttle jockey", and I
see no harm in flying faster when I am higher, and
de-celerate as I descend. Efficient and safe.

There is great value in learning to not be a "throttle
jockey". Ask the guy who landed the T-33 short of
the runway at Hamilton last year about that, if you
don't believe me.

I shouldn't mention this, but it is conventionally believed
that you have a virtuous, "stabilized" approach if your
first derivative of distance with respect to time, is
constant.

Personally, I strive to have a constant second derivative
of distance, with respect to time.

Too technical, I know, but what you pay attention to,
is the trend of the airspeed. The instantaneous value
is almost irrelevant, because as the Eagles once said,
you are "already gone".

[frog]

You could fly all the way to the flare with a transport jet, if you have enough airspeed and the path of approach, it will work...but I will not be the one to try it !

[ross1]

Hello...not sure if this is relavent..or if they wear stripes..

https://www.youtube.com/watch?feature=p ... k70hn4-ffc

Cheers all....

(C.S..... havin' a blast with the Cornell)

[Big Pistons Forever]

The style of approach that the Colonel describes is IMO "stable" in that the total energy (Kinetic + Potential) is constant. Potential energy in the form of speed is being constantly converted to Kinetic energy such that the airplane arrives at the right point ( the intended touchdown point) at the right speed.

It is an elegant way to fly light aircraft ( note: large aircraft can't be flown this way) and is a very good test of skill and judgement.

However just as you don't take driving lesson at the Molson's Indy car race, before you get to the point you can do constant total energy approach you IMO need to master the simpler "stable" approach which in the context of this discussion is a constant straight flight path on final with no significant up or down deviations from the ideal flight path, while maintaining a constant airspeed.

For all low time pilots I want to see that constant flight path speed stable approach from 500 feet AGL to the chosen touchdown point every time. As experience builds I expect them to be able to mentally see that 500 ft AGL point and arrive at it on speed and on flight path regardless of whether they are flying a normal circuit, joining straight in, joining on base or approaching it at any angle. If you can't do that then IMO you can't fly a constant energy approach safely of effectively.

I also find that always having the same 500 ft to touchdown flight path makes it easier to get consistent good landings for lower time pilots.

However when it comes to CPL training I want to see a much higher order of handling skills, including the ability to fly a constant energy approach. A good exercise for this is to start a straight in 4 mile final from 1500 feet with the aircraft pointed at the end of the runway and at full throttle. The challenge is manage the approach to end up touching down on the number with full flaps while maintaining a constant flight path.

[triplese7en]

I pity the student pilots, trying to understand this thread.

I guess that's not important.

Hmm!

[Colonel Sanders]

You could fly all the way to the flare with a transport jet ... but I will not be the one to try it!

Reminds me.

Many people have successefully landed jets with
flamed-out engines. The Gimli Boeing, the Azores
Airbus, the New Orleans 737, etc.

The list of jet fighters that have landed without
power is quite long. Bob Hoover used to do it
regularly, when he was a test pilot for North
American. To a short runway.

Probably the most impressive I know of, is the
guy - I forget his name, it was during Vietnam -
that landed a flamed-out jet on an aircraft carrier.

Most people consider landing on an aircraft carrier
difficult enough, with an operating engine. This
guy figured out how to fly his approach with no
thrust. All of the usual numbers and techniques
and visual aids would have been worse than
useless.

What a stick! He knew how to make an approach
to a very tiny spot with a constant power setting -
none.

[frog]

It is all good cs, but I don't think I'll make an industry standard to fly idle final approach on 737...
Yes in case of emergency (flame out engines) might be a useful skill to practice in a sim.
The engines in this thing are awefully slow to spool up once at idle and the sink rate will go very high !
To boot, the approach speed good be as high as 155 kt so to do that with idle engine and being able to flare properly, I am not sure how fast you will need to come.

[Schooner69A]

This may be of interest...

http://www.b737.org.uk/lossofthrust.htm#Introduction

John

[5x5]

Hmmm, seems to me that a lot of the arguing here is more over the words being used to describe the process rather than the actual process itself.

Also, if the title of the thread was "Flaring/Landing Much Too Fast" the discussion may have been more agreeable.

[pelmet]

You could fly all the way to the flare with a transport jet ... but I will not be the one to try it!

Reminds me.

Many people have successefully landed jets with
flamed-out engines. The Gimli Boeing, the Azores
Airbus, the New Orleans 737, etc.

There is one key thing to remember for these big jets landed with no power(actually, not sure about that 737). They landed with reduced or no flap. Try doing that with normal landing flap and all the drag they create on those types and good luck making the runway. And if you do, it will likely be with a very high sink rate and crash landing as you discover an inability to effectively flare. Happened to a 727 in Salt lake City many years back when an old prop driver brought his old habits to the new machine. Perhaps a few types without overly draggy landing flaps at very light weights and a high idle thrust can do it.

As for the T-33 in YHM, I heard he had idle thrust with lots of flap and when he discovered that he needed more thrust, the spool up time on the old Nene engine delayed effective power application. But that remains to be confirmed.

[LousyFisherman]

I fly nice tight circuits now

Our work here is done, Tonto.

Despite all my posting you really do not understand how bad a pilot I am
Apart from that tho: (Just to annoy those in the other thread
What is the point of yelling "CLEAR" and then starting the engine immediately?

LF

[LousyFisherman]

Very much agreed. I fly into Muskoka many days a week for work. 6000 feet. Occasionally there is something fast behind me. In the 150, no problem flying a normal height approach, crossing the fence at 110 MPH, and having a steady deceleration and descent, and clearing neatly at the far end with no screeched brakes.

I tried this today, defined the runway fence as the farmhouse where 1/2 mile final starts. 110 mph at 500 AGL on 1/2 mile final (1 mile in reality) to 65 at threshold (aka 50% down a 6000 ft runway).

First, I don't like doing descending turns to get to 110 that close to the ground, took me 4 tries to get the first one, I was reasonably consistent after achieving the first one. Once I achieved that speed and position ,,,. If I was a good pilot I believe my a side view of my track should be a straight line. Well, I did not meet that standard, but it was an awesome landing anyways since the plane flew again. Good thing I'm not afraid of slipping, cause to bleed off 50 knots I swallowed a lot of altitude.

Very interesting exercise, thank you.

LF