Pitch & power debate

[STL717]

Just watch your plane fly a coupled ILS.


Fly an ILS on autopilot with auto throttles engaged.

The autopilot will pitch for glide slope and the auto throttles will control speed.

I guess the engineers designed it that way for a reason.

 

[Super 80]

Just watch your plane fly a coupled ILS.

Fly an ILS on autopilot with auto throttles engaged.

The autopilot will pitch for glide slope and the auto throttles will control speed.

I guess the engineers designed it that way for a reason.

That's right, that's how engineers do it. Of course they also designed that Rube Goldberg device called a Super 80 too. Or how about how the F-4 got its bent wings?

What I am saying is that you can fly mechanically and get from point A to point B just fine all your life, but when one of the two control inputs is fixed you revert back to pitch for airspeed and power for altitude.

First example: Engine out. Now your power is fixed at zero. You control your speed with pitch. Each airplane has its own L/D max. In the S80 it's about 110 plus your weight in thousands for a clean configuration. Pull up too much and you'll slow down, taking a bigger bite out of the air and the resultant vector will land shorter. Push forward too much your airspeed will cause more parasite drag and you'll land shorter (real short if you pitch to 90 degrees straight down). Next time in the Sim, have your instructor let you climb out until you cross the outer marker and cut both engines with the APU running. Your airspeed quickly decays and you pitch over to maintain your best glide speed and land opposite direction. I started configuring about 2-3 miles out and landed on speed.

Second example: United 232 in Sioux City Iowa. They lost all their hydraulics and controlled their altitude with total power on the remaining two engines (and heading with asymmetrical power).

If what you're doing works for you, fine. But in extreme situations pilots can think in opposite terms that the engineers can't figure out how to do mechanically from a black box device. That's why we get the big bucks...or used to.

 

[STL717]

but when one of the two control inputs is fixed you revert back to pitch for airspeed and power for altitude.

I agree!!!!!!!!!!!!!!!

Every climb to altitude and every idle descent, power is NOT available which requires pitch to control airspeed.

BUT.....

When power is available, which is most of the time, power controls airspeed and pitch controls altitude.

 

[Toy Soldier]

Newsflash! Everyone is RIGHT! The bottom line is this, put the airplane down safely. Everything else is technique. Obviously, each person here has been making a particular technique work for themselves.

One truth - you can't change anything (pitch or power) without having to adjust the other - if you want predictable performance.

Example of how they are interchangeable:

Version 1. Fly 70 mph on final, trimmed for airspeed. Simply adjust power to maintain the appropriate glide. Like I tell my students; "If the numbers are rising - raise the power and if the numbers are lowering - lower the power!" It's that simple.

Version 2. Pitch for a 500FPM descent and then use power to control airspeed. Like I tell my students; If you are going too fast- lower the gas and if you are going too slow - raise the gas. It's that simple.

Either technique works and works well. I teach both and then let the student determine which technique they want need/want to use for different situations.

TEACHING CROSSWIND LANDINGS EXAMPLE
It's the same as teaching cross wind landings... Some prefer the forward slip method and others prefer the kick-crab method. Which one is "better" is left up to the individual flying the plane...

TEACHING THE INSTRUMENT SCAN EXAMPLE
It's the same when teaching the scan... Some teach the "spoke method", some the "round robin" method, and others the "pitch group" - "bank group" method. I teach all three and let the student determine which one fits him/her better.

Which technique is "better" is left up to the person driving the plane...

Blue skies!

 

[bobbysamd]

What controls what

I can change my altitude by only changing thrust but that isn't the most efficient or direct way to do it . . . . [W]hich one was a direct result and which one was a byproduct? Same way with pitch and power. Pitch best controls altitude and power best controls airspeed. It can be done the other way around but it isn't the most efficient way to do it.

Moved, and seconded. I am sure my Alitalia training captains would also second the motion.

But Super 80's comments are, again, persuasive, if not entertaining.

 

[Mickey]

Okay Typhoon.

I asked about the J41 because you sign your posts as J41 Driver???

Right after takeoff in your trusty CRJ you are reducing thrust and accelerating. Why? Could it be...because you are pitching down.

If you are doing 330KIAS at FL240 and ATC asks for a descent at 330KIAS I guarantee that you reduce thrust to descend. If during the descent you need to increase your airspeed to 340KIAS it is very easy to simply lower the nose.

Take care.

 

[Typhoon1244]

Typhoon, I know you're a liberal...

Compared to you? Yes, I suppose I am.

...so it's not surprising we see this differently...

And I know that you're a conservative Christian, which means you believe in things that aren't there. Let's try and stick to the subject, okay?

Next time I'm flying an MD-81 with the yoke welded in place, I'll have to use power to control altitude because my pitch control will not be variable. (Unless I use the stabilizer trim...but that's another issue.)

Originally posted by Mickey
Right after takeoff in your trusty CRJ you are reducing thrust and accelerating.

Right after takeoff in my trusty CRJ I am--usually--increasing thrust and accelerating. Only on rare occasions do we perform full-thrust takeoffs, and reduced takeoff thrust is usually about three to five percent below climb thrust.

But yeah, after takeoff I reduce the pitch attitude significantly to accelerate. "Pitch controls altitude and power controls airspeed when both are variable." During the initial climb, only a very small range of power is available. For all practical purposes, it's fixed...not variable. Therefore under those conditions, pitch attitude is governing altitude and airspeed.

But under "normal" conditions (i.e. the "front side of the power curve"), power controls altitude only indirectly. I can initiate a climb by increasing power and allowing the nose to rise until pitch and power stabilize, but it will take several seconds--perhaps even a couple of minutes--to reach that point of stability. We've all experienced flying a 150 (or whatever light-single trainer you prefer) using only the throttle to control rate-of-climb/descent, but how good is airspeed control when you do that? It's sloppy, isn't it?

If, on the other hand, I initiate that climb by smoothly raising the nose, then increase power to compensate for any change in airspeed, the result is a very smooth, controled maneuver. If you're on the ball, airspeed will seldom vary by more than a knot or two...as opposed to the ten or twenty knot change you'd see if you used only the throttle. (That's in a light-single. The increase in a CRJ would be much larger.)

Remember: the yoke is not a three-position switch. You can fly by pulling to go up and pushing to go down without making it feel "mechanical." (Well, some of us can!)

In the end, we're only talking about philosophy because...

Originally posted by Toy Soldier
...you can't change anything (pitch or power) without having to adjust the other...if you want predictable performance.

I think at this level of our training (and as the sage once said, we're all training!) we all fly that ILS by varying pitch and power simultaneously to make the airplane do what we want.

Originally posted by Mickey
I asked about the J41 because you sign your posts as J41 Driver?

It's a quote from J41driver, to be precise. I used to sign my posts with a quote from Blazing Saddles. Does that make me Harvey Korman, too?

 

[Super 80]

Compared to you? Yes, I suppose I am.And I know that you're a conservative Christian, which means you believe in things that aren't there. Let's try and stick to the subject, okay?

Okay, this is comical.

Just to get off the thread topic for a moment, I want to ask you about things you don't know are there.

First draw a circle representing all the knowledge that ever was, is and will be that encompasses everything in the universe to include the universal theory finally uniting Relativity with gravity.

Good.

Now on that same sheet of paper draw a circle in or encompassing the first circle that represents all the knowledge you know.

If yours is bigger than the total, than how can that be?

If yours is the same as the total, then you obviously know everything.

If yours is inside the first circle, then there must be by your own admission some knowledge that lies outside of what you know.

Since either of the first two cases would only be assumed by an egomaniac and you're probably in the third case, can't you then allow that there might be something outside of what you know that would allow for the presence of God?

Besides, there is one thing about the Bible that gives evidence for its veracity, and that is prophecy fulfilled.

Adious.

We now return you to a thread on related control inputs. However you would like to combine them is a matter of technique but as long as you don't spill the coffee, I can't say you're doing anything wrong.

 

[rettofly]

We now return you to a thread on related control inputs. However you would like to combine them is a matter of technique but as long as you don't spill the coffee, I can't say you're doing anything wrong.

I like it! But I'm still gonna pitch to the glideslope and keep the little pink airspeed vector at bay with the power levers.

 

[Typhoon1244]

Okay, this is comical.

Hey, I'm not the one who made it personal, big guy. If you can't take it, don't dish it out.

Comical...not as comical as thinking your primary rate-of-descent control during an approach is the throttle!

 

[Super 80]

Comical...not as comical as thinking your primary rate-of-descent control during an approach is the throttle!

Oh but the throttle is the biggest part of it. It's at least half of the thrust and drag equation.

When I approach the G/S, I go from 1.30 EPR half slats and 11 flaps to 1.15 EPR and full slats and 15 flaps, and I'll keep 170-180 to the outer marker.

So not only do I reduce thrust, I also add drag to keep the airspeed equilibrium as I head on down the slope.

Now nothing personal, but how'd you make out on that circle thing dude?

Super 80

Hey, I can take it, go ahead, dish it out.

 

[Typhoon1244]

Oh but the throttle is the biggest part of it. It's at least half of the thrust and drag equation.

Agreed. But I'll bet you don't correct minor altitude deviations during straight-and-level flight with the throttles.

...how'd you make out on that circle thing dude?

You want me to admit I don't know everything? Okay. I don't know everything.

But don't you think it's a little arrogant...and silly...to think you know more about the universe than I do because you've read a book of ancient fables?

Can we be done with that and get back to the point now?

You never answered my question about the inherent sloppiness of trying to control altitude with power during normal flight. It's like turning using the rudder, then keeping the ball centered with the ailerons. It works, but that's not the way those controls were meant to work.

If I need to make a normal descent, I begin by aplying just a hint of forward pressure to the yoke. The nose lowers a few degrees and the VSI begins to show the descent. I will watch that VSI and attempt to hold a pitch attitude that gives me the rate-of-descent I want.

As a side-effect of this, the airspeed will rise. The instant I see the speed tape creep a hair's breadth, I reduce power by about thirty percent N1, and the creep stops.

Everything that happens in the above two paragraphs happens simultaneously, but it describes what's going on in my head when I'm flying.

Now if the pitch attitude/vertical speed I need is so great that even with the power at idle the aircraft is accelerating, I can still add drag. So I guess you can add the spoiler handle to the throttle for speed control.

If I'm at idle and I've got all the drag devices I can stand hanging out and the airplane is still accelerating, then power/drag is no longer a variable and I have to make a pitch change if I want to stay on speed.

Under normal conditions (like I said, "front side of the power curve"), if you change pitch attitude you get an instantaneous altitude change and a delayed airspeed change. If you change power settings you get an instantaneous airspeed change and a delayed altitude change. That tells me that pitch controls altitude and power controls airspeed when both are available and variable.

Combine that with "Pitch + Power = Performance," and you've got a very smooth, controlled, coordinated way to fly an airplane.

 

[sabreliner]

Ummm....my answer may seem a little flip, but...

Why don't we just fly the airplane!!!

Use 'em both as needed to make it do what you want.



(I know, not that simple with a new student but...)

 

[Super 80]

Sabreliner has it right. There is no way I'm telling you to do what you say I'm telling you to do. If I'm drifting up 100' a min I'm going to put the nose down one RCH. If my airspeed drops off 5 knots, I'm going to nudge the throttles up.

All I am saying is a rote response for pulling up to the glide slope when you've been at V ref the whole time without understanding the basics that power allows you to hold that constant speed while on the glide path and that the fundamental problem you have is not pitch (you had the speed right) but NOT enough power to hold the slope. Maybe you were heavier than you thought. As one old Captain said, "I'd hate to run this thing across a scale and see what it really weighs."

One of the biggest lessons I learned about control reversibility was on the boom of the tankers. The F-4 probe was behind the cockpit, and only the WSO could see it. (That's not entirely true, if you pointed your center mirror on the canopy bow up to see your face mask in the reflection of the canopy, you would be dead on seeing the apple from the front seat.) So the pilot was dependent upon the GIB to call "back 2, back 3, back 4, back 3, back 2, back 1, on the apple, forward 1, FORWARD 5, forward 6..." And I found out that the biggest change I could make suddenly was to go up and down, and that the airplane didn't make sudden jumps in speed (yeah we had the B-52 lights underneath the belly, even though they were reversed for the heavy drivers with up and down on the left and forward and back on the right but they weren't as good as a good GIB).

Armed with my mirror triangulation I came up with and knowing I could make the boom jump four feet by pulsing the stick came in real handy over the ponds. But those are other war stories of days gone by.

So not to beat a dead horse, I push over as I pull the throttles. I step on the ball as I input aileron.

All I am saying is having an appreciation for how pitch and power work can help you out in tough situations, and one of those is being in the weather to minimums with gas running low and the alternates scarce and far away. As pilots, we do think differently than engineers. We don't just bore holes in the sky, we write in flowing curves, arcs and loops with an occasional straight line between points.

Other than that, it' just basics. Set your pitch, set your power and if you remembered them right, then all your airspeed and altitude/VVI will follow. Lead your turns and keep your nose up and you'll keep on the navigation. Try to stay one step ahead of the airplane so if it crashes you'll at least be a reliable witness.

But don't you think it's a little arrogant...and silly...to think you know more about the universe than I do because you've read a book of ancient fables?

Would you like to talk about quarks or string theory? No one knows all there is about the universe.

Sorry though, the Bible's true. And the biggest thing God put in the Bible is prophecy fulfilled. Not only did God call the winner with the first advent of Christ, He called it from long ago and far away and told everyone before hand He was doing it. And rather than being just an ancient book, it has a lot to say about our immediate future with Christ's second advent.

And when Jesus reappears this time, He's going to split Mount Zion in two just for His opening act, talk about making an entrance.

Out for another two and half day.

 

[Typhoon1244]

So not to beat a dead horse, I push over as I pull the throttles. I step on the ball as I input aileron. All I am saying is having an appreciation for how pitch and power work can help you out in tough situations...

Agreed, completely.

Would you like to talk about quarks or string theory? No one knows all there is about the universe.

Agreed.

Sorry though, the Bible's true.

Well, whatever works for you.

You have my compliments in one respect: I've always resisted the idea that elements of science and elements of religion are mutually exclusive, and it would seem you agree. You've taken that idea in a direction I wouldn't have expected, but that's okay too.

 

[El Duderino]

Flight instructors are dorks and will always be dorks.

 

[Typhoon1244]

Flight instructors are dorks and will always be dorks.

Bitter?

 

[Timebuilder]

I've always resisted the idea that elements of science and elements of religion are mutually exclusive, and it would seem you agree.

Ty, I'm reminded of the science teacher that I had for grades five through eight. We used a "block" method of learning in this small private school, and one semester we had a block on acoustics.

One morning, he brought out some thin metal plates of different shapes. They were used to demonstrate the effects of vibration on small piles of fine sand that were placed on them. He reminded us that God spoke during creation, causing the earth to form and take shape.

He took a violin bow, and slowy drew it past the edge of the plate. A pattern quickly appeared on the plate, representing the effects of sound energy as the plate resonated in a particular fashion.

The teacher was also a minister, and looked up up at us to find our mouths open in wonder. He smiled and said "the voice of God".

We were speechless.

 

[Typhoon1244]

Fascinating. Really fascinating.

And totally unrelated to pitch or power.


(NOTE: this became a partly-religious thread after Super 80 decided to resort to name-calling. It was supposed to be about aerodynamics.)

 

[Timebuilder]

No doubt His voice had several changes in pitch, and delivered a great deal of power.