Heard something interesting in my A/C engineering lecture today that was
"If you wish to increase speed of an aircraft you do not increase thrust, you must move the stick instead, aircraft speed is controlled by the stick due to angle of incidence". this hardly made sense to me as i would consider a stall to be a situation in which most thrust is required as a/c speed is lowest and during landing you would not require full power to descend. can someone explain this to me more clearly.

Cheers

This doesn't make any sense to me either. For one; the flight regime is not specified, secondly, the angle of incidence is (normally) fixed.

He might have meant something like this (my italic inserts): "If you wish to increase speed of an aircraft andyou do not want to, or are able to increase thrust, you must move the stick forward instead.

That last portion doesn't make any sense to me. The angle of incidence is the angle between the chord line of the wing and the fuselage/aircraft longitudinal axis, and has nothing to do with speed. He may be confusing this with angle of attack, though; since drag varies with angle of attack, so does the speed (or, more correctly, longitudinal acceleration). Also, with a change of angle of attack, everything else being the same, a change in load factor will occur. This will normally lend itself to the exchange between potential and kinetic energy, ie altitude and speed.

Some prefer to control the aircraft speed with pitch rather than power (thrust) at low speed (the "back side of the power curve") due to the natural speed instability at these speeds. That might also be where he's going.


edit: reading your question again, I see that you might be asking about power and pitch in a stall. If that is the case, your statement makes more sense. When an aircraft stalls, yes, it is important to set full thrust as soon as possible, but very few aircraft will be able to "power" themselves out of the stall. The first reaction, and the most vital action, is to lower the nose (really, lower the angle of attack) to regain lift. Power application is only vital to recover from a low-speed (and possibly low-altitude) regime to normal flight, but power in itself does not get you out of the stall (unless you're flying some kind of rocket!)

If that is said during a stall, ok. Although all you need is reducing angle of attack (not incidence, probably that is what he wanted to say).

Stall occurs at an AoA. Push the stick, you unstall the wings. Of course you will loose altitude. The time to add power is usually after you lower the nose, so the effects of the propeller and others do not put you in trouble before you manage to unstall the wings.

If it is the old wrong assumption that speed is controlled by pitch, and not power, well... It is wrong except during climb or descents at fixed power, where it is totally correct. In level flight, or in an ILS, speed is controlled with power and flight path with pitch.

For instance. To maintain altitude you pull or push the stick as necessary, while maintaining speed advancing or retarding the power levers as required. Altitude increasing? push the nose a bit. Speed decreasing? add some power.

If you are studiying aircraft engineering and are interested in how pilots fly an airplane there are very nice and simple books for private pilots.

Suggest the next time you take off just push and pull on the elevator and as soon as you get the speed then add power to climb.

Is this a pilot conversion course? Why didn't the whole class tell the instructor that he/she was talking rubbish? Ask your instructor the fundamental principle behind an autothrottle system - if the speed's low, it pushes the power up. It doesn't push the nose down.

If you're an effo:

"Always remember and forever take heed; right hand for glidepath and left hand for speed!".

One of the most fundamental rules of flying.

Attitude + Power = Performance

GF

I've been hearing this old chestnut since Day One of groundschool. "Pitch controlls airspeed, power controls altitude." Never understood why people keep saying that. It's the coordinated application of both. Is that concept so hard?

Except in a glider!

Bfisk hits the nail on the head...it depends on where you are with respect to the power curve. This argument is almost older than the Wright Brothers...years ago, I had a running feud with the chief at the college program I instructed at over it. "Aerodynamics for Naval Aviators" is adamant that pitch controls airspeed, and that makes sense when you are operating close to, or behind, the power curve (say during a carrier approach). But when I get slow in my 757 I sure ain't thinkin' of pitch, because I am well ahead of the power curve.

The problem arises most apparently in light aircraft, because many of them have little power margin. The power-control-airspeed approach works, but only within a small band of the approach speed range. If you get just a bit slow, there isn't enough power to get you back as quickly as your instructor might like. Naturally, this class of airplane is the one we are using to teach primary students, who have only an early comprehension of the issue. Thus, my preference was to use pitch, because it was more consistent, and it was guaranteed to be primary when the engine quit. But this should be accompanied by a thorough discussion of the relationships and an understanding that primary speed control would change from pitch to power as soon as you matriculate into a larger airplane.

A lot of bullXXXX out there....
 

GF is one million percent correct. All information contrary to that is total
BULLXXXX.

It's that simple....

There are a number of fine publications....many come from the U.S. Navy...that will confirm Galaxy Flyer's post.


Fly safe,

PantLoad

P + A does indeed = P, Pantload, but that is irrelevant to the thread. The thread is about changing the speed, not steady-state performance.

It depends quite a bit on the airplane design...

Many airplanes are speed-stable. If you increase thrust without changing trim, it will likely settle in a climb at or near the trimmed speed. This is especially true with underslung engines, where the thrust vector is well below the pitch axis.

Thrust and Speed.
 

Which came first the chicken or the egg?

Pitch Power Altitude Speed.

What controls what?


Well - think of these things...


Some military jet fighters can accelerate to a speed in excess of Mach 1 in a vertical climb...


As a flight instructor I teach my primary students the following. (in low power general aviation training aircraft)

Cruise flight - Pitch controls Altitude. You select your cruise speed with power. (small changes in pitch produce a large change in lift and very little change in drag at high speed)

Slow flight - Pitch controls airspeed, power controls altitude. ( a small change in pitch makes a large change in drag and very little change in lift therefore making the speed change)


They learn it that way and can succesfully operate an aircraft usssing that information....


If I am flying with an experienced pilot, and I ask them to do slow flight during recurrent training or transition to a new aircraft, and usually in a higher performance aircraft, I remind them to adjust pitch and power as necesssary to maintain airspeed and altitude. What a cop out!! I do not tell them how to accomplish slow flight unless they are having trouble. It is surprising how many pilots forget how to precisely control airpeed and altitude especially in higher performance aircraft. If they can make it work acceptably, I do not say anything... Many pilots get into the bad habit of using flaps and gear to control their speed and forget how it really works.


In reality.... Airspeed and altitude, power and pitch are all interrelated.


If we assume that airspeed is controled by power, and altitude is controled by pitch, then what happens in slow flight? Try getting up to lift off speed without adding full power on the runway, and try lifting off without increasing angle of attack or pitching up...

In slow flight, if we want to increase speed, we can lower the nose. (Pitch controls airspeed) When we lower the nose and decrease the drag, of the wing and airframe, the speed begins to increase but at the same time the aircraft begins to descend as there was a decreasse in lift due to the angle of attach change. We notice the descent and add power to compensate. (Power controls altitude).

Again in the low flight senario above, if we want to increase speed and we add power, if we have enough available power, the speed will begin to increase. As the speed increases more lift is produced causing a climb. We notice the climb and slightly lower the nose to compenate. (Pitch controls altitude).. The problem is in a small aircraft the available power may not be sufficient to accelerate the aircraft very much so lowering the nose and decreasing the drag has a more immediate effect.

So in conclusion..

I recommend that flight intructors teach their primary students using small low power aircraft how to control airspeed and altitude as I stated at the top of this post... Cruise and slow flight so not operate the same.

I recommend that flight instructors teach and permit their students to discover that airspeed is controlled by power and altitude is controled by pitch at all times when tranitioning to higher power high performance aircraft. That is one of the most important concepts to learn when transitioning form simple training aircraft into a high performance aircraft.

However, if a pilot can control airspeed and altitude succesfully there is no real reason to force them to adopt any particular method nor does their method need to be changed.

My 2 cents worth


Bill

Sorry Bill, I can't agree (and welcome to Prune! :ok:).

While it may work on a C150 because lighties are so speed-stable, it absolutely DOES NOT work on a jet on final, the most critical time of the flight where changes are required almost instantly.

Low-time pilots should not be taught to control the aeroplane via the secondary effects of controls, if for no other reason that when they fly something bigger, the technique doesn't work. While they are coupling effects so that the nose may come up when the thrust is increased, the primary method of changing the speed must be with the throttles (or speedbrake). Likewise, flight path change must be made with the elevator. Any speed changes are then sorted by changing thrust.

There is a case where, in the flare, the angle of attack/nose attitude is so high that jamming the thrust on may have a cushioning effect, but that is not the norm down final.

My analogy is flying down an ILS (or letting the AP do it). If you get low on the slope, you pull the nose up, just as the AP does. You don't put up the thrust and wait for the secondary effect of controls to get you back up onto the GS. Carrier pilots maybe, but not normal aircraft.

Similarly, speed. If you get slow, you definitely do not lower the nose! The speed will never increase satisfactorily; all that will happen is your descent rate will increase.

What a great discussion....
 

Carrier aircraft are definitely not real aircraft. They're top secret and fly
quite differently from conventional aircraft.

I stand corrected....


Fly safe,


PantLoad


Aerodynamics for Naval Aviators

(If you really want to know how an airplane flies.....)

Bernuli vs Newton

Pitch vs thrust

It's a wonder we fly at all!!!

There is only one way to accelerate allong the current flight path and that is to increase thrust/drag ratio. :confused:

If you are too high on the G/S (or want to descend etc), you reduce thrust.
If the plane is in trim, it will keep the speed

Vice versa if you are too low / want to climb.

Hence pitch controls speed and thrust altitude :ok:

These are all constant speed scenarios. If you want to go down you need to remove energy (thrust) from the equation - it's as simple as that.


However, if you want to change the speed you use thrust to change speed and pitch / trim to maintain altitude. But this is not a constant system or stabile environment (and not the way an e.g. an ILS is supposed to be flow).

Pantload,
I wasn't trying to be smart. The reason I said
is because my understanding is that carrier technique is (was?) to do what the original poster mentioned: low on slope, push up the power to get back on it ie hold a constant AOA and control slope via the secondary effect of power; maybe has a more useful effect because of the body angle/thrust vector.

Kramer,
You are flying the aeroplane via the secondary effects of controls. Works well in a bugsmasher, not well in a jet in my experience because the effect doesn't happen fast enough to correct the error that prompted the correction. Each to his own, tho.

Flying opposite of how an autopilot/autothrottle works doesn't seem logical. Speed gets low the autothrottle increases power. Autopilot gets high it lowers the nose. It doesn't matter if it is in altitude hold or following a glide slope.

Only the rudder and aileron have secondary (or adverse) effects. The rudder that it causes roll and vice versa with the aileron. In other words a motion in another axis than the primary.
Elevator on the other hand have no secondary effect (not causing any motion around other axis).

Kramer,

The secondary effect on the aircraft from use of the elevator (up) is that the speed reduces. The secondary effect of putting the power up is that the nose rises. It works "well" in a bugsmasher because they are so stable, but try it next time you're handflying down the ILS at 140kts in your jet.

Pull back and wait. If you touch nothing else you will soon discover a secondary effect.

Primary - pitch
Secondary - speed.

Unless you can turn off gravity of course!

Pitch for speed and thrust for altitude works extremely well in a 737.

There is no such thing as secondary effect of the elevator for the reason stated in my previous post. To write it again would only be repetition.

What you mention are not effects. Those are consequences of moving the elevator. I could add to FE Hoppy's list of "effects":
3rd - Stall
4th - spill coffee
5th - wife complains about stain on your shirt

The only controls that have secondary effects are:
Yaw - induced roll
Pitch - adverse yaw

Show me one quote from a book or one link to a webpage that mentions secondary effects of the elevator.


I'll leave the discussion here, Thank you. :hmm:

I recommend reading this: http://www.faa.gov/library/manuals/a...apter%2002.pdf

Remember aerodynamics and the four forces:

When the elevator control is pushed or pulled, the angle of attack is changed.
The angle of attack has a direct influence on lift, the aircraft starts decending or climbing.

When thrust is changed, thrust becomes greater or smaller than current drag, the aircraft accelerates or decelerates.

Lift is a function of airspeed as well, in result a change in speed is followed by a change of lift, creating a requirement to correct the angle of attack by using an elevator input in order to maintain level flight.
To maintain lift the same when accelerating, a decrease in angle of attack is required. The opposite applies to decreasing speeds, an increase of angle of attack is required.

The same applies to climb or decent, the difference is that in climb excessive thrust is used to add potential energy (altitude), while in decent potential energy (altitude) is used to overcome drag.

What about the HANDBRAKE :ok:????????

The handbrake is linked to the toilet and will result to an inflight toilet dump when pulled while not on ground. All the bull$&%t will go overboard in this case.

Kramer,

It took me 5 seconds to find this:

how to control an aircraft

What is stated there, of course, is dead right, regardless of what your theoretical definition of "effect" may be.

You would be well advised to also have a read of Handling The Big Jets, in particular the section on takeoff and landing. One bit says:
And a quote from "Fly The Wing":
Practical and safe aviation verses blinkered theory...

Good luck with that..!! :ugh:

Sorry, but it's not that simple.

Both the A-6 Intruder and the 747 were/are relatively speed-stable in the landing configuration. In both airplanes, thrust is primarily used to control rate of descent, and pitch trim is used to control airspeed.

While all the performance inputs and parameters are interrelated, there is a primary or leading control input for change of each parameter. To attempt to control speed PRIMARILY with thrust in the landing configuration in either airplane will likely result in a very unstable approach.

This discussion could expand to roll/yaw response for turning in different airplanes, but that would even further complexify the conversation...

Just as with manual control, it's not that simple...

Autopilots and autothrottles work together in autoflight to make very small incremental changes. Each change in one system will trigger a change in the other. Note that in VNAV climbs and descents, the announced pitch mode is often VNAV SPEED, where the elevators and stab control the speed...

I was taught pitch for speed and power for flight path control when flying a prop and pitch for flight path and power for speed when I transitioned to jets.

Personally I reckon it's a bit of both on finals for either type and after a while it becomes second nature and you don't consciously have to think about it.

Regards,
BH.

It is that simple. That is why I left VNAV climb out because obviously with a climb power setting only pitch could control airspeed. Alt hold or established on a glide slope the autothrottle only controls speed and the pitch axis of the autopilot only controls flight path. Most pilots flew this way before their first automated aircraft. Thrust vs drag = speed. Lift vs gravity = flight path. Any correction with either will eventually require an adjustment in the other axis to balance the other vector. When I was instructing I always showed my students how changing thrust could either increase speed or vertical rate depending on what you did with the elevator. The primary change with thrust is in the horizontal plane with speed. The primary change with the elevator is in the vertical plane with lift.

To maintain a flight path: pitch
To change or maintain speed in a constant flight path: power or thrust.

In every airplane. In Trevor Thom's IFR instrument flying books is explained like that, for light airplanes.

However, what would happen if an AP in a 737 had the A/THR coupled with the altimeter to maintain altitude and the pitch with the ASI to maintain airspeed? This egg and chicken thing can be very puzzling, indeed.

I think that, for a human brain at least, it is easier to divide the tasks conventionally, pitch for path, power for speed.

The control and performance instruments concept is quite clear and it has been stablished long time ago.

Hi MB2002,

Respectfully, doesn't it depends on the particular flight regime? With fixed power set e.g. During Climb & Descent the autopilot controls speed with pitch.

Also in a visual circuit whilst descending or when hand flying a NPA - pitch controls speed, and power ROD. When there is a profile to fly e.g. ALT, VS, FPA, GS etc. then it's reversed.

I think what is being lost here is that in all the examples of pitch for speed what ia actually being described is trading flight path angle for speed while maintaining a fixed thrust. This is not the same as controling flight path angle with pitch and controling speed with thrust.


So the example I like is fixed flight path angle. now tell me how i control speed using pitch?

Correct. I cant. I must change the thrust.

Whenever a specific vertical path is required we have to change the thrust drag ratio to change speed and that requires a change in thrust.

Either can be used to control either.

Its really not that complicated, but sadly this industry has a developed a compulsion to dumb things down to the extent that they can be rote learnt. Then people start getting dogmatic about it.

Personally, I'd rather take an energy based approach. If Thurst > Drag then KE + GPE is increasing. KE could be going up or down, GPE could be going up or down. But the sum of them is going up.

pb

Oh, and in passing:

Type dependent.

A simple experiment:

1. Steady level flight at FL100, speed 250 KIAS.
   Increase speed to 300 KIAS while maintaining level, 0 fpm rate of climb.
   => Thrust needs to be increased to increase speed. If you change pitch, you start descending or climbing.
2. Steady stable climb with 250 KIAS and 500 fpm rate of climb.
   Increase speed to 300 KIAS while maintaining 500 fpm rate of climb.
   => thrust needs to be increased to increase speed. If you change pitch, the the rate of climb changes.
3. Steady stable climb with 300 KIAS and 500 fpm rate of climb.
   Reduce speed to 250 KIAS while maintaining 500 fpm rate of climb.
   => Thrust needs to be reduced to decelerate. If you change pitch, rate of climb changes.
4. Steady level flight with 300 KIAS. Reduce speed to 250 KIAS, keep 0 ft rate of climb.
   => Thrust needs to be reduced to reduce speed while maintaining level flight.
5. Steady decent with 250 KIAS, 500 fpm rate of decent.
   Increase speed to 300 KIAS.
   => Thrust needs to be increased to accelerate. Change of pitch changes rate of decent.
6. Steady descent with 300 KIAS, rate of decent 500 fpm.
   Slow down to 250 KIAS while maintaining 500 fpm rate of decent.
   => Thrust needs to be decreased to slow down. Change of pitch changes rate of decent.

Conclusion: Thrust controls speed and pitch controls rate of climb or decent.


Special cases

1. Transition from level flight to climb:
   Potential energy is added, additional thrust is required to deliver this additional energy requirement.
2. Transition from level flight to decent:
   Potential energy is used up to overcome drag, less thrust is required to maintain constant speed.

To maintain level, 0 fpm you will need to pitch down as you accelerate. If you maintain pitch you will start to climb. Eventually an equilibrium will be reached where (Thurst - Drag) / Weight = The Rate Of Climb.

Conclusion: Both pitch and thrust affect speed and the rate of climb.

To maintain 500 fpm you will need to pitch down as you accelerate. If you maintain pitch you will increase the climb rate. Eventually an equilibrium will be reached where (Thurst - Drag) / Weight = The Rate Of Climb.

Conclusion: Both pitch and thrust affect speed and the rate of climb.


To maintain 500 fpm you will need to pitch up as you decelerate. If you maintain pitch you will decrease the climb rate. Eventually an equilibrium will be reached where (Thurst - Drag) / Weight = The Rate Of Climb.

Conclusion: Both pitch and thrust affect speed and the rate of climb.


same again

and again

and again

Conclusion: Where were you in "straight and level" part 2?


Hardly special cases when aircraft do this day in day out. The fact that you invoke these as being exceptions to your conclusion simply demonstrates your conclusion is not a generalised solution.

Its about as valid as saying 'on Fridays its always Friday'.

pb

The egg and the chicken...

But AP/FDs are all the same, aren't they?

To maintain a given flight path, they control speed with thrust, and path with pitch (as it taught to IFR pilots: pitch is primary for altitude(or G/s) and power is primary for speed)

To maintain a climb or a descent at fixed power, IFR pilots are taught that pitch is primary for speed, and AP/FD control speed with pitch, while A/THR controls thrust setting.

To maintain a given speed and a given rate of climb or descent, AP/FD use thrust for speed and pitch for rate. Probably the opposite is what is used in light piston airplanes. And probably in this case is when half of the pilots do it one way and the other half the other way.

Maintaining altidude or in an ILS I think we all keep path with pitch, speed with thrust, don't we?