Thrust and Speed
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.
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.
Join Date: Sep 1998
Location: wherever
Age: 55
Posts: 1,616
Likes: 0
Received 0 Likes
on
0 Posts
Elevator on the other hand have no secondary effect
Primary - pitch
Secondary - speed.
Unless you can turn off gravity of course!
Join Date: Jul 2001
Location: East of West and North of South
Posts: 549
Likes: 0
Received 0 Likes
on
0 Posts
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.
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.
Last edited by cosmo kramer; 10th Mar 2010 at 23:11.
Join Date: Aug 2009
Location: Germany
Posts: 72
Likes: 0
Received 0 Likes
on
0 Posts
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.
Remember aerodynamics and the four forces:
Code:
lift
!
!
!
thrust <----+----> drag
!
!
!
weight
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.
????????
Join Date: Aug 2009
Location: Germany
Posts: 72
Likes: 0
Received 0 Likes
on
0 Posts
What about the HANDBRAKE 
????????
????????
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...
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:
"a high sink rate must be countered by increased incidence coincidentally protected by an increase in thrust to counter the extra drag."
It is dangerous to believe that rate of climb or descent is strictly a function of power, that an airplane goes up or down as a function of applying power of pulling it off. A very basic understanding of aerodynamics proves that a wing in flight climbs or descends as a result of angle of attack and lift variations at various angles of attack. Power or thrust merely pushes or pulls the plane through the air fast enough for the wing to become aerodynamic, to furnish lift. From then on, climb and descent are functions of pitch attitude (lift coefficient) and are controlled by the elevators. The power controls the speed-period!. This is the whole essence of flight, particularly jet flight"
Join Date: May 2000
Location: Seattle
Posts: 3,196
Likes: 0
Received 0 Likes
on
0 Posts
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.
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.
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...
Join Date: May 2000
Location: Seattle
Posts: 3,196
Likes: 0
Received 0 Likes
on
0 Posts
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.
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.
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.
Join Date: Jun 2009
Location: US
Posts: 497
Likes: 0
Received 0 Likes
on
0 Posts
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.
Join Date: Mar 2005
Location: Uh... Where was I?
Posts: 1,338
Likes: 0
Received 0 Likes
on
0 Posts
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.
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.
Join Date: Oct 2009
Location: UK
Posts: 1,270
Likes: 0
Received 0 Likes
on
0 Posts
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.
what would happen if an AP in a 737 had ...... the pitch (coupled) with the ASI to maintain airspeed?
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.
Join Date: Sep 1998
Location: wherever
Age: 55
Posts: 1,616
Likes: 0
Received 0 Likes
on
0 Posts
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.
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.
Join Date: Aug 1999
Location: England
Posts: 1,050
Likes: 0
Received 0 Likes
on
0 Posts
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
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
Join Date: Aug 2009
Location: Germany
Posts: 72
Likes: 0
Received 0 Likes
on
0 Posts
A simple experiment:
Special cases
- 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. - 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. - 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. - 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. - 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. - 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.
Special cases
- Transition from level flight to climb:
Potential energy is added, additional thrust is required to deliver this additional energy requirement. - Transition from level flight to decent:
Potential energy is used up to overcome drag, less thrust is required to maintain constant speed.
Join Date: Aug 1999
Location: England
Posts: 1,050
Likes: 0
Received 0 Likes
on
0 Posts
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.
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.
Conclusion: Both pitch and thrust affect speed and the rate of climb.
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.
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.
Conclusion: Both pitch and thrust affect speed and the rate of climb.
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.
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.
Conclusion: Both pitch and thrust affect speed and the rate of climb.
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.
=> 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.
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.
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
Its about as valid as saying 'on Fridays its always Friday'.
pb
Join Date: Mar 2005
Location: Uh... Where was I?
Posts: 1,338
Likes: 0
Received 0 Likes
on
0 Posts
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?
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?