Primary response of elevator

[kiwicrusader]

As we know, we are taught that the primary response of the elevator is pitch, however in reality the primary response is changing the angle of attack, which in normal flight is what changes the pitch.

 

My question is, if we taught that the elevator controlled angle of attack and not pitch, would the students pick up the understanding of angle of attack easier and more quickly?

 

What do you guys think?

 

 

[facthunter]

It would depend on what level you dealt with it. Elevator does control angle of attack as we know but at the initial phase of flight training we use it to place the nose at the correct attitude for various manoeuvers. This is not a hard concept to get across. The average person can do it in a matter of minutes. especially easy if there is a reference point on the aircraft that can be aligned with the horizon.

 

The new pilot does not have to worry about stick position in this instance which has a more direct bearing on angle of attack.. Some instructors don't accept the idea of stall stick position. I have no difficulty with the concept and find it usefull. Nev

 

 

[Powerin]

I guess it comes from the sort of stuff I had read before I started to fly, but I've always thought of the elevator (and trim) as the angle of attack control and pitch as the "by-product" of angle of attack. I think it's helped me to understand the dynamics of flying a lot better and how trim/elevator and airspeed are interrelated.

 

 

[facthunter]

I don't want to be picky, but I can't understand why you have brought "trim" into it. Unless you are moving the horizontal stabiliser as some aircraft do. Trim is just a method of relieving control force. You use the relationship of power and attitude, constantly throughout the training in the climb cruise and descent phases of flight. You change the pitch of the aircraft to achieve the desired attitude, but you are always using attitude as a primary reference, whether visually or on instruments. Nev

 

 

[Powerin]

I don't want to be picky, but I can't understand why you have brought "trim" into it. Unless you are moving the horizontal stabiliser as some aircraft do. Trim is just a method of relieving control force. You use the relationship of power and attitude, constantly throughout the training in the climb cruise and descent phases of flight. You change the pitch of the aircraft to achieve the desired attitude, but you are always using attitude as a primary reference, whether visually or on instruments. Nev

To relieve the control force the trim is creating an opposite force (either by spring or servo tab) to hold the elevator at a desired position without further pilot input and thereby maintaining the desired angle of attack (or attitude if you prefer). So I've always seen trim as an integral part of setting angle of attack (but of course not as a primary flight control). But I see your point...thanks.

Off topic now (sorry)....as far as I understand it, stabilators don't actually have much control forces as the whole horizontal stabiliser always flies horizontal to the airflow. Aircraft I have seen with stabilators (Piper, Tecnam) always have an anti-servo tab to give the pilot more control force. The stabilator trim control moves the anti-servo tab out of the airflow to reduce control forces whereas an elevator trim tab moves into the airflow.

 

 

[facthunter]

No I'm not talking about a full flying tail, like a Piper. On Jets and aircraft with a wide speed range the normally fixed (forward part) is moveable through quite a large angle for pitch authority. You CAN actually fly the plane on this in an emergency so it would be considered an alternate pitch control in it's own right if the elevator failed. I have had this happen and it is no big deal, but a failed pitch control means it is all over. You can fly on a trim tab too. some primary controls that are not powered are actuated by servo tabs that relieve control pressures, but also move the primary control. The Douglas DC9 has only one hydraulic powered control surface and that is for a DOWN pitch action only on the elevators, for stall recovery. All other control movements are actuated by servotabs. Till the plane moves forward and the air moves over the surfaces the elevators go anywhere. One is often up and the other may be down. nev

 

 

[Powerin]

No I'm not talking about a full flying tail, like a Piper. On Jets and aircraft with a wide speed range the normally fixed (forward part) is moveable through quite a large angle for pitch authority. You CAN actually fly the plane on this in an emergency so it would be considered an alternate pitch control in it's own right if the elevator failed. I have had this happen and it is no big deal, but a failed pitch control means it is all over. You can fly on a trim tab too. some primary controls that are not powered are actuated by servo tabs that relieve control pressures, but also move the primary control. The Douglas DC9 has only one hydraulic powered control surface and that is for a DOWN pitch action only on the elevators, for stall recovery. All other control movements are actuated by servotabs. Till the plane moves forward and the air moves over the surfaces the elevators go anywhere. One is often up and the other may be down. nev

Ahh...I see. Like this?

 

In the end though, aren't all these different elevator systems achieving the same outcome? That is, adjusting the angle of attack of the wing? Aerodynamically the above pitch adjustable HS does exactly the same thing as a trim tab, albeit over a far wider range.

 

Also, you could fly a small aircraft with elevator trim in an emergency couldn't you?

 

 

[kiwicrusader]

So we seem to all agree that the tailplane, whatever sort, controls angle of attack primarily. At what stage in the syllabus should we teach/be taught this after the initial training of elevator controls pitch?

 

 

[Powerin]

For myself (still a student), I think knowledge of angle of attack helped me no end. Flying becomes a bit more intuitive if you know why something happens. But that's just me...I like knowing how things work.

 

If I were an instructor (if I can be so bold) the first lesson would be to take a student in a car, travel down the highway at 100km/h, and get them to stick their arm out the window and experience how much lift they can get just by holding their flat hand at different angles to the airflow (it's amazing how much force there is in 100km/h air). Then show them how the elevator does exactly the same thing for a wing....vary the angle of the wing into the oncoming airflow.

 

 

[sfGnome]

Both my daughters are school teachers. One was telling me the other day that when some of her students really struggle with the concept of multiplication, she'll tell them not to think of it like numbers along a ruler, but to think of it like numbers in a square instead. While most of the class - even the bright ones - won't have a clue what she's talking about, these kids have to see things in shapes before they get it.

 

The point of the story is just that there isn't a one size fits all when it comes to learning. You have to have a whole arsenal of techniques, and hope that one of them will work for your current student. Some will be totally confused by introducing AoA early on, while some will find it just makes perfect sense. Good luck working out which is which. I guess that's the real skill of the teacher, isn't it?

 

 

[facthunter]

I have to confess that I am an ex-schoolteacher, and I tend to apply physics (which I like) very much to my flying and It has helped ME to be a better pilot. ( meaning that without it I would have been a worse one). Plenty of pilots do not emphasise the theory of aerodynamics as some others do. The wing is a device for providing forces ( lift generally is the one we want and it will do it under certain conditions). angle of attack mainly limiting it's useful operating range.. The amount of lift available varies as the square of the speed of the airflow over it. That's nice to know too.

 

I study theory and history of aerodynamic design but a lot of pilots just want to know HOW to fly the plane and I want them to do it safely. That is the job of an instructor. You don't have to be a mechanic to drive a car well. IF you are sensitive to it's structure and understand what over revving, putting lots of torque through CV joints with a lot of turn on etc does to the mechanicals. you will be a BETTER driver and your car will last longer. But as has been said everyone is different.

 

I believe the angle of attack is important and most of my hours are in planes that gave a cockpit indication of AoA. A piece of wool will do that on pusher aircraft/ gliders, where the prop doesn't prevent it.. Pilots don't get enough serious training of flying close to the stall. Most are frightened to go there. FAIR enough to be wary, but the most common instinct when things go wrong and the ground is approaching is to pull the stick back too far. It IS your angle of attack determiner, and planes are stalled by pilots actions. Any thing that will improve the situation should be used as a training tool. Nev

 

 

[Bryon]

If I were an instructor (if I can be so bold) the first lesson would be to take a student in a car, travel down the highway at 100km/h, and get them to stick their arm out the window and experience how much lift they can get just by holding their flat hand at different angles to the airflow (it's amazing how much force there is in 100km/h air). Then show them how the elevator does exactly the same thing for a wing....vary the angle of the wing into the oncoming airflow.

I used the very same technique whilst driving back from brisbane and my wife and I had a discussion on what makes a plane fly. It did not matter how much theory I told her, she could not grasp the fundamental principle until I got her to hold her arm out the window, palms flat and vary the angle of the hand into the wind

 

Within 5 seconds she understood and could make sense of all the gobbledegook I had been telling her

 

Simple experience of the laws of nature compared to the complexities of language did it for her

 

Cheers

 

Bryon

 

 

[rage83]

I want to disagree slightly about this AoA discussion.

 

I agree that the elevator changes the AoA but my question is on what??

 

My thoughts: Elevator changes the AoA on the tailplane directly the resultant change in lift on the tail surface then pitches the

 

aircraft which results in the change of AoA of the wing.

 

So if we are talking about the AoA of the aircraft ( wing ) I would say no on a technicality because moving the elevator does not

 

directly cause a change in AoA it is the pitching moment of the aircraft caused by the change in AoA on the tailplane.

 

So in a way the elevator effects the pitch of an aircraft which changes the AoA.

 

Looking in to it too much??

 

 

[kiwicrusader]

I don't think you're looking into too much.

 

I tend to agree with you, although I have never thought of it this way.

 

The reason for the thread was to create this sort of discussion. It amazes me how many CPL's I meet that don't have a full grasp of AofA and I am hoping these sort of discussions would help.

 

Cheers.

 

 

[Guest ozzie]

Pilots should just work on the KISS method, houses get smaller- houses get bigger. They should leave the complicated why and hows to the designers and engineers. Good piloting is hard enough without over complicating it with over the top theory. Ala Air France

 

 

[Powerin]

I want to disagree slightly about this AoA discussion.I agree that the elevator changes the AoA but my question is on what??

 

My thoughts: Elevator changes the AoA on the tailplane directly the resultant change in lift on the tail surface then pitches the

 

aircraft which results in the change of AoA of the wing.

 

So if we are talking about the AoA of the aircraft ( wing ) I would say no on a technicality because moving the elevator does not

 

directly cause a change in AoA it is the pitching moment of the aircraft caused by the change in AoA on the tailplane.

 

So in a way the elevator effects the pitch of an aircraft which changes the AoA.

 

Looking in to it too much??

As far as I understand it that is exactly right. If you want to get even more technical the AoA of the horizontal stab will change with the pitching moment until it reaches a new equilibrium with wherever the pilot has put the elevator (and maintained it with trim...sorry Nev )

If you want to directly change the angle of attack of a wing I guess you need to fly a trike.

 

Pilots should just work on the KISS method, houses get smaller- houses get bigger. They should leave the complicated why and hows to the designers and engineers. Good piloting is hard enough without over complicating it with over the top theory. Ala Air France

I think you left out an important part which is the basis of this discussion: stick forward-houses get bigger, stick back-houses get smaller, stick further back-houses get bigger again really fast! Perhaps if the Air France or Colgan pilots had a better understanding of AoA and the "stick further back" bit they might be alive today?

 

 

[eightyknots]

I have to confess that I am an ex-schoolteacher, and I tend to apply physics (which I like) very much to my flying and It has helped ME to be a better pilot.

I most noble occupation Nev (I have taught at high schools, TAFE Colleges and at a university) so it's always good to marry practice with theory to enhance levels of understanding. If there's too much reliance on practice only (or theory only) there will be a learning poverty in the student.

 

I believe the angle of attack is important and most of my hours are in planes that gave a cockpit indication of AoA. A piece of wool will do that on pusher aircraft/ gliders, where the prop doesn't prevent it.. Pilots don't get enough serious training of flying close to the stall. Most are frightened to go there. FAIR enough to be wary, but the most common instinct when things go wrong and the ground is approaching is to pull the stick back too far. It IS your angle of attack determiner, and planes are stalled by pilots actions. Any thing that will improve the situation should be used as a training tool. Nev

How about a Lift Reserve Indicator? See thread for discussion on this: http://www.recreationalflying.com/threads/lift-reserve-indicator.17196/

 

 

[eightyknots]

I think you left out an important part which is the basis of this discussion: stick forward-houses get bigger, stick back-houses get smaller, stick further back-houses get bigger again really fast! Perhaps if the Air France or Colgan pilots had a better understanding of AoA and the "stick further back" bit they might be alive today?

Interesting way of remembering this; something I had not heard before.

 

 

[M61A1]

I can't remember where I got the concept from, but I have always considered the elevator (and rudder) just as devices for applying force on the lever(fuselage) that alters AoA (rudder does yaw obviously). That works for canards as well. How much thrust you have available (gravity can provide this as well) will determine how much you can change your pitch attitude without exceeding critical AoA. Short story- In my understanding, AoA is relative to airflow- most important, attitude/pitch is relative to ground- not so important.

 

Also- hold stick further back.......not only do the houses get bigger, often they will rotate too.

 

 

[naremman]

So we seem to all agree that the tailplane, whatever sort, controls angle of attack primarily. At what stage in the syllabus should we teach/be taught this after the initial training of elevator controls pitch?

Preferably before they realize that application of flap, and vaying power settings can have an influence on attitude as well!!

 

 

[facthunter]

I don't know if we are advancing the subject a lot.

 

The trike is weightshift and that is another complication.

 

The Flying Flea moves the wing angle ( front upper one) It has no horizontal stabiliser only a rudder which is used to bank the plane also.

 

In a convential plane the tailfeathers do move the tail around that is quite easy to understand.

 

The elevators control the pitching of the fuselage to which the wings are fixed. To get an angle of attack directly from this action is complex, as it depends on the lift you require, the speed you are doing and the capability of the wing. ( Area, Lift coefficient etc) and the properties of the air you are flying in density (temp and altitude) , The centre of lift will change with flap settings or often with AoA change so this will affect the pitch input required .

 

By this stage the student is probably rolling his/her eyes and looking for another hobby or instructor..

 

A good S& L session with the plane being held to an altitude across as wide a speed range as possible, followed by stalls ( at a later session) could cover this fairly well if done properly. in say a Jab 230. They usually run out of pitch trim at each end of the speed envelope. Nev