Stick & Rudder

[Methusala]

Darky, It is true that you use a coordinated mix of power (throttle) and stick (elevator) to achieve a smooth transition from one a/s to another. This is similar to the coordinated mix of stick (aileron) and rudder to turn safely. If you use an improper mix then you will either slip or skid in the turn which could result in a dangerous condition.

 

My point is that unless you understand the primary and secondary effects of control inputs then you could be in trouble and not know why or what to do to correct the situation. The idea that is being stated by some in this post that you can control speed on approach using throttle and elevator (or attitude in another name) control to nail the aiming point is WRONG and a way to get into trouble. I believe that this is important. Not just for an argument but to stay safe especially when close to the ground. Kind regards, Don

 

 

[motzartmerv]

And around the merry go round we go again.

 

Please refrain from telling students the way they are learning things is wrong.

 

Guys, POWER + ATTITUDE = PERFORMANCE. Its really that simple.

 

Pointing at the aim point and useing throttle for speed is perfectly safe, and being taught by lots of schools around the world. And it agrees perfectly with the above rule.

 

Flying dog. We don't just open or close the tap to climb or descemd, we use PAT, don't we??

 

Darky, keep doing things the way you are being taught, by a qualified instructor.

 

cheers

 

 

[Powerin]

Hmmm...interesting.

 

I think you are right Tomo...to get an increase in lift you must have an increase of airspeed over the wings for a given AoA. But I think you are incorrect in saying that trim maintains attitude. Instead it maintains AoA.

 

To my mind (and this is probably getting needlessly complicated) if you increased power the speed would increase, as Tomo says, which would cause you to climb. However climbing also changes the direction of flow of air over the wings as it now has a vertical component. So your elevator's trim will pitch the a/c up to meet the air again at the trimmed AoA. I assume now that the extra power is being spent climbing rather than speeding you up any further and things balance out to roughly your previous trimmed speed?

 

I seem to remember somewhere that if your a/c doesn't balance this out you get Phugoid oscillations?? Have to re-read about that.

 

What I haven't read anywhere is the effect of engine thrust on the equation. When climbing and pitched up, some of your engine thrust is now pointed downwards. How much effect does this have? Is it significant compared to lift from wings?

 

*Disclaimer*- I don't fly (except a flightsim) so all the above could be pure drivel (and probably is)

 

 

[Tomo]

Thomo, When the aicraft is flying straight and level at trimmed speed what happens when you open the tap is that the nose immediately rises! I know this because I have done it often. When, alternatively you close the tap, it falls.

Yes indeed, but it isn't caused by the trim in anyway shape or form... aircraft are designed with a thrust line. So when power is increased, thrust is increased, and drag is increased, which causes the nose to rise simultaneously, and vice versa when power is decreased. It's actually designed into the aircraft to make it easier and safer to fly.

 

I haven't fully grasped that the aircraft will maintain it's speed when power is added though... I've always had to raise the nose to maintain the speed if I increase power In all the aircraft I fly.

 

 

[Mazda]

As Motz says, around we go again.

 

Before going on about this any further, please, could everyone involved in this "debate", please, please read the Fly Better book 2, lesson 2, the chapter on the landing approach, from page 14. You can download it for free here. FLY BETTER......

 

It's free. You can download it right now and every little bit of knowledge we can get in aviation is a good thing. You have absolutely nothing to lose and you may have something to gain. Go on, be brave and take it in with an opern mind - even if you only read that chapter.

 

It explains the methods very clearly, gives pros and cons, and explains why the "elevator for speed" approach developed from the days when a glide approach was the norm. It mentions that a 747 check and training captain said that if he corrected a 5 knot approach speed error with an attitude change, the rear seat passengers would move up and down by 15 feet!

 

And before you say Oh, I'm in a Jab, I'm not flying a 747, I can assure you that these basic techniques work in large and small aircraft.

 

Food for thought. Every single very experienced pilot I know uses the power for speed approach.

 

 

[Powerin]

My post above is from a theoretical point of view so probably has no practical use here. Please disregard...I was just curious. Point taken Motz and Mazda.

 

 

[DarkSarcasm]

Alas, I fear I may have restarted this debate with my earlier post. Oh well.

 

I know that you're all trying to help and (some of you) truly believe that what I'm doing may well get me into trouble someday. I like discussion, I like hearing other people's opinions but no matter what you say, I'm not going to change my technique. Why? It's being taught to me by a qualified instructor, who I trust. I use the technique every time I fly, it makes sense to me and it works. :)

 

 

[djpacro]

Powewin - please stay in the discussion.

 

Well, if we're going round again I will add something new, or at least different from my earlier posts. People could go back and read all the old posts if they like.

 

Here is an extract from Stick & Rudder that I found interesting:

 

Page 256 THE POWER DESCENT

…...

 

 

 

The power approach is one extremely practical case in which it is definitely true that the stick is the airplane's speed control and the throttle is it's up-and-down control. If you want to come down more steeply, don't nose the airplane down. Cut the throttle back, and then manipulate the stick so as to keep the air speed constant. As the throttle is cut, the nose must indeed come down a little if the speed is to remain constant. But in a perfectly behaved airplane, the nose will come down all by itself if you merely hold the stick steady! Since most of our airplanes are not perfectly behaved, you may have to take some action with the stick to keep the speed steady. But as a matter of fact, this action may well consist of increasing your back pressure on the stick rather than decreasing it! This is because with decreased power, most airplense become disproportionally nose-heavy and actually want to pick up speed! At any rate, the thing to do is is to free your working of the stick from any idea that the elevator is the airplane's up-and-down control. Work the stick so as to keep your speed steady. A steady air speed is the key to a successful power approach. Work the throttle to regulate your descent.

 

 

 

…....

 

 

 

In talking this over with other pilots, you may sometimes be advised to use a different method: to put the airplane into a certain attitude, probably about level, and then work the throttle to regulate your descent-always keeping the ship in the same attitude. This method results, of course, in constantly varying air speeds and Angles of Attack. But note that in this method, too, you do not make it stay up by pulling the stick back. As a matter of fact, the handling of the stick works out just the opposite way! As you reduce your power to steepen your descent, you must come back on the stick if you want to hold the ship in its level attitude.

 

 

 

 

 

This constant-attitude method is second best. It is not quite as sure and smooth and foolproof as the constant-speed method outlined above. But it has the advantage that it is easier to teach to beginning students. A student often has no real conception of Angle of Attack and cannot sense it very well nor does he sense speed well. But he is invariably keenly conscious of his ship's attitude, and can handle the job of keeping the attitude constant, when he might fail at keeping speed and Angle of Attack constant. Also, it must be admitted that the constant-speed method outlined above depends rather heavily upon the air-speed indicator—since with power partly on, one's sensing of speed and Angle of Attack is not too keen. Now it may happen that a ship has no reliable air-speed indicator. Finally, many instructors think that the student's eye should be kept outside the cockpit as much as possible. Thus sometimes this constant-attitude method of making a power approach may be the best.

Of course, fast or big jets weren't around when he wrote that.

[Guest rocketdriver]

Forgive me everyone ... I've been biting my tongue but .....

 

I'm firmly with the stick for speed and throttle for descent rate school, but then I've done a bit of gliding (read "less airbrake" as equivalent to "more throttle"!) If you try stick for glide path, throttle for speed, in a low mass aircraft at least, you can end up with insufficient airspeed and landing heavily at best and short, or you have too much speed and land long especially in a low drag aircraft. In my experience this is true for gliders, hang gliders and piston engined light aircraft from Jabirus up to at least Harvard weights.... With high drag aircraft like the Thruster the rise in profile drag with speed does provide a mechanism for "diving" at the aiming point without too much subsequent overshoot ..... but don't try the stick back to stretch the glide theory as you will definitely come unstuck unless you add power ....

 

 

For me what works is TRIM for accurate speed, and do that early in the approach. Then adjust your aiming point with the throttle leaving the stick relatively constant. If it is trimmed, it will fly itself down final (wind gradient at the last minute excepted). I recall the theory of a constant stick position for speed (or, as last discussed on this forum, for the stall when approached slowly). Using this method, your trimmer is setting the stick position for your approach speed, leaving you to focus on the touchdown point and using small throttle adjustments and just the occasional double check on the ASI and then, finally, a flare to set the landing attitude .....

 

What to do if you get it wrong?.

 

· If slow, stick forward pressure for speed. Then adjust throttle for approach path. trim if time allows

 

· If fast, ease the stick back to stabalise the speed as desired, then adjust throttle for approach path, trim if time allows

 

· If low, Add throttle

 

· If high reduce throttle

 

· And if in doubt, go round ......

 

This simple set of rules will never cause you to stall / spin on approach ..... even when you are dragging it in on the back of the power curve in order to make a short field landing ...

 

Regards

 

RD

 

 

[Methusala]

To my fellow aviators on this site,

 

I chose to put my understanding of the relationship of power and attitude as an input to discussion. I don't want to dictate and I certainly don't intend to intrude between students and their instructors. I think that the points that I have made are logical and reasonably clearly expressed. My fear was that some people may believe from the discussion that power controls air speed and that attitude controls rate of ascent or descent which would be wrong. I will now withdraw to observer status in any further discussion. Thank you all, Don

 

 

[Mazda]

Methusala did you open that link and read the 2nd chapter?

 

 

[Guest rocketdriver]

hi Methusla

 

I have the same concerns. Please stay with the discussion. IMHO, your input is important .. especially as I agree with you! ...:thumb_up:

 

RD

 

 

[Kiwi]

Food for thought. Every single very experienced pilot I know uses the power for speed approach.

Every one of my landings, in the last 880 hours (probably more) has been a glide approach, so please explain to me how “power controls airspeed”

 

?

 

Kiwi.

 

 

[motzartmerv]

Clearly we aren't talking about glide approaches.

 

 

[GraemeK]

For example, if I want to descend, I use the stick to lower the nose and adjust power so I don't end up hurtling towards the ground at a ridiculous amount of knots.

Not so sure of that.

 

Starting descent on base - back on the throttle, back on the stick to reduce airspeed to descent speed. So, holding nose up - and the trim lever comes back to hold the reduced speed.

 

I suspect (although I haven't tried it) that Methusala is right re increasing power - in "See How it Flies" John Denker states that from straight and level in a properly trimmed aircraft, if the power is increased and no other changes are made, the airspeed will momentarily decrease slightly as the aircraft starts to climb.

 

 

[flying dog]

Mazda,

 

Because it is written in a book it doesn't mean it is correct.

 

Be it the book is called "Fly better" or otherwise.

 

I believe the way the book discribes it is "putting it simply" to help (not the word I would have used) students learn (again, not the word I would have prefered) to fly.

 

And be it the book is FREE or otherwise again: Doesn't make it true.

 

 

[Tomo]

My fear was that some people may believe from the discussion that power controls air speed and that attitude controls rate of ascent or descent which would be wrong.

Don, we all agree with you, and your concern is reasonable. Though using the above approaches, as Fly Better states it, and Stick and Rudder, isn't just using power for airspeed, and stick for ascent or descent alone.

 

Powered approaches are one thing, constant attitude approaches are another. I can make a constant attitude glide approach, and I can make a constant attitude powered approach.

 

I think that is where the confusion is, just because we say we are doing a constant attitude approach, doesn't mean we are driving it in with flat 2 mile final... though you could do that as well, but it's not practical for small aircraft. And it would be embarrassing if your engine stopped so close to the strip and you couldn't get there.

 

In an aeroplane glide approach (engine off) you are stuck with limited abilities, nose down/up for airspeed. In a glider glide approach you come in at half air brake, it gives you the power, drag necessary to perform a perfect approach. Likewise in an aeroplane with a engine running.

 

Your concern is honoured, because it is something every pilot needs to understand in each circumstance.

 

 

[Methusala]

Dear Maz, I will do as you suggest and read the link. I wish to say that I am not averse to new ways to do things or exploring more effective teaching methods. The thing that struck me was that people seemed to be condensing ideas fully expressed in a chapter of words into a simple idea. That gave the impression that suddenly power was the mechanism of choice to control airspeed and that the stick controlled glide slope or approach gradient. Full glide approaches may not be to everytone's taste but they are safe if done with the acquired skills. But trimming for approach speed and then controlling the gradient with power works in a partially powered approach as well. Whether you find this your preferred method to use or teach is your choice. By the way, the statement that everyone that I know does it this or that way is not a compelling argument for the correctness of anything. Don

 

 

[Methusala]

Dear Tomo, A full glide approach when judged correctly (what learning and practice is about) will (almost) always have sufficient stored energy to arrive safely at the threshhold. Gliders do this every time. The airbrake is NOT the same as a throttle in that it only uses stored energy and cannot add energy as can a throttle (sometimes lift disappears very quickly and gliders don't make it back). There are ways to steepen a glide approach such as side slips or S turns if too high but if in doubt make the decision to go around. There is little confusion about the concept of energy added to an aeroplane that is trimmed for a speed (this is what the trim system is there for), resulting in altitude gain. Don

 

 

[Mazda]

Here's one way to think of it. Imagine you are in the circuit and decide to slow things down a bit. Maybe you are in a higher performance aircraft than usual, maybe there is traffic ahead. What do you do? You use a lower power setting. i.e. you reduce power to reduce speed.

 

Imagine you are trying to get somewhere in a hurry. You don't lower the nose, you fly at a higher power setting. Increasing power = more speed.

 

Everyone does these exercises in their second ever flight, straight and level, cruising at different airspeeds using different power settings.

 

You are in bumpy conditions and need to reduce speed to turbulence penetration speed. How do you do that? You reduce power which reduces airspeed.

 

You are doing a cruise descent and want to maintain your cruise speed. So you reduce the power setting. Reducing power = less speed.

 

You are flying in instrument approach and need to remain within the category airspeed and on profile. You control speed with power and stay on profile with attitude.

 

You are flying in formation and need to catch up to the leader. You add power to increase speed. If you are flying too fast you reduce power to slow down.

 

You are taxying and approaching an intersection. What do you do? Reduce power to slow down (then brake if necessary).

 

The times when pilots don't use power for speed is when there is no power available - i.e. in a glide, or in a full power climb when there is no excess power available.

 

I think this is how the attitude for speed on approach started, when approaches were set up to be glides, with no power available, however that is not the way we fly in normal powered stages of flight.

 

 

[Mazda]

Wise words Dog, it pays to be sceptical. However it also pays to take advice from experts in their field, and Mr Kruse is one of those.

 

 

[Methusala]

Stick & Rudder?or...Fly Better. No contest really. My tuppence worth.(And yes I did read the section.) Don

 

 

[Guest rocketdriver]

Here's one way to think of it. Imagine you are in the circuit and decide to slow things down a bit. Maybe you are in a higher performance aircraft than usual, maybe there is traffic ahead. What do you do? You use a lower power setting. i.e. you reduce power to reduce speed.hi Mazda .. If thats all you do, you will merely loose height at much the same speed. Try it one day. At altitude on a calm day, be trimmed, hands hovering over the stick and reduce power a little. You will find increased descent with little speed change, once it has all settled out. (I did it one day when I carelesly ran a tank dry in a cherokee 6 ..no harm done but it was surprising how the nose just dropped and the aeroplane immediately adopted a glide descent at more or less cruise speed .... woke me up I can tell you!) Oppositely for a power increase.

 

Imagine you are trying to get somewhere in a hurry. You don't lower the nose, you fly at a higher power setting. Increasing power = more speed.

 

Again, if you leave the trimmer and stick alone, and add power, you will find you are climbing at a similar speed to previously trimmed. Urge you to try it ..... You do need more power for higher speed, but only because the drag has increased.

 

I think what is confusing the issue is the operational issues of cruising. In this phase of flight, we are typically focussed on maintaining altitude and then adjusting either trim to achieve level flight at a set power or adjusting power to achieve level flight at a set speed. In the cruise it is of little concern. On approach to land, it is vital to get it right ....

 

Everyone does these exercises in their second ever flight, straight and level, cruising at different airspeeds using different power settings.

 

You are in bumpy conditions and need to reduce speed to turbulence penetration speed. How do you do that? You reduce power which reduces airspeed.

 

chicken or egg? Yes you do reduce power, and then move the stick back and trim to maintain level flight as the aircraft slows. What is happening is that your thrust is now insuficient to maintain your original airspeed which starts to drop, so you have to increase the lift coeficient of the wing to compenstate as the aircraft slows. And as the speed drops to your turbulence penetration speed, you probably adjust the throttle to maintain level flight with the new (reduced) drag at the lower speed.

 

You are doing a cruise descent and want to maintain your cruise speed. So you reduce the power setting. Reducing power = less speed.

 

Disagree .... Reducing power = increasing descent at similar speed ....

 

You are flying in instrument approach and need to remain within the category airspeed and on profile. You control speed with power and stay on profile with attitude.

 

You are flying in formation and need to catch up to the leader. You add power to increase speed. If you are flying too fast you reduce power to slow down.

 

More speed demands more power to overcome increased drag. If you want to increase speed AND maintain height, you MUST add power .. and you have chop it off again as the in formation position is approached (you want to maintain height relative the leader whilst matching his speed ...) Thats why fuel use is so high in formation flying on/off,on ,off ....

 

You are taxying and approaching an intersection. What do you do? Reduce power to slow down (then brake if necessary).

 

True. Your wings are not providing the lift needed to maintain level flight, so this is a completely different situation .....

 

The times when pilots don't use power for speed is when there is no power available - i.e. in a glide, or in a full power climb when there is no excess power available.

 

I think this is how the attitude for speed on approach started, when approaches were set up to be glides, with no power available, however that is not the way we fly in normal powered stages of flight.

I hope my comments do not offend ...not meant to ......

 

 

[Guest rocketdriver]

Been thinking about this discussion ....and you know, this glide path discussion it is about energy management as others have said and maybe there are a couple of loose ends here .....

 

The total energy of a system (call it an aeroplane or a glider) consists of its Potential energy (that energy related to its mass and height) and its Kinetic energy (that concerned with its mass times its speed, to put it simply). Newtons laws say that Energy is conserved. So if we increase our descent rate by increasing speed (in inevitable result of forward stick) we reduce potential energy more quickly but increase kinetic energy so that the total energy remains fairly constant .. we trade one form of energy for another, less a drag penalty as speed increases above best glide. So if you are high and use the stick to adjust your approach path, you end up roughly over the aiming point but too fast. If on the other hand you were trying to come in less steeply, ie land further away, then you start to sink more rapidly as you move the stick back and your speed drops below best glide, and you end up short of the airstrip, short of airspeed and out of options ...... And perhaps spinning in ...... This is always true absent adjusting the engine power of an aeroplane or your airbrake setting in a glider.

 

Now I know we all know this, but a quick reminder ..... Whatever our opinions, the LAWS OF PHYSICS govern the flight of an aeroplane and these laws, well proven, say that an aircraft wing develops lift according to

 

L = 1/2* ρ *V2 * S * Cl

 

Where ρ is the air density, V2 is the speed squared, S is the wing area and Cl is the coefficient of lift. This later, as everyone would remember, is a (non linear) function of the wing profile and the angle of attack of the wing and is usually discovered from wind tunnel tests ......

 

Nowhere does this equation discuss engine power.

 

Which is why gliders and paper aeroplanes can fly as can Blackbirds, Spitfires and Thrusters to name a few.

 

Given a particular wing area and profile, flying in an atmosphere given to us by the Almighty’s gift (no I’m not particularly religious!) and given that for steady state flight (unaccelerated) the lift is also fixed at (almost) equal to the a/c weight, the only adjustment available to our intrepid aviator is the coefficient of lift (by means of levering the angle of attack of the main wing using the elevator control) to vary the speed.

 

So your speed is actually a result of natures need to satisfy the physical demands of the aircraft wing to produce the required lift at the angle of attack you are imposing on it by use of the elevator.

 

However, the speed demanded to satisfy this equation has to come from somewhere ... In a glider its purely by converting potential energy into kinetic energy plus drag ... ie the glider descends to maintain speed. So does a Jabiru, Cherokee, or Airbus with the power off. But if we have a functioning engine, we can reduce the needed descent rate by artificially, if you like, adding power to the system by adjusting the throttle ....

 

So once again, talking primary effects, stick for speed, throttle for flight path! ....

 

 

[Methusala]

Thank you Rocketdriver for your elegantly expressed and friendly diplomatic espousal of the physics relating to this discussion. I'm not a scientist but I think that this is about "frames of reference". Don