Attitude = speed control/power = pitch
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Peter
But what causes you to need to trim? When you are trimmed straight and level at say a lowish power setting and you advance the power levers fully forward what happens that causes the aircraft to need trimming to maintain the altitude? What is the initial thing that has to happen? Before as many claim you pitch for speed? (which is not the true picture!)
We are trying to dissect something into black or white chunks rather than the whole hence why I repeat both are wrong there can technically only be one right?
Trimming while vitally important is a bit of a Red Herring in this discussion some aircraft dont even have a trim wheel.
Pace
But what causes you to need to trim? When you are trimmed straight and level at say a lowish power setting and you advance the power levers fully forward what happens that causes the aircraft to need trimming to maintain the altitude? What is the initial thing that has to happen? Before as many claim you pitch for speed? (which is not the true picture!)
We are trying to dissect something into black or white chunks rather than the whole hence why I repeat both are wrong there can technically only be one right?
Trimming while vitally important is a bit of a Red Herring in this discussion some aircraft dont even have a trim wheel.
Pace
Last edited by Pace; 9th May 2012 at 11:28.
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When you are trimmed straight and level at say a lowish power setting and you advance the power levers fully forward what happens that causes the aircraft to need trimming to maintain the altitude?
Last edited by peterh337; 9th May 2012 at 14:30.
Pace; Power tries to accelerate the aircraft, the aircraft is trimmed for a speed therefore if the speed tends to increase, the aircraft will climb to maintain trimmed speed.
If you displace a correctly trimmed convential aircraft from its speed then release the controls it will return to its trimmed speed after a few phugoid excursions without any control inputs. Try it sometime in the cruise.
If you displace a correctly trimmed convential aircraft from its speed then release the controls it will return to its trimmed speed after a few phugoid excursions without any control inputs. Try it sometime in the cruise.
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but what makes it want to climb?
If you displace a correctly trimmed convential aircraft from its speed then release the controls it will return to its trimmed speed after a few phugoid excursions without any control inputs.
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M
As you add power the aircraft will accelerate (speed) as it accelerates the increase in airflow will cause lift as simple as that. The primary action of adding power to a trimmed aircraft in level flight has to be an acceleration and hence increased airflow over the wing.... as simple as that.
What the heck has that got to do with it try doing that and at the same time shove in a fistful of throttle and see what happens?
Pace
As you add power the aircraft will accelerate (speed) as it accelerates the increase in airflow will cause lift as simple as that. The primary action of adding power to a trimmed aircraft in level flight has to be an acceleration and hence increased airflow over the wing.... as simple as that.
If you displace a correctly trimmed convential aircraft from its speed then release the controls it will return to its trimmed speed after a few phugoid excursions without any control inputs
Pace
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Lots of aircraft that doesn't work on a change in power in an aircraft that has a moving stabiliser that sits inside the slipstream as a trim method will not hold the same speed. A large change in power will produce a large change in attitude that will almost certainly correspond to a large change in speed.
The pitch change is caused by a change in the lift moment created by the difference in pressure across the tail and the wings right? So if the trim method automatically compensates for power changes in the way that it does in the tomahawk, warrior, C152/C172 etc and TB series then that principle works (a relatively small trim tab that isn't that greatly affected by more airflow relative to the size of the tail, with the exception of the tommie which has an elevator that lives outside of the slip stream so only Airspeed initiates a change in trim). But in the case of the cub for instance it's the AoA of the entire stabiliser that changes so a change in power alters the lift balance between the wings and the tail in a larger way, it requires a different attitude towards trimming but it does still come down to the same basic principle that if you desire a certain RoD and Airspeed then you must set the power and attitude to achieve that and trim to maintain it without having to push and pull your way down.
Probably not a great explanation but I think that's what Pace is getting at.
a change in power in an aircraft that has a moving stabiliser that sits inside the slipstream as a trim method will not hold the same speed. A large change in power will produce a large change in attitude that will almost certainly correspond to a large change in speed.The pitch change is caused by a change in the lift moment created by the difference in pressure across the tail and the wings right? So if the trim method automatically compensates for power changes in the way that it does in the tomahawk, warrior, C152/C172 etc and TB series then that principle works (a relatively small trim tab that isn't that greatly affected by more airflow relative to the size of the tail, with the exception of the tommie which has an elevator that lives outside of the slip stream so only Airspeed initiates a change in trim). But in the case of the cub for instance it's the AoA of the entire stabiliser that changes so a change in power alters the lift balance between the wings and the tail in a larger way, it requires a different attitude towards trimming but it does still come down to the same basic principle that if you desire a certain RoD and Airspeed then you must set the power and attitude to achieve that and trim to maintain it without having to push and pull your way down
.Probably not a great explanation but I think that's what Pace is getting at.
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If it's not clear what I mean is this,
In the cub, if I trim for 65kts with zero power and then apply full power, I will not retain 65kts, the nose will pitch up way too much and the aircraft will slow down quite rapidly and no amount of waiting will bring it back to 65kts, it will wallow around the stall at 47-48kts I must push quite hard to keep the attitude to maintain 65kts and will consequently climb, I then trim to hold the attitude.
Trimming for an airspeed as such works for a boat load of aircraft though
There's no one method that works for everything but it all starts at the same place.
Power + Attitude = Performance, Select Hold Trim.
In the cub, if I trim for 65kts with zero power and then apply full power, I will not retain 65kts, the nose will pitch up way too much and the aircraft will slow down quite rapidly and no amount of waiting will bring it back to 65kts, it will wallow around the stall at 47-48kts I must push quite hard to keep the attitude to maintain 65kts and will consequently climb, I then trim to hold the attitude.
Trimming for an airspeed as such works for a boat load of aircraft though
There's no one method that works for everything but it all starts at the same place.
Power + Attitude = Performance, Select Hold Trim.
Pace: One last post from me despite your petulant response........
On all aircraft the Lift Vector is displaced from the Weight Vector.
The Thrust Vector is usually displaced from the Drag Vector.
The act of trimming resolves the moments between the four forces to achieve a stable situation. Change any one parameter and the aircraft will need to be retrimmed if it is to continue to fly at the same speed as before. Do you still not see why the application of power will tend to make a conventional aircraft climb (stick-free)??
On all aircraft the Lift Vector is displaced from the Weight Vector.
The Thrust Vector is usually displaced from the Drag Vector.
The act of trimming resolves the moments between the four forces to achieve a stable situation. Change any one parameter and the aircraft will need to be retrimmed if it is to continue to fly at the same speed as before. Do you still not see why the application of power will tend to make a conventional aircraft climb (stick-free)??
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Not sure I'm with you there. The act of trimming the elevator only resovles the difference between turning moments created by the lift vectors of the stabiliser/stabilator and the wing. Basically you're changing the effective angle of attack on the tail to maintain a given attitude. A change in power will only necessitate a change in trim for a given airspeed if the tail plane generates more or less lift, which would require a change in relative airflow - the primary change of this comes from either the slipstream or from a change in trim .
So if the tailplane lives outside of the slipstream the aircraft ought to settle at the same airspeed as it was trimmed for at any power setting. The tomahawk does this beautifully (as does the T tail arrow). The Jetstream does this really nicely as well although I haven't really had the opportunity to investigate all it's characteristics.
The application of power will ultimately lead to a pitch change but not necessarily a speed change or a change in RoC/RoD it depends very much on the design and position of the tailplane and the trim system.
this is of course my opinion and not necessarily correct.
.So if the tailplane lives outside of the slipstream the aircraft ought to settle at the same airspeed as it was trimmed for at any power setting. The tomahawk does this beautifully (as does the T tail arrow). The Jetstream does this really nicely as well
although I haven't really had the opportunity to investigate all it's characteristics.The application of power will ultimately lead to a pitch change but not necessarily a speed change or a change in RoC/RoD it depends very much on the design and position of the tailplane and the trim system.
this is of course my opinion
and not necessarily correct.
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And of course where the propulsion unit sits. In my plane if i add power i get a strong pitch up moment and speed will decay. If i reduce power there will be a strong pitch down moment and speed will increase. Simply because the thrust line is way below the CG. So any power change will lead to a trim change for the same speed.
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Meikleour
Totally but that is the point I am making it is increasing speed or airflow from an increase in power which achieves that! The trimming for speed is secondary.
My apologies for being petulant "bad hair day
Pace
Do you still not see why the application of power will tend to make a conventional aircraft climb (stick-free)??
My apologies for being petulant "bad hair day
Pace
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Silvaire
I totally agree with your comments but the OP started the thread taking about not agreeing with pitch for speed. My point is that he is partially right as both concepts pitch for speed or power for speed in their own right are wrong.
If you look at my previous posts I talked about Gliders in still air relying totally on pitch for speed and light powered aircraft more towards pitch for speed. aircraft like the lightning are at the other end of the scale power for speed being able to vertically go up to 40K on thrust alone.
With especially students the emphasis has to be pitch for speed for just the reasons you point out.
Having said that why does the Citation I fly use pitch for descent on the glideslope autopilot engaged and thrust to control speed? Obviously that works too.
It is really energy management two sources of energy from the airframe in pitch and from the engine. Both are best suited in different situations and relying on skills for one alone is asking for trouble.
Somehow I dont think I am getting my point over very well!!
It is the juggling of both sources as needed which is the correct way.
Pace
I totally agree with your comments but the OP started the thread taking about not agreeing with pitch for speed. My point is that he is partially right as both concepts pitch for speed or power for speed in their own right are wrong.
If you look at my previous posts I talked about Gliders in still air relying totally on pitch for speed and light powered aircraft more towards pitch for speed. aircraft like the lightning are at the other end of the scale power for speed being able to vertically go up to 40K on thrust alone.
With especially students the emphasis has to be pitch for speed for just the reasons you point out.
Having said that why does the Citation I fly use pitch for descent on the glideslope autopilot engaged and thrust to control speed? Obviously that works too.
It is really energy management two sources of energy from the airframe in pitch and from the engine. Both are best suited in different situations and relying on skills for one alone is asking for trouble.
Somehow I dont think I am getting my point over very well!!
It is the juggling of both sources as needed which is the correct way.
Pace
Last edited by Pace; 9th May 2012 at 21:16.
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Silvaire
I totally agree with your comments but the OP started the thread taking about not agreeing with pitch for speed. My point is that he is partially right as both concepts pitch for speed or power for speed in their own right are wrong.
If you look at my previous posts I talked about Gliders in still air relying totally on pitch for speed and light powered aircraft more towards pitch for speed.
With especially students the emphasis has to be that way for just the reasons you point out.
Having said that why does the Citation I fly use pitch for descent on the glideslope autopilot engaged and thrust to control speed? Obviously that works too.
It is really energy management two sources of energy from the airframe in pitch and from the engine.
It is the juggling of both sources as needed which is the correct way.
The old joke of the student sitting on the end of the runway on his first solo pumping the elevator up and down. His instructor approached to ask what he was doing? "I am pitching for speed but not going anywhere
Pace
I totally agree with your comments but the OP started the thread taking about not agreeing with pitch for speed. My point is that he is partially right as both concepts pitch for speed or power for speed in their own right are wrong.
If you look at my previous posts I talked about Gliders in still air relying totally on pitch for speed and light powered aircraft more towards pitch for speed.
With especially students the emphasis has to be that way for just the reasons you point out.
Having said that why does the Citation I fly use pitch for descent on the glideslope autopilot engaged and thrust to control speed? Obviously that works too.
It is really energy management two sources of energy from the airframe in pitch and from the engine.
It is the juggling of both sources as needed which is the correct way.
The old joke of the student sitting on the end of the runway on his first solo pumping the elevator up and down. His instructor approached to ask what he was doing? "I am pitching for speed but not going anywhere
Pace
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Having said that why does the Citation I fly use pitch for descent on the glideslope autopilot engaged and thrust to control speed? Obviously that works too.
When you are flying a coupled ILS, the autopilot pitch and roll servos are driving the ailerons and the elevator to maintain the localiser+glideslope. The pitch trim servo is concurrently trimming out the elevator trim tab so as to minimise the pitch servo torque. And the yaw damper is also doing its own thing with the rudder...
The autopilot doesn't care what speed you are doing. It will drive the control surfaces purely to maintain the LOC+GS. You don't have an autothrottle...
This brings many gotchas e.g. it is easy to end up on the back of the curve and then you may not have enough power to recover while maintaining the glideslope. Turkish 737 in Amsterdam... Thompson did it with a 757 at Bournemouth but they got away with it.
You get funny things happening when on autopilot e.g. you are flying along and suddenly your airspeed has shot up. But your altitude is constant (obviously). This is because you are in an updraught, so the AP pitches down to maintain altitude, so the airspeed goes up as a consequence. Or the reverse, in a downdraught.
But I am sure you know all this. The autopilot scenario is a total redherring.
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In a 152, which the OP seems to be flying, there's nothing wrong with "point and power". All you have to do is aim at the runway, and the ASI tells you what to do with the power.
On the other hand, on a nice calm day, it's quite satisfying to be able to set one power setting, or no power at all, and make it all the way down only using flaps and attitude to control the speed. As long as you meet Vref, it's all good.
On the other hand, on a nice calm day, it's quite satisfying to be able to set one power setting, or no power at all, and make it all the way down only using flaps and attitude to control the speed. As long as you meet Vref, it's all good.
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But I am sure you know all this. The autopilot scenario is a total redherring.
Its funny how I am totally agreeing! but not if you get my Gist! Yes I do know that
But dont agree the autopilot is a red herring.It shows that in descent pitch for descent rate power for speed works I would even go as far as stating that in some aircraft pitch for climb! power for speed works too!
In another situation such as a high AOA you may need not only pitch but power too to save the day! What is your stall recovery? pitch alone?
Ie it just confirms that my argument that neither method pitch for speed or power for speed is right and I hold that you are asking for trouble following one method.
It has to be pitch for energy power for energy and both are so linked that you cannot divorce them. It should be a skillful blend of the two!!!
Pace
Last edited by Pace; 9th May 2012 at 22:25.
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I think the OP would be best advised to listen to his instructor! Sorry EGKB but you are demonstrating all the signs of " I know best", you will get away with it 999/1000, but that arrogance will see you in a smoking hole one day I'm afraid....you are 17 years old with very,very low hours, listen to the qualified instructor who is teaching you how not to kill yourself or your unfortunate passengers..I am 31, & have held my PPL for 7 years, my instructor was 23, so we are not all old miserable gits!
However, if you carry on as you are...
EGKB, Coming to you via an AAIB report within 5 years, I would put money on it
However, if you carry on as you are...
EGKB, Coming to you via an AAIB report within 5 years, I would put money on it
Last edited by Kengineer-130; 9th May 2012 at 23:05.
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Works great until you accelerate past flap speed and can't slip because you're going too fast. Sometimes you need to get past terrain then descend. Its not a Lear 35
Do they actually allow modern students to do potentially dangerous things like slipping nowadays? Thought the training was all incipient this and that and just aircraft drivers at the end not pilots?
Its ok just stirring
Again! A joke Pace