stick forces-please make them optional

[Echo38]

Going by the bit outlined in yellow, it sounds like the pedals do not move throughout the maneuver, because the pilot is holding them in a single position. Keeping a roll coordinated involves moving the pedals at different points in the roll, even at a constant stick deflection, because of gravity.

[Yo-Yo]

Going by the bit outlined in yellow, it sounds like the pedals do not move throughout the maneuver, because the pilot is holding them in a single position. Keeping a roll coordinated involves moving the pedals at different points in the roll, even at a constant stick deflection, because of gravity.

 

Yes, you are right. Coordinated in this case means that the rudder must be triimmed for centered ball, fixed in this position and then the stick is deflected to the predetermined position (Germans used a chain to limit its movement). Moreover, the roll rate was measured for its highest value, so the overall bank was not more than 100-120 degrees, as far as I remember. And moreover - at least Germans extrapolated roll rate to its highest value to eliminate sideslip effects.

The reason is to get more or less pure spiral coefficient that is the function of ailerons.

Edited March 3, 2015 by Yo-Yo

[PhoenixBvo]

Yep!

 

Rudder "fixed" at the trim point simply means the pilot keeps the roll coordinated with his foot.

 

Crumpp, just drop it please. As a flight dynamics engineer I can confirm that effte, Yo-Yo and Echo38 are right.

 

Fixed controls means that the specific control input is held at a constant position during the maneuver. That is usually the position for trimmed steady-state flight immediately before the start of the maneuver.

[MiloMorai]

Crumpp, just drop it please. As a flight dynamics engineer I can confirm that effte, Yo-Yo and Echo38 are right.

 

Fixed controls means that the specific control input is held at a constant position during the maneuver. That is usually the position for trimmed steady-state flight immediately before the start of the maneuver.

 

Agh, a practicing engineer. :thumbup:

[effte]

Yes...just YES!!

 

You and Yo-Yo are correct from the point of view of the calculator.

 

I am correct from the point of view of the test pilot.

 

While the flight testing I have been involved in has not included the title of 'calculator' in their organisations, I think I can figure out what you're attempting to say.

 

Rest assured you are not correct from the point of view of either position - who, coincidentally, tend to be very much in agreement on exactly how to go about their mutual task.

 

You're approaching this from the point of view of someone who does not appear to be able to understand the meaning of the word 'fixed' in general, and in relation to flight controls and control surfaces in particular. Your example is rather illuminating. Just how do you suppose they'd get meaningful data on dynamic stability if the controls are being moved throughout the test?

 

I suspect this lack of understanding is intentional, to avoid having to go back on previously expressed views or to make performance figures match your perceived take on reality.

 

It is rather annoying, as it decreases the signal to noise ratio of this forum, wastes ED bandwidth and wastes the time of myself and everyone else trying to discuss the matters at hand.

 

Please stop.

 

Regards,

/Fred

[effte]

Agh, a practicing engineer. :thumbup:

 

Two, in the field. One of whom should have read the new posts in the thread prior to posting... ah well! Let's call it emphasis! :pilotfly:

 

Thanks, PhoenixBvo.

[Crumpp]

Just how do you suppose they'd get meaningful data on dynamic stability if the controls are being moved throughout the test?

 

There are not being moved throughout the test. They are held fixed by the pilot. In fact, if I don't have ability to fix the controls in the position I want to make the airplane do what I want....I am not a pilot....I am a passenger.

 

Exactly the way the NACA did it and is in practice today.

 

Force gauges, protractors on the control system, tensiometers on the cables, and standard photographic instruments developed by the NACA. It is exactly what they did. It is standard instruments of the day adopted for their purpose.

 

Gather the data and run it thru the math.

 

Again, that was one of the breakthroughs in Stability and Control engineering that the NACA gets credit for Effte. They did flight measurements or forces, hinge moments with control surface deflection while the aircraft was under the pilot's control.

 

I went to college too for this stuff, too. If you have issues with that fact, PM me and I will put you in touch with the professor and career test pilot that taught the class.

 

Here you can see in the NACA flight testing of the F6F. Rudder fixed, the control surface is deflected by the increase in force and the PILOT compensates.

 

The engineer has all the data he needs, control deflection, force measurement, velocity, etc. to calculate the lateral control characteristics of the design.

 

 

Yo-Yo says:

Germans used a chain to limit its movement

 

I have no doubt it was done this way as well.

 

You can examine typical directional trim curves and deduce that this method will work for a majority of flight conditions as the directional trim is typically speed stable for a good portion of the envelope. It does not work for all of them. The result is the same though as the information needed for the calculator is available.

 

 

 

Again, that is one of the break through in Stability and Control research that the NACA gets credit for...the ability to measure all the important parameters in flight with the pilot at the controls.

[Echo38]

Crumpp, it looks to me that we may be saying the same thing, but two different ways. In which case, I think, the issue stems from your phrase, "fixed by the pilots foot as he puts in the amount of rudder required to keep it trimmed." From what you said in your post immediately preceding this one of mine, it sounds as though you meant what I meant (foot put in one place before the test, for coordinated straight & level flight, and held in that place throughout the test), but, without clarification, it sounded like you meant (by your original phrase) that the foot moves to continually keep the aircraft coordinated throughout the roll (because in order to "keep" coordinated flight during the roll, you have to move the foot). Perhaps this is merely a misunderstanding of phrasing, then, and we're all attempting to describe the same thing?

[PhoenixBvo]

There are not being moved throughout the test. They are held fixed by the pilot.

:doh: So now it turns out there isn't any difference of understanding (anymore)...

 

Case closed.

 

PS All these graph are very nice, but hardly relevant to the OP, that being the model of Bf-109 controls in the DCS simulator environment. Those yellow boxes show a rudder at constant deflection with varying forces acting on it. We all agree that is what happens during such a maneuver with rudder held fixed :) Congratulations:music_whistling:

[Crumpp]

In fact, this is the entire reason for confidence levels in test flying. It tells the engineer how well the pilot flew the profile.

 

I have included chapter 1 of the USN Test pilot manual that explains the confidence level scale.

 

Here is a flight test procedure for determining the stick fixed and stick free nuetral points of any airplane.

 

Here is the instrumentation used to measure the data required:

 

Instrumentation :

Neutral points are determined by measuring the elevator deflection angle Se , airspeed V, stick force FS, or tab angle te.

The airspeed may be obtained from the ASI and correcting the readings using a calibration chart. The elevator angle is measured installing a potentiometer in the elevator torque tube system so that the elevator deflection may be transformed to an electrical signal. The potentiometer is calibrated on the ground by physically measuring the elevator angle with an inclinometer and plotting it against the potentiometer reading.

The stick force may be measured by placing four strain gauges in a bridge circuit on the stick and sealing it off against moisture and dust. The signals are amplified before feeding it to an indicator. Calibration is done by applying known loads to the stick and plotting it against reading.

 

Notice at NO POINT does the test require the pilot to "fix" the stick. He flies to the trim point and data is measured for later reduction by the engineers.

 

Here the flight procedure suggested will enable collection of both the stick fixed and stick free neutral points together.

1. A turbulence free procedure and a stable prescribed altitude is chosen and the airplane trimmed at a suitable speed so that the stick forces, in the entire range of investigation, are within the pilot's control. This speed may be determined by trimming the airplane at some speed and checking for the stick forces by flying at the extreme ends of the range of investigation. Two or three trials should be sufficient to determine a comfortable trim speed. This, however, need not be done if the tab is used to trim the airplane at each speed.

2. The airplane is flown at various speed (and trimmed if t is to be measured) from rear stall t the maximum attainable speed at a chosen altitude. When the speed stablizes the readings from the ASI, elevator potentiometer and the stick forse potentiometer or the trim tab are taken.

3. This procedure is repeated for different power settings, flap deflections and various external configurations to obtain a complete picture of the longitudinal stability of the airplane.

 

http://www.iitk.ac.in/aero/fltlab/stability.html

 

The NACA used similar analog instrumentation..old fashion strain gauges and tensiometers. In fact, I used a 1942 tensiometer to check cable tensions on a Piper Cub as part of my A&P practical test years ago.

 

http://aviationmiscmanuals.tpub.com/TM-1-1500-204-23-9/css/TM-1-1500-204-23-9_124.htm

[Crumpp]

Crumpp, it looks to me that we may be saying the same thing, but two different ways.

 

We are and that is what I said that in the beginning.

 

Crumpp says:

 

Yes...just YES!!

 

You and Yo-Yo are correct from the point of view of the calculator.

 

I am correct from the point of view of the test pilot.

[Crumpp]

it sounds as though you meant what I meant (foot put in one place before the test, for coordinated straight & level flight, and held in that place throughout the test), but, without clarification, it sounded like you meant (by your original phrase) that the foot moves to continually keep the aircraft coordinated throughout the roll (because in order to "keep" coordinated flight during the roll, you have to move the foot). Perhaps this is merely a misunderstanding of phrasing, then, and we're all attempting to describe the same thing?

 

You can see from the trim curves, your foot does not need much if at all depending on the aircraft.

 

If you don't move the elevator that is....

 

In the air, you do coordinated banks or rolls NOT by looking at the inclinometer (ball and fluid filled tube).

 

You do it visually and by feel by noting the position of the nose on the horizon and adding the amount of rudder required to keep the nose at that point as aileron is applied.

 

You keep the nose rotating straight around the longitudinal axis.

 

http://www.langleyflyingschool.com/Images/Flight%20Training%20Manual/Aircraft%20Axis.jpg

[Crumpp]

Oops,

 

 

I forgot to add the USN Test Pilot manual chapter 1 with the confidence scale.

 

So now it turns out there isn't any difference of understanding (anymore)...

 

There never was any misunderstanding of the information or process. Only in the communication of it.

 

For the pilot, stick fixed means hands on the controls...stick free hands off.

 

:thumbup:

 

(because in order to "keep" coordinated flight during the roll, you have to move the foot

 

Depends on what you are measuring. If you are measuring maximum rolling velocity, there is no reason to move it as the roll will remain coordinated until maximum rolling velocity is reached.

 

The NACA testing keeps the rudder fixed in the initial coordinated roll entry that is required for basic roll velocity measurement to determine adverse yaw.

 

Any yaw that develops after the coordinated entry and after maximum roll velocity is attained is a function of the adverse yaw of the aileron design.

 

What will happen if the rudder is not coordinated is the roll rate will slow down because of the sideforce component developing from the adverse yaw. The difference in that rate will give the sideforce component. If the pilot corrected that yaw, roll rate would stay the same.

 

Correcting that would defeat the purpose of measuring adverse yaw.

c1[1].pdf

[Echo38]

For the pilot, stick fixed means hands on the controls...stick free hands off.

 

Argh! So we do have different definitions, after all? Because what the rest of us are saying is that "stick fixed" means that hands are on the controls, holding them in a fixed position throughout the maneuver, i.e. our hands make sure the stick doesn't move from its initial position for the duration of the time in which the stick is said to be "stick fixed."

 

If you are measuring maximum rolling velocity, there is no reason to move it as the roll will remain coordinated until maximum rolling velocity is reached.

 

Okay, start out in straight and level flight, coordinated. Don't touch the throttle, don't move the elevator, don't move the rudder. Simply deflect maximum aileron and hold it there. Elevator and rudder stay where they are, you hold it there with your hand & foot, never mind trim settings.

 

During the roll, three things will happen. At some point, the nose will drop below the horizon and you'll enter a shallow dive, because you were "trimmed" (either by actual trim, or by holding the controls with your hands & feet) for straight and level flight, but then you changed your lift vector's position relative to the gravity vector, effectively reducing your lift vector's ability to cancel out the gravity vector, right?

 

The second part, which is the first of the two relevant parts: as you deflect aileron, adverse yaw causes you to leave the state of being coordinated; you are now in a slip.

 

The third part is, as you roll into different points of the roll manuever, something changes in the forces (TBH, I'm not sure exactly what, but one of the factors is gravity), with the net effect that (in a WWII fighter and modern light aircraft, at least; I don't know if jet fighters are affected by this, as their weight distribution et al. are considerably different) the tail will slip out of coordination, regardless of whether the adverse yaw from deflected aileron was accounted for via rudder (which, in this specific case, recall, it wasn't, so the slip from adverse yaw is added to the slip from the bank angle having changed without being accounted for with rudder).

[Merlin-27]

Argh! So we do have different definitions, after all? Because what the rest of us are saying is that "stick fixed" means that hands are on the controls, holding them in a fixed position throughout the maneuver, i.e. our hands make sure the stick doesn't move from its initial position for the duration of the time in which the stick is said to be "stick fixed."

 

 

I think Crumpp meant...

 

Stick fixed = hands on

Stick free = hands off

 

It threw me off at first too.

[Crumpp]

During the roll, three things will happen. At some point, the nose will drop below the horizon and you'll enter a shallow dive, because you were "trimmed" (either by actual trim, or by holding the controls with your hands & feet) for straight and level flight, but then you changed your lift vector's position relative to the gravity vector, effectively reducing your lift vector's ability to cancel out the gravity vector, right?

 

Rolling is a an energy neutral behavior. Your velocity will not change because of a coordinated roll.

 

At some point....that some point is when maximum roll velocity is attained, then the aircraft will move to maintain that trimmed speed as sideforce from adverse yaw slows the airspeed causing the aircraft to lose altitude to maintain trim speed but the point is not to keep a constant altitude.

 

That has nothing to do with the roll being coordinated up to the point of maximum roll rate and is a function of adverse yaw effects.

 

The third part is, as you roll into different points of the roll manuever, something changes in the forces (TBH, I'm not sure exactly what, but one of the factors is gravity), with the net effect that (in a WWII fighter and modern light aircraft, at least; I don't know if jet fighters are affected by this, as their weight distribution et al. are considerably different) the tail will slip out of coordination, regardless of whether the adverse yaw from deflected aileron was accounted for via rudder (which, in this specific case, recall, it wasn't, so the slip from adverse yaw is added to the slip from the bank angle having changed without being accounted for with rudder).

 

If you are doing an aerobatic slow roll or rolling below maximum velocity, you are correct.

 

We are not doing aerobatics, our pilot is doing test flying.

 

So we do have different definitions, after all?

 

No. Think of what happens in a force reversal.

 

In a force reversal, the stick free neutral point moves ahead of the CG while the stick free neutral point remains behind the CG in a conventional tractor design.

 

The pilot feels the force change as reversal of the control forces. He thinks "dammit" I had to pull back and now I am having to push forward to maintain the same turn!!

 

The airplane still flies where he wants with the stability of stick fixed neutral point location.

 

What happens to the stability if he lets go??

 

It becomes unstable because he is now allowing the controls to float.

[Crumpp]

I think Crumpp meant...

 

Stick fixed = hands on

Stick free = hands off

 

It threw me off at first too.

 

Exactly. You can see that in the illustration of what goes on during a force reversal.

[sport02]

before with ffb joystick this limitation was " automatic " , now we must get used to .

but all people haven't a ffb joystick , and rudder have not ffb and now is also affect .

interresting feature .

[Echo38]

I think Crumpp meant...

 

Stick fixed = hands on

Stick free = hands off

 

There's actually three concepts being discussed, here. They are:

 

"stick fixed," used to mean hands on, but not moving the controls from their position, nor allowing them to move ("definition one");

 

"stick fixed," used to mean hands on, moving the controls to adjust for various phenomena ("definition two");

 

and "stick free," used to mean hands off the controls.

 

And I am thoroughly confused now. Crumpp, when you say "stick fixed," do you mean definition 1 or definition 2?

[Crumpp]

And I am thoroughly confused now. Crumpp, when you say "stick fixed," do you mean definition 1 or definition 2?

 

Why do you see definition 1 and 2 as mutually exclusive? They are not and both represent the pilot holding the controls fixed to make the airplane do what he wants....

 

The only difference is the flight profile he might be expected to fly. That is why you get additional training as a test pilot.

[Flagrum]

Why do you see definition 1 and 2 as mutually exclusive? They are not and both represent the pilot holding the controls fixed to make the airplane do what he wants....

 

The only difference is the flight profile he might be expected to fly. That is why you get additional training as a test pilot.

"not allowing the controls to move" and "moving the controls" ... how on earth can that not be mutually exclusive? The controls either move or they do not move - they can not do both at the same time!?

 

I am getting more and more confused by this thread ... how can one single term mean different things in the same context?

Edited March 4, 2015 by Flagrum