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How do I increase pitch-stability in turns? (C172SP)

L

LOWI

Members +
Hello :)

I'm new here and I'm a student starting training soon, practicing on the Microsoft FSX SP1, no add-ons (I only adapted the C172SP configuration myself a little), running on Windows 7, using the Saitek Flight System Yoke.

I would like to make the Cessna 172SP more stable when turning.
I use it to practice certain maneuvers having nothing but the instruments in view (makeshift IFR so to say).
When I go for a 20° bank, the plane will naturally tend to sink unless I counteract by using the elevator (pulling the yoke) or pitch trim, however, in the exam environment we are only allowed to use the yoke, no trimming.

While this effect is desired of course, I want to make it less prominent, so I was wondering which parameter I have to change in the aircraft.cfg

The RPM for horizontal flight should stay at 2200 RPM, this is a value that we were already given by the instructor. So I am technically not allowed to change throttle while in turn.

I was thinking about changing one of the following paramters:

power_scalar=1.24 //Piston power scalar
thrust_scalar=0.80 //Propeller thrust scalar

but maybe I'm wrong and I need to change one of these:
cruise_lift_scalar = 1.00
oswald_efficiency_factor=0.68 //Measure of lift effeciency of wing


The question is: Will a higher propeller thrust result in a better pitch stability during turns or is it something that depends on the wing geometry itself, however, the IFR simulator the exam will be taken on (a C172R simulator) shows much better pitch stability in turns for some reason...Almost like it has sort of an auto trim function but it has not, I checked.



Thank you very much in advance
 
Last edited:
To answer your question: No, a higher RPM will simply increase the rate of nose down pitch. Get in to the habit of just adding a little power - say 200-300 RPM to assist the turn and ease the amount of yoke required.
Naturally the aircraft nose pitches down in turns and you counteract with yoke only - real world and sim. You don't use trim in the turn until the end of the turn and asses whether you need to because of wind effect on the new heading, etc. Anyway...

First things first, you not going to get a very accurate rendition of the flight dynamics of the Cessna 172 using the default C172 in FS. If you want realism then go for the A2A Cessna 172. Look no further. It's payware.

If you want freeware then give yourself the best chance of getting something approaching reality by downloading this freeware C172 .air file for it.
It's very good and improves the flight dynamics immeasurably. Installation instructions are included and are easy to follow. It says it's for FS2004/fs9 but I can confirm it works just fine with FSX.

It's the 3rd one down in the list and is called: Cessna C172 for FS2004

http://www.realairsimulations.com/list_box.php?page=downloads

Many many people have played with the values you list above but these guys have nailed it - in so far that you can for the default C172. If you're doing real world flying you should think carefully about investing in some payware such as above. It at least will give you the best real world for sim experience particularly with walkarounds, checklists, weights and balances, systems modelling, procedures, as well as flight dynamics.
I fly a Piper Cherokee real world and the Cherokee 180 modelled by A2A is very very close to how things feel in the cockpit of the real thing.

The other thing to say is if you fly real world you'll know that the numbers are there as a guide not a list of requirements to be followed to the letter. Sometimes, in a turn you might get a gust of wind that will lift the nose out of its nose down pitch - effectively doing the job on the yoke for you. # lazy pilot :encouragement:
 
Ah yes, just downloaded it and gave it a try, very very nice and smooth handling, I love it, feels even closer to our IFR simulator, with only the minor difference that the C172R in our simulator maintains its bank angle, so it doesn't yaw out of the bank by itself. However, from what I've heard this is a setting they have to help us focus on heading, pitch and airspeed as well as the clock first. (we do get instructions such as "climb for 10 seconds, then immediately turn 45° left, then maintain climb for 5 seconds...etc.)

I might take a look into the A2A C172 as well, however, considering that I will soon be able to start flying on a real one I'm not sure if it's necessary if I get along with the freeware C172 :)

So far, thanks for your help, I will keep you updated in case I will stumble upon new things or tweaks.
 
What are you using - Redbird?

I fly real world and I find the Cherokee from A2A along with Orbx regional England to be most useful for practice flights VFR. The A2A will allow you to do EVERYTHING by the book. Take a look at their site. The more Procedure training you do - sim or real world - the more embedded will your knowledge and procedures become. (And the sim doesn't cost £150/ hour!):encouragement:

Good luck with everything.

Jim
 
You're really addressing elevator effectiveness (sensitivity) versus pitch stability with angle of attack change.

I suggest you play with elevator effectiveness in small increments using the [flight_tuning] section of the aircraft.cfg file.

Also, practice scanning the VSI in turns, making smooth small pitch corrections to play the altimeter and VSI to hold altitude. However, many FS airplanes have overly sensitive VSIs caused by a poorly set [pitot_static] section. An entry may exist, or can be added to that section:

vertical_speed_time_constant=1.0 The time constant can be increased or decreased to change the damping, or "lag" of the VSI. A VSI should show a somewhat gradual, predictable rate of movement. Airplanes, like any physical object, cannot instantaneously accelerate upward or downward at a high rate unless impacted by a drastic change in force. Normal maneuvering does not cause such dramatic changes.
 
Ganter said:
You don't use trim in the turn until the end of the turn and asses whether you need to because of wind effect on the new heading, etc.
Click to expand...
? Wind has absolutely zero effect on the plane when turning. It makes no difference at all if you turn into a head or tailwind!
 
What's really called for are changes to the airfile which counter the nose-down attitude during a turn/bank. You want the bank to make the turn while maintaining attitude and altitude as you pull back on the stick.

I live under one of the approaches to Hollywood Ft. Lauderdale Int'l and observe the Boeings and Airbuses coming in from all different directions. What I find most interesting is watching that bank they make when turning towards final, and how easily those aircraft change heading without losing any altitude. What is really amazing is how fast they make that turn. I think this is one of the most challenging and difficult settings to get right when creating sim flight dynamics. You're trying to get the aircraft to maintain a slight nose up attitude so that the bank rapidly brings the nose around while maintaining a near level attitude. Fun in the sim! Guess that's why flight dynamics guys make the big bucks...not really. :biggrin-new:
 
If I understand the opening post you haven't started your flight training yet.

The forces acting on an aircraft in flight are some of the basics your instructor will cover in your first few lessons.

But to answer your questions about turning, what you're trying to overcome are the natural effects of an aircraft in banked and turning flight.

This extract is from the New Zealand CAA Flight Instructors manual .....



Lift Vector
It is very important that the student understands
that in order to turn the aeroplane an acceleration
towards the centre of the turn must be provided.
This is done by banking the aeroplane with aileron.
Breaking lift down into its two components
shows that it is the horizontal component of lift
(centripetal force) that provides this acceleration
towards the centre of the turn.

With the lift vector inclined, the vertical component
of lift no longer supports the aeroplane’s
weight. To maintain a constant altitude or height,
the total lift vector must be increased so that the
vertical component now equals the weight.
The appropriate amount of backpressure on the
control column achieves this.

Figure 1a
Figure 1b

Of the options available for increasing lift,
changing the angle of attack is the most practical.
Any increase in lift will produce a corresponding
increase in drag, and therefore, a reduction in
airspeed. In the medium level turn, the lift and
drag increases are very slight and the decrease
in airspeed is minor – only subtle elevator
application may be necessary.

Adverse Yaw
From the Effects of Controls lesson, the
student knows that ailerons are used to bank
an aeroplane, and this is achieved by changing
the shape (camber) of the wing, which in turn
changes the lift on that wing. In order to bank
right, for example, the left (or up-going) wing
has more lift and the right (or down going)
wing has less lift.

One of the side-effects of increasing lift is a
corresponding increase in drag. So even though
there is more lift on the up-going wing, and the
aeroplane rolls, there is also more drag on that
wing, and that produces a yaw, away from the
direction of the turn – termed adverse yaw.

To overcome this effect and to achieve balanced
flight, rudder pressure is applied in the direction
of turn, while the ailerons are being moved.
Once the required bank angle is achieved, and
the ailerons centralised, the rudder pressure can
be reduced to maintain balance.

The amount of rudder required to overcome
adverse yaw is dependent on the rate of roll,
for example, during a rapid roll more rudder will
be needed than at lower rates. The benefits of
differential and frise ailerons may be discussed.

Overbanking
Overbanking is the tendency of an aeroplane to
want to continue the roll into the turn, or increase
the bank angle of its own accord.
In a level turn, the outside wingtip travels further,
and therefore faster, than the inside wingtip.
This increase in airspeed results in an increase
in lift, which produces a tendency to roll into the
turn. Even though this effect is minimal in small
training aeroplanes, there will be a tendency
for the aeroplane to increase its angle of bank
if uncorrected.

For the purpose of this briefing, the increased
tendency to overbank in both medium level turns
and in climbing turns is caused by the outer wing
travelling faster than the inner wing, thereby
producing more lift and causing the aeroplane to
increase the bank angle. Emphasis must be placed
on negating these tendencies by maintaining the
required angle of bank with aileron, commonly
referred to as holding off bank.
 

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>....what you're trying to overcome are the natural effects of an aircraft in banked and turning flight

And that's the reason why there's basically nothing in the air or cfg file which can reduce this natural effect.....(apart from certain FBW equipped planes)

>One of the side-effects of increasing lift is acorresponding increase in drag. So even though there is more lift on the up-going wing, and the aeroplane rolls, there is also more drag on that
wing, and that produces a yaw, away from the direction of the turn – termed adverse yaw.

This effect can be minimized by the use of differential ailerons and/or roll spoilers

>Overbanking is the tendency of an aeroplane to want to continue the roll into the turn, or increase the bank angle of its own accord.

Spiral stability can be controlled by careful airplane design. Most airplanes do have a neutral or even positive spiral stability at least up to 30° bank.
 
bbrz said:
? Wind has absolutely zero effect on the plane when turning. It makes no difference at all if you turn into a head or tailwind!
Click to expand...

Quite right bbrz - thanks. I was referring to gusty or sheer conditions met after the turn, etc. but yep, zero effect on the plane in the turn.
Cheers:encouragement:
 
Sorry guys, I was not at home since Sunday.

Thank you so much for your advice, yes, indeed I haven't started flight training yet, and yes, I do understand that the nose-down-tendency is a natural one due to aerodynamics.

I am very content with the Real Air C172 so far, let's see how I will perform in the simulator soon.

I'll keep you updated!
 
LOWI If I may offer you some good advice re your pilot training and using flight sim.

I would strongly recommend you get used to looking out the window first, see what attitudes look like, straight and level, climbing descending and turns, 15 degrees and 30 degrees maximum for the time being. You must get a handle on the fact that flying an aeroplane well depends upon setting a correct attitude and TRIM TRIM TRIM, in other words every time you change the attitude and or power you need to retrim the aeroplane, no matter when, no matter what. Forget about adverse yaw etc, these are secondary effects of controls that most aeroplanes do not have as they were designed out.

The key to understand how to fly and aeroplane well is the basic formula that: ATTITUDE+POWER=PERFORMANCE.

I cannot give you any further tips but avoid trying to fly on instruments to begin with as instruments in real life suffer from lag and errors etc and if you do not learn to fly a proper visual attitude you will spend your time with your head in the cockpit chasing instruments.

Trust me I was a Military QFI (RAAF) and Check and Training Captain (Multi-Engine and IFR) for over 25 years and I am gently trying to point out use the sim by all means to have a look at what it is all about, but I would not like to see you get into bad habits as it will frustrate you and cost you later on.

All the best.
 
There is also the response to air turbulence that is not apparent in flight sims, one is always correcting for pitch & roll, thats what the joystick is for, unless of course one is lazy & sets it to autopilot!
Keith
 
What you are describing is a desire to change the stability of your aircraft. This is inherent in the design of any plane. My advice to you and any student pilot. Don't try and change the plane. Learn to fly it.

Trim the plane for level flight PRIOR to entering the turn. Then you won't have to fight it as much. The point is to learn to fly the airplane, and not the other way around. The first rule of learning is paraphrasing here: what's learned first, is learned best. Meaning if you practice something incorrectly from the start, you will develop a habit and need to work harder to overcome it than had you learned it correctly the first way.

Some additional advice to you, if you are actually a student pilot, is this: Fly the REAL plane. Anything you do in the simulator, without an IP present to inform you of what you are doing wrong or potential bad habits is going to hinder and not help you along the way. Until you've got your ticket in hand, or are 100% sure you are flying a particular maneuver correctly, the desktop simulator is a tricky proposition. You need to be able to take what it does well, and apply that to your learning, but understand what it's limitations and failures are in order to really use it as a tool. Which is why Simulators are good, but almost always accompanied by an instructor.
 
Good points by Bendflyer.

I never liked the terms "push" and "pull" for control movements - normally, a trimmed airplane only needs subtle guidance and small, smooth control inputs for flying, much like driving a car. Pulling G, engine out, etc are obviously a different matter, but in general, you do nut have to muscle an airplane around if you TRIM -TRIM - TRIM! Every attitude, configuration or power change requires retrimming. The airplane's stability is based on it's wanting to re-establish it's trimmed condition if disturbed from its trimmed speed in it's CURRENT CONFIGURATION. You do not, let's say, trim to hold altitude, you trim to hold that cruise IAS you establish in level flight. Then, if disturbed, the airplane, and what you sense in your hand, is the airplane trying to reseek it's trimmed speed by climbing or descending.

Career Naval Aviator
Flight Instructor (USN / FAA)
USN Test pilot
 
When you simply use ailerons to turn, the nose often doesn't want to track with the turn (adverse yaw) so apply rudder to get the nose going (enough to center the ball on the turn indicator. With the wings banked, there's a loss of lift so apply back pressure (elevators) to keep the nose on the horizon. This back pressure with no addition of power will cause a loss of airspeed, so apply some additional power. The plane will seem most stable at 30 deg of bank. So ailerons to 30 deg - simultaneous rudder input to center the ball - back pressure to maintain altitude and power to maintain airspeed. Becomes second nature.
 
I'm having a hard time believing your NOT allowed to trim during the exam!?? That sounds incorrect to me. If anything trimming should be an integral part of how you hand fly an airplane.
 
LOWI –

First, best of luck in getting started on your RW flight instruction. There’s a great community out there with a lot of knowledge, help and encouragement ready to step in. I don’t post here often, but the subject holds much interest for me.

As far as my two cents respecting the software/hardware discussions:

1. As far as tweaking pitch stability/response, I think most would agree that most models are pretty decent but there are many that could benefit from some modifications because they are too twitchy, too ponderous, too whatever. The FSX default aircraft are a good case in point which, in my view, are largely too sensitive in pitch (and some other axes) which results in a lot of unrealistic bobbing up and down, etc. None of that response nonsense is conducive to developing good habits if trying to use FSX simulation as a learning tool. For any given aircraft/publisher there are plenty of suggestions out there to tweak things in the aircraft files to iron out the wrinkles. Others are much more knowledgeable than I am on this topic, so I won’t offer any particular advise other than it’s well worth a search and a look. If you end up staying with the FSX default aircraft, there is a zip file out there with replacement files for the default aircraft you might be interested in. I don’t think I have it any more, but you can try Googling “Metzgergva” and maybe it’s still floating around out there.

2. I fly with a Saitek yoke (Pro Flight). I’m not sure that’s the same as the Saitek Flight System Yoke you reference above. If we’re talking about the same yoke, that could be a big part of any struggle with pitch commands. The Saitek has a very pronounced mechanical pitch detent that makes applying smooth back pressure (or forward pressure for that matter) difficult to achieve and a challenge. The result is a tendency to overshoot the desired pitch attitude when too much backpressure has to be applied just to overcome the detent. There is a hack out there that overrides the detent mechanism and reconfigures the centering springs. I have watched the YouTube and even bought a junker Saitek yoke off eBay to try the hack, but haven’t gotten around to it. On balance I think it would be worth a try, assuming you don’t care that you void your warranty (at a minimum) or , at worst, are OK with the possibility that you might brick your yoke.

To weigh in on some of the practical pointers:

1. I agree with 000rick000, Mike71, etc., that getting the aircraft properly configured and trimmed is a habit that cannot be stressed enough. However, trimming out the backpressure in a turn is unnecessary and bad form since the turn is only a transitory state. Maybe some will disagree with that, but that’s how I was taught and, in turn, that’s how I taught. I think this might be what the Exam "no trimming" is in reference to.

2. I like the NZ CAA manual excerpt that PeteHam posted. I think it’s all good stuff, including the explanation of the need for backpressure and the accompanying graphic in Figure 1b. To a greater or lesser degree most of this is realistically simulated in FSX.

3. I agree with BendyFlyer that, at this stage of your training, you’ll need to develop the habit of flying the aircraft based on external references, e.g., the horizon, and the feel of the controls. In the beginning this is easier said than done, as most students have a tendency to fixate on the panel in front of them and end up chasing needles and the attitude indicator. Those internal references have their place, it’s just that it’s not at this phase of your training.

4. I will have to disagree with BendyFlyer on one point. I won’t speak to military aircraft (which may very well deal with adverse yaw through more sophisticated engineering), but most, if not all, GA aircraft require some rudder to overcome the adverse yaw that occurs whenever the ailerons are deflected. In the context of your original question, a little rudder will be needed when entering the turn (easing up once the proper bank is established) and again, but this time in the opposite direction, when banking out of the turn when returning to wings level.

Tom
 
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