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Von Target

AirfoilLabs C172...

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At another thread someone mentioned some open problems with this add-on.

 

I own the C172, and updated it to the latest version.

 

Overall I find it amusing, but there are some notorious glitches in some aspects of flight behaviour, such as the oerbanking tendency when even a mild bank is set, returning the yoke to neutral, at any power settings, turning by the left or by the right.

 

The real C172s are, just as most GA aircraft, roll stable up to a significant amount of bank. For bank angles above 30º ( 45º) opposite aileron is required to counter overbanking, specially if turning through the left, but not at a mild 10º or even 20º bank angle, where the aircraft will tend to return to wings level, specially if turning through the right and with mid to high power settings ( due to prop effects ).

 

In the AirfoilLabs C172, no matter what bank angle and or power / picth settings you start from, the aircraft will always overbank, towards a spiral dive if left at it's own will.

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Not to bash, but weird conclusions. What are you basing your observations on? Do you know which engine is moddeled in airfoillabs? Do you know the difference in actual fligh behaviour between 160 and 180 horsepower engines on 172s? between different power settings? Do you take trimming settings into account? Speed?

 

I am all for analyzing things, as long as there is some substance to it. Here you make a general statement on something and say it's wrong without actually saying anything. 

 

I know it sound stupid, but give me few weeks and I will get you a video where I get a 172 into spiral from 15 degree left bank.

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Lena, I just hope you don't get hurt!  Spiral dives can be dangerous!  Take care!

 

Joke aside - it's basic flight dynamics, and, actually, some knowledge of how various models of the C172 actually fly ...

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Lena, I just hope you don't get hurt!  Spiral dives can be dangerous!  Take care!

 

Well, entering and recovering from them is a part of every basic training.

I mean, if you gave me a specific situation that you think is wrong and why, then we can discuss it at least. Saying your whole point relies on having "some knowledge about it" is a bit non-substantial.  

I guess, or hope, that you made this thread to actually spark such discussion. 

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I guess you guessed right... But, I also though what I wrote was clear - namely, that, at any speed, load ( leaving out asymmetric fuel and payload situations ), power settings, trim settings, if, you're flying level, descending, or climbing in this C172 and bank either right, or left, not more than 10º ( first mark ).

 

Return the yoke to neutral...

 

Observe what happens to your bank angle. You can either pull the yoke to avoid diving and gaining speed or simply leave the controls, and you can coordinate or not with rudder ( * ). Whatever you do, and that's the problem, overbanking will be the end result.

 

That's what is wrong.

 

Why? Well I am not going to start here a "Principles of Flight" or "Roll Stability" thread, because my point was exactly to point out that something is obviously wrong with the roll stability in this C172 FDM.

 

( * ) Although my point refers to sideslip situations. In my glider most of the time I use a lot of outside/ opposite stick at 45+º bank angles in coordinated tursn, but that's another story - coordinated turn in a glider, at high bank angles...

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The real C172s are, just as most GA aircraft, roll stable up to a significant amount of bank.

 

Apparently, the C172 and many GA singles have a slightly unstable spiral mode.

 

From "Airplane Flight Dynamics and Automatic Flight Controls - Jan Roskam":

 

ByHCwfX.jpg

 

1o4ugX9.jpg

sLwqmHd.jpg

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Going back to what I remember about 172s.

 

Mild roll, and the plane returns to neutral. My Vans RV6, just stayed where you let go of the aileron. It was quite different from the Cessnas. More along the lines of aerobatic low & mid wings.  As to how long the RV stayed there, I don't remember. Never went to the point of testing it.

Another item I tried in the Cessna 172 for flight sim purposes years ago, was to quickly roll the yoke & then let go. The plane would quickly roll back to neutral & past it. Then it would level out. I don't remember any sim models doing the same.  For the Piper low wings; after a certain point of roll, it could tighten up to a steeper bank.

 

Now...............as to how I feel about real life, and the exact modeling, I could care less. Too many planes were different to make assumptions that apply in the majority of cases.  I never entertained the idea of using a sim model to predict what the real plane would actually do. I also never compared the actual  movement of the yoke or stick, to the real thing (arc wise dimensions). My objective with a desktop yoke or stick, is just to get the plane to do what I want.  I don't think in terms of rotating the yoke a quarter circle, or whatever. 

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Yes, modern Cessnas and especially the "S" model are used in many flight schools and known for good stability and even pretty much feet on floor, just like many GA, even if this characteristics actually tends to be associated with higher overbanking tendency ( use of ailerons and differential deflection and aileron frise hinges ).

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Sorry to ask this silly question here , but how does the default 172 compare ? I don't own the airfoillabs 172.

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Apparently, the C172 and many GA singles have a slightly unstable spiral mode.

 

From "Airplane Flight Dynamics and Automatic Flight Controls - Jan Roskam":

 

ByHCwfX.jpg

 

1o4ugX9.jpg

sLwqmHd.jpg

 

 

Missed this one Murmur... Will have a look at it. Thx! Reading through it will help - I also have this one :-) 

 

Larry, thx also for the personal experience notes on the real C172.

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When I read this thread I feel like -

 

"Gee wow... I like the planes that go ZOOOOOMMMM.  They are NEAT."

 

Just like my four year old boy does. :smile: 

 

Kidding, but only sort of. I understand the above, but my passion in regards to aviation has always been more about the history, design, and operation of the equipment itself. I appreciate the fact that mathematics and physics, or rather, our quest to understand and overcome the limits imposed by mathematics and physics, has been a primary factor in the evolution of aeronautical design, but I've never really had the desire to actually interpret anything beyond the type of pilot report that Larry gave above.

 

For example, I enjoy reading about how undesirable flight characteristics in a given aircraft caused engineers to make changes to try and remove those characteristics, which in turn may of had other effects and forced other design changes in turn, but that's as far down the rabbit hole as I ever care to go. :smile:

 

I always find it fascinating however, that there are so many different facets to this 'hobby' that people can enjoy.

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I don't like the formulas either... they're a rather formal way of expressing sometimes very intuitive / common-sense interpretations of complex systems...

 

Of course, it's good to have a formal language to express it, and in the field I work in IRL it is actually very important, but I guess most of the 

excellent ideas that ended up in solutions for many engineering problems in aviation, mostly during war time, but also in many other fields, started from rather intuitive / common sense interpretations of the causes ... 

 

There are things I've long learned when I started to fly many years ago, and could only understand in terms of aerodynamics decades after... 

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I have about 200 hours in the C172S. For reasons that I will never understand, the real a/c has the issue that it is more stable in nose up/down pitch and less stable in the bank attitude than any of the sims that I have flown since 1994, including all of the FS versions, XP, and even the ASA instrument sims. And the same applies to the Fresca sim that the flying club owns. Must be a feature of a software model rather than the real aerodynamic thing.

 

With that said, I agree with the OP that any bank in the real thing, less than 25 degrees, will return to approximately level. That is, a sudden bank change (less then 25 degrees) will result in a rather quick return to level flight. Its's the gradual change in bank over time that makes it susceptible to graveyard spirals.

 

The real thing is extremely stable in nose up/down pitch, unlike almost any simulation. I often think that sims must put people off ever wanting to learn to fly when managing nose up/down pitch.....

 

Can't comment on the AirFoilLabs model- I have it but haven't had any time to even open it let alone fly it....

 

Thanks, Bruce.

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The real thing is extremely stable in nose up/down pitch, unlike almost any simulation. I often think that sims must put people off ever wanting to learn to fly when managing nose up/down pitch.....

 

 

 

This is due cheap desktop grade controls in my opinion.

 

THE REAL THING:

1. The real aircraft has a 14 or 16" pitch travel on the yoke, you have TONS of granularity to control/maintain the pitch.

2. The real aircraft also restricts your inputs due to the airflow forces over the surfaces pushing agains you. This makes easier and smoother to apply pressure.

 

THE SIMULATOR:

1. Desktop hardware tend to have a very short 3-5" pitch travel at best, every minuscule movement translates into a lot of input for the aircraft due to conversion/mapping.

2. Desktop hardware yokes does not provide you any feedback, you have not the real airflow surfaces pushing against you leading into too much input too easily unnoticed.

3. Also, cheap potentiometers keeps sending spikes, noise while you use them.

 

I moved to a certified force feedback yoke, real pitch travel length, force feedback pressure based on the aircraft IAS to mimic the real thing. All bumpiness and instabilities for nice pitch control went away.

 

It feels now quite similar to the real thing! It is simply amazing when you are flaring and the stall horn kicks in how the yoke elevator force washes out as the real thing.

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