# Questioning the Accuracy of the VSI and Turn Coordinator in the Cessna 172

I was trying out the Cessna 172 with the Steam Gauge and I had a few questions regarding the accuracy of the VSI and Turn Coordinator in Infinite Flight compared to real life. I currently believe they are not accurately represented in IF, but I am not 100% sure, I would love to hear from people to gain further insight. Here’s why I believe they are inaccurate:

# 1. The Vertical Speed Indicator: In real life, it has a delay, but in Infinite Flight there seems to be almost no delay (seems negligible in IF).

Here is the FAA source I will be using throughout this post: https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/phak/media/10_phak_ch8.pdf

From the FAA source: “If the pitch attitude is held constant, the needle stabilizes after a short period (6–9 seconds) and indicates the rate of climb in hundreds of fpm. The time period from the initial change in the rate of climb, until the VSI displays an accurate indication of the new rate, is called the lag”

In Infinite Flight though, there is almost no lag for the needle to reflect an accurate vertical speed.

# 2. The turn coordinator, specifically, the inclinometer, has 2 things that seem inaccurate

First, according to the inclinometer, I always seem to be in a skidding turn. I don’t feel like this makes sense because I’m not apply any rudder, and I thought it would only be doing that if I’m applying too much rudder.

From the same FAA source above: “If inadequate right rudder is applied in a right turn, a slip results. Too much right rudder causes the aircraft to skid through the turn. Centering the ball results in a coordinated turn.”

Second, it seems impossible to center the ball while turning, even if I’m using rudder; the rudder doesn’t seem to meaningfully change it.

Example: If I banked 30 degrees to the right (if I was turning left, left leaning tendencies could apply more which would make it possible that I might need to use right rudder while turning left depending on the situation, but here I am doing a right turn), I would think that I would need some right rudder to keep the turn coordinated.

While using no rudder, the ball goes to the left even though I would expect to turn right (and I’m supposed to use rudder depending on the direction of the ball) but still, no matter which direction I apply rudder, left or right, the ball doesn’t center while turning.

Specifically, I’m trying to do a coordinated turn (meaning the ball should be approximately in the middle).

From the same FAA source above: “To center the ball, apply rudder pressure on the side to which the ball is deflected. Use the simple rule, ‘step on the ball,’ to remember which rudder pedal to press. If aileron and rudder are coordinated during a turn, the ball remains centered in the tube. If aerodynamic forces are unbalanced, the ball moves away from the center of the tube.”

Although I am not 100% sure because I could be doing something incorrectly, at the moment I believe these are not accurately represented in IF, but I would love to hear from people to gain further insight. Let me know if any videos or pictures are need to show what I’m describing above. You can also try it out for yourself to see what results you get.

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I think you’re right on both of these. We could probably argue just how important the delay in the VSI is… but the skid/slip indicator definitely doesn’t match IRL behavior.

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Yep also I haven’t noticed the left turning tendency in IF that I notice IRL especially when taking off

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Speaking about the turn coordinator, i remembered an observation that a colleague made that the rudder in IF does not have much effect, it seems like it should make the airplane turn, but in almost all aircraft in IF (XCub and TBM don’t have this problem from what I’ve noticed) it just “bends” the airplane, without change the path…
An example of this is that on the C172 I was unable to follow the wing low method when I was practicing crosswind landings a few weeks ago, because with ailerons to the right and even with a lot of rudder to the left (crosswind from right), the plane kept turning.

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true, in IF I think it only occurs on the ground at high speeds

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Agreed, the delay in the VSI isn’t as important, but it would be a nice touch of realism. I hope these are reported internally, so that there is at least a chance that changes/fixes can be implemented at some point in the future.

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Interestingly, though the ball is not centered when you switch to HUD view, the FPV appears to always be centered (with wind set to zero). The FPV should be showing a slip, skid, or centered (from left to right) as well as does the turn coordinator.

It always appears coordinated, unless you purposely do a skid or slip by cross controlling aileron and rudder.

For the vsi, I never notice this because it is a secondary reading. You target vsi indirectly rather than flying the vsi needle.

Try the following:

With a crosswind, fly toward a runway lined up with and above the centerline. Keep wings level and keep the aircraft nose pointed to the end of the runway with rudder only. You’ll see the flight path vector is pushed to the side due to the wind.

You will drift to the direction the FPV is pushed. The only way to stop this is to bank slightly against the wind drift.

The purpose of the level wing exercise is to show that the bank does have an effect in counteracting the side drift.

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Great points! I was thinking you would reply sooner or later since you love these topics and always bring up some very interesting points.

Interesting, they are contradicting each other; hopefully IF nails downs these inaccuracies sooner or later

Agreed; I just started flight training a few weeks ago and I was over-relying on it, and when I realized IRL that it’s delayed it really made me more conscious to not use it much, especially to keep straight and level flight (since that’s mainly done by looking outside, though the artificial horizon & altimeter also help; the VSI often threw me off cause of the delay so it’s not that helpful). So it’s just a little thing I noticed, it’s not major

Thanks for the insight!

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Best of luck with that, what an adventure!

The VSI is of course definitely useful too.

If you assume you are trimmed in a steady pitch up attitude climb with constant power, and the VSI reading is much less than you expected, that’s a message to find out why.

In general, as you descend or climb, with attitude and power, where the VSI tends to hang out as it stabilizes gives you feedback on the adequacy of those attitude and power adjustments.

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I started doing it like this, after trying the wing low method and it didn’t work (it’s the crab method, isn’t it?)

It’s definitely hard to clearly identify, because the control movements are so subtle. The difference between over and under control (the bank angle, especially as the FPV seems very sensitive to movement while you’re trying to get the bank right) is quite small.

I guessed maybe one reason it seems so sensitive for me might have something to do with my device having a bit lower frame rates (not completely sure though).

No, in a crab you are not cross controlling rudder and ailerons, such as would happen in the case you described:

The differences (the first two are to counter-act crosswinds):
1)Crab: fly with controls as usual but keep nose aim upwind enough to track runway centerline (so, heading not aligned with the runway, to keep course aligned with runway)
2)Side-slip: cross contolled rudder and aileron, to keep both heading and course aligned with runway (wing low method)
3)Forward-slip: used without a crosswind to add drag to increase descent rate; heading not aligned with runway, to keep course aligned with runway in the absence of wind (your wing will also be low for this).

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Got it, thanks a lot for the explanations! soon I will make a topic about my doubt about the wing low method on the C172 so as not to deviate from the subject of this one, I take the opportunity and record a video trying to execute it…

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That sounds like a good idea. Hopefully others can shed some useful light on what they do. I think I kind of get where you’re coming from. Maybe I’m wrong though.

I’ll just say that the reason for the low wing is that you are directly pointing a portion of your lift from straight up, to upwind (sideways) to counteract the force of the wind trying to blow you off track.

In theory that’s the only way you can keep aligned with the runway in both heading and ground track, with the wind forcing against you sideways (horizontal lift = crosswind force).

So to see this when we fly, there would presumably be some visual sensation that the low wing is actually working against the side drift.

edit: a direct 20kt crosswind will move you a runway width to the side:

1. 60 ft runway (18.3 meters), in about 2 seconds
2. 200 ft runway (61 meters), in about 6 seconds
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