Airspeed indicator calibration incorrect under 40ktas

[Tim_Fragmagnet]

I'm going to start this with
yes

I know the airspeed indicator isn't supposed to indicate speed perfectly. There is a degree of error at different speeds.

This is about the module's airspeed indicator not properly following the error the real aircraft has.
I'm going to preface with this, yes, it's a discrepancy of 8 knots, normally it wouldn't be THAT bad.

The problem is that this error is at a true airspeed under 40 knots. While you're trying to land. Where accurate speed monitoring is important.

Here is a profiling of 30-130knots true airspeed.

 

You'll notice at speeds above 40 it's pretty much perfect, completely acceptable. I have ZERO issues with the calibration above 40knots.

But you can see what's happening below 40.
Here are some profilings of 50-30knots true airspeed

 

 

 

 

You can see that there is a very clear pattern of error in our airspeed indicator that the real thing does not follow.

 

This is part of why it hangs under 20 for so long. Another part of why is because the indicator doesn't really start moving until you hit about 25knots TAS. Documented data points toward this likely being inaccurate and 15knots TAS at 0 indicated likely being correct instead.



Here is a chart comparing the current calibration vs the real one








Here is that same chart but with what I suggest as a more reasonable adjustment



This isn't really a critical issue like the performance model or the tail rotor being wrong, but it is an error that could be corrected.

 

The expected IAS reading data were taken from the huey's flight manual. And the charts were taken from the composite blade performance profiling document

Edited March 3, 2023 by Tim_Fragmagnet

[Sandman1330]

This is accurate.

The airspeed indicator is actually inaccurate below 40kts in the real aircraft (and most others).

Below 40kts you shouldn't be looking at your instruments for landing cues, you need to be looking outside.

Edited March 3, 2023 by Sandman1330

[Tim_Fragmagnet]

1 hour ago, Sandman1330 said:

This is accurate.

The airspeed indicator is actually inaccurate below 40kts in the real aircraft (and most others).

Below 40kts you shouldn't be looking at your instruments for landing cues, you need to be looking outside.

 

Read the post again

I directly mention that, yes, the airspeed indicator is SUPPOSED to be inaccurate at low speeds.

However the way ours is implemented isn't inaccurate in the same way that the real one is. Something that we have explicit documented data for.

 

Our indicator starts reading at about 25knots true airspeed and reads 12knots indicated at about 30 knots true
The real indicator starts reading at about 15knots true airspeed and reads 20 knots indicated at about 30 knots true.

[Sandman1330]

Are you seriously worried about such a small discrepancy? You shouldn’t even be looking at it below 40kts. I’d rather the dev team focus on the bigger issues personally.

And 1500hrs flying helicopters has taught me even the real ones don’t adhere to the book numbers that closely.

Edited March 4, 2023 by Sandman1330

[ShuRugal]

On 3/4/2023 at 9:58 AM, Sandman1330 said:

And 1500hrs flying helicopters has taught me even the real ones don’t adhere to the book numbers that closely.

I'd go so far as to say real aircraft ESPECIALLY do not adhere closely to the book numbers, especially near the envelope edges.  

Looking through TM 55-1520-210-10, I can't find a single instance of a procedure calling for an airspeed of below 40 KIAS, and the HV diagram forbids flight at less than 50 KIAS above ground-effect and below traffic-pattern height.  You certainly shouldn't be flying that slow attempting an instrument approach, which is the only scenario i can think of where you'd be flying with your eyes glued to the gauges, especially in a helicopter.