no bug AH-64 True Airspeed on Up Front Display Incorrect

[Shugsta]

Hi,

I have noticed of late that when I try to hover, the True Airspeed never gets to 0, even when the aircraft is stable.  I landed it and checked, and the True Airspeed showed 15.  I restarted the mission with a hot start and still the True Airspeed shows 15 on the ground.  I went and tried one of the default AH-64 training scenarios and the True Airspeed on the ground started at 0, as expected.  I created a blank mission with just the AH-64 in it, set to hot start; True Airspeed shows 15 on the ground.   I don’t know when precisely this started but started noticing it in the last week.  I am on the current DCS release and ‘witched’ all files before updating.  I don’t have any addons that might influence this.  Bit of a puzzle really.  I also added another AH-64 to my mission file and that behaved the same i.e. True Airspeed shows 15 on the ground.

[Snow-Bird]

What do you mean with Up Front Display?

[Shugsta]

The readout on the front screen, as per the attached image.

[Snow-Bird]

Thats the IHADS. 

Anyway, For me its working just fine, I cant replicate the issue. When exactly does this happen to you?

[Mad_Shell]

1 hour ago, Shugsta said:

Hi,

I have noticed of late that when I try to hover, the True Airspeed never gets to 0, even when the aircraft is stable.  I landed it and checked, and the True Airspeed showed 15.  I restarted the mission with a hot start and still the True Airspeed shows 15 on the ground.  I went and tried one of the default AH-64 training scenarios and the True Airspeed on the ground started at 0, as expected.  I created a blank mission with just the AH-64 in it, set to hot start; True Airspeed shows 15 on the ground.   I don’t know when precisely this started but started noticing it in the last week.  I am on the current DCS release and ‘witched’ all files before updating.  I don’t have any addons that might influence this.  Bit of a puzzle really.  I also added another AH-64 to my mission file and that behaved the same i.e. True Airspeed shows 15 on the ground.

Is there some wind in the mission? If there is a 15 knots wind, then in a hover or on the ground the true air speed is 15 knots.

[Shugsta]

Constantly, in the mission I am working on.  I even removed all triggers and objects, set the aircraft to player role, cold start, add another AH-64 but I still get this issue.  As I mentioned in my original post, Start a new mission or use one of the ED Trg missions and it’s fine.  It’s like the issue is with the mission file but removing everything from the mission file and leaving only the ah-64 in it, it still has a true airspeed of e.g. 15 or 16, even when on the ground and not moving.

 

2 minutes ago, Mad_Shell said:

Is there some wind in the mission? If there is a 15 knots wind, then in a hover or on the ground the true air speed is 15 knots.

There is wind in the mission - hadn’t thought about that.  Will have a look tomorrow and let you know.

[Smashy]

I'm guessing it's wind too.  You can check ground speed by selecting transition symbology.  The TSD is also able to display wind speed and direction, which can be helpful.

[flanker0ne]

@ShugstaThat value represent, as you said, the Airspeed.

The hovering in the Apache, among others helicopters, is mantained with the Doppler system, whose task is to mantain 0 Ground Speed, not 0 Air Speed.

So if there is wind in the mission, you will always have an Airspeed readout different from 0

As a verification of what I said, you can select a waypoint, hovering and read the Ground Speed (toward this waypoint) 0 or a very low value, in the lower left corner of the IHADSS

Edited June 14, 2024 by flanker0ne

[jubuttib]

4 hours ago, Mad_Shell said:

Is there some wind in the mission? If there is a 15 knots wind, then in a hover or on the ground the true air speed is 15 knots.

FWIW, is there a term for wind corrected air speed? I'm thinking kinda like "ground speed", but which would also work in vertical. IAS is instrument indicated, CAS is corrected for positional and instrument errors, TAS is true air speed without correcting for wind, can't think of one that'd be for what I'm talking about...

[bradmick]

12 hours ago, flanker0ne said:

@ShugstaThat value represent, as you said, the Airspeed.

The hovering in the Apache, among others helicopters, is mantained with the Doppler system, whose task is to mantain 0 Ground Speed, not 0 Air Speed.

So if there is wind in the mission, you will always have an Airspeed readout different from 0

As a verification of what I said, you can select a waypoint, hovering and read the Ground Speed (toward this waypoint) 0 or a very low value, in the lower left corner of the IHADSS

 

The INUs provide ground speed data. The doppler does not. 

[Shugsta]

Hi All

15 hours ago, Mad_Shell said:

Is there some wind in the mission? If there is a 15 knots wind, then in a hover or on the ground the true air speed is 15 knots.

Mad_Shell was right.  This was the 1st mission I had created with wind, hence not noticing the effect on True Airspeed, before -  oops!  To be fair though, every demo on hovering I have seen, they reference the TAS and it comes down to zero, so they ain’t using wind.  Anyway; all solved and thanks to all of you for your help replying.

Thanks. Hugh

[mcfleck]

FWIW, is there a term for wind corrected air speed? I'm thinking kinda like "ground speed", but which would also work in vertical. IAS is instrument indicated, CAS is corrected for positional and instrument errors, TAS is true air speed without correcting for wind, can't think of one that'd be for what I'm talking about...

It has been a while and please correct me if I am wrong:
IAS: Indicated Airspeed. Assumes the air is incompressible, temperature and pressure is constant
CAS: Calibrated Airspeed, correct explanation, in modern aircraft with digital instruments you could say CAS is nearly equal to IAS
TAS: True Airspeed, CAS corrected for non standard (ISA) temperature and pressure/altitude. Nothing to do with wind.

The "Airspeed corrected for wind" you are talking about is indeed your Groundspeed.
Hovering at a ground speed of 0kts, your IAS will show you the current wind speed at your nose.
In order to get your vertical speed, you will refer to your vertical speed indicator, which simply visualizes an ambient pressure change and by that directly shows your vertical speed without wind in ft/min.

Wind is just a word for a moving airmass. With an airspeed of 0, you just move with that mass like a hot air balloon. Any other speed means you move relative to said air mass. There are mainly 2 situations where you care about wind: Navigation, as it influences your time enroute and your ground track and being close to the ground like during takeoffs and landings

[jubuttib]

21 hours ago, mcfleck said:

The "Airspeed corrected for wind" you are talking about is indeed your Groundspeed.

Only in the case of moving horizontally AFAIK. Feels weird that there's no ground referenced speed that allows for arbitrary direction of travel...

[bradmick]

On 7/2/2024 at 2:30 PM, jubuttib said:

Only in the case of moving horizontally AFAIK. Feels weird that there's no ground referenced speed that allows for arbitrary direction of travel...

There is, it’s called the velocity vector. It represents 6 knots of ground speed in hover mode symbology and 60 knots of ground speed in transition mode symbology. It’s a literal top down, gods eye view of the helicopters magnitude and direction of travel. The center of the line of sight reticle represents the mast, and serves as the origin of the velocity vector. Its sole purpose in life is to tell the pilot in what direction and how fast they’re moving.

Edited July 3, 2024 by bradmick

[jubuttib]

Well no, the "top down" is already a problem, implying it just shows horizontal speeds.

To be fair this is not related to the Apache directly, I'm just trying to figure out if there's a name for a speed that's basically the 3D equivalent of ground speed. Going 200 kts straight up, away from the ground, would read the same speed as going 200 kts horizontally along the ground, instead of 0 kts like you get with normal ground speed. And of course at any arbitrary heading and climb/dive angle in between.

[mcfleck]

Well no, the "top down" is already a problem, implying it just shows horizontal speeds.
To be fair this is not related to the Apache directly, I'm just trying to figure out if there's a name for a speed that's basically the 3D equivalent of ground speed. Going 200 kts straight up, away from the ground, would read the same speed as going 200 kts horizontally along the ground, instead of 0 kts like you get with normal ground speed. And of course at any arbitrary heading and climb/dive angle in between.

You could calculate that if it is necessary at any given time (V-SlantSpeed = Sqrt(VGroundSpeed^2 + VClimbrate^2). Bare in mind that you would need to convert climbrate from the feet/min to nm/h(kts) first.

But to be honest: I struggle to see any usecase for the "slant speed". The aircrafts computer could do it for you as it has all the data, but I never heard anyone interested in that specific value.

Could you please elaborate what that speed could be used for?

[bradmick]

You also have the flight path vector which tells you this information too…so I fail to see what the issue is. The FPV is available in the transition symbology when The 3D velocity of the helicopter is >5kts

[jaylw314]

On 7/3/2024 at 7:28 PM, jubuttib said:

Well no, the "top down" is already a problem, implying it just shows horizontal speeds.

To be fair this is not related to the Apache directly, I'm just trying to figure out if there's a name for a speed that's basically the 3D equivalent of ground speed. Going 200 kts straight up, away from the ground, would read the same speed as going 200 kts horizontally along the ground, instead of 0 kts like you get with normal ground speed. And of course at any arbitrary heading and climb/dive angle in between.

That's just your vertical velocity off your VVI.  Barometric altitude should not "theoretically" affected by wind, although I suppose practically it could be