reported DTOT-fed Required speed in HUD might have issues

[Rongor]

R-speed wants me to fly 170 kts, while I am very right on time doing 195 kts.
 

[ASAP]

The R-speed is trying to get you there +- 0 seconds. It's actually telling you that you are going to get there 7 seconds off your DTOT and it it wants you to slow down in order to get back on time. The jet is trying to get you there at exactly 18:26:31, and its 18:13:11 right now with another 13:25 at your current speed. That will put you there at 1826:36. It's also trying to account for winds. Did you adjust to fly the R-speed and see what time it put you over the steerpoint? The single snapshot in time really doesn't provide any information because the jet is doing a lot of math to calculate the R-speed, and it's predictive.

[Rongor]

7 minutes ago, ASAP said:

The R-speed is trying to get you there +- 0 seconds. It's actually telling you that you are going to get there 7 seconds off your DTOT and it it wants you to slow down in order to get back on time. The jet is trying to get you there at exactly 18:26:31, and its 18:13:11 right now with another 13:25 at your current speed. That will put you there at 1826:36. It's also trying to account for winds. Did you adjust to fly the R-speed and see what time it put you over the steerpoint? The single snapshot in time really doesn't provide any information because the jet is doing a lot of math to calculate the R-speed, and it's predictive.

It doesn't really make sense to slow down from 195 to a constant R170 to shave off 7 seconds deviation when I have to go for another 47 NM right?

The reason I was doing 195 kts is that by experimenting for some minutes before taking the screenshot I found out that maintaining this very 195 kts speed kept me on time.

[ASAP]

yeah the computer is predictive, and taking its own internal wind table into account. it is also stupid. It's telling you what you need to fly at to fix that deviation RIGHT NOW. You could dampen out your control input over the course of those 47 NMs to arrive on time.

Did you fly 195 the whole way in? how far off if of the DTOT were you? Unless you flew 15 knots faster than what it calculated whole way and still shacked the TOT I don't see any reason to think the computer was telling you the wrong speeds.

[Rongor]

I think you still don't get it (please don't take it the wrong way, I appreciate you participating here)

Flying the R-speed in the example above wouldn't have prevented arriving 7 seconds late. It would only have gotten me even more late.
The 195 kts did keep me right on time. (7 seconds is nothing at this distance, basically equals right on time). Reducing to R-speed did increase the negative delta rapidly.

Just do the math: 195 : 170 = 1.147
13:25 = 805 seconds

1.147 * 805 seconds = 923 seconds (15:23)

Flying R-speed would have taken me 15 minutes 23 seconds. I would have arrived at 18:28:35, more than 2 minutes after DTOT.


Here is another example which might make it more visible, because two pics this time, I fly constant speed of around 260 keeping the delta at zero, while the R speed tells me to do 233.
1st pic at 43 Nm distance, 2nd at 25 NM distance almost 4 minutes between these pics.
The R-speed doesn't make any sense here.

[Solo_Turk]

I didn't have any problems. If you don't use GMT+0(zulu time), you should . I put wp1 on middle of incirlik 05. Entered 4:55:00 zulu in wp1's dtot and flew what Rspeed was needed and got there on time. I did mistake at the beginning, disregard it(entered time in wp0. I haven't flown a10 for ages )

A10tot.trk Screen_241225_205121.bmp Screen_241225_205044.bmp

[ASAP]

On 12/25/2024 at 10:33 AM, Rongor said:

I think you still don't get it (please don't take it the wrong way, I appreciate you participating here)

Flying the R-speed in the example above wouldn't have prevented arriving 7 seconds late. It would only have gotten me even more late.
The 195 kts did keep me right on time. (7 seconds is nothing at this distance, basically equals right on time). Reducing to R-speed did increase the negative delta rapidly.

Just do the math: 195 : 170 = 1.147
13:25 = 805 seconds

1.147 * 805 seconds = 923 seconds (15:23)

Flying R-speed would have taken me 15 minutes 23 seconds. I would have arrived at 18:28:35, more than 2 minutes after DTOT.


Here is another example which might make it more visible, because two pics this time, I fly constant speed of around 260 keeping the delta at zero, while the R speed tells me to do 233.
1st pic at 43 Nm distance, 2nd at 25 NM distance almost 4 minutes between these pics.
The R-speed doesn't make any sense here.
 

 

Not taking it the wrong way at all, the point of a forum is to discuss the issues.

1) Having the multiple snapshots in time are better, but a trackfile would be ideal.

2) Is it just on this one mission? Or are you seeing consistent issues across multiple missions? I didn't have any issue when I tried hitting a TTT or TOT like what you are seeing.

3) Was this part of a flight plan with a series of TOTs?

4) (I'm guessing the real problem) in mission planning did you specifiy a set speed to fly? It likes to default to a set TAS in the mission planner and then the jet thinks it needs to be flying something stupid regardless of the TOT. (i.e mission planner says the leg needs to be flown at 200KTS TAS so the jet thinks it needs to fly at 170 KTS IAS).

 

[Rongor]

On 12/26/2024 at 10:14 PM, ASAP said:

1) Having the multiple snapshots in time are better, but a trackfile would be ideal. yeah, you know this happens about 30 minutes into the mission so watching a file of this length... I'll consider it

2) Is it just on this one mission? Or are you seeing consistent issues across multiple missions? I didn't have any issue when I tried hitting a TTT or TOT like what you are seeing.
I have this in a campaign mission of Maple Flag's Advanced Training Qualification canpaign, Its the #02 mission (nighttime air to air refueling) and arriving at the specific waypoints on time is mission critical for rendezvous with the tanker. I am currently presenting this very case in the dedicated subforum too:
So at this point it might totally be something in the mission file, only I can't rule out anything yet.

3) Was this part of a flight plan with a series of TOTs? Yes

4) (I'm guessing the real problem) in mission planning did you specifiy a set speed to fly? It likes to default to a set TAS in the mission planner and then the jet thinks it needs to be flying something stupid regardless of the TOT. (i.e mission planner says the leg needs to be flown at 200KTS TAS so the jet thinks it needs to fly at 170 KTS IAS). As above, the DTOTs are from the mission and they don't look unreasonable at all, only the R-speed calculation is obviously failing

 

 

[Strannix]

Hi,

Just my 2 cents. In your exemple, the aircraft ask you to reduce speed to 170 to loose the 7s but 170 is not the speed you will maintain all the remaining leg of your flight.

Don't think you can maintain the same speed for TOT. It's like close formation, you have to compensate your speed quite often because the calculator continuously recalculating. 

 

[Rongor]

On 12/28/2024 at 2:34 PM, Strannix said:

Hi,

Just my 2 cents. In your exemple, the aircraft ask you to reduce speed to 170 to loose the 7s but 170 is not the speed you will maintain all the remaining leg of your flight.

Don't think you can maintain the same speed for TOT. It's like close formation, you have to compensate your speed quite often because the calculator continuously recalculating. 

 

The R-speed didn't change.

And btw -:07 actually means I am already 7 seconds late, so reducing speed further makes no sense.

[Strannix]

Ok my bad.

I just did some test and i think i've got the solution or at least an explanation.

By default the HUD display IAS and the request speed is also an IAS. IAS can't be good for maintaining TOT because it doesn't take into account things like wind and other stuff and the informations are only good at sea level with standard weather.

So, in your exemple, you've got 33kts of wind roughly on your back that make a big difference for TOT and IAS can't deal with that.

Currently,the only solution you have, is to display on HUD or CDU page the Ground Speed that take wind, altitude and pression into account and you're gonna have the good value to follow.

@BIGNEWYAt this time, i pretty sure that IAS can't work for TOT except for low altitude flying with roughly no wind but maybe i'm wrong? TAS doesn't take into account of wind, only altitude and pression and from my test, i've to add the wind to the RTAS to find the good speed. A10C manual is pretty simpliste in term of DTOT explanation and maybe there is some constraints with IAS and TAS?  

 

[Yurgon]

2 hours ago, Strannix said:

At this time, i pretty sure that IAS can't work for TOT except for low altitude flying with roughly no wind but maybe i'm wrong?

The aircraft does have all information needed to calculate the RIAS (required indicated airspeed) and the manual says as much:

Quote

Figure 371. Waypoint Information Page

Once a DTOT is set, you will be provided the required speed you need to fly at to reach the waypoint at the set DTOT.

When the DTOT waypoint is also the steerpoint, you can view the STEER page to view the required airspeed. This is located on the right side of the page and can be displayed  according to airspeed type:

• RIAS. Required Indicated Air Speed.
• RTAS. Required True Air Speed.
• RGS. Required Ground Speed.

By adjusting your airspeed to match this value, you should reach the steerpoint at the desired time.

As I understand it, EGI can calculate the wind at the current altitude by comparing true airspeed and groundspeed, and calculating the required indicated airspeed is then fairly simple math as well.

On 12/23/2024 at 1:34 AM, Rongor said:

R-speed wants me to fly 170 kts, while I am very right on time doing 195 kts.

Can you provide a mission or a track that shows the issue?

[ASAP]

2 hours ago, Strannix said:

Ok my bad.

I just did some test and i think i've got the solution or at least an explanation.

By default the HUD display IAS and the request speed is also an IAS. IAS can't be good for maintaining TOT because it doesn't take into account things like wind and other stuff and the informations are only good at sea level with standard weather.

So, in your exemple, you've got 33kts of wind roughly on your back that make a big difference for TOT and IAS can't deal with that.

Currently,the only solution you have, is to display on HUD or CDU page the Ground Speed that take wind, altitude and pression into account and you're gonna have the good value to follow.

@BIGNEWYAt this time, i pretty sure that IAS can't work for TOT except for low altitude flying with roughly no wind but maybe i'm wrong? TAS doesn't take into account of wind, only altitude and pression and from my test, i've to add the wind to the RTAS to find the good speed. A10C manual is pretty simpliste in term of DTOT explanation and maybe there is some constraints with IAS and TAS?  

 

Not really.

You are correct it is showing Indicated Air Speed.  However the EGI and CADC will take all the other factors you mentioned into account and give the pilot an IAS to hit the TOT without the pilot having to do any other guess work. IAS isn't better or worse than for the task it's just showing the pilot a number that is more useful to him. There are actually 5 speeds, and the EGI and CADC know all of them, it just displays the one to the pilot that is selected (in almost all cases indicated in the HUD.)

   Indicated airspeed > what the gauge in the cockpit is reading (All your ops limits like TO speed, stall speed, L/D max, maneuvering speed, final approach speed, and max air speed are based off of indicated airspeed so the pilot only needs to know one set of numbers and not interpolate based on pressure)

   Calibrated airspeed > IAS adjusted for installation error and other aerodynamic effects around the aircraft effecting the pitot system

   True Airspeed > Calibrated Air speed taking the effects of air pressure into account (Thinner air means you go faster for a given indicated airspeed, A-10's at tactical airspeeds hang out   around 300 knots true even if the best speed you see in the HUD is 210 up above 20K your TAS is much higher). This is also why people tell a flight in the mission planner to fly 200 knots True at 15K feet and they are actually crawling along at a super untactical 170 knots indicated. << Again I think this is probably the source of the issues the OP is having. I bet the flght plan in the mission planner has a specified TAS to fly for a leg which is why the jet thinks it needs to be going 170 KIAS.

   Equivalent airspeed > ... Not really relevant to any conversation about A-10s speeds Its something to do with mach equivalent at ground vs at current pressure/temperature or something A-10s don't fly fast or high enough for this to ever matter (SR71 ops limits were in equivalent speeds)

   Ground speed > True airspeed adjusted for the effects of winds.

What actually matters for the pilot getting to the target on time is Ground Speed. The Jet knows the indicated airspeed, and the ground speed, and the air pressure and temperature and it gonculates all that information to know exactly what speeds you need to fly. The R-speed is showing you required indicated speed, because that the HUD is set to show you. If you change it to show true airspeed the R-speed would show you the required true airspeed to fly to get to the target. If you set HUD to show ground speed the R-speed would show you the required ground speed to fly. They would all be different numbers, but they would all accurately show you the correct speed to fly to get to your target on time.

[Strannix]

So, I can confirm what Rongor said.

Every tests i made today doesn't work wtih IAS or TAS if you have wind.

 

[BIGNEWY]

if you have short track replays showing an issue please attach them, if possible only with the units needed to show the issue and on caucasus terrain. 

I will ask the team about this when they return from their break 

thank you 

[Strannix]

On 1/2/2025 at 10:33 AM, BIGNEWY said:

if you have short track replays showing an issue please attach them, if possible only with the units needed to show the issue and on caucasus terrain. 

I will ask the team about this when they return from their break 

thank you 

Hi, sorry for the delay.

 

A10C DTOT issue with IAS_TAS.trk

[Yurgon]

I can confirm the issue. Running the same mission with different wind settings, flying at RIAS the TOT is going to be late with a head wind, on time with no wind, and early with a tail wind. Looks like wind is not taken into account. The deviation between head wind and tail wind is also relatively consistent (4:30 minutes late vs. 3:30 minutes early).

The DTOT is 10:55:00 in all 3 tracks and screenshots.

@BIGNEWY I'll also post this to the Closed Beta Testers.

No wind: On time (give or take a few seconds over 24 minutes of flight time remaining to the waypoint):

Head wind: 4:34 minutes late:

Tail wind: 3:25 minutes early (even though I'm 1 KIAS slower than required):

A-10C_II_RIAS_No_Wind.trk A-10C_II_RIAS_Head_Wind.trk A-10C_II_RIAS_Tail_Wind.trk

Edited January 8 by Yurgon

[BIGNEWY]

A report has been made for the team to check. 

thank you