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HSI TACAN Info - Any idea what this data is?


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The data block underneath the TACAN identifier is the calculated fuel remaining once the aircraft reaches the station. The data block underneath that is the calculated range at which the aircraft should begin descent in nautical miles (assuming the station is at ground level).

 

The same applies to waypoints underneath the waypoint data blocks on the right when WYPT is boxed.


Edited by Tholozor
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18 minutes ago, Tholozor said:

The data block underneath the TACAN identifier is the calculated fuel remaining once the aircraft reaches the station. The data block underneath that is the calculated range at which the aircraft should begin descent in nautical miles (assuming the station is at ground level).

 

The same applies to waypoints underneath the waypoint data blocks on the right when WYPT is boxed.

 

Great to know, thanks. Any idea why this isn't always visible? Sometimes I have it, sometimes i don't. Just need to know if it's me 🙂

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31 minutes ago, Tholozor said:

[...] The data block underneath that is the calculated range at which the aircraft should begin descent in nautical miles (assuming the station is at ground level).

 

is this assuming descent at current mach or ground speed, or in idle descent? do you know? thanks.

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The NATOPS didn't specify if it's calculating a normal descent or maximum range descent. I would assume normal, which would be idle thrust, speedbrake retracted, and maintaining a descent speed of 250 KCAS, roughly 4000~6000 fpm (NOTE: This is according to the NFM-200 Performance Chart for the older GE-400 engines, the chart may be different in the NFM-210 and the GE-402 our Hornet has).


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1 hour ago, -ORION- said:

Great to know, thanks. Any idea why this isn't always visible? Sometimes I have it, sometimes i don't. Just need to know if it's me 🙂

1. It's only visible if you have TCN or WYPT boxed.
2. FPAS calculations are only possible when you are at or below Mach 0.9. If you're going faster than Mach 0.9, the info goes away and you'll also get an FPAS advisory.

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I believe you have to be heading somewhat towards the station as well.  Pretty tough to calculate fuel remaining without a positive closure. 

 

That said, sometimes the Tacan will glitch.  If it's not behaving as expected, turn it off and back on, that'll usually square it away. 

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The thing there is that the NATOPS doesn't specify whether or not the range calculation stops once the aircraft begins the descent (unless you've got additional info not in the NATOPS).

 

At least it's being looked into from your initial report: 

 


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As mentioned above:

The top number is calculated fuel remaining when you reach the tacan/waypoint.

The bottom number is at which distance you should start your descent.

 

You don’t have to be heading towards it.

 

As Harker said, above 0,9 Mach the FPAS-calculations are out the window, so you lose this data.

 

 

 

Regarding the question about descent-rate:

 

The number given is always very close to pr. 1.000 feet of altitude.

So if you are at 20.000 feet, the descent number will be close to 20.

At higher altitudes the descent-number will slightly deviate from this, but not very much.

 

So, according to trigonometry, there is a 1:1 ratio between 1000-feet-altitude and 1-nm of distance at a 9,46 degree descent.

 

In other words: if you are at 42.000 feet, the descent-number will usually be around 40. Then, at 40 nm (and still at 42.000 feet altitude) away from the tacan/waypoint you start a descent with 9-10 degrees down, you should hit the ground/water fairly close to the tacan/waypoint, within a couple of nautical miles 😛

 

*This is for a tacan or waypoint at sealevel. I haven't checked this for a tacan/waypoint at altitude.

 

With Tacan/waypoint at altitude: the descent/number seems to aim for a 9-10 degree down too.

 

This is at least my best take on the descent-rate 😛


Edited by TimRobertsen
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10 hours ago, Tholozor said:

The thing there is that the NATOPS doesn't specify whether or not the range calculation stops once the aircraft begins the descent

It's been fixed. It used to count down to descent. E.g. you are 100 miles away and it would count down 70, 69, 68, 67, 66... as you approached. Now it is static 30, 30, 30, 30.

 

On the other topic it makes sense that the calculated range for descent will be constantly updated as the airplane changes altitude and it does in DCS. This is helpful to track your descent that you're on schedule and almost certainly how the real airplane functions.

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On 2/19/2021 at 7:06 PM, TimRobertsen said:

 

With Tacan/waypoint at altitude: the descent/number seems to aim for a 9-10 degree down too.

 

I noticed that, putting a waypoint on the TACAN station, the descent point is different. At 9 ° on the waypoint I arrive on the ground, while from tacan, at 5000 ft (same rate).

[sIGPIC][/sIGPIC]

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16 hours ago, emibat said:

I noticed that, putting a waypoint on the TACAN station, the descent point is different. At 9 ° on the waypoint I arrive on the ground, while from tacan, at 5000 ft (same rate).

 

Jupp, there is something off with the descent-calculation for tacan. It might be a bug.

In Persia you end up at around 5900 feet above any given tacan, regardless of the tacans elevation, in caucasus this point is about 6600 feet.

I dont know if this is an actual feature of the Tacan system, or just a programming-error in dcs.

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17 hours ago, emibat said:

I noticed that, putting a waypoint on the TACAN station, the descent point is different. At 9 ° on the waypoint I arrive on the ground, while from tacan, at 5000 ft (same rate).

 

Personally, I start a 10 degree descent when the distance (from tacan or waypoint) intersects the aircrafts altitude. So, if Im at 40.000 feet, I start a 10 degree descent at 40 nm distance.

 

If the tacan/waypoint is at an elevation, I subtract the elevation from the distance. For example an airfield at 2000 feet elevation, I start descent at 38nm.

 

If I want, f.ex, 3nm of level flight before I reach the point I add that to the range, 43nm of from the point.

 

This can be useful for when you approach for a carrier landing. You want to be at your given stack-level at 10nm from the carrier. At 40.000 feet alt, I’d start the descent at 50nm. If you have a stack-level of 3.000 feet, you could add that to the equation, but it’s not really necessary as you have start the descent that much earlier, the trigonometry of it is way off in that case 😛 In short: you will arrive at favorable altitude at around 14-17nm off from the carrier, giving you plenty of time to adjust and prep for the stack 🙂 

 

It might seem like Im making a big fuzz about a simple issue of descent, but I thought it might be worth mentioning, in case someone would find it interesting 😊

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8 hours ago, TimRobertsen said:

 

Personally, I start a 10 degree descent when the distance (from tacan or waypoint) intersects the aircrafts altitude. So, if Im at 40.000 feet, I start a 10 degree descent at 40 nm distance.

 

If the tacan/waypoint is at an elevation, I subtract the elevation from the distance. For example an airfield at 2000 feet elevation, I start descent at 38nm.

 

If I want, f.ex, 3nm of level flight before I reach the point I add that to the range, 43nm of from the point.

 

This can be useful for when you approach for a carrier landing. You want to be at your given stack-level at 10nm from the carrier. At 40.000 feet alt, I’d start the descent at 50nm. If you have a stack-level of 3.000 feet, you could add that to the equation, but it’s not really necessary as you have start the descent that much earlier, the trigonometry of it is way off in that case 😛 In short: you will arrive at favorable altitude at around 14-17nm off from the carrier, giving you plenty of time to adjust and prep for the stack 🙂 

 

It might seem like Im making a big fuzz about a simple issue of descent, but I thought it might be worth mentioning, in case someone would find it interesting 😊

I certainly appreciate it! This has bugged me for some time and I think I naturally used the altitude  per distance 40k for 40 miles but I often descended quicker than 10 degrees. I will try and do this going forward. Thanks for the research and posts!

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20 hours ago, LTRMcrew said:

I certainly appreciate it! This has bugged me for some time and I think I naturally used the altitude  per distance 40k for 40 miles but I often descended quicker than 10 degrees. I will try and do this going forward. Thanks for the research and posts!

 

I take back my previous statement about omitting the stack-level from the equation on the carrier approach/setting up for the stack 😛 

 

When approaching a carrier from 40.000 feet, for the 10NM/See you at 10-point. If you have Stack at Angels 3, f.ex.

You can simply subtract 3 from the range, and add the 10NM, giving you a descent-go at (40-3+10=) 47NM.

If you “cradle” the Velocity Vector in the 10-degree ladder-step, like this.

This seems to work, pretty much, spot-on for a good stack-setup.

 

I know I keep going on with this, but I’ve gotten a little bit carried away this 😛

VV Cradle.jpg

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