VOR/DME distance limit?

[divinglyc]

Hi! I am enjoying the aircraft more and more...

I have a question. What is the upper limit of the distance for the aircraft to receive VOR/DME?

Today I made a flight from VNKT to VNLK. I planed to fly along KTM/VOR radial 096 for 70nm, but on my way near that point( I guess it was about 60 or 65 nm to KTM/VOR), I lost the DME signal so I could only stick with HDG 096 to my turning point.

I did fly this route by Twin otter and it could receive DME until more than 70nm from that VOR. So what happened then?

Thanks!

[JetNoise]

Range can differ due to various reasons AND that IS modelled in the TBM ;-)

JetNoise

[divinglyc]

8 hours ago, JetNoise said:

Range can differ due to various reasons AND that IS modelled in the TBM ;-)

JetNoise

Yes.... maybe...

Thanks~

[flyboydanmke]

Service volumes are listed in the US FAA AIM.

[cwjohan]

Here's a good discussion of VOR range in X-Plane:
https://forums.x-plane.org/index.php?/forums/topic/128843-vorndb-range/

Littlenavmap shows the range for VORs in X-Plane.  For KTM (Kathmandu VN) it shows the frequency 113.2 and range 130 nm, which indicates it is a moderately long range VOR.

Of course, altitude and a few other factors affect the actual VOR range.

[divinglyc]

On 11/2/2018 at 9:44 AM, flyboydanmke said:

Service volumes are listed in the US FAA AIM.

 

On 11/2/2018 at 12:38 PM, cwjohan said:

Here's a good discussion of VOR range in X-Plane:
https://forums.x-plane.org/index.php?/forums/topic/128843-vorndb-range/

Littlenavmap shows the range for VORs in X-Plane.  For KTM (Kathmandu VN) it shows the frequency 113.2 and range 130 nm, which indicates it is a moderately long range VOR.

Of course, altitude and a few other factors affect the actual VOR range.

Thank you both so much for the information!

[skiselkov]

We use a custom VHF and HF navaid modeling algorithm that is not based on X-Plane's service volumes. Instead, we use the NTIA Irregular Terrain Model to estimate radio wave propagation between the navaid and the aircraft. We also properly model terrain obstruction. The reason you lost DME and could still see the VOR radial was because DME and VOR signals use different frequencies (DME is at approx 1.1 GHz, VOR at around 100 MHz) with different propagation characteristics. VOR signals are more resilient in partially masked conditions due their longer wavelengths having a greater propensity to diffract over knife-edge mountain tops. You can observe the radio model at work in real time by tuning a frequency, and from the simulator menu choosing Plugins > TBM900 > Debug > Navaid reception profile. The pick the navaid you wish to analyze from the drop down menu and the systems simulation will show you a terrain relief of the terrain along the path from you to the navaid:

[divinglyc]

24 minutes ago, skiselkov said:

We use a custom VHF and HF navaid modeling algorithm that is not based on X-Plane's service volumes. Instead, we use the NTIA Irregular Terrain Model to estimate radio wave propagation between the navaid and the aircraft. We also properly model terrain obstruction. The reason you lost DME and could still see the VOR radial was because DME and VOR signals use different frequencies (DME is at approx 1.1 GHz, VOR at around 100 MHz) with different propagation characteristics. VOR signals are more resilient in partially masked conditions due their longer wavelengths having a greater propensity to diffract over knife-edge mountain tops. You can observe the radio model at work in real time by tuning a frequency, and from the simulator menu choosing Plugins > TBM900 > Debug > Navaid reception profile. The pick the navaid you wish to analyze from the drop down menu and the systems simulation will show you a terrain relief of the terrain along the path from you to the navaid:

 

Oh.. I got it now! So under such circumstances, what can I do instead? I mean if I am supposed to fly to 70nm DME and turn left, but I loose the DME reading since 60nm, what else can I do?

Thank you so much!

[skiselkov]

25 minutes ago, divinglyc said:

Oh.. I got it now! So under such circumstances, what can I do instead? I mean if I am supposed to fly to 70nm DME and turn left, but I loose the DME reading since 60nm, what else can I do?

The easiest solutions are to either climb higher, pick a different navaid that's closer, or use a different method of navigation (e.g. GPS). VOR navigation in mountainous terrain is a challenge in real life too. In your case I was able to confirm that solid KTM reception at 70 miles was possible only from 19,000 ft and higher. Any lower and the mountain tops around Kathmandu start interfering with the signal considerably. If you absolutely need a lower flight altitude, you can always try to use a secondary navaid for positional triangulation (the screenshot below you can see I used VTN NDB to get a station bearing - this can be used to confirm your along-radial position).

[divinglyc]

10 hours ago, skiselkov said:

The easiest solutions are to either climb higher, pick a different navaid that's closer, or use a different method of navigation (e.g. GPS). VOR navigation in mountainous terrain is a challenge in real life too. In your case I was able to confirm that solid KTM reception at 70 miles was possible only from 19,000 ft and higher. Any lower and the mountain tops around Kathmandu start interfering with the signal considerably. If you absolutely need a lower flight altitude, you can always try to use a secondary navaid for positional triangulation (the screenshot below you can see I used VTN NDB to get a station bearing - this can be used to confirm your along-radial position).

Thank you so much! So this means that this aircraft is simulated very realistically? 

I own another Twin otter and I can get the DME all the way at flying altitude of 13000, so maybe it's not that accurately simulated.....