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How to calculate the Radial a Fix is on ?

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Hi guys!

How do I calculate Radial a Fix is on? I am planning a flight from KRDD Redding, to KSTS.

  This is the plan: KRDD  HOMAN2 RBL V25 GETER V494 KSTS

HOMAN2 SID guides me till RBL VOR. It says that I have to fly R357 on the RED BLUFF VOR. There is where the SID finishes. Then I have to follow Victor-25 to the  'GRENY' Fix. So, from Red Bluff VOR to GRENY fix I have no clue what radial V25 is on, and I don't know how to see it. Using SimBrief, there is no info about radials. Any help here? Would other tools like PFPX, help me with this? Thank you for your time!

Lets make the question more generic and see if it helps. How do i calculate the radial any Victor airway is on? And what tools do i need?

ps: I am using a Piper Comanche 250. And the rule for the fly is no GPS. A fix is usually defined as the intersection of two VOR radials (Quoting Wikipedia here, and I know its probably more than just that), so I should be able to fly the Victor airway using the VORs and no GPS.

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Thank you Jim! i know how to use VORs. But, are you suggesting me to just tune the next VOR that follows the Fix?

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As David says, you can't "calculate" the radial, you would need to read it from an enroute chart.

Fortunately US enroute charts are available free at SkyVector.

Be aware, however, that in many parts of the world it is increasingly impossible to fly airways using only radio nav kit - many airways now require RNAV and the fixes along them are just GPS coordinates and not based on ground-based navaids at all.

I suspect many of the US Victor airways are probably still conventional nav though so you will probably be alright on that side of the pond for now (I may be wrong though).

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There is no formula to calculate the radial that any given airway is located on. The only way to find the location of a given fix without a GPS is to use a chart - either paper or digital.

https://skyvector.com is one popular online source for free IFR and VFR charts.

If you check the “L2” low-altitude IFR chart for Northern California, you’ll see that GRENY intersection is on the 185 degree radial of RBL VOR at 20 miles DME. If you have no DME, GRENY can also be identified as the crossing point of the  RBL 185 and CIC 254 degree radials.

Another reason to use a chart is that it will show the minimum altitude you need to fly a given airway segment to insure safe terrain clearance when flying on an IFR flight plan. For instance, once you fly past GRENY southbound on V25, you need to be at an altitude of at least 9000 feet. That does not apply on a VFR flight, where terrain clearance is the pilot’s responsibility - but the IFR chart will at least show if a given route segment might have a minimum altitude that could possibly exceed the aircraft’s performance capability. Important planning info to know when flying a piston GA aircraft.

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IRL you would have to file a IFR flight plan before the tower at KRDD would clear you for the HOMAN2 SID, sounds like you are planning a VFR flight in which case you would probably depart KRDD on Rwy 34, 30 (depending on the wind) and ask the tower for a southbound departure to the Red Bluff VOR (RBL) then on crossing that VOR fly outbound on the 185 radial (v25) to GRENY as Jim mentioned above. Have fun!

Edited by MartinRex007

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As others have mentioned, the real way to do this is with charts. 

However, nerding out, you technically can calculate the radial as long you know the coordinates and reference system (lat/long, mgrs). You can the made this a trigonometry problem with a right triangle of E/W and N/S travel based on the changes in these coordinates and solve using sin/cos. This can be done with straightforward Euclidean geometry/trigonometry for short distances where the curvature of the Earth is negligible, but for long differences, polar reference or non-Euclidean geometry is needed to account for the curvature of the Earth (sorry flat Earthers). 

Of course this is widely impractical and will always just be referenced on charts. But my inner nerd wanted to speak that it is technically it can be “calculated”. 

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Thank you boys, that was what I was looking for. Sincerely I didn't know that chart had an IFR usage. I thought that was for VFR and that I had to use the low altitude V airways for my FPL, but looking closer, I see the victor airways on that chart too!. I am learning every day haha Thank you!

 

Thank you Jim Young!

Thank you DavidP! I didn't know about that chart and its usage lol.

Thank you skelsey! I just fly around the west coast of USA so SkyVector is perfect.

Thank you JRBarrett! thanks for the explanation! very clear.

Thank you MartinRex007!  

Thank you ESzczesniak! you are the best lol that calculation made me laugh haha. I bet you I will never use that math lol I think I misused the word calculate xD there was no better word for what I wanted to say haha but thank you for your time!

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Since you seem interested in radio navigation, VOR to VOR in this instance. Here is a bit of history for you.  Back before the days of GPS and the addition of so many new ▲intersections on Enroute charts, crossover or transitions points were printed as a guide for when to sequence NAV tuning to the next upstream VOR.  On my annotated map below you may see the route on Airway J60 between highlighted VOR's at GSH (Goshen, Indiana), and DJB (Dryer, Ohio, near Cleveland).  Look to my orange highlight and you will find a crossover point labeled  90 | 85. Note also along that airway in each segment on either side of that transition there is a box containing 175.  That is the total distance between GSH and DJB. The values at the crossover point sum to 175.

Also note that if you were flying this route from West to East, the outbound radial from GSH is 092°.  The inbound radial to DJB however is 280°.  So the transition requires not only a frequency change from 113.7 (GSH) to 113.6 (DJB), but a NAV or Course radial change as well.

39761866793_f17ec4c039_b.jpg

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