VOR Range

[Cricket23]

No doubt, the effective range of a VOR beacon will depend on your altitude, but is there a rule of thumb, or indeed, somewhere that officially has the info.

Regards,

C23

[EastMids]

See AIP: http://www.ais.org.uk/aes/pubs/aip/pdf/enr/20401.PDF

Andy

[Mark 1]

DOC only works if you have line of sight with the station.

Rule of thumb for line of sight (in NM) = sqrt(height in feet)
Assuming no big hills in the way etc.
e.g 2500' - 50NM
5000' - 70NM

[Cricket23]

Thanks Guys.

C23

[High Wing Drifter]

Rule of thumb for line of sight (in NM) = sqrt(height in feet)
I believe the RoT is 1.25 * sqrt(height in feet).

[Mark 1]

The exact solution for length of tangent (assuming station at GL) is:
sqrt(2rh+h^2)
where r is the radius of the earth
and h is the height of the observer.

To a first order the h^2 term is negligible.
So length of tangent = sqrt(2r) * sqrt(height)
In nautical miles the coefficient works out at 1.0634
In statute miles it is 1.2245

So 1 is an easy conservative value for a rule of thumb.;)

[swervin'mervin]

I'm sure for the ATPLs it was something like height of Tx + height of Rx (feet), square rooted, x 1.25. Anyone more current?

[bookworm]

The exact solution for length of tangent (assuming station at GL)...
In nautical miles the coefficient works out at 1.0634


Your exact solution assumes that the ray travels in a straight line. In fact it is curved by refraction in the atmosphere. The magnitude of the effect depends on the frequency: for light it's about 10% greater distance to the horizon than the geometrical solution, for VHF it could be rather more.

[High Wing Drifter]

The exact solution for length of tangent (assuming station at GL) is:
sqrt(2rh+h^2)
I admit it, I am mathematically challenged, but I don't get that. If I'm at 4000' then my range is 4000nm plus a shed load more? Which units?
I'm sure for the ATPLs it was something like height of Tx + height of Rx (feet), square rooted, x 1.25. Anyone more current?
It would have to be 1.25 * sqrt(H of Tx) + 1.25 * sqrt(H of Rx).

Bookworm,
The ATPL assumes line of sight.

[Mark 1]

Back to the original question....

For a rule of thumb, I prefer 1 as its easy to remember and slightly conservative.

I remember seeing 1.25 in one of the CPL text books, but this may be for a distance in stat. miles.

If the VOR is positioned significantly higher than the surrounding land then you can add a bit for this, as bookworm says.

Given the variability with local geography, I'd go for the conservative factor.

This is only for planning anyway. If you have a flag and ident, and are less than DOC distance, then it's OK to use it.

[S-Works]

Straight Line Propagation Paths - Direct or Space Wave

D (NM)=1.25(sqrt HTTX Station + 1.2 sqrt HTRX Station)

Example.

VOR 400ftamsl
Aircraft 5000ft amsl

D= 1.25 x (sqrt400 + sqrt5000) = 113.38NM

[IO540]

None of this ATPL ground school stuff is very relevant in practice, because if you potter about the UK at low levels you won't be receiving anything a lot of the time (except GPS) and if flying UK/European airways then ATC will send you all over the place and quite happily DCT some VOR which is way outside the DOC - they simply assume you have BRNAV which means a GPS.

It's the damned exams one has to get through :yuk:

[S-Works]

Yes and didnt I learn something damned clever and utterly useless!!!

[Ni Thomas]

And to help complicate things a bit more:-
We ancient master mariners were taught:-
Distance of the horizon = (1.15 x sqrt H) + (1.15 x sqrt h)
Were H = Your height of eye and
h = Height of object (normally a ruddy lighthouse)
Although they did make a consession that a constant of 1.17 a better value for average conditions.
Just thought you ought to know.

[High Wing Drifter]

Given the variability with local geography, I'd go for the conservative factor...This is only for planning anyway. If you have a flag and ident, and are less than DOC distance, then it's OK to use it.
Can't argue with that. Nowt wrong with a pprune style sometimes heated, often accademic and probably pointless debate though :}