Most probably all this is well known to many people, but since I ran some tests I thought I should post them for reference:
VASI22:
Note:In both cases the angle difference should be 30 arcminutes, and that is why especially smaller aircraft have frequent red papi's when following ILS in FS. This also makes following the PAPI's in steep approaches more difficult than it should.
Having the above in mind, the formulas to place them correctly are:
(VASI) Distance from threshold = MEHT / tan(pitch)
(PAPI) Distance from threshold = MEHT / tan(pitch-10arcminutes)
*MEHT (Minimum Eye Height over Threshold) as published in AIP's.
Such placing will yield the best simulation of real life conditions (better than copying GoogleEarth).
VASI22:
- A transition of the light beam is simulated correctly with 0.25 degree, but as solid red (and not pink as in reality).
- The upwind light bar has an aiming line equal to "pitch" (as defined in ADE). It goes white at pitch+0.25.
- The downwind light bar has an aiming line of pitch-0.50degree (as per real specification). It goes white at pitch-0.50+0.25.
- No transition is simulated (2 arcminutes of pink in reality).
- The angle difference between successive lights is 20 arcminutes.
Note:In both cases the angle difference should be 30 arcminutes, and that is why especially smaller aircraft have frequent red papi's when following ILS in FS. This also makes following the PAPI's in steep approaches more difficult than it should.
Having the above in mind, the formulas to place them correctly are:
(VASI) Distance from threshold = MEHT / tan(pitch)
(PAPI) Distance from threshold = MEHT / tan(pitch-10arcminutes)
*MEHT (Minimum Eye Height over Threshold) as published in AIP's.
Such placing will yield the best simulation of real life conditions (better than copying GoogleEarth).