Flying without an HSI
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Hey guys,
short question relating to this subject: When flying with RNAV or KLN-90B where are the heading info does come from respectively what will happen if the DG is continually loosing it's correct heading thru drift?
I think at least the RNAV system is relying on the DG.Regards,
Zacke@Zacke As far as I understand it, the RNAV 511 doesn't actually know the aircrafts heading. It identifies the radial you are on using the phase difference between the VOR’s reference and variable signals. That phase difference tells the receiver your magnetic azimuth from the station, regardless of which direction the aircraft is facing. Think of it like a rotating lighthouse with a separate “north” flash: the lighthouse flashes in every direction when its beam points north, the beam then rotates clockwise, the receiver measures how long after the north flash the rotating beam reaches you, the time delay tells you your direction from the lighthouse. It then combines that radial with DME distance to determine your position relative to the VOR and calculate the bearing and distance to the entered waypoint...
Regarding the KLN-90B and other GPS units, they can only gather directional track information from movement. IRL on initial startup while stationary, depending on the unit and if the unit is in track up mode, it will either face aircraft north, or at it's last known track until movement is made and a track can be identified. The GPS satellites themselves provide the aircraft with position, groundspeed, and ground track, not aircraft heading. I haven't really paid attention to how/if different GPS units simulate this properly in the sim.
*Side note: Some GPS units can be equipped with external inputs connecting the unit to the aircraft’s heading system allowing for HDG up display (this would connect to an AHRS/ directional gyro/ etc...).
CPL MIFR 🍁
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@Zacke As far as I understand it, the RNAV 511 doesn't actually know the aircrafts heading. It identifies the radial you are on using the phase difference between the VOR’s reference and variable signals. That phase difference tells the receiver your magnetic azimuth from the station, regardless of which direction the aircraft is facing. Think of it like a rotating lighthouse with a separate “north” flash: the lighthouse flashes in every direction when its beam points north, the beam then rotates clockwise, the receiver measures how long after the north flash the rotating beam reaches you, the time delay tells you your direction from the lighthouse. It then combines that radial with DME distance to determine your position relative to the VOR and calculate the bearing and distance to the entered waypoint...
Regarding the KLN-90B and other GPS units, they can only gather directional track information from movement. IRL on initial startup while stationary, depending on the unit and if the unit is in track up mode, it will either face aircraft north, or at it's last known track until movement is made and a track can be identified. The GPS satellites themselves provide the aircraft with position, groundspeed, and ground track, not aircraft heading. I haven't really paid attention to how/if different GPS units simulate this properly in the sim.
*Side note: Some GPS units can be equipped with external inputs connecting the unit to the aircraft’s heading system allowing for HDG up display (this would connect to an AHRS/ directional gyro/ etc...).
@SadBucket All 100% true. I was waiting for someone to post an excellent explanation. It's a common misconception that a VOR receiver needs some knowledge of your orientation to produce what you see in the cockpit, but it's completely heading-agnostic.
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@Black-Square would you consider adding an optional HSI such as the KI 525A?
An HSI would absolutely make the Commander one of my fav Black Square aircraft. Sadly, it's been rusting in my virtual hangar since purchase. I simply cannot convince myself to fly it, so much so that I somewhat regret I purchased it.
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Thats a shame. There is so much to love about the 114 with or without an HSI. Most GA aircraft I own have an HSI and to be honest I really dont notice not having one as all the sources of info you need are there. But we all have our own likes and dislikes. Thats the fun of it.
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After having many hours in the A2A Comanche 250 I'm now committing to the Commander 114. In the Piper I got accustomed to using my HSI needle to fly circuits. It made me able to turn various legs with precision, and keeping me on track for most of them. I also find it very useful for my spatial awareness when looking for a field.
Any tips for doing such a thing with the Commander it's avionics? How do you guys do this without just looking at the field? I tried the heading bug but it's not as visible.
@Gatlingorange said in Flying without an HSI:
Any tips for doing such a thing with the Commander it's avionics? How do you guys do this without just looking at the field? I tried the heading bug but it's not as visible.
I'll set the heading bug to the runway heading. It's not as visible as an HSI but it gets the job done well enough for pattern work.
Another thing I'll do on the GNS 530 for visual approaches is I'll switch the CDI to VLOC mode and then enable OBS mode, set the runway heading on the NAV1 CDI. That gets you a magenta line to follow right to the field. If you key in an approach procedure for the particular runway, then Direct To to the RW waypoint, it'll be even more precise but for most airfields, I won't even bother.
For extra credit, set one of the display fields to the Cross Track Error (XTK) and you'll get a read out of exactly how far you are from the field on your downwind leg in NM.
If you fly using the GNS 750 it's an absolute cake since it has built in visual approaches.
