I have been using the GNS430 simulator. I have set the option to automatically set the course heading. It occurs to me that it may not work this way. When flying with GPS navigation and not using GPSS, do you have to manually set the course on the HSI or is it automaticlly changed to the GPS DTK? If I am reading the instrument manuals properly the GPS is sending left/right corrections to the HSI, so if it doesn’t automatically set the course needle what is the function of the left right correction?
I have been using the GNS430 simulator. I have set the option to automatically set the course heading. It occurs to me that it may not work this way. When flying with GPS navigation and not using GPSS, do you have to manually set the course on the HSI or is it automaticlly changed to the GPS DTK? If I am reading the instrument manuals properly the GPS is sending left/right corrections to the HSI, so if it doesn’t automatically set the course needle what is the function of the left right correction?
You do have to twist the course needle when using the 430/1000/55 combination, assuming that you’re flying on autopilot (if you’re hand-flying, I suppose you could just look at the CDI sideways and take your wind correction from that. This is because the autopilot in this installation has no direct connection to the GPS; it gets all information (heading/course/deviation) from pickoffs on the HSI.
Basically, NAV mode the autopilot initially flies in the direction of the course needle (much like it follows the heading bug if in HDG mode.) As the needle moves off center, the autopilot will adjust the heading, working up a wind correction angle. Assuming constant winds, it will end up settling with the needle centered and the course needle pointing in a somewhat oblique direction.
The other reason the course needle is necessary for the 55 is in intercepts–if you press NAV mode with the needle fully deflected, the autopilot will fly a 45 degree intercept angle to the course, and then turn to intercept the course. (So it has to know ahead of time what the desired course actually is.)
With GPSS, none of this is necessary–you can leave the course needle pointing in whatever direction you want. (With the Sandel, you can set it so that the course needle is automatically set to the desired track at each waypoint, so you don’t have to touch it, whether you’re using GPSS or not!)
In contrast, with the S-Tec 20 and 30, since they have no intercept capability anyhow, the course needle doesn’t matter–you have to hand-fly them onto the desired track for the NAV capture to take place, so the autopilot doesn’t care about the course.
I have been using the GNS430 simulator. I have set the option to automatically set the course heading. It occurs to me that it may not work this way. When flying with GPS navigation and not using GPSS, do you have to manually set the course on the HSI or is it automaticlly changed to the GPS DTK? If I am reading the instrument manuals properly the GPS is sending left/right corrections to the HSI, so if it doesn’t automatically set the course needle what is the function of the left right correction?
You do have to twist the course needle when using the 430/1000/55 combination, assuming that you’re flying on autopilot (if you’re hand-flying, I suppose you could just look at the CDI sideways and take your wind correction from that. This is because the autopilot in this installation has no direct connection to the GPS; it gets all information (heading/course/deviation) from pickoffs on the HSI.
Basically, NAV mode the autopilot initially flies in the direction of the course needle (much like it follows the heading bug if in HDG mode.) As the needle moves off center, the autopilot will adjust the heading, working up a wind correction angle. Assuming constant winds, it will end up settling with the needle centered and the course needle pointing in a somewhat oblique direction.
The other reason the course needle is necessary for the 55 is in intercepts–if you press NAV mode with the needle fully deflected, the autopilot will fly a 45 degree intercept angle to the course, and then turn to intercept the course. (So it has to know ahead of time what the desired course actually is.)
With GPSS, none of this is necessary–you can leave the course needle pointing in whatever direction you want. (With the Sandel, you can set it so that the course needle is automatically set to the desired track at each waypoint, so you don’t have to touch it, whether you’re using GPSS or not!)
In contrast, with the S-Tec 20 and 30, since they have no intercept capability anyhow, the course needle doesn’t matter–you have to hand-fly them onto the desired track for the NAV capture to take place, so the autopilot doesn’t care about the course.
I thought a GPS only gave left/right guidance to a CDI, and that it didn’t matter what direction the HSI arrow was pointing. Your point about the 45 degree intercept brings up a good thought, though. All this said, I’m somewhat confused on this. Are you, or other readers, sure about this?
I thought a GPS only gave left/right guidance to a CDI, and that it didn’t matter what direction the HSI arrow was pointing. Your point about the 45 degree intercept brings up a good thought, though. All this said, I’m somewhat confused on this. Are you, or other readers, sure about this?
As you say, normally the GPS only gives left/right guidance to the CDI/HSI, which in turn passes it on to the autopilot. However, the HSI itself (by virtue of turning the course knob) provides course information to the autopilot. Furthermore, if you have the Garmin/Sandel combination, the GPS provides course information to the HSI as well (so that it can be displayed, and so that the “slew” function (whereby the GPS turns the course knob for you) will work.
GPSS is almost overkill for the 430/Sandel combination, since the autoslew mode will do most of the work for you. I don’t know if it will tweak the course as you move around a DME arc, though (GPSS will fly that arc for you.)
I thought a GPS only gave left/right guidance to a CDI, and that it didn’t matter what direction the HSI arrow was pointing. Your point about the 45 degree intercept brings up a good thought, though. All this said, I’m somewhat confused on this. Are you, or other readers, sure about this?
As you say, normally the GPS only gives left/right guidance to the CDI/HSI, which in turn passes it on to the autopilot. However, the HSI itself (by virtue of turning the course knob) provides course information to the autopilot. Furthermore, if you have the Garmin/Sandel combination, the GPS provides course information to the HSI as well (so that it can be displayed, and so that the “slew” function (whereby the GPS turns the course knob for you) will work.
GPSS is almost overkill for the 430/Sandel combination, since the autoslew mode will do most of the work for you. I don’t know if it will tweak the course as you move around a DME arc, though (GPSS will fly that arc for you.)
Dave, thank you for the info. Would it be safe to conclude that on the SR20 (no Sandel) that moving the HSI pointer, in the GPS mode, provides information to the autopilot, but there is no obs function, if I were intercepting a non-localizer radial or GPS course? (I realize that there would be no obs on an ILS or localizer in any case)
Dave, thank you for the info. Would it be safe to conclude that on the SR20 (no Sandel) that moving the HSI pointer, in the GPS mode, provides information to the autopilot, but there is no obs function,
There is, but you have to put the Garmin into OBS mode. In normal (non-OBS) mode, the Garmin ignores the OBS setting, but in OBS mode, it uses the OBS setting of the HSI or OBS indicator to draw the course line on the map, and in general behaves just like a VOR.
The OBS mode is switched on and off with the OBS button on the Garmin 430.
Incidentally, the Apollo GX60 GPS does not have this mode, in fact it does not read the OBS setting from the indicator at all.
Dave, thank you for the info. Would it be safe to conclude that on the SR20 (no Sandel) that moving the HSI pointer, in the GPS mode, provides information to the autopilot, but there is no obs function,
There is, but you have to put the Garmin into OBS mode. In normal (non-OBS) mode, the Garmin ignores the OBS setting, but in OBS mode, it uses the OBS setting of the HSI or OBS indicator to draw the course line on the map, and in general behaves just like a VOR.
The OBS mode is switched on and off with the OBS button on the Garmin 430.
Incidentally, the Apollo GX60 GPS does not have this mode, in fact it does not read the OBS setting from the indicator at all.
Clyde, I tried it on the simulator and you’re absolutely correct. I am a Apollo veteran, and I wasn’t aware of this feature. Tremendous help - thanks for the input! Another example of the benefits of your web site.
Andy