DC3 VOR Gauge

[YolkyApple26624]

OK, I understand VOR, but the gauge, switch and knobs on the bottom left of the instrument panel has be stumped.

The only manuals I’ve seen just say it for VOR/DME. I don’t understand what the switches do and the the dials and arrows never seem to lineup to anything that makes sense for a given flight.

Thanks.

[TCPD5091]

I am no expert with the DC-3, but I believe the RMI on the bottom left has to be used for VOR tracking just as a bearing pointer would be used when navigating with an automatic direction finder to an NDB. The traditional VOR receiver on the bottom right row in front of the pilot does not have an OBS knob as that instrument is for a LOC and GS signal on an ILS which does not require a course input since LOCs transmit one course vs a radial in 360 degrees like a VOR.

[NixonRedgrave]

Like you I am puzzled by the implementation.

The 1935 Douglas DC-3

I’m a bit confused by the behavior of the CDI and associated arrows and switch. I was under the, potentially incorrect, understanding that a CDI, when paired with two NAV radios, used the solid arrow (in this case green) for NAV1 and the hollow arrow (in this case white) for NAV2. The opposite behavior is modeled here. The switch is labeled “Swap OBS Compass Rose”, yet it also toggles on/off the CDI instrument lighting when the panel lights are on. Additionally, I’d have thought the switch was…

However, I can say that you can use NAV1 with the CDI by keeping the switch in the NAV1 position. Dial your desired radial with the “CDI” knob and you will see the HSI needle swing as you dial in a radial that leads TO/FROM the VOR.

Note: the compass card is incorrectly calibrated (This sort of thing seems par for the course with AH’s work). If you turn on LOCK style tool tips you can see the actual degrees you’ve dialed in. Note in my screenshot the dial is not pointing to 177 degrees, but that is what I do have it set to. Also note that the needles are swapped for NAV1 & NAV2 unlike any other NAV radio setup I’ve seen. The white hollow needle is NAV1 and the green thin needle is NAV2.

I like to load C&D at KPRB parking spot 4. Whist parked, I can tune MQO (112.40) and PRB (114.30) without having to take flight and both will be picked up on the NAV radios.

I’ve got NAV1 tuned to MQO and, from where I’m parked, a heading of 177 degrees will fly you straight to the VOR. You can see that reflected in the CDI, because the needle is now centered.

Note, you cannot use NAV2 with this setup, it doesn’t work, so you’re stuck only being able to navigate via NAV1. The needle on the RMI will point towards NAV2’s VOR, but since the compass card is both incorrectly calibrated and will be rotated for NAV1, the bearing it shows is useless. It’s more like a “it’s thatta way…” sort of a pointer.

Take a look here. I’ve turned on tooltips so you can see what I’m talking about in these screenshots:

EDIT:

Let me add, if it isn’t obvious, that the needle on the CDI will swing left or right as you deviate from your course, as expected.

[YolkyApple26624]

Some very useful info in your reply. Thanks.
I some follow up.

1. You said “…by keeping the switch in the NAV1 position.” Are you saying the switch is NAV1 to the left and NAV2 to the right?
2. Also, I didn’t realize that the two needles are backwards. That helps.
3. Turning on the tool tips is a great idea.
4. Do you know if the compass card is a “fixed” amount off? If so I can just manually add or subtract when reading it. A pain, but doable.

I’ll have to getup in the air and try it again.

Thanks much.

[NixonRedgrave]

@YolkyApple26624

You said “…by keeping the switch in the NAV1 position.” Are you saying the switch is NAV1 to the left and NAV2 to the right?

Correct, the switch will toggle between NAV1 and NAV2 (and incidentally toggle off the backlight for the instrument…).

@YolkyApple26624

Do you know if the compass card is a “fixed” amount off? If so I can just manually add or subtract when reading it. A pain, but doable.

I believe it is, but I have not confirmed this to be able to say for certain.

All I know is I didn’t realize this the first time I flew the aircraft over the Nevada desert and couldn’t understand why I ended up somewhere I didn’t expect. Clearly, the amount it is off by is going to change your course drastically. The navigational system is really not a place where imprecision on the part of the developer is acceptable.

[YolkyApple26624]

Thanks for your help. I just took a quick flight and at least now I can make sense of what I’m seeing.