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Spir4
9th Jun 2013, 10:04
Hello,

In a book I've read the following about an RMI:
If the aircraft's variation is different from the VOR station's variation, the indication of the relative bearing is incorrect, but the QDM indication is still correct.

Does this mean that if you have a variation difference of 20° between the aircraft's position and the VOR position, you will be flying in an arc ('homing') to the VOR if you follow the VOR pointer on the RMI (the QDM indication)?

This all in no wind conditions.

Thanks.

rudderrudderrat
9th Jun 2013, 16:05
Hi Spir4,

If the difference in variation was 20 degrees between the VOR and the aircraft, then flying with the needle pointing directly upwards would send you away by 20 degrees initially.
If you wanted to fly a constant QDM, then your heading would have to be 20 degrees away from the needle initially (seen as apparent drift), and as the difference in variation reduced to zero, then you'd finish with the needle pointing directly ahead.

hvogt
9th Jun 2013, 16:55
Of course you're right, rudderrudderat. I just deleted my above post, which was written in a haste.

Turbavykas
9th Jun 2013, 19:13
Don't worry you will not fly an arc :) Radio waves travels in straight lines so you will fly directly to the VOR. Of course you heading will be changing all the time.