Hamish has a posting that mentions how much easier DME arcs are with an RMI display.
Sometimes I feel lucky that I was never taught the official way to a DME arc during my instrument training. We have one nearby, but it just never came up. I flew my first DME arc alone in the plane in actual IMC, and because I was never taught to be stressed about it, it seemed like a simple maneuver. Here’s all I do in the arc itself (assuming that the DME and VOR are already tuned and identified):
- turn perpendicular to the DME source (so that it is off one of my wingtips)
- fly my heading until the DME hits about .2 to .3 miles more than the DME arc distance;
- turn 5 or 10 degrees towards the DME source, and repeat (to allow for winds, turn more if the DME doesn’t start decreasing; less if it decreases too much; don’t let it get less that .2 to .3 miles less than the DME arc distance).
I have one VOR set up as a fence to tell me when to turn inbound, of course. Sometimes I twist the other one to see what radial I’m on, just to relieve boredom, but it’s really not a necessary part of the procedure. I guess that I use the DME as a kind of a digital CDI, and I’ve been happy with the results so far. With my technique, an RMI wouldn’t make much difference, but I can see how it would help if you wanted to track your radial all the way through.