Drift and ground-speed
Quote from john_tullamarine:
From training work I've done in the past, I did some detailed reviews of several styles of prayerwheel (Dalton, Jeppesen, and Aristo) and all worked fine. Most of the Daltons I've seen don't have highspeed indices available so that will present a problem for jets .. but, for lower speeds aircraft all were fine.
[Unquote]
Yes. When I went on to VC-10s, managed to obtain one that could deal with TAS up to 500. Think it was also good for GS up to about 700 (wouldn't have been much use otherwise). I had got fed-up with having to double all the figures on my previous one. They are hard to beat for a convincing, pictorial representation of the 3 vectors (HDG/TAS, W/V and TRK/GS). Must dig it out some time. [It might even persuade some of my less knowledgable "weathercocking" critics on the "critical engine" thread.]
For the youngsters: in the 1960s and early 1970s (pre-INS), some of us were using Doppler in flight on jets, to provide drift and GS information. [On some older aeroplanes, like DC-3s, there was a drift sight...] The trouble with Doppler, as any member of the contemporary "Afrika Korps" can confirm, was that it was almost useless over calm sea or smooth desert. So you could be experiencing over 20 degrees of drift over North Africa in the winter sub-tropical jetstream, and Doppler would be no use whatsoever. And, unlike today, the forecast winds could be 30 degrees in error, which would have an effect of about 50 - 90 kts on your GS in the same case.
There was also no ADC to calculate the TAS. These are some of the reasons that we were still enjoying the company of navigators...
Sadly, it all changed with the advent of retro-fitted INS, around 1975.
Last edited by Chris Scott; 29th Feb 2008 at 10:33.
Reason: Addition of ADC and INS