DR2 Dreieckrechner, Dennert & Pape (Part 3): Turn inbound when 7 minutes away from the runway

In this third video on Siegfried Knemeyer's DR-2 Dreieckrechner ("Triangle Computer"), we investigate the mysterious locking cursor pin located at the 7-minute mark. On later devices (those produced in the 2nd half of 1941 and thereafter), the 7 minute pin was replaced with a simple gauge marking. Ronald van Riet's 2009 article on the Dreieckrechner mentions that the 7-minute pin was added because "7 minutes was the duration of the final flight segment in an instrument approach." Indeed, the ZZ-Verfahren ("ZZ Procedure") required aircrew to fly a 7 minute final inbound course to the airport, and this video briefly describes the procedure. For a more detailed explanation of the ZZ Procedure (in German), see the following excellent video (which includes a slightly different approach to using the DR2 for the same purpose):    • Folge 5 - Blindlandung! Das ZZ-Verfahren   This video quickly explains the ZZ procedure and how the DR-2 was used to handle the required math. First, we calculate the relative wind angles, then the wind-correction angles, and finally the "time to turn" on the outbound leg to ensure the final approach leg would be 7 minutes. 00:00 – 1. Introduction 01:36 – 2. The ZZ Instrument Approach Procedure 03:28 – 3. Time to Turn Problem: Relative Wind Angles (Out and In) 04:23 - 4. Time to Turn Problem: Wind Correction Angles (Out and In) 05:30 – 5. Time to Turn Problem: Groundspeeds (Out and In) 06:38 – 6. Time to Turn Problem: Using the 7-minute cursor pin 07:40 – 7. Conclusions Notes: Three obvious tongue slips: 1) "Bearing 333 to the airport" should have been "Bearing 333 from the airport." 2) "Our outbound speed was 25 degrees on the sine scale" should technically have been "Our outbound speed can be found across from 155 degrees on the sine scale." 3) I critically misstate: "that tells us the equivalent amount of time to fly that leg at that slower speed" when I should have said "that tells us the equivalent amount of time to fly the outbound leg at our faster speed." The procedure and result are correct. It's a bit of mind bender to read the "outbound time" over the "inbound speed" and vice versa! See part 1 here:    • DR2 Dreieckrechner, Dennert & Pape (Part 1...   See part 2 here:    • DR2 Dreieckrechner, Dennert & Pape (Part 2...   #e6b #aviation #flightcomputer #deadreckoning #navigation #math #history #pilottraining #dr2 #knemeyer #windtriangle #airnavigation #dreieckrechner #ZZVerfahren #ZZProcedure