mawingho
Topic Author
Posts: 41
Joined: Sun Jul 22, 2012 4:23 pm

Calculating Heading And Ground Speed

Sat Sep 08, 2012 7:10 pm

"Given the following, calculate heading and groundspeed:
Track 270 Degree T; TAS 110KT; W/V 230/20; VAR 10 Degree E

Convert the track and wind to magnetic.

Complete the details you know:
TAS = 110
TR(M) = 260
W/V(M) = 310/20
HDG(M) = ________
GS = _______

1. Set TAS and mark W/V. Using an ASA E6-B flgiht computer, mark the wind on the wind face - set 310 against the "true index". Move the slide to put the TAS of 110 kt under the centre grommet then mark a small dot 20 kt below the grommet (at the 90 kt point) to represent the W/V.

2. Drift and HDG. Rotate the transparent face (inner direction ring) to set the TR of 260 against the true index. Read the drift; it is 9 degree left. We know the wind is from 310 so from out track of 260 turn the 9 degree into wind (towards 310). The heading looks like 269 but because we have turned the direction ring, the indicated drift is now 8 degree. So the refined HDG is 268; the drift is 8 degree left.

3. Track and groundspeed. The track is known as 260. To find the G/S, read it off under the wind mark; it is 96 kt."

Reference: Robson, David. "Chapter 12: Introduction to Navigation" Basic Aeronautical Knowledge (BAK). Darra: Aviation Theory Centre Pty, 2009. 360. Print.

I do not understand the sentence "The heading looks like 269 but because we have turned the direction ring, the indicated drift is now 8 degree. So the refined HDG is 268; the drift is 8 degree left."

and I have got no idea why the we need to refine the HDG to 268?

I hope someone can help me out. Thanks!

[Edited 2012-09-08 12:12:00]
 
SAAFNAV
Posts: 350
Joined: Wed Mar 17, 2010 5:41 pm

RE: Calculating Heading And Ground Speed

Sat Sep 08, 2012 9:10 pm

When you turn heading, your drift will be different than the first heading. So if you need turn left 10° to maintain track, and you see you only have 8° drift after the compensation, you need to correct for that 2° difference.

When you turn the ring, the drift will differ to the new heading.

So, you turn the ring, assess the drift, adjust for it again, asses the drift, adjust again. Until the change you make is less than one degree.


Hope that helps.
Erich
On-board Direction Consultant
 
David L
Posts: 8552
Joined: Tue May 18, 1999 2:26 am

RE: Calculating Heading And Ground Speed

Sun Sep 09, 2012 7:20 pm

Quoting mawingho (Thread starter):
"Given the following, calculate heading and groundspeed:
... W/V 230/20; VAR 10 Degree E
Quoting mawingho (Thread starter):
Convert the track and wind to magnetic.

Complete the details you know:
...
W/V(M) = 310/20

Should the unconverted wind data read "320/20"?

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