Whizz Wheeling across the sky...

Having been nose into the books lately on Nav and progressing through the Aviation based witticisms compared to the Maritime Nav I have for taught for years, I have come to appreciate that Nav is such a huge subject it is impossible to learn all there is to know. Physically impossible.

When I started the Air Nav studying I was shown a very useful method by one of my part time instructors, Mike Odonihughe (mentioned in other posts to date), with regards to using the ‘Whizz Wheel’ or CRP-1 or Flight computer or E6B or whatever you want to call it. I feel obliged to put this picture of Mr Spock from Star Trek up as everyone who has ever put a post of this subject has used the same picture.

Sorry had to be done.  

The analogue flight computer has been around since the late 1930’s and was developed in the United States by Naval Lt. Philip Dalton.

In this picture is Capt Claude W. Cambell’s crew in the 303rd Bomb Group at Molesworth, England. Circa 1943.

The design hasn’t changed much over the years and still carries the same functionality today as it was intended back then. The ability to perform very complex algebraic equations without even using a pencil is pretty impressive. Because of the lack of batteries and the reduced chance of it ceasing to function correctly without driving over it with a large vehicle, the flight computers are still a major part of navigation training for all types of aircraft. If you can do it on one of these then it can only get easier with the use of technology, however if technology fails you have to be able to take over and do it the ‘Old Fashioned’ way.

For my examples the sharp witted will notice I’m using the Pooley’s CRP-5 which is the larger commercial variant on the CRP-1. This is because I intend on going commercial with my flying and learning on this now would make sense instead of adapting to it later. Start out as you mean to go on.

 So here goes for an example of using the Computer to work out GS and Headings.

First information we need is the Direction and strength of the wind. This is best got from a met form 214 and  215. I’ve’ linked skylinkweather.com where it can be sourced with ease. Another very good resource is Skydemonlight.com for route planning. I could write a blog on just this so I’ll leave it for now.

I digress. Now you have your wind direction and speed for the area and height you are going to be flying you set the central blue dot at the Zero position for wind speed as shown in the picture.

Now you can make a mark at the value of your wind speed below this blue dot. This method is the Dot Down method. The other option is to put the blue dot over your intended aircraft speed and subtracting the wind speed from it. This is the Dot Up method. In both methods you must set your wind direction where it says True Heading at the top of the protractor before using a permanent or non permanent pen. Permanent can be removed by scribbling over it using a non permanent pen and wiping off. Using non permanent means there is a risk of wiping it off prematurely. The same goes for marking on your chart. In this case my wind is blowing 20 knots from 120 degrees.

Which ever method you are using, once you have marked your dot for the wind you can now dial up your first heading. As you can see my air speed is set at 70 knots and the effects of the wind from the direction it is travelling, I will end up being pushed 16 degrees to the right of my intended track and also it is showing my ground speed as 68 knots. It doesn’t end here I’m afraid. There is a process where you have to now take this into account to get back on track with the wind effects and you ‘wiggle’ the dial till you get something that looks right. It is called balancing the drift. YOu take the amount off track you are then alter your course back that amoutn to cancel it off then take the next error and do the same till you reduce the error and get a final bearing. A bit like 'boat builder's eye' (Arm out stretched, looking past thumb and stating "that's straight enough"). Ok so that’s not the party line however I couldn’t understand this process until Mike O'Donoghue, one of my part time Instructors and the Chief Executive of GASCo (General Aviation Safety Council), showed me an easier to understand method. His comments were “It’s not an exact science but its good enough for government work and is within 1 or 2 degrees of the other method”. That was enough to sell it to me! It does work out with the same possible errors as doing it 'by eye' so ‘jobs a good un’.

    

   

So what you do at this stage is you take a straight edge and draw a line down from the ‘red’ dot keeping in line with the lower grid as shown in the picture

Now to correct the errors as briefly eluded to above, instead of ‘wiggling’ it aimlessly till it looks right (my personal take on the other method) you rotate the disk till the red line runs parallel to the drift lines. In this example it would mean your course to steer to remain on track is about 179 or 180 degrees. The picture isn’t very good and the line is not very square and should read 180, but you get the idea. 
   

From this point you can move on to your next leg. Unless further legs are close to your initial leg you can leave the mark on so you can check your working out later, however for longer routes with similar legs it is prudent to clean these marks off. Another tactic is to use different colours.
On a CRP-1 you will have no problems with this however using the CRP-5 you may find in helicopter world where your True Air Speed (TAS) can be quite low compared to a fixed wing, there is a chance the resultant dot ends up below the zero line. if this does happen the speed cannot be acurately read. After a robust Q&A session involving two other instructors (as neither had come acoss this method) it was agreed that the way round it was to apply some simple and logical trigonometry and double all values inputted and half the resultant. for example 60 knots TAS would become 120 and my wind speed if 120 degrees at 30 knots would be 60 knots. This would result in 66 knots at 151 degrees. As already mentioned, half this to give 33 knots.

As you can see using the CRP-1 there is less need to double your values as the scale goes as low as 20 knots.

I hope this has been of use as the other method can be confusing if you are afflicted by dyslexia as I am