A Tale of Two Whiz Wheels: E6-B versus CR Wind Solutions

Paul Heim
November 19, 2007

Since the CR-3 calculates effective true airspeed does that make it more accurate than the traditional E-6B? Thanks.

Jim Maher
December 04, 2007

Thanks for the detailed desc. Been a longtime since I used my CR-3; your article helped jumpstart the gray matter upstairs.

Terry
June 12, 2008

More of a question: while studying for IFR, came across problem for which the only correct answer required changing the wind direction from true to Magnetic by subtracting the MAG-VAR before performing the wind-triangle calc. I have never seen this done before — FAA question error? or just something everyone assumes we all know to do?

Peter B
January 16, 2009

The US Navy and US Marine Corps use the CR-3 and CR-5 models exclusively for primary and advanced training in jets and helicopters. It is a better tool with more uses, allows one hand manipulation, and promotes a better understanding of fundamental concepts.

Lynn Parker
June 14, 2009

I have a E6-3B computer from aero products so was surprised to see yours is 10" long. Mine is 5.75×4.25". It seems to be the same as your longer one with the snap on calculator on the back.

Alex
October 22, 2009

This is a great comparison. Very helpful. Thanks!

Sandy
January 20, 2010

Is there any monetary value to either of these wind-easy computers. Either the E6B or the CR?

Just curious. Thanks.

Henry
April 07, 2010

Hi Stefan, I was recently shown how to do a reverse windspeed calculation on an E6B, i.e. how to calculate the wind speed and direction based on the airplane’s true course, heading, and groundspeed. I was unable to figure out how to do the same thing on a CR… can you help? thanks, henry

Bart Casey
January 02, 2011

excellent review of the CR-3, takes me back to my training in the military. We used the clunky E6-B which the CDN military bought soon after the Wright brother’s maiden flight….the CR-3 is much more convenient. Thanks again.

André Ranulfo
February 07, 2011

You helped a lot — TKS!

Jay
April 02, 2011

Stefan, Thank you for the explanation . . . I was having trouble doing these calculations using the included manual. Your explanations and the highlights proved invaluable.

Jessica Lima
May 22, 2011

stil confused about the wind triangle

helped a bit.

Gary Williams
August 17, 2011

lost my instructions this helped me thank you…defo for planning at home…ever tried doing these calcs why trying to fly a helicopter?

Shriraj Kanhere
September 16, 2011

Well after all the advantages of CR over E6B, you cant work other way around on CR. You can calculate track if heading and winds are known on E6B, while CR doesn’t support this reverse calculation!. Like that it matters, how often we calculate other way around anyways?

Claes M Johansson
November 04, 2011

I think you are overlooking the existence of the Aristo Whizz-wheels that came(?) in two versions: with a traditional sliding plate, but also in a round only variant which exploits the pure trigonometric solution of the sinus theorem. Not quicker but very elegant. Can provide photo another time.

Earl R. Benedict
February 27, 2014

Been flying for the last 60 years both civ. and mil. and have used both the E6B and the CR computers , still use them to keep in practise

Michael Fox
November 05, 2014

I have used both and teach both. My most recent discovery with the cr6 is the ability to do sin, cos and tan calculations which are used for stall speed in a bank calculations. Once you know how to do the calculations it is way faster than anyone on an electronic calculator.

Dr Alan Blackwood
August 02, 2015

As a long-time user and collector of whizz-wheels I was greatly interested by your article and I wondered if you might like to read my reflections upon the various flight computers I regularly use.

Jeppesen CR – when I fly I always have a CR-2 in my jacket pocket and a CR-3 in my flight bag. I do not usually use a CR to solve wind triangle problems but I keep myself in practice in case the need arises. The CR is probably the best whizz-wheel to use when it becomes plain that the forecast air temperature is wildly inaccurate and you wish to recalculate TAS using a reading from the OAT probe. The temperature correction is never likely to exceed 2.5 degrees (C) for a PPL but we want to be as accurate as is possible and the CR computer allows for this. I recently purchased an ASA copy of the CR-3 – the ASA-E6B-CIRC – and, amazingly, it appears to be of superior materials and construction when compared to the Jeppesen original.

Aviat 617 (formerly by Aristo of Germany, now by Pooleys of England) – this is simply the Rolls-Royce of whizz-wheels. The smoothness of the movement of the disc and cursor on the calculator side make it a joy to use – even one-handed. The wind side has a fixed wind-arm eliminating the need to mark the wind on the disc in pencil. The smoothness of the movements of the wind azimuth ring, the wind-arm and the slide allowed me one-handedly to solve the problem posed in the article in 10 seconds. I use the Aviat 617 for all my pre-flight planning and I have it in my flight case when I fly. The ARC-2 with wind-arm (by AFE) is my back-up whizz-wheel – it is just as smooth as the Aviat but is plainly of somewhat flimsier construction.

Pooleys CRP-9 (formerly Airtour CRP-9) – this is another pocket whizz-wheel I like to keep in my jacket. Its calculator side has all the features of the best ‘professional’ flight computers except that it lacks a cursor. Interestingly, the wind side of this computer offers a third non-electronic method of solving wind triangle problems – however, its use of ratios (which must be calculated) and iterations make the method cumbersome and time-consuming – needless-to-say, I keep in practice just in case!

ASA CX 1a – I never use this electronic machine for real flight planning, I do not carry it with me when I fly and have not felt inclined to purchase its successor. These machines are ingenious and perhaps a useful back-up on the ground, but I just can’t see myself trawling through its menu while flying an aeroplane.

Apart form that one afternoon back in 1989 when I learned to use my first whizz-wheel (Airtour/Pooleys CRP-1 – ubiquitous in the UK – I still have mine), I have often wondered why we bother with slide flight computers not fitted with a wind-arm. It might well be easier to learn the techniques by drawing them out, but once the learning stage is passed the computer can be used much more quickly if it is fitted with a wind-arm. Perhaps the answer for student pilots should have been a removable wind-arm, but neither the USA nor UK makers seem to offer such a machine.

Gary LaPook
November 28, 2015

Here is a link to a better picture of the Air Force computer, this time to the MB-9
http://www.rekeninstrumenten.nl/pages%20and%20pictures/12071.jpg

gl

Gary LaPook
November 29, 2015

In fact, you can do the same computation on any of your slide rules by using the sine scale positioned against the “D” scale. Line up the RWA on the sine scale against the TAS on the D scale. Then read out the WCA on the sine scale against the wind speed on the D scale. Then add the WCA to the RWA if a tail wind, or subtract if a head wind, and read out the ground speed on the D scale opposite the total of the RWA and WCA on the sine scale.

gl

Gary LaPook
January 25, 2016

Those other computers that utilize the law of sines are the most accurate way to do the calculation, The CR comes up with the effective ground speed as a “cludge” but is not necessary on the E-6B and not necessary using the exact method using the trig solution with the law of sines. You can do this on a calculator to 10 digits of precision if you knew your airspeed and wind speed to that level of precision. The law of sines solution is exact, no approximations, no estimation of cross-wind and head-wind component from a small grid on the CR.
Sin a/ A =sin b/B =sin c/C = K a constant

Using the example that I posted,

” Try this example, true course 240°; true wind, 270° at 30 knots; TAS 110 knots. The correct answer is ground speed of 83 knots and the WCA of 8°. When you draw the wind dot on the CR if you estimate the cross-wind is 16 knots then you get the correct 8° WCA but if you read it as 17 knots then you find the incorrect WCA of 9°. The other method actually uses trig and you can see how it works by using that method with your CR since the CR has the requisite scales. Subtract the TC from the wind direction and you find the “relative wind angle” (RWA) of 30°. Now line up the 30 degree (on the white sin scale) mark on the CR with the TAS of 110 knots on the outside scale. Next look at the wind speed on the outside scale, 30 K, and read out the WCA on the white sin scale of 7.8° Since you have a headwind, subtract this 7.8° from the RWA of 30°, 22.2° and opposite this 22.2° read out the ground speed on the outside scale, 83 knots.”

Do this on a calculator.
a is relative wind angle (RWA) 30 degrees and A is the TAS 110 K
b is the WCA and B is the wind speed
C is the ground speed.
sin a /A
Sin 30 /110 = 0.500000000/110 = 0.004545455 this is a constant used later, call it “K”

So sin b /B also must equal K
So sin b = KB
So b = arcsin KB

then multiply this “K” by the wind speed, 30 X 0.004545455 = 0.136363636
So b, the WCA, = arc sin(0.136363636)

arc sin (0.136363636) = 7.837479763 degrees which is the most accurate possible wind correction angle (if the wind speed were known to 10 digit, the TAS to 10 digits and the wind direction to 1/1000000000 of a degree.)

Angle c is the WCA combined with the RWA subtracting WCA when there is a head wind and adding it when it is a tailwind.
sin c/C must also equal K
Solving for C the groundspeed.
sin c/ C = K
sin c =KC
C =sin c/K

Then subtract the WCA from the RWA
30.00000000000 – 7.837479763 = 22.16252024 = c
C =sin c/K

sin (22.16252024) / 0.004545455 = 82.99171148 knots ground speed.
Since we never know our TAS or wind speed or course or wind direction very accurately then the CR, the E=6B and the and MB-2A and the TELEX PT are as accurate as they can be given the precision of the input data. But, given the additional inaccuracy introduced by estimating the cross wind component and the head wind component form the grid of the CR, the CR has the potential to have the largest error compared to the other methods. In fact, if using the CR, you would be better off ignoring that grid and using the trig method that I demonstrated using the existing sine scale that is on the CR.

gl

Erwin Eijsermans
March 30, 2019

Hi,

Thanks for this interesting atricle, big fan of the CR series myself.

Do you, or anyone else reading this, have any experience with (or documentation on) the Batori Flight Computer?
Trying to figure out how to calculate the Groundspeed based on wind.

Regards,
Erwin

Erwin Eijsermans
August 17, 2020

Hi,

I have been looking at Gary LaPook’s comments and alternate method for using the CR2/3/5. It is quite fascinating, but limited on the CR series.
He refers to the MB2/9, both have a windscale up to 90 degrees, whereas the CR only goes up to 45.
The method is completely clear and I use it on the MB-9, but what to do if the RWA is more then 45 degrees, or if the RWA+TW is more then 45 degrees. In these cases I get stuck on the CR series. Am I missing something here?

Regards,
Erwin

P.S. found a manual for the Batori Navigational computers (they are stunning pieces of kit)

Biggles B
November 09, 2020

Hi Stefan, excellent article.

When comparing the advantages of each computer, you wrote, “the CR computer can be operated with one hand after drawing the wind dot, which is handy when recomputing headings mid-flight.”

Is this not also the case with the E6-B?

Cheers!

Michael Do
January 03, 2022

Cool. It’s amazing how a solution like that can be achieved with less mechanical complexity. But. There is absolutely no way that the same amount of work is required for both methods. Reading the CR instructions made my head spin. Mental math, sparse markings, and having to go through at least 2 successive readings before accessing the stored information. Good thing I don’t fly aircraft–then again, maybe it’s all fun and games up there if one is expected to have the spare clock speed for all those hoops. Jokes aside, I wonder about the alternate reality where Dalton’s computer didn’t use a slider.