ye olde whizzwheels

[Private jet]

I still carry not 1 but 2 in my flightbag, a Jeppesen CR3 and a Pooleys CRP5 ( i've never used them in 8 yrs of professional flying but they are there...) I seem to recall that for any given set of input conditions that they would often yield markedly different answers for things like TAS, Mach, drift etc. (thats why we had to use the CRP5 in the ATPL's) So, not wishing to start a bun fight, which one is correct? Why do they give different results? Surely the mathematical formulae these devices work to must be the same that ADC's use and they are always spot on. I did jot down the numbers in the cruise one day and ran them thru the whizzwheels and the Jeppesen was almost spot on compared to the ADC generated numbers. The Pooleys was way out (20 kts). However this was hardly a definitive survey as i only did it the once! I'm curious to know why something as straightforward as this results in little consistency between these devices.

[john_tullamarine]

I've never seen a Pooley's whizzwheel but presume that it is pretty standard in layout ?

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.

One of the main problems was oddball shortcut techniques which weren't always consistent with the design of the instrument. Indeed, I have had well-meaning folk who really should have known better tell me all sorts of outrageous ways to misuse the devices ...... sometimes it is just easier to give up rather than show them the technical error of their ways ....

[galaxy flyer]

I carried one (Jepp CR-?) for years, but never found a use for it, that wasn't already displayed somewhere in the cockpit. In my current flying, I sometimes need to do ETPs and it might be useful there, BUT the Honeywell FMS can do it or I can do it on a electronic calculator just as well and compute my expenses. I love E-6Bs , though and the two Pickett Slide Rules, I have. Might even be worth putting on Ebay

[411A]

I have carried a Jeppesen CR-3 for years and find that it is spot on in comparision with the aircraft ADC and FMS.

[galaxy flyer]

411A

I have no doubt that it would be spot on. With 3 ADCs in my current steed, I am wondering why you would do this computation. And besides, the data you would be entering comes from the ADC, so what's the point.

[merlinxx]

Jepp spinwheel

Still got mine from 1963, but print now not really readable & too many scratch marks for money conversions etc. Not gonna sling it though, untill the early 80s t'was still faster than a lecky calculator, never got to master an abacus, though they had them on the Chinese 70s & Ground Grippers!

[411A]

411A

I have no doubt that it would be spot on. With 3 ADCs in my current steed, I am wondering why you would do this computation. And besides, the data you would be entering comes from the ADC, so what's the point.

Ahhh, well mostly for time/distance comutations when the African ATC folks mandate a route change, and they want five estimates...right now.

[Checkboard]

I have carried a Jep CR3 for nearly 20 years now, and I still use it for fuel calculations and such. Once a year or so I complete PNRs and Mach calculations just for fun, but I don't need them here in Europe on the 737. In Oz on the steam driven aircraft the calculations were useful.

When I needed to complete the 14 JAR ATPL exams I was advised to buy the CRP, as "the Jep wouldn't give the correct answers." A little research showed that the Jep is set up for a recovery coefficient of .8 (matching most temperature probes on jets, certainly on Boeings) while the CRP is set up with a recovery coefficient of 1. In order to get the jep to match the CRP it is simply necessary to add an extra step of dividing by .8

I used the jep in all of the JAR exams, and passed all of them.

[BelArgUSA]

I still play with mine...

Gentlemen (and Ladies) -
xxx
Being an old fart, I have the privilege, and the right, to use a "whizzwheel". And my favorite is the Jeppesen CR-3 type. Yessssss. Actually, mine are "clones" of the Jeppesen originals. AeroProducts copied the CR in the 1970s. The only reason I prefer the AeroProduct model, is that they are white/yellow colors, unlike the original grey/white of the Jeppesen originals. The yellow/white makes them more "readable".
xxx
I have two actually. One is the 6 inch (15 cm) diameter model, which is in my flight bag, the other, the smaller is the 4 inch (10 cm) diameter "pocket size", which fits my shirt pockets. Of course the large one is more accurate, and is better for my waning eyesight (don't worry, I retire in a few months).
xxx
I think I bought them from some US$ 14 or 15.oo back then. A friend pilot in Europe told me that the "Aristo" whiizzwheels were superior. Well, the Aristo was maybe a better quality of material maybe, and certainly higher in price, about 4 or 5 times the price of the Jeppesen standard issue back then.
xxx
I had the pleasure to meet Ray Lahr, back then a UAL DC-8 captain, at a meeting at Mount San Antonio College near Los Angeles, which has an aviation department of excellent reputation, and where he was occupying a position in the academic team. Ray Lahr designed the CR slide rules. He told me that in effect, the CR was "too accurate" to use for some problems in the FAA written tests (ATP and F/E), and that the FAA was then using the USAF E6B type (metal) issue for computations in their performance problems.
xxx
The issue that has been mentioned about the "Ct" recovery coefficient of .8 is correct, but is extremely minor. Besides, my "Aeroproduct" clones, have a choice of .6 through 1.0 included. I fly a Classic 747, and the Ct of .8 seems to be accurate enough. Sorry if my TAS is 487 instead of 485 that I manage to read with my "confuser", but the ATCO of Dakar FIR don't mind if my estimate for the boundary is 04:32 and 17 seconds, rather than 04:32 and 23 seconds.
xxx
Funny is, some of the F/O nerds and geeks who punch numbers (with their fat fingers) on the FMS cannot beat my dexterity and speed of solutions that I derive from my old CR. My US$ 14.98 technology is at least equal to their US$ 14,980.98 FMS contraptions. Sorry for the devaluation...
xxx
So for me - my recommendation, is a large size CR-3 for your exams, and learn to use it, and study how they work. After all, I am sorry if you do confuse IAS and CAS. When I retire in November, I will still keep my little CR in my pocket when I travel, for exchange rates conversions of Pesos, to Dollar or Euros... darn convenient (and impressive) to use a CR to buy a bottle of 50 years old Courvoisier cognac in a store. Makes you almost look like an intellectual (or like there above mentioned, "geek or nerd").
xxx
Sorry, I can't stop getting back at the new generation of future captains, who occasionally might find the destination airport, can even speak Level 6 ICAO jargon, but are sadly limited to Level 1 for spelling on Pprune...
xxx

Happy contrails
.

[Chris Scott]

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.

[Kerosene Kraut]

IWA have good ones. Easy to read and durable quality. Find their website and choose "Produkte" up right.
and go to "Flugrechner" down on the very right.
You can even play around with it and move the wheels.


Last edited by someone else, not me.

[Denti]

Still have an Pooleys Aviat 617 in my flightbag. We got it in flightschool (was included in the fee) and i have used it ever since. Nowadays mostly for conversions and to cross check fuel (ltr. vs kg vs lbs vs whatever). All the other stuff is better done by the FMC and in Europe we don't really need to use it for navigational calculation.

But to be on the safe side i even still carry the booklet it came with, nice to explain the stuff i've forgotten about it .)

[Pugilistic Animus]

Yes, I know it's not much useful for Jet drivers, but for GA pistons the 'ol pocket E-6B deserves some recognition as well as the aforementioned the CR-3---

you can also do drift and track calculations but you need a good pencil


I love walking up to folks whilst turning that wheel and requesting " ask me Anything--- Anything!!

[Tinstaafl]

I keep my CR-5 in my flight bag. The CR-5 is the smallest of the CR types at ~3 1/2". Pretty much haven't used any other type since the late '80s. Can't beat the convenience & accuracy of CRs compared to slide types. Still have my Kane slide type though for a memento & due to them becoming a rarity. Rather heavy due to the thick aluminium construction and lacks Mach No. scales.

Mind you, the whiz wheel I use the most is the slide rule on my watch. It's just so bloody handy as a calculator.

[BelArgUSA]

Tinstaafl -
xxx
Fully agree with you for the CR-5 (in my shirt pocket) -
And like you, my old fashon Breitling slide rule is always set with the GS dialed above the "60" index arrow...
Old habit, but works great.
xxx
Too bad my eyesight is going to the dogs... soon will need a white cane.
And tap my way climbing the stairs to the flight deck.
Well, at least I will retire before the need of wheel chair and potty seat.
xxx

Happy contrails

[ITCZ]

Originally Posted by Private jet

Why do they give different results? Surely the mathematical formulae these devices work to must be the same that ADC's use and they are always spot on.

The answer to your question lies not in mathematics, but in the engineering and manufacture of your whizzwheel.

Interesting (and true) urban legend: Many mathematicians had sought to work out formulae or methods by which to play Roulette and break the bank at a Casino and thereby leave behind the icy garrets of their university chambers and take off to the Mediterranean and enjoy the company of wench(es) of agreeable proportions, etc.

But the first and reputedly only person to do so was not a mathematician, but an engineer.

In 1873 Englishman Joseph Jaggers, an engineer in Yorkshire cotton mills, wondered whether the roulette wheels at Beauz-Arts Monte Carlo Casino were balanced. He found one that was not. His three day stint at the Casino netted him around $325000 (in 1873, when the Colt from Old Regret was worth a thousand pounds!).

I digress. Engineering is the key, you see, not mathematics.

Whizz wheels are circular slide rules and work on the basis of representing numbers as 'distances' or positions on the wheel.

In 1614, John Napier discovered the logarithm which made it possible to perform multiplications and divisions by addition and subtraction.

a*b = 10^(log(a) + log(b))
and
a/b = 10^(log(a) - log(b))

See http://www.hpmuseum.org/sliderul.htm for full explanation.

Get yourself two sticks in the case of a slide rule, or two concentric wheels for a whizz wheel, and mark them with Logarithmic scales. Slide the scales until the one of the multiplicands is under the index, then the rule 'adds' the scales and the product is adjacent to the other multiplicand. Adding the logarithms in this way by lining up the logarithmic scales on the wheels/sticks gives you multiplication and division without batteries.

The precision (not accuracy) of the device then depends upon how closely your gadget can resolve numbers. This is a function of size of the scale.

So, first up, your 5" Pooleys yields much more accurate results than a 3" pocket Jepp whizz wheel, because it has a circumference 2.77 times the size of the pocket whizz wheel.

This is also why those circular computers on 'pilots watches' are nearly useless, being 1/25th the precision of a 5" and 1/9th the precision of a 3" whizzwheel.

For high precision up to the time of electronic calculators, you might have bought yourself not a straight slide rule,



nor a circular slide rule,



but a cylindrical slide rule with an enormous scale! This one had an outer scale that was 61' long and could still fit in your kitbag:




But even if you had a 5" Jepp to compare to your 5" Pooleys, you would probably still gain different results from the same calculations.

"A badly made slide rule will always give you the same answer for a given calculation ... and it will be just as wrong each time. So it all comes down to how accurately those scales were laid down on the rule in the first place, and how well they have stood up to the ravages of time since then. This is a much harder question to answer, and it can be virtually unique for each rule."

Accuracy of a circular rule may also be affected if the pivot in the centre of the wheel is not exact centre (eccentric movement) or badly worn, printing of the logarithmic scales during manufacture is not accurate, and as said above, accuracy of the logarithmic scales themselves. So better engineered and manufactured circular computers of the same diameter could yield better answers than cheap and cheerful ones.

Therefore if you are taking a Nav or other ATP exam requiring the use of a whizzwheel, use the same make and model that the examiner used!

http://www.sliderule.ca/intro.htm

All a bit rough and off the cuff but there you are.

[Capt Claret]

Bloody 'ell ITCZ, you've got way too much spare time on your hands!

Back to the PGC for you me thinks!!!!!!!

[ITCZ]

Whats a PGC?

B.Sc. in pure and applied mathematics, 1982-1985, old boy. Slide rule theory was a topic. Would have passed it had I not been kidnapped by the University XV. Damn those drinking games.

"Yippee-I-Ay, Yippee-I-Oh,
Fourier skins in the sky!"

Or something like that.

[parabellum]

When based in Germany made a special trip to Düsseldorf to buy the Aristo Aviat in the airport shop, best investment ever. Had a choice of slides, high and slow speed and the rotatable cursor on the front was invaluable. When it came to Flight Planning, Plotting and Nav Gen in the exams it saved many valuable minutes. Useful book of instructions and a nice leather case too!

[Lemurian]

I still carry a circular Jepp in my flight bag, used mainly for currency rate / prices.
Also use it for best TAS altitude computations.
But for nostalgia sake, I'd be very pleased to find an ARISTO AVIAJET 647 to buy . Lent mine to someone for his exams and I never saw him since...I loved that flight calculator, and I still wonder why it seems to have been discontinued.