WW2 Speed Measurement

[stona]

Dava Sobel in her book "Longitude" relates the story of an British fleet of 4 warships that ran aground in Sicily this way.

I think you mean the Isles of Scilly rather than Sicily. I've read Sobel's little book and very good it is too. She referred to the disaster that befell Sir Cloudsley Shovell's fleet in 1707. The 'Longitude Act' of 1714 was passed under Queen Anne and established the Commissioners of Longitude with prize money to reward a longitude solution that was 'practicable and useful at sea.'

Cheers

Steve

 

[FLYBOYJ]

Sure, but in ye good old days of WW2 a man called a navigator would still use a chronometer and sextant to workout longitude and latitude. If he knew his speed in knots as well as heading he could conveniently estimate his change in position, between fixes, in terms of degrees, minutes and seconds. The knot and nautical mile is superior for this. In many cases fixes were via radio navigation beacons.

You see plexiglass bulbs in the dorsal position of many bombers to take a celestial reading, the end of the glass house in the Lancaster I assume but often evident in flying boats.

Maybe in the RAF

There were sextants installed in some US aircraft. When I worked on the P-3 production line, we were putting them in some production aircraft as late as 1983 IIRC. They were hardly used from what I was told and weren't going to help you much if you couldn't get a fix.

Pilotage (visual reference to the ground), dead reckoning (using true airspeed, winds aloft, heading and time to calculate new position from last known), radio, celestial, or any combination of these four were mainly used by a USAAF navigator. I don't think chronometers and sextants were widely used. The main tools of a AAF navigator was an E6B and plotter. There was also a tool called a plotting board.

 

[stona]

Every RAF navigator in WW2 was equipped with and could use a Mk IX sextant. There were five slightly different versions. It was as much a tool of his trade as a watch and compass.

Many/most missions were flown at night which inevitably posed different problems to those faced by his US colleagues. Not least he could rarely, if ever, see the ground but he could see the stars and other heavenly bodies. 10/10 cloud prevented US navigators from seeing the ground, sometimes with disastrous results.

Cheers

Steve

 

[Clayton Magnet]

I grew up in Canada in the 80's, post metric adoption, so all I learned in school was metric. Everyone still measures height and weight in feet and pounds, but distance and volume in kilometres and Litres. I had no real knowledge of imperial units until I graduated college as an aircraft mechanic, and was thrust into the realm of american manufactured aircraft. So now we get to deal with evrything, for example, fuel is dispenced in Litres, the aircraft measures its fuel load in pounds, we calculate the capacity in american gallons, but the fuel truck picks it up from the refinery in imperial gallons. One gets used to it , but hopefully in a few more generations the use of metric will actually become universal, as was intended 35 years ago.
unrelated to aviation, but I recently bought a Subaru Impezza. Fuel economy listed on the website reveiw was in miles per US gallon, same figures from the canadian dealer listed it in miles per imperial gallon, and the sticker at the dealer was in L/100Km. Juggling various units can be annoying at best, or dangerous at worst, like the mars probe mission a few years ago.

 

[stona]

Juggling various units can be annoying at best, or dangerous at worst, like the mars probe mission a few years ago.

Air Canada Flight 143 (the Gimli Glider) being a case in point.

Cheers

Steve

 

[pbehn]

England should adopt the metric system for football (soccer). While the pesky Germans have only 11m to score a penalty the poor English have to do it in 36ft.

 

[fastmongrel]

England should adopt the metric system for football (soccer). While the pesky Germans have only 11m to score a penalty the poor English have to do it in 36ft.

So thats why Germany keep beating England in shoot outs. They cheat by spotting the ball closer nothing to do with England being rubbish at penalties

 

[pbehn]

So thats why Germany keep beating England in shoot outs. They cheat by spotting the ball closer nothing to do with England being rubbish at penalties

I worked in Germany for many years and with German people in many other countries, they were always amused and a little surprised when I pointed out how their obvious and cynical use of the system of measurement to blatantly cheat to gain a victory had been rumbled.

I have looked up the measurements on the FA website ......in metric it is 11m in imperial it is 12 yards (36ft) but 11m isnt 12 yards they have a 27mm advantage....I will write to my MP it is an outrage.

 

[FLYBOYJ]

Many/most missions were flown at night which inevitably posed different problems to those faced by his US colleagues. Not least he could rarely, if ever, see the ground but he could see the stars and other heavenly bodies. 10/10 cloud prevented US navigators from seeing the ground, sometimes with disastrous results.

Not as easy as you may think. If you have any high clouds a sextant is all but useless. I knew navigators who never used them. Dead reckoning worked well and although the ground could obscured one could hope for "breaks" so visual references could be made. I've flown at night "over the top" and you could still pick up a lot of visual references through patchy clouds. Although the same could be said for celestial navigation, you were still in the blind when calculating you're exact location when over a target. Additionally attaining a celestial fix required the aircraft to be straight and level. I believe that the USAAF mainly used celestial navigation as a crosscheck to DR (when possible) and when traveling over long water routes.

 

[pbehn]

Not as easy as you may think. If you have any high clouds a sextant is all but useless. I knew navigators who never used them. Dead reckoning worked well and although the ground could obscured one could hope for "breaks" so visual references could be made. I've flown at night "over the top" and you could still pick up a lot of visual references through patchy clouds. Although the same could be said for celestial navigation, you were still in the blind when calculating you're exact location when over a target. Additionally attaining a celestial fix required the aircraft to be straight and level. I believe that the USAAF mainly used celestial navigation as a crosscheck to DR (when possible) and when traveling over long water routes.

I think it was a surprise to American crews posted to Europe that the whole continent could be cloud covered for long periods. Dropping below the cloud is hardly an option if you are over the sea and if you dont know where you are it is possibly fatal, I have walked many times in the clouds on the N York moors which are mainly 1500ft and close to the sea, many many bomber boys died there.

 

[davparlr]

When I got out of the AF in late '74, the C-141 navigators still used the sextant. Our navigational equipment used by the navigator consisted of a dead reckoning computer and a Doppler computer, which used a Doppler radar provided ground speed and drift (a wonderful flying aid for approaches), Loran, radar (primarily a weather radar), and sextant. Good navs used all their assets in plotting positions. Pilots used "fly East", "fly West". When I was flying the Atlantic from Europe I always figured that if I flew west I would eventually run into the USA, and, we could always depend on some F-106s to escort us in. Piece of cake. Also, in the Atlantic, Ocean Station Vessels (Coast Guard Cutters), were stationed capable of giving radar fixes. Flying near the poles the nav took over control of the gyro compasses from the magnetic azimuth detector (MAD) and told the pilots which headings to fly, which often made no sense. Another interesting note about the sextant, which was like a periscope, removing it and connecting a vacuum hose, provided, made a great cleaning aid, sucking up everything that would fit. Also, prior to leaving, the crew was issued a computer generated flight profile. Using that was reasonably accurate but not enough for the Air Defense Zone (ADIZ).

 

[soulezoo]

I can attest to the above as it relates to the C-141. The sextant tube was located quite conveniently at the navigator's table just behind the pilot. When INS (Inertial Navigation) was employed, the navigators were "unemployed" and the navigator's table became a nice place for the loadmaster or crew chief to hang out.

 

[stona]

The sextant needs to be straight and level. The Mk IX and its predecessors were all 'bubble sextants'. Obviously taking readings whilst manoeuvring violently would be impossible, but a bomber flying in the stream would be flying as straight and level as is reasonably possible.

One of my late father's colleagues (also, alas, no longer with us) was a Bomber Command navigator and regaled me with many humorous stories about sextants and celestial navigation amongst other things. Let's just say that despite the best efforts of the training staffs some were better at it than others. My now longstanding interest in Bomber Command and the men and women who served in it stems directly from that man.

Cheers

Steve

 

[fastmongrel]

Theres a MkIX bubble sextant for sale on ebay. Tempted to put a cheeky bid in.

Old RAF bubble sextant war II used in Wellington Bombers plane. Model No MK IXA | eBay

 

[Token]

In the U.S.A. we've had car speedometers with both mph and km/hr for more than 35 years. We know how fast we're going in either unit and see no reason to change the units in our own country. If foreign people come here and rent a car, the speedometer is clearly marked in both units. There is NO excuse for speeding and saying you didn't know. The cops don't buy it.

This dual marked speedo can lead to its own issues. For folks in other countries the US cars typically have a speedometer with MPH in larger numbers around the outside of the dial indicator, and km/h in smaller numbers around the inside of the dial. So that looking at the speedometer you can read out MPH or KM/H, just by looking at the outside or inside markings.

Since street signs in the US are in MPH (sometimes with KM/H included) you get in a habit of ONLY reading the outside, larger font, numbers. Most people ignore the inner, smaller font, KM/H numbers.

No problem.

On a recent business trip to New Jersey my rental car had Canadian tags. While I noticed that as I walked up to the car I really gave it no thought, in states near the Canadian border this is not uncommon when renting from large rental companies.

Driving along the freeway I was doing 65 MPH on a 55 MPH marked road. And traffic was passing me at a significant clip. I just thought folks in NJ had a healthy disrespect for the posted speed limit on freeways. Then I got on surface streets, marked at 45 MPH. So I drop down to 45 MPH, and I was the slowest traffic on the road, by far.

Somewhere in there I realized I was reading the larger font numbers on the outside of the speedometer dial, as I was used to. However on this Canadian car the outside numbers were KM/H, and the smaller inside numbers were MPH. DOH! When I thought I was at 65 MPH I was really at 65 KM/H.

T!

 

[pbehn]

Somewhere in there I realized I was reading the larger font numbers on the outside of the speedometer dial, as I was used to. However on this Canadian car the outside numbers were KM/H, and the smaller inside numbers were MPH. DOH! When I thought I was at 65 MPH I was really at 65 KM/H.

T!

In Saudi Arabia the marked speed limit is per person so a Merc with 4 teenagers in is unrestricted, anyways, thats the only explanation we could figure out for how they drive.

 

[Koopernic]

Pilot manuals for F4U-1, Avengers and SBD-3 all give ranges in Nautical miles and give aircraft restrictions (dive speeds, lowering landing gear, flaps etc) and landing speeds in knots. One would assume that the airspeed indicator was knots (photos are too small to tell) to prevent mental gymnastics in the cockpit. When or even if there was a change over I don't know. US Navy may have used Knots in the 30s if not before.

Manual for the TBD-1 (Douglas Devastator) uses knots.

One would assume that when on landing approach to the aircraft carrier (speed in known in knots) with a headwind(in knots) that the airspeed indicator on the aircraft would best be in like units.

 

[GregP]

Out-thought by a speedometer? I suppose it had to happen sooner or later.

The nautical mile will never go away; it's too handy for navigation unless they redefine lattitude and longitude to be metric. So you'll be dealing with mixed units if you go to sea or fly aircraft ... or use a GPS. The only good thing about the GPS is it can convert to km for those who are lattitude and longitude impaired.

Upon reading this later it sounds a bit sarcastic, but was in fact a poke at myself since that happened to me once, too. Live and learn. Never happened again!