UK Altimeter Settings Pre-WWII

[punkalouver]

Hi,

Could anybody tell me what altimeter settings were used pre-WWII. Was it inches of mercury or millibars?

If it was inches of mercury, when was the switch made to millibars?

Thanks

[longer ron]

I am certainly not an instrument basher but perhaps with the advent of the Mk XIV Altimeter and similar ?
pic is an early Mk XIV which clearly shows millibars.



Early Mk XIV

https://i.imgur.com/Yzke1Ot.jpg

[longer ron]

I have not been able to find a definitive list of RAF Altimeter types.
But from a quick look at various articles online I am doubting that many (if any) pre WW2 in service altimeters even had a subscale for precision altimeter setting.
Set the altimeter to 'zero' before take off 'simples' - what could possibly go wrong :)

[longer ron]

I have been trying to find out when Paul Kollsman designed the 'Kollsman Window' for displaying the altimeter pressure setting,but have thus far failed to find out when this feature was introduced into service altimeters.His original 1928/29 sensitive altimeter did not have it so I am assuming not introduced until mid/late 1930's.

[India Four Two]

punkalouver's question made me wonder when the Met. Office changed from inches of mercury to millibars in their weather reports. A cursory search of their website didn't reveal the date, but they do have a complete archive of daily weather reports, stretching back to 1860!

So I started doing a binary search through the archives and eventually I found this on Page 3 of the January 1914 archive (https://digital.nmla.metoffice.gov.uk/IO_85e78c53-82d9-487a-84da-345eaabfb916/):


https://cimg1.ibsrv.net/gimg/pprune.org-vbulletin/1524x336/screenshot_2023_02_18_at_17_14_47_5fb6c0517745f4c639c8ed94d3 109dc1b39dac83.png
https://cimg3.ibsrv.net/gimg/pprune.org-vbulletin/1056x678/screenshot_2023_02_18_at_17_15_10_e74e945d2c0971fcac588bfd1e 301a634a6d302e.png


So the date was the 1st of May 1914.


https://cimg4.ibsrv.net/gimg/pprune.org-vbulletin/1054x1154/screenshot_2023_02_18_at_17_16_04_119ba147d59f81e924502e5b31 d71fd9ebafdd8c.png



The comment about the United States Weather Bureau adopting metric units surprised me since public weather reports and TAFs and METARS still use inches of mercury and degrees F. So I decided to check and discovered that for their soundings and surface pressure plots, they do use millibars and degrees C. I had never noticed this before, since my limited flying in the States has mainly focused on TAFs and METARs.



https://cimg6.ibsrv.net/gimg/pprune.org-vbulletin/1255x842/screenshot_2023_02_18_at_17_46_41_e90fdf2010cde8e0288e6b00d2 102a59b6ca2de8.png


https://cimg1.ibsrv.net/gimg/pprune.org-vbulletin/1506x1800/screenshot_2023_02_18_at_17_51_14_9beacb1a41bdd3e0ed71f8874e 0c33055dd22062.png

[DuncanDoenitz]

Cracking bit of detective work, India42; quite a significant historical document. Very interesting that US agreed to the change but is still firmly in the "pounds, shillings and pence" camp in day-to-day life as well as aviation.

[India Four Two]

Thanks Duncan, it was an interesting exercise.

In Canada, we started using kilometres and km/hr in 1977 and started selling gasoline in litres in 1979. However, aviation is a mixture of metric units and "pounds, shillings and pence", as you put it. Altitudes and cloud heights are in feet, surface and in-flight visibility are in statute miles, DME ranges in nautical miles, runway lengths are in feet and temperatures are Celsius. One thing that will never change is the Altimeter Setting*, which for continental consistency is in Inches of Mercury.

So there are comparisons with Canadian English - a mixture of US and British terms!

* QNH everywhere else, but never used in North America. Most pilots would have no idea what a Q Code was. As an aside, QFE is not used, thank goodness. At my gliding club near Calgary, the elevation is 3700' ASL. Out of interest, I once tried winding an altimeter back to zero feet. I ran out of sub-scale! As a practical matter, students have no problem with releasing from tow at 5700' (2000' AGL) and planning to be in the downwind leg by 4500' (800' AGL).

[megan]

I have been trying to find out when Paul Kollsman designed the 'Kollsman Window'Likewise lr, absolutely nothing to enlighten. Kollsmans first altimeter pictured belowThe first rules of the air, agreed in 1919 by CINA in Versailles (France) after WW1, already mentioned 300 m vertical separation. The first “flight altitudes“ were defined as 400, 700 and 1000 metres above ground, so using QFE rather than QNH. The initial altitude of 400m was chosen to ensure clearance from obstacles (trees, chimneys, etc.) and compensate for the change in air pressure along the route. Hardly anyone ventured above 1000 metres in those days. Documents and procedures from those days referred to metric altitudes.In 1929, German-born Paul Kollsman, who had emigrated to the USA, invented a precision altimeter. The device was so accurate that it allowed the USA to experiment with 500 ft separation in the 1930s. The device used a scale in feet, with 1000 ft (roughly equivalent to 300m) which allowed for an easier to read scale. A calibration dial adjusted to the pressure on the ground (i.e., using QFE rather than QNH). Later models added the so-called Kollsman window to set the altimeter to the pressure on the ground. The design quickly became the industry standard and is still used today.The altimeter, before the introduction of the Kollsman window, was promoted as a level flight meter, set the needle to a thousand feet mark for reference, and maintain the altitude.


https://cimg6.ibsrv.net/gimg/pprune.org-vbulletin/996x1024/kolsman21_996x1024_48dc4c6ef7db8f52f65723e8d9f3b11f48b7bfd5. jpg

[India Four Two]

The altimeter, before the introduction of the Kollsman window, was promoted as a level flight meter, set the needle to a thousand feet mark for reference, and maintain the altitude.


​​​​​​​Wow, that would be REALLY easy to misread!

[longer ron]

Just talking about pre war altimeters,as far as I can make out the Gloster Gladiator Mk1 (1937) had an altimeter without the 'Kollsman Window' whereas the Glad Mk2 (1938) variant had a Kollsman Window type similar to the fairly ubiquitous Mk14 Altimeter.
So looks like the Glad Mk2 pilot could set the required millibars in the 'window' :) - thus I suspect that the window type Altimeters were coming into service use from approx 1937.
As far as I can make out - the elementary trainers probably carried on with the older windowless Altimeter until at least fairly late in the war.

[condor17]

India 42 , lovely detective work , thanks .
3 pointer altimeter still on lots of training Cessnas and Pipers , and still easy to misread ..
USA somewhere around millenium went to C from F in Tafs and Metars . 1st atlantic for skipper and myself on a 76..
ATIS gave -3 , '' that's not very cold '' we said .. Until exiting the a/c ... -3 F is Very cold !
Likewise having to use a conversion chart to work out QNH in millibars from Altimeter setting in Inchs ,,,,,, as bad as going through the Iron curtain , and converting Metres to Feet for our level off ...
TV screens on B744 made those charts redundent , we could use M or Ft , Millibars or Inchs.....
Begging forebearance , who named the Hector Pascal , and what idiot decided it had to be used on R/T if pressure below 1000mb ?
Mb would work just as well so US cousins set Mbs not Inchs of mercury .

rgds condor .

[India Four Two]

condor17,

Thanks.

Yes, all light aircraft I have ever flown had three-pointer altimeters, easy to misread but unlikely to affect most pilots, who never fly above 10,000' this side of the pond or FL100 over North Daarset*.

I have a similar story about arrival temperatures. One winter, I was flying home to Calgary from Chicago on United. The crew gave us the Calgary arrival weather at TOD. The temperature was a fairly mild -5º C. The American girl sitting next to me was horrified and I had to explain to her that it was equivalent to 23º F.

I read that adding "Hector Pascals" when the QNH is below 1000, is required so that US pilots don't mistake 996 for 29.96, which would be a serious error.

* PS Compton Abbas is one of my all-time favourite aerodromes.

[dixi188]

condor17,

Thanks.

Yes, all light aircraft I have ever flown had three-pointer altimeters, easy to misread but unlikely to affect most pilots, who never fly above 10,000' this side of the pond or FL100 over North Daarset*.

I have a similar story about arrival temperatures. One winter, I was flying home to Calgary from Chicago on United. The crew gave us the Calgary arrival weather at TOD. The temperature was a fairly mild -5º C. The American girl sitting next to me was horrified and I had to explain to her that it was equivalent to 23º F.

I read that adding "Hector Pascals" when the QNH is below 1000, is required so that US pilots don't mistake 996 for 29.96, which would be a serious error.

* PS Compton Abbas is one of my all-time favourite aerodromes.
Compton Abbas airfield has just been bought by Guy Richie. He wants to expand flying activity there.

[punkalouver]

Compton Abbas airfield has just been bought by Guy Richie. He wants to expand flying activity there.

How ironic. I heard that Madonna wanted to close it down when she lived nearby.

Was very busy when I flew in. Had difficulty finding it.

Thanks for the replies. It would be helpful if anyone who has photos of aircraft cockpits right out the factory to post. My preference is for Moth aircraft.

So many cockpits photos I find have instrument panel changes.

[longer ron]

Hi Punkalouvre
This is a pic of DH 60 G G-ABDX - looks like it has an original anti clockwise reading 'Zenith' altimeter :)

https://i.imgur.com/h0PBUxD.png

[longer ron]

The Zenith Altimeter pictured above is almost identical to late WW1 RFC Altimeters - presumably built by the Zenith Clock/Watch Company from Switzerland.

[22/04]

How ironic. I heard that Madonna wanted to close it down when she lived nearby.

I think the airfield responded by inviting her and Guy to visit. Seems to have worked.

[punkalouver]

Hi Punkalouvre
This is a pic of DH 60 G G-ABDX - looks like it has an original anti clockwise reading 'Zenith' altimeter :)

https://i.imgur.com/h0PBUxD.png
Thanks. I never did understand the reason for placing some instruments at an angle.

Does anybody have old black and white photos of later model Moth cockpits as out of the factory.

[longer ron]

Thanks. I never did understand the reason for placing some instruments at an angle.

.

I guess sometimes for 'ease' of mounting - here is a pic of another moth with similar Altimeter but mounted on the face of the Panel so that the 'zero' knob could be placed in a sensible position :)
Similar with the RPM gauge - mounted on the face of the panel so that the orientation makes it easier to read at a glance.


https://i.imgur.com/vX5TKtt.jpg

[megan]

I never did understand the reason for placing some instruments at an angleWas something done even by operators of large equipment at one time with engine instruments, dial would be mounted so that the needle when giving a "normal" reading would be aligned to a certain clock position, three o'clock for example. Made for simple scanning, any non normal reading would be obvious.

[punkalouver]

Was something done even by operators of large equipment at one time with engine instruments, dial would be mounted so that the needle when giving a "normal" reading would be aligned to a certain clock position, three o'clock for example. Made for simple scanning, any non normal reading would be obvious.
Like the many hydraulic pressure gauges on the C-130 givin 3000 psi at 9 o’clock.

[longer ron]

Yep sometimes for orientation for ease of instrument scan,sometimes for ease of fitment,in the pic I posted at post #18 - the altimeter has been mounted at the angle to have the adjustment knob a the 6 ' clock position because with the instrument mounted fwd of the panel it just meant a small cutaway to be able to twiddle the knob :)
The pic I posted in post #19 has the instruments screwed onto the face of the panel so that they can be orientated where preferred,the altimeter still being a little 'squint' but positioned to put the knob clear of the centre portion of the Slip Ball - but of course the panel looks much less 'tidy' than the panel in post #18.

[longer ron]

'Jason' appears fairly original - this is a pic of rear cockpit,the mix of instruments seem fairly consistent on most moths but obviously the mounting does vary quite a bit,but the Altimeter type (Zenith) does seem to be the standard fit.

https://i.imgur.com/mWLLONn.png