Service ceiling vs operating ceiling

[Ansonross]

In my uncle's diary (Ace Archie Nathaniel Jenks, RFC, Squadron #20) he describes taking reconnaissance photos in an FE2b from an altitude of 16,000 feet. This seems very high compared to a stated service altitude of 11,000 feet. Is there an error here? It must have taken a long time to reach that altitude.

Worth quoting Archie's notes "It was bitter cold at this height-my fingers ached with the cold- on the way home I had to hold the "joy-stick" while my pilot warmed his hands. When we got to the ground the camera, magazines, guns, etc. were covered with frost. It was the highest I had ever flown and tgeweather was the coldest."

[gipsymoth236k]

I think there's a description of "Service Ceiling" that being where the rate of climb reduces to 100 FMP max, whereas "Absolute Ceiling" is where any further climb capability stops.

Is this correct?

Regards, Gary

[YavorD]

Originally Posted by gipsymoth236k

...

Is this correct?

Regards, Gary

Yes! The real meaning is one can reach the service ceiling within reasonable time and spend some time on that altitude but the fuel supply and cold will not permit a journey too long.
Going any further up is practically impossible because any small air disturbance and control action will tend to increase the drag and the gravity is going to pull the aircraft downwards.
The absolute ceiling is just a theoretical value.
Both the service ceiling and the absolute ceiling are function on aircraft weight and air density (i.e. pressure and temperature).

Best regards,
Yavor

[R Gannon]

Hi

I think the misconception is that the ceiling of 11,000ft pertained to the FE2b with 160hp Beardmore, whilst Jenks served with 20 Sqn May-Oct 17 which were equipped with the FE2d powered by a 250hp RR and which had a ceiling of 17,500ft.

Cheers Russ

[HoHun]

Hi,

Originally Posted by Ansonross

In my uncle's diary (Ace Archie Nathaniel Jenks, RFC, Squadron #20) he describes taking reconnaissance photos in an FE2b from an altitude of 16,000 feet.

That's quite interesting, as roughly 16000 ft or 5000 m is the height our fellow forum member Bletchley gives as the operating height for high-quality cameras equipped with the rare 50 cm focal length lens.

Here a couple of relevant paragraphs I copied from Bletchley's article in this thread: https://www.theaerodrome.com/forum/s...ad.php?t=75645

From 1917 onwards the British stock of camera lenses was supplemented by a small number of 50cm (equivalent to 20 inch) or 120cm lenses ceded from the French, although in the negotiations with the French at an inter-allied conference on the glass situation as late as April 1918 the British representative commented that they had only 12 of these for the entire British air force and required a minimum of 62 a month.

[...]

An even smaller number of 50cm and 70cm lenses were taken from German high flying reconnaissance aircraft brought down reasonably intact within the British lines (mostly from engine failure, lost or disorientated pilots, or by anti-aircraft fire – but also by a remarkable run of success by just one pilot, McCudden, over a period of a few weeks in the winter of 1917/18, in a scout personally modified for very high altitude interception) (Leaman; McCudden).

[...]

The adoption of a longer focal length and the larger plate size meant that the French, from a relatively early point in the war, could take photographs at the same scale and level of detail as the British but from a much higher altitude, and could get better ground coverage from each photograph (so fewer photographs needed to be taken).

The difference this made can be seen clearly in a comparison that was made in the Gorrell Report: with their standard ‘L’ or ‘LB’ type camera and an eight and a quarter inch focal length the British could take photographs at a map scale of 1:9522 from 6562 ft (or with a ten inch focal length, 1:9830 from 8202 ft, with ground coverage of 857x1141 m) on a 4” by 5” plate.

By contrast, the French with an ‘F.2’ camera and a 50 cm focal length could take photographs at the same approximate scale of 1:10000, and the same level of detail, from 5000 m (16404 ft) or about twice the altitude, with ground coverage of 1700x2300 m on a 18x24 cm plate (which is approximately four times the coverage). (Gorrell)

The French and British both organised photographic reconnaissance missions into two echelons. Close reconnaissance of the front was the responsibility in both the French and British air force of squadrons or escadrilles that were tasked to support infantry and artillery (along with observation for artillery, close support, and cooperation with infantry). Long-range reconnaissance for Army Headquarters became the responsibility of a smaller number of specialist units equipped with faster aircraft capable of reaching higher altitude.

If your uncle's diary happens to mention anything related to the cameras he used, Bletchley would probably love to learn more about it, I imagine ;-)

Regards,

Henning (HoHun)

[Ansonross]

To Henning (HoHun) I'm inept at navigating this site so I hope I'm hitting the right keys to thank you for this detailed reply. There were no details about cameras or lenses in Archie's diary. Concentration seemed to be on just getting the job done.

Thanks again for the detail. Most interesting. Anson