Interpreting marks on cockpit instruments

[RCnoob]

My first post...
I have been examining photos of Luftwaffe cockpits to see what kinds of supplemental information were available to pilots. I have become curious about one in particular. Many altimeters appear to have red marks at altitudes that look to me like ~300m and ~700m.

Am I reading this correctly? What would be the purpose of such marks?
Here is one that appears to have the altitudes adjustable:


In other cases e.g. airspeed, the markings are probably limit marks. For example here, maximum permissible indicated air speed at different altitudes:


I have many other questions about aircraft cockpits, especially use of checklists and procedures, but I'll save those for another message.
Thanks for any information.

[Snautzer]

(remarks made by gc cooper on lemb)
Fein-und Grobhöhenmesser Fl.22322
Two adjustable pointers are attached to the rim of the altimeter, one behind the glass, one in front. These can be utilised for the following:

- to indicate the prevailing (Altitude) air pressure at the airfield.
- to indicate the elevation of obsticles along the flight route
- to indicate the altitude that is desired to fly on the mission
- to indicate the base and tops of cloud when flying through cloud layers.

[harrison987]

Hi...

The altimeter worked via air pressure (like a barometer). As such, at ground level, the air pressure needle will change the altitude reading indicated by the main needle. So one day, it could be set at "zero"...but the next day could read 0.1 or even -0.1, as the surrounding air pressure changes.

By turning the millibar knob at the bottom, this turned the needle, the small white indicator at the top (980...975), AND white arrow simultaneously, so the pilot/ground crew could accurately re-adjust the main indicator to "zero" before flight. They all worked in conjunction with each other.

The red triangular indicators were moved by adjusting the E/F sliders. These only indicated 100m increments, and as such they could not indicate:

- the altitude that is desired to fly on the mission
- the base and tops of cloud when flying through cloud layers.
- to indicate the elevation of obstacles along the flight route


On the later altimeters (1943 and onwards), the white arrow and red "E/F" sliders were removed, as they were never used or needed.


In your 2nd photo, the markings are indicating the MAXIMUM suggested airspeed at the indicated altutudes. For example, at 6km in altitude, 400 km/hr is the recommendation.
Mike

[RCnoob]

Thank you! I never would have figured this out on my own. These marks appear on a lot of altimeters. But it did not occur to me that since the main dial only covers 1000m, they could not be used for very much.

Now a follow-on question. I have seen diverse instrument markings. But there is little consistency across aircraft. These markings are useful, and for example the US went to more and more of them over the course of the war.

For example on one He 111 engine instrument panel, there are:
Hand-marked temperatures at 40 and 80 degrees C. Presumably these are high and low limits. (Gauge label = drücken Eintr. Temp. = ??)
A metal placard showing maximum temperatures at different altitudes.
RPM gauge with hand-marked limit at 2100 rpm. Presumably this is normal operating level.

Question: does anyone know history/use of such markings? Why weren't they used more widely, especially as less trained pilots became common?
Question2: The instruments are numbered eg M50, M52. Are these original labels, or added later by archivists?
thanks for any insights.
Roger

Higher resolution version of the panel is:
http://www.cockpitinstrumente.de/dow...0panel%20d.JPG

[harrison987]

The markings were generally used on all aircraft. And of course, depending on the aircraft and engine type, the markings varied.

However...I have found both early and late instruments panels that did not have any markings at all...it was really dependant on the ground crew in many cases.

The "M" codes on the He111 panel are electrical codes, so the mechanics and ground crew know which plugs and connections go where and for what purpose.



mike

[Pete63]

Originally Posted by RCnoob

My first post...
I have been examining photos of Luftwaffe cockpits to see what kinds of supplemental information were available to pilots. I have become curious about one in particular. Many altimeters appear to have red marks at altitudes that look to me like ~300m and ~700m.

Am I reading this correctly? What would be the purpose of such marks?
Here is one that appears to have the altitudes adjustable:


In other cases e.g. airspeed, the markings are probably limit marks. For example here, maximum permissible indicated air speed at different altitudes:


I have many other questions about aircraft cockpits, especially use of checklists and procedures, but I'll save those for another message.
Thanks for any information.

Hi RCnoob,

For what it's worth: could the red indicators on the first instrument not simply mean that the power is off and the instrument should not be trusted (red warning) until the power came on..?

The second instrument shows max speeds on applicable altitudes, meaning:

do not exceed 490 km/h at 3000 metres
do not exceed 465 km/h at 4000 metres
do not exceed 435 km/h at 5000 metres
do not exceed 405 km/h at 6000 metres

This has everything to do with air pressure dropping when you're climbing (gaining altitude)... The change in outside air pressure calls for slower speed read-outs. This only tells you something about indicated air speed, it doesn't tell you what the actual ground speed is at that moment...

From Wikipedia: some Aeronautical terms concerning 'air speed':

Prior to 1969, airworthiness standards for civil aircraft in the United States Federal Aviation Regulations specified that distances were to be in statute miles, and speeds in miles per hour. In 1969 these standards were progressively amended to specify that distances were to be in nautical miles, and speeds in knots. (Note: WW 2 Luftwaffe was using kilometers (per hour)..., Pete63)

The following abbreviations are used to distinguish between various measurements of airspeed.
KTAS is "knots true airspeed", the airspeed of an aircraft relative to undisturbed air.
KIAS is "knots indicated airspeed", the speed shown on an aircraft's pitot-static airspeed indicator.
KCAS is "knots calibrated airspeed", the indicated airspeed corrected for position error and instrument error.
KEAS is "knots equivalent airspeed", the calibrated airspeed corrected for adiabatic compressible flow for the particular altitude.
Note that the indicated airspeed is close to the true airspeed only at sea level in standard conditions and at low speeds. At 35,000 ft, an indicated airspeed of 300 kts may correspond to a true airspeed of 500 kts in standard conditions.

Just my and Wikipedia's 50 cents...

Many happy landings!
Piet

P.S. The German text "Höchst Zulässig" means "Highest admissable/allowed" read-out for that specific instrument... The word "Anzeige" means "indication"...

[Pete63]

RCnoob,

I did some more research and the red triangles are certainly not 'off flags', as I suggested earlier...

The hand adjustable "E"-slider moves the red triangle on the left and is used for indication of 'QFE' pressure. (atmosferic pressure at airfield elevation - on the ground your altimeter would indicate "0", in case of the correct QFE setting... Even if your landing ground was at 300 metres above sea level, e.g.)

The hand adjustable "F"-slider moves the red triangle close to it for indication of 'QFF' pressure. (pressure calculated for sea-level (The place at which the pressure was measured was taken into account as well as the atmosferic conditions) - QFF corresponds with values found on isobaric weather charts for ground level)

The turning wheel at the bottom of the "Höhenmesser" (altitude indicator) can be used before and also during the flight to set the proper pressure setting that is valid on the ground.

(This "Fein-Grobhöhenmesser" was compensated for temperature differences for the entire read-out range. A producer of such instruments was R. Fuess from Berlin-Steglitz.)

In German the original text about this instrument reads:

Besondere Merkmale: temperaturkompensiert über den ganzen Meßbereich.
Bodenluftdruck vor oder während des Fluges durch Drehknopf an Hillfs-Millibar-Skala einstellbar. Relative "Null"-Einstellung (auf den Boden bezogen) stets möglich.
Beim Fein-Grobhöhenmesser erlauben die mit E (QFE) und F (QFF) bezeichneten von Hand verstellbaren Marken das Festhalten der angesagten Luftdruckwerte.

(source: © page 245 / Flugzeug-Typenbuch / Helmut Schneider / originally: 1939/1940 / book was re-issued after the war)