German Constant speed props

[rc.gardner]

I am having difficulty translating a paragraph of Propellermerkbuch Der Luftschrauben-Abteilung der Prüfanstalt und Werft der Fliegentruppen which was a propeller handbook for units issued by the P & W department of Idflieg at Aldershof in 1916. My German is limited and whilst I have struggled through the rest of the book, paragraph 13 below has defeated me. I also include para 12 and 14 to give some minor continuity, but it is para 13, which is about constant speed props, that I can't get my head around. I would much appreciate a translation.


12. Man darf die Leistung einer Schraube nicht nach
der Turenzahl beurteilen. Sämtliche Schrauben
typen sind im Fluge geprüft, und man kann mit
jeder Schraube, die für den betreffenden Motor ge
prüft ist, gute Flugleistungen erzielen, unbekümmert
um die Drehzahl.

13. Das Turenaufholen der Schrauben ist nicht
unbedingt nötig. Es hat sich im Gegenteil heraus-gestellt, daß Schrauben, die so konstruiert sind, daß sie wenig oder garnicht aufholen, bessere Flugleistungen und kürzeren Start haben, weil der Motor beim Start und beim Steigen seine volle Leistung hergibt. Ferner haben diese „Schrauben mit konstanter Drehzahl" den Vorteil, daß man, ohne den Motor zu überlasten, bei J400 bis 1480 Uml./Min. ganz flache Gleitflüge mit Vollgas bei ganz erheblich gesteigerter Geschwindigkeit ausführen kann; der Verlust an Höhe bleibt dabei auch bei großen Flugstrecken sehr gering. Eine andere Eigenart dieser Propeller ist, daß die Turenzahl bei starkem Ziehen unter die Standdrehzahl zurückgehen kann. Diese Erscheinung hat mit der Wirkung der Schraube nichts zu tun, und beeinträchtigt die Flugleistung und Flugsicherheit nicht.
Der Turenzähler ist ein Kontrollapparat für den Gang des Motors, nicht für die Leistung der Schraube.

Es kommt häufig vor, daß in größeren Höhen der Turenzähler bei gleicher Fluggeschwindigkeit weniger Uml./Min. anzeigt, als unten. Diese Erscheinung ist auf den Motor zurückzuführen, und hat mit der Schraube nichts zu tun.

14. Wer nicht das Gefühl für die Lage seines Flugzeuges hat, und daran gewöhnt ist, nach dem Turenzähler zu fliegen, muß sich, da bei Schrauben mit konstanter Drehzahl dieser Anhaltspunkt versagt, einen Geschwindigkeitsmesser in sein Flugzeug einbauen, und danach fliegen.

With regards,

Bob

[YavorD]

Hi, Bob!

Sorry, my Deutsch is not good enough to submit a translation, only a simple note! It is not about controllable pitch "constant-speed" propellers in a modern sense. As much as I can comprehend, it is about propellers optimized for take-off and climb, which can not use full engine power at high speed level flight, at least at low altitude. Flying an aeroplane with such a propeller, pilot should keep in mind "red-line" rpm.

Regards,
Yavor

[rc.gardner]

Hello Yavor,

Many thanks. It's the bit about constant speed propellers that has puzzled me. I can't get the rest of my translation to fit in with this concept. Most of the book has very basic information about how to fit props to aircraft etc so a paragraph on Schrauben mit konstanter Drehzahl seems a bit out of context. Although I can translate the words, I don't understand them in English!

Bob

[rammjaeger]

a fast try for 13 with my Pidgin-English: .

It is not absolutely necessary that the (air) screw is catching up with the „Touren“ (= revolutions of the engine). To the contrary it was found that screws - which are constructed in a way that makes them only a bit or not at all catching up – have a better flying performance and shorter start (runaway) because the motor gives the full performance during start and climbing. Furthermore these "(air) screws with constant revolution" have the advantage that they are allowing – without overstressing the motor – very flat gliding flights with full throttle and considerably increased flying speed with 1400 to 1480 revolutions per minute. During this the loss of altitude is low even over longer distances. Another characteristic of the propeller is that the number of revolutions can sink below the standard number of revolutions during strong pulling (climbing).
This appearance has nothing to do with the effect of the screw and is not affecting the flight performance and safety of flying. The revcounter is a controlling device for the running of the motor and not for the performance of the screw.

It happens frequently that the revcounter is displaying fewer revs/minute during the same flight speed in higher altitudes than down (in lower altitudes). This appearance is caused by the engine and has nothing to do with the screw.

[Catfish]

Hello,
i am german but i have to admit i do not fully understand what is meant with this "Aufholen" of the propellor (i think in english it is propellor rather than screw(?)). It seems the propellor does not reach the engine rpms, and it does not have to (!) according to the text.

Is there any information on for which kind of plane this constant revolution propellor was used ? Because there is another thread where a reduction gear was used in the G and R planes, and this text seems (not sure!) to indicate that the propellor has another revolution than the engine - but not a fixed reduction as in the other thread, but rather maybe with some kind of gliding clutch (then made of leather, nowadays would have used visco-coupling).

Greetings,
Catfish

[rammjaeger]

English/American English:

airscrew
air-screw
screw-propeller
(air) propeller
(air) propellor
airplane propeller

[YavorD]

Originally Posted by Catfish

Hello,
....
this text seems (not sure!) to indicate that the propellor has another revolution than the engine - but not a fixed reduction as in the other thread, but rather maybe with some kind of gliding clutch (then made of leather, nowadays would have used visco-coupling).

Greetings,
Catfish

Hi, Catfish!
Just my opinion. I do not think it is the case in Paragraph 13.
It is not about reduction gear or variable coupling either but a simple note about the fact engine can not always attain rated rpm.

Regards,
Yavor

[rc.gardner]

Sehr geehrter Herr Rammjaeger und Catfish!

Viel Dank für Ihre Hilfe.

I am relieved that your translation is much the same as mine. The problem now is that I don't understand paragraph 13 in German or English!

The rest of this handbook is very simple. It explains, for example, that you must fit the propeller to a hub, then tighten the bolts, then run the engine for a few minutes, then check the tightness of the bolts etc.

But then this paragraph describes the characteristics of 'constant speed propellers' which were not widely available at Jasta level in 1916. And I do not understand the description of a flat gliding flight at full throttle reaching a high speed which does not overstress the engine with little loss of height.

Yavor's advice that it simply refers to some props which can't reach the correct speed (or condition speed indicated by STAND) is a considerable help but I have not yet grasped what the author is describing. Like Catfish I don't even know what Turenaufholen means; Turning up-get?

Can anyone help?

In hope,

Bob

[Roadhog]

Dear R.C. I always want to pitch in and help a fellow Welshman but my technical German lingo ends with the severe warning: "Actung! Keinen mitten graben ven das lichten blinken!" I'm soooooooo sorry but I just coudn't pass that one up. VR, Scott

[Taz]

Bob- I think all they are trying to say is you can exceed the normal rev limits at full throttle for the engine and prop for increased speed in a shallow dive without affecting prop performance or safetly. Similarly in a climb or where pulling strongly (max performance turn or high speed at low altitudes), propeller revolutions and engine speed may be reduced due to the high Q (dense air) or heavy load during climb (essentially hanging on the prop in a climb) without affecting performance or safety.

Essentially, air density, flight attitude, and flight regime (g load) may affect engine and propeller speed without substantially affecting performance or safety. This would become even more important with the überkomprimierte (overcompressed) engines coming on line in late 1916, where horsepower remained constant up to a given altitude as high as 3200 m (BMW.IIIa) and the high horsepower and low Q could make both engine and propeller speed higher.

Taz
Terry Phillips