The Ju 88 propeller controls-How did they really work?

[ATAG_SKUD]

So I've been trying to find out exactly how the Ju 88 propellers worked in the A-1 and A-4 models.

I'm kinda stuck on a few key understandings so I'm turning to the great bastion of knowledge and good German speakers on this forum for help.

I've read a lot including original German manuals that I probably don't fully understand because my lack of skill in basic German. But this is what I think I know:

1) The 88 could have either VDM or VS11 props although the VS 11 was  more likely until later model 

2) They both were constant speed props

3) They both had automatic feathering

4) Both had switches to change from automatic control to manual control (although I have seen pictures of the switch missing on both IL2 rendered cockpit and original manuals. I have also seen it included on original manuals)

Here's where they differ:

1) The A4 has finer adjustment of RPM through a lever

2) The A1 seems to be set at 2400 RPM when set to automatic

Here's what I don't know:

1) Was RPM setting variable on the A1?

2) Was manual pitch adjustment possible on the A4 independent of RPM setting (for example if you wanted to calibrate the RPMs between engines)?

3) Were they different from the VDM and the VS11? (I think that's what the picture in the  next post is telling me, but my German isn't good enough)

4) When was the VDM used and when was the VS11 used?

5) Most literature says the VDM had finer pitch controls but the layout pictures show the VS11 with the big levers- it seems backwards

Here are some pics:

From A-1 Manual

From A-4 Manual

From a different A-4 Manual

 A picture and some sketches of the panel from an A4 looks like prop pitch switches:

Edited May 8, 2020 by ATAG_SKUD
clarity

[Retnek]

6 hours ago, ATAG_SKUD said:

So I've been trying to find out exactly how the Ju 88 propellers worked in the A-1 and A-4 models.

I'm kinda stuck on a few key understandings so I'm turning to the great bastion of knowledge and good German speakers on this forum for help.

I've read a lot including original German manuals that I probably don't fully understand because my lack of skill in basic German. But this is what I think I know:

1) The 88 could have either VDM or VS11 props although the VS 11 was  more likely until later model 

2) They both were constant speed props

3) They both had automatic feathering

4) Both had switches to change from automatic control to manual control (although I have seen pictures of the switch missing on both IL2 rendered cockpit and original manuals. I have also seen it included on original manuals)

Here's where they differ:

1) The A4 has finer adjustment of RPM through a lever

2) The A1 seems to be set at 2400 RPM when set to automatic

Here's what I don't know:

1) Was RPM setting variable on the A1?

2) Was manual pitch adjustment possible on the A4 independent of RPM setting (for example if you wanted to calibrate the RPMs between engines)?

3) Were they different from the VDM and the VS11? (I think that's what the picture in the  next post is telling me, but my German isn't good enough)

4) When was the VDM used and when was the VS11 used?

5) Most literature says the VDM had finer pitch controls but the layout pictures show the VS11 with the big levers- it seems backwards

 

In short: the VDM-props were set by electric motors, the VS-11 by hydraulic pressure. The metal VDM-props were used for the early Ju-88 A-1 & A-5 plus derivatives, the wooden VS-11-paddels for the A-4 and later. Both were constant speed props and had a feathering-mechanism released by the pilot. The VDM used the electric motors for that, the VS-11 had an extra electric motor just for the feathering-mechanism - still working, when the hydraulics are lost.

 

The early VDM had electric switches only to control the rpm. Up and down, default middle-setting was off. Just by the rotating direction of the electric motor, no lever. The rpm usually were set manually by the electric switches ("Handbetätigung") except take-off and dive. Here the switches were set to "Automatik'" with the outer switch, fixing rpm to constantly 2350 rpm.

 

Later VS-11 rpm were set by manually by the levers all the time. Except the switch to start the electric feathering-motor, bringing the prop to "Segelstellung". Switching back to "Rückholung" (to start a damaged engine short before the landing f.e.) re-activated the hydaulics-driven standard control.

 

Both props were easily adjusted as fine as needed, the only difference was the settings-procedure for the pitch. For the questions:

1) Should have been as variable as for A4 model, both set the rpm manually.

2) Both were constant-speed and afaik there was no way to de-couple that automatic to get a fully manually handled procedure.

3) electric vs hydraulic pitch regulation

4) VDM with the early models until 1940/41 - I suspect the D-5 recon-models might have been in use the longest time, best guess until end 1943. VS-11 were used with all the later Ju-88 A-4 models and the Jumo-211 F, J and later, until 1945.

5) Maybe the electric motors of the VDM allowed a more precise fine-tuning compared to the VS-11-hydraulics. In that case I'd suspect the VS-11 having an advantage in reacting more quickly to the pilots input. Haven't seen that topic noted somewhere. Not that much pilots with a lot of experience on both models in 1945 were still alive to tell about such details.

 

For details in English:
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=2ahUKEwjm97b7j6XpAhVtUhUIHWF0DLwQFjAAegQIAhAB&url=https%3A%2F%2Ftheairtacticalassaultgroup.com%2Fforum%2Fattachment.php%3Fattachmentid%3D33656%26d%3D1515517035&usg=AOvVaw0WCO8_1IDCAEELmosdSs3L

 

(sorry for that link)

 

Here are the abstracts from the handbooks, A-1 / VDM first:

And the passage for the A4 / VS-11:

 

 

 

Edited May 8, 2020 by Retnek

[41Sqn_Skipper]

The system in the A-1 (with VDM propeller) sounds like the system used in Hs 129, where there is only one RPM setting for the constant speed control. This was only used during take-off and and dive. During other flight conditions the pitch is controlled manually.

 

BTW: Don't get confused by the "Drehzahl" (=RPM) label on the pitch control of A-1. The same confusing label is used in Bf 109 and Fw 190 on the manual pitch control.

Edited May 8, 2020 by 41Sqn_Banks

[ATAG_SKUD]

Thanks guys, great info.

My  (I mean Google's) rudimentary translation of Retnek's documents seem to support 41Sqn_Bank's and Retnek's conclusion that on the VDM "automatik" was only used during take-off and dive.  It does seem that when the set to other positions RPM had to be regulated manually via  propeller pitch adjustments made by the pilot when the aircraft changed speed or throttle position was changed.

 

Ju 88 A-1 (VDM)

Luftschraube (VDM)

Beschreibung

Zum Einbau gelangen dreiflügelige VDM-Luftschrauben mit automatischer Gleichdrezahlreglung bei Abflug und Sturzflug sowie elektrischer Blattverstellung mittels Einheitsverstellgerats. Der Luftschrauben- Durchmesser beträgt 3,60 m.

=

Propeller (VDM)

Description

Three-wing VDM propellers with automatic constant speed control for take-off and dive and electrical blade adjustment using a standard adjustment device are installed. The propeller diameter is 3.60 m.

 

and 

Abb. 2 Schalter fur Luftschraubenverstellung

Die Wechselschalter (1) (Abb 2) zum Ein -bzw. Ausschalten der Fliehkraftregler (Automatik) und die Handwahlschalter (2) zum Einstellen der Luftschraubensteigung befinden sich im Bedientisch an der linken Fuhrerraumseitenwand. Die Fliehkraftregler (1) (Abb. 5) sind unter Dazwischenschalten von Getrieben (3) an den Motoren angeflanscht. Das Einheitsverstellgerat (3)  (Abb. 3) und die Gerätetafel mit  dem mechanischen  Stellungsanzeigegerat (5) fur Luftschraubenstellungen sind an den Motortragern  befestigt. Die Gerätetafel ist austauschbar und kann am linken oder rechten Motorrager in vorgesehenen Halterungen angebracht werden.  Der Antrieb des mechanischen Stellungsanzeigers (5) erfolgt durch eine biegsame Welle (1) vom Verstellgerät (3) aus. Wird es durchTrieb werk wechsel erforderlich, die Geratetafel an dem linken.

=

 

Fig. 2 Switch for propeller adjustment

 

The changeover switch (1) (Fig. 2) for switching on or off. The centrifugal governor (automatic) and the manual selector switch (2) for setting the propeller pitch are located on the operating table on the left-hand side of the driver's compartment. The centrifugal governors (1) (Fig. 5) are flanged to the motors with the interposition of gears (3). The unit adjustment device (3) (Fig. 3) and the device panel with the mechanical position indicator (5) for propeller positions are attached to the motor mounts. The device panel is interchangeable and can be attached to the left or right motor mount in the holders provided. The mechanical position indicator (5) is driven by a flexible shaft (1) from the adjusting device (3). If it is necessary to change the engine, the equipment panel on the left.

 

and

 

 

Luftschraubenverstellung mittels Fliehkraftregler

Die automatische Drezahlregelung mittels des Fliehkraftreglers wird, wie bereits anfangs erwahnt, nur bei Abflug oder Sturzflug eingeschaltet. Der fliehkraft regler (1) (Abb. 5), welcher auf eine Drezahl von 2350/U/min eingestellt ist, wird vom Motor uber das Zwischengetriebe getriebe (3) angetrieben. Andert sich die Motordrezahl, dann wird vom Fliehkraftregler uber den Relaiskasten das Einheitsverstellgerat eingeschaltet und somit die Luftschraubensteigung verandert, bis der Motor wieder mit einer Drezahl von 2350 U/min {Reglereinstellung} lauft.

=

 

 

Propeller adjustment using a centrifugal controller

The (VDM) automatic speed control using the centrifugal governor is, as already mentioned at the beginning, only switched on during take-off or dive. The centrifugal governor (1) (Fig. 5), which is set to a speed of 2350 rpm, is driven by the engine via the intermediate gearbox (3). If the engine speed changes, the centrifugal controller switches the unit adjustment device on via the relay box and thus changes the propeller pitch until the engine runs again at a speed of 2350 rpm {controller setting}.

 

Now on to try to figure out the details of the VS-11  in the A-4 and the sometimes there and sometimes not switches.

 

Thanks guys 

skud

Edited May 9, 2020 by ATAG_SKUD

[ATAG_SKUD]

Ok the A-4

Using the info provided by Retnek

Confirming that manual prop pitch control independent of the speed governor was not available with the VS11 on the A-4.

The A-4 with VS11

Betätigung des Handschalters

Der handschalter (10) ist am Bedientischim Führerraum eingebaut. Seine Stelungen sind "Segelstellung" and "Rückholen", wie Abb. 2 zeigt. Der handschalter wird nur dann betätigt, wenn bie Motorstörung die Luftschraube zum Zwecke der Motorstillsetzung auf "segelstellung" gebracht werden soll. Zur kurzzeitigen Wiederinbetriebnahme des beschadigten Motors zu bie für Landung muß der Handschalterauf "Rückholen" gedrückt werden. Die beiden Handschalter sind mit je einer Schutzkappe abgedect.

=

Actuation of the hand switch

The hand switch (10) is installed on the operating table in the driver's cab. Its positions are "feathering" and "return", as shown in Fig. 2. The hand switch is only activated if the engine screw is to be brought to "sail position" in the event of an engine malfunction. To restart the damaged engine too short for landing, the hand switch must be pressed to "Retrieve". The two hand switches are each covered with a protective cap.

Edited May 9, 2020 by ATAG_SKUD

[Retnek]

I try to disambiguate the Google-translation:

 

For the Ju-88 A-1 with VDM-propellers

----------

Ju 88 A-1 (VDM)

Luftschraube (VDM)

Beschreibung

Zum Einbau gelangen dreiflügelige VDM-Luftschrauben mit automatischer Gleichdrehzahlreglung bei Abflug und Sturzflug sowie elektrischer Blattverstellung mittels Einheitsverstellgerats. Der Luftschrauben- Durchmesser beträgt 3,60 m.

=

Propeller (VDM)

Description

Three-blade VDM propellers with a) automatic constant speed control for take-off and dive and b) electrical pitch adjustment using the standard-regelator-device are installed. The propeller diameter is 3.60 m.

---------

 

---------

Abb. 2 Schalter fur Luftschraubenverstellung

 

Die Wechselschalter (1) (Abb 2) zum Ein -bzw. Ausschalten der Fliehkraftregler (Automatik) und die Handwahlschalter (2) zum Einstellen der Luftschraubensteigung befinden sich im Bedientisch an der linken Führerraumseitenwand. Die Fliehkraftregler (1) (Abb. 5) sind unter Dazwischenschalten von Getrieben (3) an den Motoren angeflanscht. Das Einheitsverstellgerat (3) (Abb. 3) und die Gerätetafel mit  dem mechanischen  Stellungsanzeigegerät (5) fur Luftschraubenstellungen sind an den Motorträgern befestigt. Die Gerätetafel ist austauschbar und kann am linken oder rechten Motorträger in vorgesehenen Halterungen angebracht werden. Der Antrieb des mechanischen Stellungsanzeigers (5) erfolgt durch eine biegsame Welle (1) vom Verstellgerät (3) aus. Wird es durchTriebwerkwechsel erforderlich, die Gerätetafel an dem linken.

=

Fig. 2 Switch for propeller adjustment

The changeover switches (1) (Fig. 2, page 7-03) for a) switching on or off the centrifugal governor (automatic) and b) the manual selector-switches (2) for manually setting the propeller pitch are located on the console on the left-hand side of the pilot's area. The centrifugal governors (1) (Fig. 5, page 7-05) are flanged to the motors with the interposition of gears (3). The constant-speed-unit (3) (Fig. 3, page 7-04) and the instrument display with a mechanical position indicator (5) for the propeller pitch are attached to the motor mounts. The indicator is interchangeable and can be attached to the left or right motor mount in the holders provided. The mechanical position indicator (5) is driven by a flexible shaft (1) from the constant-speed-unit (3). During engine-change it might become necessary ...

----------

 

----------

Luftschraubenverstellung mittels Fliehkraftregler

Die automatische Drezahlregelung mittels des Fliehkraftreglers wird, wie bereits anfangs erwähnt, nur bei Abflug oder Sturzflug eingeschaltet. Der Fliehkraftregler (1) (Abb. 5), welcher auf eine Drehzahl von 2350/U/min eingestellt ist, wird vom Motor über das Zwischengetriebegetriebe (3) angetrieben. Ändert sich die Motordrehzahl, dann wird vom Fliehkraftregler uber den Relaiskasten das Einheitsverstellgerat eingeschaltet und somit die Luftschraubensteigung verändert, bis der Motor wieder mit einer Drezahl von 2350 U/min {Reglereinstellung} lauft.

=

Propeller adjustment using the centrifugal controller

As already mentioned at the beginning, the automatic (fixed) rpm control using the centrifugal governor is only switched on a) during the take-off or b) for a bomb-dive. The centrifugal governor (1) (Fig. 5, page 7-05), set to a (fixed) speed of 2350 rpm, is driven by the engine via the intermediate gearbox (3). If the engine rpm changes (while automatic rpm-control switched on), the centrifugal controller activates the constant-speed-unit via a relay-box and thus changes the propeller-pitch until the engine runs again at a speed of 2350 rpm (fixed controller setting).

----------

 

 

For the Ju-88 A-4 with VS-11-propellers

----------

The A-4 with VS11

Betätigung des Handschalters

Der Handschalter (10) ist am Bedientisch im Führerraum eingebaut. Seine Stellungen sind "Segelstellung" and "Rückholen", wie in Abb. 2 zeigt. Der Handschalter wird nur dann betätigt, wenn bei Motorstörung die Luftschraube zum Zwecke der Motorstillsetzung auf "segelstellung" gebracht werden soll. Zur kurzzeitigen Wiederinbetriebnahme des beschadigten Motors zu bie für Landung muß der Handschalterauf "Rückholen" gedrückt werden. Die beiden Handschalter sind mit je einer Schutzkappe abgedect.

=

Actuation of the hand switch

The hand switch (10) is installed on the console at the pilot's area. Its positions are "feathered" and "fetch-back" as shown in Fig. 2 (page 7-05). The hand switch is only activated when an engine-malfunction enforces an engine shut-down and the propeller has to be set to "feathered position". To restart the damaged engine (right before a landing f.e.) the hand-switch must be set to "fetch-back". The two hand switches are covered with a protective cap each.

-----------

 

The Finnish used Ju-88 A-4, two documents in English from Finnish sources, may it help:

 

Ju 88 Finnish experiences translated.txt

Ju 88 Finnish Pilots Notes translated.zip

 

 

 

Edited May 10, 2020 by Retnek
typo

[ATAG_SKUD]

14 hours ago, Retnek said:

I try to disambiguate the Google-translation

 

Much better-Thanks! 

I think a better English word for "Ruckholen" might be "Re-engage"? As in "re-engage the constant speed unit".

skud

[Bremspropeller]

4 hours ago, ATAG_SKUD said:

Much better-Thanks! 

I think a better English word for "Ruckholen" might be "Re-engage"? As in "re-engage the constant speed unit".

 

Not really, but kind of. It doesn't make much sense in German either - "Rückholen" it just used for the lack of a better word.

You might also translate it with "recover" - as in "recover the feathered prop back to normal".