Ratier Hollow-Bore Propellers for Moteur Canon: A Technical Description

[Tom Fey]

A video for those of you that like insight into the insides, mechanics, and operation of the French Ratier moteur canon hollow-bore propeller used on the Morane-Salnier M.S.406, Dewoitine D.520, and Swiss D-3801 aircraft:
View: https://youtu.be/LaU2SQp9088

 

[ThomasP]

Cool!

 

[Engineman]

Thanks for your descriptive video Tom! The Ratier electric hollow shaft prop is ingenious, but it is very complex and with a high parts count. I notice that there is basic similarity in the electrical switching and functionality of the VDM hollow shaft electric propeller, but the VDM electric drive and pitch change mechanical system is very much less complicated.
The VDM electric version with 1.5 deg/sec blade pitch change was noted as a relatively slow pitch change rate. However, modern experience with this system in the Bf 109 versions that have the automatik pitch change function working shows that the VDM system is responsive and accurate in control during all flight and aerobatics. The only caution in the original Bf 109 flight manual with the automatik system is that pilots should be careful of rpm control if entering a full power dive from a low-power cruise.
Thanks again for your presentation.

Eng

 

[Tom Fey]

Thanks for your descriptive video Tom! The Ratier electric hollow shaft prop is ingenious, but it is very complex and with a high parts count. I notice that there is basic similarity in the electrical switching and functionality of the VDM hollow shaft electric propeller, but the VDM electric drive and pitch change mechanical system is very much less complicated.
The VDM electric version with 1.5 deg/sec blade pitch change was noted as a relatively slow pitch change rate. However, modern experience with this system in the Bf 109 versions that have the automatik pitch change function working shows that the VDM system is responsive and accurate in control during all flight and aerobatics. The only caution in the original Bf 109 flight manual with the automatik system is that pilots should be careful of rpm control if entering a full power dive from a low-power cruise.
Thanks again for your presentation.

Eng

Thanks for watching and your comments. Many of the German pilot accounts from WWII note the limitation/concern for over-speeding in dives during combat. The Curtiss Electric hollow bore prop (P-39) also used the VDM-type gear train but with a hub mounted, hollow-armature motor. Interestingly, this gear system was patented by engineer/pilot Robert Stanley in 1935 (US1986229).

 

[Engineman]

The chance of overspeeding the engine with a WW2 VDM electric propeller would depend upon several factors. The first possibility is that the system was not selected to Automatik or, it was a purely manual (Hand) version. Sticking with the Bf 109 E, this was a Hand-only system until about early 1940. With this Hand system, the pilot had to select the pitch change with an electric switch. This was a difficult task in combat, and no doubt was a pain for the pilots. When the Automatik function with the governor was introduced, Automatik could be used and the pilots' task was removed. The Automatik mode remained available for all Bf 109 versions after about mid 1940, with Hand mode as a back-up.
The 1.5 degree/sec pitch change does not sound much, but it gave a response to equal an airspeed change of about 75kmh/sec (about 50mph/sec) which is considerable.

Eng

 

[MiTasol]

There is a manual for another French prop you might be interested in here. One of the two looks like a fixed pitch 4 blade but the other is, if I read it right, for the Morane 406..

Some assorted French publications

The Hispano one is self explanatory and the other two are propellers. If I am reading them correctly, given I failed French in school, the second file is for the Bloch 152 and the third file is for the Morane 406.

ww2aircraft.net