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

 

[Larrythepilot]

For Engineman, and Tom Fey:

Thank you for your prompt response to my inquiry about the prop hub, which turned out to be a Ratier hollow shaft electric propeller system. I have passed that info on to the two volunteers who are working on this item. Since we at the Freeman Army Airfield Museum are dealing primarily with captured German equipment, I imagine the hub came to us originally on a Bf-109 variant.

Larry

 

[Engineman]

Hi Larry,

I suspect that your Ratier hub probably came on an ex-German operated but captured French-built equipment such as a Dewoitine D.520, or other.
I am certain that no German WW2 Bf 109 variant ever had a Ratier propeller.

Cheers

Eng

 

[Larrythepilot]

Hi Larry,

I suspect that your Ratier hub probably came on an ex-German operated but captured French-built equipment such as a Dewoitine D.520, or other.
I am certain that no German WW2 Bf 109 variant ever had a Ratier propeller.

Cheers

Eng

Oh, OK, thank you.

Larry

 

[Snautzer01]

Hi Larry,

I suspect that your Ratier hub probably came on an ex-German operated but captured French-built equipment such as a Dewoitine D.520, or other.
I am certain that no German WW2 Bf 109 variant ever had a Ratier propeller.

Cheers

Eng

Would it have fitted on a 109? I mean just as a hub. Without any linkage to war time 109?
Just to have a working prop.

 

[Engineman]

Would it have fitted on a 109? I mean just as a hub. Without any linkage to war time 109?
Just to have a working prop.

Well, it could have been engineered to "fit", but it could not just be fitted. I am not certain that the Hispano-Suiza propshaft was even anywhere near the sizes that the
DB engines used, I think not. However, many different propellers were used on other DB engines in some Foreign use, such as Italian and Japanese, but those were engineered.
Beyond that, whether such precision engineered "things " can just fit on entirely different machines is almost unheard of, even where engines use different
but similar propellers, they are rarely able to just "fit".
BTW, Try researching all the RR Merlin propellers in 1940 and all the different installation standards !

Eng

 

[Engineman]

Well, I suppose I should give you all a bit of the early Merlin propeller manual detail, as I mentioned it. Note that this is early (1940) and applies to the
early engines. There are specific details for the specific props. Also, there are just three types of propshaft here.
These photos are of an original manual off the net but the manual is available as a digital copy.
I will put half a dozen up. Hope you like it!
Eng

 

[Snautzer01]

Very nice.

 

[SaparotRob]

It's amazing how all these precision machined components and assemblies, connected and spinning in different axises, within extremely tight dimensions, don't just blow the f#@+ up. At least, not all the time.