Bf 109 variable pitch gearbox

wrbrd · 12-23-2006, 09:09 PM

I'm trying to find out how the internal planetary gear sytem works in the variable pitch gearbox for the propeller. I have limited information and a sectional view but with little detail. If anyone could explain it to me or direct me to someone who might know it would be most appreciated. I do have the maintenance manual for the VDM prop but it gives no explanation of the internals.
Thanx and have a Merry Christmas!!!

FLYBOYJ · 12-24-2006, 12:20 AM

Quote:

Originally Posted by wrbrd

I'm trying to find out how the internal planetary gear sytem works in the variable pitch gearbox for the propeller. I have limited information and a sectional view but with little detail. If anyone could explain it to me or direct me to someone who might know it would be most appreciated. I do have the maintenance manual for the VDM prop but it gives no explanation of the internals.
Thanx and have a Merry Christmas!!!

OK - first off there is no real planetary gear/ gear box in a WW2 constant speed propeller. It is actuated by a hydraulic piston or electrical (Curtiss) solenoid. Regardless of the manufacturer the principal is the same. Here is a real basic diagram for all constant speed propellers..

I am not totally familiar with the prop on a Bf 109 but the principal should be about the same. Hope this helps.

mkloby · 12-24-2006, 04:27 AM

wrbrd - hope I can help you. It's 4am and I can't sleep!

The basic operating principle behind the constant speed prop, in the aircraft I have flown, is as flyboy said. The max efficiency prop RPM will be determined by specific powerplant considerations. However, tension of the speeder spring can be adjusted w/ a prop rpm lever, or also a combined prop RPM/condition lever as I've seen in some A/C, which will adjust the operating RPM that the governor will maintain prop speed at, below max. The propeller governors will act to monitor and adjust propeller blade angle to maintain this prescribed max prop efficiency.

If you are running your prop at maximum RPM, let's say 2200, and you increase engine power, at the same given prop blade angle, you would create an overspeed condition. The governor's function is to be able to sense this overspeed condition, and correct by adjusting prop blade angle to bring prop RPM back to it's maximum efficiency.

The prop governor acheives this monitoring and adjusting of prop blade angle through the basic components that were shown in flyboy's above post. So, we'll continue w/ our example: you increase power, creating an overspeed condition. The flyweights serve to sense this momentary overspeed condition, as centrifugal force will force them outward in their rotation. This will open the pilot valve, which will drain pressurized oil from the dome assembly. The high pressure oil acts to exert force upon a servo-piston(the force in this case is decreasing), which resists a feathering spring and bladeshank counterweights to increase blade angle (since the piston's counterforce is decreased because we drained the high pressure oil) and maintain the desired prop RPM.

The opposite is true if you decrease your power setting. The flyweights will move inward in their rotation, increasing flow of high pressure oil through the pilot valve, increasing force exerted on the servo piston and overcoming the bladeshank counterweights and feathering spring and decreasing the prop blade angle.

Hope this quick rundown of how a constant speed prop works helps. They also include a feathering provision, and can employ a backup or overspeed governor in case the primary governor fails. If you would like to know how anything else functions - just ask!

Matt

the lancaster kicks ass · 12-24-2006, 06:42 AM

all makes for a very interesting read gentlemen, well done

FLYBOYJ · 12-24-2006, 08:19 AM

Thanks Lanc!

Damn Matt, ever thought of getting your A&P and becomming an instructor? That's a better explination then some textbooks I have!

mkloby · 12-24-2006, 08:30 AM

Quote:

Originally Posted by FLYBOYJ

Thanks Lanc!

Damn Matt, ever thought of getting your A&P and becomming an instructor? That's a better explination then some textbooks I have!

I'm proof that military education works

Break things down barney style - and they're easy to understand... even for us Marines

Somehow I think the military would object to me moonlighting w/ another job!

However, it's always a possibility in the future after my service is complete...

FLYBOYJ · 12-24-2006, 08:37 AM

hehehehe...

Hey, I found out the Bf 109B used a Hamiliton Standard prop made under license. Here's one from a a "D."

mkloby · 12-24-2006, 08:41 AM

Great pic - shows nicely some geometric twist!

FLYBOYJ · 12-24-2006, 08:43 AM

Yep - I suspect the gear on the aft plate drive an accessory, maybe the prop governor.

mkloby · 12-24-2006, 09:14 AM

Here's a schematic of the TC-12B prop system and a pic of the prop governors on a TC-12B....

FLYBOYJ · 12-24-2006, 09:25 AM

Cool! What model PT6 are on those?

mkloby · 12-24-2006, 09:30 AM

PT6A-41 baby. 850shp, max transient 5 second 1150shp!

FLYBOYJ · 12-24-2006, 09:40 AM

Very Cool! We have -34s on the Twin Otters we take care of for the USAFA.

Denniss · 12-24-2006, 02:06 PM

Quote:

Originally Posted by FLYBOYJ

hehehehe...

Hey, I found out the Bf 109B used a Hamiliton Standard prop made under license. Here's one from a a "D."

License contractor was VDM, the Bf 109B with this prop got the unofficial name B-2 instead of B-1 with the fixed pitch wooden prop built by Schwarz (AFAIK was a deHavilland license). The B-2 designation was never officially used by RLM or Mtt.

FLYBOYJ · 12-24-2006, 02:40 PM

Quote:

Originally Posted by Denniss

License contractor was VDM, the Bf 109B with this prop got the unofficial name B-2 instead of B-1 with the fixed pitch wooden prop built by Schwarz (AFAIK was a deHavilland license). The B-2 designation was never officially used by RLM or Mtt.

Gotcha - the point here early Bf 109s used a Ham Standard prop.

Here's a nice cutaway of a Gustav prop.