Nobody will just open his Mühlbauer Prop for fun, just to know how it looks like inside! Well, it was an opportunity to get a broken prop to try it!
Just look at the pictures:
Picture 5: take off the top ball bearings, the drive (Spindel) and the leading tubes.
Now the bronze cube is now ready for extraction. In order to get it up you must rotate the 2 blades by hand. This is a quite sophisticated cinematics. Compliment to Mr Mühlbauer who developed this system. Don´t ask me now how I did, but in any case I managed to get the bronze block out of the hub!
Picture 11: Here you see the fat-free foot of the blade, the anchor-screws maintaining the wooden blade in its shoe and the pin enabling the rotation of the blade inside the hub. Look at the inside ball bearing cage pressed in the hub.
Picture 12: here you see how the system works. The spindle rotates through the electromotor, driving the bronze block up or down.
The black semi-cylinders are stuck in the pins of each prop blade which force them to a rotation. The rotation of the blades forces the black half-cylinders to slide along in their cage. The pitch of the prop is controlled by a rev meter monitoring the electro motor according to a pre-set engine rev. setting.
Assembling: This is indeed the same work the way back but there are 2 difficult steps.
- Inserting the balls in the cage: I tried several times alone and did not manage. With a second person holding the blade and rotating it carefully and using enough fat to stick them, it was then easy to insert all the balls again.
- Inserting again the bronze block with its 2 half black cylinders. We had to try several times to find the correct position in oder to slide the complete system into the hub. It looks difficult but after a few trials you find the way !
Now you know how to dismantle and re-assemble your MT constant speed prop by yourself. I did not take off the wooden blades out of their shoes because this is only possible by destruction!
You can do it you have somebody who can manufacture new blades and is able to insert them with the necessary symetry.
Remark: The Mühlbauer construction has no ajustment device. This means there is no way to adjust the ball bearing pressure. The centering of the blade occurs through the centrifugal forces on the outside ball bearing cage.
The black O-ring on the blade helps to maintain it in its position and avoids the fat to be ejected.
Therefore there is no way to make any assembling mistake. Whether you manage to rebuild the system without using a big hammer and it will work again … or you do not manage and you hang your prop over your club bar!
CFI Germany – December 2002