HELP NEEDED ... 11 Foot Mystery Propeller with Hub

[acenflygirl]

Greetings Dave and Wooden Prop Fans.

I picked up this propeller about thirty plus years ago from an older/retired crop duster. He had told me it was quite special, but could not recall the airplane.
I would like to know if any one has knowledge or interest of this 11 foot prop.
I measured what I could and this is what I found,

The prop is approximately 11 foot from end to end, has brass plates on the leading edges and looks like lead was used to fill the dimples from the screws holding on the brass leading edges. The widest part of the 11 foot propeller is 11 3/4 inches and there is a number "2935" stamped or burned into the wood near the hub. I could not find any other markings on the wood, but the hub is still attached if this may help.

(1) The hub is 10 inches in diameter with a recessed machined ring cut 9 inches diameter just inside the 10 inch outside diameter.
(2) There are 8 bolt holes drilled in the hub at .620 for the ( 1/2 inch diameter bolts that holds the prop between two pieces of hub.
(3) The 8 bolts look to be spaced at 3 inches apart
(4) There is one pin hole or dowel hole drilled at .350 into the hubs plate. between 2 of the 8 bolt holes )
(5) There are 8 larger (decorative) holes are drilled at 1.350 diameter between the shafts hub and the ( 1/2 inch mounting bolts.
(6) On the convex side of the propeller,the hubs hole is smooth/maybe tapered and the shaft's size appears to be 2.4250 inside diameter. with a key way cut at .4850. (Looks like the convex side goes toward the engine)
(7) On the flat side of the propeller, the hubs hole is threaded and measures 2.500 inside diameter.
( Hub is painted or primed a green color on the hub's threaded side, and there are ( 1/2 inch splines spaced at .725 outside the threads.
See attached photos
(9) Photo # 2 shows the keyed/smooth side of the hub. (Concave) From the pilot looking backwards,and the prop was turning clockwise, it would make since.
(10) Photo # 4 shows the threaded side of the hub (Flat)

From the pitch of the prop to the hub's position, I think it may have been a pusher.
(All measurements are approximate)

Sure hope this info helps you to help me identifying this propeller and hub.
If you need more pictures, just email.

THANKS for all you do.

GARY HACKWORTH
530-260-4225
acenflygirl@frontiernet.net

[Dave]

Gary, thanks for posting here and for the photos. A couple of observations:

1. It is indeed a left hand thread, which is the less "typical" rotation and usually indicates either a pusher, a geared engine or a left hand rotating engine, so the likelihood of a pusher application is fairly high.

2. It certainly looks like a Liberty engine sized hub. The critical measurement is the 8 inches "bolt hole circle" which is the distance between the centers of two bolts furthest away from each other.

3. Frankly, I have NEVER seen this style of numbering on a propeller from that era. I'm wondering if this might have been added by someone after its manufacture. The absence of stamped numbers always makes identification difficult, and usually impossible to do much more that narrow it down to lots of possibilities.

4. There is no inherent characteristic of the airfoil that indicates pusher or tractor (pitch, rotation, etc.) Propellers have the same geometry whether they push or pull, and the direction of rotation is determined by engine geometry. Since most Liberty engines were tractors and were right hand rotation, the "assumption" is that it was a pusher.

5. I'm wondering if the hub may have been removed and then replaced backwards. With a pusher configuration I would expect the widest part of the taper in the hub (and the keyway) to be on the propeller surface that is more curved (the forward facing surface), since the tapered crankshaft would insert from that direction. It looks as if yours is assembled the other way, which would make it a left hand tractor rather than a pusher. It looks as if the side of the hub that has the thread bolts showing doesn't fit flush onto the hub surface. That may be because it's rounded on the inside edge and fits into a similar configuration on the wooden hub. If you remove the hub, look for a difference between the hub surfaces and see if the hub components can be reversed and fit snugly. The nuts would typically be applied to the side of the hub away from the engine, and the bolt heads closer to the engine.

6. A propeller with that diameter is bordering on airship size, so it could be from a blimp or an airplane.

7. It's unfortunate that someone has tried to sand it down. That has a considerably adverse effect on any value to a collector.