Sensenich DES 70F1 - Info, please??

[monomoit]

Hello All,

Had the good fortune recently to acquire the following Vintage Sensenich Propeller:







Markings on front of blade, adjacent to hub, as shown in the above photos are:

DES 70F1
SER 7977
HP 50
RPM 2300

Front of opposite blade is marked SENSENICH. The backside of hub is stamped 7977 (the serial number), and the single digit 2.

Length is 70 inches, hub thickness 3-1/4 inches and hub diameter 6 inches.
Center Bore diameter is 2 inches, bolt hole diameter 3/8 inches, and the bolt circle diameter 4 inches.

I have been unable to obtain any definitive information of the Design Number 70F1.
Rummaging around the ‘net, however, it looks like this prop may have been for a Piper J3F-50 powered by a Franklin 4AC-150 engine.

I’m entirely new to all of this, so any assistance in accurately identifying the propeller would be greatly appreciated.

Many thanks,

Rob

[dbahnvt]

I think your guess is probably as close to correct as you will get. Lamar Bevil has the most complete listing of Sensenich props that I know of, and it shows several 70F... models, all for that Franklin engine on a variety of aircraft. The number following the "F" is usually just the pitch, so "1" is an unusual digit to see there. It may represent a prototype of some kind or may just pre-date the more logical numbering system. It does look like a very early Sensenich.

Here's the link to Lamar's web page, if you haven't already seen it.

[monomoit]

Thanks for the input. Based on the hub dimensions, and the information that I was able to get from the Sensenich web site, it seems that this prop was definitely for the Franklin 4AC-150 Series 50 engine. As you mentioned, this leaves several possibilities for aircraft.

Any suggestions on how to determine the pitch? I don’t know if there is a trick or technique for measuring this.

[MWP_Lamar]

Sensenich props with a non-letter prefix serial number were manufactured between 1932 and 1942.

Lamar

[monomoit]

Hi Lamar,

From what I’ve been able to gather, the 4AC-150 was introduced in 1938, so I guess that my propeller was made between 1938 and 1942.

Your web site is exceptional – thank you for all the hard work and useful information. Has anyone been able to compile any production data or serial number info for Sensenich props during the early years, 1932-1942? Information for this time frame seems very sparse.

Many thanks,

Rob

[MWP_Lamar]

Thank you for your kind words on the website. Much credit goes to Dave Bahnson for his inspiration and support as well as supplying lots of the information.

I have not been able to compile earlier serial numbers and my contact at Sensenich says they don't have them either so we may never know.

Lamar

[monomoit]

It would be an intriguing project to compile a database of these earlier propellers as they surface. The specs, along with serial numbers, might allow at least a partial reconstruction of production data by year...