6 bolt propellers for Stinsons
I have had some interesting discussions about propellers recently. I have a 6A4-165-B4 engine (220hp Crankshaft) which has a six bolt hub. I have the legal Sensenich prop on the airplane. during the discussion I was having, I was told that the only legal six bolt propeller for my Stinson was this prop and there aren't any other options. I had thought there was a McCauley that had a six bolt pattern but I don't really know. Anyone have any ideas?
I am sure there are McCauley 6 bolt propellers that would physically fit. However, unless McCauley or someone has done a vibration analysis which would be required to certify the propeller for the engine/crank combination then there probably isn't a certified prop for it. My guess is that the Sensenich may have been certified for the 220 Franklin many years ago and remains the only one certified for a Franklin and may have never been tested with a 150/165 legally using the 220 crank. Franklin issued a service letter/bulletin before they went out of business in the '70s authorizing the 220 crank on the 150/165 engines.
I just checked the hangar 9 website and here is some information that should be good:
"Parts for the 150 and 165 HP engines in our Stinsons are becoming hard to find. For those in need of a crankshaft, one solution that falls short of a complete engine conversion is the installation of the crankshaft from the 220 HP PZL-Franklin in the 165 HP engine. Unfortunately, now that PZL has discontinued production of Franklin engines, availability of the 220 crank will be limited. But it is an option for those with access to whatever stock remains.
The 220 crank has a different bolt pattern on the prop flange (with a 4" bolt circle instead of the original 5.25") so it requires a different prop. Bruce Junes of the International Stinson Club has installed the PZL crank in his airplane and provided the following information that appeared in the April 1999 issue of the SWSC "Skywriter", courtesy of SWSC president Dennis Dow:
The crankshaft substitution is covered in Franklin Service Letters 72-1, 72-2, and 72-3. When the new crank is installed, the 6A4-165-B3 becomes the 6A4-165-B4 and can be operated with either a McCauley 1A170 SFC propeller or a Sensenich M74DC. The 6A4-150-B2 becomes the 6A4-150-B4. The only STC involved may be the one Univair holds on the new backing plate and bulkhead required to adapt the spinner. This information is confirmed by FAA Designated Engineering Representative Carl Gerker. Details on this crankshaft substitution are sprinkled throughout several of Gary Murdock's articles in the "SWSC Technical Corner" compiled by Rich Fischer. See page 113.
Further information on Sensenich propellers for the 220 Crank in the F-165 is available on the Sensenich web site at:
http://www.sensenich.com/misc/frank165.htm " end of quote.
Maybe this is helpful information.
Thank you for the data. I found the items you quoted on Hangar9Aeroworks. Are the Franklin Service letters online somewhere? I am having no luck searching for them and I am not at home where I can reference them. I may be getting the props confused but I thought the 1A170 was an 80inch seaplane prop and I have heard of people getting really good takeoff and climb performance out of these in exchange for poor cruise performance. If it is the standard 76in McCauley but just modified for the 6 bolt hub, that is good too.
I would think that if Roman or Susan are able to start producing parts, the 220HP Crankshaft will become more common. Hopefully we can get more props certified with any crankshaft so that there will be more options in the future.
Well, the Sensenich (M74DC?) prop I have on my plane and the McCauley 1A170 are both still made and the only two metal props legally available for the B4 modded engines. I could get the Sensenich or MT wood prop but I think I will pass on that for now. While I would love to try a direct comparison between the two metal props on my airplane, the cost for getting a new McCauley propeller makes it prohibitive right now. If I can find one used, I might try it and let everyone know.
The link that Larry shared to the Sensenich website is now broken. I dug around and found a current link to the TCDS for the Sensenich 74DC props.
Ten years later I am trying to find information on props for a Franklin 6A4-165-B4. Does anyone know of any additional ones other than the McCauley 1A170 SFC propeller or a Sensenich M74DC?
I have not found any other options for six bolt metal propellers at this time. I did make a post about the new Sensenich composite ground adjustable propeller and I am trying to find out information about the prop flange to see if it matches any other engines out there. If it does and it is one that Sensenich already makes, that prop may be usable through a 337.