The International Cessna 170 Association

Hello Everyone! In the quest to advance the options for the 170, I am working on getting a field approval or STC in motion for a Sensenich 82" GA propeller. I have spoken a few times with some supporting individuals and we have come to the point where we are searching for a 170 with an o300 a,b,c,or D model engine that could be used for a ground vibration study. This will be done near Tampa Florida sometime in the next few months. If anyone is willing, please send me a DM and we can move forward!

If ya can’t find one down south I’d gladly loan mine in Rhode Island. Last I asked sensenich they didn’t have a hub for an o300 and had zero plans to make it happen.

Glad to hear that’s changed. I’d happily buy one.

I have a Sensenich ground adjustable prop on my experimental J3 copy with an O-200. It’s a great prop. So I hope this works out. A few years ago, one of the guys at my airport volunteered his plane for testing of a Sensenich GA prop for his experimental with a Lycoming engine. The engineer flew up from Florida and the test equipment was set up and run from my hangar. The engineer was a great guy and the experience was interesting and fun. I’m glad to see Sensenich is now pursuing the STC route.

Will the 170 still meet the propeller clearance requirements of CAR 3.422 with an additional 3" propeller radius? Maybe add some Curtiss Jenny wheels as part of the STC!

? What are the benefits of having a prop that size of 82 in over the standard size prop. The engine must still spin to the required RPM for the power curve . Okay the pitch will have to be flatter but then drag comes into it especially with tips at the speed of sound . So how close is the tips of a 82in prop near to the speed of sound . With a prop that size what are the effects of gyroscopic progression on the airframe and engine bearings? Harmonics could also come into the equation also. While not wishing to start a revolution of the masses on the advantages /disadvantages of MT props or their problems but there is a study being carried out on MT prop failures. It seems that MT props fitted that were larger than the standard prop [but approved ]have a higher incidence of failure . It was suggested it was due to ground resonance . Nothing is concrete of the results as this study has just been started and data is hard to obtain.

The stoots STC is flying with an 83” prop seemingly without clearance issues.

With a 82” blade the tips are turning 659 mph @ 2700rpm.

I met the engineer this past year at Oshkosh and am pushing to either get a field approval or forward progress on an STC. Paperwork is easy as long as data supports safe operation. For me, the largest gain from having the large diameter is more static thrust. The best part about carbon and wooden props is resistance to those ugly first and second order harmonics. Due to their nature, they are inert.

Firstly my knowledge of props is very limited . What I know would fit on the sharp end of a needle. I am still learning. But with the Stoots STC the engine is putting out 195HP. So we are needing that extra HP to turn the prop. to 2700 rpm. The tip drag on a prop 83 ins would be a lot more than a prop of 76ins . The speed of sound changes as per temperature and the density it travels through . The speed of sound is about 740mph at 0 deg centigrade . So there fore at take off on a cool day ,the tips are at a transonic situation ,vibrating away merrily with shock waves etc. . BUT as previously stated wooden props absorb all this “inert” vibration. But energy can neither be created nor destroyed ,it can only be transformed . I was witness to a German wooden composite prop disintegrating on an American Champion on landing at idle. It was alleged [by insurance company and authorities] that the pilot had nosed the aircraft over so bad that the prop hit the runway. The pilot stated “It felt like a giant hand had picked the aircraft and thrown it into the swamp drain besides the runway. “ No marks on the runway . Aircraft repaired and every body forgot about it. Then some many months later I was putting my crab pots in the swamp and in a tree about 600 feet away was the missing prop half. It had snapped off very clean near the prop hub and the tip was in perfect condition. My sensenich 76in all metal prop cuts grass and small bushes, and birds into sizes that makes Kentucky Fried envious when on take off on bush strips .
So what are the advantages of having a 83in prop on a Cessna 170 . I was told they look good.
PS . I am sure Mr Stoots and MT props produce a fine product .

ghostflyer wrote: ↑Mon Nov 06, 2023 3:18 am… The speed of sound changes as per temperature and the density it travels through . The speed of sound is about 740mph at 0 deg centigrade . So there fore at take off on a cool day ,the tips are at a transonic situation ,vibrating away merrily with shock waves etc. …

According to the prop tip speed calculator on P.Ponk’s website it would have to be -52°C for the tip speed of an 83” prop to reach the speed of sound at 2700 rpm.

Yes there is an adapter made by saber , purchased thru sensenich for the o300D 6 bolt crank. 82 “ prop.
No adapter for 8 bolt crank that I know of.
Ummmm if you want info holler at me.

Have available engine with prop from sensenich. Does 300plus hours count all, vibe analysis done with dynavibe.

eskflyer wrote: ↑Mon Nov 06, 2023 5:57 am Yes there is an adapter made by saber , purchased thru sensenich for the o300D 6 bolt crank. 82 “ prop.
No adapter for 8 bolt crank that I know of.
Ummmm if you want info holler at me.

Have available engine with prop from sensenich. Does 300plus hours count all, vibe analysis done with dynavibe.

Ahhh, makes sense. I asked specifically about the 8 bolt crank.

Just sent a PM. Let me know.