The International Cessna 170 Association

My Cessna has the O-300 B engine which has the mechanism for a verible pitch prop. Any one know what hub and prop this takes and where the parts might be available, and also maybe an approximate cost. Also, what is the pitch range with this set-up. I've talked to A&P's, IA's, and other owners, and it seems no one, or not many, has ever seen the actual verible pitch prop installed on this engine. Thanks.

Search this site for the Aeromatic prop.
That's what used the prop control on the 170.
Sadly, the Aeromatic with the prop control over-ride is not supported anymore by the person that bought the rights to the Aeromatic prop.
I did TONS of research into that prop a while ago but just coudlnt justify the $6,000 price tag and still needing a field approval to install it.

Not sure which "mechanism" you are referring to. The lever that pivots between two stops as shown in the O-300 IPC I believe is for the McCauley two position propeller ... not sure though. What I do know is that the Aeromatic Hi-Cruise propeller uses that same port to mount an adapter that allows oil to flow to a pitch control unit mounted on the top of the engine. See the picture of the adapter here.

The mechanism is a on-off type of control for a propeller. The Aeromatic prop which changes pitch automatically uses this control to override the auto feature and lock the prop in low position. As already stated that propeller is not being supported by the owner of the prop type certificate. So you would have to be lucky to find one and then find it in airworthy condition.

The McCauley two position prop is the other prop approved for the 170 which uses this control to change from low to high pitch and back. There is only one known example of this propeller. It is still being flown by a member in Texas. He and his prop mechanic didn't even know what he had till we educated him a few years ago.

As far as I know there is not much known about this prop other than the first hand experience from this member. He is not impressed with the prop but has no other experience to judge his against. I had one demo ride in his plane with the prop. To me it was pretty cool and I thought in my brief flight the prop was worth it but it is a compromise. It is neither a good climb nor a good cruise prop. But then maybe he didn't have it set up correctly.

I would think you would be lucky to find an airworthy example and then I'd not sure you could maintain it in that condition.

Bruce, I recall that you took that ride in Michigan (I think). I don't recall if that was prior to or after that member overhauled his engine and had the prop "tuned up". I think he has told me that the adjustment the prop shop made to the prop did help somewhat. However the unit is pretty heavy compared to the fixed pitch, but I don't know if it is as heavy as a constant speed prop and there is no governor on the two position one. I have that same B model engine on my plane.

Would love to see a modern Aeromatic prop using carbon fiber blades.

For a short while back in about 1949, I had a Aeromatuc prop on my Stinson L-5 up in Alaska. It was a pain in the ass to keep adjusted. When properly set up it did give the airplane a kick in the butt for take off since the engine could grt full high revs. I went back to the fixed pitch Sensenich when I blew the Aeromatic on a nose up taking off on a soft sandbar on the Chena river.
The fixed pitch prop that I used was a Sensenich (sp ?) that was a made for a Fairchild PT-19 and was selling as war surplus in 1949 by Lew Liebee in Selma, CA., brand new , two to a beautiful pine box, for $29.00, The box would be worth about five times that today.

What am I doing that is resulting in my posts appearing two times?

Frank,
You're probably double clicking on submit.

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Aryana wrote:From Bruce's testimonial, it sounds like the Aeromatic is a dud.

If it was really that great I'd think we'd have seen more installations of this prop in the last 60 years.

No I did not say the Aeromatic was a dud.

I've heard others say it was a dud but to be honest I don't put much weight on those opinions. The Aeromatic and how it works is a mystery to many. If you don't know how it works, your probably not going to have it adjusted correctly and if that is the case you won't be happy with it. It probably takes more fouling with than the run of the mill aluminum fixed pitch prop you can install and run with no further maintenance for 20 years and people didn't see the advantage. Add the fact the props got a bad rap because they started slinging blades which probably had a lot to do with lack of proper care and maintenance and you can see why they aren't prevalent.

The fact you needed to have a C-145-2H or 0-300B for the prop might be a good reason you don't see more of them or there isn't much info known about them on a 170.

Just because you don't see them today doesn't mean they were a bad idea or dud. There are lots of good ideas and products that never succeed and amount to much.

After all my reading on the Aeromatic, I think it was a great prop that was misunderstood and died out cuz a metal prop is considered zero maintenance.

It takes a bunch of flights and counter weight changes to get dialed in correctly which requires an A&P to do. PITA

Yes, it loses performance when you change operating altitudes by 5,000 or so feet but how often does the AVERAGE 170 pilot take off from a field a sea level and need short field performance at 5,000 feet in the same flight?
I can't remember the last time I FLEW at 5,000 feet, let alone landed.

People make it sound like you need to carry a pocket full of shims and adjust the prop cuz your DA changed. Thats simply not true.

How much is the performance degraded? Probably no worse than if you had a cruise prop at 5k feet vs a climb prop.
The -2H override requirement was so that Cessna could maintain a service ceiling of 12,000 feet for the plane. OK, I've never ever ever flown above 7,500 feet with any propeller.

Wood rot and throwing blades? Debunked and not a concern with a well serviced prop.

The kicker for me is, without the -2H motor (rare) and the Hi-Cruise hub (even rarer) - you need a field approval (OMG approve a prop swap???) to install it.
And that was just too much on top of the $5k or $6k for the prop - just to find out how it would actually perform.

and I keep 81D outside which would be hell on the wood blades.

So, I decided to keep it simple and install a Continental IO-360 instead

Aryana wrote:

Bruce Fenstermacher wrote:... It is neither a good climb nor a good cruise prop...

The testimonial you gave earlier about it being a compromise but not really superior in any given flight phase is what made me say it sounded like a dud. I wasn't trying to put words in your mouth, but rather sharing my opinion based on the description you gave.

I was talking about the McCauley two position prop based on one flight demonstration.

I can always be used as a bad example.

No I don"t think so , that's my position around here, get your own!

David Ross,
It is not at all uncommon out here in the far west to have rather gross elevation changes on a single flight. Our mountains are closer and higher than most of the eastern part of the country.
It was my observation that an elebvation change of about three thousand feet was enough to have an effect on the prop seting of the Aeromatic prop.
The prop that I had was an experimental model that had been made for the Air Force and had a hub designed for a #10 SAE splined prop shaft on the Lycoming O-435 engine rather than a flanged shaft of the more common civil engines. It did not have any provision for any hydraulic operation and was totally isolated from anything other than the counter weghts and centrifugal twisting moment.
Those Aeromatic props seemed to became very common on the Stinson 108 seris of airplanes powered with Franklin Engines using a flanged prop shaft.