Does anyone have experience getting a field approval for longer prop on C-175 with Lycoming STC? Understand 76 inch is specified. looking to get a 78 inch approved

I don't think you'll get that approved on stock gear from what I've seen. Do you have a heavy duty fork or tailwheel conversion? Which 78" prop are you looking at? Most of the approved props I've seen are either 76" or 80"

There is no 78 inch constant speed propeller approved on the O-360 in an Avcon conversion. Length is not the issue, there's just no prop of that length.

There is an STC for an 80 inch Hartzell propeller on that engine/airframe combination. That prop is a cut down 84 inch prop originally approved on Pawnees. Hartzell owns the STC.

The big down side (other than buying a brand new prop) with that setup is it's heavy. The blades are pretty big compared to the standard prop on the Avcons. But, that prop also requires installation of a harmonic damper assembly for vibration control. That damper assembly weighs about ten pounds by itself.

I've run these props on both an Avcon 170 B and a Avcon 175. They pull hard, and they do eliminate the restricted operating range required on the standard prop.

Not sure what Hartzell gets for one of these props these days, but frankly, I'd spend a little more and buy an MT prop for that plane. Almost thirty pounds lighter than the big Hartzell, and smooth as butter.

Last I checked, Hartzell won't sell the STC. So, if you gather up parts and have a prop assembled, good luck getting it approved. Field approvals are specifically prohibited for any mod for which an STC exists, which is the case here.

Give Hartzell a call and ask about that prop, and make sure they include the price of the damper assembly.....I'm guessing they almost NEVER sell one of these props, so might overlook the damper, and that's not cheap either.

MTV

I think Stoots have an STC for that 80” on a 170. Not sure about 175.

daedaluscan wrote:I think Stoots have an STC for that 80” on a 170. Not sure about 175.

I'd bet he's selling the Hartzell props, with the Hartzell STC. That STC was developed by a gent in Minnesota for the 170 with Lycoming O 360. He then sold the STC to Hartzell.

There were several of these props in Fairbanks, but left at the 84 inch length years ago, running mostly on seaplane 170s. An instructor at the local A & P school tried to get these props legal. He was persistent, and worked on Hartzell till Hartzell actually did a vibration survey on that engine/prop combination. They found destructive harmonics at basically takeoff rpm.

Hartzell cut down the blades and applied one of their harmonic damper assemblies, and the prop passed. The A & P school mechanic then got field approvals after the local props were cut down. He got me a field approval for my 170 for that prop.

The guy in Minnesota took the vibration analysis from Hartzell, and applied to the FAA for an STC, which he got. He'd rebuilt a beauty of a 170. Hartzell then bought the STC from him.

It's a good prop, but heavy.

MTV

It was the weight that put me off. Just put a 76" on and I'm heavy already. Guess I need more AMUs for a composite prop.

daedaluscan wrote:It was the weight that put me off. Just put a 76" on and I'm heavy already. Guess I need more AMUs for a composite prop.

Go on an OM C of A and hang a Catto on the nose, 12 lbs.

Mapleflt wrote:

daedaluscan wrote:It was the weight that put me off. Just put a 76" on and I'm heavy already. Guess I need more AMUs for a composite prop.

Go on an OM C of A and hang a Catto on the nose, 12 lbs.

Yes, and lose the benefits of a constant speed prop. Like actual rated horsepower.

MTV

Owner Maintenance has zero attraction for me. If you have ever flown in Idaho, Oregon, Utah, Colorado or Nevada you would no why. The flying in the US is just amazing, and I meet so many nice people. missing coming down there.

Agreed the limited it puts on some destinations is unfortunate. I spend my Summers on floats and there’s no shortage of lakes and like minded pilots in Ontario thankfully.

Flight Resource owns the STC and supplies all the props for all Cessna 170, 172 and 175 models as long as they have ANY version of a Lycoming -360 series engine and hydraulic propeller governor. The STC has two 2-blade versions including the popular Ultra and a 3-blade version.
https://flight-resource.com/stcs-available/

All are in stock for immediate delivery. No RPM range restrictions and only 46 lbs. Money back satisfaction guarantee!

Call me for info.

Thank you,
John Nielsen

daedaluscan wrote:It was the weight that put me off. Just put a 76" on and I'm heavy already. Guess I need more AMUs for a composite prop.

So, does your plane have an AVCON STC'd engine installation? Because if you do, that STC calls for a maximum propeller length of 74 inches. A friend just had to have his prop cut down from 76 to 74 because of this. Which is right up there with the dumbest thing I've heard of, but that's what the STC calls for.

MTV

john54724 wrote:Flight Resource owns the STC and supplies all the props for all Cessna 170, 172 and 175 models as long as they have ANY version of a Lycoming -360 series engine and hydraulic propeller governor. The STC has two 2-blade versions including the popular Ultra and a 3-blade version.
https://flight-resource.com/stcs-available/

All are in stock for immediate delivery. No RPM range restrictions and only 46 lbs. Money back satisfaction guarantee!

Call me for info.

Thank you,
John Nielsen

These are the guys who sold me an MT prop to replace the 80 inch Hartzell on my old 170 and to replace the 80 inch Hartzell on my current 175. I'd go there again in both cases. These props are very light weight, and they pull really hard. Take it from a serial offender.....I've run MT props on Huskys as well....

As I noted earlier, all the Hartzell metal props are pretty heavy. And, frankly, the Hartzell 74 really doesn't release much of the capability of that O-360 engine.

The 80 inch Hartzell pulls fine, but it's between 28 and 29 pounds heavier than an MT Ultra prop. And, on a tailwheel converted 175, which is nose heavy to start with....that's a lot of weight right out front.

So, if you're considering a new or different prop, I'd put the MT Ultra really high on that list.

MTV

mtv wrote:

daedaluscan wrote:It was the weight that put me off. Just put a 76" on and I'm heavy already. Guess I need more AMUs for a composite prop.

So, does your plane have an AVCON STC'd engine installation? Because if you do, that STC calls for a maximum propeller length of 74 inches. A friend just had to have his prop cut down from 76 to 74 because of this. Which is right up there with the dumbest thing I've heard of, but that's what the STC calls for.

MTV

Pretty sure my STC allows 76 or 76-2. I will check. I found a non AD hub that is zero timed to just under 76” if I remember correctly. I am delighted with the way it pulls, but my CG is forward. Two fatties and low fuel needs aft ballast.

That post above by John is just unkind. I mean money back guarantee. Definitely on the wish list.

daedaluscan wrote:

mtv wrote:

daedaluscan wrote:It was the weight that put me off. Just put a 76" on and I'm heavy already. Guess I need more AMUs for a composite prop.

So, does your plane have an AVCON STC'd engine installation? Because if you do, that STC calls for a maximum propeller length of 74 inches. A friend just had to have his prop cut down from 76 to 74 because of this. Which is right up there with the dumbest thing I've heard of, but that's what the STC calls for.

MTV

Pretty sure my STC allows 76 or 76-2. I will check. I found a non AD hub that is zero timed to just under 76” if I remember correctly. I am delighted with the way it pulls, but my CG is forward. Two fatties and low fuel needs aft ballast.

That post above by John is just unkind. I mean money back guarantee. Definitely on the wish list.

All the AVCON STCs I’ve seen specify 74 inch prop. I have no idea where that came from.....the “standard” blades for that hub are 76 inch. Might be able to field approve a deviation......

MTV

My Delaire STC specifies HC-C2YK-1BF/F7666A or A-2 for the Constant speed, no length limits.

I had assumed it was the same as the AVCON, but maybe not?

daedaluscan wrote:My Delaire STC specifies HC-C2YK-1BF/F7666A or A-2 for the Constant speed, no length limits.

I had assumed it was the same as the AVCON, but maybe not?

No, it's not. As I noted, I have no idea why AVCON chose the 74 inch length.....probably was some logic back then. Sorry for the confusion, but the title of this thread was av/con, which I mistakenly assumed was AVCON.

But, you still need an MT Ultra prop....trust me.

MTV

daedaluscan wrote:

mtv wrote:

daedaluscan wrote:It was the weight that put me off. Just put a 76" on and I'm heavy already. Guess I need more AMUs for a composite prop.

So, does your plane have an AVCON STC'd engine installation? Because if you do, that STC calls for a maximum propeller length of 74 inches. A friend just had to have his prop cut down from 76 to 74 because of this. Which is right up there with the dumbest thing I've heard of, but that's what the STC calls for.

MTV

Pretty sure my STC allows 76 or 76-2. I will check. I found a non AD hub that is zero timed to just under 76” if I remember correctly. I am delighted with the way it pulls, but my CG is forward. Two fatties and low fuel needs aft ballast.

That post above by John is just unkind. I mean money back guarantee. Definitely on the wish list.

MT Ultra is worth every penny. I have one and I love it. The Ultra would be perfect on any 180hp Cessna, I cant imagine a better option. And as mentioned many times before here on this site, John and Larry at Flight Resources are top notch, these are the only guys to buy an MT prop from.

Kurt

I know that you're both right, I am just smarting a little from the final total of the install.

John was very kind and gave me lots of advice and encouragement when I was starting the swap.

I believe that the /F7666A is the basic blade model for a 76 inch prop and that the A-2 is minus 2 inches (not a dash) giving a prop length of 74 inches.

Tim