My newly acquired C180 has a McCauley 2A34C203/90DCA-8 prop. Even 82 inches already seems pretty short for 230 thundering horsepower, but I noticed that the blades are pretty close to minimum length of 80-1/2". This prop is approved under STC # SA388NW, which also allows for the 88" long 90DCA-2 blades. This prop seems to be working just fine, but I'm thinking about talking to the prop shop about putting a set of the longer blades on it, and giving the hub a once-over at the same time, since it's been 1150 hours and 21 years since it was OH'd.
The 88" prop is generally considered a seaplane prop, although a lot of wheel airplanes run them, and should pull quite a bit harder at the low end. However, I'm pretty unfamiliar with c/s props, so I don't know if there is a corresponding penalty at the upper end due to drag or whatever.

Simple answer: Nope.

MTV

I lost 4 knots replacing a 82" C66 to 88" C203. Big difference in thrust out of the hole though, well worth it in my opinion. Wish you luck finding longer blades, they are available but not cheap. You'd be better off buying my 88" C203.

Flynengr

I have a low time 82" that hasnt been cut if you want to go that way... (love to sell it)

Way cheaper than the 88.

I know 185's w/ "seaplane" prop is about the noisiest single engine piston plane out there.

I did some numbers and it looks like at 2500 rpm the tips will be turning about 960 ft/sec while speed of sound is 1,125 fps; therefore, you should be much quieter if that makes a difference.

TD

Just curious who is your prop-shop?

Bigrenna, I may me in the market for a prop for my 182. What model and price for the prop youv'e got. My apologies if this isn"t the place to be asking.

Jim

There's two different local prop shops, NW Props in Puyallup and AC Props in Seattle. I've done business with them both and they're both good to deal with.
Ponk has a tip speed calculator on his website, but as it warns might be the case it didn't wanna work with my browser. But here's the formula he shows for determining tip speed:
Prop diameter in inches x pi (3.14) / 12 x rpm x 60 / 5280 = tip speed in mph
In my case, an 88" prop turning 2600 rpm has a tip speed of 680 mph- or .895 mach.
Mach (speed of sound) is 760 mph on a standard day at sea level.
Ponk says optimum tip speed is .88 to .92 mach, so an 88" prop at 2600 is about as good as it gets.
Noisy, yeah, but you can't really hear it from inside the airplane.
Besides, it's pretty easy to start pulling the knobs back right after takeoff if climb performance isn't critical.

You would like the 88"Mac.

I swapped an old Mac C36 82" out for a Mac C66 88" and the difference was very noticeable. It really helped out up here with the high density altitudes, almost a must imo.

Plus a prop is an airfoil, so even if it's traveling sonically it can have local supersonic flow. Trans sonics are really interesting!

mountainmatt wrote:I swapped an old Mac C36 82" out for a Mac C66 88" and the difference was very noticeable. It really helped out up here with the high density altitudes, almost a must imo.

That's what I'm talking 'bout!
I don't wanna throw money at the airplane just because, but a noticeable improvement wold be well worth a couple grand. Esp since it wouldn't be a bad idea to have that prop checked over anyway.

hotrod180 wrote:There's two different local prop shops, NW Props in Puyallup and AC Props in Seattle. I've done business with them both and they're both good to deal with.
Ponk has a tip speed calculator on his website, but as it warns might be the case it didn't wanna work with my browser. But here's the formula he shows for determining tip speed:
Prop diameter in inches x pi (3.14) / 12 x rpm x 60 / 5280 = tip speed in mph
In my case, an 88" prop turning 2600 rpm has a tip speed of 680 mph- or .895 mach.
Mach (speed of sound) is 760 mph on a standard day at sea level.
Ponk says optimum tip speed is .88 to .92 mach, so an 88" prop at 2600 is about as good as it gets.
Noisy, yeah, but you can't really hear it from inside the airplane.
Besides, it's pretty easy to start pulling the knobs back right after takeoff if climb performance isn't critical.

You can pull the prop a couple turns before you takeoff if you don't need it all. Keeps the neighbors happy

[I know 185's w/ "seaplane" prop is about the noisiest single engine piston plane out there.}

I agree and it is actually painful for those on the ground.
It is also a negative effect on general aviation, both in the backcountry and the local airport.
I'm all for performance, but not at the damage to our pursuit that this prop definitely causes.
The colder the day the more the damage and there is no need for it as the tip speeds producing that NOISE are producing LESS thrust.

... could be that all that obnoxious noise from the 185 comes from the prop turning 2850 rpm (!!!) on take off (as opposed to 2600rpm). YOWZA!!!!
Once that prop tip starts breaking the sound barrier, I believe the co-efficient of lift goes down signifigantlly. so in making all that noise (shockwave) you are actually losing thrust potential, in the section that is travelling supersonic. and we all know that the tip is where all the work gets done.

Very little gets done at the tip except for vortex shedding. Roughly 12% inboard of the tip (as a rule of thumb) is where vortex shedding drastically increases.

Props are a 3d airfoil.

boyfalldown wrote:Bigrenna, I may me in the market for a prop for my 182. What model and price for the prop you've got. My apologies if this isn"t the place to be asking.

Jim

Jim,

Here is the link to the prop....
https://www.backcountrypilot.org/community/forum/latest/fs-mccauley-2a34c203-90dca-c180-182-16126?p=219563#p219563

If it were me I'd go with either a 86 or 88" C66, unless money is no object . If you think you may ever end up with a Pponk my first choice would be the 86", but I like both.
Gary

I'm not familiar with the C66 prop, I thought the C203 "threadless" hubs were the good stuff. I already have the prop, so it should be easy (but maybe not cheap) to swap out the blades for the 88 inchers. Probably won't get much if anything in trade for the 82's, esp since they appear to be close to minimum length already.

CamTom12 wrote:Props are a 3d airfoil.

I'm not a quantum physicist but I'm fairly certain everything in the physical universe (not considering time) is three-dimensional.

Regarding static thrust prop measurements, I'm not sure I would make that the defining determiner of propellor climb efficiency or choice. It's better then no data - but the prop is not screwing itself thru clean air (relatively speaking) as it would moving the airplane forward.

My first trip into the Idaho backcountry I was standing next to my instructor at some strip, don't recall which one - probably one with food, and as we saw rafters go by and watched a plane take off with its prop noise reverberating against the canyon walls, I commented something like "I'll bet those rafters don't like airplanes". Without missing a beat my instructor said "Airplanes are part of the backcountry experience. They bring in clients, food, supplies, help and rescue".

Prop length. Last year I talked with all the Cessna 185 STC prop holders for McCauley, Hartzell, and MT. They all provided information about their STC.

Steve Knopp of PPonk, and Donna Jones of Davis Aviation were the only ones that started the conversation by asking what my mission was and whether I'm on floats, wheels, or both. They provided great information, while the others were just trying to sell me their STC propellor.

The short of it (pun not intended) is the longer blades will get off the ground quicker and climb faster, but cost as much as 4 knots cruise speed.

The longer blades will also perform better at high altitude (like above 10,500 feet). Steve told me his PPonked 182 which he uses as his prop test bed, when fully loaded, climb deteriorates significantly at 10,500 feet with an 80" 3-blade, but goes to 12,500 before significant deterioration with an 86" 3-blade. If memory serves I think the load was sky-divers.

Steve also told me that although he hadn't tested it, at even higher altitudes he believed the 86" would be faster in cruise then the 80". I can see how the extra drag of the 86" would be lessened to a point where the extra thrust of the 86" could give a greater cruise speed then an 80".

I'm still flying the 86" 2-blade seaplane prop.