C85-8F seaplane prop pitch

[gcgilpin]

I've got a C85 with a McCauley 1B90CM7142 prop. I'm thinking about flattening it to somewhere in 40, 39 or 38 pitch area. I'm trying to improve takeoff performance, I'm not concerned about cruise.

Anyone out there with a 7140, 7139 or 7138 prop?

How is your take-off performance? Are you over-taching?

[Dano"T"]

Re: C85-8F seaplane prop pitch

I have a 71-42 McCauley on my C85-8 and I get 2475 static. I'm pretty sure you'll redline if you go to a 40. If you go to a 74" with a 40 pitch it'll likely still be at or below redline and you'll get the off water benefit. I get pretty good takeoff performance on Baumann 1500's...about 8 seconds solo.....berween 20 & 24 seconds with 2 - 200 pounders on board. Cruise is 95 on floats, 105 on wheels. Re-pitching will help you off the water....but like I said, you'll redline it on takeoff. We also have a T-craft with a C-90 in it. It has a 76AK-2-40 Sensenich which is a 74" with 40 pitch.....I may try it on my floatplane this spring to see if it's any better....it sure works well on the 90! and it doesn't redline on takeoff. I should note that we originally thought my prop was a 40 pitch, but at my recent annual my IA said it's 42......The only way to tell for sure is if we measured the pitch....which I do not know how to do.

[gcgilpin]

Re: C85-8F seaplane prop pitch

The recommended sensenich prop is a 72 by 40 pitch. McCauley recommends a 71 by 42 pitch.

Both manufacturers mention that these settings can be adjusted so long as you stay within static rpm limits.

I'm more worried about red-lining too early (before I even get off the water) and less worried about static rpm limits.

[barnstmr]

Re: C85-8F seaplane prop pitch

I will look up some stuff and get back to you. Sounds to me like the way you should go is with a longer prop diameter. Usually seaplanes are approved for longer props.

[barnstmr]

Re: C85-8F seaplane prop pitch

which aircraft model are you flying?

[Yellow Duck]

Re: C85-8F seaplane prop pitch

I have a 74 x 40 on the Duck. Works great.Still cruise 100 mph at 2150.

[gcgilpin]

Re: C85-8F seaplane prop pitch

I'm flying an Aeronca Super Chief 11CC w/ C85-8F. It's on PK 1500 floats (same as EDO 1400).

(I know, not a Taylorcraft but you guys have a more active discussion forum)

[Jim Hartley]

Re: C85-8F seaplane prop pitch

Hi Gord!
Keep sharing the info as we all can learn from it. I run a sensenich 74-ck-0-40 on my C-85, BC12-D,floats wheels and skis. Tach shows close to 2500 RPM at take off at sea level,give or take...never checked for accuracy but I think it is in the neighborhood.

By the way,check out the www.supercub.org forum as well. A lot of knowledge exchanged there as well.

Ahhh...If I had looked a little closer I would have see your posts on the Super Cub and Aronca forums. Any other sites out there that you would reccomend?

Jim

[matsuthunder200]

Re: C85-8F seaplane prop pitch

When i first went on floats i had a 72-40 mc prop. it seemed to work ok and it didnt go over red line. cruse was about 90-95 Then i tried a frends prop it was a Ak-74-40 i liked it alot better. Finaly i found a good used 74 inch ak prop but it was pitched at 38 i have the 90 hp cont. and the red line is 2675 for the first 5 min so i thought i would try it. it works great for getting off the water i get 2600 rpm on take off but i realy suffer on cruse i get about 80 mph at 2300 rpm its great for small lakes and its a rocket on wheel and skes.
Most every one here in alaska has a 74-40 on floats with a 85 hp.
It seems to be the hot set up. I dont think i know anyone up here on floats with a 71 or a 72 inch prop with floats.

[gcgilpin]

Re: C85-8F seaplane prop pitch

Has anyone out there used the McCauley 1B90CF7538?

I think this is a Cessna 150 seaplane prop, but I've heard of guys using it on C85s and C90s.

[Jim Hartley]

Re: C85-8F seaplane prop pitch

It would appear that it may just be the right set up,and I would like to know more as well...

Jim

[NY86]

Re: C85-8F seaplane prop pitch

Carefull what you slap on there! McCauley only allows up to 73" on a C90 and 71" on a C85....

[Dan Mahalak]

Re: C85-8F seaplane prop pitch

type cert...................... so what does that REALLY Mean to a guy who'll never make money flying his airplane.......................................... ............

I know what the books says, but why not put a larger prop, say a Mac 1A90 7438 on the front of my tcraft?
What is the difference? Only thing I can think of is

Fouling plugs due to lower RPM...Hmm dont think so.
Bad vibrations at cruise and/or climb?..hemmmm possibly?
stronger torgue on the crank and/or bolts in power changes?.... potentially
Potential prop strikes with longer prop on ground....doubt it.....

what, what is the difference for my seaplane between 74 and 72 inches....how does two inches take the c-85 our of safety margins and endangeres my flight? why cant I put on a 7438...please inform me...but not what the book says. I simply must know how that larger prop will ruin my engine and the 72 inch prop will not.

Curious, thats all.

[Dano"T"]

Re: C85-8F seaplane prop pitch

I think the reason the type cert says what it does is because that's what they used for the certification and that's what worked. 74" props are approved for the C85 and C90 etc.....it's just that Taylorcraft didn't certify with them on their airframe.....Is this true Forrest???? I don't think anyone meant that it was a safety risk or anything....I think he meant a picky IA wouldn't sign an annual if he knew....or if you got ramped by the FAA.....you'd get dinged....I just put the 74-40 prop on my 337 for the C90 installation stating that "it is an FAA Certificated engine and prop combo" and it was approved. Try that...the key would be not exceeding static rpm limits.
Just MHO.

[NY86]

Re: C85-8F seaplane prop pitch

The data specifically says "vibration considerations". I've always understood this to mean that the resonance of the crank/rods/pistons/prop assembly compared to the number of power pulses at usual cruise speeds should not set up reinforcing harmonics.

One reason I think it is more than just "what works" or "what was tested" is the difference between the C75 and the C85. Internally, they are identical. The only difference is RPM, yet the C75 can go up to 74" whereas the C85 is limited to 71". There has to be a reason.

A 74" Sensenich is allowed, but that's a whole different animal...