Engine Experts... C-85 Question

[Ragwing nut]

Re: Engine Experts... C-85 Question

There is a hundred issues that can cause low rpm, not as simple as just the wrong pitch. 71-50 is too much, I don't like anything more than a 71-48 for cruise prop.

Flat engines not like to be ran over square, unless you have a constant speed. Without the CS, you are burning more gas without increase in prop efficiency.

Performance will be about the same if the stampings are true. The increase in length with offset the decrease in pitch.

Mike

[VictorBravo]

Re: Engine Experts... C-85 Question

OK, ignore me. I don't care.

Wouldn't DREAM of it ! I appreciate your input.

My tachometer is somewhat suspect because there is a reversing adaptor on it. Meaning that I am using the same tach that the A-65 used, which I should not be able to do with an 85. I suspect that this was a common thing where people wanted to use the same tach as the previous 65HP engine used.

I will check the RPM's soon with some sort of an optical tack checker.

[crispy critter]

Re: Engine Experts... C-85 Question

The A65 tach and the C85 tachs are calibrated different. I would guess your tach is wrong.

[NY86]

Re: Engine Experts... C-85 Question

You can request a field approval to install the Cessna Sea Plane prop, its 76-74"

Where do you find that? The only one I'm aware of is on the C90 where up to 73" is permitted. The C90 has a different crank and RPM limit, so vibration characteristics are different. AFAIK, there's no approved 1A90/1B90 installation on a C85 longer than 71".

The markings on the A65 tach will be wrong, but if you get it to turn the right way it should read right. Both are "1:1". Problem is most old tachs are really inaccurate.

[astjp2]

Re: Engine Experts... C-85 Question

The C-90 and O-200 have EXACTLY the same crank by part number...The same rods and even pistons.....per the manual that I currently have. The C-150 had a 74+ inch seaplane prop approved on the O-200. Its a 1A90CF (seaplane only) not over 75 and not under 73.5, on page 4 of the TCDS

http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/a01fa66c9a3bc9498625745100674f44/$FILE/3A19.pdf

[astjp2]

Re: Engine Experts... C-85 Question

The A65 tach and the C85 tachs are calibrated different. I would guess your tach is wrong.

The tachs are calibrated for the HOBBS if it has one, if not they rotate at a 1-1 ratio for both, The only thing that can really cause a Tach to go out is the flying magnet may lose some of its ability to pull the needle through the swing. Some Tachs do have an adjustment for the spring tension on the needle, if in doubt send in your tach for test. Most speedo shops also have that ability to check it. If you are lush for funds, you can buy a photo tach and compare the acft tach at several different rpms for comparison. Tim

[Vasey fan]

Re: Engine Experts... C-85 Question

Coming in on this one a little late, but I'll throw in my 2 cents anyhow.

I'm with Eric as far as the too much prop opinion, 50 inches of pitch is a pretty big bite. I'm running a 71-48, and most days I barely make static. (Yeah, I check it every time - I fly from a 5k field elevation).

As far as all the theories about the rpm/map relationship, I'm just gonna sit on the sidelines & watch..maybe get some popcorn...

[VictorBravo]

Re: Engine Experts... C-85 Question

The tach that was in the airplane originally when I got it is a "normal" 3 1/8 size unit, with an integral hour meter / Hobbs. I don't know if this is affecting anything as was suggested.

I have a brand new NOS tach in a box that I can try, but if this "new unit" is 40 years old then could the magnet be weak already?

To the chagrin and annoyance of everyone in the FAA, this is a job for a good $20.00 model airplane tachometer!

[Ragwing nut]

Re: Engine Experts... C-85 Question

Where do you find that? The only one I'm aware of is on the C90 where up to 73" is permitted. The C90 has a different crank and RPM limit, so vibration characteristics are different. AFAIK, there's no approved 1A90/1B90 installation on a C85 longer than 71".

The markings on the A65 tach will be wrong, but if you get it to turn the right way it should read right. Both are "1:1". Problem is most old tachs are really inaccurate.

cam is different, not the crankshaft. Only other major difference is the carb.

[Ragwing nut]

Re: Engine Experts... C-85 Question

Wouldn't DREAM of it ! I appreciate your input.

My tachometer is somewhat suspect because there is a reversing adaptor on it. Meaning that I am using the same tach that the A-65 used, which I should not be able to do with an 85. I suspect that this was a common thing where people wanted to use the same tach as the previous 65HP engine used.

I will check the RPM's soon with some sort of an optical tack checker.

If the reversing adapter is 1:1, then it should be fine. However, I would have the tach checked just to be sure it is reading correct.

[NY86]

Re: Engine Experts... C-85 Question

The C-150 had a 74+ inch seaplane prop approved on the O-200. Its a 1A90CF (seaplane only) not over 75 and not under 73.5, on page 4 of the TCDS

I thought we were takling about a C85...

[NY86]

Re: Engine Experts... C-85 Question

cam is different, not the crankshaft. Only other major difference is the carb.

Now I guess I'm confused. I was talking about the C85 vs. C90. Different cranks. Different cams, too, but I doubt if the cam has much bearing on vibration characteristics.

I stand by my original statement (for now). I know of no certified C85 installation with a McCauley 1A/B90 over 71 inches.

[jCandlish]

Re: Engine Experts... C-85 Question

I thought we were takling about a C85...

To continue off topic...

What is the certification basis for flying an o-200/c-90 in the a-696 airframe?

It seems to me that if the factory wanted to generate some business and goodwill there would be such an STC available. Didn't they demonstrate an LSA model that was o-200 powered, and couldn't the engineering data from that ship substantiate an STC?

Cheers
jCandlish
.

[astjp2]

Re: Engine Experts... C-85 Question

There is an STC already applied for.

[crispy critter]

Re: Engine Experts... C-85 Question

To continue off topic...

What is the certification basis for flying an o-200/c-90 in the a-696 airframe?

It seems to me that if the factory wanted to generate some business and goodwill there would be such an STC available. Didn't they demonstrate an LSA model that was o-200 powered, and couldn't the engineering data from that ship substantiate an STC?

Cheers
jCandlish
.

I have a one time STC for an 0200 on a short mount approved. Your welcome to have copies.