I'm sorry the C90 is the blade model I guess. My prop is a 2A34C203-C/C-90DCA-2

So I guess it's a C203, which is good news. How do I tell if it's the 285/300hp variant?

C180_guy wrote:2A34C203 TCDS P3EA (p.2) shows different #'s:

90DC[X]-0 to 90DC[X]-18
max continuous: 285 hp, 2700 rpm
max take-off: 300 hp, 2850 rpm

That's on page 2 of the TCDS.
Check page 9, it specifically lists the O-470 series and sez up to 230hp @2600.
So the TCDS has conflicting data.
I would say the snippet you quoted should allow a C203 on a ponk, which are what- 270 hp at 2700?
but a guy I know who was trying for a field approval for that combination
told me that FAA cited the hp limitation on page 9 as the reason they couldn't approve it.

soyAnarchisto wrote:I'm sorry the C90 is the blade model I guess. My prop is a 2A34C203-C/C-90DCA-2

So I guess it's a C203, which is good news. How do I tell if it's the 285/300hp variant?

No, no it's not. And no the reason the 'C203' didn't make the Pponk STC was not hp it was vibration. Look closely at TCDS for the dampners required on the C58/66 vs the 203/4. If you look at the TCDS and the Application Guide from McCauley you will notice the C66 was rated for 190hp continuous and that along with the C58 has been approved numerous times over and over. I *think* where people get stuck on the 'C203' being approvable, (is that a word?) is because the D2A37C230.... is an approved 2 blade. Although it uses a very different blade than the C58/66 or the C203.

The last two numbers after the dash in C180_guy's post are simply how much is clipped off the end of the prop. All of these props mentioned are 90" in their full dress. a -18 is a 72" prop, probably used in a Conti powered twin or? because the shortest approved on the 180/2 is -8.

If it were me and I absolutely had to have a 2 blade, I'd decide just how much I cared whether running an 'obsolete' prop mattered to me. In my case it doesn't matter a lick. FWIW, your entire plane is obsolete. If I didn't get hung up on that I'd scrape scour and scrounge until I sourced (likely built up) a C58 or C66 with good life remaining on blades no shorter than 88". Barring that option, I'd look long and hard at the C230 or MT, they both offer compromises. Sell your vastly superior 'non obsolete' prop to someone who forgot their airplane is 70 years old and walk away smiling...

Or buck the trend and fight till you get a prop approved, that people smarter than most of us already deemed out of the vibration compatibility range of our engines.

Take care, Rob

If that last bit sounded a bit assish, it's because I have had the distinct displeasure of riding out a catastrophic prop failure. That experience makes an engine failure benign in comparison. YMMV.

Take care, Rob

Rob wrote:... the reason the 'C203' didn't make the Pponk STC was not hp it was vibration. Look closely at TCDS for the dampners required on the C58/66 vs the 203/4. ...

I've heard that vibration issues were why the C203 isn't approved on the ponk 470-50 / Northpoint XP470, as Rob states.,
and that it was due to incompatibility with the crankshaft damper configuaration.
But I'm kinda confused....
The NorthPoint website just sez "XP470 engines are equipped with four-counterweighted crankshafts".
The 470U uses four: two 6th order, one 5th order, and one 4-1/2 order dampers.
The 470K & 470L use four 6th order dampers.
Not 100% sure, I'm relying on my memory (which is always risky), but I believe the ponk 470-50 engine used the same crankshaft counterweight configuration as the 470K & L.

If you check the C180 TCDS, you will see the C203 prop is listed for the 180A (with 470K engine).
Apparently Cessna determined there were no vibration issues with that combination, at least when it's making 230hp at 2600 rpm.
However, the McCauley TCDS sez the C201 & C203 are for a 470 with one 5th order damper & one 6th order--
which are the 470A, J, & R engines. It doesn't list any 4-damper 470's at all.
So the Cessna & McCauley data are somewhat in conflict.

I'm pretty sure my "K" crank dampers were changed to the same configuration as "U" crank when I made it a Pponk/Northpoint. While the converted "K" engine is on the 180K now and not the 54 180, the same MT prop is being used and I think it is smoother. Although, some days seem smoother, too, and maybe because of atmospheric conditions.

As I've been exposed to in many prop/engine configuration tests in the last few years "smooth" is in the eye of the beholder.

Unless your plane is all rigged up with proper instrumentation (strain gauge / vibration gauge etc) we all tend to "feel what we expect or want". I've done the same myself. I've spent many hours doing vibration testing comparing many different engine/airframe/mount/prop comparisons.

All I can say after all of that is unless you have all the data and compare each set up empirically against another then it all comes down to personal opinion.

I'm not endorsing nor denying any product in any way shape or form.

All the above being said-I do appreciate the open and honest thoughts and experience of those who go before me.

Rob has true wealth of real experience and I appreciate all he offers this site.

MW

185Midwest wrote:
Unless your plane is all rigged up with proper instrumentation (strain gauge / vibration gauge etc) we all tend to "feel what we expect or want". I've done the same myself. I've spent many hours doing vibration testing comparing many different engine/airframe/mount/prop comparisons.

MW

100% agree, and it happens in reverse as well. Like when you fly through a flock of starlings, or nip an alder and just "know" you feel a 'new odd' vibration in your rig

185Midwest wrote:As I've been exposed to in many prop/engine configuration tests in the last few years "smooth" is in the eye of the beholder.
MW

That is the good stuff, and good stuff that everyone else gets to benefit from. Thank you for that, I would have loved to be a fly on the headliner on those tests. I am looking forward to the turning loose of the composite.

And thank you, that was very kind.

Take care,
Rob

You bet Rob.



MW