Hi All,
New to forum with question I've searched my best to uncover, but no luck.
I have a 1970 C172K with Avcon 180 conversion and CS Hartzell, the common STC. Most of my time with this plane has been on floats at sealevel. Now I plan to base at about 2,000 feet on a small lake and really need better performance. I'd like to put a seaplane prop on, such as McCauley 1A200DFA-8244. I'd save weight up front and get 6 more inches - who could complain about that.
The problem is the STC for the application. Penn Yan's STC only applies to their installations. I've called Del Air, Kenmore (who did my conversion), Burl Rogers, written to Air Plains and Bush Conversions - very knowledgeable, but no luck for my application.
"Coordinated field approval" to get deviation of installation suggested, but may need engineering and the forums say field approvals unlikely these days.
Does anybody have updated info on approval for FP prop for C172K with Avcon 180hp?
I would think a lot of people might be in the same situation?
Thanks for any advice. And glad to be part of this group!

First, what makes you think that engine will perform better with a fixed pitch prop? Equipped with a fixed pitch, the engine is static rpm limited. Not so with CS.

With CS engine can make 2700 rpm, and is capable of making rated power.

No way I’d go to a Fixed Pitch on an Avcon conversion, even if it were legal.

You do realize you’d have to modify the engine as well?

MTV

For certification reasons I run a fixed pitch prop on a Lycoming 0-360A1D in order to be complient with the Canadian Owner Maintenence (OM) C of A rules. First I'll say that MTV is correct you will loose performance due to the inherent limitations of a FP prop but "rules are rules" so I had no choice. In addition within the same rules I was also able to switch out my aluminum prop for a much lighter one thereby hoping to gain back some "lost" rpm at TO power. Other's have installed a ground adjustable prop; again an option in Canada, maybe not below the 49th parallel.

Lycoming does publish an FAA Approved Service Instruction # 1435 that details the conversion process and referances use of a FAA 337 application as well. It is a very easy, straight forward process to follow however the Special Instruction does lack in some details that I learned about by trial & error. I'd be happy to share them with you if required.

mtv wrote:First, what makes you think that engine will perform better with a fixed pitch prop?

He said it in his question... Less weight up front and more clearance.

The plan for my 180HP 170B has always been for a fixed pitch for weight. For the mission for that bird, weight and simplicity was my priority. The peanut gallery can wallow about in the semantics, but in some ways, lighter will get better performance.

Greg-

Bigrenna wrote:

mtv wrote:First, what makes you think that engine will perform better with a fixed pitch prop?

He said it in his question... Less weight up front and more clearance.

The plan for my 180HP 170B has always been for a fixed pitch for weight. For the mission for that bird, weight and simplicity was my priority. The peanut gallery can wallow about in the semantics, but in some ways, lighter will get better performance.

Greg-

Same, same with my ride it was always about lighter and simpler

Bigrenna wrote:

mtv wrote:First, what makes you think that engine will perform better with a fixed pitch prop?

He said it in his question... Less weight up front and more clearance.

The plan for my 180HP 170B has always been for a fixed pitch for weight. For the mission for that bird, weight and simplicity was my priority. The peanut gallery can wallow about in the semantics, but in some ways, lighter will get better performance.

Greg-

You just keep telling yourself, Greg, while you save a few pounds over a composite CS prop, and make all of 150 hp or so…. That engine simply cannot legally make rated power at the restricted static rpm required by a fixed pitch. Acceleration will suffer, fuel flows will suffer, etc.

If that’s within your desired performance parameters, go for it.

MTV

mtv wrote:You just keep telling yourself, Greg...

Thanks Mike. I'm glad someone has all the answers...

All,
Thanks for all the comments, insight and advice.
I will have to look into the static rpm restrictions on the Lycoming A1D. I thought 2700 rpm would still be the engine's limiting rpm and that the 82-inch McCauley would fall close to the 0.88 to 0.92 Mach tip speed that fits the optimal power band (don't remember the site that provided these calculations).
Until I figure out more, sounds like the composite, CS prop might be the best, but with significantly higher cost.
MTV - the Penn Yan 180 hp conversions with McCauley FP props don't have static rpm restrictions similar to A1D or Avcon?
Thanks again.

Mapleflt wrote:For certification reasons I run a fixed pitch prop on a Lycoming 0-360A1D in order to be complient with the Canadian Owner Maintenence (OM) C of A rules. First I'll say that MTV is correct you will loose performance due to the inherent limitations of a FP prop but "rules are rules" so I had no choice. In addition within the same rules I was also able to switch out my aluminum prop for a much lighter one thereby hoping to gain back some "lost" rpm at TO power. Other's have installed a ground adjustable prop; again an option in Canada, maybe not below the 49th parallel.

Lycoming does publish an FAA Approved Service Instruction # 1435 that details the conversion process and referances use of a FAA 337 application as well. It is a very easy, straight forward process to follow however the Special Instruction does lack in some details that I learned about by trial & error. I'd be happy to share them with you if required.

Thanks for the FAA instruction info. I'll look into it. If I need more details, I'll appreciate the opportunity to be in touch.
Cheers!
I did also hear about a Sensenich "2 position prop" for 180hp cubs, but don't know much about them or approval for C172K with Avcon O-360. Is this the 'ground adjustable' you were talking about?

Welcome. I have only flown the fixed pitch McCauley prop on the 180 hp C-172. Flew little faster than 150 hp 172 but used a lot more fuel. On the pipeline I didn't need the extra climb performance.

PBitty wrote:All,
Thanks for all the comments, insight and advice.
I will have to look into the static rpm restrictions on the Lycoming A1D. I thought 2700 rpm would still be the engine's limiting rpm and that the 82-inch McCauley would fall close to the 0.88 to 0.92 Mach tip speed that fits the optimal power band (don't remember the site that provided these calculations).
Until I figure out more, sounds like the composite, CS prop might be the best, but with significantly higher cost.
MTV - the Penn Yan 180 hp conversions with McCauley FP props don't have static rpm restrictions similar to A1D or Avcon?
Thanks again.

I believe that all fixed pitch prop and engine combinations have static rpm limits. If not, the prop can permit the engine to over speed in level flight…..that’s the purpose of static limits, to protect the engine.

Here is information from EAA’s article at: https://www.eaa.org/eaa/aircraft-buildi ... er-dilemma


“Static RPM Is Important
A static rpm check is the best assurance you can have that your engine can handle the installed propeller. Perform your static rpm check by starting the engine and accelerating it smoothly up to full throttle (no wind condition and wheels chocked, of course). The engine should be able to reach approximately 80% to 85% of its rated (redline) rpm. A minimum static rpm has been established for each aircraft engine.

For example, Lycoming advises that, when fixed pitch propellers are used with their engines, the static rpm should be 2300 plus or minus 50 rpm for all engines rated at 2700 rpm. Lycoming also points out that this may vary slightly depending on the type of propeller. That is, if it is a climb, cruise or economy propeller.

When the static rpm is too high, there is the chance of overspeeding the engine at full throttle in level flight . . . perhaps even during take-off.”

So, 2350 rpm is your static limit…legally. At that rpm, your engine is not making rated power. Granted, as the airplane accelerates, rpm will increase, but unless you’re in a dive, it should never reach max rpm: 2700 for this engine.

Finally, each propeller must be approved (which requires vibration testing and rpm limits) on a given engine. The approved fixed pitch prop for a particular engine will specify pitch limits for that engine. Installing a flatter pitched prop is not legal.

With a constant speed prop, the Governor protects the engine from overspeed, but permits max rated rpm and power.

MTV

Getting static 2300 at high DA is not always possible and an engine that has run to near TBO at high DA will not get as much max RPM at lower DA as well. Having a really worn metal prop seems to help, however.

Bigrenna wrote:

mtv wrote:First, what makes you think that engine will perform better with a fixed pitch prop?

He said it in his question... Less weight up front and more clearance.

The plan for my 180HP 170B has always been for a fixed pitch for weight. For the mission for that bird, weight and simplicity was my priority. The peanut gallery can wallow about in the semantics, but in some ways, lighter will get better performance.

Greg-

I'm quite sure he'll lose clearance going to an 8244. He's gaining 6" of prop length, so by my limited math knowledge he'll loss 3" of clearance. On floats it's not a big deal.
If it fits his mission profile then a fixed pitch prop will work. Not saying it will perform better necessarily. All the scouts I have flown with 180hp had better takeoff performance with the CS then a FP. Also may be worth noting, but a lot of the 180hp scouts have RPM restrictions with the 8244. Again from my experience with the Scout and 180hp lycoming. May be worth looking in to and making sure they will work with your mission profile.
On the other hand we can help you spend your money and tell you just to put a MT CS prop on there and you'll have the light weight as well as the performance...

Thanks for all the comments and input. Great to be a part of this forum and be able to discuss my specific issues.

After reading all the comments, I think you are spending my money on a MT CS - A1Skinner!
Yes, I will lose clearance, 3" as you say and will probably need to get different nose fork, wheels and tires to make the 8244 work. But the 83" MT CS will require the same, so MT prop cost and new wheel gear, will be even more expensive. With the FP I thought I'd change prop when changing from floats to wheels - FP on floats and CS on wheels.

MTV - if you don't mind, I'd like to continue my questions:
You mention: "With a constant speed prop, the Governor protects the engine from overspeed, but permits max rated rpm and power."
As I understand, my governor doesn't actually change the pitch of my prop depending on engine rpm. Instead, my governor is set to make a prop pitch setting that achieves 2700 rpm max at max throttle, probably in some fairly high forward speed - I think it's adjusted to 2700 rpm at takeoff speed. As the engine wears, the governor may be reset again to achieve 2700 rpm, but I would worry about cylinder ridges, etc. in an older engine. Anyway, even an MT CS prop STC'd for my Avcon O-360 would probably be set for the same limitations of 2700 rpm, right?.
I thought I'd heard that FP seaplane props (flatter pitch) were used on O-360 Lycomings, but I only needed the STC for my particular application. So static rpm limits may have been tested, etc.
Finally, if Penn Yan STCs a McCauley FP prop for a different model O-360, wouldn't the vibration and rpm limits be similar to my Avcon A1D? Is it only that they've jumped through the hoops and I haven't/can't? Or can I not assume this?
Thanks again!

This doesn't address the posters question regarding approvals. For what it is worth, I was involved with the TW conversion of MTVs 175, I was also doing my plane. I installed a fixed 76 58 pitch for cg issues. I flew a lot with Karl, the owner at that time, he had the Hartzel CS. In level flight side by side our speeds were the same and I believe the take off was about the same. Level you can exceed 2700 but I control that with the throttle. It should be noted this prop is approved for this engine on the C-170. I have about 1000 hrs. on it and am happy. Karl had CG issues and I think he installed a different prop latter, I am not aware of how this changed the plane. Maybe MTV could respond. I feel the Sensenich was more efficient than the Hartzel.

I also have a 0-200 powered Cub with a McCauley sea plane prop approved for that engine which I love. Also can exceed max RPM, again use the throttle.

My Stearman with the ground adjustable set in low pitch will exceed max RPM.

Bush Master, please read the EAA article I posted. The rpm limits from the manufacturer are achieved by specifying the pitch of the prop. I’ve never seen a legal fixed pitch prop/engine combination that didn’t have static limits, BUT there are a lot of props out there, sooooo. FYI, my 175 now wears an MT Ultra prop, which pulls far harder than the previously installed Hartzell, and is 29 pounds lighter.

Comparing cruise speeds may or may not mean much….too many variables in airframes, wings, rigging and engines. My old 170 B was slower than any other 170 I’ve met, but had a strong engine, and I ran three different props on it at various times.

PBitty, the current crop of MT props are the Ultras, which are all 80 inches diameter. The older MTs were 83 inches, but blade design of the Ultra produces more thrust than the older longer props….yes, really.

Second, I doubt you could ever get an 84 inch prop approved on a nose dragger on wheels. Clearance would be a serious problem.

The prop Governor controls prop pitch to achieve the rpm the pilot selects. There are a few different ways to accomplish that, but overspeed is controlled by blade stops, generally. But, bottom line, engine if set up right, will go to max rpm static. So max power on takeoff and climb.

Just make sure you consult with a good mechanic to make sure whatever you install is legal, and safe. If you want to know static rpm limits for your engine, call Lycoming.

You can bolt any prop on that engine that matches the bolt pattern of the engine. Doesn’t mean it’s legal or safe. O-360 Lycoming engines have a lot of vibration issues, and limitations. To make the Pawnee prop legal and safe, it had to be cut down to 80 inches from 84, and have a harmonic damper assembly installed (9pounds weight). Same dampers we’re required on some 360s in twins. Harmonics can cause a prop to come apart…..

MTV

PBitty wrote:MTV - if you don't mind, I'd like to continue my questions:
You mention: "With a constant speed prop, the Governor protects the engine from overspeed, but permits max rated rpm and power."
As I understand, my governor doesn't actually change the pitch of my prop depending on engine rpm. Instead, my governor is set to make a prop pitch setting that achieves 2700 rpm max at max throttle, probably in some fairly high forward speed - I think it's adjusted to 2700 rpm at takeoff speed.

I’m not MTV, but the low pitch stops are set somewhere that you can achieve your maximum RPM at wide open throttle with the airplane parked. The high pitch stops would keep you from underspeeding the motor or going into a feather situation.

The governor is given an RPM setting to hold through the blue knob, and it increases or decreases pitch in the blades to maintain that selected RPM.

On a takeoff roll as you accelerate from a stop and the prop becomes more efficient, it will try to over-speed the RPM setting in the governor (currently max RPM), which then pumps some high pressure oil pressure to the prop, increasing the blade pitch off the low-pitch stops until the selected RPM is met again.

Now, say you’re at cruise and are approaching your destination: you start pulling back the throttle and the RPM will try to under-speed from your selected RPM setting in the governor. The governor will let some oil out of the prop, allowing the pitch to decrease and the RPM to recover back to the selected RPM setting. This will continue as you pull the power back until eventually the blades will be sitting on the low pitch stops and can’t adjust any farther. Then the prop RPM will decrease below the selected setting.


EDIT: Looks like MTV beat me to the submit button by 8 minutes! In my defense, my dog was being a distracting pain in the rear haha!

Cam’s explanation is far more detailed than mine.

That is by far the most common operational method for modern CS props.

Another major advantage of Constant speed props over fixed pitch is the ability to operate at reduced fuel flows, while cruising faster. Do the math, the fuel savings add up over time.

Bottom line: If CS props didn’t actually offer significant advantages, why would a manufacturer even offer them?

Go fly a Super Cub, then get in a Husky, and you’ll see the value pretty quick.

MTV

Cam explanation is very good. To add a little tidbit, the governor is almost always constantly changing your blade pitch to keep your engine running at the set RPM. Any little bubble in the air, slight climb or decent, or anything that can change your rpm is rectified by the governor.

I put an O-360 on my C175, Initially was planning on putting that C/S Hartzell on it but while I waited to find a good deal on a prop I put a sensenich 60 pitch 76" FP on it (Both props approved on Avcon conversions). After flying around awhile on the FP prop I abandoned looking for a C/S, the FP performs great, I still climb over 1,000fpm at gross and often see over 1500fpm climbs while light. Static RPM is 2350 but at 60mph I'm seeing near 2500rpm. I can hit redline if I'm low and firewalled but on longer flights I'll climb way up and keep it wide open and leaned out, will see about 145mph TAS and less than 8GPH. I'm sure a CSP would offer performance gains but between the weight penalty, complexity and cost I'm convinced its not worth it. If it were a higher HP engine or you absolutely needed that minor margin of performance gain then for sure but for 180hp I just don't see the value in a CSP.