My K model 172 with 0320 E2D has this placard on the panel "Avoid Continuous Operation above 75% and full throttle climb above 2500 RPM" The placard has a cessna part No. 0505027-1. I googled it seems to be rlated to the propeller.

If I operate my plane within these confines, I am not going over 115 mph indicated. The static RPM is 2550 and it can get as high as 2750 but does not exceed redline. If I cruise at full power (for short distances) the speed increase is upwards of 25 mph. The climb out is rather nice too so I am guessing I have a climb prop. The airplane has a STOL kit and has been converted to taildragger too so its a nice combination. I am just wondering if anyone knows why the engine is limited to these power settings. Can the full performance of the engine be had with a different prop?

I'd take a look at Lycoming Key Reprints, here: http://www.lycoming.textron.com/support ... index.html

It is a great resource for ANY Lycoming engine questions.

If you want to talk to a tech rep from Lyc (and I would if I were you), call them at 570 323 6181. Ask to speak to a technical rep for small recip engines. Those guys are VERY knowledgeable and very helpful.

MTV

I'm curious what prop you have. I run a 320-E2A with a Sensenich 74DM6-56 prop, and am not aware of any special rpm restrictions.

You are right. The TCD lists the following statement for the placard:

Near tachometer on Models 172I, 172K and 172L (with IC172/MTM propeller):
"Avoid continuous operation
1. Above 75 percent power in cruise
2. Above 2500 rpm in full throttle climb."

There are other props that are type certified for the plane that do not have this restriction. I am thinking that I need to look at other prop options if I want to gain some cruise speed. My speed loss is probably attributed to other things as well like the tailwheel conversion and STOL kit.

The TCD also states :

McCauley 1C172/MTM 7653
Static rpm at maximum permissible throttle setting:
Not over 2360, not under 2260
No additional tolerance permitted

My static RPM is too high. It must be a climb repitch

I can get a full 2700 in climb (although I am to avoid this), but static (on the ground withthe brakes on) is about 2550. The limit is 2360 so it apears to have been repitched for climb. The airplane never has had a prop log. The entries for the prop are in the last pages of the engine log. There are only 4 entries. One of them shows that the prop was overhauled and returned to servivce. another shows that the prop was installed when the engine was replced (factory overhaul) and the two others are just inspections indicating it's airworthy.

I searched through most of the maintenance records last night. I need to look inthe airframe manual I guess to see if there is a yellow tag or something indicating that the prop was overhauled and what they did to it. I am going to explore buying another prop that is identified in the TCD without the restriction and have it ptched for climb.

I bought a new Sensenich prop for my 320E2A-powered airplane about a year ago. Surprisingly, Art Mattson of AMR&D in Illinois (pipermods.com) turned out to have the best price, which included his STC'd tip mod which is supposed to let the engine turn up a bit more than the pitch would indicate. I don't know if it does that or not, but his pricing is such that you pretty much get the tip mod thrown in for free.

Eric

It is a common mistake to think that more rpm will give you more thrust. Even with constant speed props.

In fact the prop is designed to make maximum thrust at at certain rpm and that rpm should be maintained. Overspeeding it will give less thrust.

Over speeding the engine also leads to more wear and increases the chance that something will break.

Follow the TSDS for both the engine and the prop.

obxbushpilot wrote:I can get a full 2700 in climb (although I am to avoid this), but static (on the ground withthe brakes on) is about 2550. The limit is 2360 so it apears to have been repitched for climb. The airplane never has had a prop log. The entries for the prop are in the last pages of the engine log. There are only 4 entries. One of them shows that the prop was overhauled and returned to servivce. another shows that the prop was installed when the engine was replced (factory overhaul) and the two others are just inspections indicating it's airworthy.

I searched through most of the maintenance records last night. I need to look inthe airframe manual I guess to see if there is a yellow tag or something indicating that the prop was overhauled and what they did to it. I am going to explore buying another prop that is identified in the TCD without the restriction and have it ptched for climb.

The prop isn't stamped with the pitch?

At the time of the first posting, I did not know the pitch. I now know that it is 53" pitch and 75" diameter.

I agree with you MauleOne. However, the plane picks up considerable speed in cruise when I operate between 75% power and 100% (2700 rpm. ) Additionally there is another prop for this plane that does not have this placard associated with it (same manufacturer) so it would seem to me that I could use the other prop listed in the TC data and repitch it to a climb prop and operate it through a full range of rpm with no restrictions.

All I have to do to resolve this is sell the one I have now and buy the other and have it repitched. The prop I have currently only has this placard because there is a resonance frequency with the C 172K airframe in that RPM range. The other TC prop for this model has no restriction.

It's not my intention to operate beyoond the redline. The engine is designed to run at near redline continuously. The wobbly prop on there now is the only thing preventing full use of the RPM range. I am limited to 2500 RPM in a full throttle climb and 75% power in level cruise. The power curve is not flat in this RPM range (I have the graphs provided by lycoming after factory reman). There is more juice to squeeze out, but the prop placard tells you to avoid continuous operation on the top end of the scale.

My prop/engine combo has a similar placarded limitation due to resonance. "Avoid continuous operation between 2150 and 2250rpm."

Just a thought?
WHAT is continuous? 1 min, 3min. 5min, 10 min, 30 min, all the way there?
Full rpm for 5 min climb and pull back?
The old 165 Franklin in the Stinson liked being at redline all the time, Guy I got it from said as long as I ran it like I stole it it would Make TBO, If I turned it slow and easy said would crap on me early??
It's still going and has way more than the TBO on it.
So have kind of run most of my engines that way.
Only have lost 2 cyls. both to cracks. Then they put a ad on them and you had to pull them anyway?

$.02

obxbushpilot wrote:My K model 172 with 0320 E2D has this placard on the panel "Avoid Continuous Operation above 75% and full throttle climb above 2500 RPM" The placard has a cessna part No. 0505027-1. I googled it seems to be rlated to the propeller.

If I operate my plane within these confines, I am not going over 115 mph indicated. The static RPM is 2550 and it can get as high as 2750 but does not exceed redline. If I cruise at full power (for short distances) the speed increase is upwards of 25 mph. The climb out is rather nice too so I am guessing I have a climb prop. The airplane has a STOL kit and has been converted to taildragger too so its a nice combination. I am just wondering if anyone knows why the engine is limited to these power settings. Can the full performance of the engine be had with a different prop?

What you may be missing here is your not going to have above 75% power unless you stay pretty low. Just leave it alone fly the hell out of it. Your not going to see any huge performance gains with an O-320.

mr scout wrote:

obxbushpilot wrote:My K model 172 with 0320 E2D has this placard on the panel "Avoid Continuous Operation above 75% and full throttle climb above 2500 RPM" The placard has a cessna part No. 0505027-1. I googled it seems to be rlated to the propeller.

If I operate my plane within these confines, I am not going over 115 mph indicated. The static RPM is 2550 and it can get as high as 2750 but does not exceed redline. If I cruise at full power (for short distances) the speed increase is upwards of 25 mph. The climb out is rather nice too so I am guessing I have a climb prop. The airplane has a STOL kit and has been converted to taildragger too so its a nice combination. I am just wondering if anyone knows why the engine is limited to these power settings. Can the full performance of the engine be had with a different prop?

What you may be missing here is your not going to have above 75% power unless you stay pretty low. Just leave it alone fly the hell out of it. Your not going to see any huge performance gains with an O-320.

Panel mounted tachometers can be off as well, have you tried one of those optical jobs?

I agree with Mr. Scout. If you are happy with the performance, leave it alone.

gb

I am not entirely happy with the performance. The speed is compromized by the reduction in power and there appears to be no reason other than that this prop model is required to have this placard (due to resonance with this aircraft). Since the other prop that is legal to put on this plane does not have this restriction, it seems that more can be achieved in way of performance by simply changing the prop even if the prop has the exact same pitch

Additionally, the placard does not state only 75% power is to be avoided. Level cruise above 2500 RPM is also to be avoided. Here is where the the performance sucks. If I was able to cruise at or near redline (engine is rated for 2700 RPM continuously), I pick up a lot more speed (25mph).

If I climb high enough, I suppose I can only expect to get 2500RPM in level flight so perhaps there is a no real advantage except at or near sea level (where most of my landings and takeoffs occur).

Although I am in no hurry to solve this problem. If the prop needs work for any reson, its getting replaced with the other type certified prop without the restriction.

I am going to look into the tach accuracy at annual using an optical device.

Good discussion though and thanks for all of your insights.

V. Model 172I, 4 PCL-SM (Normal Category), 2 PCLM (Utility Category), approved December 15, 1967
Model 172K, 4 PCL-SM (Normal Category), 2 PCLM (Utility Category), approved May 9, 1968
Engine Lycoming O-320-E2D
*Fuel 80/87 minimum grade aviation gasoline
*Engine Limits For all operations, 2700 rpm (150 hp)
Propeller and 1. Propeller
Propeller Limits (a) McCauley 1C172/MTM 7653
Static rpm at maximum permissible throttle setting:
Not over 2360, not under 2260
No additional tolerance permitted (see Note 3)
Diameter: not over 76 in., not under 74 in.
(b) Spinner, Dwg. 0550320

You may want to do some more research, just because the placard is there......doesn't mean it should be........if it says climb then it means climb not cruise.......NOTE THREE IS A JETTING CHANGE....COULD BE THE ONLY CONCERN do your research before spending money for nothing

Mr. Scout,

I have researched this extensively. If you read further down the TCD, it lists all limitations and placards. The placard is required for all models I, K and L models with the IC172MTM prop and is to located near the Tach.

The other type certified prop (not sea plane) has near the same operational limitations (re static RPM) and yet requires no operational limitations with regard to power setting or RPM in climb or cruise .

Note 3 indicates that complaince with a Service letter allows minor increases in static RPM from not more than 2360 and not less than 2260 to Not more than 2420 and not less than 2300 (my airplane complies)

So my static RPM is a little too high (abot 100 RPM). OK, I can reduce power a little to reduce it by 100 RPM until I am in a full climb out. Once the plane begins moving (no longer static), the engine can withstand a continuous 2700 RPM. So climb and cruise speeds are limited due to the propellor model by limiting to 75% in climb and 2500 in cruise.

The other TC prop has the same static RPM tolerances, but has no limitations regrding climb power or cruise RPM.

Conclusion: I will not need to avoid continuous operation above 75% in cruise and operating above 2500 RPM in a full power climb which will result in more speed and better climb performance if the IC172MTM prop is replaced with the IC160CTM of the same pitch (or maybe a pitch that gives me the correct static RPM).

But you have a good point Mr Scout. It may not be worth the expense to get the extra cruise speed. However, as I mentioned earlier, if the prop needs any serious attention, I am selling it and buying the other.

If you are turning more static rpm than allowed, and you are interested in cruise speed, and not take off performance, then get the other prop,(to eliminate the restriction), and pitch it so that you are only turning 2260 static. There will be a significant increase n your cruise speed.
You can likely find a good used prop on barnstormers, or trade a plane, and can sell yours if it is decent shape.

I Just annualed my plane and removed the prop to see what I had and to my delight, I found that my prop has been been replaced with he Ic160 prop (which has no restrictions on continuos operation), but not documented correctly in the prop log. The placard I have near the Tach does not apply to me! I can cruise at 2700 RPM and have gained 20 MPH in cruise and some more climb performance!

Overall, I found the documentation and logs to be real good. A separate log for the prop was probably never conveyed in a previous sale. It has one now.

I always like it when problems solve them selves.
Cheaper too.