Continental 0-200: HP -vs- cylinder compression - vs- RPM?

[Gone Flyin]

Wondering if anyone has any data to that will help compare the Continental 0-200's RPM and cylinder compression to the horsepower it is producing.

In other words... this, from the internet:
"The Continental 0-200 will give its maximum rated HP of 100, for a period not exceeding 5 minutes, at 2750RPM under correct atmospheric conditions".

I read the last part as a standard day at around sea level.

They do not say this... but, can one assume this is an engine producing a compression of (near) 80 over 80 for each of the four cylinders?

That being the case, is there a way to determine horsepower based on RPM? If an engine producing less than 80/80 on some cylinders is only producing an RPM of 2600 what is the approximate horsepower?

Let's forget about using a dyno to do this the right way. Just looking to get a rough idea, here.

 

[Bell206]

That being the case, is there a way to determine horsepower based on RPM?

The engine TCDS will have what the engine is rated at. But 80/80 is merely a test parameter as the cylinders actually operate at a higher compression.

 

[Capt. Geoffrey Thorpe]

Rings have to get REALLY REALLY bad before there is a significant impact on power.

Worn cam lobes will likely get to you first (in terms of power), but won't show up on a leakdown / compression test.

 

[Steamflyer]

As noted a compression test is a leak down test, not a measure of what happens when the engine is running. It tells you if the rings are sealing decently and if the valves are closing properly.

Read once that Continental ran an engine with essentially infinite leak down (no residual pressure on the test) but otherwise in good shape and it still made rated power. Obviously in use it would have been a mess.

The Continental operators manual has graphs of HP vs. rpm for each small engine from A-65 through O-200.

 

[Gone Flyin]

The Continental operators manual has graphs of HP vs. rpm for each small engine from A-65 through O-200.

Interesting.

So, looking at the chart, above, on the left...

Am I reading this correctly that (at sea level) at an RPM of 2750 (max for the 0-200) it is considered to be making 100% power and at around 2500 it is closer to 90%?

Reason I'm asking... pilot friend with a 150G said his IA has his mags set to provide 2500 max rpm in an attempt to make the engine run cooler. Never heard of doing this... has anyone here?

For me, in an emergency go-around situation, I'd want to be pulling 100% for that few minutes and then do my own retarding of the throttle for straight and level flight.
But, that's just me.

 

[Steamflyer]

Am I reading this correctly that (at sea level) at an RPM of 2750 (max for the 0-200) it is considered to be making 100% power and at around 2500 it is closer to 90%?

Reason I'm asking... pilot friend with a 150G said his IA has his mags set to provide 2500 max rpm in an attempt to make the engine run cooler. Never heard of doing this... has anyone here?

Power will decrease as rpm is decreased, that is a correct observation.

Mags should be set per data such as on the engine data plate or STC. With a fixed pitch prop there will also be static limits (greater than x, less than y) typically found for specific prop/engine combinations on the TCDS. Generally one can't just change timing to limit rpm as it would contravene the approved data and reduce power, potentially significantly.

 

[Dan Thomas]

As noted a compression test is a leak down test, not a measure of what happens when the engine is running. It tells you if the rings are sealing decently and if the valves are closing properly.

Read once that Continental ran an engine with essentially infinite leak down (no residual pressure on the test) but otherwise in good shape and it still made rated power. Obviously in use it would have been a mess.

The Continental operators manual has graphs of HP vs. rpm for each small engine from A-65 through O-200.

View attachment 127281

Propeller load is more accurate. See below.

Am I reading this correctly that (at sea level) at an RPM of 2750 (max for the 0-200) it is considered to be making 100% power and at around 2500 it is closer to 90%?

No. 2680 gives 90% HP.



Note that 90% power is at 2680 RPM.

 

[Witmo]

There's an AD for early O200 cylinders that changed the timing of the magnetos to decrease the likelihood of the cylinder cracking. They never said what this did to the rated power of the engine and I wondered how much of an effect it had. I'm sure most of those effected cylinders are out of service and the AD no longer applies.

 

[Bell206]

Never heard of doing this... has anyone here?

FYI: takes a bit more to limit max RPM both mechanically and legally than a simple mag timing change.

I'm sure most of those effected cylinders are out of service and the AD no longer applies.

There is also TCM MSB94-8 that gives the same info. But I never officially heard either that the timing change the rated engine power.

 

[Mikey52]

But if you have Millenium cylinders that doesn't apply.

 

[Dan Thomas]

But I never officially heard either that the timing change the rated engine power.

It has to reduce it somewhat. It would increase fuel burn, too. I was surprised that the AD didn't require a POH amendment for it. Obviously, no dyno testing was done. The O-200's claim of 100 HP is already suspect without reducing it further.

 

[Witmo]

It has to reduce it somewhat. It would increase fuel burn, too. I was surprised that the AD didn't require a POH amendment for it. Obviously, no dyno testing was done. The O-200's claim of 100 HP is already suspect without reducing it further.

The Continental claim of 100 HP is at 2700 rpm. I've never flown a Cessna 150 that could achieve 2700 rpm in anything but a dive so the claim is pretty much marketing hype. Perhaps with a prop very finely pitched, you'd see the 100 HP in normal flight but your cruise speed would suffer.

 

[Dan Thomas]

The Continental claim of 100 HP is at 2700 rpm. I've never flown a Cessna 150 that could achieve 2700 rpm in anything but a dive so the claim is pretty much marketing hype. Perhaps with a prop very finely pitched, you'd see the 100 HP in normal flight but your cruise speed would suffer.

The O-200's redline is 2750, and in a 150 I could just get it to do that in level flight at full throttle. That's how OEM propellers are usually pitched.

But I also flew a 1967 Alon Aircoupe, one of the last iterations of the Ercoupe. It had C-90, the engine immediately before the O-200, and on the same TCDS. The Aircoupe had the same power-to-weight ratio as our 150s, but it could fly circles around the 150s. Took off shorter, climbed faster, cruised faster, all on the same 16:1 power:weight ratio as the 150.

Even with fresh engines the 150s were dogs. There are some homebuilt propeller makers that size and pitch props for O-200s using 85 HP as the baseline.

 

[William Pete Hodges]

Wondering if anyone has any data to that will help compare the Continental 0-200's RPM and cylinder compression to the horsepower it is producing.

In other words... this, from the internet:
"The Continental 0-200 will give its maximum rated HP of 100, for a period not exceeding 5 minutes, at 2750RPM under correct atmospheric conditions".

I read the last part as a standard day at around sea level.

They do not say this... but, can one assume this is an engine producing a compression of (near) 80 over 80 for each of the four cylinders?

That being the case, is there a way to determine horsepower based on RPM? If an engine producing less than 80/80 on some cylinders is only producing an RPM of 2600 what is the approximate horsepower?

Let's forget about using a dyno to do this the right way. Just looking to get a rough idea, here.

This is a little off topic but it relates to your question about rings.

In 1980 I was sent to perform an in-frame overhaul of a CAT G342 naturally aspirated natural gas engine at the Richmond Colesium. It was an old engine at the time and had 27,000 hours on it. The cylinder head had been rebuilt twice and the hour meters had been replaced 3 times. It ran a refrigeration compressor to make floor ice for the hockey rink. They had two engines, the other one was G353. To make ice they both ran at full power for about 24 hours to freeze the floor and then the G342 ran continously cycling between 40-80% load to keep the floor maintained. We had a service contract on these engines and during use would service them every 10 days.

The engine ran well but could no longer maintain 80% power during its continuous run. The valves were acceptable and weren't due for another 3000 hours, but the rings had deteriorated and now power output was being affected.
That is why the overhaul was scheduled. The G342 was 5.75" bore x 8.00" stroke, 1246 CID, with 10:1 compression ratio and was rated 225 bHP continuous at 1200 RPM. It would still pull 75% load but not 80%.

In the industrial engine business an older engine is considered healthy if it will pull 95% of its rated power. If your dry compression check is good, the engine should be able to do that. Once things start going bad they can do so rather quickly, and overhaul should be scheduled before failure.

 

[Dan Thomas]

In the industrial engine business an older engine is considered healthy if it will pull 95% of its rated power. If your dry compression check is good, the engine should be able to do that. Once things start going bad they can do so rather quickly, and overhaul should be scheduled before failure.

I believe the specification for a type-certified engine, brand new, requires the power output to to be within -5/+10% of rated power. I can't find the FAR for that, but it's somewhere. I looked for it in FAR33 but don't see it.