Cessna 150 full throttle above redline

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bobkiksass

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bobkiksass
Hi, I have a cessna 150.
Today when flying it the plane at full throttle was showing the rpm being just above the redline. Its the first time I have ever seen this. Sometimes in the past at full throttle it would ride right up to the redline. It was maybe 100-150 above the redline at full throttle today during flight. I was concerned climbing out with the power set like this.

I am wondering if my gauge was off or if there is something to be concerned with. The plane was just annual-ed a few months ago, my motor has only 300 hrs. I

any advice ?
 
If your RPM is above red line, pull the throttle back.

Also, most tachometers are not very accurate.
 
Lycoming has a Service Instruction discussing overspeeds -- I'm sure Continental has a similar one. An overspeed in the 100-150 RPM range is about a 5% overspeed, which is where the Lycoming SI starts calling for a number of checks. See if you can get the Continental SI for more guidance.

That said, it is not unexpected to see the RPM run past redline at full throttle in level flight with a fixed pitch prop, especially at lower altitudes. That's because of the balance between cruise and climb performance. As you probably know, in climb, there's a lot more drag load on the prop, so the RPM's stay down well below redline at normal climb speeds. OTOH, when you accelerate to cruise speed, the drag load is reduced and RPM's climb. Of course, you probably don't want to cruise at 100% power anyway, so the prop is designed to give an RPM below redline at normal cruise power (typically 65-75%).

The other side of this is you should not see anything near redline at normal climb speed. If the tach was showing 100-150 RPM above redline in climb, either the engine is putting out an astonishing amount of power (way beyond rated power) or the tach has gone bonkers.

So, if you saw this in level flight, it's expected, and your response should be to pull back to appropriate cruise RPM (see your owner's manual performance charts). OTOH, if it happened at climb speed, I think I'd start by checking the tach for accuracy, because it shouldn't be possible to turn that much RPM in a climb.
 
Skylane81E said:
An accuracy check on the tach may not be unwise
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Agreed. That's usually the problem.

Quick and dirty method for double checking before going to the shop...

Go out at night and park where you can see the prop strobing in the airport's sodium vapor lights.

They're usually fed with 60Hz power.

This usually works best with the light behind the aircraft backlighting the prop, and a nice dark area in front of you.

As you approach RPM numbers divisible by 60... 600, 1200, 1800, 2400... You'll see the prop "freeze" and it'll look like the blades are standing still.

The electric power grid is a VERY accurate 60 Hz.

Stop the prop in the light via the strobe effect, which will take some VERY small tweaks on the throttle (I recommend 1200 RPM, since some engines won't run well at 600, and the higher numbers will just suck crap into the prop and airplane) and then note the RPM gauge, trying to lean over and remove any parallax involved by not viewing the gauges dead-on straight.

Works well. My tach was off approximately 50 RPM. We were able to tell our shop which direction also.

Kinda nice to know without investing money in an optical prop tach. :)

If it's off by a significant margin, turn it over to the shop to determine if the tach needs adjustment or what the problem might be.

The only thing that's hard to check, is redline... if it's not divisible by 60. And of course, because of the aforementioned FOD issue. Let the shop deal with that... they ding up the prop, they can always be asked to dress it... ;)
 
bobkiksass said:
Hi, I have a cessna 150.
Today when flying it the plane at full throttle was showing the rpm being just above the redline. Its the first time I have ever seen this. Sometimes in the past at full throttle it would ride right up to the redline. It was maybe 100-150 above the redline at full throttle today during flight. I was concerned climbing out with the power set like this.

I am wondering if my gauge was off or if there is something to be concerned with. The plane was just annual-ed a few months ago, my motor has only 300 hrs. I

any advice ?
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Tach error or good atmospheric conditions.
 
There is a free tach program for your computer out there somewhere. Listens to the engine sound and tells you the rpm.
 
No reason this won't work to check your tach, at least to give you an idea of what's going on before taking it to a mech:

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXPT32&P=FR



$25


It says you have to hold it within a foot of the prop :)hairraise:), but that's for a model airplane. Should work from a longer distance (and through the windshield) with a a full sized plane.
 
It's very common for the 150 to have a climb prop and they will show number over the red line on the tach.

that's no problem, the 0-200 is rated at 2800 RPM in several installations, So, No worries the annual may have adjusted a few tweaks and now you see the difference.
 
Ron Levy said:
...like an ambient pressure of about 34 inches of mercury.
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I really don't think it would take that much to get a 100 RPM, but this isn't a weather related issue. Some one at annual cleaned the plugs, tweaked the carb mixture and now it shows a little high, many of the 150s have the prop pitched to the highest RPM allowed and it doesn't take much to see the needle over the red line a little.

But I'll wager it's a tach issue.
 
Ron Levy said:
Lycoming has a Service Instruction discussing overspeeds -- I'm sure Continental has a similar one. An overspeed in the 100-150 RPM range is about a 5% overspeed, which is where the Lycoming SI starts calling for a number of checks. See if you can get the Continental SI for more guidance.
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here's the list of active SB's show me one
http://tcmlink.com/servicebulletins.cfm
Ron Levy said:
That said, it is not unexpected to see the RPM run past redline at full throttle in level flight with a fixed pitch prop, especially at lower altitudes. That's because of the balance between cruise and climb performance. As you probably know, in climb, there's a lot more drag load on the prop, so the RPM's stay down well below redline at normal climb speeds. OTOH, when you accelerate to cruise speed, the drag load is reduced and RPM's climb. Of course, you probably don't want to cruise at 100% power anyway, so the prop is designed to give an RPM below redline at normal cruise power (typically 65-75%).

The other side of this is you should not see anything near redline at normal climb speed. If the tach was showing 100-150 RPM above redline in climb, either the engine is putting out an astonishing amount of power (way beyond rated power) or the tach has gone bonkers.

So, if you saw this in level flight, it's expected, and your response should be to pull back to appropriate cruise RPM (see your owner's manual performance charts). OTOH, if it happened at climb speed, I think I'd start by checking the tach for accuracy, because it shouldn't be possible to turn that much RPM in a climb.
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The major criteria for RPM output of any aircraft engine is the load on the prop shaft, so, tell me which prop pitch he has.
 
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Tom-D said:
It's very common for the 150 to have a climb prop and they will show number over the red line on the tach.
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Not at normal climb speeds. OTOH, even with a cruise prop, you will exceed redline in level flight at most any altitude.

that's no problem, the 0-200 is rated at 2800 RPM in several installations, So, No worries the annual may have adjusted a few tweaks and now you see the difference.
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There are still worries about overspeeding the engine/prop/installation system limits even if the basic engine may be rated to higher RPM's in other systems. There may still be destructive vibrational or other loads in your system. The redline is there in your airplane to cover a lot of issues besides what the engine can do in isolation. Exceed it at your own risk, and there is no way to know what those risks are since they've never been explored or tested by the manufacturer/certification authority.
 
Tom-D said:
I really don't think it would take that much to get a 100 RPM,
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At climb speed? Yes, it would.

but this isn't a weather related issue. Some one at annual cleaned the plugs, tweaked the carb mixture and now it shows a little high, many of the 150s have the prop pitched to the highest RPM allowed and it doesn't take much to see the needle over the red line a little.
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In cruise, sure, but not at climb speed -- just no way.

But I'll wager it's a tach issue.
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Me, too.
 
Tom-D said:
The major criteria for RPM output of any aircraft engine is the load on the prop shaft
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That's only one of many criteria, and you don't know which one was the limiting factor in this installation without going back to the original design/certification data.
 
Ron Levy said:
At climb speed? Yes, it would.

In cruise, sure, but not at climb speed -- just no way.

Me, too.
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Did you realize that the only RPM guidance we have for the C-150/0-200 is the STATIC RPM, given in the TCDS? There is no guidance for CLIMB RPM.

Climb props are all about RPM in the climb, and all of them will over speed in level flight.
 
Tom-D said:
Did you realize that the only RPM guidance we have for the C-150/0-200 is the STATIC RPM, given in the TCDS? There is no guidance for CLIMB RPM.
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That may be so, but it isn't relevant -- you will not see RPM anywhere near redline at normal climb speed in a C-150 with a legal prop and stock engine, even if it's a climb prop. If it did, you would not be able to cruise at any speed above climb speed, and that's one of the factors in deciding the minimum pitch for a climb prop.

Climb props are all about RPM in the climb, and all of them will over speed in level flight.
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So will cruise props in level flight at full throttle at most any altitude below about 9000 feet.
 
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Ron Levy said:
That may be so, but it isn't relevant -- you will not see RPM anywhere near redline at normal climb speed in a C-150 with a legal prop and stock engine, even if it's a climb prop. If it did, you would not be able to cruise at any speed above climb speed, and that's one of the factors in deciding the minimum pitch for a climb prop.

So will cruise props in level flight at full throttle at most any altitude below about 9000 feet.
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Prop pitch and what is allowed is very much relevant, the normal pitch on a McCalley prop will produce 2500-2550 RPM on climb out at 70 MPH in the 150, but a climb prop will produce 2700+ RPM at 70 on climb out.

So, when we level off the climb prop pitched to 2700 RPM will overspeed, WOP Throttle on a cruise prop will not over speed, because they are pitched to the lowest RPM allowed in the TCDS. (3A19)

OBTW, running the 100 horse power test club on my test stand while testing the 0-200 will produce 2750 RPM WOT, reducing the MAP 1 inch of mercury will see a drop of 350-400 RPM.

The MA3 carb running WOT the throttle plate is virtually non existent because it is totally flat with the air passing it. and it requires about 10-12 degrees of travel before it makes much difference in MAP. changing the throttle plate that much requires the throttle to be pulled well over 1/2".

Thats just information I have learned with over 25 years of building and testing the 0-200.

edit:
any prop that complies with the limits of the TCDS is a "LEGAL" prop. thus any prop that will produce ANY RPM with in the allowable requirements, and is of the length required is a LEGAL prop.
Those RPM requirements leaves us with a very wide range of operational options from cruise to climb.
 
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Ron Levy said:
It may or may not be the limiting factor in any installation -- there's no way to know without seeing the design/certification data.
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Your limiting factors are the TCDS (3A19)
I - Model 150, 2 PCLM (Utility Category), Approved July 10, 1958 Model 150A, 2 PCLM (Utility Category), Approved June 14, 1960 Model 150B, 2 PCLM (Utility Category), Approved June 20, 1961 Model 150C, 2 PCLM (Utility Category), Approved June 15, 1962
Engine *Fuel
*Engine limits
Propeller and propeller limits
Continental O-200-A
80/87 min. grade aviation gasoline
For all operations, 2750 r.p.m. (100 hp.)
1. Sensenich 69CK
Diameter: not over 69 in., not under 67.5 in. Static r.p.m. at maximum permissible throttle
not over 2470, not under 2320 No additional tolerance permitted
2. McCauley 1A100/MCM
Diameter: not over 69 in., not under 67.5 in. Static r.p.m. at maximum permissible throttle
not over 2475, not under 2375 No additional tolerance permitted
3. McCauley 1A101/DCM
Diameter: not over 69 in., not under 67.5 in. Static r.p.m. at maximum permissible throttle
not over 2600, not under 2500 No additional tolerance permitted
 
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IIRC from my 100+ engine related test flights in 150's the McCauley pitched to 48" will turn 2750 level at an IAS of 108 mph not in climb. Pitched to 50" it takes an IAS of 114 and sligh nose down to turn 2750. Charlie Melot Zephyr Engines
 
Ron Levy said:
Take a break, Tom -- go fishing again.
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Not on your life, I've got 2 to build and test.

Charley got it right again :)

Pitch any of the 3 optional props to indicate 2750 static and you'll see red line in all phases of flight, Pitch the prop to show 2300 static and you'll never see red line in any phase of flight. In every 150 I've flown is some where in between.
 
charlie said:
IIRC from my 100+ engine related test flights in 150's the McCauley pitched to 48" will turn 2750 level at an IAS of 108 mph not in climb. Pitched to 50" it takes an IAS of 114 and sligh nose down to turn 2750. Charlie Melot Zephyr Engines
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and the only way to know what you have is to pull the spinner and read the numbers.

We don't know what this guy has. He may be well with in the parameters for the pitch he has. Until he tells us what the static numbers are we can't guess what is right or wrong.

Seeing red line - + during climb doesn't tell us much.
 
Tom-D said:
Pitch any of the 3 optional props to indicate 2750 static and you'll see red line in all phases of flight,
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Well, yes, you will, but you'll also be unairworthy because the highest static RPM permitted on any stock 150 is 2600.

Pitch the prop to show 2300 static and you'll never see red line in any phase of flight.
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...and if you do that, you'll be unairworthy for being below the lowest permitted static RPM for a stock 150, and most of them are above 2400.

All I'm saying, and continue to say, is that if you have a legally airworthy Cessna 150, you will not see an overspeed at normal climb speed no matter what you do with the throttle, but at full throttle in level flight, it's easy to get the RPM beyond redline at most altitudes. You want to illegally underpitch or overpitch the prop like you suggested, all bets are off.
 
Wow, lots of responses. I am not sure what type of prop I have on my plane. I was noticing the motor going above redline when leveling after climbing and when practicing my steep turns. When I put full throttle in to make my turn, it would just pass the red line.

Also, The airp pressure was low yesterday when flying 29.76. Could the air pressure have something to do with the propellor having higher rpms? That seemed to make sense

I learn a lot reading all your responses. Thanks
 
bobkiksass said:
Wow, lots of responses. I am not sure what type of prop I have on my plane.
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Check the prop log. If you don't have one, check the engine log, as that's usually where they put prop stuff if there's no prop log (which is a practice the FAA is trying very hard to discourage). Then you can go in the C-150 TCDS and find out what the proper static RPM range is for your aircraft/prop combination. Static RPM is checked with brakes locked, full throttle, and the airplane perpendicular to any wind, and normally at sea level/standard day. There are tables to correct for higher elevations and nonstandard temp, but I'm not sure where to find them.

I was noticing the motor going above redline when leveling after climbing
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Then you need to pull the throttle back a bit more aggressively after you lower the nose. My technique is to climb at full throttle and normal climb speed, and take whatever RPM I get. As I approach the desired altitude, I push in some forward trim so the airplane is trimmed more for cruise speed (makes leveling off a lot easier), lower the nose to cruise pitch, and then as the RPM picks up to the desired cruise setting (you should have a preplanned cruise power setting), I throttle back to keep it there until I reach cruise speed, then finish trimming for cruise speed.

and when practicing my steep turns. When I put full throttle in to make my turn, it would just pass the red line.
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As discussed in earlier posts, that's not particularly surprising. You have plenty enough power to stay level in steep turns without using full throttle. I'd suggest adding only 100 RPM or so as you roll in (not before you start rolling). If you need more to keep your speed up once established in the turn, use it, but be ready to throttle back to the original cruise position as you roll out and the airplane unloads and accelerates.

BTW, it's a lot easier to demo this than to describe it.

Also, The airp pressure was low yesterday when flying 29.76. Could the air pressure have something to do with the propellor having higher rpms?
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No. If anything, lower air pressure reduces power output.

I learn a lot reading all your responses. Thanks
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Happy to help.
 
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Which changes more, power or resistance? You know that lower pressure has 2 effects on power, one increase and one decrease. Increase due to reduced drag inside the crankcase, decrease due to less air for the fuel.
 
Henning said:
Which changes more, power or resistance? You know that lower pressure has 2 effects on power, one increase and one decrease. Increase due to reduced drag inside the crankcase, decrease due to less air for the fuel.
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Actually, it's reduced drag on the prop, not reduced drag inside the crankcase, which has the other big effect besides the density of the induction air. Not sure what drag there is inside the crankcase which could be significantly affected by ambient air pressure.
 
Ron Levy said:
Actually, it's reduced drag on the prop, not reduced drag inside the crankcase, which has the other big effect besides the density of the induction air. Not sure what drag there is inside the crankcase which could be significantly affected by ambient air pressure.
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Air density on the back side of the piston.
 
Ron Levy said:
Check the prop log. If you don't have one, check the engine log, as that's usually where they put prop stuff if there's no prop log (which is a practice the FAA is trying very hard to discourage). Then you can go in the
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The only way to really tell what you have is to remove the Prop spinner and read the numbers stamped there, logs get AFUed, and may or may not reflect the change in prop pitch that occurred after the log was created. or simply never got logged.

The prop shop that did the pitch change will stamp the new pitch in the front of the hub.
 
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