Cessna 150 full throttle above redline

[Tom-D]

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.

The DA effects the prop and engine in the same manner, you loose horse power. but you don't need as much to make rated RPM.

the prop looses effectiveness, the engine looses horse power, the RPM will remain with in the TCDS requirements.

 

[kgruber]

Now I'm POed, that should have shown up on my subscription and in TCMs list.

but as the 0-200 does not show on that list It must not be important.

Tom,

The O-200 is on that list. Just hidden a little.

Best,
Karl

 

[Henning]

So why do drag racers seek low altitude strips?

Because the result is disproportional on a land based vehicle because the drive resistance doesn't change, in an airplane it's proportional between loss and gain giving it a greater advantage in an airplane. You won't see anything though unless you are turboed. Same RPM/MP at 15,000' will produce more HP than at SL.

 

[Tom-D]

Well, yes, you will, but you'll also be unairworthy because the highest static RPM permitted on any stock 150 is 2600.

WRONG

...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.

Wrong again. the only requirement is a STATIC RPM.

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.

wrong again, legally airworthy C-150 is one that complies with the Aircraft TCDS, which allows a rpm of 2750 for all operations (100HP)

why did CESSNA place this on the TCDS

*Engine limits
Propeller and propeller limits Continental O-200-A
For all operations, 2750 r.p.m. (100 hp.)

If the STATIC RPM is within the listed Prop spec listed for each of the 3 in the TCDS you are legal and airworthy.

 

[Tom-D]

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.
No comment, way too many variables to make a SWAG.

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

No it doesn't, your engine looses or gains power as air density increases or decreases, the prop gains or looses effectiveness in the same manner for the same reason.
So with high DA your engine can't make as much power, but the prop is less effective and requires less power to make the same RPM.

I learn a lot reading all your responses. Thanks

WE love to teach..

 

[poadeleted20]

wrong again, legally airworthy C-150 is one that complies with the Aircraft TCDS, which allows a rpm of 2750 for all operations (100HP)

why did CESSNA place this on the TCDS

*Engine limits
Propeller and propeller limits Continental O-200-A
For all operations, 2750 r.p.m. (100 hp.)

If the STATIC RPM is within the listed Prop spec listed for each of the 3 in the TCDS you are legal and airworthy.

Tom is confusing redline limits for max RPM under any conditions with the allowable RPM range for static run-up.

The redline is an absolute limit regardless of what you're doing. If you exceed the redline limit, you follow the manufacturer's instructions for dealing with an "overspeed." This may involve anything from a fairly cursory inspection to a complete engine teardown.

The static RPM limits apply only to a static run-up, i.e., zero airspeed, zero DA, zero wind. If you see more more or less RPM than the static run-up range for your engine/prop/aircraft combination, the aircraft is legally unairworthy. If it's too low, you're not developing enough power for safe performance. The problem could be almost anywhere from insufficient fuel flow to carb settings to ignition issues to cam wear to valve problems. If it's too high (something rarely seen), you may have an excessively worn prop. But either way, if you do a proper static run-up and the RPM stabilizes outside the allowable range, the aircraft is legally unairworthy and may be unsafe to fly.

 

[Tom-D]

Tom is confusing redline limits for max RPM under any conditions with the allowable RPM range for static run-up.

The redline is an absolute limit regardless of what you're doing. If you exceed the redline limit, you follow the manufacturer's instructions for dealing with an "overspeed." This may involve anything from a fairly cursory inspection to a complete engine teardown.

The static RPM limits apply only to a static run-up, i.e., zero airspeed, zero DA, zero wind. If you see more more or less RPM than the static run-up range for your engine/prop/aircraft combination, the aircraft is legally unairworthy.

NOT TRUE, if the RPM is with in limits for the prop make and model it is airworthy.
If it's too low, you're not developing enough power for safe performance. The problem could be almost anywhere from insufficient fuel flow to carb settings to ignition issues to cam wear to valve problems. If it's too high (something rarely seen), you may have an excessively worn prop. But either way, if you do a proper static run-up and the RPM stabilizes outside the allowable range, the aircraft is legally unairworthy and may be unsafe to fly.

All the discrepancies you sited will not produce a RPM acceptable for airworthiness. and should be repaired prior to returned to service.

If that red line is 2750 I'll agree with you.

Read the TCDS, then understand airworthiness. there is no requirements other than static.

2750 is the maximum RPM allowed by the TCDS for all operations, that means the operator must not exceed that

Yes it is that simple.

Any C-150/0-200 will exceed the maximum RPM (2750) in a dive, you the pilot are required to not allow that to happen. You/pilot are the operator, you control all operations and must comply with all restrictions given in the TCDS.

And I'm not confusing that.

I go thru this on every Annual I declare airworthy. Does it meet it's type design or its properly altered condition.

and set at propeller limits, it meets the requirements of the TCDS.
Many of the rag draggers are set this way, they go slow, but haul the load.

Any limit in the TCDS given for each prop will produce a safe operable aircraft.

 

[poadeleted20]

If that red line is 2750 I'll agree with you.

Read the TCDS, then understand airworthiness. there is no requirements other than static.

2750 is the maximum RPM allowed by the TCDS for all operations, that means the operator must not exceed that

Yes it is that simple.

Any C-150/0-200 will exceed the maximum RPM (2750) in a dive, you the pilot are required to not allow that to happen. You/pilot are the operator, you control all operations and must comply with all restrictions given in the TCDS.

And I'm not confusing that.

I go thru this on every Annual I declare airworthy. Does it meet it's type design or its properly altered condition.

and at 2750 RPM STATIC, it meets its requirements of the TCDS.

You were doing fine until that last line. Read the TCDS again -- it very clearly states that the static RPM must be within the stated static RPM limits, the highest of which for any C-150 without an STC or field approved alteration is 2600 RPM. If it isn't within the limits for whatever prop is installed, the aircraft does not meet the requirements of the TCDS, is not in conformance with its type certificate, and is not legally airworthy. So, any C-150 that turns 2750 RPM in a static run-up at standard conditions is not legally airworthy unless it has a field approval or STC for a different prop with an upper limit on static RPM of at least 2750 -- and I've never seen one like that.

Many of the rag draggers are set this way, they go slow, but haul the load.

I don't doubt that this happens, but unless they have some sort of STC or field approval for their underpitched props, they aren't operating legally and the IA who signs their annuals is risking his/her ticket for certifying as airworthy an aircraft that isn't.

 

[Tom-D]

You were doing fine until that last line. Read the TCDS again -- it very clearly states that the static RPM must be within the stated limits. If it isn't, the aircraft does not meet the requirements of the TCDS, is not in conformance with its type certificate, and is not legally airworthy.

That is what I have been saying all along, when it is with in limits it is good to go. The TCDS gives us these requirements for each prop.

I don't doubt that this happens, but unless they have some sort of STC or field approval for their underpitched props, they aren't operating legally and the IA who signs their annuals is risking his/her ticket for certifying as airworthy an aircraft that isn't.

Have you ever set up a rag dragger?

I have, and they want the lowest blade angle they can get for a climb prop. but you must stay with in the limits of the prop.

 

[Tom-D]

I don't doubt that this happens, but unless they have some sort of STC or field approval for their underpitched props,they aren't operating legally and the IA who signs their annuals is risking his/her ticket for certifying as airworthy an aircraft that isn't.

no such thing, you are exaggerating the issue, the prop is pitched to the lowest blade angle that will produce the highest RPM allowed in the Prop requirements set forth in the TCDS.

That is legal always has been, always will be.

 

[Tom-D]

Tom,

The O-200 is on that list. Just hidden a little.

Best,
Karl

It's not on the Continental active list. They must not be too concerned.

 

[Skylane81E]

I was going to stay out of it but

Propeller and propeller limits

1. Sensenich 69CK
Diameter: not over 69 in., not under 67.5 in. Static r.p.m. at maximum permissible throttle setting:
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 setting:
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 setting:
not over 2600, not under 2500 No additional tolerance permitted

I will grant that some models go higher in the RPM range, but the highest I found was 2600, still short of the 2750 engine limit

 

[Tom-D]

I will grant that some models go higher in the RPM range, but the highest I found was 2600, still short of the 2750 engine limit

Please explain the difference between STATIC and what is allowed in flight.

 

[Skylane81E]

Stationary with no wind vs. well flying

 

[poadeleted20]

no such thing, you are exaggerating the issue, the prop is pitched to the lowest blade angle that will produce the highest RPM allowed in the Prop requirements set forth in the TCDS.

That is legal always has been, always will be.

Right -- and the static RPM limits are part of those prop requirements. So, if the static RPM range for that prop is 2500-2600, and you set it up so it turns 2750 static (as you said you did in post #47), you've broken those limits and the aircraft is not airworthy.

 

[Tom-D]

Right -- and the static RPM limits are part of those prop requirements. So, if the static RPM range for that prop is 2500-2600, and you set it up so it turns 2750 static (as you said you did in post #47), you've broken those limits and the aircraft is not airworthy.

I see your point, my bad, my wording should read as it does in post 49&50.

I'll fix it. but don't forget to read the embedded statements.

 

[poadeleted20]

I see your point, my bad, my wording should read as it does in post 49&50.

I'll fix it. but don't forget to read the embedded statements.

THANK YOU!

I'm exhausted.

 

[Tom-D]

THANK YOU!

I'm exhausted.

Before you take your nap, tell the folks how the prop shops make a cruise prop out this example.


2. McCauley 1A100/MCM
Diameter: not over 69 in., not under 67.5 in. Static r.p.m. at maximum permissible throttle setting:
not over 2475, not under 2375 No additional tolerance permitted

 

[poadeleted20]

Before you take your nap, tell the folks how the prop shops make a cruise prop out this example.


2. McCauley 1A100/MCM
Diameter: not over 69 in., not under 67.5 in. Static r.p.m. at maximum permissible throttle setting:
not over 2475, not under 2375 No additional tolerance permitted

With some big heavy tools and a lot of muscle.

 

[Tom-D]

With some big heavy tools and a lot of muscle.

With them big heavy tools they do what?

 

[poadeleted20]

With them big heavy tools they do what?

You're the mechanic -- you tell me.

 

[Tom-D]

You're the mechanic -- you tell me.

They'll do what the manual tells them they can.

 

[bkspero]

There's one for the iPhone, but not for Android phones.

There is Heli Headspeed for Android. Written for RC helicopters, but works fine from the front seat of my Tiger either on the ground or in flight.

http://digitizeit.de/heli/

$3.99 on the Google Play App store

https://play.google.com/store/apps/details?id=de.ibo.helitach.android&hl=en

It agrees with the tach on my plane over the range 1100 rpm to 2550 rpm to the precision I can interpolate the analog tach (about +-10 rpm). It reads about 90 rpm higher than the tach on a friend's plane...which I presume is evidence that his tach may be under-representing the actual rpm.

 

[Tom-D]

It reads about 90 rpm higher than the tach on a friend's plane...which I presume is evidence that his tach may be under-representing the actual rpm.

Come annual time, that tack may prevent his aircraft from passing the run up at the end of the annual.

 

[poadeleted20]

Come annual time, that tack may prevent his aircraft from passing the run up at the end of the annual.

Only if the IA doing the check doesn't have a strobe tach or other device to confirm the actual RPM as opposed to what's indicated on the installed tach.

 

[poadeleted20]

There is Heli Headspeed for Android. Written for RC helicopters, but works fine from the front seat of my Tiger either on the ground or in flight.

http://digitizeit.de/heli/

$3.99 on the Google Play App store

https://play.google.com/store/apps/details?id=de.ibo.helitach.android&hl=en

I'll have to try it.

It agrees with the tach on my plane over the range 1100 rpm to 2550 rpm to the precision I can interpolate the analog tach (about +-10 rpm).

If the mechanical tach in your Tiger is that accurate, either it's a recent replacement or quite extraordinary.

It reads about 90 rpm higher than the tach on a friend's plane...which I presume is evidence that his tach may be under-representing the actual rpm.

Pretty typical of aging mechanical tachs. For many reasons, it's a good idea to have a "tach correction card" for old mechanical tachs so you know what the engine is really doing.

 

[Tom-D]

Only if the IA doing the check doesn't have a strobe tach or other device to confirm the actual RPM as opposed to what's indicated on the installed tach.

The Tach contain placards that are required. white line, red line etc.

If the tach isn't accurate is it airworthy?

I can use the electronic tach for trouble shooting but, 91.205 says the tach is required so it can't be placarded out.

 

[Tom-D]

For many reasons, it's a good idea to have a "tach correction card" for old mechanical tachs so you know what the engine is really doing.

That's bad advice, get it fixed.

 

[Skylane81E]

I'll have to try it.

If the mechanical tach in your Tiger is that accurate, either it's a recent replacement or quite extraordinary.
Pretty typical of aging mechanical tachs. For many reasons, it's a good idea to have a "tach correction card" for old mechanical tachs so you know what the engine is really doing.

When I did the dynamic balance of my propeller it was accurate to 5RPM or less so it's not unheard of.

Then it did die dramatically only a few hundred hours later...

 

[poadeleted20]

The Tach contain placards that are required. white line, red line etc.

If the tach isn't accurate is it airworthy?

What do the ICA's for tachs say? If you can find guidance on how far out a tach may be before repair/replacement is required, please let us know.

 

[Tom-D]

What do the ICA's for tachs say? If you can find guidance on how far out a tach may be before repair/replacement is required, please let us know.

Show me the ICAs for an old mechanical tach.

My ink, My call.

accurate cockpit indications are a safety issue for me.

For rears you have been preaching safety, now your saying it is ok to fly junk.

 

[Dan Thomas]

That's bad advice, get it fixed.

In Canada we have to calibrate the tach yearly. We're allowed no more than a 4% error in the middle of the cruise range, and the tach must be placarded as to what the error is.

Dan

 

[poadeleted20]

Show me the ICAs for an old mechanical tach.

My ink, My call.

accurate cockpit indications are a safety issue for me.

So you also check fuel gauge accuracy and don't sign the annual until it's accurate over the full range? How about the airspeed indicator and pitot system? Check that too?

 

[Irish_Armada]

Zombie thread alert:

So our Cherokee 180 has a climb prop on it. We were flying the other day and went about 150 over redline on the tach when leveling out in cruise. Obviously we pulled the throttle back and the plane flew fine and we sipped 8.2gph that flight. But thaqt did catxh our attention. We then noticed on take off and climb out around sea level on a hot day that day, that we were almost redlining in about a 700-900ft/min climb. See the attached pics. Anything to be concerned about herw or is this just good/normal performance with a climb prop? (Normally we get about 1000 ft/min but I had the nose lower here). Thanks.

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.

 

[Norman]

Have you checked the tach for accuracy?

 

[poadeleted20]

I'm with Norm -- check your tach. No way your should be overspeeding in an 800 ft/min climb. If you have a smartphone, that's easy enough to do with one of the head speed tach apps. The one I use on my Android phone is:
https://play.google.com/store/apps/details?id=at.idsoftware.headspeedtach&hl=en

 

[Silvaire]

All that over such a simple question

 

[coloradobluesky]

Here's the math for using the 60Hz light.
1800 revolutions/min = 30 rev/sex. A two blade prop comes by twice so it matches 60 cycles per second.

With a 3 blade its 1200rpm and 2400rpm where it synchs.

Park with the plane's back to a street lamp. It works, I've tried it.

 

[jesse]

If overspending by 150 rpm on a O200 C150 hurt the airplane we wouldn't have any 150s left flying. Doing a bunch of mx as a result of that is ridiculous.

Just check and fix the tach.

 

[Dan Thomas]

If overspending by 150 rpm on a O200 C150 hurt the airplane we wouldn't have any 150s left flying. Doing a bunch of mx as a result of that is ridiculous.

Just check and fix the tach.

The propeller suffers much more than the engine. The Formula 1 racers run those O-200s up to 4000 RPM with a small prop.

The propeller has to withstand some of the highest forces in the entire airplane. Centrifugal forces are huge. A 150 RPM overspeed is a 5.5% overspeed, which translates into a 10% increase in centrifugal stresses. A 10% overspeed is a 21% increase in forces. The propeller makers get nervous about that and want NDI done of the prop. 10% for five seconds, IIRC. It happens sometimes in spin recoveries, when a student gets confused between stall recovery (full throttle) and spin recovery (throttle closed).

Dan