Static RPM Test

Jaybird180

Jaybird180

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Jaybird180
I have on good word the information that states that an engine that doesn't produce POH static rpm spec is unairworthy,:dunno: but I don't know where to look to confirm this in writing, regulation, etc?

Also, need the formula for translating tested result to standard day for baseline comparison.
 
Jaybird180 said:
I have on good word the information that states that an engine that doesn't produce POH static rpm spec is unairworthy,:dunno: but I don't know where to look to confirm this in writing, regulation, etc?
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The Limitations section of your POH and/or the Type Certificate Data Sheet for your aircraft. If you need further official explanation/confirmation, I suggest contacting an Airworthiness Inspector at your local FSDO.
 
I have the figures but nothing that says, 'if it's not this then it's unairworthy'. The thought is that performance degradation happens and meeting the book....no engine older than a few hundred hours SMOH can do that.

I'm hoping to find something spelled out.
 
Jaybird180 said:
I have the figures but nothing that says, 'if it's not this then it's unairworthy'. The thought is that performance degradation happens and meeting the book....no engine older than a few hundred hours SMOH can do that.

I'm hoping to find something spelled out.
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Generally engines will make book power for a very very long time, often to TBO and beyond, an engine's performance degrading to a noticeable amount means something is wrong with it.
 
If the aircraft does not comply with it's type certificate it is unairworthy.

If a static RPM is listed in the TCDS the plane must meet it, just the same as the weight and balance limitations and the airspeed limits, control surface deflections etc...
 
Jaybird180 said:
I have the figures but nothing that says, 'if it's not this then it's unairworthy'. The thought is that performance degradation happens and meeting the book....no engine older than a few hundred hours SMOH can do that.

I'm hoping to find something spelled out.
Click to expand...

A 3000+hr O-320 still made static RPM with a wiped out camshaft...

These engines are tough
 
Look in the TCDS (at least for the planes I'm aware of). Because a plane doesn't make static on the tach, doesn't mean it's not making static... use an optical tach for a good reading. I typically do a static check before every takeoff, sort of like a short field T/O. Firewall it, check RPM, release brakes and go.
 
Jaybird180 said:
I have the figures but nothing that says, 'if it's not this then it's unairworthy'. The thought is that performance degradation happens and meeting the book....no engine older than a few hundred hours SMOH can do that.

I'm hoping to find something spelled out.
Click to expand...

The only place you will find the static RPMs allowed for your aircraft are in the Type Certificate and data sheet for the make model and serial number for your aircraft, simply because there may be several props approved for the aircraft and each will have different static RPM requirements.
The FAA will not tell you what is not airworthy, they only tell what is. so, any thing else is not airworthy.
 
Ron Levy said:
The Limitations section of your POH and/or the Type Certificate Data Sheet for your aircraft. If you need further official explanation/confirmation, I suggest contacting an Airworthiness Inspector at your local FSDO.
Click to expand...

I would't get the FAA (FSDO) involved until my mechanic has a go at fixing/explaning the problems. You may get a Compliance inspection and a lot of troubles for no reason.

They may stuff you with 91.405 for any discrepancy they find.
 
Jaybird180 said:
I have the figures but nothing that says, 'if it's not this then it's unairworthy'. The thought is that performance degradation happens and meeting the book....no engine older than a few hundred hours SMOH can do that.

I'm hoping to find something spelled out.
Click to expand...

That is completely untrue, infact most engines pick up horsepower as they age when kept properly tuned. An engine makes the most power right before it throws the rods out of the case lol.

If your engine isn't making power, it has a problem, engines don't get tired, they get loose, loose doesn't cost power.
 
Inadequate static RPM isn't an engine not making power. It's a propeller problem. RPM doesn't degrade over time. Without your propeller, your engine is quite happy to run to much higher RPM's; it will do many thousands of RPM's more than what it will do as installed on your aircraft. The reason it can't do more on your fixed wing airplane is the propeller. The reason for the RPM limitations are also attached to the propeller. The engine will produce far more power at higher RPM's, but it doesn't operate at those higher RPM's because of the propeller.

Some engines use geared drives to operate at higher RPM's while driving the prop at a slower RPM.

If you're not within the static RPM tolerance for your engine-propeller combination, as spelled out on the Type Certificate Data Sheet, then your aircraft is not airworthy. It does not comply with the TCDS.
 
Jaybird180 said:
I have the figures but nothing that says, 'if it's not this then it's unairworthy'. The thought is that performance degradation happens and meeting the book....no engine older than a few hundred hours SMOH can do that.
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Perhaps not the book performance tables in Section 6, but it still must operate within the Limitations in Section 2, and that's where you find the static RPM limits.

I'm hoping to find something spelled out.
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You won't. The closest you'll find is the FAA's definition of airworthiness, which is (nearly verbatim) "in conformance with its type certificate and in a condition for safe flight." If it's not meeting the static RPM limits (which are clearly enunciated in the Type Certificate Data Sheet), it is not "in conformance with its type certificate." As I said, you can confirm this with an Airworthiness Inspector at any FSDO.
 
Tom-D said:
The only place you will find the static RPMs allowed for your aircraft are in the Type Certificate and data sheet for the make model and serial number for your aircraft,
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It's also in the Limitations section of the POH in planes built after 1977, including Jaybird's.
 
Tom-D said:
I would't get the FAA (FSDO) involved until my mechanic has a go at fixing/explaning the problems. You may get a Compliance inspection and a lot of troubles for no reason.
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Not a chance if you just call them and ask the question, "Is an aircraft which doesn't meet static RPM limits in the TCDS airworthy or not?" You don't even have to give your name, just call and ask to speak with an Airworthiness Inspector, and then ask your hypothetical question. The FSDP folks are not out looking to "get" people, just trying to keep us all safe, and education is part of that task.
 
DouglasBader said:
Inadequate static RPM isn't an engine not making power. It's a propeller problem. RPM doesn't degrade over time.
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That is not true for fixed pitch props like the one on Jaybird's C-172S, and that's why they set lower limits for static RPM on such planes. Static RPM is indeed a measure of power output with a fixed pitch prop, and if the engine can't overcome the prop drag at that RPM, it's not putting out enough power to be safe.
 
Ron Levy said:
That is not true for fixed pitch props like the one on Jaybird's C-172S, and that's why they set lower limits for static RPM on such planes. Static RPM is indeed a measure of power output with a fixed pitch prop, and if the engine can't overcome the prop drag at that RPM, it's not putting out enough power to be safe.
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Exactly. To get a static RPM spec we need a good prop and a good engine, or a really worn-out prop and a weak engine. The prop manufacturer has dimensional and pitch angle limits in his maintenance manuals so the bad prop doesn't stay on the airplane.

Low static RPM can be a result of poor carburetion, a leaking carb heat box, plugged filter, weak mags or off-time mags, weak plugs, broken piston rings, worn cam, on and on and on. It's a good check of not only the prop but the health of the engine, same as the doctor putting us on the treadmill to see if our cardiopulmonary systems are up to standard.

Dan
 
Is the static RPM range regardless of atmospheric conditions (ie Density Altitude, humidity, etc) or is there a mathematical conversion that must be applied to the result?
 
You do have to consider the density altitude.

I do not have a formula handy
 
Along with all this noise about making RPM, better remember to check the accuracy of the tachometer...
 
Ron Levy said:
It's also in the Limitations section of the POH in planes built after 1977, including Jaybird's.
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Show me one.

You'll see power charts but the POH does not know which prop is installed. the TCDS shows all props authorized and their limits.

Any STCed prop installed will have the allowed STATIC RPM and length given in the STC. POHs will not

And remember all 172s are built on the same TCDS issued way long time ago, and they only have owners manuals.
And the one in front of me says nothing but "Power and Speed.......... 145BPH at 2700RPM." that is the only engine operation limitation given. (page 4-2 172 owners manual)
 
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bartmc said:
That's why theres's a range you should be able to make it year round. Static RPM will be lower in the Winter...
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In the MM you will often find instructions to make allowance for "non standard conditions"
 
what ever DA you have will effect the prop and engine at the same time. and the RPM out put will remain the same, because what ever effects the prop will effect the engine.

cold weather the prop is more efficient and requires more power to spin it at the required RPM. but the engine is able to make more power at colder temps so it will equal out. IOW the engine will make the same RPM on a cold day as it will on a hot day.
 
Tom-D said:
what ever DA you have will effect the prop and engine at the same time. and the RPM out put will remain the same, because what ever effects the prop will effect the engine.

cold weather the prop is more efficient and requires more power to spin it at the required RPM. but the engine is able to make more power at colder temps so it will equal out. IOW the engine will make the same RPM on a cold day as it will on a hot day.
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It's not a linear relationship. But, I agree, close enough since we're playing horseshoes. Static would be slightly lower in the winter given everything else equal. If I need to dig out the equations, I'll try to find 'em.
 
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bartmc said:
If I need to dig out the equations, I'll try to find 'em.
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The only ones I know of are for figuring actual horse power. They a are a bunch of charts and graphs that end up showing shaft horse power. The only ones I have access to are for the RR dart, and the Allison T-56.
 
We noticed an increase in RPM on climb out with warmer, 100F plus temps from winter operations. We checked the mech Tach with an optical tach inflight.

The engine will indicate over red line on climb out in the summer, full throttle with a glider on tow at 60kias. it's over by about 50 RPM. In winter at about 50F, it remains about 50 RPM below redline at full throttle power.

The engine checks ok for the Static RPM, the lower part of the range in winter, and the higher range in summer. We are using the lighter weight, fixed pitch prop approved in the TCDS for our engine/airframe, an O-540, 235 HP with an STC upgrade to 250HP. The STC did not change the static RPM or max RPM limits.

Temp, and effects of density altitude, does make a difference. Less air for the prop to bite on, but the engine seems to be getting enough air on hot days to develop the power.
 
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bartmc said:
It's not a linear relationship. But, I agree, close enough since we're playing horseshoes.
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It is close enough you will never read it on any tach in GA.
Plus you will never be able to duplicate the data from a cold day to a hot day in the same engine prop combination.

Good theory, but in every day practice it doesn't exist.
 
Tom-D said:
It is close enough you will never read it on any tach in GA.
Plus you will never be able to duplicate the data from a cold day to a hot day in the same engine prop combination.

Good theory, but in every day practice it doesn't exist.
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Some folks claim to notice lower readings in winter, I've fired up in -27F to 105F and never really noticed, though I've never really paid it much attention as long as it's in the range in the TCDS. But I suppose the physics are that drag increases more than the increased engine power can overcome in the winter.
 
Point simply being that at high DA the RPM may not get remotely close with out some leaning
 
Tom-D said:
Show me one.

You'll see power charts but the POH does not know which prop is installed. the TCDS shows all props authorized and their limits.
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My POH has limitations and prop model number. Sorry unable to post it, I'm on iPad.
It's pg 1-4 in the General Section Chapter 1

bartmc said:
It's not a linear relationship. But, I agree, close enough since we're playing horseshoes. Static would be slightly lower in the winter given everything else equal. If I need to dig out the equations, I'll try to find 'em.
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Yes, please.
 
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Jaybird180 said:
My POH has limitations and prop model number. Sorry unable to post it, I'm on iPad.
It's pg 1-4 in the General Section Chapter 1
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Are you sure that is a POH??

because the TCDS says
Production Basis Production Certificate No. 4. Delegation Option Manufacturer No. CE-1 authorized to issue airworthiness certificates under delegation option provisions of Part 21 of the
Equipment:
Federal Aviation Regulations.
The basic required equipment as prescribed in the applicable airworthiness requirements (see Certification Basis) must be installed in the aircraft for certification. This equipment must include a current Airplane Flight Manual effective S/N 18266591 through 18268586 and R18200584 through R18202041. In addition, the following item of equipment is required:

as posted before, flight manuals only apply to the S/Ns given.
 
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Are you guys talking about this page ?
POWER PLANT LIMITATIONS
Engine Manufacturer: Teledyne Continental.
Engine Model Number: 0-470-U.
Engine Operating Limits for Takeoff and Continuous Operations:
Maximum Power: 230 BHP.
Maximum Engine Speed: 2400 RPM.
Maximum Cylinder Head Temperature: 460°F (238°C). Maximum Oil Temperature: 240°F (116°C).
Oil Pressure, Minimum: 10 psi.
Maximum: 100 psi.
Propeller Manufacturer: McCauley Accessory Division.
Propeller Model Number: C2A34C204/90DCB-8 Propeller Diameter, Maximum: 82 inches.
Minimum: 80.5 inches.
Propeller Blade Angle at 30 Inch Station, Low: 15.0°.
High: 29.4°

then show me where there is a lower limit for the RPMs or where these are a airworthy requirement?

There are no statements as to what the static RPM of the engine should/required to be it gives the maximum RPM and the chart on the next page gives the normal operating ranges of the aircraft/engine but no mention of the static RPM or what is a legal airworthiness limit.

The TCDS does.

I'll give half credit because Ron got half the statement right in his first statement. but the POH statement is not correct, because it is a Flight manual, and not used to declare airworthiness, as the OP was asking.
 
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Tom-D said:
Are you guys talking about this page ?
POWER PLANT LIMITATIONS
Engine Manufacturer: Teledyne Continental.
Engine Model Number: 0-470-U.
Engine Operating Limits for Takeoff and Continuous Operations:
Maximum Power: 230 BHP.
Maximum Engine Speed: 2400 RPM.
Maximum Cylinder Head Temperature: 460°F (238°C). Maximum Oil Temperature: 240°F (116°C).
Oil Pressure, Minimum: 10 psi.
Maximum: 100 psi.
Propeller Manufacturer: McCauley Accessory Division.
Propeller Model Number: C2A34C204/90DCB-8 Propeller Diameter, Maximum: 82 inches.
Minimum: 80.5 inches.
Propeller Blade Angle at 30 Inch Station, Low: 15.0°.
High: 29.4°

then show me where there is a lower limit for the RPMs or where these are a airworthy requirement?
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That's not from a C-172S POH/AFM. Cessna never built a C-172S with a Continental O-470 engine.
 
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