Skylane81E
Final Approach
Static RPM need not be redline with a fixed pitch prop, in fact I'm not aware of any case where it is.
Static RPM Test
- Thread starter Jaybird180
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Dan Thomas
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Dan Thomas
He's asking whether the max static can be legally exceeded. For instance, if the TCDS says "not under 2300, not over 2400," and he gets 2450 in the static condition, is it airworthy?
I'd say not. There's something wrong with the prop, most likely. Not enough HP being absorbed by it, or maybe the tach is overreading.
Redline with a fixed-pitch prop will only be achieved in flight.
Dan
bnt83
Final Approach
Simple
For fixed pitch, static is the minimum RPM range that must be achieved at full throttle and will not be redline maximum. The only way to get to redline in a fixed pitched equiped airplane is in flight, with tons of air flowing through the prop.
So just made up example:
Busmasher 123 has a Static RPM spec of 2400-2500, Redline RPM is 2,700.
Climb Prop Installed (lower pitch) - Static RPM we read on the optical tach was 2495. We take off and in straight and level flight with full power the airplane accelerates to 80 MPH indicated airspeed as the tach reaches the 2700 rpm limitation. Ground roll was 500 feet
Cruise Prop Installed (higher pitch) - Static RPM we read on the optical tach was 2415. We take off and in straight and level flight with full power the airplane accelerates to 100 MPH indicated airspeed as the tach reaches 2700 rpm limitation. Ground Roll was 750 feet.
----Both are airworthy.
Bugsmasher 123 is having a bad day and we only get 2300 RPM on the optical tach. Engine leaned for highest RPM, both mags check fine but she just can't turn the prop to 2400. Something is amiss. We pull the cowling and do a compression check and find that one of the cylinders has vey low compression. We spray that cylinder with soapy water and find the cylinder head cracked about 1/2 way around the barrel. With a shiny new jug installed it again turns the prop 2400-2500 RPM on the ground with the brakes locked and leaned for highest RPM.
Bugsmasher 123 comes to the shop and is having a bad day and we get 2650 Static RPM on the optical tach. Something is amiss. We pull the spinner and find the wrong prop installed.
Bugsmasher 123 comes to the shop and is having a bad day and we get 2650 Static RPM on the optical tach. Something is amiss. We pull the spinner and find the correct prop installed. We call a prop shop and they say "send it in". They call back and say the pitch is way out of spec, with too low pitch, or the blades were cut too short, or.....
For constant speed, its a limitation, and will be redline RPM. Since Redline RPM can be achieved around 1/2 throttle, RPM alone cannot be used to determine engine power output/health.
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bnt83
Final Approach
Skylane81E
Final Approach
Read it again, agreed,
Very cut and dry, if it ain't in the range it ain't airworthy.
Just have to make sure the prop going on to correct the problem is an approved prop
Frank
Pre-takeoff checklist
The prop coming off is higher pitch than the TCDS specifies, but the static rpm was in range with the old prop. I was wondering if the new prop might have too little pitch to keep the full throttle static rpm below the maximum, and if so, what happens?
bnt83
Final Approach
Frank
Pre-takeoff checklist
Not backward at all. I am suggesting concern about exceeding the max static rpm because the new prop is lower pitch than what is coming off. If the new pitch were higher then the concern would be the minimum static rpm, which is what most of the thread had been about. I was asking about maximum static rpm, because the conditions are slightly different going from higher pitch to lower. If an engine/prop combination cannot reach minimum static rpm, then nothing you do to the throttle could change that. If the engine/prop combination can exceed max static rpm at full throttle, does reducing the throttle below max static rpm make everything compliant?
bnt83
Final Approach
Silvaire
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The answer is NO. Static RPM is WOT.
bnt83
Final Approach
Tach accuracy
8-95. TACHOMETER INSPECTION.
Due to the exceptionally high stresses that may
be generated by particular propeller/engine
combinations at certain engine revolutions per
minute (RPM), many propeller and aircraft
manufacturers have established areas of RPM
restrictions and other restrictions on maximum
RPM for some models. Some RPM limits do
not exceed 3 percent of the maximum RPM
permitted, and a slow-running tachometer can
cause an engine to run past the maximum
RPM limits. Since there are no postmanufacture
accuracy requirements for engine
tachometers, tachometer inaccuracy could lead
to propeller failure, excessive vibration, or unscheduled
maintenance. If the tachometer exceeds
2 percent (plus or minus) of the tested
RPM, replace it.Due to the exceptionally high stresses that may
be generated by particular propeller/engine
combinations at certain engine revolutions per
minute (RPM), many propeller and aircraft
manufacturers have established areas of RPM
restrictions and other restrictions on maximum
RPM for some models. Some RPM limits do
not exceed 3 percent of the maximum RPM
permitted, and a slow-running tachometer can
cause an engine to run past the maximum
RPM limits. Since there are no postmanufacture
accuracy requirements for engine
tachometers, tachometer inaccuracy could lead
to propeller failure, excessive vibration, or unscheduled
maintenance. If the tachometer exceeds
2 percent (plus or minus) of the tested
Frank
Pre-takeoff checklist
That would have been my thought. Is there a reference for that? I could not find one. Further, what do you do about exceeding maximum static rpm, if the prop is the only one authorized on the TCDS?
Frank
Pre-takeoff checklist
Good info. What is the source?
bnt83
Final Approach
Example http://www.sensenich.com/files/documents/Repairs_Trouble_Shooting_Repitch_Limits_1303228075.pdf
Each prop has a TCDS of it's own that will list the "standard pitch" (range)that it should be. Running over static RPM then the prop shop bends the blades to adjust the pitch.
Assuming the is engine right, correct timing and whatnot.
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bnt83
Final Approach
Silvaire
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The reference is the TCDS which lists the static rpm range for the aircraft/propeller combination. Static RPM simply means wide open throttle, that is just a given - what else could it possibly mean? If it is a new prop and the tach accuracy is confirmed as well as magneto timing and you're certain you have no tailwind then you've got me stumped.
bnt83
Final Approach
Undocument blade angle tweak with a prop paddle to get a little bit better takeoff performance for too high static rpm....
Skylane81E
Final Approach
kgruber
Final Approach
Skylane81E
Final Approach
It can be
kgruber
Final Approach
Ditto....constant speed.
kgruber
Final Approach
bnt83
Final Approach
Not so fast. Maybe your plane is mis-rigged.
Service Manual D991-3-13 Change 1 dated September 1 1974: 177RG (1974-1975) "...average results of the RPM obtained should be within 50 RPM of 2660" 2700 RPM Redline per TCDS
Service Manual 123 dated December 1998: M20J "Static RPM may be 50 RPM less than 2700" 2700 RPM Redline per TCDS
Service Manual D206-4-13 Sated March 1 2004 (O470 powered) "...average results of the RPM obtained should be within 50 RPM of of 2570" 2600 Redline per TCDS
Service manual 753-564 dated January 1, 2009: PA-23-250 "... should be against the high RPM fine adjusting screw (4). With the throttle full forward, observe engine RPM which should be 2575 RPM with high RPM properly adjusted." Redline 2575 per TCDS
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Skylane81E
Final Approach
Hiyup
kgruber
Final Approach
Nope. See note at bottom of page 102: (directly from the manufacturer)
http://www.mccauley.textron.com/MPC26OWrev1.pdf
NOTE: On static runs, the propeller should prevent the engine RPM from going to redline. This is done to prevent overspeeding and is a design characteristic of the propeller. However, it should be within 100 RPM of red line.
bnt83
Final Approach
Wrong
Page 103 in your link:
Improper Propeller Maximum RPM in Flight (Constant Speed Piston)
A. Incorrect propeller speed with maximum RPM selected in flight.
(1) Possible Cause:
(a) Inaccurate tachometer reading.
(b) Linkage is out of rig.
(c) Governor stop screw requires adjustment.
(2) Corrective Action:
(a) Repair or replace the tachometer.
(b) Governor stop screw requires adjustment.
1 Do a test flight.
2 Pull the propeller control back until it reaches redline RPM.
3 Allow the RPM to stabilize.
4 Land the aircraft without touching the propeller control lever.
5 Adjust the propeller stop screw to the propeller control location.
6 Rig the aircraft power controls in accordance with the instructions of themanufacturer.
A. Incorrect propeller speed with maximum RPM selected in flight.
(1) Possible Cause:
(a) Inaccurate tachometer reading.
(b) Linkage is out of rig.
(c) Governor stop screw requires adjustment.
(2) Corrective Action:
(a) Repair or replace the tachometer.
(b) Governor stop screw requires adjustment.
1 Do a test flight.
2 Pull the propeller control back until it reaches redline RPM.
3 Allow the RPM to stabilize.
4 Land the aircraft without touching the propeller control lever.
5 Adjust the propeller stop screw to the propeller control location.
6 Rig the aircraft power controls in accordance with the instructions of themanufacturer.
7 Do another flight test to verify the correct setting.
And with all this set correctly, the prop will turn much closer to redline or at redline as stated in the Aircraft Service Manual, at static runup.
The prop will come off the low pitch stop at full power low density altitude with a proper running engine, meaning its gonna turn at whatever RPM the gov is set to.
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kgruber
Final Approach
If it hits redline statically it will go over redline on takeoff. Do what you want, but McCauley knows props better than you do.
bnt83
Final Approach
Read an airplane maintenance manual for once or be smoother on the throttle.
Skylane81E
Final Approach
Not if redline is where the governor takes over and holds the speed
bnt83
Final Approach
I bet I could make an airplane you rigged IAW the airplane maintenance manual overshoot too.
bnt83
Final Approach
Skylane81E
Final Approach
I've never seen one that isn't in governing range during static runs
And even if you did, rig the governor to 2400rpm at the stop and unless something brakes 2400 is all you will get short of a little wiggle if you are ham fisted.
kgruber
Final Approach
I've never seen one that isn't in governing range during static runs
None are.
Skylane81E
Final Approach
If they aren't in the governing range how can I "misrig" it and get to to (or over if I so desired) redline RPM static?
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bnt83
Final Approach
bnt83
Final Approach
What happens in the real world vs on paper are two different things. As said before, I've never seen one that wasn't in governing range at static. Prop shop set the low pitch stop, not me. Some airframers say it should turn Redline some say within 50 RPM.
What McCauley says:
Static Run-Up - What is Normal?
There has been some confusion in the field concerning propeller low blade angle setting, the governor setting and how it relates to static run-up and take-off RPM. As a general rule, engine redline RPM cannot be reached during a full power static run-up. Contrary to popular belief, the governor is not controlling the propeller at this time, the propeller is against its low pitch stop. Attempting to increase propeller static run-up RPM by adjusting the governor high RPM screw will have no effect and will probably result in a propeller overspeed during the take-off roll. On a single engine aircraft several considerations determine both the low and high blade angle settings. Normally 25 to 100 RPM below rated take-off RPM is desirable and acceptable during a static run-up. McCauley's practice is to set the low blade angle so that rated take-off RPM is not reached until the aircraft has reached some significant groundspeed during roll out. At this time, and only this time, the propeller is controlled by the governor. There are two advantages to this practice. First, the maximum static RPM can be used as a check on developed horsepower as with a fixed pitch propeller. Any loss of maximum power over time is readily apparent during a preflight check. Second, if the propeller remains in a flat pitch after take-off due to some malfunction, the higher angle low pitch setting will permit more thrust to be developed to fly the aircraft without overspeeding the engine.
http://www.mccauley.textron.com/pga_governors.html
What McCauley says:
Static Run-Up - What is Normal?
There has been some confusion in the field concerning propeller low blade angle setting, the governor setting and how it relates to static run-up and take-off RPM. As a general rule, engine redline RPM cannot be reached during a full power static run-up. Contrary to popular belief, the governor is not controlling the propeller at this time, the propeller is against its low pitch stop. Attempting to increase propeller static run-up RPM by adjusting the governor high RPM screw will have no effect and will probably result in a propeller overspeed during the take-off roll. On a single engine aircraft several considerations determine both the low and high blade angle settings. Normally 25 to 100 RPM below rated take-off RPM is desirable and acceptable during a static run-up. McCauley's practice is to set the low blade angle so that rated take-off RPM is not reached until the aircraft has reached some significant groundspeed during roll out. At this time, and only this time, the propeller is controlled by the governor. There are two advantages to this practice. First, the maximum static RPM can be used as a check on developed horsepower as with a fixed pitch propeller. Any loss of maximum power over time is readily apparent during a preflight check. Second, if the propeller remains in a flat pitch after take-off due to some malfunction, the higher angle low pitch setting will permit more thrust to be developed to fly the aircraft without overspeeding the engine.
http://www.mccauley.textron.com/pga_governors.html
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Skylane81E
Final Approach
Some general rule,
Every time I've out on an overhauled or factory new prop it would happily go spinning off into the red at flat pitch
Every time I've out on an overhauled or factory new prop it would happily go spinning off into the red at flat pitch
Frank
Pre-takeoff checklist
Why is there a maximum static rpm for fixed pitch props? It cannot be for overspeed, because the value is well below redline. It could be because of torque loads on the engine mount but if the remedy were to increase pitch, the torque would increase. It could be to prevent an overload in tension on the engine mount, but the mount has to be fairly sturdy to accommodate g loads in flight, so it does not seem likely that the engine could overload the mount in tension.
bnt83
Final Approach
Your over thinking it.
Because your plane would be SLOOOOOW if you were running a pitch so flat you exceed the max Static RPM. The airplane was built & certificated to an ideal spec with the best compromise of climb & ground roll VS cruise speed and performance charts written to reflect those performance #'s To get those performance #'s the prop needs to be over a certain pitch and under a certain pitch and the engine needs to have good power output to turn the prop with the correct pitch at the required speeds.
You want the best of both worlds, high RPM with good climb and get good cruise performance, buy a plane with a constant speed prop, that's what they were designed for.
Why wouldn't the governor prevent that?