Cessna 172C Performance
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Re: Cessna 172C Performance
My aircraft is 28 years old and the engine is 45 years old.
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Thales Coelho
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Re: Cessna 172C Performance
Thats my problem, to understand what can be my real gross weight limit.Big Pistons Forever wrote: ↑Sat Jan 27, 2018 5:19 pm SBPR is 3044 MSL. 34 C there is going to be pretty marginal unless you are well below gross weight
Of course that temperature is not what we find early in the morning, neither is an everyday temp, but can reach that much.
Other problem is that the real engine will not meet the manual standards, as people reminded me here.
Re: Cessna 172C Performance
I call bs on that theory. If it’s maintained properly, it will. The airframe may have picked up some extra drag, through rough paint, poor rigging, etc., though.Other problem is that the real engine will not meet the manual standards, as people reminded me here.
Oh - and check the equipment list to see if wheel pants were included as standard. If so, all the performance data is is with the wheelpants on. If yours are off, that’s a bunch of extra drag, too.
DId you hear the one about the jurisprudence fetishist? He got off on a technicality.
Re: Cessna 172C Performance
Calculate the takeoff distance using the POH and take that as the best case scenario. Then try on a cooler day, lightly loaded, and gradually experiment with hotter conditions and more load and you'll soon learn what the plane can do safely.Thales Coelho wrote: ↑Tue Jan 30, 2018 9:12 am
Thats my problem, to understand what can be my real gross weight limit.
Of course that temperature is not what we find early in the morning, neither is an everyday temp, but can reach that much.
Other problem is that the real engine will not meet the manual standards, as people reminded me here.
Re: Cessna 172C Performance
If you believe that your engine will not meet the manual standards, then you have made the determination that the engine is not airworthy, and you should not fly the plane. It could not be more simple.Other problem is that the real engine will not meet the manual standards, as people reminded me here.
The engine does not know its age, it knows how it has been maintained. If it is maintained well (in accordance with the standards), it will produce its rated power. It's simple physics. If you let its condition deteriorate, it will produce less power at full power, until eventually, it scares someone into knowing it needs maintenance. By the time it scares a pilot, it's been way too long since it should have received maintenance.
I've owned my O-200 for nearly 31 years. In that time, I've put more than 3000 hours on it. It produces the same power now, as it did when I first bought it (well, probably a little more, I bought it as a near to TBO engine). I have maintained it over the years, and it has rewarded me with dependable power the entire time, with the only exception being a stuck exhaust valve once. Otherwise, perfect reliability and performance.
Re: Cessna 172C Performance
Well, first of all you need to run-up and then (perhaps) fly the plane to see how it flies. It's probably best not just jumping into a plane you don't know, filling it up to full gross, and blasting off from a short runway on a hot day
Is there any way a pilot can determine whether the engine meets the standards (other than reaching the required static rpm)?
Will the static rpm guarantee that the engine is delivering the certified power if you don't have a MP gauge?
Re: Cessna 172C Performance
Upon discussion, someone was kind enough to point out to me that prop condition can make a difference: a beat up prop can lose some (a lot?) of efficiency in turning torque into thrust.
Also: for a fixed pitch prop you can get a good power check by noting the full-throttle RPM at the start of the takeoff run. (That's why it's noted in the POH). If you get the proper RPM, your engine is making near enough the rated power.
Also: for a fixed pitch prop you can get a good power check by noting the full-throttle RPM at the start of the takeoff run. (That's why it's noted in the POH). If you get the proper RPM, your engine is making near enough the rated power.
DId you hear the one about the jurisprudence fetishist? He got off on a technicality.
Re: Cessna 172C Performance
Given that an engine attached to a fixed pitch prop never develops anywhere near full power on takeoff, I'm somewhat skeptical that the full throttle static runup is a reliable indicator of engine health.photofly wrote: ↑Tue Jan 30, 2018 3:39 pm Upon discussion, someone was kind enough to point out to me that prop condition can make a difference: a beat up prop can lose some (a lot?) of efficiency in turning torque into thrust.
Also: for a fixed pitch prop you can get a good power check by noting the full-throttle RPM at the start of the takeoff run. (That's why it's noted in the POH). If you get the proper RPM, your engine is making near enough the rated power.
Re: Cessna 172C Performance
A full throttle run up reaching (say) 2300rpm requires more power than the same engine develops in cruise flight at 2300rpm (perhaps 65% power) because the prop is harder to turn when the aircraft isn't moving, and shaft power is torque x rpm. So it's not 100% rated power, but it's a significant proportion of 100% power.
I'm trying to think of some kind of engine defect that *wouldn't* affect the static rpm but would prevent the engine reaching full power. Some very specific magneto fault that only shows up at >2300rpm perhaps? But that would be a very specific fault, wouldn't it? Anything like a mis-timed mag, blocked induction system or fuel flow blockage should show up on a static check, no?
If we're talking only about takeoff roll distance, the static rpm is a very good proxy for engine health during that manoeuvre, since the rpm never reaches red-line (and the engine never develops 100% power) until the aircraft is settled in a fast cruise climb, at the earliest.
I'm trying to think of some kind of engine defect that *wouldn't* affect the static rpm but would prevent the engine reaching full power. Some very specific magneto fault that only shows up at >2300rpm perhaps? But that would be a very specific fault, wouldn't it? Anything like a mis-timed mag, blocked induction system or fuel flow blockage should show up on a static check, no?
If we're talking only about takeoff roll distance, the static rpm is a very good proxy for engine health during that manoeuvre, since the rpm never reaches red-line (and the engine never develops 100% power) until the aircraft is settled in a fast cruise climb, at the earliest.
DId you hear the one about the jurisprudence fetishist? He got off on a technicality.
Re: Cessna 172C Performance
Yup, Photofly has it. The full throttle static RPM is the required demonstration of engine performance for a fixed pitch prop aircraft, when that RPM is stated as the requirement.
For example, have a look at page 2 of the 172TCDS here: http://rgl.faa.gov/Regulatory_and_Guida ... Rev_84.pdf
You'll see here, and throughout the TCDS, references to static RPM requirements. This is the pilot's way of knowing that a fixed pitch prop plane they are flying is making rater power at full throttle. As Photofly states, you're not going to get full engine red line RPM still on the ground, as the prop blades may be somewhat aerodynamically stalled, and creating lots of drag. That drag prevents maximum engine speed. If the correct prop for the plane will exceed the maximum stated RPM, I'd be looking at the prop condition, has it been reworked to be toothpick blades? If the engine won't make the minimum of the stated RPM, I'd be looking at engine condition - low compression cylinders. If an interested pilot wants to check for that, while employing all cautions about turning propellers of stopped engines, listen at the exhaust and crankcase breather for blowby - poor exhaust valve seating or rings. If you've gotten that far, again, great caution turning props, you may just feel a flat cylinder, it takes no muscle to pull the engine through that compression stroke.
The reason that the maximum RPM is limited to a lower value still on the ground is that there is also a prop overspeed requirement in a power off dive, and that maximum RPM assures compliance with that too. I have flown 172's in which a full throttle takeoff was around 2350 RPM at the beginning, and the throttle had to be pulled back a little in cruise flight to prevent an overspeed.
No, for a fixed pitch prop equipped engine, the MP gauge is of no value, as long as the prop conforms as demonstrated above. If you did have an MP gauge on your fixed pitch propeller engine, it would rise and fall nicely with throttle setting - so what's the point? And, What would it's limitations be anyway?
Not all TCDS for fixed pitch prop planes state static RPM limits, but if in doubt, its the first and best place to look for an uncertain pilot. The flight manual may not present this information, as it is not limiting in the pilot operating sense, it's really a maintenance activity.
The only factor which could affect engine power at altitude, while not on [lower altitude] ground could be bad mag leads. On the ground, the dense air is too much for the spark to jump across broken mag lead insulation. But, at altitude, the less dense air allows the spark to jump to ground before it gets to the spark plug business end. I had this in my 150 at about 9000 feet, when I first bought it. New mag leads, and never a problem since. That's rarely a factor for takeoff of a 172 in North America, but, because someone asked...
For example, have a look at page 2 of the 172TCDS here: http://rgl.faa.gov/Regulatory_and_Guida ... Rev_84.pdf
You'll see here, and throughout the TCDS, references to static RPM requirements. This is the pilot's way of knowing that a fixed pitch prop plane they are flying is making rater power at full throttle. As Photofly states, you're not going to get full engine red line RPM still on the ground, as the prop blades may be somewhat aerodynamically stalled, and creating lots of drag. That drag prevents maximum engine speed. If the correct prop for the plane will exceed the maximum stated RPM, I'd be looking at the prop condition, has it been reworked to be toothpick blades? If the engine won't make the minimum of the stated RPM, I'd be looking at engine condition - low compression cylinders. If an interested pilot wants to check for that, while employing all cautions about turning propellers of stopped engines, listen at the exhaust and crankcase breather for blowby - poor exhaust valve seating or rings. If you've gotten that far, again, great caution turning props, you may just feel a flat cylinder, it takes no muscle to pull the engine through that compression stroke.
The reason that the maximum RPM is limited to a lower value still on the ground is that there is also a prop overspeed requirement in a power off dive, and that maximum RPM assures compliance with that too. I have flown 172's in which a full throttle takeoff was around 2350 RPM at the beginning, and the throttle had to be pulled back a little in cruise flight to prevent an overspeed.
No, for a fixed pitch prop equipped engine, the MP gauge is of no value, as long as the prop conforms as demonstrated above. If you did have an MP gauge on your fixed pitch propeller engine, it would rise and fall nicely with throttle setting - so what's the point? And, What would it's limitations be anyway?
Not all TCDS for fixed pitch prop planes state static RPM limits, but if in doubt, its the first and best place to look for an uncertain pilot. The flight manual may not present this information, as it is not limiting in the pilot operating sense, it's really a maintenance activity.
The only factor which could affect engine power at altitude, while not on [lower altitude] ground could be bad mag leads. On the ground, the dense air is too much for the spark to jump across broken mag lead insulation. But, at altitude, the less dense air allows the spark to jump to ground before it gets to the spark plug business end. I had this in my 150 at about 9000 feet, when I first bought it. New mag leads, and never a problem since. That's rarely a factor for takeoff of a 172 in North America, but, because someone asked...
