Going from Cessna 152 to 172
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Not a lot of margin for error there—and again, remember that that's with a brand-new aircraft, perfect technique. With the somewhat clapped-out aerial conveyances given to most of us to fly, that may translate in real terms to 0 fpm.
The prevailing design requirement states in respect of the foregoing (with my bold):
Sec. 23.45
General.
(a) Unless otherwise prescribed, the performance requirements of this part must be met for--
(b) Performance data must be determined over not less than the following ranges of conditions--
(c) Performance data must be determined with the cowl flaps or other means for controlling the engine cooling air supply in the position used in the cooling tests required by Sec. 23.1041 to Sec. 23.1047. (d) The available propulsive thrust must correspond to engine power, not exceeding the approved power, less--
(e) The performance, as affected by engine power or thrust, must be based on a relative humidity:
(f) Unless otherwise prescribed, in determining the takeoff and landing distances, changes in the airplane's configuration, speed, and power must be made in accordance with procedures established by the applicant for operation in service. These procedures must be able to be executed consistently by pilots of average skill in atmospheric conditions reasonably expected to be encountered in service. (g) The following, as applicable, must be determined on a smooth, dry, hard-surfaced runway--
Amdt. 23-62, Eff. 1/31/2012
General.
(a) Unless otherwise prescribed, the performance requirements of this part must be met for--
(b) Performance data must be determined over not less than the following ranges of conditions--
(c) Performance data must be determined with the cowl flaps or other means for controlling the engine cooling air supply in the position used in the cooling tests required by Sec. 23.1041 to Sec. 23.1047. (d) The available propulsive thrust must correspond to engine power, not exceeding the approved power, less--
(e) The performance, as affected by engine power or thrust, must be based on a relative humidity:
(f) Unless otherwise prescribed, in determining the takeoff and landing distances, changes in the airplane's configuration, speed, and power must be made in accordance with procedures established by the applicant for operation in service. These procedures must be able to be executed consistently by pilots of average skill in atmospheric conditions reasonably expected to be encountered in service. (g) The following, as applicable, must be determined on a smooth, dry, hard-surfaced runway--
Amdt. 23-62, Eff. 1/31/2012
These procedures must be able to be executed consistently by pilots of average skill
Thanks for the post. Too many people seem to think that the POH performance is only achievable by test pilots in new aircraft.
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Well, well, as you please. All flying-school or rental aircraft that have managed to pass an annual inspection, with compressions probably in the low-mid sixties, draggy and leaky doors and seals, and props that may or may not be identical to the one used for the model's original certification test (or may or may not be out of balance, and may or may not have been filed down to limits to eliminate nicks) may always be depended upon to turn in the performance figures contained in the POH.
Good to know. Back in the real world, some points to consider:-
1. For aircraft manufactured in the U.S., book performance figures are calculated by the manufacturer at the time of certification. They are notorious for erring on the side of optimism. Barry Schiff, formerly of TWA and Flying magazine, has a good piece on this in one of his "Proficient Pilot" columns.
2. Until March 1, 1979, POHs were not legally required to be provided at all. That date cut-off includes a lot of aircraft currently flying, including the one I own.
3. Most pilots do not include in their pre-flight check many things that can affect performance, e.g. tyre pressures, or whether the RPM figure shown on the tachometer actually represents how fast the propeller is turning (hint: it typically isn't).
4. The FAA points out that each individual aircraft will differ in its flying and performance characteristics.
5. U.S. AOPA's Air Safety Institute recommend that pilots flying light piston aircraft factor in a safety margin of 50% above book performance chart figures for takeoff, landing and rate of climb.
6. Mathematically, it is improbable that all pilots are "of average skill." If they are, it is improbable that their own performance on any given day will invariably be at or above average.
As you were, gentlemen. Keep chasing that sizzling 175 fpm promised by the book—I'm sure it'll always be there whenever you need it!
Good to know. Back in the real world, some points to consider:-
1. For aircraft manufactured in the U.S., book performance figures are calculated by the manufacturer at the time of certification. They are notorious for erring on the side of optimism. Barry Schiff, formerly of TWA and Flying magazine, has a good piece on this in one of his "Proficient Pilot" columns.
2. Until March 1, 1979, POHs were not legally required to be provided at all. That date cut-off includes a lot of aircraft currently flying, including the one I own.
3. Most pilots do not include in their pre-flight check many things that can affect performance, e.g. tyre pressures, or whether the RPM figure shown on the tachometer actually represents how fast the propeller is turning (hint: it typically isn't).
4. The FAA points out that each individual aircraft will differ in its flying and performance characteristics.
5. U.S. AOPA's Air Safety Institute recommend that pilots flying light piston aircraft factor in a safety margin of 50% above book performance chart figures for takeoff, landing and rate of climb.
6. Mathematically, it is improbable that all pilots are "of average skill." If they are, it is improbable that their own performance on any given day will invariably be at or above average.
As you were, gentlemen. Keep chasing that sizzling 175 fpm promised by the book—I'm sure it'll always be there whenever you need it!
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That's an interesting point actually. We all apply the recommended fudge factors to runway length (33%/43%/whatever), don't we, but I don't think I've seen any guidance as to what fudge factor to apply to climb rate?
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If a pilot chooses to apply their own factor of conservatism that's up to them, it's probably exercising good judgement. And, it is true that aircraft performance can vary, as a result of tire pressure, inaccurate instruments (I'd be more worried about the ASI, rather than tach), more antennas, poorly fitted (or missing) fairings, or poor paint condition. A pilot is expected to fly an aircraft which has been maintained so as to be airworthy, and conforming to it's type design (about the way the manufacturer tested it). If the pilot willingly flies an aircraft with defects, they choose to take responsibility for any effect upon performance.
If a pilot cannot consistently apply skill to takeoff and climb which meets the mark of "average" when needed, some introspection is appropriate. It may not be the fault of the plane or its performance data, if the pilot cannot achieve "book" performance".
Otherwise, For my experience with Cessnas, and their performance data as published as far back as 1958, I have found it to be very accurate, and I have formally done the climb testing on many Cessna types. That said, I have done the testing on other types too, and for one, have found "optimistic" data in the POH (which was a separate document from the FAA approved Flight Manual, which did not contain climb data) - but this was not a Cessna.
Understand what you are reading. If you are reading a document which meets the requirements of "Flight Manual" and it is FAA (or other authority) approved, the performance data will be accurate, as it was gathered and presented in accordance with the certification requirements, and the authority was overseeing that. If you are reading AOPA material, sales information, a third party training manual or other such document, you may have erroneous data.
All that said, if you're used to a 152, and you start to fly an airworthy 172 with decent 152 skills, you will not be disappointed by 172 performance.
If a pilot cannot consistently apply skill to takeoff and climb which meets the mark of "average" when needed, some introspection is appropriate. It may not be the fault of the plane or its performance data, if the pilot cannot achieve "book" performance".
Otherwise, For my experience with Cessnas, and their performance data as published as far back as 1958, I have found it to be very accurate, and I have formally done the climb testing on many Cessna types. That said, I have done the testing on other types too, and for one, have found "optimistic" data in the POH (which was a separate document from the FAA approved Flight Manual, which did not contain climb data) - but this was not a Cessna.
Understand what you are reading. If you are reading a document which meets the requirements of "Flight Manual" and it is FAA (or other authority) approved, the performance data will be accurate, as it was gathered and presented in accordance with the certification requirements, and the authority was overseeing that. If you are reading AOPA material, sales information, a third party training manual or other such document, you may have erroneous data.
All that said, if you're used to a 152, and you start to fly an airworthy 172 with decent 152 skills, you will not be disappointed by 172 performance.
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"Fun" to watch the unknowing trying to fly a C172/PA28 IFR in the New Mexico mountains in summer. MEAs of 10,000' with temps at the surface near 100 f. Since it wasn't our place to try to talk sense into them on the radio before departure, we'd wait until they'd staggered up to near 7000' MSL, where they would have to cancel IFR, or return to land. Apparently, they slept through the chapter on density altitude.
Have also seen aircraft crash after departing a 9000' runway, and never get as high as the control tower cab before impact. (probably had it full rich too.)
Have also seen aircraft crash after departing a 9000' runway, and never get as high as the control tower cab before impact. (probably had it full rich too.)
