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C172P/R/S flaps

Old 24th Nov 2021, 14:37
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C172P/R/S flaps

What is the reason that the C172P/R/S series flaps are max of 30 while earlier series are 40?

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Old 24th Nov 2021, 14:46
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Originally Posted by shumway76 View Post
What is the reason that the C172P/R/S series flaps are max of 30 while earlier series are 40?

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Old 24th Nov 2021, 15:22
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Originally Posted by shumway76 View Post
What is the reason that the C172P/R/S series flaps are max of 30 while earlier series are 40?

Cheers!

Can't say exactly, but having flown the Rocket with a 40 position available, I can tell you it helped me out a few times with a good finish from a crappy approach.

You should be careful with them though - the drag at 40 becomes noticeable and you should monitor your power setting and airspeed closely. I think (speculation) they got rid of that setting in later models precisely for this reason (I might be wrong).

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Old 24th Nov 2021, 15:39
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This reduction from 40 degrees to a maximum of 30 degrees was applied to a range of Cessna singles. There were a number of landing and particularly take-off incidents that were attributed to the enormous amount of drag produced from a run on to 40 degrees which had been inadvertently allowed. I never found 40 degrees itself an issue but the electric flap switch operation was. With some models you had to actively neutralize the switch position, whether raising or lowering the flap or it would run on. Cessna did change this to a system where it became necessary to maintain pressure on a spring loaded switch or it would reset to the neutral position. The flap indication was poor which could have a lot of lag. They then changed this again to a gated system allowing the pilot to select the required flap position.

The excess thrust over drag was marginal with 40 degrees of flap and required skilled and accurate flying in order to climb.
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Old 24th Nov 2021, 17:35
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I got caught out many years ago when learning to fly on a C150 with flap switch (not gated) and 40 degrees available. Solo student at the time in the circuit. Climbing out from a touch & go and I retracted the flaps on the runway......but must have knocked the switch back down again when moving hand from there back to the throttle......the climb out became very interesting in both pitch and airspeed until I noticed the ever increasing flap angle! Luckily I was solo and light on fuel so got away with a prompt re-retraction! Certainly focused the mind of a low hour student!
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Old 24th Nov 2021, 19:24
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The Cessna 170B and 180 were originally designed with 40 flap available, as they were commonly used "in the bush" and on skis and floats, where the 40 flap was useful in getting into tight places. The original 172 was pretty well a tricycle 170B, so the wings continued to have 40 flap. The 180/185s had 40 flap through their entire production run. However, in the late '70's, Cessna obviously thought that the 152, and 172 no longer needed 40 flap, as they rarely fly in a role which demands that configuration.

The Cessna 150 had 40 flap through it's production run, perhaps until the very few 1977 models built. The 152 was never offered with 40 flap. Keeping spare fuses available for the mid year 150's was a good idea! I did blow the flap fuse with full flaps extended on a night overshoot once (deer on the runway), but it climbed away fine, as long as you were gentle with it.

The Cessna 305 AKA L19/O1 and Bird Dog, was a variation of a Cessna 170B, though with a very different (tandem) cockpit. But the wings were pretty well 170B wings, other than flaps which extended to 60 degrees. This was common to the later Siai Marchetti 1019, which was a turbine derivative of the Bird Dog. 60 flap landing do require some mentoring, and a gentle touch!



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Old 24th Nov 2021, 20:12
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If you’re on final approach with a reasonable headwind in a 150, put 40 degree flap on and you’re flying a Harrier !

i have had to go round with 40 degree flap a few times, the most memorable was two up, when some cretin pulled onto the runway and started a slow takeoff run when I wasn’t far from touching down. Treat the elevator gently and it will climb away , very slowly

in that situation the other advantage of the 150 (mine’s a model L from 1973) is that the flap lever can be used gradually, it doesn’t have to move in ten degree notches

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Old 24th Nov 2021, 21:17
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the other advantage of the 150 (mine’s a model L from 1973) is that the flap lever can be used gradually, it doesn’t have to move in ten degree notches
The Cessna flap system does give the pilot the ability to raise or lower the flap very gradually and also to the flap deflection the pilot chooses. This ability wasn't lost with the "Gated" upgrade. There isn't a notch or lock at intervals which must be used. The surface plate is profiled at each ten degrees giving both a tactile and a visual positioning but you are not committed to these, you can still raise or lower the flaps gradually and position as you choose.
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Old 24th Nov 2021, 22:10
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A low level baulked landing in a 172 with flap 40 needs to be handled very carefully. My 1980 model was the last year with flap 40 I believe.

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Old 25th Nov 2021, 01:01
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I believe that when the Gross weight was raised from 2300 lbs to 2400 lbs on the N model there was an identified issue as to whether or not the airplane would meet the FAR 23 climb requiremttn in the even of a balked approach. Therefore Cessna elected to reduce the maximum fap setting to 30. Realistically this had no operational flaps as the landing distance is shorter than the takeoff distance.
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