10 degree flaps increase our lift, reduce stall speed, reduce ground roll. Seems like all advantages with no disadvantages. So why does the Cessna 172 POH say normal take off is 0-10 degree flaps? Why not always use 10 degree?
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$\begingroup$ Welcome to aviation.SE! This question might be helpful. $\endgroup$– PondlifeJul 29, 2020 at 1:15
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2$\begingroup$ In some headwinds you might take off backwards. $\endgroup$– J...Jul 29, 2020 at 14:20
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$\begingroup$ 10 degrees flaps is standard in a 177. There are wind situations where less flaps make the plane mor controllable. I don't think I've ever had to. If the elevator trim is set correctly, basically where it was for the prior landing, the plane will lift off with very littl back pressure. I've only flown a 172 once, for a BFR so I could move my plane on a ferry permit, and I think I took off the same way. May not have used flaps, I don't recall what that plane's check list said. I do remember that awkward sitting up in a high-back chair feeling to see out the front; the Cardinal is much nicer. $\endgroup$– CrossRoadsAug 1, 2020 at 0:08
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$\begingroup$ "trim is set correctly, basically where it was for the prior landing" -- don't do that. Take-off checklist specifically requires neutral trim. I've crashed a C172 simulator because of out-of-the-way initial trim made the plane uncontrollable, and I couldn't figure out why until ground. $\endgroup$– Dzmitry LazerkaMay 15 at 20:29
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4 Answers
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Flaps out will reduce the ground run, but you're forgetting that they also increase drag. This is why you don't climb all the way to cruise altitude with flap extended. A 172 will climb better without flaps.
With a take-off, you have to consider both the ground run and initial climb. After all, the take-off distance required is defined as the distance required to climb to screen height (50ft in Australia, sorry if the US is different). The aircraft also has to meet a legal minimum climb gradient to that height.
Without looking at the data, it is possible that in certain conditions, taking off with flaps 10 will get you off the ground quicker, but will actually take longer to reach 50ft compared to a takeoff with no flaps. In any case, retracting flaps in a busy time after takeoff is a potential hazard, and in a training aircraft like the 172 simple procedures are best.
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7$\begingroup$ Also, in many places the runway is just way longer than a 172 needs, and it doesn't really matter if you take of at 1/4 of the runway or at 1/3 -- but the faster takeoff takes you out of the airport control zone faster. $\endgroup$ Jul 29, 2020 at 10:39
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16$\begingroup$ Using flaps creates drag. If you have a nice, smooth paved runway, it's more efficient to take off with no flaps. On a rougher surface like grass or dirt, you have more drag from the wheels, so it's better to get them off the ground sooner. $\endgroup$– jamesqfJul 29, 2020 at 14:36
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$\begingroup$ Also, in gusty crosswinds, the increased flaps & drag make it harder to control the aircraft. $\endgroup$ Jul 29, 2020 at 19:41
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$\begingroup$ @Kolom I’m not sure what “screen height” is, but the performance charts for my C172 show distance to clear a 50ft obstacle. $\endgroup$– StephenSNov 15, 2020 at 12:30
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The issue is how one wants to optimize their flight operations. Generally the emphasis is on time to climb, however for some operations, such as out of standing snow, slush, mud and grass, and in the case of seaplanes, glassy water, the preferred optimization may be to minimize ground roll, rolling drag, tire wear or other factors. I teach both techniques, so that the pilot understands the choices he has, and the ways he can accomplish things.
Concerns about "stalling out" after rotation, are an issue of proficiency. Correct instruction and recurrent practice help address proficiency.
Probably 2/3 of my flight review students rarely use flaps in a C172 for take off, and generally only when doing soft field or turf takeoffs. So with those students, we tend to review takeoffs with flaps, and how they may be operationally effective in situations other than just a turf or dirt field. For those more fluent in flapped takeoffs, there are other things we might spend time on.
From a personal perspective, I probably use 10 deg flaps on a C172 95% of the time, because I like to minimize wear on my tires.
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$\begingroup$ Using flaps is really like saying why not add 4 feet of wing on either side. Same answer, safer in wind taking off and landing without them. Tricycle gear also helps by keeping AOA low before rotation. You don't want to pop up into the air with barely enough speed to fly. Really the same for landing. students must realize flaps increase AOA, and will stall that part of the wing at a lower nose AOA. $\endgroup$ Mar 24, 2021 at 15:37
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With 10 degrees of flaps and the trim wheel in the "take-off position" my C-172 will rotate without any back pressure on the yoke. You have to apply forward pressure to keep the speed above 62 knots. A flight instructor a few years ago during a flight review suggested I always use 10 degrees of flaps during take-off. After using this method for a few months, I concluded that using 10 degrees introduced a new hazard. A stall during take-off was more likely. I went back to 0 degrees flaps.
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2$\begingroup$ This answer could benefit from some sources other than your personal experience $\endgroup$– dalearnNov 15, 2020 at 3:01
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There’s nothing saying that you can’t. And for a performance takeoff like a short field take off, you will use 10° of flap. It’s just in general conditions combined with the fact of the Cessna 172 only has a takeoff roll around 1000 feet or so at sea level conditions, there’s not much need to use flaps. You can use up to 10° of flaps if desired. But generally most pilots don’t .
answered Mar 22, 2021 at 23:53