My 18 y.o. son is learning to fly. This is good! His instructor is teaching him to make all landings with 20 degrees of flaps. I'm a 40 degree/ full stall kind of guy.
You didn't specify what type of airplane, but I assume it's a C-150 or 172.
For most airplanes I agree with "full flaps all the time." I landed my Cheetah with full flaps all the time, and do so now with my Bonanza -- except the two times when the flap motor quit. IMHO the C-150 and C-172, lightweight, relatively underpowered airplanes with oversized flaps, are exceptions.
Their manuals all say "[n]ormal landings are made power off with
any flap setting" [emphasis added] I've flown both extensively since the 1960's, have owned both, and my experience is that their handling and control response in the flare is better at flaps 20-30 than at flaps 40.
It's slower, so crashes break less (equipment and crew)
Saves brakes
Saves tires
Is touchdown faster at flaps 20? More wear and tear on the gear and brakes? According to the C-150 manual there is a
one mph (0.87 knot) difference between power-off stall at flaps 20 vs flaps 40. So if a proper approach speed is maintained on final, there will not be excessive float and the full-stall touchdown speed will be virtually the same as at flaps 40. I would routinely land my C-150F with flaps 20, gently on the mains with stall horn blaring, and hold the nose off until elevator power dissipated (longer than is possible at flaps 40) and the nose gear touched at a speed barely above a fast walk, and make the first turnoff with no braking or added power at all. I'd submit that's easier on the undercarriage (especially the relatively fragile nose gear). Less wear on the flap motor and flap tracks, too.
Runway efficiency (possibly clears rwy quicker)
Depends on the airport. If the first turnoff is 600 feet down the runway, full flaps may help. If like at my airport it's 1500 feet away, a full flap landing might slow things down, require the use of power to 'expedite' to the turnoff, and increase pilot workload.
At flaps 40 a Cessna 150 is not a healthy bird. In event of a balked landing drag is so great it ain't gonna climb worth beans until flaps are milked up to 20. (If you gotta go around at flaps 40 what do you do if the flap motor quits?) On approach with flaps 20 the potential pilot workload is decreased and safety margin increased.
At flaps 40 the airplane is more affected by gusty conditions, with less control response to deal with it. For crosswind landings the C-150 book calls for "minimum flap setting required for the field length," and the late Bill Thompson (former Cessna Manager of Flight Test & Aerodynamics, in his book
Cessna -- Wings for The World, The Single-Engine Development Story, p. 41) said that was "for better rudder control."
Pro's: It's designed to do it (POH)
With regard to the C-150 and C-172 I don't buy that. The C-150 and C-172 are direct descendants of the C-140A and C-170A, respectively. Those models did just fine with the much smaller, plain flaps (of about the same chord as the ailerons) with which they were originally designed. The C-120, the low-cost version of the C-140, had no flaps at all. The "barn door" flaps were later adapted for the civilian models from the specialized, grossly overpowered L-19/O-1 Bird Dog. They give the C-150 and C-172 wonderful extra short-field capability, but they do not fundamentally change the way the basic designs were "meant" to be flown, as borne out by the "any flap setting" language in the manual. And I think it's telling that the factory limited flap travel to 30 degrees in the latest iterations of both designs (C-152 in 1978; C-172P through S since 1981). That the 30-degree limit allowed gross weight to be raised a little bit (70 lb on the C-152, even with a 10% increase in horsepower) suggests that full-flap performance was marginal to begin with.
Thompson wrote that he was initially unenthusiastic about the "projected low-performance C-150 with enlarged tail surfaces and more powerful flaps." So
why did the C-150 have the big flaps?
"Our experience with tricycle gears on other airplanes, indicated that most low-time pilots use about 10-mph excess speed in the approach glide, and then they would float many hundreds of feet before touching down. Thus the C-150 would need lots of drag with big flaps."
[Thompson, p. 8]
I looked my old Piper Cherokee 140B manual. It says:
"The amount of flap used during landings and the speed of the aircraft at contact with the runway should be varied according to the landing surface and existing conditions, both windwise and loadwise. It is generally good practice to contact the ground at the minimum possible safe speed consistent with existing conditions.
"[...] In high wind conditions, particularly in strong crosswinds, it may be desirable to approach the ground at higher than normal speeds or with partial or no flaps."
That said, please don't interpret my comments as disdain for the use of full flaps, and I certainly don't agree with training for
only flaps 20 landings. The pilot should be profcient in all of the configurations as recommended by the manufacturer, so that he/she is familiar with all of the options available to complete a safe flight with minimal physical or emotional trauma to machine and occupants. Full flap? Partial flap? No flap? Sideslip? Forward slip? No slip? Oversquare or undersquare with a controllable prop? Wheel landing or full-stall in a taildragger?
If it's recommended or permitted by the book (as it is in the case of the airplanes we're discussing), be familiar with it, know its advantages and disadvantages, and use your judgment to fly the way that is best for you under the circumstances.
But hey, I am right....
