Flap Use During Landing

 

 

Itís amazing what controversy can arise, from the use of flaps during landings in light single engine aircraft.Youíd think it was a pretty dull subject, but people sure can get cranked up about it.

 

Let me first say that in a heavier, faster aircraft such as the C421 or L39, especially with a short runway, I always use full flap for landing.But they are different animals than a light single engine trainer, which might not even have any flaps (e.g. Cub, Champ, Chief, T-craft, etc).

 

A light single engine trainer can almost always be landed with no flap, any amount of partial flap, or full flap.Generally there is considerable excess runway available.A light single engine trainer can actually be landed in 500 feet but you will rarely see it use a 500 foot runway.Or even a 1000 foot runway.So when you are using a 4000 or 6000 or 8000 foot runway, there is considerably room for error.

 

Some people will opine that full flap should be used all the time for light aircraft, but thatís wrong, for several reasons.For example, in the C172M POH, it says to use minimum flap required during crosswind landings.Hint: do what the POH says, not what some ďexpertĒ tells you.

 

The ďfull flapĒ crowd will point to the reduced stall speed (resulting in slower touchdown speed) as compared to no flap.But thatís wrong too, because if you (again) look at the POH, the decrease in the stall speed beyond 10 or 15 flap will be minimal.

 

And thatís an important lesson:the overwhelming majority of stall speed reduction will come before 15 degrees of flaps - look at your POH.Beyond that, simple flaps in light single engine trainers merely increase drag, which is really only useful when you are approaching over a very steep obstacle, and have difficulty keeping your approach speed down on short final without slipping.

 

That is NOT a normal approach, which pilots perform to a certified runway at a public airport.

 

The older C150 had 40 degrees of flaps.But on the newer C152, Cessna decreased the maximum flaps to 30.Older C172ís had 40 flap.Newer C172ís have 30 flap.Heck, the original O-1 Cessna Birddog had 60 flap, for landing on 400 foot strips on the sides of limestone karst mountains in Laos, during the Vietnam war.

 

But Iím betting you probably donít do much of that.Obviously, Cessna thinks that 30 flap is plenty, for any kind of normal operations.In fact, there is an STC for older C172 to reduce the maximum flap from 40 to 30 which results in an increase in maximum gross weight.

 

This is because the maximum gross weight of the 172 is determined by itís ability to overshoot, and successfully climb with full flap.This is actually a very dangerous phase of flight.If you go through the accident reports, an amazing number of people crash and die, unsuccessfully trying to overshoot with full flap.This is a serious problem.

 

This brings me to a crucial point:in a training environment, we have to leave room for student error, even if some self-professed experts (somewhat incredibly) loudly proclaim that this isnít required.

 

With this in mind, I recommend that students use maximum 15 flap for touch and go landings (which frankly, I donít like much in the first place).This yields a slow stall speed, but doesnít have so much drag (of full flaps) that they require large amounts of throttle on final, and they will have better luck climbing after an overshoot without the drag of full flap.

 

Depending on the aircraft, they might not want to use any flap at all.For example, doing tailwheel training, I do NOT want the student looking inside the cockpit for the flap lever, as we careen down the runway at high speed after landing.Thatís a really great way to give your mechanic a winter project.Or more likely, write the aircraft off entirely.So for tailwheel training, doing touch and goes, I really like to approach with whatever flaps work for takeoff (in the Maule, 15 degrees) so that there is no re-configuration required on the runway.For most little taildraggers, that means we will be approaching no flap.

 

Some people will complain that they need to use more than 15 flap, to get drag when they are high on final.Horse puckey.Youíre in a light single engine trainer, so first reduce power and then do a slipping turn from base to final, and a forward slip on final.If reducing the power to idle and slipping doesnít kill enough energy to fix your incredibly high and screwed-up approach, time to go around, which is no big deal because you only have 15 flap, right?

 

Donít push a bad approach into a bad landing.Donít be afraid to overshoot Ė which is no big deal, if you only have 15 flap.

 

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acboyd@gmail.com

Sep 2014