Why do some types recommend full flap for short take off

Just fantasizing: Might full flaps further increase lift in ground effect?

The husky POH is full flaps for short take off. Although full flap is not so much a drag flap.

That being said, I always just power on, tail up then pop full flap, then clean up in the climb with a bit of speed.

There are some types for which flaps are up or down, for those, it’s full flaps for takeoff.

I too use the full aileron – match the flap trick for electric flap Cessnas, where the POH would allow it. On a standard Cessna, more than 20 flap will lengthne your ground roll, and impede climb. However, in a soft field, the slight benefit of ground effect might get you out of the muck. Do not attempt this if available runway length is a concern.

For manual flap Cessnas (typically 180/185 – though other older models too), the “pop on full flaps” is a float flying trick, and it does work. That said, if you need to use that trick to get off the water, you’re probably already operating the plane outside ideal conditions, and should be asking yourself why. The plane won’t accelerate onto the step well with full flaps, but once on the step, near takeoff speed, the sudden application of full flaps gives a bump of lift, without having to pitch up much. Pitching up in a floatplane risks dipping the aft hulls of the floats back into the water, and then you slow down again from the water drag. There is no corresponding benefit for landplanes, as they are okay having the nose raised to lift off.

For electric flap Cessnas, it’s pointless, the flaps move too slowly to create any benefit from rapid movement. On the 172 and 182 floaplanes, set as the POH says, and leave alone.

Full flap takeoffs, post liftoff flight in ground effect, and very cautious climbout in Cessnas are not the horror story some people say, but still, an added risk for very little benefit for any operations which the plane is intended to be doing!

If we fly constant speeds as per POH then effect of flaps is very intuitive, anytime one start to talk about Drag/Lift trade-off people will advise to fly one speed and set one stage of flaps to make their life easier

STOL guys always fly near stall speeds and don’t do by book speeds and will dynamically change their flap settings, I think best climb angle is dynamically achieved by accelerating on clean flap for best wheel grip, tail up to zero AoA, pop more flap to lift off to max AoA in ground effect, accelerate on less flaps on initial climb and clean later, if the aircraft is already highly overpowered (150hp) and a really low stall speed (35kts), one can just start with full flaps?

Obviously, the effect of flaps near stall speed is not that intuitive at all, in absence of power polar curve is fully parametrised by 3 values: stall and min sink speeds (kts on ASI) and the min sink value (aka fpm on VSI), so we have 3 type of flaps:
A) Stall flaps (same “landing flaps”): reduce stall speed while min sink speed and min sink value remain the same
B) Climb flaps (same as “lift only flaps”): reduce sink value while stall speed and min sink speed remain the same
C) Speed flaps (same as “drag only flaps”): increase min sink speed while stall speed and min sink value remain the same

Thinking in terms of Stall/Climb/Speed flaps is far more intuitive than Drag/Lift curves, any aircraft flap design and setting can be decomposed into a combination of A, B, C), those with high ratio B to C should be used for max angle climb (basically allows you to fly higher and slower)

This thinking is used in “glider flaps”, these flaps don’t change stall speeds (so never used for landing one use spoilers, airbreaks or sideslip), to climb steeper one sets climb flaps and fly slower (full flaps allow lower min sink rates), to glide shallower one sets speed flaps and fly faster (no flaps or negative flaps allow faster min sink speed), I think PA18-150 on full power is flown like glider in a strong +1500fpm thermal: full flaps and just few kts above stall maybe this is applicable to LaMaule which have that many flaps setting as gliders (including negative flaps) ?

Ibra wrote:

people will advise to fly one speed and set one stage of flaps to make their life easier

Not this people. I don’t know what a “stage” of flap is, but I will fly at speeds suitable for the phase of flight, and us flaps as recommended in the POH. In float flying, alternative flaps settings are occasionally used, when water conditions makes getting unstuck from the water difficult. Otherwise, the use of flaps is not “dynamic”, they are not a flight control. They are set to supplement the plane’s flying characteristics as desired.

Ibra wrote:

STOL guys always fly near stall speeds and don’t do by book speeds and will dynamically change their flap settings,

Not this STOL guy. Flying close to stall speed, other than for practice stalls at altitude, or in the flare at touchdown, introduces risk far out of proportion to any benefit. Most STOL modified planes, and all STOL manufactured planes, have flight manuals which describe the most suitable speeds for operation, and those speeds are best. Yes, there are some very foolhardy pilots who push performance past being safe (I’m thinking of the Valdez Alaska STOL competitions). Yes, they get better STOL performance, but with horrible safety, and damaged planes. Experienced STOL pilots operating their planes in the real world, and keeping safety in mind, fly the flight manual speeds and flap settings.

The Twin Otter is an example of an airplane with amazing STOL performance. I was trained to fly STOL takeoffs and landings in it by a retired deHavilland test pilot. However, the procedures he trained me were removed from approved flight manuals, as pilots kept wrecking Twin Otters trying it. The benefit of the 100 foot shorter ground roll was not balanced well against the number of wrecked Twin Otters.

Aside from goofing around at your home airport, doing things you would never admit to your insurance company, when you’re “away”, you’ll do whatever you can to avoid needing to fly STOL techniques. I’ve flown into lakes with no road within 200 miles, and no people within 75. I’m hardly going to start fooling around flying at stall speeds to squeeze into a tiny spot, when a failure would leave me really far from help, and very difficult to recover the wreck. I’ve flown into remote lakes to help recover wrecks, caused by fools doing that kind of thing. When I’m landing into a small lake, to recover a wreck, I’m thinking to myself: “Gee, the last guy to land in here wrecked his plane, what will I do differently?”. So I fly a normal, on the numbers book approach and set myself up for a similarly compliant takeoff later.

I was asked to mentor a formal test pilot, on a formal test flight, in a Robertson STOL Cessna 337. He wanted to do a STOL landing. He had not flown a propeller powered plane in 25 years, so I told him no. I still had to take control away from him to prevent his crashing it when he started to fly too slowly on approach. I guess he’d been reading about STOL operations and wanted to try for himself. Not during my flight with him!

RobertL18C wrote:

on early tricycle types (182A) where it doesn’t make sense, with potential wheelbarrowing if not carried out perfectly.

The 182A with a STOL kit was a good performer. I used to present the improved capabilities by explaining to prospective STOL kit customers, that with a STOL kit, the plane would safely and comfortably do at gross weight, what it would do at a light weight in a factory configuration. I was firmly told by my boss that I was demonstrating the STOL kitted Cessnas too aggressively to STOL kit customers, after learning after a demo flight that I had scared a customer speechless with my standard demonstration routine. The fact that I could fly the plane foolishly did not make it a good idea! After that, I just flew good demonstrations, by the numbers, and everyone was happy…

RobertL18C wrote:

Just intrigued why drag flap would help – there is no appreciable reduction in stall speed between 20 degrees and full drag flap, and yet backcountry practitioners pop full flaps on short T/O – and then demonstrably accelerate sluggishly in ground effect.

I would say it is largely a factor of engine power. Flaps will increase lift, but also drag, both proportional to the square of the IAS. Keeping IAS low enough, and the propeller thrust has no problem overcoming the drag. But, at that IAS the plane also has to fly. Then there is the flap itself. Lots of different configurations, and different effectiveness.

Will be good to know the spread between 50ft obstacle takeoff distance with half flaps and full flaps on PA18-150? you may find that all the discussion is about 30ft

Gear up on complex for best angle climb is a similar exanple, the gear does not change stall speed and extra drag from the gear down on slow Vx climbs is highly negligeable, so not worth fiddling around on steep climb, the resulting difference on 50ft obstacle takeoff performance is barely 100ft reduction of distance (of course raising gear up will make a huge difference to Vy or cruise climbs but allmost no difference for a Vx climb)

Obviously, all becomes irrelevant when you have lot of excess of power but could be problematic in low power (say aircraft can’t accelerate on gear down? or full flaps?), the same apply to anyone fiddling with full flaps: there is a power setting where one is able to lift off way less than Vs0 with the yoke but not able to accelerate level or climb to anywhere higher with the power

During my ppl training in US (C152) full flap was recommended for soft field TO to transfer the weight of the airplane to the wings as soon as possible. when airborne remain in ground effect and reduce flap to normal take off before continuing to climb. Good fly the b..y thing exercise :)