Flaps for take-off, why?

Maoraigh wrote:

C152 has 3 flap notches.

Yes, but you can still position the flap lever at any point you want….

Airborne_Again wrote:

The PA28 POH recommends either no flaps or two notches (25°). So why use one notch of flaps on a PA28 and not two!?

One or 15 notches, it doesn’t matter.

LeSving wrote:

One or 15 notches, it doesn’t matter.

Now you’re just being silly.

Some airliners have both: Notches for particular settings and “Dial a Flap” settings for take off. The MD80 comes to mind as one example, where you could set a particular flap setting using a wheel on the center pedestal, which would allow any flap setting between 0- to 13- and 15- to 24-degrees.

The MD11 had a similar setup with settings between 10 and 25° in addition to being able to use the ailerons as additional flaps using what was called a deflected aileron system, which would set the ailerons parallel downwards to a particular position. This gave additional lift on take off. Weight penalty with deflected ailerons u/s was quite massive.

Airborne_Again wrote:

Now you’re just being silly.

Indeed It was a silly answer to a silly question But of course, no questions are silly and all that, as you probably know, so I have probably misunderstood your line of reasoning somewhere?

MattL wrote:

I often encounter this when testing on PA28s
“why did you use 10 deg flap for take off?”
Candidate – “my instructor told me to”

For take-off PA28 use flaps 0 or flaps 2 only. Bad instructor, except for last point below.
MattL wrote:

reconfigure on the runway or when climbing away?

On the runway, it takes literally 1s with a manual bar. On planes with electric flaps I don’t do Touch&Go’s on short runways.
Ibra wrote:

if one selects 2 stage of flaps in PA28 and drive it on the ground up until 80kts, the benefit of 2 stage of flaps is likely to vanish away

Impossible, even if you bury the nose-wheel into the ground the plane will want to fly before 80kts.
Ibra wrote:

The other thing, I saw people putting 2 stage of flaps in PA28 which is the correct performance takeoff setting but holding it to “rotate at 65kts” rather than just letting it “liftoff”

Exactly, a little bit of pull on the yoke (in particular if the short field is also soft) and the plane wants to fly att 50-55kts on flaps 2, let it go.
Airborne_Again wrote:

The PA28 POH recommends either no flaps or two notches (25°). So why use one notch of flaps on a PA28 and not two!?

Had to learn to do flaps 1 take-offs on a 2km runway during my IR training. I’m pretty sure this is done on purpose to force students to use checklists.

Arne wrote:

Had to learn to do flaps 1 take-offs on a 2km runway during my IR training. I’m pretty sure this is done on purpose to force students to use checklists.

In that case, why not flaps 2…?

Airborne_Again wrote:

In that case, why not flaps 2…?

Excellent question… Went through the documentation I had and all the documents edited by the club says 10° normal take-off…while the POH says no flaps…

hanski wrote:

I cannot tell if using flaps save any money, as it probably adds gas consumption a little, but as tires cost about 300 a piece, it hopefully saves them. Decades ago I read about some (probably German) test about car tires, where they found out that the tire wear increased dramatically (30-50% if I remember right) when the car speed went up just a little like 80→100. So I hope to avoid some wear if the plane gets airborne 10 km/h earlier. But like mentioned, I have no clue if that actually saves money if we count everything…

I think it’s quite different for car. They still need to turn and adjust speeds and also the amount of friction remains the same (you don’t want a car designed to have some lift effect from its aerodynamics because then you quickly end up outside of the road when it turns). For airplane, the extra ground roll before lift off is at speeds where the wings are generating lift, but in case of 0 flap not enough to get you airborne, which means less friction between the tires and runway and since you are not turning (curved runaway are rare) I would expect the wear of the tire to be minimal, but that’s just a guess maybe I forgotten some other factors?

For the 185; on wheels, we can use 20° of flaps for take off which can be good for soft field take off, but in general no flaps. But on floats, as mentioned by pilotDar, we use 20° and now thanks to him, I know why :-)

There is a difference between 4×4 car drive with engine on wheels and getting pulled by a propeller

The wear on the tires during takeoff is very minimal, anyway lot of weight have moves from wings to tires as you get past VS0, as we know the wings wear out with aerodynamic forces but it takes 20000h the amount of tire wears on flapless takeoff is likely to be very minimal, proportional to extra distance ((VS1-W)^2/(VS0-W)^2), it should vanish at VS1 liftoff and at VS0, only a small fraction pass-through (this likely depends on L/D drag ratio and T/N friction and MTOW), long story short, it’s “rien du tout”, please find another “material” excuse, on wet soft grass, the tire wear is likely to be the flaps are used for a different reason…

For flapless landing, it’s different story, you actually using flaps to avoid burning wheel breaks or burning rubber…I was teaching flapless landings (it has to be learned with electric flaps and going to try on grass was not a good option), we had few until the tower called “N-FM, I think you had some smoke on the last touchdown” !