C150 Flaps

[newtrainer]

Hi there, ive just started my PPL training and was out with an instructor a few days back.

Taking off from our home grass strip, he asked me to put 10 degrees of flap on. Then after taking off from a solid runway which was longer she said not to bother.

I realise that on a longer runway you have all the time in the world to generate enough speed to creat lift however im a little unclear as to why, on a shorter runway with more friction from the grass you select 10 degrees of flap as surely it creates drag?

Could someone please clarify this for my newbie mind?!

[nick14]

The purpose of using 10 deg of flap for takeoff is that it reduces the takeoff run by producing more lift at slower speeds. The first stage of flap on the C150 (10deg) is all lift and very little drag, the next stage is more drag then lift which is why it is used for landing (20deg) and the 3rd stage(30deg) is all drag and is used for short field landings.

So the first stage is a small deflection and produces more lift and very little drag therefore reducing the takeoff run compared to no flap.

Any clearer?
buckle up
Nick
:ok:

<<edit: Stands back to wait for "Incoming!!">>

[newtrainer]

Perfectly! Cheers ;)

[Tinstaafl]

[pedantic hat on] (with a wave to Keygrip)

Each of those stages of flap add to the ability of the wing to create lift. They also add to the drag produced as a result. It's not really correct to say that 30 deg is all drag & no lift. Without appropriate data in the a/c's manuals it's difficult to say what the proportion of lift & drag increase is as flap is extended.

[/pendantic hat off]

Many a/c are approved to take off or land using a range of flap. Generally for take off as the flap setting increases, the a/c will get airborne in a shorter distance but then not climb as steeply. At some point the additional drag from increased flap is excessive. Fitting a higher horsepower engine could allow more flap for take off since the added HP can be used to maintain climb performance in spite of the increased drag.

C150 performance charts I've seen specify 0 deg for take-off & 0 to 40 deg for landing, with 40 deg specified in the landing chart.

On the other hand, the charts I've seen for C152s specify 10 deg for take off & 30 deg for landing. Cessna increased the HP as one of the changes between these two a/c. They also limited the max. flap setting to 30 deg.

Other a/c types use other flap settings eg C182 can use from 0 to 20 deg for take off, PA32 that I've flow used 0 for normal & 25 for short field deg, etc.

[Speed Twelve]

The sole reason for selecting t/o flap in a light aircraft is to allow a lower rotate speed, and a correspondingly shorter take-off run. Once airborne, even with only 10 degrees flap selected in a Cessna, the climb performance is degraded slightly as the l/d ratio is slightly worse than it is flap up. Otherwise light aircraft would climb with flap selected.

I've asked a few pilots to show me a short-field take-off on check flights in the past and had them rotate at the normal clean Vr with 'short-field' flap selected.

ST

[pilotbear]

I've asked a few pilots to show me a short-field take-off on check flights in the past and had them rotate at the normal clean Vr with 'short-field' flap selected.

What is the point of that? the idea is to leave the ground sooner.

[Final 3 Greens]

Tinstaafl

Interesting that you used flap zero on the PA32, the POH for the -300 version that I flew mandated flap 10 for normal take off and 25 for soft/short and I always wondered what difference the first notch really made (although I did comply with the POH, as I am sure you did with the version that you flew.)

pilotbearWhat is the point of that? I believe that a little inadvertent ambiguity has crept in here, Speed Twelve means either.....

They just did it when he asked them to demonstrate a short field t/o on a check ride, proving that their airmanship was challenged

-or-

He asked them to do it, to demonstrate that the t/o roll was the same or a little longer and the climbout performance and thus the obstacle clearance ability was reduced.

I bet 10p on the first option ;)

New Trainer

In addition the other posters info, another reason for using flaps 10 on a grass strip might be to fly a little earlier and save the landing gear some extra bangs and bumps, if the field is rough, although this would be a secondary consideration to field performance.

Why don't you ask your instructor for his reasons? he'll be delighted that you are thinking through the details of the lesson :D

[Tinstaafl]

Maybe it was 10 deg. It's been 15 years since I flew it.

[Final 3 Greens]

Tinstaafl

Fair enough, wasn't trying to be pedantic, I still don't understand why f10 was required for a normal take off, as it seemed to be a relatively ineffective setting, whereas f25 did make an obvious difference out of a short field.

[newtrainer]

Thanks everyone, you've been a great help

[Maude Charlee]

From the flight manual for the FRA150M (150 Aerobat to you and me) I fly;

"Normal take-offs are performed with flaps up. The use of 10 degree flaps will shorten the ground run approximately 10%, but this advantage is lost in the climb to a 50 foot (15m) obstacle. Therefore, the use of 10 degree flaps is reserved for minimum ground runs or for take-off from soft or rough fields with no obstacles ahead."

Pretty self-explanatory I hope. Given the book take-off distance (clean) to 50 feet at sea level ISA conditions is only 236m with a 10 kt headwind component, then it would need to be a pretty short field to justify 10 flap. However, as the landing distance from 50 feet is considerably longer than the take off distance, then I would suggest that if you can get in, then you can get out again without the need of 10 flap.

Go figure. :confused:

[ComJam]

MC

I think the other point is, the rough field rather than the short field operation, why bounce along with a rough grass strip hammering the aircraft when you can be airborne earlier?

Cheers

As for the PA32........well it'll never replace the aeroplane will it! :)