notch of flap for take off

[kaz3g]

I was going to say where did you learn all that and then I saw the link. Kaz if you fly a Noster on a rough strip and it bounces (as it does) on take off, and you lift it into the air (or give the take-off away) you will get plenty of practice at flying in ground effect. Anyhow that is a comprehensive well written article, very applicable to what we do. Have you had your new tyres fitted yet ? Nev

Hi Nev

 

Pretty good I thought, too.

 

Yes, I can grease 4 or 5 out of every 10. I can manage with no more than a tiny skip for most of the rest. But OMG, just now and then....especially when doing wheelers! You can't ever take a lady for granted.

 

I fitted new tyres AND new bungees a couple of weeks ago. So the first couple of landings after that were exciting. They were on bitumen so I went down to Wahring Field (grass gliding strip about 20 NM south) and did half a dozen T&G's to bed the bungees in. Much more sensible :-)

 

Lethal weapons those bungees, aren't they?

 

Kaz

 

 

[Marty_d]

The POH for some aircraft with flaps don't recommend flaps for takeoff. e.g The C172 POH says zero flap for normal and short field takeoff and 10 deg flap for soft/rough field takeoff.

Really?

 

It was a lot of years ago but I remember always using 10 degrees flap on take off in the C172. Can't remember what the POH said but it was certainly on the checklist.

 

 

[kgwilson]

Really?It was a lot of years ago but I remember always using 10 degrees flap on take off in the C172. Can't remember what the POH said but it was certainly on the checklist.

Yep really. A lot of schools teach 10 deg flap for all takeoffs & that is their prerogative so it will be in their checklist. The manufacturer says otherwise though if the field is not soft, rough or short but it does change with the model. The 172N says zero deg for short field takeoff but the 172P says 10 deg for short field takeoff. Go figure. All say zero deg for normal takeoff & 10 deg for soft/rough field takeoff.

 

 

[Marty_d]

Yep really. A lot of schools teach 10 deg flap for all takeoffs & that is their prerogative so it will be in their checklist. The manufacturer says otherwise though if the field is not soft, rough or short but it does change with the model. The 172N says zero deg for short field takeoff but the 172P says 10 deg for short field takeoff. Go figure. All say zero deg for normal takeoff & 10 deg for soft/rough field takeoff.

To use Dazza's quote... "whale oil beef hooked!"

 

 

[Bandit12]

This thread and many more like it are why I love recflying.com. Interesting aviation topic, plenty of technical explanations and an auld Auster to boot - where else can you get stuff this good!

 

I was thinking from memory that all of my C172 time was zero flap for standard take off and 10 degrees of flap for soft/short-field, but I am a little rusty. I did watch one accelerate on a grassy strip before pulling on full flap to break the ground contact and balloon over the trees at the end of the strip, followed by sink into ground effect again afterwards. Looked very hairy and would not want to have been on the inside at the time.

 

 

[nong]

If your 172 is lightly loaded in thick air it doesn't matter if you ignore the book and use flap for take-off.

 

If you're hot, high 'n heavy, ignore the book at your peril.

 

 

[Dafydd Llewellyn]

OK, thanks FH, so what you're saying is that since climb (any climb at all - rate or angle doesn't matter) is purely a factor of power in excess of that required to maintain height, then the total power available reduces as DA increases, and so the excess power available also reduces as DA increases. Therefore, as DA increases, we run out of of excess power available at some stage? If that's Ok so far, then since the plane requires a bit more power to maintain height (or rather, fly straight and level) with any flap at all, than it does without any flap (because there is a bit more drag with any flap extension), it would run out of excess power sooner (i.e. at a lower DA) with some flap, than without any flap.OK, I can see that but we haven't factored in the wing performance issues and the 'cleanness' of the airframe. A little flap gives a relatively large increase in lift compared with the small amount of induced drag increase, and that allows the plane to fly slower than it would without the flap. So whilst the induced drag might be marginally higher, the parasitic drag at that lower speed is likely to be lower by more than the increase in induced drag because parasitic drag is a square function of speed and induced drag is linear with lift increase.

 

This is why I don't think the recommendations for jet aircraft operations should be applied to our kind of aircraft. Jet aircraft are so clean that their parasitic drag is very small compared with their induced drag whereas our aircraft have exactly the opposite drag characteristics, parasitic being the main consideration.

 

From a practical point of view in our Lightwing for example, if we were taking off at a DA where we were so close to not having any power margin available for climb we probably shouldn't be attempting to fly, but if we assessed the conditions, strip length and all that, and considered that we could make it, but only just, would you use 10 degrees of flap or none?

Oh well, in for a penny...

 

There are three fundamental aerodynamic considerations: Firstly, when the aeroplane is at fast cruise, it needs a small angle of attack, so the fuselage attitude tends to be nose-down. Unless the designer wants it to look like a shovel-nose shark hunting mud-crabs, he mounts the wings on the fuselage at an angle such that the nose-down attitude at cruise is minimised. That usually means that it needs a very tall undercarriage to allow the maximum angle of attack at takeoff. Flaps can be (often are) used to allow the wing to achieve its maximum lift at takeoff without needing to be excessively nose-down at cruise. In other words, extending the flaps has (to a degree) the same effect as changing the wing rigged incidence. Handily, this also increases the maximum lift available - Yay! Two birds with one stone!

 

However, there's no free lunch; flaps increase the drag as well as increasing the lift. So in order to take full advantage of flaps, the aircraft requires some excess power. So at higher density altitudes, when the power available is reduced, the benefit of flaps tends to be cancelled by the reduction in available power to climb.

 

The manufacturers of small aeroplanes generally do not go to the trouble of producing elaborate performance data that describes where the cross-over points occur - though they will sometimes (especially in the older Cessnas - if they had Flight Manuals at all) - provide take-off and climb data for both take-off flap setting and flaps retracted. Nowadays they mostly don't bother, because the average pilot never reads the FM anyway.

 

I hope this goes a little way to explaining why . . .

 

 

[turboplanner]

My theory studies became very practical one day when I faced a row of pine trees at low level and the nose wouldn't come up any higher than about half way (100 kt cruise at zero flaps).

 

Fortunately in the BAK course a few of us did together the instructor made it very simple - "Full flap = greatest climb angle at slowest forward speed"

 

Through that I was able to climb over the pines.

 

One stage of flap on takeoff gives you a higher departure angle on takeoff than no flap, and one day will come in handy and allow you to say SH$T!!! as a powerline slips underneath you just off the runway end.

 

 

[Dafydd Llewellyn]

My theory studies became very practical one day when I faced a row of pine trees at low level and the nose wouldn't come up any higher than about half way (100 kt cruise at zero flaps). Fortunately in the BAK course a few of us did together the instructor made it very simple - "Full flap = greatest climb angle at slowest forward speed"

 

Through that I was able to climb over the pines.

 

One stage of flap on takeoff gives you a higher departure angle on takeoff than no flap, and one day will come in handy and allow you to say SH$T!!! as a powerline slips underneath you just off the runway end.

Indeed it does - provided you have sufficient power. Don't try it in a PA 28-140 on a hot day at full load, though.