Flaps

[benflyn]

At what angle does max lift end ?


Thanks

Benflyn

[Lowflybye]

At the critical angle of attack of course.

[MikeW]

When you can't pull the handle back any farther

Mike W.

[Hottshot]

I thought it was when you ran out of power!!..... man back to the drawing board.....

[Mountain Doctor]

When you run out of MONEY. We all know that's what really makes an airplane fly.

[MikeW]

No bucks, no Buck Rogers

[iceman]

geez we're getting into the technical stuff again...

[maules.com]

Benflyn, you awoke the comics in this group. Well done.
I imagine the question to be related to where lift becomes drag in flap angle settings.
Maybe a rephrase and challenge for the best description is in order.
Over and out.

[benflyn]

I will try one more time before I bring out the crayons and a picture.

At low flap angles say 20 degrees it is mostly lift, very little drag.

At high flap angles say 40 to 48 degrees there is no increase in lift it is all an increase in drag.

Maules.com

I imagine the question to be related to where lift becomes drag in flap angle settings.

This is another way to state it.

Thanks

[Lowflybye]

Benflyn, you awoke the comics in this group. Well done.

Hey Jeremy, I resemble that remark. However, I did answer his question by deninition.

At what angle does max lift end ?

Critical Angle of Attack - noun: The angle of attack, greater than or equal to the angle of attack for maximum lift, at which there is a sudden change in the airflow around an airfoil with a subsequent decrease in lift and increase in drag.

[Lowflybye]

I will try one more time before I bring out the crayons and a picture.

At low flap angles say 20 degrees it is mostly lift, very little drag.

At high flap angles say 40 to 48 degrees there is no increase in lift it is all an increase in drag.

All flap settings beyond 0 degrees add some form of drag...induced drag and parasite drag. If I remember correctly, in high wing aircraft the general rule of thumb is 15 degrees deflection (or the first notch) produces greater lift than the corresponding drag coefficient...this is why the first notch is often recommended for takeoff. As deflection increases past this point the drag coefficient increases exponentially until an angle is reached at which the flap is generating greater drag than lift.

All of this would be dependent on airspeed as induced drag is greater at slower speeds (inversely proportionate to the square of the airspeed) while parasitic drag is greater at higher speeds (proportionate to the square of the airspeed).

All that to say, as I understand it the answer to your question is not a fixed angle of deflection but variable dependent on speed and angle of attack. The first notch is typically greater lift than drag with all subsequent notches adding more drag than lift at normal approach speeds and angles of attack. If you use power and high angles of attack for short field landings then the critical flap angle will be different from a more shallow approach with higher speed on a wheel landing.

***DISCLAIMER - this is my limited understanding of the aerodynamic laws...someone with a better understanding may add some corrections***

[noe flightrisk]

I liked benflyin’s original question and Lowflybye’s answer, which was right if by “maximum lift” we mean maximum coefficient of lift (which is used along with speed, wing area, and air density to calculate lift). As Lowflyby correctly points out, maximum coefficient of lift occurs at an angle of attack (AOA) just slightly less than the AOA at which the boundary layer separates and the airfoil stalls. For a given airfoil (and flap setting), AOA determines both coefficient of lift and the ratio of lift to drag (L/D). The main purpose of flaps is to allow the wing to reach a higher coefficient of lift than without them, but they also cause more drag for a given coefficient of lift than would be the case with no flaps, which may actually be beneficial at times. On the Maule, both 40 and 48 degree flap settings do provide a higher maximum coefficient of lift, proven by the fact that each notch does incrementally reduce stall speed.

It didn’t come up in this discussion yet, but I often hear statements about changes in lift and drag in absolute terms for a given change in flap angle. However, there are no absolute statements we can make about “the” lift or “the” drag for a given wing and flap setting. In fact, for a specific wing configuration, lift and drag are determined by all of the following: speed, air density, and AOA (which determines coefficient of lift). And the ratio between them, L/D, changes with speed and AOA.

Nevertheless, we can answer some questions about the incremental effect of the last notch of flaps on lift and drag using the fact that glide ratio (forward travel divided by altitude lost) is identically equal to L/D, the lift to drag ratio. Does the last notch of flaps add more drag than lift? Yes, we know it does, because it reduces the glide ratio. Does it provide any additional lift? See above for why that is a vague question. OK, then, does it provide additional lift at a given airspeed, air density, and AOA? Yes, all things equal, at speeds below the 40 degree stall speed, the wing with 48 degrees of flaps does generate more lift than the one with 40 degrees.

I suspect much of the confusion about flaps and lift is because commonly used texts plot coefficient of lift versus absolute angle of attack. Things are much clearer when relative angle of attack (where the coefficient of lift is zero at zero degrees AOA) is used instead.

[a64pilot]

The Jim Bob, crop duster / bush pilot answer is, match your flap angle with the aileron max deflection angle, anything more than that is more drag than lift.
Not scientific at all, but it seems to work, the theory being the aircraft manufacturer has set the aileron throw at a point that produces the most roll rate, but doesn't let adverse yaw get out of hand.

[Mountain Doctor]

On the Maule that would correspond with 1 notch (past 0) or 24 degrees.

Makes sense.

[noe flightrisk]

I respectfully note that some facts seem counterintuitive. And some well-known "facts" are actually folklore.

On our airplanes TOTAL lift is always greater than total drag at every flap setting, at least for speeds above stall and below redline. The proof can be seen by using the aerodynamic fact that glide ratio is identically equal to the ratio of lift to drag, and noticing that at every flap setting our planes’ glide ratios are greater than 1:1. Just think, at 60 statute mph a glide ratio less than 1:1 (i.e. one where drag is greater than lift) would imply a sink rate of more than 5280 fpm and steeper than a 45 degree glide slope! We never see that in calm air, so lift is always greater than drag at these speeds.

If, on the other hand, we are talking about INCREMENTAL lift versus drag added by each notch of flaps, the answer is that each notch beyond 0 degrees adds more drag than lift. Even 24 degrees. We know this because the glide ratio decreases each time we add a notch. My M7’s best glide ratio at 0 degrees is about 10:1 and at 24 is about 8:1. So, despite the folklore, it is not true that 24 degrees adds more lift than drag. I haven’t tested -7 degrees, so I don’t know if it is an exception.

Note that the maximum (i.e. at max AOA before stall) coefficient of lift goes up for each notch of flaps. Based on inflight measurements of my M7, I calculate a maximum coefficient of lift of 1.3 at 0 degrees flaps, and a maximum of 1.7 at 24 degrees. For this type of wing I expect (but have not actually measured) about 2.5 at 48 degrees. The parasitic drag coefficients are 0.038 and 0.066 respectively.