Flap Type and Efficiency

[colmbo]

Since extending flaps increases your lift for the same speed and pitch, you have to trim nose down to continue flying level. You might think this means you decreased your AOA instead of thinking that you effectively increased the incidence of the wing so you adjust for that by lowering your nose.

You do not climb because of extra lift, you climb as a result of excess power.  If the airplane maintained the same speed after flap extension you would have to reduce power to maintain level flight.  Any power change will requires a trim adjustment.

[FLS]

You do not climb because of extra lift, you climb as a result of excess power.  If the airplane maintained the same speed after flap extension you would have to reduce power to maintain level flight.  Any power change will requires a trim adjustment.

Why do you suddenly have excess power?

Flaps increase camber, not AOA.

How is the effect of more camber different from the effect of increased AOA?

[Anaxogoras]

Increasing lift is not what makes a pitch-up moment on the aircraft.  Dropping flaps on most aircraft in-game does induce a nose-up pitching moment--very important to understand the difference.  HTC has mentioned that flap-induced pitching moments are not necessarily modelled correctly in-game.  I'm not sure what the issue is, but he hinted in another thread that they were looking at a method to correct it.

link?

[FLS]

Increasing lift is not what makes a pitch-up moment on the aircraft.  Dropping flaps on most aircraft in-game does induce a nose-up pitching moment--very important to understand the difference.  HTC has mentioned that flap-induced pitching moments are not necessarily modelled correctly in-game.  I'm not sure what the issue is, but he hinted in another thread that they were looking at a method to correct it.

Just to clarify my question, I understand that the pitch down moment from flap extension is not caused from the increase in lift. I don't know if HTC models the change in location of the center of pressure from flap extension on a cambered airfoil but I assume that the pitch up in Aces High is caused by increased lift.

What I don't understand is the interaction of a pitch down moment and the increased lift when extending flaps. The P-38 POH mentions both and I don't expect it would drop it's nose and climb.

[Stoney]

link?

I'm trying to find it.  It was in the thread where we went around and around over whether or not the elevators provided an up trim force or a down trim force.

[Stoney]

Just to clarify my question, I understand that the pitch down moment from flap extension is not caused from the increase in lift. I don't know if HTC models the change in location of the center of pressure from flap extension on a cambered airfoil but I assume that the pitch up in Aces High is caused by increased lift.

What I don't understand is the interaction of a pitch down moment and the increased lift when extending flaps. The P-38 POH mentions both and I don't expect it would drop it's nose and climb.

Well, this is where things start to get complicated.  You are correct in identifying the discrepancy between the P-38 POH and what happens in-game.  The P-47 does the same thing--there may be others that should but don't--I don't know.  Not all aircraft will experience a nose-down pitching moment from flap deployment.  I'll go ahead and profess I won't be able to describe the entirety of issues within a short post.  The best thing I can recommend is to do some reading online.  Even Wiki has some decent aerodynamics pages.  Ultimately the net pitching moment of the aircraft includes a lot of variables, but read about both the center of pressure, aerodynamic center, and pitching moments.  What happens in the P-38 POH is that using the flaps creates a negative (nose down) net pitching moment, whereas what happens in-game is a positive (nose up) net pitching moment.

To answer your last question though, Like Colombo said, flaps increase camber, not AoA.  Generally speaking, camber increases lift at the same angle of attack, so that at an even lower angle of attack, the wing could produce the same lift, theoretically.  So, you could have a lower angle of attack without sacrificing lift generation, and ultimately, this is another benefit of flaps for landing, as a steeper approach can be made (increasing the pilots view of the runway environment) without sacrificing lift generation.

[colmbo]

Why do you suddenly have excess power?

Since extending flaps increases your lift for the same speed and pitch, you have to trim nose down to continue flying level.

You don't have excess power in your example, therefore no climb.

Excess power is that above what is needed to maintain altitude at a specific speed.  You can slow the airplane and get a sustained climb at a lower airspeed without increasing power.  If you increase power and maintain airspeed you will climb.  And, of course, if you reduce power and maintain airspeed you descend.  Climb comes from power, not lift.  Lift equals weight in unaccelerated flight.

How is the effect of more camber different from the effect of increased AOA?

Camber is the shape of the wing, AOA is the angle of the chord line to the relative wind.

[Mace2004]

To answer your last question though, Like Colombo said, flaps increase camber, not AoA.  Generally speaking, camber increases lift at the same angle of attack, so that at an even lower angle of attack, the wing could produce the same lift, theoretically.  So, you could have a lower angle of attack without sacrificing lift generation, and ultimately, this is another benefit of flaps for landing, as a steeper approach can be made (increasing the pilots view of the runway environment) without sacrificing lift generation.

You're partially right.  Extending flaps does increase camber but it also increases AoA.  AoA is determined by the angle between the wing chord line and relative wind.  The chord line is an imaginary line drawn from the leading to trail edge.  As the flaps are lowered, the trailing edge is lowered changing the angle between the chord line and relative wind, i.e., AoA.  As flaps are lowered this increase in AoA and C/L will usually cause an airplane to "balloon" upwards during the deployment (especially if you're relatively fast when you drop the flaps) so the nose needs to come down to counteract this and lower the AoA.  Essentially, flaps change the angle of incidence of the wing (angle between the chord line and aircraft centerline) so it changes the pitch attitude required for a specific AoA.  This is why a properly trimmed aircraft will have a lower pitch attitude with flaps down then it has with them up.

Also to answer the question of the difference on the effect of increased camber vs increased AoA...well they both are means to increase C/L.  The question is how much lift do you need and at what speed?  A thin, relatively flat wing cannot generate a C/L as high as an equivalent highly cambered wing.  The problem is that a highly cambered wing is "fat' and you've got to push that through the air which is easier with a thin wing.  Flaps let you have both, a thin low drag wing for speed and a thick high C/L wing at low speeds.

[BnZs]

A tendency to pitch nose-down rather than up would be a benefit to flap-using planes. The nose up pitching tendency is quite awkward to fight against when trying to fly/gain a guns solution, the nose down tendency is not in my experience.

[thorsim]

does it not also effect the efficiency of the flap?  or efficiency using the flap

as your wing camber changes so does your angle off your most efficient chord line(in most planes the line of the wing re the horizontal stab (i am thinking) ...

so would not your efficiency suffer more in climbing and turning here as you are "pulling" up even more against your new nose down "natural" state of flight.

obviously the lift improves but here is another reason for drag as most planes can't change the angle of attack of it's horizontal stab so it would be in a skid.

don't the flaps and assumed associated lower speeds adversely effect the achievable and or sustainable AOA?

errr does it make pulling the nose up and or keeping the nose up more difficult?
 
t

[Angus]

Horizontal stab and a skid?
It will mean a different A.o.A. which makes a different lift, so some difference to the elevators.

[FLS]

... I'll go ahead and profess I won't be able to describe the entirety of issues within a short post...

Ya I don't know either.     Do you think the P-38 climbs while pitching down? The POH suggests that there is a small pitch down within the greater lifting force but maybe I'm misunderstanding it. Hard to imagine adding lift and losing altitude although I know the flap extension requires a trim change. I'm wondering if the effective change in incidence can change the pitch attitude down while increasing the AOA.

I still see no reason to think the P-38 looping behavior is incorrect even if it's not the proper way to fly a loop.


Colmbo you consistently miss the point and define basic concepts that we already know. I'll try to be easier to understand.

[Stoney]

You're partially right...Essentially, flaps change the angle of incidence of the wing (angle between the chord line and aircraft centerline) so it changes the pitch attitude required for a specific AoA.

Thanks for the clarification vis a vis AoA.  I have a tendency to think of the chord line and angle of incidence as "fixed".  Still, the "balloon" effect is not common to all aircraft.  Like we've discussed before, introducing flaps in the P-38 and P-47 as two examples, should introduce a noticeable nose-down pitchiing moment, per their respective POH's.  Yet, in-game, there is a conspicuous nose-up pitching moment. 

[hitech]

Stoney:

HTC has mentioned that flap-induced pitching moments are not necessarily modelled correctly in-game.

Center pressure,Cl,Cd,Zero Lift angle, Max AOA are all accounted for with change of flap settings.

We currently do not account for the change in the Cm curve.

HiTech

[FLS]

Stoney:

Center pressure,Cl,Cd,Zero Lift angle, Max AOA are all accounted for with change of flap settings.

We currently do not account for the change in the Cm curve.

HiTech

Do you use the Cl curve for the tailplane instead of the Cm curve?

...I have a tendency to think of the chord line and angle of incidence as "fixed". Still, the "balloon" effect is not common to all aircraft.  Like we've discussed before, introducing flaps in the P-38 and P-47 as two examples, should introduce a noticeable nose-down pitchiing moment, per their respective POH's.  Yet, in-game, there is a conspicuous nose-up pitching moment.

Another interesting thing that happens when extending flaps and increasing the incidence of the flapped section is that the washout increases so the flapped section of wing stalls first. This lets the ailerons remain effective further into the stall.

So if the P-38 pitches down with flap extension it's setting a higher trim speed with a higher coefficient of lift and if left alone it will nose up when it exceeds that trim speed? I can see where that might be a problem in a loop if it pitched down for every flap setting. Aircraft like the F4U that pitch up with larger flap angles would do better.