Hi Robert,There has been heated discussion on Flight1 forum related to their latest product - Piper Meridian. Contrary to what some of us recall from our flying experince lowering flaps on this simulated craft causes a pitch *down* moment. I am curious how it matches your vast flying experience ?BTW, this is what I found on the subject on some internet site:Just adding flaps will cause an aircraft to pitch up or down depending on how the change in lift and drag created is positioned around the center of gravity. Flaps lowered on high-wing usually cause a nose-up pitching moment as the camber changes the lift around the center of pressure. The resulting drag also causes a nose-up pitch. Low-wing aircraft flaps causes drag that pitches the nose down. Only the aggregate of pressures of lift and drag determines the direction of pitch change. Best,Michael J.

Michael J.-(NOTE: I've edited 3 paragraphs here because I mixed AOA and aircraft pitch angles when writing the first time. Of course- I KNEW what I meant...but that doesn't help you! So here you go...)Well thanks for soliciting my opinion. I'm flattered!In my experience, the pitch moment that is described in your quote is indeed correct. Many folks misnuderstand the difference between the pitch change caused by the flaps and the resultant change in the airfoil dynamics that follow!*(Following paragraph edited for clarity)*On a low wing airplane, adding flaps will initially cause a decrease in the pitch angle, while simultaneously resulting in an increase in the AOA because of the change in the shape of the wing. We all know that increasing the AOA while keeping speed constant results in an increase in lift. Increasing lift without changing the trim or elevator position will result in a climb, or the airplane pitching up.Thus some folks *may* describe the results of adding flaps as "the airplane pitched up."Let me give you some RW examples from the J41. The J41 is a low wing turboprop with three flap settings. Flaps9, Flaps15, Flaps25.Example 1: On the J41 we can add FLAPS9 below 200KIAS. When FLAPS9 is selected, the airplane exhibits a STRONG tendency to pitch up into a climb of 400-1000fpm. You offset this tendency by feeding pressure into the yoke. It takes some time to get used to this particular configuration change and even the autopilot can occasionally have trouble handling it. If you were to ask most pilots why happens when you select FLAPS9, they will tell you that the airplane pitches up, or "balloons" when FLAPS9 is selected.*(following paragraph edited for clarity)*Indeed this feels true based on the seat of the pants and the control inputs required, but the "balloon" is actually a **result** of the decrease in pitch angle combined with the increase in AOA that occurrs when FLAPS9 changes the shape of the wing. (Scientifically: The pitch up is a result of the aggregate changes of L/D based on the increase in AOA while holding speed constant.)If you watch the EADI closely, as soon as FLAPS9 is selected, the airplane pitch angle changes approximately 1-2 degrees depending on the weight and loading of the airplane. If the airplane is travelling at 200KIAS and this change is made, the commensure increase in lift is rather dramatic. I will generally watch for the pitch change, then begin pressing forward on the yoke as I feel the pressure changes coming through the controls. I trim downward approximately 1/2 revolution of the wheel and the airplane returns to a trimmed state while slowly decelerating.(Note: As a matter of personal preference, I generally slow the airplane to below 170 before adding FLAPS9, as I find this gives a better ride for the passengers during the congifuration transition because it eliminates the dramatic ballooning tendency that has to be corrected for.... Adding FLAPS9 at 200KIAS is a smart idea if I've been slammed dunked and need to get the airplane dirty to slow it quickly, but in most cases a slow change in configuration is my preferred method...)Example2: When selecting FLAPS25 from FLAPS15, the airplane exhibits a very noticable pitch down. The pitch down is approximately 3-4 degrees depending on weight and loading of the airplane. FLAPS25 must be selected below 140KIAS and our target approach speeds are normally 130-140 KIAS. At these speeds, the pitch down is most noticable because at the slower airspeed, you do not get as large of a ballooning from the change in the lift dynamic. This is due in part to the fact that FLAPS25 adds a significant amount of drag for only a nominal change in lift... This a subtle pitch down, adjust the trim, adjust the power. Normally after the FLAPS25 pitch down, less than 1/4 turn on the yoke is required to return the airplane to a neutral state.*(paragraph edited for clarity)*So in summary, it is my experience that low winged airplanes will pitch down as a result of adding flaps. The lower pitch angle is caused by the addition of flaps, but this is counteracted by an increase in the resultant AOA for the wing BECAUSE THE WING CHANGES SHAPE. At a constant airspeed this will cause an increase in lift, which in turn MAY cause the airplane to initially pitch up in seach of a neutral state. If the airplane is then trimmed properly, level flight or descent can be maintained....It is exaclty this type of control input/interface that I find most lacking in our desktop sims (and even in the Level C sim that I train in!).Maybe one of these days I'll spend some time playing around with the force feedback stuff and find a way to make it work in MSFS!Hope that explanation helps, Michael J.!

Many thanks RR.So it does sound like it varies. Your Flaps 9 causes pitch up but Flaps 25 causes pitch down so it can't be uniformly stated that low wing airplane always pitches down on flaps deployment. Am I correct ?Michael J.

Hi Robert and Michael J.,I am no expert on this, but by some reasoning using physical principles I beleive this peculiarity can be explained:1.) Changes in pitch, by definition, are angular displacements about the airctaft's center of rotation (Center of gravity*, correct me if I am wrong please). These should be brought about by applied moments about the C.G. *When you are checking for C.G. limits you are dealing with this, a see-saw basically.2.) A moment is defined as a force times a distace. In an aircraft, a moment that causes a change in pitch would be the result of a force (lift/drag) x moment arm (distance from lift/drag force to the center of rotation (the C.G.). Changes in mass distribution can also affect pitch *see above(Concorde anyone?).3.) How close that force(lift/drag) is to that center of rotation (C.G.) and how big it is will determine the severity or magnitude of that moment. The higher the lift/drag value and the farther this force is, the stronger this pitching tendency will be (moment).4.) Of course, it is the sum off all the moments acting on the airplane that will dictate how much the plane tries to pitch in either direction. 5.) I understood that an increase in angle of attack (AOA) brings about an increase in lift (for a same speed), correct me if I am wrong. So if adding flaps to the wing decreases the AOA it should decrease its lift, so I am at odds with this explanaton(forgive me Robert :) ). If we apply the princilpes mentioned above, we can conclude that if a plane "ballons" up and pitches up when flaps are applied, it is because of two reasons: a.) you are increasing the overall lifting force on the wing and b.) this force is being applied behind the center of rotation (C.G).6.) Thus, when flaps are applied, I have to push forward on the stick or trim down, to keep that pitching moment from making me stall the plane. It also helps counteract the extra lift force that messes up your approach profile by changing the direction of thrust and decreasing the AOA of the wing. On the 727 recently released by a competitor of PMDG, I can see this dramatically when flaps 15 are applied, and even the AP has a hard time keeping up. I thought it was weird at first, but apparently it does happen in other bigger aircraft.Hope this makes sense and clears this a bit. Any comments or suggestions are welcome.Can't wait for the 737 :)regards,Max M.

MJ-Yes- but not exactly as I explained it.... heheh...I have my deck angles and AOA's reversed in my answer... (Reading back through it there are a few places where I mix pitch angle and AOA...oops... Pardon the confusion- I'm home with the flu and not feeling the best!I've edited my longer post to clarify with more specific language...see if that helps....

I need to make a correction too. The increased lift should act forward of the center of rotation (C.G.), not behind it. If this was the case the plane would pitch down. Whatever the case, saying whether a plane pitches up or down depending on whether the wing is high or low, should not be generalised, it is a case by case problem. I guess you could get an idea of how a plane might behave, but if you don't analyze the problem properly and test it, it is futile. This is specially true when comapring performance based on simulators, I guess if you want to make comparisons, you would have to get into the modeling aspect of it too. Doing otherwise would be comparing apples to oranges. There is a lot more to this than a simple free-body diagram explanation, you can get into how changing a shape changes the lift/drag vector (and all the shapes in a plane too), transient state considerations, etc., etc., etc..... It can get hairy....regards,Max M.

In pilot reports from magazines, they'll usually point out, if the aircraft has a pitch-down tendency with flap extention. I couldn't find a report on the Meridian, but I did find one for the TBM700 which is also a low wing, single turbine. It definately does pitch-down on flap extention, and was so noted.I would also agree, that it can't be generalized what the aircraft will do. You either have to fly it, or find out from someone who has.L.Adamson

Forgive my bad drawing, but I think it can illustrate the point. There is a book called the "The art of flying" by Wolfgang Langswiecge (can't spell either sorry), that is easy to read and can give anybody a good idea on this subject. Jeppesen study books or or any basic learn-to-fly books usually cover this pretty good too. regards,Maxhttp://forums.avsim.com/user_files/5957.jpg

As a real world pilot myself (albeit only a PPL holder with 50-odd hours or so), I have noticed this pitch-down tendency, but at the same time, there's a specific seat-of-the-pants feeling of being lifted up. In other words, once I apply half-flaps (it goes none->half->full on the TB-9, no degrees or anything fancy), I feel the aircraft gaining a few feet in the air (a certain balooning effect), but at the same time, I can "see" the runway (or ground, depending how good a pilot I am ;-)) better i.e. I've pitched down more.Hope this helps a bit...

Max,I agree with you that to properly analyze flaps deployment one must get into far more complex studies than the typical forces acting on the airplane from a PP manual. For example typical graphs (like the one above) only show the horizontal relation between the CG and the center of lift - but the vertical relations become important too. Then all the drag forces ... BTW, in you graph above the plane would hopelessly pitch down since the force on the elevator should point down (not up) if things are to be in equilibrium.Michael J.

Michael J., Yes, I you are right, but for the sake of simplicity I left it like that. That is why I put above the elevator a (+/_) or an up or down. I should have labeled the moment arm too in relation to all forces, where, as you point out, some act in vertical and horizontal planes that I did not include in the diagram. Like I said before, even with a simple FBD, there is quite some fat to trim before you arrive to a "complete" nodel. regards,Max