Torque Monster picth attitude during landing...
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Thread: Torque Monster picth attitude during landing...

  1. #1
    Senior Administrator PRB's Avatar
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    Torque Monster picth attitude during landing...

    What part of the flight model controls the pitch attitude at which the plane sits under various flap and airspeed configurations?

    The issue is this: I could be wrong, but I’ll bet a dollar that in a P-47, for example, at the correct landing weight and approach speed, with gear and flaps down, you really can see the runway over the nose. Same with a P-51, F4U, P-40, and Mitsubishi J2M3 (just for example, of course…)

    I can understand the nose obscuring visibility forward if the nose is stuck up in the air, as in the final moments before a pretty three point landing, or during the last seconds of a navy carrier landing, but if you’re in a 3 degree glide slope two miles out, on speed and configured for landing, I’m just not buying that the runway is obscured by the nose, even in a P-47. And in fact, Jeffrey Ethell, who did a “Roaring Glory” episode on the P-47, says explicitly that on final, with full flaps, you can see the runway over the nose.

    So, if I wanted to mess around with the flight model, in an attempt to get the plane to fly with more pitch down at slow speeds, which table should I look at?
    - Paul

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  2. #2
    The F4U suffered from terrible forward visibility during ground movements and landing. This is one reason it did not enter carrier duty until 1945. The British actually developed a landing pattern that overcame the forward visibility problem. They flew a very short final, featuring a turn to port until just before reaching the stern of the carrier. In short, there is poor visibility over the nose if you make a long and straight approach.
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  3. #3
    Senior Administrator PRB's Avatar
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    Well, maybe so, but sometimes I think some FS planes over do the lack of visibility thing in these type of planes. If we know that in fact the pilot can see the runway just fine over the nose during a straight in approach, as we apparently do in the case of the P-47, then I’m looking for a way to “tweak” my P-47 so I can see where I’m going from the VC on final!

    To that end, I have found that increasing the lift scalar in the [flaps] section of the aircraft.cfg file seems to achieve the desired effect.

    The three values listed here, lift, drag, and pitch scalars, are sometimes found to be all zeros. I’m guessing these values simply bias the characteristics of the flaps built into the air file, otherwise values of zero would mean a flap that has no effect, right?
    - Paul

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  4. #4
    The CL vs AoA curve determines the attitude at ALL speeds. CM affects elevator and trim settings, but not aircraft attitude.

    The lift equation is: Lift = 1/2 ρ V^2 S CL

    Where:
    L = lifting force (pounds)
    ρ (rho) = air density (slugs per ft3)
    V = velocity (feet per second)
    S = wing surface area

    The lift required to fly level is the weight of the aircraft, so there are really only two variables in the lift equation: V and CL

    If one of these variables decreases, the other has to increase to keep the aircraft flying.

    The airspeed is a function of engine power, but CL is a function of angle of attack. (Remember the CL vs AoA curve?)

    If you are flying at a certain speed on approach, you need a certain amount of lift, which is obtained from the CL vs AoA curve. If you wanted to decrease the attitude on approach, you would need to modify the lift curve so that the whole curve moves to the left. (CL = 0 and CLmax are both located at lower AoA values) The result is that CL is higher at lower values of AoA (so the pitch attitude decreases).

    This is exactly what increasing CL via the flaps does. CL increases at all values of AoA, effectively moving the lift curve to the left and at the same time increasing CLmax. If you drop the flaps on approach and maintain the same altitude and the same airspeed, the nose will drop to keep CL the same. (requires simultaneous adjustment of flaps, power and elevator - much easier to say than do)

  5. #5
    Senior Administrator PRB's Avatar
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    Thanks, sparks! I will see what I can mess up now...
    - Paul

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  6. #6
    Paul:

    You have my hose nose FM... I did probably 300 carrier landings working that one up. Two things you can do, one is the circular approach, with only 500 ft or so in the grove, which was also used by the USN. Another is to open the canopy (also correct) and slide your eyepoint over to the left such as to sight somewhat along the nose, the LSO position (if we had one) always in view.

    The Army guys probably did a lot of wheel landings. In my Supercub, ya cann'a see anything in the flare either.

    I don' know if you are using it, but M. Davies's Essex is great in FSX accel.

    Cheers: Tom

  7. #7
    Senior Administrator PRB's Avatar
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    Rgr that Tom. Actually, both the A2A P-47 and the Aircraft Factory F4U (with your FM) work about like what I would expect after watching Steve Hinton and Jeff Ethell fly those ships in the "Roaring Glory" DVDs. It's a different plane I'm trying to modify (mess up?) It makes sense that you would loose sight of the runway in the flare, but I'm less convinced that the nose would be stuck up in the air when your're on speed or faster, with full flaps, and on a -500 FPM descent... I'm curious to see if I can get it to behave a little different by screwing around in the air file. For all I know, maybe the real plane really did fly that way, but I kind of doubt it...
    - Paul

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  8. #8
    Another method that might work, if a specific AOA range is involved is to bend the CL curve a bit if you know what the offending AOA is. I have done this to give a better deck angle in cruise where the other parts of th flight envelope were ok. The dynamics of various airfoils are well known, but the effect of thrust and overall shape of the aircraft can modify things a bit. Things such as pitching moments and drag from gear can have an effect as well, though the basic relationship sparks describes is paramount, higher CL equals a lower AOA for a given speed weight.

    Cheers. T

  9. #9
    Senior Administrator PRB's Avatar
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    Quote Originally Posted by sparks View Post
    The CL vs AoA curve determines the attitude at ALL speeds. CM affects elevator and trim settings, but not aircraft attitude.

    The lift equation is: Lift = 1/2 ρ V^2 S CL

    Where:
    L = lifting force (pounds)
    ρ (rho) = air density (slugs per ft3)
    V = velocity (feet per second)
    S = wing surface area

    The lift required to fly level is the weight of the aircraft, so there are really only two variables in the lift equation: V and CL

    If one of these variables decreases, the other has to increase to keep the aircraft flying.

    The airspeed is a function of engine power, but CL is a function of angle of attack. (Remember the CL vs AoA curve?)

    If you are flying at a certain speed on approach, you need a certain amount of lift, which is obtained from the CL vs AoA curve. If you wanted to decrease the attitude on approach, you would need to modify the lift curve so that the whole curve moves to the left. (CL = 0 and CLmax are both located at lower AoA values) The result is that CL is higher at lower values of AoA (so the pitch attitude decreases).

    This is exactly what increasing CL via the flaps does. CL increases at all values of AoA, effectively moving the lift curve to the left and at the same time increasing CLmax. If you drop the flaps on approach and maintain the same altitude and the same airspeed, the nose will drop to keep CL the same. (requires simultaneous adjustment of flaps, power and elevator - much easier to say than do)
    Just to follow up on this. Adjusting the CL_df , in the primary aerodynamics section, which I'm guessing is the lift coeficient of the flaps, has the desired affect. Just bumping it up a little works beautifully. I just wanted to "fix" a couple of planes out there that seem to just sit there with no change in pitch, when I put the flaps down.
    - Paul

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  10. #10
    For experiment you might just adjust the flap lift scalar in the .CFG file. Also the shape of the lift curve will affect this. Many of these airfoil curves and drag polars are available and can be helpful in adjusting things.

    Note that in the case of the P47 the manual suggests a steeper approach, mainly for visibility.

    T

  11. #11
    Senior Administrator PRB's Avatar
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    I did try adjusting the lift scalar in the .cfg file first. At first I thought it helped, maybe a little. But then I read in the SDK that the lift scalar represents the total amount of lift that particular flap entry is responsible for, when fully down, with 1.0 = 100%. So in the case of big jets with two sets of flaps, one would have 0.6 and the other 0.4, so together you would get 1.0. So then I wondered if the FS engine ignores values greater than 1.0, and started second guessing whether or not I was really seeing any difference after adjusting the lift scalar.

    However, adjusting the CL_df in the air file made an unmistakable difference, in just the way I wanted.

    In the end I made this adjustment only to Piglet's J2M...

    - Paul
    - Paul

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  12. #12
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    There is also Cm_df in the Pitch section of block 1101 as well as 'Pitch scalar' in the Flaps section of the .cfg file. I tend to use these.
    Keith

  13. #13
    The above mentioned pitch adjustments only affect the pitch moment with flap extension-retraction, and the ammount of trimming necessary. The overall pitch is a function of thee flap area and extension, and overall lift generated.

    T

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