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Thread: Inertia?

  1. #11
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    Very interesting, maybe I can answer a bit of the question from real world experience.
    I was connected with developing various bits on the GAF/ASTA Jindivik drone on the Aberporth range in the late 80's through til ops ceased in 2004. Having the radar track data & the aircraft telemetry & command signal recordings using the common timing system it was possible to establish that the aircraft track was delayed by about 2 seconds - this for a fixed bank angle rate of 10 degrees per second. Note that 10 degrees per second sounds slow, but it surprised a lot of pilots - possibly because the ailerons on the Jindivik go to max deflection almost instantaneously before reducing to maintain the rate of bank ( rate gyro feed back). If a Rapid roll was selected the instantaneous rate of roll could be 60 to 80 degrees per second, diminishing to zero as the desired bank was achieved, but was only used with demanded bank angles between 60 & 78 degrees.
    Keith

  2. #12
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    Mallcott, I wasn't advising him to play around with unknown parameters, I was offering values that had been worked out by an expert (not me) and, more importantly, were tested to show an improvement in handling, and that would alleviate his specifically stated problem.

    AND, I reiterate that, so long as he saves a copy of the original, he can't hurt anything, since the original can then be reinstated.

    Larry N.

    As Skylab would say:
    Remember: Aviation is NOT an exact Science!

  3. #13

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    Quote Originally Posted by lnuss View Post
    Mallcott, I wasn't advising him to play around with unknown parameters, I was offering values that had been worked out by an expert (not me) and, more importantly, were tested to show an improvement in handling, and that would alleviate his specifically stated problem.

    AND, I reiterate that, so long as he saves a copy of the original, he can't hurt anything, since the original can then be reinstated.
    Disagree, again.

    If one cannot get the results one expects, frustration is the ONLY likely result.

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  4. #14

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    Quote Originally Posted by keefpee View Post
    Very interesting, maybe I can answer a bit of the question from real world experience.
    I was connected with developing various bits on the GAF/ASTA Jindivik drone on the Aberporth range in the late 80's through til ops ceased in 2004. Having the radar track data & the aircraft telemetry & command signal recordings using the common timing system it was possible to establish that the aircraft track was delayed by about 2 seconds - this for a fixed bank angle rate of 10 degrees per second. Note that 10 degrees per second sounds slow, but it surprised a lot of pilots - possibly because the ailerons on the Jindivik go to max deflection almost instantaneously before reducing to maintain the rate of bank ( rate gyro feed back). If a Rapid roll was selected the instantaneous rate of roll could be 60 to 80 degrees per second, diminishing to zero as the desired bank was achieved, but was only used with demanded bank angles between 60 & 78 degrees.
    Keith
    This only raises more questions than answers: Was the track response delayed by the rudder? Aileron? Yaw drag? Control surface response to radio input? Delays caused by radio control? Basic design of the Jindivik drone? Weight/inertia against size of control surfaces?

    All of these questions require answers before the solution can be proposed...

  5. #15
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    Some people have the utmost contempt for anything they don't understand.
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  6. #16
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    Quote Originally Posted by mallcott View Post
    This only raises more questions than answers: Was the track response delayed by the rudder? Aileron? Yaw drag? Control surface response to radio input? Delays caused by radio control? Basic design of the Jindivik drone? Weight/inertia against size of control surfaces?

    All of these questions require answers before the solution can be proposed...
    All valid questions, but I no longer have the raw telemetry data to double check, but here goes from memory. Jindivik has no rudder. Aileron movement can be checked relative to control input timing, which at say a control transmission & telemetry return distance of 150 miles & a radio speed that of light is very small (.0016secs). There is a built in delay of 1/3 sec in analogue controlled aircraft to allow throttle, roll & pitch control to be 'trilled' i.e. to effectively allow transmission of two or three commands simultaneously. So yes there are delays if using the command timing, but not if aileron deflection is measured, the aileron deflecting as quoted in my original response. As with all aircraft the basic design along with weight/inertia vs size of control surface affect response, but forward inertia is possibly a greater value in a large passenger aircraft, so possibly delaying change in flight path even more? So if I say that accounting for delays in transmission etc the delay in change of track is in the order of 1.5 seconds, it means that with a bank angle rate of 10 degs/sec the aircraft is at least at 15 degs of bank before a track change can be seen, & this is with a fairly agile small aircraft travelling at 400+ knots. As speed diminishes then one can envisage the track delay to be smaller.
    This leads onto an interesting thought about 'fighting' drones flown presumably by pilots in a ground station some many miles away & the delays in that type of situation if using satellites - think of the delays news correspondents suffer......
    Keith

  7. #17
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    So if I say that accounting for delays in transmission etc the delay in change of track is in the order of 1.5 seconds, it means that with a bank angle rate of 10 degs/sec the aircraft is at least at 15 degs of bank before a track change can be seen, & this is with a fairly agile small aircraft travelling at 400+ knots.
    This is all well and good, but has little to do with the OP's question, which is about a problem in the flight model of the FSX default C-172, which has the airplane sliding sideways (defying laws of physics) for a few seconds after wings level. That same problem will also result in sustained turns with more than a gentle bank (30º plus, for certain) causing the aircraft to start descending after a bit, but back pressure causing the nose to rise (much as if top rudder were added, rather than in the fashion of real aircraft). So one cannot hold altitude (you can, in a real aircraft, including the C-172, in at least a 45º bank).

    This problem is NOT the same as larger, heavier aircraft taking longer to react, this is an aircraft doing the (real world) impossible. If it makes no sense to you, go back, read our descriptions, then try it yourself. Fly the FSX C-172 in slow flight just a few hundred AGL, then make a turn (yes, try to keep the ball centered, too) such as turning base to final, then level your wings, with NO wind. Do this from the 6 o'clock locked (not rubber band) spot view, and see what happens. Did you slide sideways for a bit?

    Now get more altitude, then add full power to the C-172 and make a 45º (or even a 30º) banked turn. Hold that turn (use cockpit or spot view here, makes no difference) round and round and round, attempting to maintain altitude. What happens to altitude? What happens to pitch attitude?

    Now use a modified .air file with the values I supplied above and go through those exercises again. Is there a difference? Check out other facets of handling. Is there any change? For better? For worse?

    Bye.

    Larry N.

    As Skylab would say:
    Remember: Aviation is NOT an exact Science!

  8. #18
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    Inuss,
    Just tried the Cessna 172, but I get annoyed with it because its always left wing low if power is on, but if one throttles back & put it into a glide at 60 kn, then the torque is almost zero & it will fly straight, but is very responsive to almost zero aileron. I had though misread the original question, so sorry for going off at a tangent.
    Keith

  9. #19
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    so sorry for going off at a tangent.
    Not a problem, Keith, I just wanted to get us back on track for the OP.

    its always left wing low if power is on
    Sometimes a fuel imbalance can cause wing low problems in many FS aircraft, often to a greater degree than I ever saw in real aircraft.

    Larry N.

    As Skylab would say:
    Remember: Aviation is NOT an exact Science!

  10. #20

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    Quote Originally Posted by keefpee View Post
    Inuss,
    Just tried the Cessna 172, but I get annoyed with it because its always left wing low if power is on, but if one throttles back & put it into a glide at 60 kn, then the torque is almost zero & it will fly straight, but is very responsive to almost zero aileron. I had though misread the original question, so sorry for going off at a tangent.
    Keith
    So, how have you modified the C of G? Off-center weight and balance is exaggerated in FSX.

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