I am trying to understand Flight dynamics, particularly I am using Missile Datcom to get aerodynamic parameters of a missile, then use MATLAB, simulink to simulate its trajectory. It seems there are a lot of dynamic derivatives, have a look at this, look at some dynamics derivatives.
So why don't we have Normal-force derivatives due to yaw rate or Normal-force derivatives due to roll rate ? why don't we have Yawing-moment derivatives due to pitch rate ? etc...

  • $\begingroup$ It depends on the File Type you look at. File Type 42 (the most recent) has more dynamic derivatives. (If I understood correctly your question) $\endgroup$
    – Afe
    Mar 29 '19 at 18:24
  • $\begingroup$ @Afe, I mean which dynamic derivatives do we need in order to simulate a flight of an aircraft? I see Cn, Ca, Cy, Cm, Cl,...(6 coefficients) and pitch rate, roll rate, yaw rate, rate of angle of attack, rate of side slip angle (5 rates) so we could have 6x5 = 30 dynamic derivatives. Why don't we have other dynamic derivatives like: yawing-moment derivatives due to rate of angle of attack? $\endgroup$
    – Dat
    Mar 30 '19 at 1:48
  • $\begingroup$ Why was this question voted to be off-topic? It's perfectly legitimate question to ask about flight dynamics... $\endgroup$
    – JZYL
    Sep 1 '19 at 6:37

A plane is subject to 5 forces: Thrust, Lift, Drag, Weight/gravity (and side force). In addition, there are 3 moments: Rolling, Yawing and Pitching moment. With these 7 vectors you are able to represent how a plane behaves in the air. The problem of simulations is how to compute these 7 vectors for a complex shape like is an aicraft in different flight conditions. To obviate these issues, engineers came up with 'coefficient of ..' which is indicated by C_letter.

To make estimation of these coefficients more accurate, engineers decided to compute the partial derivative of each coefficient due to 'something'. However, some of these derivatives have a small influence on the coefficient such that only for high fidelity simulations they are used (for example in Level-D simulators). Moreover, depending on the type of aircraft, some derivatives may be important or not: if a plane has no slats then there is no lift coefficient due to slat failures.

DATCOM was developed in the seventies and computing power has improved a lot since then, therefore some coefficients are not included (yawing moment due to angle of attack).

A nice reference to understand why coefficients are used if the book Boeing - Jet Transport Performance Methods.

  • $\begingroup$ could you help me out, looking at mathworks.com/help/aeroblks/digitaldatcomforcesandmoments.html It seems like: $C_{L \space total} = C_{L \space static} + C_{L \space dyn} = C_L + (C_{Lq}q + C_{L\dot \alpha}\dot \alpha)(c_{bar}/2V)$. I understand static coefficient derivation, where do dynamic derivative contribution formulas come from ? $\endgroup$
    – Dat
    Mar 31 '19 at 16:43

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