Flight Path vector - behavior

[acheo]

Hi,

Could anyone confirm this. When initiating a turn, should the flight path vector be going in the opposite direction of the turn. Same things when pitching down abruptly, should the FPV be going up a bit?

tx

acheo

[NoHoverstop]

Is this an indication in a HUD/HMD? If so, then without wishing to sound trite, the symbology will do whatever it was programmed to do based on the inputs it gets and the characteristics of the display device. For example, this may include "quickening" terms (not unknown on HUD flighpath or climb/dive markers) which may result in "interesting" transient effects (be very odd to cause the effect you're describing, but who knows with software!). Or even if the fp vector is a true display (subject to how good the velocity measurement is), then it's possible for it to do what you say depending on the aircraft characteristics. Consider a conventional (wing/tail) aircraft with conventional controls. Pull the stick back and the first control effect is to deflect the elevators or tailplane up, which increases downforce (usually) on the tail and on the overall aircraft. So the immediate response is a downwards acceleration, before the nose-up pitching moment also generated has had time to rotate the aircraft enough for the increased AoA to give enough extra wing/body lift to reverse the effects of the initial downwards acceleration. I've seem this in simulations, but really only by scrutinising time-histories, as it's typically a pretty rapid transient (though perhaps worsened by a flatter wing/body lift-curve slope and more-powerful control surfaces). If you're seeing something much more noticeable, on a real aircraft, then I'd investigate the whole sense/compute/display path. Whereabouts on your aircraft is your (inertial?) velocity sensor located? Lateral/direction stuff (as you first asked about) is probably more complicated, for example adverse yaw characteristics may dominate the initial transient velocity response, but again ask yourself in which direction is the inertial sensor going, transiently, in response to the control input? Hope that makes some sense!

[indie cent]

Acheo,

In a word, the answer to your question is - yes!

An fpv initially lags any change in aircraft attitude - because there will always be inertia - and an actual aircraft flight path through the sky does not change instantaneously. Essentially, the fpv is showing exactly where the aircraft is flying at that given instant.

The result, in your examples of a turn and pitch down, is that the fpv appears to b****r off in the wrong direction at first - not to worry as it soon catches up.

The fpv is effectively tied to the attitude indicator with a variable tension elastic band - the "tension" depending on airspeed, mass, density etc etc.

I've noticed a tendency when hand flying for many pilots to use the fpv as the primary reference when hand flying. It makes for easy, accurate flying but can become misleading near the stall!

Rgds,

ic