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?
In basic terms, the FPV should point in the direction the aircraft is travelling through the air (relative to the pitch and horizon indications on the Primary Flight Display).
So if you push forwards on the yoke, the aircraft will pitch down but initially the aircraft will still be travelling in the same direction due to its inertia, once the aircraft starts to descend in this example, the FPV indicator will start to move towards the 'Airplane symbol' on the PFD.
"the FPV indicator will start to move towards the 'Airplane symbol' on the PFD."
I don't think this is possible. The FPV displays in pitch the angle of the Flight Path relative to the horizon. The a/c symbol displays a/c attitude. The FPV will be displaced sideways from the centre position on due to drift and this reflects the Track Line. We all know that B737 flies level between 6 degrees & 2 degrees nose up depending on speed. The FPV will be at ZERO degree on the PFD. The a/c will climb at low/medium levels about 7-10 degrees and the FPV will be significantly below that. It'll descend from high level 290kts with about 0 degrees; the FPV will be below that. On approach the attitude is 1-2.5 degrees and FPV is -3 degrees. In my experience it is impossible to stabilise the FPV on top of the a/c symbol. I once saw a PPL'er in a fun sim session. He'd done the apptitude tests where you move a small square to follow a moving dot on a screen using a joy-stick. He tried to do the same with the FPV and a/c symbol similar to a Flight Director. It is impossible and he was very confused, plus we ended up in some very interesting positions.
Location: Boldly going where no split infinitive has gone before..
Yes, all true, but what MP was saying is that, when you initiate a descent, the attitude leads the flight path initially, so the Attitude will indicate nose down BEFORE the FPV indicates a downward flight path. As the vertical speed inceases, the FPV will indicate a descent, thus moving "Towards the AC symbol".
It may or may not GET TOO the aircraft symbol (in most aircraft attitude is seldom the same as FPA, so it probably won't) but it will move in that direction.
WizofOz got what I was trying to say but in hindsight, using a descent was a bad example from me, as on a normal descent on a Boeing type would of course be made at around 0 degree pitch hence the FPV would actually move AWAY from the airplane symbol.
However Acheo mentioned an abrupt pitch down which put in my mind a steeper than normal descent i.e from level flight, push forward to pitch 5-10 degrees nose down, what happens to the FPV? It would move toward the airplane symbol.
I've over complicated this now haven't I?
Last edited by Mercenary Pilot; 21st Sep 2012 at 12:07.
Reason: To clarify
The FLP can be located on both the HUD or the PFD. Mine is located on the PFD.
Here's the issue I have. I was looking at the PFD in a coordinated stabilized turn while the FPV on my PFD was pointing a way inside the turn. It tought it was wrong since the flight path in a turn can be, at best, 90 degrees of the turn radius. With strong winds, maybe slightly inside the turn.
Now I'm testing my PFD in a SIL and I'm using various simulators which could send wrong inputs. I mentionned the "descent" scenario and most answers confirm was I already knew. My real problem is the "steady level turn" scenario.
The dictionary I'm looking at defines "Vector" as "a line representing a physical quantity that has magnitude, and direction in space as velocity and acceleration. The aircraft attitude is in relation to the horizon. It could be indicating one degree nose up attitude but descending at a three degree attitude towards the earth. What you would see then is a slight nose up (one degree) attitude on the flight director and at the same time a three degree indication on the FPV. If you could attach a length of string to the nose of the 'plane and extend it to the point of impact on the earth, that would be the plight path vector. Forget about the shape of the 'plane. Think of it as a round ball. So the vector is the path of the ball through the air. It has nothing to do with the attitude of the 'plane. If you look at the FPV as you fly with a cross wind in flight, you will notice the FPV off to one side, representing the vector of the cross wind. Nothing to do with the direction (heading) of the 'plane. T
acheo your observations are correct but use of the words "opposite direction" to describe the initial movement if the FPV is wrong. As someone said earlier, when u initiate a change in pitch or go off wings level into a roll, the aircraft takes a fraction of a second to actually change direction.
So take the "steep turn" exercise in the simulator. upon initiating a turn to the left, the fpv continues going straight momentarily with inertia but will start changing heading very soon. this delay is visible on the pfd by a slight increase in the gap between the aircraft symbol and the fpv. this isn't because the fpv is going away from you, but you are going away from the fpv.
during the turn, the fpv doesn't come to the centre of the pfd because there is a slight lag which is caused by the minor but constant difference in the direction of the aircraft longitudinal axis and the direction that the aircraft is actually flying.
however, when you stop banking and return to wings level, you will find that the fpv returns to the centre of the pfd. Or as per your observation, goes towards the direction of the turn. (no crosswind conditions of course).
So to sum up, you are going away from the fpv and it is trying to follow when you initiate any manouver.