Pitch ladder and Angle of Attack?
William T. Overton
> the same amount of angle as I increase my angle of attack. This same
> behavior is evident on video recordings of "real" F-16 flights.
>
> When the AOA is not zero, the pitch ladder is not indicating pitch.
> What would the informed pilot say this condition is really indicating?
Very interesting. I havn't ever looked that closely at Falcon, but I will
next time I play with it. The concept of a HUD pitch ladder is to tell
you the aircraft pitch with respect to the local horizontal. So, if you
put your velocity vector on the 0 pitch line, you should have exactly 0
altitude rate. Above it, you go up, below it you go down. If your pitch
ladder is centered at 15 degrees on your HUD, but your velocity vector is
still on the zero line, that means you are at zero altitude rate, with a
15 degree angle of attack. The velocity vector placement on your HUD
should show you your angle of attack in pitch and your sideslip in yaw.
Thus the velocity vector is a really good indicator of what you are doing
aerodynamically (your plane with respect to your velocity vector). Then
the pitch ladder is a reference to the local horizontal. Between the two,
you should have a really good idea what is up.
I don't know why the pitch ladder in Falcon would "depress below the
horizon" like you describe, but 0 pitch is supposed to be 0 pitch. You
should see the pitch ladder remain "constant" with respect to the horizon
(horizon being roughly horizontal). But, while increasing your AoA, you
should see the relative position of the velocity vector and the pitch
ladder changing.
More or less confusing? :) Only reason I know much about any of this is
because it wasn't that long ago that I had to dig through our HUD code
here in the Shuttle Engineering Simulator for the implementation of PILOT
(Portable In-Flight Landing Operatoins Trainer). One thing is for damn
sure, our velocity vector is never anywhere near the boresight (constant
nose reference)! ( that implies high angle of attack).
WTO
---
William T. Overton
ove...@l14h13.jsc.nasa.gov (Primary)
ove...@pat.mdc.com (Secondary)
Larry Dwyer
the same amount of angle as I increase my angle of attack. This same
behavior is evident on video recordings of "real" F-16 flights.
When the AOA is not zero, the pitch ladder is not indicating pitch.
What would the informed pilot say this condition is really indicating?
Given the previous question, what useful information is it telling me?
How useful is it when the pitch ladder drifts off the HUD (generally
because the aircraft has high AOA and is not flying wings level to the
horizon)? As the pitch ladder drifts back on the HUD, how can I
optimize the information it is telling me to correct my flight (assuming
I am trying to get the AOA back to zero)?
Are there any good books someone can recommend to explain better than
the F3 manual the effects of flight path on the instruments?
Thanks,
Larry
Eyal Lebedinsky
>I notice that the (F3) HUD pitch ladder depresses below the horizon by
>the same amount of angle as I increase my angle of attack. This same
>behavior is evident on video recordings of "real" F-16 flights.
>When the AOA is not zero, the pitch ladder is not indicating pitch.
It does. The pitch ladder will always show you your pitch and it will
not move with the AOA. Your pitch is a feature of your geometrical
attitude and it is not affected by the AOA which is a dynamic feature.
Maybe you mean to say something else which I missed?
>What would the informed pilot say this condition is really indicating?
>Given the previous question, what useful information is it telling me?
>How useful is it when the pitch ladder drifts off the HUD (generally
>because the aircraft has high AOA and is not flying wings level to the
>horizon)? As the pitch ladder drifts back on the HUD, how can I
The pitch ladder may get off view if your velocity vector does so. This
is due to the fact that it is most customary to have the pitch ladder
centered on the vv. However, this is not always the case. For example,
the F/A-18 will not ley the pitch ladder to get off the HUD but will
rather set it onto your waterline mark (a fixed point on the HUD) while
the vv is away.
Another feature is to have the vv caged, in which case it does NOT show
the correct vv at some times. This will tend to keep the pitch ladder in
site more often.
>optimize the information it is telling me to correct my flight (assuming
>I am trying to get the AOA back to zero)?
You do not want to get the AOA back to zero. The necessary AOA varies
with the flight conditions and is hardly ever zero - you need it for
lift. What you want it to avoid having a too-high AOA for your situation
so that you maintain control and avoid unhelthy situations (like, most
commonly, wing stall).
>Are there any good books someone can recommend to explain better than
>the F3 manual the effects of flight path on the instruments?
There are many books on the subject but they all concetrate on
aerodynamics. It will probably will be a bit too much for most.
Nevertheless, I will recommend a very readable book:
The illustrated guide to aerodynamics (2nd edition) by H.C Smith
McGraw Hill (TAB books) ISBN 0-8306-3901-2
It is very easy to find and is on the cheap side.
--
Regards
Eyal Lebedinsky ey...@ise.canberra.edu.au
Robert Dorsett
>
>I don't know why the pitch ladder in Falcon would "depress below the
>horizon" like you describe, but 0 pitch is supposed to be 0 pitch. You
>should see the pitch ladder remain "constant" with respect to the horizon
>(horizon being roughly horizontal).
While playing with another game recently, I noticed that zero pitch at
sea level corresponded to zero pitch being on the horizon. Zero pitch at
40,000' corresponded to zero pitch being about 1" above the horizon.
I asked several fighter pilots about this, and, yes indeed, there will be
some degree of depression the higher you get.
The reason for this is simple: the earth is not an infinite projection,
while the HUD is. The higher you get, the greater the zero-pitch angle
gets with the apparent horizon. My back-of-the-envelope calculations
suggest it wouldn't be much more than three or four degrees at 50,000'.
--
Robert Dorsett Moderator, sci.aeronautics.simulation
r...@netcom.com aero-si...@rascal.ics.utexas.edu