correct as-is HUD display problems

[SUHANG]

Anyone has this problem, the hud display is not centered, as shown in the attached picture. How to fix this?

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[razo+r]

Fly directly into or with the wind and it will be centered.

Edited May 29, 2022 by razo+r

[Hive]

This is not a bug, but a feature. It happens with crosswinds. As your plane does not fly straight because of the winds, your TVV (Total Velocity Vector) moves outside the visible HUD (as implied by the arrow on it). Give some rudder to compensate.

[Yurgon]

3 hours ago, Hive said:

This is not a bug, but a feature. It happens with crosswinds. As your plane does not fly straight because of the winds, your TVV (Total Velocity Vector) moves outside the visible HUD (as implied by the arrow on it). Give some rudder to compensate.

I feel this deserves a bit of clarification.

My understanding is that in a crosswind, aircraft do fly perfectly straight. It's just the ground track that is offset.

In other words, an aircraft in a crosswind still flies straight relative to the air.

If the aircraft doesn't fly straight relative to the air, the turn and slip indicator that is part of the ADI will show the ball off center, and the aircraft will fly uncoordinated. This is usually caused by pushing one of the pedals forward, asymmetrical loads, asymmetrical weight distribution, or asymmetrical thrust. However, uncoordinated flight is not caused by (steady) crosswinds.

The thing about the total velocity vector is that it shows where the aircraft is actually going. And in a crosswind, this absolutely takes the sideways motion of the aircraft relative to the ground into account, and as a result, the TVV and the pitch ladder are offset to let the pilot know that these external forces are acting on the aircraft.

Thus:

3 hours ago, Hive said:

Give some rudder to compensate.

Generally speaking: no. Use rudder to ensure coordinated flight with a centered ball.

When using rudder to get the TVV back into the center of the HUD, the aircraft will fly uncoordinated and its aerodynamics will suffer. Because of the yaw input, there is going to be a roll momentum, which, to be countered, then requires crossed controls (right pedal, left stick, or vice versa) and puts the aircraft into a side slip or forward slip. This is a valid maneuver to slow the aircraft down, and can be used for crosswind corrections, but it's not generally the right response to "my TVV and pitch ladder are off center left or right".

The simple response is: that's fine. The jet does exactly what it's supposed to be doing, which is informing the pilot of the aircraft's motion in an intuitive manner. And if the TVV happens to be so far offset from the HUD's center that it can't be seen anymore, it might be a good day to stay at home and not go flying. Or just do some pilot stuff and deal with it.

[jaylw314]

6 hours ago, Hive said:

This is not a bug, but a feature. It happens with crosswinds. As your plane does not fly straight because of the winds, your TVV (Total Velocity Vector) moves outside the visible HUD (as implied by the arrow on it). Give some rudder to compensate.

as @Yurgon noted above, no, leave the rudder alone.  The plane is flying fine, although I question whether it's smart to climb at 167 KIAS, a little faster might be better.

The crosswind effect on the FPM and pitch ladder will be most noticeable when the plane is flying slower, too.  If the crosswind is more than 1/6 your forward true airspeed, the FPM will be more than 10 degrees left or right, which will be off the HUD.  You'll notice also the symbology for a FPM that is off the HUD--there's a little arrow pointing left superimposed over the FPM

Edited May 29, 2022 by jaylw314

[ASAP]

3 hours ago, Yurgon said:

This is a valid maneuver to slow the aircraft down, and can be used for crosswind corrections, but it's not generally the right response to "my TVV and pitch ladder are off center left or right".

You are correct but I would pile on and say that using uncoordinated flight to lose altitude faster or slow down is fine in a Cessna or other GA plane. It’s a bad idea in a fighter like this. 1) with asymmetric stores yaw can build up to a point that makes a side slip departure possible, 2) your speed brakes will do the job better anyway. 

Also you only CAN but SHOULD use the wing low method to land this airplane like you described. It is the procedurally correct way to do it from everything I’ve read/heard. Other jets like the F-16 or the T-38 land in a crab. The A-10 isn’t one of them though.

52 minutes ago, jaylw314 said:

I question whether it's smart to climb at 167 KIAS, a little faster might be better.

That’s situation dependent. 160 is right around the aircrafts best climb speed. But it’s not very tactical because you dont have much energy to react if you need to defend yourself. On a departure when you’re trying to get to altitude fast it’s fine. 

[Yurgon]

12 minutes ago, ASAP said:

You are correct but I would pile on and say that using uncoordinated flight to lose altitude faster or slow down is fine in a Cessna or other GA plane.

Totally true!

It's certainly not the preferred way to do it in the A-10. However, thinking of the Gimli Glider, it's possible to use forward slipping in aircraft that weren't meant for this kind of GA-flying. So when I said "it's a valid maneuver", I meant that it's something that works with aircraft in general.

12 minutes ago, ASAP said:

Also you only CAN but SHOULD use the wing low method to land this airplane like you described. It is the procedurally correct way to do it from everything I’ve read/heard. Other jets like the F-16 or the T-38 land in a crab. The A-10 isn’t one of them though.

Oh, that's interesting! So far I was under the impression that the A-10 would approach in a crab when crosswinds are above a certain value, and below that value it's up to the pilots whether they prefer crab or sideslip.

That's what we have in our virtual squadron documents, but I don't recall what the exact source is for this paragraph, whether we took this from some public A-10 documentation or derived it from other airframes or some general guidelines.

Edited May 29, 2022 by Yurgon

[ASAP]

1 hour ago, Yurgon said:

It's certainly not the preferred way to do it in the A-10. However, thinking of the Gimli Glider, it's possible to use forward slipping in aircraft that weren't meant for this kind of GA-flying. So when I said "it's a valid maneuver", I meant that it's something that works with aircraft in general.

Oh I see what you're saying. It would certainly get you down. There's a couple of other reasons you'd generally want to avoid it in jets. Disrupting airflow into your intake by high side slip angles can compressor stall the engines for instance. To be fair though the Gimli Glider didn't have to worry a whole lot about killing the engines after they ran out of gas .

1 hour ago, Yurgon said:

 So far I was under the impression that the A-10 would approach in a crab when crosswinds are above a certain value, and below that value it's up to the pilots whether they prefer crab or sideslip.

That's what we have in our virtual squadron documents, but I don't recall what the exact source is for this paragraph, whether we took this from some public A-10 documentation or derived it from other airframes or some general guidelines.

 

So there is the approach phase when you can do whatever you want really, probably crabbing is the easiest. Everything I found says on final approach the manual recommends a combination of wing low and crab, at the same time. It specifically says before entering the flare though you should use the rudders to align the aircraft fuselage with the runway center line and land using the wing low method. I normally fly the last half mile like that so I'm not transitioning low to the ground. In any rate you shouldn't land with an aggressive crab like an F-16 would.

[jaylw314]

18 hours ago, ASAP said:

You are correct but I would pile on and say that using uncoordinated flight to lose altitude faster or slow down is fine in a Cessna or other GA plane. It’s a bad idea in a fighter like this. 1) with asymmetric stores yaw can build up to a point that makes a side slip departure possible, 2) your speed brakes will do the job better anyway. 

Also you only CAN but SHOULD use the wing low method to land this airplane like you described. It is the procedurally correct way to do it from everything I’ve read/heard. Other jets like the F-16 or the T-38 land in a crab. The A-10 isn’t one of them though.

That’s situation dependent. 160 is right around the aircrafts best climb speed. But it’s not very tactical because you dont have much energy to react if you need to defend yourself. On a departure when you’re trying to get to altitude fast it’s fine. 

Cool beans, I figured 180 or so was best climb, if it's around 160 that makes sense and is good to know!

For the final approach per the flight manual's recommendation, I think of it as a "partial" slip, just enough to get the runway in the HUD (or at least to get it out from behind the HUD pillars).  Then on short final the full wing-low sideslip to align with the runway.