correct as is Continuous (all be it slow) pitch up

[Frederf]

3 hours ago, DummyCatz said:

If the former is the case, then a reschedule of the AOA limiter and g-command module of F-16 FLCS is required.

I'm assuming cruise gains AOA less than 10 where pitch command is not AOA blended at all. AOA is irrelevant in this case.

What I'm asking is that if F-16 is ZSL at +2° pitch and FPM at 0° pitch (level, 2 AOA), does the G meter read 1.000 or the cosine of 2°?

[DummyCatz]

47 minutes ago, Frederf said:

I'm assuming cruise gains AOA less than 10 where pitch command is not AOA blended at all. AOA is irrelevant in this case.

What I'm asking is that if F-16 is ZSL at +2° pitch and FPM at 0° pitch (level, 2 AOA), does the G meter read 1.000 or the cosine of 2°?

Ideally it should be the cosine if 2°. It measures body frame acceleration.

An indirect proof would be from -1, where it states that it's approximately 1g or -1g for upright and inverted deep stalls, respectively.

A direct proof would be from the definition of normal acceleration or normal load factor itself, that the FLCS explicitly uses as feedback.

Edited July 2, 2022 by DummyCatz

[Frederf]

If the input is body vertical then 1g level flight with a 1g trim is impossible. It must get AOA modified.

[TheBigTatanka]

Why can't the jet maintain 1 G and stay pointed where you point the nose? The FBW aircraft that I fly is capable of that. A FBW system that can't maintain level flight doesn't pass the common sense test.

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[DummyCatz]

9 hours ago, Frederf said:

If the input is body vertical then 1g level flight with a 1g trim is impossible.

That's true and is the case for F15, F16 and F18 to name a few. For any flight with pitch angle not at 0°, a slight push of stick is required to maintain that pitch angle. This is most noticeable when flying at a higher pitch. It's subject to the sensitivity of normal accelerometer, that if it's able to sense that tiny amount of acceleration increments. And also affected by other control logic designs, such as the pitch-rate dampening logic, that if it's strong enough to suppress the pitch up.

There's some design I know of that do help to stabilise the FPM within a small amount of normal acceleration, so that a true 1g level flight can be achieved. Some makes pitch and roll angle compensations to normal acceleration, so that the aircraft can hold the pitch when pitch or roll angle is not at 0°. The EF-2000 for example even uses pitch-rate command when the stick is neutral, and gradually changes to g-command at a max stick input.

[FusRoPotato]

I don't think the F16's FLCS injected attitude mods to G control until Block 60, so yes, if you roll upsidedown or pitch straight up, it will apply up pitch until you reach 1G. This doesn't get inhibited until 24ish degrees AoA, which I haven't checked in DCS if that is applied or not. 

[DummyCatz]

On 7/3/2022 at 3:48 AM, TheBigTatanka said:

Why can't the jet maintain 1 G and stay pointed where you point the nose? The FBW aircraft that I fly is capable of that. A FBW system that can't maintain level flight doesn't pass the common sense test.

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As long as it passes flying quality requirements i.a.w MIL-STD 1797A, it’s good.

FBW designs differ. Try holding a pitch attitude of 25 deg, and see if the G-meter reads 0.9 G. Then release the stick and see if the aircraft pulls up to seek 1G.

If your aircraft does not pitch up but instead holding 0.9G, then it’s not like the F-16 at all.

[TheBigTatanka]

As long as it passes flying quality requirements i.a.w MIL-STD 1797A, it’s good.
FBW designs differ. Try holding a pitch attitude of 25 deg, and see if the G-meter reads 0.9 G. Then release the stick and see if the aircraft pulls up to seek 1G.
If your aircraft does not pitch up but instead holding 0.9G, then it’s not like the F-16 at all.

I can appreciate that at high angles like that it's going to seek that 1G and may need to pitch for it, until AOA logic takes over (at 15 deg AOA I believe); but it would be weird if the jet couldn't hold level flight hands off at one G, which is what we have in DCS now. I don't know, I've never flown a viper, it would just be maddening to pilot such a craft.

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[Hawkeye91]

1 hour ago, TheBigTatanka said:

I can appreciate that at high angles like that it's going to seek that 1G and may need to pitch for it, until AOA logic takes over (at 15 deg AOA I believe); but it would be weird if the jet couldn't hold level flight hands off at one G, which is what we have in DCS now. I don't know, I've never flown a viper, it would just be maddening to pilot such a craft.

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What I've noticed is that the FBW pitches up or pitches down in relation to horizontal acceleration as well. I don't think this should be the case. I don't know why you would want the FBW to be this way, but if you pull the throttle to idle, the nose will continue to drop a little and if you increase speed the nose will climb. I have no idea why the FBW wouldn't compensate for accelerations/decelerations, but DCS's doesn't. This is the most anger inducing when trying to make small speed adjustments for A2A refueling and any throttle change results in a pitch change.

Edited July 6, 2022 by Hawkeye91

[FusRoPotato]

Sounds right to me. When you apply thrust at a high AoA, there is a vertical component to that thrust vector normal to your flight path that reduces the amount of work your wings need to do to maintain that flight path. That flight path lift component belongs to the aircrafts normal lift, but the thrust line doesn't really have a vertical component perpendicular to lift, so I'd expect a sudden small loss of G's that the FLCS would attempt to correct by pitching up.

This however should depend on the slope of your overall lift curve for your given AoA. In some cases, like a stalling speed where the slope drops and NP moves back, I'd expect the opposite. Since the lift curve slope will be negative in that condition, any reduction in AoA by an added thrust component vertical to the flight path will push the flight condition towards a point in the curve where the wing can produce more lift and sensed normal force. However, if the AoA limits are passed, it will no longer hunt for a G target, thought at those speeds, the aircraft should have stronger stability coefs. It seems like one of two areas the DCS F16's model does not operate quite as expected and I suspect it might be due to a fixed NP location prior to transonic speeds. Reason being that I can get stuck in a tailslide or inverted stall. If the NP doesn't move back when approaching a stall, you could end up with the effect of G increase due to added thrust being countered by an invented instability.

The only other weirdness I've seen in the flight model is overcorrection, oscillation of yaw at supersonic speeds and low altitude.

 

Edited July 11, 2022 by FusRoPotato