Fox One

Test was done selecting "Takeoff from runway" from ME. Please read post #11.

From real flight manual, the limiter works only in FCS mode "flight". With gear down the FCS is in "takeoff-landing" mode. The limiter is a stick motion restrictor using inputs of AOA, G, AOA rate, G rate, pitch rate and whatever. It's not like the limiter has 2 parts for G and AOA and one or the other works. It is a single stick motion restrictor that works to limit the AOA or G, whichever happens to be above a certain value. And even if the limiter worked with gear down too, it needs AOA or G input to be above a certain value. With aircraft on the runway I am giving it an input of 1G and zero deg AOA. In such a situation the limiter does not restrict or slow the stick motion in any way. Yes!

^^^ Yes, with W key pressed the stabilizer moves fast. By pressing W we tell the simulator that we are applying an additional 15Kgf to the stick to overpower the AOA/G limiter. The problem is in the RL videos the stabilizer can be moved in pitch at a rate that is not available in simulator with W unpressed, but it should. The pilot in video links on this page moves the stabilizer at a faster rate than what is possible in DCS without overpowering the limiter because the limiter is OFF anyway due to gear down. He also doesn't press the W key because in Cyrillic alphabet there is no W letter :)

Other videos where stabilizer deflection rate in pitch is visible:

In this video at 51s time the pilot performs a final flight controls check on the runway just before takeoff (as RL manual recommends). He does a full nose up deflection of the stabilizer, and such a deflection rate is certainly impossible in current DCS version. Obviously the flight control system was in "takeoff-landing" mode. The AOA/G limiter works only in "flight" FCS mode (IRL and in simulator). Switching between "takeoff-landing" and "flight" mode is done with the landing gear handle. So the AOA/G limiter doesn't work with gear down and does not limit the stabilator rate in any way in the test I done with aircraft on the runway.

I made the timing with time acceleration set to 1/16, then divided the result by 16. Measurement was made with aircraft on runway just before takeoff, not in direct control mode.

Since the last few versions of DCS the Su-27 stabilizer moves too slowly in pitch. I timed it with the aircraft on ground and a full nose up deflection (that is a 20deg angle) takes 1.1s. This means the available rate is about 18deg/s. I don't believe for a second this is realistic :D I searched youtube and found several adequate videos and timed how long it takes IRL. Concluded that a full nose up deflection of the stabilizer takes about 0.65-0.7s. This means the available rate is about 30deg/s. So in simulator we have an available rate that is more than 1.5 times slower than IRL. This slowness you can really feel in flight. When the rate was reasonably accurate (a few months ago, I can't say precisely) the pitch "nimbleness" was already pretty mediocre due to size and weight of the aircraft. Now it is rather poor and I think stabilizer slowness in pitch is the cause.

@foxbat155 The device in your pictures is for calibrating the DUAS-69 probe (the alpha/beta probe on the Pitot boom), as you can see from its name DUAS69 and the alpha/beta rows in the table. DUAS comes from datchik ugla ataki i skoljenia - that is alpha/beta probe. The probe on the side of the air intake feeding cockpit AOA indicator is called DUA-3.

And what exactly are you LOLing about? I only corrected an affirmation made by Frederf about the real aircraft. I didn't say if 1° is a big deal or not. That's nice but I do want to contradict you right now. The attached image is a page from "MiG-21bis flight-technical chracteristics" manual.

Wrong. The 1° angle you are talking about is actually zero for MiG-21.

https://youtu.be/IXUDx7bsDYE?t=62

Any news about this? It's been reported five months ago...

Yes, almost ;) Allow me to help by pointing out only the most obvious, visible-from-the-moon errors, look at image in post #81 The windshield and canopy are like 20% too tall, air intakes are like 10% too tall and are not tilted down. The air intakes on the real aircraft are tilted down 3 deg. Ejection seat headrest is a complete joke. Ventral fin is inaccurate. I'm not sure if you know that Skylark's drawing is made by measuring the real aircraft, so everything you see there is accurate to the last mm. Also, nice try with your attempt with overimposing Skylark's drawing on your model showing "perfect match". I appreciate the honesty :thumbup:

It's a 360 deg video. Use the mouse to rotate the view until you see the instrument panel. What is interesting to this thread starts at 63s as my original link shows.

Currently in simulator the elevation cursor in search mode is obviously showing the angle between the antenna and the local horizon. Antenna pitch stabilization in search works fine, it's just the elevation cursor that is incorrect. Real manual states clearly enough that cursor shows angle between the antenna and the ARL, which implies that due to antenna pitch stabilization in search, if you change pitch the elevation cursor should move. In video link in first post it is clearly visible that elevation cursor moves in opposite way to the nose movement in pitch - nose moves up, elevation cursor moves down. Just as expected from flight manual description. So there is no misunderstanding of the system on my part.

bump :)

It seems to me what you are describing here would happen to an aircraft with unboosted elevator control, lowering the flaps would change downwash and that would change airflow direction over elevator, producing an elevator hinge moment that would translate into a force that would be transmitted via elevator control linkage back to the pilot. As you know, this does not apply to the F-86 which has an irreversible hydraulically actuated elevator. It doesn't matter if due to flaps lowering the elevator hinge moment changes; at 140kts the actuator will easily keep the elevator in the same place and no force will be transmitted back to the pilot. The F-86 having an irreversible hydraulically actuated pitch control with no pitch ratio changer or anything (just a classic force simulator spring and a trim actuator), this means applying 7 pounds of pulling force on the stick will ALWAYS produce an elevator leading edge down deflection, no matter what the elevator hinge moment is, what the airspeed is, etc. Only exception might be at very high speeds where elevator actuator might have insufficient force to deflect the elevator the commanded amount, but that's definitely not the case here, we're talking about 140kts experiment here. The actuator at that kind of speed would have no problem coping with any kind of elevator hinge moment. The pitch control being what I described above, with an F-86 aircraft trimmed for horizontal flight (as the table in discussion shows) applying 7 pounds of pulling force on the stick will ALWAYS cause a stick back movement, and that will ALWAYS produce an elevator leading edge down deflection.

Actually, on F-14A the airspeed is not displayed on HUD in any of the modes. You have to use the cockpit instrument...

I think I found what is the problem here. Or at least a part of the problem. Silly me for not figuring this sooner. I did a ground effect test. With the MiG-15 with gear down and full flaps I performed perfectly horizontal flight at 250Km/h very low above the runway, main wheels about a diameter above runway. Then performed the same test at 50m altitude. In both cases, the necessary AoA was exactly the same. This means there is no ground effect simulated. I performed similar tests with all Belsimtek aircraft. F-15, F-86 - same thing, no ground effect simulated. The only aircraft with ground effect simulated is the F-5. This is quite surprising, considering the F-5 is recent, but the initial release of F-15 and F-86 was more than two years ago! In MiG-15's case ground effect would easily decrease touchdown speed with like 15Km/h, probably more. Obvious request to Belsimtek: please implement ground effect for all aircraft. Pretty please :)

jojo, you are overcomplicating things when there's really no need to. What inputs the real flight control system uses to do its "magic" or how exactly does it is not what I'm asking here. In the attached track I'm flying the F-15. At low altitude and supersonic speed I pull the stick until I hit 3G, then for the rest of the loop I don't move the stick at all. Despite the great variation in speed and altitude during the loop, G remains between 2.8 and 3.2. That could be described as deplacements par G sensiblement constants. Le manche permet donc de piloter un facteur de charge. - that is exactly what I am doing here! With the stick in a certain position in pitch I am asking the aircraft to give me a certain G, and the flight control system will do its best to try to give me that, as long as it is still possible. I believe the real Mirage 2000 at speeds above 300 behaves in exactly the same way as I described above for the F-15. Actually I would be very surprised if it does not. 15test6.trk

You probably mean "max available G for the current altitude". Are you 100% sure about that? The manual says " deplacements par G sensiblement constants au-dessus de 300kt environ ", it doesn't say this applies only if altitude is constant. Personally I interpret this "constant" as "constant in the entire flight envelope as long as speed is above 300." If at sea level the "max available G" is 9 and I pull the stick half, this will give me 4.5G. But if I'm at 40Kft altitude and the "max available G" there is 4, pulling the stick half will give me 2G. But this kind of behaviour surely can't be described as deplacements par G sensiblement constants. In fact, they are very far from constant. This type of flight control logic will give you along the entire flight envelope of the aircraft very large variations in stick displacement per G, in fact as large as an aircraft with conventional pitch control, like for example a MiG-23. What kind of fly-by-wire "smartness" is this? In the F-15 if you pull 4G at sea level and enter an Immelmann and keep the stick in precisely the same position, the aircraft will remain at 4G(+/-0.2G) as long as this is still possible, it doesn't matter how hight you climb.

From real aircraft flight manual: Les commandes de vol sont reglees pour avoir des deplacements par G sensiblement constants au-dessus de 300kt environ. Le manche permet donc de piloter un facteur de charge. It seems to me they are describing a classic G-command type of control there. First experiment At low altitude with full AB with neutral trim in horizontal flight with 600kts I pulled the stick until I see 4G, then kept the stick fixed in precisely the same position. During the Immelmann the G continuously decreased and over the top speed was a little above 300 and G was 2.1 That's some serious variation in stick deflection per G. If I put the stick in a position that commands 4G, shouldn't the flight control try to maintain 4G, just like it would do in an F-15 or F-16? Second experiment At low altitude in horizontal flight with about 400kts constant speed with neutral trim I roll the aircraft inverted, then let go of the stick. The flight control will create about -1.1G. As if the aircraft was expecting inverted flight to last for quite some time. This doesn't make any sense IMO. What's the point of such kind of flight control behaviour? Help pilot recreate Top Gun inverted flight scene? As long as the speed is above 300kts, shouldn't the flight control try to maintain 1G, no matter the flight conditions or aircraft position in space? Am I misinterpreting something? Maybe someone knowledgeable in Mirage 2000 could provide some answers if current simulator behaviour is right or wrong.

I see in the diagram renhanxue posted that Viggen can sustain 7.5G at 1Km altitude and M0.9. That's not bad at all! Actually, this is pretty awesome IMO. This aircraft will easily sustain 8G at sea level. I put the Viggen data for M0.9 and 1.1 at 1Km altitude in a diagram to compare it with MiG-21bis performance using the most powerful ЧР engine mode. See below how it looks like. At M0.5 the MiG-29 can sustain about 5.1G. So for M0.5 I decided to put the Viggen somewhere in the middle between MiG-21 and MiG-29.

The Viggen has such a feature? That's pretty neat! :thumbup: I see in the diagram that at 1Km altitude and M1.1 the Viggen will sustain about 4.6G. In similar conditions a MiG-29 will sustain 6.1G (see attached diagram). Here is a little calculation, yeah it's really rocket science :D 4.6/6.1=0.75 At 5000m and M1.1 the MiG-29 will sustain 5.2, see diagram in my previous post. 5.2*0.75=3.92 Here you go, a Viggen at 5000m and M1.1 will sustain about 4G Thanks for your posts, good stuff!

:doh: I not only highly doubt that, I AM SURE of it, I thought I made that pretty clear in my posts. A MiG-21 is not comparable with a MiG-29 in any respect. My example with MiG-29's split-S diagram was just to show that a MiG-29, a vastly superior fighter compared to MiG-21 will need close to all the lift it can generate to be able to split-S in 1000m. My example was meant to show there's really zero chance a MiG-21 would be able to do the same.