FM Changes

[khajaja]

3 minutes ago, Bremspropeller said:

Says the user with a grand-total postcount of "1"

been lurking since 2020, only posted cause get_lo linked your post lmao

Edited August 25, 2022 by khajaja

[gnomechild]

I think this conversation is somewhat pointless until Aerges weighs in with what their long term plan is for these changes. It seems pretty clear to me that these changes were merged unintentionally considering there are several very significant differences completely absent from the patch notes. I personally don't think a stock F1 should be able to set an IAS speed record. But, I'll wait to argue about it until Aerges says it's intentional. They very well could be in the middle of re-working failure conditions and whatnot 

[SuperEtendard]

45 minutes ago, sedenion said:

The alleged maximum speed of Mirage F1 at sea level is 1450-1470 km/h depending the source... so ~780-790 kts, which seam reasonable maximum reached speed for such aircraft.

1450 km/h for top speed clean at sea level is plausible, after all other fast fighters of the era had speed limits around that (MiG-23, JA 37). However 1620 km/h surpasses that by a fair amount.

Also, the 1984 Soviet intelligence technical report places the Mirage F1 top speed with two Magics at around 1300 km/h at sea level, as drag limited, a bit higher up is where it becomes dynamic pressure limited (10,000 kgf/m^2) and then Mach limited.


 

45 minutes ago, Badger1-1 said:

But Mass has nothing to do with Topspeed, just how fast you get there...( in a reasonable Airplane, were not talking Wright brothers here)

It's not about the mass, but about removing those external components and sealing/fairing over the fuselage and wing leading edge which would present a significant drag reduction. Even if these components are retractable, tolerances aren't perfect so you will always have seam lines causing some level of drag.





It was a very cleaned up plane

44 minutes ago, Bremspropeller said:

Lighter doesn't change the top-speed. Only the time to get there. No engine thrust-changes, no aero refinements and no shock-come refinements (which would have been available).

That's false. The F1 is an interceptor. The F1 even has a highter CIT limit than the 104 (135°C vs 120°C). Plus the F1 has an area-ruled fuselage, which the 104 doesn't.

In regards to the modifications same as what I said above.

About area rule, it helps reduce the drag of a given design, but then it's speed will be the result of the interaction of it's total drag (including lift induced drag) and engine thrust. MiG fighters weren't area ruled yet they still were among the fastest fighters of their times, the MiG-21 reaching Mach 2, the MiG-23 being able to reach up to Mach 2.6, the MiG-25 being able to surpass Mach 3.

A plane being area ruled or not without further analysis shouldn't be indicative of it's speed characteristics.

Also you can see in that second photo of the RB F-104, the F-104 does seem to be area ruled, the fuselage decreases it's diameter at the mid point where the wings are present. And here in this photo you can see the intake duct volume decreasing as it reaches the mid point of the wings too.

Edited August 25, 2022 by SuperEtendard

[Bremspropeller]

10 minutes ago, Get_Lo said:

I also have no evidence it cant go over Mach 2 at sea level, or mach 5. You're right

Another strawman.

You're completely missing the point here. We're not talking some arbitrary book number that comes out of a flight-test to satisfy a requirement but we're talking absolute thrust-drag equilibrium airspeed. Until somebody actually tries that out, nobody knows how fast the aircraft will go. It takes a special kind of "brave" to fly the airplane 150kts beyond it's redline speed. Hit a bird? You're dead. Lose a SAS channel? You're pink mist.

And that is precisely the point. Nobody knows how fast the F1 could go. It's not a number out of the handbook (that's just an operational limitation) or out of any magazine. It's a matter of trying it out. That's precisely why I came up with the 104 example, which has a redline of 750, which didn't keep pilots from going far into the 800s. The airplane could and would do it readily. The same (easily exceeding redline numbers) is true for most cold war turbojet fighters.

One more thing about speed records: The main focus isn't going as fast as physically possible, but beating the previous record-holder by enough a margin to get the record oneself. It's not a manifestation of what the record-aircraft could do, not what any other aircraft around could do, since they weren't measured. The speed-record is not a meaningful metric in this discussion.

 

[Get_Lo]

3 minutes ago, Bremspropeller said:

Another strawman.

You're completely missing the point here. We're not talking some arbitrary book number that comes out of a flight-test to satisfy a requirement but we're talking absolute thrust-drag equilibrium airspeed. Until somebody actually tries that out, nobody knows how fast the aircraft will go. It takes a special kind of "brave" to fly the airplane 150kts beyond it's redline speed. Hit a bird? You're dead. Lose a SAS channel? You're pink mist.

And that is precisely the point. Nobody knows how fast the F1 could go. It's not a number out of the handbook (that's just an operational limitation) or out of any magazine. It's a matter of trying it out. That's precisely why I came up with the 104 example, which has a redline of 750, which didn't keep pilots from going far into the 800s. The airplane could and would do it readily. The same (easily exceeding redline numbers) is true for most cold war turbojet fighters.

One more thing about speed records: The main focus isn't going as fast as physically possible, but beating the previous record-holder by enough a margin to get the record oneself. It's not a manifestation of what the record-aircraft could do, not what any other aircraft around could do, since they weren't measured. The speed-record is not a meaningful metric in this discussion.

 

How about you just read the post above, im not interested in speculation that would undermine the modelling of every aircraft's top speeds and G limits, after all, the F-15 can theoretically pull 30Gs right?

[Bremspropeller]

12 minutes ago, SuperEtendard said:

About area rule, it helps reduce the drag of a given design, but then it's speed will be the result of the interaction of it's total drag (including lift induced drag) and engine thrust. MiG fighters weren't area ruled yet they still were among the fastest fighters of their times, the MiG-21 reaching Mach 2, the MiG-23 being able to reach up to Mach 2.6, the MiG-25 being able to surpass Mach 3.

A plane being area ruled or not without further analysis shouldn't be indicative of it's speed characteristics.

Also you can see in that second photo of the RB F-104, the F-104 does seem to be area ruled, the fuselage decreases it's diameter at the mid point where the wings are present. And here in this photo you can see the intake duct volume decreasing as it reaches the mid point of the wings too.

The 104 wasn't specificly area-ruled. It just happens to have a good enough fineness-ratio distribution. The Mirage (even the Mirage III) has applied area-ruling for wave-drag optimization. It's very (!) subtle on the III, but readily apparent on the F1, where the rear fuselage bulges out a good deal hence creating a true coke-bottle.

 

 

[sedenion]

10 minutes ago, Bremspropeller said:

Another strawman.

You're completely missing the point here. We're not talking some arbitrary book number that comes out of a flight-test to satisfy a requirement but we're talking absolute thrust-drag equilibrium airspeed. Until somebody actually tries that out, nobody knows how fast the aircraft will go. It takes a special kind of "brave" to fly the airplane 150kts beyond it's redline speed. Hit a bird? You're dead. Lose a SAS channel? You're pink mist.

And that is precisely the point. Nobody knows how fast the F1 could go. It's not a number out of the handbook (that's just an operational limitation) or out of any magazine. It's a matter of trying it out. That's precisely why I came up with the 104 example, which has a redline of 750, which didn't keep pilots from going far into the 800s. The airplane could and would do it readily. The same (easily exceeding redline numbers) is true for most cold war turbojet fighters.

One more thing about speed records: The main focus isn't going as fast as physically possible, but beating the previous record-holder by enough a margin to get the record oneself. It's not a manifestation of what the record-aircraft could do, not what any other aircraft around could do, since they weren't measured. The speed-record is not a meaningful metric in this discussion.

I would agree the general reasoning... now, the question remain : Is this mentioned 1470 km/h max speed of the Mirage F1 an operational maximum speed, or the maximum sustained speed actually reachable by the aircraft according thrust/drag parameters.

[Get_Lo]

41 minutes ago, sedenion said:

I would agree the general reasoning... now, the question remain : Is this mentioned 1470 km/h max speed of the Mirage F1 an operational maximum speed, or the maximum sustained speed actually reachable by the aircraft according thrust/drag parameters.

1300kph(700knots) is the safe operational speed. appears to be 1470 is the drag limit. which funny enough is 794 knots. the exact same as my source earlier.

Edited August 25, 2022 by Get_Lo

[sedenion]

21 minutes ago, Get_Lo said:

1300kph(700knots) is the safe operational speed. as listed above in the Soviet report, 1470 is the drag limit. which funny enough is 794 knots. the exact same as my source earlier.

What disturbs me is that the alleged Mirage 2000 max speed at sea level is the same, 1470 km/h / Mach 1.2... however Mirage 2000 have 2.5 tons more thrust than the Mirage F1.

Edited August 25, 2022 by sedenion

[Get_Lo]

1 minute ago, sedenion said:

What disturbs me is that the alleged Mirage 2000 max speed at sea level is the same, 1470 km/h / Mach 1.2... however Mirage 2000 have 2.5 tons more thrust than the Mirage F1.

 

Thrust only gets you so far, look at the MiG-25's top speed at sea level, iirc its barely or not even Mach 1, Another example is the J79 F-16 which was just as fast as the normal F-16A

Edited August 25, 2022 by Get_Lo

[sedenion]

8 minutes ago, Get_Lo said:

Thrust only gets you so far, look at the MiG-25's top speed at sea level, iirc its barely or not even Mach 1

Possible, but this 1470km/h number seam to be nothing more than the conversion from Mach 1.2, a well rounded number, sounding more arbitrary than "scientifically" measured...

Edited August 25, 2022 by sedenion

[Get_Lo]

Just now, sedenion said:

Possible, but this 1470km/h number seam to be not more than the conversion from Mach 1.2, a well rounded number, sounding more arbitrary than "scientifically" measured...

perhaps, I wouldnt know anything about it other than whats published.

[IvanK]

Clean, best I can do at Sea level is 790k IAS with Buffet onset at around 750 K IAS

Rapid rolls with feet on the floor result in visible uncommanded rudder pedal movement in tune with the oscillations post roll.

Edited August 25, 2022 by IvanK

[Bremspropeller]

3 minutes ago, Get_Lo said:

1300kph(700knots) is the safe operational speed. as listed above in the Soviet report, 1470 is the drag limit. which funny enough is 794 knots. the exact same as my source earlier.

So your secondary source is quoting the soviet intelligence report, which in turn is based on calculations, giving ballpark numbers. They don't take actual installed engine performance into account. The report is not gospel. Unless it's based on actual numbers by Dassault, who at least could validate wind-tunnel data against flight-test (installed) thrust-curves to determine the real numbers. The Russians had acces to the F1 when South Africa sought to re-engine theirs. But that was about 10 years after said report was published.

At least now we know there your magazine-figures are coming from.

22 minutes ago, sedenion said:

I would agree the general reasoning... now, the question remain : Is this mentioned 1470 km/h max speed of the Mirage F1 an operational maximum speed, or the maximum sustained speed actually reachable by the aircraft according thrust/drag parameters.

We'll never know, as most jets were never tested to equilibrium airspeed, which would be a useless test in the first place as it has zero real world signifigance. Picture this:

Nobody is zipping around clean and going at +800kts away from the airfield, looking when the ASI needle is eventually going to stop moving, which is probably at the same time the tanks are empty (or something breaks first). It's really only an issue when sitting behind a computer screen with a refly button.

3 minutes ago, sedenion said:

What disturbs me is that the alleged Mirage 2000 max speed at sea level is the same, 1470 km/h / Mach 1.2... however Mirage 2000 have 2.5 tons more thrust than the Mirage F1.

That's because it's not the M2k's "top speed". It's most probably bourne from some limitation with a given margin to a failure-mode. I'd personally rather see that failure than a top-speed that somebody thinks is valid, based on some airspeed-record. And I think you're thinking the same way.

9 minutes ago, Get_Lo said:

Thrust only gets you so far, look at the MiG-25's top speed at sea level, iirc its barely or not even Mach 1

That "top speed" isn't. It's most likely a gust-load limitation due to the Foxbat's low structural rated g limits. If you can go M2.5 plus at high altitude, you WILL go through the Mach on the deck. Easily. Thrust-wise, that is. You may fold yourself in half in a Foxbat in the process...

[sedenion]

13 minutes ago, Bremspropeller said:

I'd personally rather see that failure than a top-speed that somebody thinks is valid, based on some airspeed-record. And I think you're thinking the same way.

Well, not realy, my perspective is more flight-model accuracy related. Imagine for example our simulated Mirage F1 can reach 1500kts at sea level, this would obviously mean that drag is not properly adjusted or thrust way too powerfull, so the flight-model is potentially all wrong. EDIT : the same problem exist in the opposite situation, in the case the simulated Mirage F1 is stupidly stuck at 750 kts to fit an arbitrary limit given by standard specifications.

Edited August 25, 2022 by sedenion

[Get_Lo]

4 minutes ago, Bremspropeller said:

So your secondary source is quoting the soviet intelligence report, which in turn is based on calculations, giving ballpark numbers. They don't take actual installed engine performance into account. The report is not gospel. Unless it's based on actual numbers by Dassault, who at least could validate wind-tunnel data against flight-test (installed) thrust-curves to determine the real numbers. The Russians had acces to the F1 when South Africa sought to re-engine theirs. But that was about 10 years after said report was published.

 

That "top speed" isn't. It's most likely a gust-load limitation due to the Foxbat's low structural rated g limits. If you can go M2.5 plus at high altitude, you WILL go through the Mach on the deck. Easily. Thrust-wise, that is. You may fold yourself in half in a Foxbat in the process...

Ill rather take my sources over your speculation, thank you

12 minutes ago, IvanK said:

Clean, best I can do at Sea level is 790k IAS with Buffet onset at around 770 K IAS

Seems to be another case of our F1s being different, here is 845 no problem
null

[IvanK]

Yes you are right just didn't give it long enough 1G accel ended up at 836K IAS.

[gnomechild]

[Get_Lo]

I have also noticed the wobbly rudder you mentioned, nose/rudder pedals try to defect to the Soviets every time I roll the jet.
Whats just as bad if not worse is this pitch, it has a mind of its own too! 

Edited August 26, 2022 by Get_Lo

[Vek17]

Top out at about 880kt from takeoff (so not max fuel) to hitting the limit before I had to burn more fuel to get faster. 893kt by the time I ran out of fuel. Clean at 200ft

[Get_Lo]

15 minutes ago, Vek17 said:

Top out at about 880kt from takeoff (so not max fuel) to hitting the limit before I had to burn more fuel to get faster. 893kt by the time I ran out of fuel. Clean at 200ft

new record, can we do 900 next?

Edited August 26, 2022 by Get_Lo

[MiG21bisFishbedL]

I'm getting a right roll accompanied by a weird buffeting and one of the elevators being deflected while the other isn't.

Still, 848KTAS @ 200ft MSL on the Persian Gulf.

[rossmum]

5 hours ago, Get_Lo said:

Thrust only gets you so far, look at the MiG-25's top speed at sea level, iirc its barely or not even Mach 1, Another example is the J79 F-16 which was just as fast as the normal F-16A

25's top speed at low level is limited by severe flutter @ 1200 IAS. It could go faster (albeit not by much) if you really hate having your ailerons still attached. It is however also a very big aircraft that has a surprisingly poor TWR when fully fuelled.

Regardless, good luck finding any aircraft that can exceed M 1.2 on the deck in standard conditions, while in combat configuration (ie full onboard equipment, painted up, external antennas present, etc.) - especially from that era. You won't, because they either physically don't have enough thrust to keep them accelerating, or because something happens at that speed which is mutually exclusive with continued flight.

Any claim the F1 could achieve north of 800 knots at sea level is naive at best and intellectually dishonest at worst, which fits with the moving of goalposts and failure to address any argument which isn't easily deflected or dismissed as some sort of logical fallacy, as if fluid dynamics care about high school debating technique.

Edited August 26, 2022 by rossmum

[Bremspropeller]

1 hour ago, rossmum said:

Any claim the F1 could achieve north of 800 knots at sea level is naive at best and intellectually dishonest at worst, which fits with the moving of goalposts and failure to address any argument which isn't easily deflected or dismissed as some sort of logical fallacy, as if fluid dynamics care about high school debating technique.

There are no moving goalposts here. People seem to have a hard time managing uncertainties. The only things we know for certain so far are:

- There's a soviet report with unknown confidence levels (could be reasonably accurate or could be off) taken as gospel.

- Speed records are poorly understood on this forum.

- Top speed is poorly understood on this forum.

- There still hasn't been a single trackfile pointed forward. Talk about intellectual dishonesty...

A max achievable airspeed of north than 800 knots is certainly reasonable. If the soviet report is off by 5%, we're at 820kts or more.

6 hours ago, sedenion said:

Well, not realy, my perspective is more flight-model accuracy related. Imagine for example our simulated Mirage F1 can reach 1500kts at sea level, this would obviously mean that drag is not properly adjusted or thrust way too powerfull, so the flight-model is potentially all wrong. EDIT : the same problem exist in the opposite situation, in the case the simulated Mirage F1 is stupidly stuck at 750 kts to fit an arbitrary limit given by standard specifications.

So is mine. Trouble is, we don't have enough data. All we do have is the soviet report and no actual flight test data, as that part of the envelope isn't explored during flight testing.

I'll give you there's something off. It'll happily go plus 600 in MIL on the deck (two tips, single tank), but won't push through the Mach in blower at high altitude. It also has a good deal of thrust-drag divergence going on at M2+ at high altitude (I had to pull up more than 15° at FL550 to keep her from overspeeding). The thrust-divergence to me seems more realistic than the magic brick-wall with the tank.

[sedenion]

4 minutes ago, Bremspropeller said:

The thrust-divergence to me seems more realistic than the magic brick-wall with the tank.

I think we almost all agree that payload drag is exaggerated, this was already observed prior to the last update... But anyway it seem many thing still to be adjusted.