F1 Engine Airspeed Limitations No Longer Present

[gnomechild]

It seems that the only engine limit that currently affects the F1 is the mach limit. The 'LIM' light does not come on for the F1 over 700kts at sea level, and the engine never dies. 

 

[Get_Lo]

If we go off of what the manual says is safe (700knots) and what the brochure says is possible (794knots) we should get our failure point of the engine somewhere in the middle. As is ive seen the F1 in this update go well north of even 870 knots at sea level without engine failure. As ive seen others report the LIM light is working when it hits the Mach criteria, but not working when the IAS criteria is met.

Edited August 24, 2022 by Get_Lo

[sedenion]

What tell you that this is engine that must fail ? The manual simply speak about maximum speed... It is logical that engine may fail according mach number since the problem is the mach shockwave against turbines, but for IAS, my guess is that this is more general structure stress problem.

Edited August 24, 2022 by sedenion

[gnomechild]

Just now, sedenion said:

What tell you that this is engine that must fail ? The manual simply speak about maximum speed... It is logical that engine may fail according mach number since the problem is the mach shockwave against turbines, but for IAS, my guess is that this is more general structure stress problem.

 

The "LIM" warning light should illuminate above 700kts under 20,000ft and above 750kts above 20,000ft. That no longer happens. Additionally, prior to this patch the engine would flame out when you exceeded the limit speeds after some variable amount of time. That also no longer happens

[sedenion]

2 minutes ago, gnomechild said:

The "LIM" warning light should illuminate above 700kts under 20,000ft and above 750kts above 20,000ft. That no longer happens. Additionally, prior to this patch the engine would flame out when you exceeded the limit speeds after some variable amount of time. That also no longer happens

Ok, considering the previous engine modeling was adjusted to flame out each time you sneeze, I think these are two separated problems.

[Vek17]

28 minutes ago, sedenion said:

What tell you that this is engine that must fail ? The manual simply speak about maximum speed... It is logical that engine may fail according mach number since the problem is the mach shockwave against turbines, but for IAS, my guess is that this is more general structure stress problem.

 

It is possible that the previous limit was modeled a bit too low, I am not sure. But Sea level 1200+ IAS should not be possible without destroying the engine. That goes so far beyond any limits I can find anywhere for the aircraft.

Edited August 24, 2022 by Vek17

[Get_Lo]

Highest ive ever seen for the F1 at SL was this brochure, and as expected it shows the ABSOLUTE completely unpractical limits such as a landing speed of 125 knots which would imply a fuel amount so low that you dont even have guaranteed go around
 

Edited August 24, 2022 by Get_Lo

[sedenion]

12 minutes ago, Vek17 said:

But Sea level 1200+ IAS should not be possible without destroying the engine.

In such situation I think several things break apart, not only engine... that's my point, I think the 700kts limit is not engine related, but airframe.

[Vek17]

Well currently the plane basically disintegrates at ~1215 IAS, but the failure point should realistically be much lower by all reasonable accounts.

[Get_Lo]

2 minutes ago, sedenion said:

In such situation I think several things break apart, not only engine... that's my point, I think the 700kts limit is not engine related, but airframe.

well either way, something should be breaking but it isnt, 1200knots on sea level has been done already. Wish I paid more attention to how it worked pre-patch.

Edited August 24, 2022 by Get_Lo

[sedenion]

Just now, Get_Lo said:

well either way, something should be breaking but it isnt, 1200knots on sea level has been done already.

Well, yes and no... the 700kts is probably a safe limit as you pointed out, meaning that above this speed aerodynamics behavior become somewhat unpredictible and dangerous or/and stress on airframe will abnormaly worn out the structure. However, this does not mean the aircraft disintegrate suddenly above 710kts... but ANYWAY, the "LIM" warning should light up.

[IvanK]

1 hour ago, sedenion said:

but ANYWAY, the "LIM" warning should light up.

Reading the Flight manual this is not the case. The LIM light will illuminate for Gear and Flap excedences but not raw IAS excedence in clean config.

It will illuminate if TAT excess of 135C ... which wont happen at 700Kts at Sea level .... or 750 Kts I suggest. Typically you will only see this at very Mach numbers say M2 or >

[Get_Lo]

10 minutes ago, IvanK said:

Reading the Flight manual this is not the case. The LIM light will illuminate for Gear and Flap excedences but not raw IAS excedence in clean config.

It will illuminate if TAT excess of 135C ... which wont happen at 700Kts at Sea level .... or 750 Kts I suggest. Typically you will only see this at very Mach numbers say M2 or >

for the mirage 3, what limited the top speed at low altitude? engine? airframe? heat? ive heard the Mirage 3 was similarly quick to the F1

Edited August 25, 2022 by Get_Lo

[IvanK]

Mirage III Limitation at lo level was primarily Airframe IAS Limit Mir III was 750Knots.

Clean aeroplane at sea level ISA+20 would achieve 730KIAS in a level acceleration and sustain it till the fuel ran out.

There were however cases of the Mirage III doing 810KIAS+...  (typically unloading out of a fight looking backwards) ... Engine change required, Visible damage typically showed most Burner liners flattened and or cracked.

At Altitude Limitation was 750KIAS/M2.0 or 125C TAT. At M2.0 the aeroplane was still accelerating.

[gnomechild]

1 hour ago, IvanK said:

Reading the Flight manual this is not the case. The LIM light will illuminate for Gear and Flap excedences but not raw IAS excedence in clean config.

It will illuminate if TAT excess of 135C ... which wont happen at 700Kts at Sea level .... or 750 Kts I suggest. Typically you will only see this at very Mach numbers say M2 or >

I didn't think to check the manual. I was assuming the previous behavior + RedKite's tutorial from Aerges info was correct but it looks like this was an intentional change that didn't make it into the patch notes. Your information is correct

 

 

[Harlikwin]

2 hours ago, IvanK said:

Reading the Flight manual this is not the case. The LIM light will illuminate for Gear and Flap excedences but not raw IAS excedence in clean config.

It will illuminate if TAT excess of 135C ... which wont happen at 700Kts at Sea level .... or 750 Kts I suggest. Typically you will only see this at very Mach numbers say M2 or >

Honestly I'd unmark that as solution and maybe change it to under investigation... Mirage F1 seems to have serious overspeed issues. Mind you this is in a dive with AB on but you can hit this pretty easily. 

 

Literally the world speed record at sea level is 896kts... So The F1 is like 200 over that... And actually I think it goes to 1200 before blowing up in DCS... That is unless you know something we don't. So unless Aerges position is that the F1 can do mach 1.8 at sea level this isn't a solution. 

World speed record:

"The speed was set by a civilian F-104 with a borrowed military engine. The world low-altitude speed record was set by Darryl Greenamyer in a rebuilt F-104 on 24 October 1977 at 988.26 mph (869.67 kts; 1,590.45 km/hr). Since no one else has bested that record, the official answer is the F-104."

Edited August 25, 2022 by Harlikwin

[Vek17]

I mean regardless of the limit light the plane is still capable of FAR too much speed at sea level without failure right now and it needs to be addressed.

[Harlikwin]

54 minutes ago, Vek17 said:

I mean regardless of the limit light the plane is still capable of FAR too much speed at sea level without failure right now and it needs to be addressed.

Something on the plane needs to blow up well before 1000kts.... 

[sedenion]

6 hours ago, Vek17 said:

I mean regardless of the limit light the plane is still capable of FAR too much speed at sea level without failure right now and it needs to be addressed.

The problem I see is that as IvanKA explained, aircraft can go overspeed during some time and still be able to RTB and land normally, the damages are spotted during mechanical checkup on the ground and this cannot be simulated.

What you can simulate is in-flight clear failure or damage, but between the safe limit and obvious break point (let say, 1200kts for example) there is an unknow territory where aircraft take more or less invisible dammages that may or may not directly impact the aircraft for the next houres of flight...

Edited August 25, 2022 by sedenion

[felixx75]

https://forum.dcs.world/topic/253872-mirage-f1-project-update/?do=findComment&comment=5034826

Here's an example with 1100+kts

Edited August 25, 2022 by felixx75

[sedenion]

16 minutes ago, felixx75 said:

https://forum.dcs.world/topic/253872-mirage-f1-project-update/?do=findComment&comment=5034826

Here's an example with 1100+kts

I wonder which is the true problem, the fact it still in one piece at IAS 1100, or a high-speed drag wrongly modelised. Is a real aircraft even able to reach this speed at sea level ? My intuition tell me that drag would prevent such thing to happen.

Edited August 25, 2022 by sedenion

[Loukuins]

Also if the plane achieve this speed I don't think the wings will handle that ^^'

[MysteriousHonza]

1 minute ago, Loukuins said:

Also if the plane achieve this speed I don't think the wings will handle that ^^'

Wings? The canopy would melt under that speed. Mirage 2000C is limited due to canopy mainly and antenas and stuuf, it will melt away.

[Vek17]

Attaching some tracks of excessive low altitude speed.

Marianas - 840kt Before normal acceleration stopped 847 kt top speed at 600 feet
South Atlantic - 888kt before normal acceleration stopped 893kt top speed at 200ft
Caucasus - 840kt before normal acceleration stopped 847kt top speed at 500ft

These were flown with altitude hold and in some cases the plane just didn't want to sit as low as it started gaining several hundred feet after engaging. They all include takeoffs and run until fuel depletion, but only South Atlantic was from a cold start. Not sure what hot start is doing differently to lose -46kt.

893kt-SouthAtlantic.trk 847kt-Marianas.trk 847kt-Caucasus.trk

[Bremspropeller]

18 hours ago, Bremspropeller said:

I gave it a couple of shots - all the "high IAS" tests ended with me blowing up at 1110'ish IAS with the LIM light blaring.

 

1) Low level, I maxed out at 890IAS (briefly). The airplane struggles at around M1.2, but when the shock-cones are starting to travel, she starts accelerating at a higher rate (beyond 790-800'ish). She never quite reaches (close, though) M1.4 where the engine would go into survitesse and whjere it would add 500RPM (8900RPM) automaticly.

There's some sh1tty flying on my part. I did get hung ailerons/ spoilers in a turn at 880IAS. The ailerons/ spolers went full direction at zero effect. There certainly is something off here, but it's most likely unrelated.

test lo.trk 727.16 kB · 0 downloads

2) I tried the 1100IAS run pretty much the way you described, but i started subsonic, went supersonic and pitched down around M1.2'ish to get beyond the transonic drag rise. Survitesse at M 1.4. The airplane would accelerate beautifully up to the point where it blows both wings. I had that happen on all three trials I did. The LIM light at that point had been on for about 5-10s.

test hi3.trk 298.57 kB · 0 downloads

 

 

I like quoting - especially quoting myself, so here's my tests from the other thread. The LIM light comes on around 1000KIAS (second track), which is about expactable. Both tests are at ISA (standard temp and pressure at SL).

Giving this whole thing some thought (see the other thread), I think there's no real big global toss-up here. What can be observed is that the aircraft struggles around 790KIAS'ish (about M1.2) and slows down it's acceleration significantly. Only when the souris (intake shock cones) are moving forward, the acceleration picks up again.

This is ballpark expected behaviour and it would still be about in tune with the russian intel-report. What's not in tune with the report is that the aircraft manages to power through the transonic drag-rise and have the intakes start moving so that it will eventually get "on step", only reaching it's thrust-drag equilibrium at about 890. That's with the motor at 8400RPM, just short of another thrust bump, when gettig into survitesse at M 1.4.

The 1100KIAS figure can only be achieved coming down in a dive with the engine in survitesse. I haven't yet been able to nurse the aircraft onto the deck and observe whether ths speed can be maintained, though.