Engines performance above 20,000ft

[howie87]

20% fuel, Takeoff with full afterburner and reach 350 knots, pitch to 45 degrees nose high and hold attitude.

 

True airspeed beings to increase rapidly above 20,000ft and the Mirage hits Mach 1.46 during this climb.

 

Where airspeed should begin to bleed off the aircraft seems to take off like a rocket.

 

For proof that something is very wrong...

 

Streak eagle F-15 time to climb world records:

 

15,000m 49,213ft 1:17

20,000m 65,617ft 2:03

 

RAZBAM M2000 time to climb:

 

15,000m 49,213ft 1:47

20,000m 65,617ft 2:03

Edited December 25, 2015 by howie87

[Pikey]

I got to 96 thousand feet altitude. Reproducible. Get to 35K casually, build to top speed - a little over m2, take it to vertical, the thing is trying to find Kerbal's.

[golani79]

Had a flameout at 72k yesterday - haven´t tried to go up that high again though ^^

[Manuel_108]

Lol, casually going 2x the service ceiling of 50 000 ft. - Just 2000C things.

[Aginor]

I tried accelerating at around 40,000ft (goes very well), pitched up with Mach 2 and got to around 85,000, with the flameout happening somewhere between 70,000 and 80,000 (forgot when).

I also had the impression that the high altitude performance might be too good. I am not sure whether it is too low drag or too much thrust.

 

@Manuel: Going far above the service ceiling is nothing unusual though (see definition).

[howie87]

The issue isn't the max altitude you can climb to, it's how quickly it gets there.

 

A Mirage 2000 shouldn't be able to match the Streak Eagle to 65,000ft.

 

Especially in a 45 degree climb from sea level!

 

Just fly the profile I outlined and you will see what I mean. IAS and Mach increase at an unrealistic rate right at the point they should be decreasing in such a steep climb.

[sedenion]

20% fuel, Takeoff with full afterburner and reach 350 knots, pitch to 45 degrees nose high and hold attitude.

 

True airspeed beings to increase rapidly above 20,000ft and the Mirage hits Mach 1.46 during this climb.

 

With 20% fuel the T/W ratio of the M2000 with AB is near 1.2...

 

The issue isn't the max altitude you can climb to, it's how quickly it gets there.

 

A Mirage 2000 shouldn't be able to match the Streak Eagle to 65,000ft.

 

And i ask : Why ?

 

From Wikipedia (fr):

F-15 claimed ascensional speed: 15 240 m/min

M2000 claimed ascensional speed: 18 000 m/min

 

Don't know how or why, but that is the claimed ascensional speed... An answer can be that: even if M2000 has a less good T/W ratio, it has less drag than the F-15 (which is obvious, the question is: HOW many less)...

 

Maybe the flight model for M2000 must be tweaked, and the engine is may be a little too powerful at high altitude... but, don't underestimate the M2000 and don't overestimate the F-15...

Edited December 27, 2015 by sedenion

[jojo]

The thing is pilot should passed out about operational ceiling.

 

This ceiling is due to cockpit pressurization.

[codefox]

I got to 96 thousand feet altitude. Reproducible. Get to 35K casually, build to top speed - a little over m2, take it to vertical, the thing is trying to find Kerbal's.

 

That's called a zoom climb. That's perfectly fine, the F-15 and Su-27 are also able to do this.

[howie87]

With 20% fuel the T/W ratio of the M2000 with AB is near 1.2...

 

 

 

And i ask : Why ?

 

From Wikipedia (fr):

F-15 claimed ascensional speed: 15 240 m/min

M2000 claimed ascensional speed: 18 000 m/min

 

Don't know how or why, but that is the claimed ascensional speed... An answer can be that: even if M2000 has a less good T/W ratio, it has less drag than the F-15 (which is obvious, the question is: HOW many less)...

 

Maybe the flight model for M2000 must be tweaked, and the engine is may be a little too powerful at high altitude... but, don't underestimate the M2000 and don't overestimate the F-15...

 

You're quoting facts from Wikipedia about the regular F-15.

 

First of all the Streak Eagle was stripped of all none essential avioncs and even paint and had an empty thrust to weight ratio of 1.33. It also only carried only just enough fuel for each flight and had to fly a very specific flight profile to reach that altitude in that time. Not just point 45 degrees nose up and accelerate.

 

Thrust decreases at altitude as air density decreases. Even with a thrust to weight ratio of better than 1 at sea level, by the time you're up at 30,000ft it would be much less.

[KansasCS]

Lol, just wanted to open a thread on this.

In any case, I attached some screens.

 

I ended up out of fuel at 61k feet.

I took off with basically nothing in the tanks.

[mvsgas]

So far I have not found a thread about this and this one seems to have similar bug.

NTTR DCS 2 open alpha 2.0.2.52658.72

At 57k feet, I was able to achieve mach 3.25 without AB, just at mill power. It was online in the virtual-aerobatics server. No weapons or external tanks. Did not use AB at all, not even on takeoff. Could someone verify?

[Rlaxoxo]

So far I have not found a thread about this and this one seems to have similar bug.

NTTR DCS 2 open alpha 2.0.2.52658.72

At 57k feet, I was able to achieve mach 3.25 without AB, just at mill power. It was online in the virtual-aerobatics server. No weapons or external tanks. Did not use AB at all, not even on takeoff. Could someone verify?

 

Wat ...?

 

Mach 3.25 with no afb?

[mvsgas]

Here is the track. Is long, like I said it's from online. I tried to watch it twice, but it crash DCS every time. I was hoping someone could confirm to see if it was a lag issue or I did something wrong during the engine start, like shutting off the probe heat of something.

 

Edit

I'm trying to load the track but is not letting me, file is to big. I already compress it with 7z. How can I make it smaller? I guess I will go back to the server see if more people can join and confirm.

[mvsgas]

I got it, is the probe heat, I think it is. Using the RWR and fuel pump switches as an example, I was setting the ECS panel switches to "M" position, making the assumption that was the on position, but those switches are reverse. It appears they have to be on "A" to work properly...or it could be the fact that I have no idea what are they for and what is the correct positions.

[ridbobkan]

@CptSmiley: Hello, this is quite easy to recreate. Climb to 35000 feet. Then go supersonic (around 1.2 for exemple). Switch off AFB, and climb slowly to 47000. You'll see how fast is the bird :)

 

I can reproduce this situation in 30 seconds, just playing single and compressing time :)

 

Thanks.

[mvsgas]

I'm very confused, how does this correlate to engine/performance behavior?

 

You mention probe heat, RWR, and fuel pump all of which don't have anything to do with engine or aerodynamic performance. To add I'm not sure what this post is trying to say :( maybe a language barrier issue?

 

EDIT: To add, I went on that server and was unable to recreate myself.

 

Ok, let me try to explain;

During a flight in the virtual aerobatic server, I notice abnormal speed indication and altitude indications. Speed of over mach 3 and altitude of 57kfeet with engine at mil power. I did not know what cause this speed/altitude indication, but the discrepancy seem similar to the one mention on this thread. I posted here in hopes anyone could verify this version (NTTR DCS 2 open alpha 2.0.2.52658.72) had a bug or if I made a mistake.

 

During the engine start on this first missions, on the environmental control panel, I move all three switches forward, to the "M" position. I have been doing this because some of the switches in the cockpit, including the RWR switches in the RWR panel, the power switches and the fuel pump switches are moved to the "M" position.

 

Example;

 

Now, after your response post;

Hi mvgas, I will need more info to possibly replicate, tried a few times and nothing close at all. If you can provide a video or track if you manage to recreate. I'll actually get on the virtual aerobatics server in a bit and try there to cross-check everything.

 

I was unable to upload a track file, so I went back to the virtual aerobatic server, in an attempt to duplicate the speed and altitude readings. On this second flight, I forgot to turn environmental control switches forward and did not see the abnormal speed and altitude reading. When I noticed the environmental control switches position on this second flight, I assume they where the cause of the initial flight problem, but I have been unable to verify this.

 

Hope this make since.

Edited May 1, 2016 by mvsgas

[mvsgas]

I was able to reproduce in single player. I can verify that turning environmental control switches forward, after starting without ground power can cause the speed and altitude abnormal readings. So any chance we could get more info on those switches and their proper positioning? Obviously, right now I just need to leave them alone, just wondering what are they for?

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[Rlaxoxo]

@CptSmiley: Hello, this is quite easy to recreate. Climb to 35000 feet. Then go supersonic (around 1.2 for exemple). Switch off AFB, and climb slowly to 47000. You'll see how fast is the bird :)

 

I can reproduce this situation in 30 seconds, just playing single and compressing time :)

 

Thanks.

 

I can't seam to reproduce the bug using this method is this 2.0.2?

Edited May 1, 2016 by Rlaxoxo

[mvsgas]

It's really really hard to, I was able to, but you have to do everything just right and never go into AB.

 

BTW mvsgas, although this helped find this issue, operating procedure always calls for full AB takeoff.

 

Cool, thanks for the info.

[TheSnark]

Well done smiley! Identified and fixed in a single day, and a sunday no less! I'm glad I got the M-2000C!