Abrupt stop of accelleration at M1.72

[razo+r]

The setup was following: Instant mission (Beachhead Interdiction), fired of mavs and the RB-24s, Then ditched the tank and also pressed the button to drop stores, flew to 11Km altitude with around Mach 1.1 in the climb, then levelled of at that altitude and flew with zone 3 AB straight.

 

Then after a while, I noticed that I couldn't go past M1.72. I climbed a bit, nothing. Descended a bit, no change.

 

Then I repeated this test, but in a new mission. Default weather settings, no stores and 60% fuel.

 

Starting point at 11km with M1.3, altitude autopilot on and Zone 3. I accellerated, and at point M1.72, I hit like a wall and couldn't accellerate anymore. Below that point, the speed was rising quickly, and at M1.72 an abrupt stop in accelleration.

 

This can't be true, can it?

[Vilab]

It is not a recent issue

 

The viggen accelerate (too) fast until it hit that speed wall

 

It used to be mach1.85ish, now it looks like it is lower, but it is the same

[frosen]

I hope Heatblur will fix all these bugs soon so this bird finally can leave Early Access. It's kind of flabbergasting that anything can be considered (and allowed by ED) to be early access 2.5 years after it's initial release... :(

[fl0w]

Not a new issue, this is the same as from the past with the Viggen Mach 1.8+ bug. Tweaks of the flight model from HB has made it lower, but it still persists from likely the colder temperature by rising altitude increasing engine performance.

[TOViper]

Not a new issue, this is the same as from the past with the Viggen Mach 1.8+ bug. Tweaks of the flight model from HB has made it lower, but it still persists from likely the colder temperature by rising altitude increasing engine performance.

 

 

This issue was posted long time ago, see here:

https://forums.eagle.ru/showthread.php?t=194415

 

 

To sum it up:

 

A few think its a mathematical problem with the model, some think "the wall" is ok due to compression effects happening at M1.72, some are unsure. HB made one post there stating they fixed some overspeed effects.

Most of us are sure that the model currently accelerates too fast from M1 to M1.5.

[Katj]

This issue was posted long time ago, see here:

https://forums.eagle.ru/showthread.php?t=194415

 

 

To sum it up:

 

A few think its a mathematical problem with the model, some think "the wall" is ok due to compression effects happening at M1.72, some are unsure. HB made one post there stating they fixed some overspeed effects.

Most of us are sure that the model currently accelerates too fast from M1 to M1.5.

As I'm sure you know, the Viggen's RM8 engine has a very high bypass ratio, which means a lot of air for the huge afterburner. There are charts somewhere around the forum that clearly show that at zone 3 burner the thrust increases with speed at roughly the same rate as the drag. So acceleration should be fairly constant in a pretty large envelope.

 

But the Viggen also has fixed inlets that will give you an abrupt end to said acceleration.

 

The in game Viggen may have the wrong numbers, and that 40 000' test in the linked thread seems way off. But conceptually it's correct (in accordance with the declassified charts) that you will have very good acceleration that comes to an abrupt end (although maybe not as abrupt as the current simulation).

 

By the way max speed in terms of mach is temperature dependent, and the advertised mach 2 top speed requires cold conditions.

 

I recently read a blog post written by a former pilot that said that his record was mach 1.97, and he didn't know any air force pilot that broke mach 2.

 

However, he also said that he was still accelerating when he ran out of fuel, and implied that higher speed could be possible with certain flight profiles. This was with a SF-37 reconnaissance aircraft.

[Oscar81]

As I'm sure you know, the Viggen's RM8 engine has a very high bypass ratio, which means a lot of air for the huge afterburner. There are charts somewhere around the forum that clearly show that at zone 3 burner the thrust increases with speed at roughly the same rate as the drag. So acceleration should be fairly constant in a pretty large envelope.

 

But the Viggen also has fixed inlets that will give you an abrupt end to said acceleration.

 

The in game Viggen may have the wrong numbers, and that 40 000' test in the linked thread seems way off. But conceptually it's correct (in accordance with the declassified charts) that you will have very good acceleration that comes to an abrupt end (although maybe not as abrupt as the current simulation).

 

 

By the way max speed in terms of mach is temperature dependent, and the advertised mach 2 top speed requires cold conditions.

 

I recently read a blog post written by a former pilot that said that his record was mach 1.97, and he didn't know any air force pilot that broke mach 2.

 

 

However, he also said that he was still accelerating when he ran out of fuel, and implied that higher speed could be possible with certain flight profiles. This was with a SF-37 reconnaissance aircraft.

 

 

I´ve read that interview a long time ago but i thought it was a Ja 37. Then the Ja 37 would have no problem passing mach 2, with the bigger engine. And the AJS could probobly do just over mach 2.