[NO BUG?] VSTOL issue with the new patch?

[Supmua]

Is it me or you have to push the engine harder for VTO and VL now?  I’m also having trouble taking off from the Tarawa with STO in a loaded jet, no issue before the patch using the my own mission which hasn’t changed.

[Ramsay]

AFAIK engine thrust has been reduced in the latest Open Beta patch

 

DCS AV-8B N/A by RAZBAM Simulations

• Improvement: Various FM performance adjustments

 

https://forums.eagle.ru/topic/170893-dcs-world-25-changelog-and-updates-of-open-beta/?do=findComment&comment=4652887

 

Edited May 6, 2021 by Ramsay

[Beltza]

 

Wellcome to the new turtle. It is as slow as the A10. All we have learn with this module can be throw to the trash, all the missions we have edited can be throw to the trash.

It has been my favorite module but with this state it is to be kept in a drawer. Damn! 

 

[myHelljumper]

25 minutes ago, Beltza said:

 

Wellcome to the new turtle. It is as slow as the A10. All we have learn with this module can be throw to the trash, all the missions we have edited can be throw to the trash.

It has been my favorite module but with this state it is to be kept in a drawer. Damn! 

 

I don't know what you want us to do about that..... Should we have keept the unrealistic performances ?

[Beltza]

So you mean RAZBAM has give us a cheating module for years? I'm not an specialist, but always has been said the harrier is a fast strike ground attack. Now it has nothing of fast, it is a really turtle, not woth it.

[myHelljumper]

If you can prove that there is a difference between the module performances and the real aircraft, please make a bug report with supporting info.

Edited May 6, 2021 by myHelljumper

[Beltza]

Of course I can't. It's just my obervation. I love this module. I have a lot of them but i only fly the harrier. Now I am very surprised with this update. If I am wrong, sorry. And I can't expres me better in english...

[Aernov]

I didn't compare current engine performance to NATOPS performance charts (because using those is a puzzle I can't fully comprehend yet), but at a glance, this engine is closer to reality than what we had before. It still can do 450+ kts at ground level with less than 100% RPM (well within time-unlimited engine ratings) and full load, you just can't VTO/RVTO with more than 22 000 lbs as you could before (NATOPS allows calculations only up to 21 000 for "short lift wet" rating, which is limited to 15 seconds) and get to 40 000 ft while maintaining 0.80+ Mach at 90% RPM (which was almost better performance than some fighter jets). We'll need to relearn a lot, but at least our Harrier is closer to reality now.

Edited May 6, 2021 by Aernov

[Vakarian]

I'm just loving that for quite some time after Harrier has left early access and is considered "feature complete" we get such fundamental FM change.

 

Although it is good that FM got bit more like it should be, it is quite funny that in 3+ years FM was good enough that module can be considered as no longer in early access and after that gets FM change that changes how aircraft behaves in all its flight regimes.

[Kappa]

The funny thing is how Razbam do develop a module... It seems they like to do things twice or more...

 

Anyway... If this gets us closer to reality, changes are welcome and we have to say thanks to Razbam for this, because it seems they are tryng to do things the right way this time.

 

 

 

[Crash *]

vor 1 Stunde schrieb Kappa:

Anyway... If this gets us closer to reality, changes are welcome and we have to say thanks to Razbam for this, because it seems they are tryng to do things the right way this time.

 

That's also my opinion. They caught up a lot and are back at the front.

[Wisky]

vor 6 Stunden schrieb Vakarian:

I'm just loving that for quite some time after Harrier has left early access and is considered "feature complete" we get such fundamental FM change.

 

Although it is good that FM got bit more like it should be, it is quite funny that in 3+ years FM was good enough that module can be considered as no longer in early access and after that gets FM change that changes how aircraft behaves in all its flight regimes.

well very easy explanation to this.

 

before 2.7 update it was literally impossible to create a FM that would get closer to the real Harriers flight performance. Thanks to ED adding more variable to FM with 2.7 Razbam is finally able to finetune enough to get even closer to the real jet.

 

and thank god the ridiculous drag is gone, that was added with previous FM so Harrier doesnt go into space or fly mach 2.0

Edited May 6, 2021 by Wisky

[Vakarian]

What does ED have to do with it? Does every developer not develop their own FMs? That contradicts everything I've heard about so far about how modules are generally being made.

[Wisky]

you develop your own FM based on the physics ED gives you.

 

like drag, drag while turning, engine thrust and so on.

and what changed now is that Razbam can change engine thrust based on current altitude and lots of other extra variables that can be changed, that wasnt possible prior to 2.7

 

[wess24m]

Going off the real AV-8B manuals hover check charts "Figure 10-4. Engine RPM Required to Hover, F402--RR--408 Engine" the thrust seems accurate as far as the hover thrust to weight requirements.

 

Still investigating the airspeed at altitude changes.

 

Edited May 8, 2021 by wess24m
Read the wrong line in the chart.

[Beltza]

Well, after few flights my impressions have changed. The FM is very complex and is a new challenge to master it. I have a good time doing it.
Sorry about my firsts complains and thanks to RAZBAM for all this hard work.

[Supmua]

I can still get away with VT/VL without using water if light enough, but have to watch the engine closely and need to be in the early R zone most of the time.  On the carrier with a loaded plane, no more taking off in the middle of the runway though.  Have to taxi all the way to the back or the plane would sink like a rock upon takeoff.

Edited May 8, 2021 by Supmua

[myHelljumper]

Hey guys. I will keep this topic open for a bit so you can report if you see issues with the FM in the new patch.

[Falcon41]

I'm still thinking its underpowered. I was just at an airfield with no stores on at all and 25% fuel weighing around 16500lb and wouldn't VTOL off the ground unless the engine was pushed way past 100% with water on. 

[JaBoG32_Herby]

7 hours ago, Falcon41 said:

I'm still thinking its underpowered. I was just at an airfield with no stores on at all and 25% fuel weighing around 16500lb and wouldn't VTOL off the ground unless the engine was pushed way past 100% with water on. 

Based on the available performance data for a 408 Series engine, the aircraft, at ISA temp and pressure altitude sea level with 16500 lbs gross weight and zero wind, should require between 104 and 106 % RPM wet and that’s exactly what is required to lift off and hover the ingame Harrier.

So it does appear neither over- nor under-powered.
It rather is spot on.

Edited May 9, 2021 by JaBoG32_Herby

[wess24m]

As I said in the above comment, the hover settings to power required at a specific weight is accurate. However, then transitioning from forward flight somethings off. Coming in with an empty jet and 2k fuel and you’ll need water and a high rpm% to maintain a hover. 
 

In the included campaign you can’t land back at the boat empty with 3k fuel. You will just keep your sink rate right into the water at full throttle with water injection. 
 

I think that the transition from forward flight needs to be looked at. 
 

I’ve flown the av8b since release and even being overtly gradual with the transition phase doesn’t make a difference in the way that you need an exorbitant amount of thrust all the way to the ground. 

Edited May 9, 2021 by wess24m
Punctuation

[Wisky]

i did land the harrier no problems in NTTR in hot weather, creech AFB (pretty hight altitude), 2 x 9 m, 2 x empty bag, ~2.000 pounds of fuel.

It did take ~114% RPM wet but i could hold her pretty stable before finishing my transition from brake stop to RVL with ~84° nozzles.

 

maybe you had some overspeed/overtemp/dmg problems with your engine during your flight.

[wess24m]

1 hour ago, Wisky said:

i did land the harrier no problems in NTTR in hot weather, creech AFB (pretty hight altitude), 2 x 9 m, 2 x empty bag, ~2.000 pounds of fuel.

It did take ~114% RPM wet but i could hold her pretty stable before finishing my transition from brake stop to RVL with ~84° nozzles.

 

maybe you had some overspeed/overtemp/dmg problems with your engine during your flight.

You can check the real manual with your weight, temp and baro to see if that’s accurate and see if that’s realistic. 
 

Off the cuff I’d said that even at high temperatures you shouldn’t need water to VL at that weight. I can’t link the real chart here but if you DM me I can give you a link if you can’t find it. 

[Eldur]

On 5/9/2021 at 4:15 PM, JaBoG32_Herby said:

Based on the available performance data for a 408 Series engine, the aircraft, at ISA temp and pressure altitude sea level with 16500 lbs gross weight and zero wind, should require between 104 and 106 % RPM wet and that’s exactly what is required to lift off and hover the ingame Harrier.

So it does appear neither over- nor under-powered.
It rather is spot on.

 

 

Having noticed the change just recently, and having checked that chart myself as well, I think I found the error both you and RAZBAM made.

 

Just think about it for a minute. The 408 puts out 23800 lbf of thrust, probably at 109% fan RPM ("maximum thrust", which is dry) and 710°C JPT which is limited to a usage of 15 minutes. (Fig 4-2, pg 4-5). TBH I don't know if that's maybe the maximum dry or wet thrust for the short lift settings. Anyway, there's also the LIDS and the fences, adding effectively around 1k lbf to the hover thrust helping the lift-off and hovering at low altitudes near the ground (I think that isn't modelled as I haven't benn able to tell a difference with LIDS on or off, except for visually the front fence coming down or not).

Now just imagine that 23800 lbf pushing a 16500lb jet up. TWR is 1.44 at this point. No one can tell me you need ~ 105% fan RPM to be able to lift off.

 

Because of that, I tried to understand how you got to that 104-106% value which would be needed for hovering (not lift-off which has ground effect and the LIDS lowering the required thrust!). I quickly found out what made the difference:

You picked your TO weight at the far left of the table and then immediately followed the roughly parallel diagonal lines until you hit that 29.92 ISA line, then went right to meet the datum line (no fan RPM correction), then down to the 15°C ISA line, following the diagonal parallel lines down to the fan RPM scale. And yes, this is roughly the RPM needed to lift-off now on a standard DCS day -5°C (to match ISA, standard DCS is 20°C).

The thing is: You missed out on one thing: Right at the beginning you have to set your starting point with both the weight and the air pressure / altitude and then go to the 29.92 line diagonally accordingly. By starting out on the far left like you did, you assume ISA conditions, but trying to take off from 6000 ft pressure altitude. Now if you correct that error and start out directly on the 29.92 line at 16500 lb, you'll roughly end up at a required fan RPM of around 92-93% - which pretty much is what was needed for that weight before RAZBAM changed all of this.

So basically, they had it just about right before 2.7.0.5659. It was possible (with wet TO power) to lift-off considerably decently with weights of up to ~ 22000 lb and it was easily possible to do so with 3000 or less lb of fuel with a clean airframe, without even exceeding 103% / 640°C JPT. That's basically impossible now even with just 1% of fuel (and set to unlimited), which is slightly less than 15000 lb TO weight. That can't be right.

 

BTW I'd love to show this visually directly on the chart, but 1.16... if needed I might try to draw a rough sketch of it to make it easier to understand.

 

Just as a side note, the other changes made to the thrust seem reasonable though, as I was able to get to ~ M .089 at 31k (numbers I could find are 0.91 max, so it's within a margin of 0,02 - but I couldn't find the actual altitude for max speed) and around 0.87 on the deck (numbers I could find say 0.85, again within a margin of 0.02). Before the change I could get the thing a bit faster, but mostly get a lot more of acceleration out of the engine, but also with a lot more FF which was unbelievably high at that point and now seams more reasonable again.

[lukeXIII]

8 hours ago, Eldur said:

Now just imagine that 23800 lbf pushing a 16500lb jet up. TWR is 1.44 at this point. No one can tell me you need ~ 105% fan RPM to be able to lift off.

 

The engine thrust is much less than 23800 lbf at 105% rpm. Also, thrust does not increase linearly with rpm. The data for the hover charts is directly from flight tests, so yes you do need that rpm to lift off at that weight.

 

8 hours ago, Eldur said:

Because of that, I tried to understand how you got to that 104-106% value which would be needed for hovering (not lift-off which has ground effect and the LIDS lowering the required thrust!). I quickly found out what made the difference:

You picked your TO weight at the far left of the table and then immediately followed the roughly parallel diagonal lines until you hit that 29.92 ISA line, then went right to meet the datum line (no fan RPM correction), then down to the 15°C ISA line, following the diagonal parallel lines down to the fan RPM scale. And yes, this is roughly the RPM needed to lift-off now on a standard DCS day -5°C (to match ISA, standard DCS is 20°C).

The thing is: You missed out on one thing: Right at the beginning you have to set your starting point with both the weight and the air pressure / altitude and then go to the 29.92 line diagonally accordingly. By starting out on the far left like you did, you assume ISA conditions, but trying to take off from 6000 ft pressure altitude. 

 

It looks like you are using the chart incorrectly. Using the charts with standard conditions (15°C and 29.92 inHg) you do not have to make any corrections to hover weight or fan speed. Basically all the lines you follow are horizontal and vertical. 

 

8 hours ago, Eldur said:

Now if you correct that error and start out directly on the 29.92 line at 16500 lb, you'll roughly end up at a required fan RPM of around 92-93% - which pretty much is what was needed for that weight before RAZBAM changed all of this.

 

The lowest fan speed on the chart for the 408 engine is 98%, which indicates that you are using the wrong chart (the 406 engine chart).

Edited May 28, 2021 by lukeXIII