SU-27 and J-11 slower to regain airspeed after maneuvering..

[Ironhand]

36 minutes ago, stefasaki said:

That's pretty much what I mean. You found exactly a 50% difference, which is not realistic at all (my disparity was slightly larger because my time with the eagle was slightly lower). Should we post this as a different thread? This risks to go unnoticed otherwise (as it did for 3 or so years)

I used the default 59% fuel load for the Su-27 and adjusted the F-15's to match the same fuel to empty weight ratio. That got the Su-27 156km downrange before the first fuel warning announcement.

 

Go ahead a post as a separate thread. Provide numbers for both aircraft. It seems wrong but, without an Su-27 chart of some sort to check it against, the most we can do is voice our suspicions and ask if they have charts they can check against.

 

I wouldn't expect any quick action but...you never know.

Edited January 14, 2021 by Ironhand

[Ironhand]

14 hours ago, Cmptohocah said:

Performance charts in the Su-27 manual are usually for a configuration with: 50% fuel, 2xR-27 and 2xR-73

Can’t access the sim right now to see what 50% fuel equates to but it’s probably close to what the manual indicates for a “basic” refueling—filling tanks 2 and 3 which yields a total of 5220 kg.

[Cmptohocah]

12 hours ago, Ironhand said:

Can’t access the sim right now to see what 50% fuel equates to but it’s probably close to what the manual indicates for a “basic” refueling—filling tanks 2 and 3 which yields a total of 5220 kg.

I actually don't know what "50% of fuel" represents, as it's only depicted like that on the charts. I guess if the total fuel capacity is X, that this is X * 0.5? Su-27 has no external tanks, so it should be straight forward, no?

Edited January 15, 2021 by Cmptohocah

[GGTharos]

It's not the total fuel capacity.  It's 50% of 'basic fuel load' which like Ironhand said, means filling tanks 2 and 3 only.

This is written in the manual, and because most of us can't read it, it has been a huge point of contention when testing turn rates etc.

Edited January 15, 2021 by GGTharos

[Ironhand]

2 hours ago, Cmptohocah said:

I actually don't know what "50% of fuel" represents, as it's only depicted like that on the charts. I guess if the total fuel capacity is X, that this is X * 0.5? Su-27 has no external tanks, so it should be straight forward, no?

 

Maybe yes, maybe no. This is where I got the 5220 figure from. In the sim, 50% turns out to be 4700:

 

”8.2. Workings of the fuel system.

The aircraft fuel system is designed to provide fuel to the engines in all modes of operation, as well as various cooling units, aircraft systems modules and equipment.

 

The fuel system is operated on RT, TS-1 fuels or a blend in any proportions. The fuel is placed in the No. 1 and 2 tanks in the center fuselage, in tank No. 3, consisting of two compartments located one each in the wing sections, and tank No. 4, located in the rear fuselage between the engine compartments.

 

The operational available capacity of the fuel tanks (at γ=0.785):

 

- Tank No. 1 --3180 kg;

- Tank No. 2 --4160 kg;

- Tank No. 3 --1060 kg;

- Tank No. 4 --1000 kg;

- TOTAL --9400 kg.

 

8.2.1. There are several possible variations for refueling the aircraft: complete, basic, and partial. During a basic refueling, only Tanks 2 and 3 are refilled. A complete refueling refills all tanks. Refueling is undertaken by the “closed” method-either pressurized or open-through the filler mouth. For a partial refueling, Tank 2 is completely filled by the open method (with visual monitoring) or to at least 3400 kg (as indicated on the fuel gauge). Fuel from the tanks is automatically processed through the supply compartment in Tank 2. The sequence in which fuel is drawn from the tanks is regulated by the STR7-2AK fuel metering system.

 

Fuel is drawn from the tanks in the following sequence:

 

When fueled completely:

- 1720 kg from Tank 1;
- the entirety of Tank 4;
- the remainder of Tank 1;
- 70 kg from Tank 2;
- the entirety of Tank 3;
- 3210 kg from Tank 2, except for the feed chamber;

- the entirety of the feed chamber in Tank 2.

 

For a basic refueling:
- completely from Tank 3;
- 3210 kg from Tank 2, except for the feed chamber;

- the entirety of the feed chamber in Tank 2.

 

The specified sequence for drawing fuel from the tanks is for the non-afterburning regimen of the engines.” 

Edited January 15, 2021 by Ironhand

[Cmptohocah]

26 minutes ago, GGTharos said:

It's not the total fuel capacity.  It's 50% of 'basic fuel load' which like Ironhand said, means filling tanks 2 and 3 only.

This is written in the manual, and because most of us can't read it, it has been a huge point of contention when testing turn rates etc.

 

Which part of the manual states this being 50% of "basic fuel load"? I would love to have a look.

[GGTharos]

^^^^

IH solidly beat me to it.

[Ironhand]

3 hours ago, GGTharos said:

It's not the total fuel capacity.  It's 50% of 'basic fuel load'...

So those charts would be based on 2610 kg of fuel (50% of 5220)?

[BBCRF]

Нормальная заправка для Су-27 6680л

[Ironhand]

6 minutes ago, BBCRF said:

Нормальная заправка для Су-27 6680л

So about 4810 kg.

[BBCRF]

3 минуты назад, Ironhand сказал:

So about 4810 kg.

нет если y=0.82 то 5480 кг

[Seaeagle]

1 minute ago, Ironhand said:

So about 4810 kg.

No its closer to the 5220 kg you mentioned.

 

Edit: sniped :)

Edited January 15, 2021 by Seaeagle

[GGTharos]

1 hour ago, Ironhand said:

So those charts would be based on 2610 kg of fuel (50% of 5220)?

 

2740 according to the above information from @BBCRF.

[Seaeagle]

The exact amount in kilograms depends on the fuel density - which fuel type and at what temperature.

 

I don't know which BBCRF used for his 0.82, but IIRC for;

 

F34/JP8 its ~ 0.8 at 15 deg. (6680L = 5344 kg)

TS-1 its 0.78 at 20 deg. (6680L = 5210 kg)

 

 

[GGTharos]

As per IH's post, the specification is:

 

The operational available capacity of the fuel tanks (at γ=0.785):

 

At 6680 liters this gives us 5244kg.   Half is this will be 2622kg.

 

The graphs are based on this basic fuel load.

Edited January 15, 2021 by GGTharos

[BBCRF]

проблема игрового прототипа от реального что в реальности самолет испытывался только с 2-мя балками АКУ-470 под фюзеляжем.В игре масса самолета выше на 450кг

[Seaeagle]

17 minutes ago, GGTharos said:

As per IH's post, the specification is:

 

The operational available capacity of the fuel tanks (at γ=0.785):

Yes I see that now - looks like TS-1 then. But as a nitpick, I don't think its the "operational available capacity", but rather the nominal capacity of the tanks.....not that it matters in this connection though.

17 minutes ago, GGTharos said:

 

At 6680 liters this gives us 5244kg.   Half is this will be 2622kg.

 

The graphs are based on this basic fuel load.

Yes I believe Yoyo mentioned this at one point.

 

[Ironhand]

1 hour ago, BBCRF said:

y=0.82 то 5480 кг

And, then, came the dawn!

 

It wasn’t until your post that I realized what “y=0.785” in the manual referred to.

 

Thank you.

[stefasaki]

ok I have found something that may be called as proof for the current poorly depicted transonic acceleration.

 

This is the video of an accident due to engine fire of an su-30 MK2 (same engines as the su-27) during a maximum acceleration test.

 

The HUD shows an acceleration from 600 to 1100 km/h (indicated airspeed) in around 21 seconds and a 1100 to 1300 km/h run in 18 seconds. Mach 1 at 3000m should be around 1015 km/h (again ,indicated airspeed), so the transonic regime is fully captured here. What happens in DCS is a huge disparity in both ranges but the 1100 to 1300 suffers particularly. Take the su-27 in DCS, bring it to 3200 m of altitude as in the video and perform this same test. The disparity is just unbelievable.

 

I'll post here my DCS times when I'll have time to run a few tests with different fuel loads and temperatures. I thought that some of you might like to try this themselves first.

Edited January 26, 2021 by stefasaki

[GGTharos]

That is an excellent find.  @BIGNEWY could you please get this investigated?

Edited January 26, 2021 by GGTharos

[BIGNEWY]

I will show it to the team, but bare in mind a video does not show the whole picture. 

Its a different airframe, and we dont know the weight of the aircraft in the video. 

 

[GGTharos]

1 minute ago, BIGNEWY said:

I will show it to the team, but bare in mind a video does not show the whole picture. 

Its a different airframe, and we dont know the weight of the aircraft in the video. 

 

You are absolutely correct, but it won't matter; the lightest Su-27 in game can't accelerate as fast as this (heavier airframe) Su-30Mk2, and it's not going to be more slick either since it's a larger airframe.  The engines are the same - this is why the video itself is an excellent starting point for investigation.

[bies]

On 1/13/2021 at 6:34 PM, Ironhand said:

I haven’t been in the F-15’s cockpit for years. Just flew a profile and was shocked at how quickly it got to altitude and speed compared to the Su-27.

 

This are FC3 planes, there is lot of simplifications. Still i think they did some great job given they are low fidelity planes for extremally affordable price.

 

Consider just this one thing:

F-15 had been intentionally designed with requirement to have four semi-recess low-drag fuselage pylons, non-universal (they could carry AIM-7 missile only, and later AMRAAM) but they offered far lower drag increase when carrying a missile - semi-recessed inside the fuselage and within uniform fuselage aerodynamic boundary layer, this missiles had far smaller drag index, especially backward missile being additionally completely shielded by the forward missile.

 

 

(Other F-X competitors - North American and Fairchild shown below - also had to include similar solution)

 

 

In DCS if you put the missile i.e AIM-120 on semi-recess low drag fulelage pylon - it doesn't matter.

On forward (YELLOW) or even backward station (GREEN) AIM-120 still has full drag index exactly identical as AIM-120 on normal full drag under wing pylon (RED).

You can test by yourself.

 

What does it mean? If ED wanted to make F-15C close to real life chart with weapon they had to decrease clean aircraft drag to compensate for excesive weapon drag in semi-recess stations (4 big missiles) which are adding far more drag in DCS than they do IRL.

 

 

In full fidelity i.e. F/A-18C they are adressing such things and drag of the missile on semi-recess fuselage pylon is considerably smaller than under wing pylon. Similar situation with wing-end pylons.

Thay are still tuning this things, there are still some stations to include in different modules as i've noticed testing it from patch to patch but there is definitely work being done.

 

Edited January 26, 2021 by bies

[BBCRF]

замерь разгон масса самолета 20000кг высота 1000м разгон от 600км до 1100км/ч

[stefasaki]

16 minutes ago, BBCRF said:

замерь разгон масса самолета 20000кг высота 1000м разгон от 600км до 1100км/ч

Subsonic acceleration is mostly correct, I did that test and the result was close to 15 seconds, which should be the correct value. The problem is in the transonic regime.