Pegasus a little bit too powerful / Drag miscalculated?

[Vakarian]

Yesterday in my squadron we were goofing off, so I thought to give a Harrier another chance after I gave up on it with the frequent breaking of working things and implementing stuff incorrectly.

 

 

Loaded 10 Mk-82 AIRs (singles on station 1&7, doubles on stations 2,3,5,6) + gunpod and wanted to see how high I can go.

 

I got to FL380 without much issues and settled there at M0.6. That seemed fine, but then I started to accelerate as I leveled off. Next, as I got quicker, I started to climb more and got to FL450 and when leveled off there I got as quick as M0.88.

 

So, M0.88 @ FL450 while having 10 Mk.82s and a gunpod. That seems a little bit too powerful, something seems off.

I did a little checking in NAVAIR 00-110AV8-4 and nothing there suggests that this should be valid, as service ceiling with only 6 Mk-82s + gunpod is at FL331, combat ceiling is FL364 and I got 10000ft higher with a way draggier aircraft.

 

Did anyone else notice anything similar?

[Wisky]

what Drag are you talking about at Angels 45?

 

natops actually does say that you only need like half throttle at this angels because thin air allows the engine to get way too fast.

(in terms of RPM)

Edited March 9, 2021 by Wisky

[Vakarian]

I mean, I know that the air is thin up there, but M0.88 seems a bit fast as I wasn't in clean config. Didn't see what was the max speed there as I went for the bombing runs, but I will try to replicate this in the next couple of days.

 

Yeah, for the RPM, I did test the maximum RPM and it didn't go over 110% which is what I thought was the max.

 

I am aware that this engine is a beast and it can climb a lot, but this seems way too easy. Also, as you can see, I mostly type "seem". I'm not sure it's a bug, so I'm trying to see what all of you think of this. I'm always open to learning new things and would like to be corrected if I'm wrong.

[Spurts]

all the NATOPS stuff is likely at the 102% RPM setting for Max Continuous.

[Vakarian]

Ofc, 102% max contionuous, and also watch out for the JPT.

The "max" I wrote was in regard to the Wiskeys comment that higher altitudes allow the engine to go too fast, and I understood it as it might go over 110%

[Wisky]

it might go over 110% (in Manuel Fuel) but its not modeled ingame yet.

 

Natops basic check flight to test aircraft systems expects a maneuver at M0.8 at Angels 40.

 

it also strongly advises in various parts to not exceed M0.87

 

but it never states a ‚possible to reach speed at x altitude‘ other than the max speed of Mach 1.0 for the Pegasus engine.

[Vakarian]

@WiskyThanks for this info. This thing is more powerful than I thought then... I expected to have some issues climbing up there with this kind of loadout, but apparently it's close enough to the real thing that it's fine my me.

[Wisky]

so what i am trying to say is:

 

the harrier has no FCS like the Hornet.

Its not that you are technically not able to reach that speed.

but instead its your job as pilot to observe the speed going too high and take actions against this (reducing throttle)

[Bog9y]

I undertand what the OP is posting and I think it is a flightmodel coding issue.  The Harrier did outclimb the F-104 in real life(take off to 10,000 ft).  So, down low the engine is a beast, higher up however I think it should become wheezy and not pump out as much thrust as it does.  I think creating this flight model is probably much harder than your standard plane or helicopter...with this jet you have to combine the 2, I think that's how Razbam did it. 

I guess if you wanted to check for climb performance accuracy check NFM-400 and find a time to climb graph and figure out how long it should take to get to a certain level then compare in DCS. In fact...I'll go and do that later and let you know. 

Edited March 9, 2021 by Bbow

[Bog9y]

So I did some testing. Reading in the NFM-400 performance manual you get the following data for a climb with these conditions:

 

Engine = 408

Drag Index               :  17.7

GW at start of climb : 22,000 lbs (7200 lbs of fuel)

CLB Speed : 300 KCAS / .75 M

Max thrust climb, this is 109% / 710 degrees C JPT for the -408 engine

Test carried out in ISA conditions, winds calm 

 

EXTRAPOLATED DATA FROM THE CLIMB CHARTS VS DCS :

 

                        TIME TO CLIMB  - DCS  /  FUEL REMAINING - DCS /   DISTANCE - DCS 

SL to 10,000 ft = 0:48 mins  / 0:25      /    7040 lbs / 7094                /  3.5 nm    / 2.5

SL to 20,000 ft = 1:42 mins   / 0:54      /    6850 lbs / 7010                / 10.5 nm   /  5.1

SL to 25,000 ft = 2:30 mins   / 1:13     /    6770 lbs  / 6967               / 16 nm        / 7.1

SL to 30,000 ft = 3:24 mins   / 1:35     /    6660 lbs / 6922                / 24 nm       / 9.6

SL to 35,000 ft = 5:00 mins   / 1:56      /   6580 lbs  / 6881               / 32.5 nm    / 12.0 

SL to 40,000 ft = 7:34          / 2:24        /   6430 lbs  / 6836              /  53 nm      / 15.3

 

So...yes...it's way overpowered and it gets further away from realistic performance the higher you go. 

 

[Jarlerus]

Bbow: You are a legend. That's some excellent testing there.

I've been commenting on the surprising performance of the harrier for some time now, and it's affirming to see it in numbers like that.

[Vakarian]

@Bbow Thanks a lot man for the testing. This basically proves my hunch that even if the Pegasus is really powerful engine, it is still not that much powerful as I saw the other day. I mean, I climbed (although not at the constant rate, I did 2 stage climb) to a FL400 and had 7000lb of fuel when I got there. So 700lb of fuel spend for a climb from Nellis to a FL400 with a not so light bomb load...

 

@RAZBAM_ELMO Can engine performance / FM get another look on? From the testing done, there is enough discrepancy to warrant another check. We are not talking about 5-10% difference from a real thing but a way much more

[Bog9y]

Thanks guys, I'll do some more tests with the 350 KCAS and 400 KCAS charts and some higher drag indexes but I suspect there won't be much difference in the findings. I'm not trying to diss the AV8B module...I would just like it to be made more realistic. I may also see if I can find the file that controls weight/drag of the jet. Editing that may give more realistic performance. 

 

Ironically, when you do an overhead break the guidelines say , thrust idle, extend speedbrake and break at 4G up to 10 units AoA and then maintain 10 units. If I do that in DCS I very quickly slow down to a silly low speed. So for an overhead break I tend to just go idle and no speedbrake, sometimes I even leave the throttle at a low power setting to get a better abeam distance.  

[Wisky]

vor 22 Stunden schrieb Bbow:

So I did some testing. Reading in the NFM-400 performance manual you get the following data for a climb with these conditions:

 

Engine = 408

Drag Index               :  17.7

GW at start of climb : 22,000 lbs (7200 lbs of fuel)

CLB Speed : 300 KCAS / .75 M

Max thrust climb, this is 109% / 710 degrees C JPT for the -408 engine

Test carried out in ISA conditions, winds calm 

 

EXTRAPOLATED DATA FROM THE CLIMB CHARTS VS DCS :

 

                        TIME TO CLIMB  - DCS  /  FUEL REMAINING - DCS /   DISTANCE - DCS 

SL to 10,000 ft = 0:48 mins  / 0:25      /    7040 lbs / 7094                /  3.5 nm    / 2.5

SL to 20,000 ft = 1:42 mins   / 0:54      /    6850 lbs / 7010                / 10.5 nm   /  5.1

SL to 25,000 ft = 2:30 mins   / 1:13     /    6770 lbs  / 6967               / 16 nm        / 7.1

SL to 30,000 ft = 3:24 mins   / 1:35     /    6660 lbs / 6922                / 24 nm       / 9.6

SL to 35,000 ft = 5:00 mins   / 1:56      /   6580 lbs  / 6881               / 32.5 nm    / 12.0 

SL to 40,000 ft = 7:34          / 2:24        /   6430 lbs  / 6836              /  53 nm      / 15.3

 

So...yes...it's way overpowered and it gets further away from realistic performance the higher you go. 

 

 

so i have been looking at the NFM-400 and for the -408 engine the climb charts are only Estimated.

 

i dont know if you have a different chart i have but we are splitting hairs here.

and we dont even know how dcs simulates the engine. my guess is reducing power would make hover in dcs impossible, so Razbam added a looooot of drag (what is making you loose waaaaay too much speed in turns)

Edited March 10, 2021 by Wisky

[Fri13]

On 3/9/2021 at 6:18 PM, Bbow said:

I undertand what the OP is posting and I think it is a flightmodel coding issue.  The Harrier did outclimb the F-104 in real life(take off to 10,000 ft).

 

It has as well outclimbed the F-15. The Harrier maintains the world record in climb to specific altitude (9000 ft IIRC) and after that the F-15 takes the lead in west.

 

It is a beasty engine, but some pilots has said that it is slow to accelerate (in the fighter pilot podcast, so likely meaning in combat loadout) but as well said that it is very rapid to decelerate with nozzles control like when joining with the lead. 

 

 

[Bog9y]

13 hours ago, Wisky said:

 

so i have been looking at the NFM-400 and for the -408 engine the climb charts are only Estimated.

 

i dont know if you have a different chart i have but we are splitting hairs here.

and we dont even know how dcs simulates the engine. my guess is reducing power would make hover in dcs impossible, so Razbam added a looooot of drag (what is making you loose waaaaay too much speed in turns)

 

The charts I used are from NFM-400 published with change 5 - Feb 2003.   These charts are indeed based on estimates but to climb to 40,000 in less than 1/3rd of the distance and about a 1/3rd of the time (compared to the NFM estimates) either shows that the flight models is out by a considerable amount.  I'll have a play around with hovering today and see how it does with different fuel loads (maybe compare it to the hover charts in NFM -400).  

[Bog9y]

Did a quick test. Empty aircraft, full fuel load. VRST VTO page says around 4800 lbs f+w for a wet VTO.  I easily did a VTO without using any water. So nearly 3000 lbs of fuel more and did it dry. Hovering at 50 ft needed around 109% RPM.  Pretty sure it's not supposed to be able to do that. 

[derfritz]

Thank you Bbow for the testing. The harrier indeed feels overpowered, I was able to perform a vertical takeoff while being massively over the weight limit: Fuel set to F+W (from VREST page) and adding 4 GBU-38+litening+gun after calculation. This might tie in with the problems we found regarding the VREST page as outlined in this bug report explaining the higher performance.

[Bog9y]

1 hour ago, derfritz said:

Thank you Bbow for the testing. The harrier indeed feels overpowered, I was able to perform a vertical takeoff while being massively over the weight limit: Fuel set to F+W (from VREST page) and adding 4 GBU-38+litening+gun after calculation. This might tie in with the problems we found regarding the VREST page as outlined in this bug report explaining the higher performance.

 Oh wow, just read that bug report thread. It's from Nov 2020?? Nothing seems to have been done about it.  Elmo did say on the Discord channel that Razbam will look into the flight model. No idea how long this will take. I'm quite keen to see if I can change the flight model myself, just need to learn how to do it.   This is also why I have amended the joystick & keyboard LUA files to be able to assign commands for all the switches. Lots of keybinds are missing and I am building a pit, didn't want to wait so I did it myself. 

[Vakarian]

I do believe FM is in the .dll files (haven't checked for Harrier, but for other modules it is) so you can't really change it as that's compiled C++ code. But yeah, FM does seem weird sometimes as Harrier manages to pull off something that logic says it really shouldn't be able to.

 

Thanks for sharing the info from the Discord. Too bad that the forums is the last place RB posts their info, if they post it here at all

[Bog9y]

I heard it was C++ DLL stuff....well, that's out the window then. That's way beyond my chimp brain ability. 

[derfritz]

Soo... What does it take for this to be acknowledged?

[Fri13]

On 3/11/2021 at 9:51 AM, Bbow said:

The charts I used are from NFM-400 published with change 5 - Feb 2003.   These charts are indeed based on estimates but to climb to 40,000 in less than 1/3rd of the distance and about a 1/3rd of the time (compared to the NFM estimates) either shows that the flight models is out by a considerable amount.  I'll have a play around with hovering today and see how it does with different fuel loads (maybe compare it to the hover charts in NFM -400).  

 

I am yet to even test the Harrier flight modeling against any specs, but that sounds very worrisome. As so far the Harrier is so full of wrongly working systems or missing systems that I didn't want to even add to that bag the flight modeling part. But what continually reminds me is its capability to accelerate to high speeds so easily without noticing it while being engine RPM at 60-80% and loaded with something like 2x mavericks, 2x GRA-20 and gun. The feeling is like a driving a tesla, you just suddenly notice that you are going 130 on a normal road with 80 limit as you do not feel and hear the speed like with example 20 year old car you do.

 

Regardless the Harrier has very powerful engine, has done those record climbs etc. Some pilots say it doesn't accelerate like at all, and some say that you can effectively brake with it as it is so draggy (especially with engine nozzles control) but as well some do say that it is easy to win a dog fight against F/A-18C pilots who has combat experience against Harrier, and yet that they can turn tighter and faster than Hornet can because wiffing, how they can maintain challenge in combat for other pilots. 

 

But there is something one can't put a finger on it. And I wish that wouldn't be anything serious but what You have stated there is definitely requiring more checking. 

[Hawkeye_UK]

THe EM state considering turn rate to mach also needs work.

 

I have a separate bug report inline with fuel consumption following the patch this week.  Figures are way off reality.

 

In short summery 100 mile radius flight for on call CAS with 6 x 500lb class bombs mangaged 50 min loiter time prior to running out of fuel.  That's with a with correct climb / flight profile with mach parameters.  Result is circa 50 mins off endurance in addition to the thrust issues / fuel.

 

Real issues with the Harrier performance and flight model.

 

 

 

 

[Wisky]

so RAZBAM said on discord today that turn rate for the Harrier will increase with next patch.

Also engine thrust will decrease by ~10% at low altitude and ~50% at high altitude, to get closer to performance charts