Incorrect Harrier thrust values at cruising speeds

Currently, AV-8A and AV-8C produce the most thrust at hover and decreasing thrust at increasing IAS - for example, my (unspaded) AV-8C at 100% generally produces around 9,300 kgf of gross thrust in hover at sea level and around 5,400 kgf at 900 km/h IAS as reported by http://localhost:8111/.

While this may be intuitively correct for a commercial turboprop or low bypass turbofan engine (usually modeled as constant power, variable thrust), in reality the Harrier is more of a hybrid between low and high bypass jet engines and like other low bypass jet engines produces increasing thrust with increasing IAS. Source for this claim includes the AV-8A flight manual (AV-8A Harrier Flight Manual.pdf | DocDroid) and the Princeton white paper on AV-8A trim maps (

To quote the latter:
“Gross thrust increases as a function of freestream velocity due to the higher pressures at the compressor face. This gross thrust increase (Fig-ure 60) is added to the aforementioned thrust vs. RPM curve.”

It is also worth noting that this effect is even more pronounced on “proper” low bypass jet engines and pretty much all jets should be producing increased thrust at increased IAS instead of the current modelling of constant thrust across all IAS.

This is to make the hovering work in game, and is intentional.

Not 100% sure what you mean by this. Doesn’t OP’s document show that the Harrier in game has either too much thrust at a hover, or not enough thrust as high IAS?

So it’s either nerfed at speed, or the physics engine is too rubbish to properly simulate a hovering aircraft?..which should be the least complicated scenario for the physics engine to simulate…

Then again this is GJN we are talking about, so probably both.

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Specifically the low speed thrust is increased to get the hovering to work. That’s all I was commenting on.

Why does the hover not work with it’s actual thrust though? Aerodynamic forces are non-existent in a hover, so this should be easy for GJN to get it right. The only thing it has to counter is the weight.

Don’t know why it doesn’t work I just know that’s how they got it working.

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Im not even surprised anymore. Just recode.


maybe planes in game are heavier than their real life counterparts

share a proper link

The thrust at hover is correct, the thrust at cruise is not. The harrier is easily able to exceed its never critical speed under level flight in real life, just like e.g. F-89B, while in WT ARB you need to dive in order to do it.

Basically, it’s nerfed at speed. For most aircraft the inaccurate thrust vs IAS modelling is pretty meaningless since they just tweak the coefficient of drag to make the real-life thrust give the real-life rate of climb at the real-life climb airspeed - if they made more thrust at these speeds they would just increase the drag and the net result would be the same. For the Harrier though, the climb rates at low speeds (where the reduction in thrust is significant but the drag isn’t) is way off, and it really limits how well it should be able to turn fight. It should also be able to accelerate from Mach 0.5 through to Mach 0.8 much better than it can in-game.

In response to Miraz05, http://localhost:8111/ is where War Thunder reports a lot of stuff under the hood and is where I am getting things like gross thrust from, since it doesn’t get reported in game. I am, of course, assuming it is accurate, even though other numbers are known to be very wonky - for example, Drag is used as a catch all for a bunch of stuff so when you use things like rocket boosters instead of more thrust you actually get less (even negative) drag.


Wouldn’t thrust be theoretically equal?

If they had hidden/protected air intakes like cars do, yes, however because they have large forward facing scoops these act like forced induction in piston engines (turbo/superchargers) and in a similar fashion let the engine make more power (or in this case, thrust). As the fast moving air hits the big scoops it is forced to slow down and this results in higher pressure at the intake.

More specifically, the limiting factor for any fuel burning engine (be it piston, rotary, or turbine) is how much oxygen you can get into it. Adding more fuel is easy, but it only actually helps if you also have the oxygen to burn it with. All the usual engine additions like turbochargers, superchargers, and even nitrous oxide is all about forcing more oxygen into the combustion chamber so you can, in turn, burn more fuel.

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Yeah, I’m pretty sure that there was something similar with the J35, it would have continued to accelerate, had it not burned its fuel. The faster it gets, you can push more air out, eventually, and most importantly, Theoretically would continue to accelerate until something breaks. It just depends on the drag/weight/thrust ratio.

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You run into diminishing returns the faster you go, so it’s only about 20-30% extra thrust over the entire flight envelope. it gets even worse as you get above Mach 1, as the air has to be subsonic throughout the engine, usually achieved through baffles or restrictions in the intake which in turn limits how much air can be inducted. Additionally, much like piston engines there is a limit to how much thrust/power the internals can deal with before they just grenade themselves.

edit: incorrect info about Concorde, apologies. Brain fart.

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Some extra thrust for better acceleration would be nice. Not spent any time in the US harriers, but I do enjoy the British Harriers. So this should be a buff for them too. Make sure you actually submit a bug report for it:

While we’re at it, the airbrake switch in the AV-8A is backwards, with the brake out on the in setting and in on the out setting as marked on the throttle.

Also, as for thrust, I am not sure how it should be modelled, because the water injection system utilized at the maximum thrust settings is not modelled. If it is, the water needle in my cockpit doesn’t indicate it.

I think it is modeled. That is what the WEP does (at least it does in the British Harriers) and it only last so long, I guess because you run out of water (though I doubt the weight is modeled, however I dont know what the difference in wieght would be with and without water)

That im not suprised about, quite a few cockpits dont have functional components. The Phantoms dont even have working air speed indicators in the cockpit. iirc

Gaijin do actually model the weight of the water. As you use WEP the water gets used up, you have enough for about 90 seconds of WEP.

The impact on weight is fairly minimal though (223 kg)


Correct, it isn’t modeled accurately (the RPM is meant to rise and the exhaust temp is meant to fall), but that is also true for other water-injection WEP systems.

In the Harrier water injection actually has the highest maximum engine temperature. But yes Gaijin is certainly simplifying engine management in the Harrier.

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