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Pegasus Mk.101 overperforming thrust .


1)  Vehicles affected :    Harrier GR.1

 

2) Sources used :

 

Two sources used for this report . Primary and main source is the  book  Pegasus the heart of the Harrier by Andrew Dow  ,  ISBN: 978 1 84884 042 3 . This is the most in-depth and authoritative public source in relation to Rolls-Royce  Pegasus family of engines .

 

Spoiler

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Secondary source is the book Turbofan and turbojet engines database handbook by  Elodie Roux , ISBN : 978-2-9529380-0-6 . This source is just going to serve as validation for the main source .

 

Spoiler

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3) The issue It appears that the Pegasus 11 Mk.101 engine is overperforming in terms of the produced thrust in several  regimes but before  going into specifics the following needs to be established :

 

Pegasus engines starting from the Pegasus Mk.101 and on  ( it was firstly named Pegasus 6 then renamed/rebuilt to Pegasus 10 and finaly to Pegasus 11 but the Mk.101 standard is what  matters )  were using water injection to allow for higher thrust during certain regime . Indeed the water injection allowed to cool down the engine in order to produce supplementary thrust . The water tank had enough supply for 15 seconds of operational usage . This mode was only used for vertical take off and the transition to horizontal flight :

 

Screenshot_2020-12-29_173228.png

 

This is referred to as ( short lift wet in the document ) so i need you to keep this in mind . Here are the specifications of the different Pegasus variants :

 

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Screenshot_2020-11-29_164633.png

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Screenshot_2020-11-29_151049.png

 

(A) Maximum (wet) thrurst during vertical take off :  In this regime according to the documents the Mk.101 engine should be producing 19000lbf static thrust which equals to 8618kgf . In game measurements show that the engine is capable of producing as much as 9290kgf during vertical take off. Now it needs to be noted that to my knowledge water injection is not modeled into the game ( there should be a 15 second counter ) so the engine should be producing much less thrust at WEP than the historical 8618kgf  yet somehow is producing much more thrust which shows by how much it is overperforming !

Spoiler

Short_lift_wet.png

 

( B ) Maximum ( dry ) take off thrust   : This is regime without water injection . Given water injection is not implemented this regime corresponds  to WEP thrust  during take off ingame . In this regime accoring to the documents Mk.101 engine should be producing 16250lbf static thrust which equals to 7371kgf . It needs to be noted that this is static thrust therefore this value should be even lower ingame by 5-10% due to channel loss . In  game measurement show that the engine is capable of producing as much as 9290kgf during vertical take off or as much as 9100kfg during horizontal take off . The engine is overperforming by  1920kgf of thrust .

Spoiler

Horizontal_take_off_thrust.png

 

( C ) Maximum continuous thrust :  This regime corresponds to 100% engine  in game . In this regime according to the documents Mk.101 engine should be producing 13150lbf of static thrust which equals to 5964kgf . It needs to be noted that this is static thrust therefore this value should be lower ingame  by 5-10% due to channel loss . In game measurements show that the engine is capable of producing as much as 6420kgf . The engine is overperforming by aproximately 754kgf of thrust .

Spoiler

100_thrust_.png

 

 

4) Solution :

 

Given those historical facts , several modifications need to made to the Pegasus Mk.101 engine in order to reflect it's historical performance :

 

(a) A wet engine regime for vertical take off with a  15 second counter needs to be implemented when the engine nozzles are fully oriented for vertical take off . Under this regime the engine should be capable of producing a maximum of 8618kgf of thrust  , once the 15 second counter has been consumed  the maximum  engine thrust should fall to 7371kgf .

 

(b) Maximum take off  thrust ( read without channel loss ) when WEP is engaged should be 7371kgf.

 

(c) In all other flight regimes the maximum engine thrust ( read without channel loss ) should be 5964kgf when the plane is static and go down from there by as much as 10% when the plane is at maximum speed .

 

 

 

Best Regards .

 

 

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  • 3 weeks later...

Hi.

 

The data and numbers are known to the devs.

 

However, for gameplay purpose / aircraft experience, the very low speed (hover) thrust has been buffed to allow for vertical take off.

 

In real life, the Harrier could only do vertical take off with limited fuel and almost no load.

 

Performance when flying or taking off in a short take off mode (not vertical) are correct

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