VSKYLABS Update on F-4 Phantom II Project XP

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The VSKYLABS 'Test-Pilot': F-4E Project for X-Plane by LaminarResearch (Work-In-Progress) - The exhaust nozzles:

The F-4E is powered by two J79-GE-17 engines, where each engine isequipped with an afterburner.

A fact that may be new to some:

Engines with afterburners are equipped with variable area exhaustnozzles. The purpose of the variable area nozzle is to utilize maximumthrust from a given jet-flow, and to accelerate the exhaust-jetvelocity from subsonic to supersonic velocity (in afterburner mode),to fully utilize the afterburner system.

The internal geometry of the nozzle in this case must be of aconvergent-divergent cross section, as convergent nozzles cannotaccelerate the exhaust jet velocity into the supersonic regime (inshort - as the flow exceeds the sonic regime in the nozzle, shockwaves are formed in the convergent cross-section, reducing the jetvelocity to subsonic right after...).

To form a convergent-divergent cross-section that allows supersonicflow, the variable area exhaust nozzle includes TWO sets ofcylindrical nozzles, that are working together (per engine).

The inner nozzle controls the convergent section of the nozzle,while the outer nozzle controls the divergent section. The two nozzlesections are linked together, forming the required cross-sectionduring engine operation.

When the engine is set to full "dry" power (without afterburner),the inner nozzle opens while the outer nozzle closes. The whole nozzleis working in this case as a convergent cross-section nozzle.

When the afterburner is ignited, the inner nozzle closes, while theouter nozzle opens widely. Now the nozzle is set with aconvergent-divergent cross section (similar to a rocket nozzle).

Jet flow accelerates in the convergent section and proceeds to thedivergent section, becoming supersonic. The shock waves may be visibleas "rings" as the high energy, high velocity jet leaves the divergentsection, behind the aircraft.

The VSKYLABS F-4E is equipped with functional variable area exhaustnozzles that works with two, animated nozzle sections for each engine,forming a convergent-divergent cross-section during engine operationfrom idle to afterburner. To note that when on idle, the nozzles arewidely opened, mainly to reduce the thrust to minimum.

The attached screen shot shows the (Work In Progress) variable areanozzles in action, where the right-hand engine is set to maximum "dry"thrust (no afterburner), and the left-hand engine is set to idle.

Stay tuned for more development news of this fascinating project!

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