F-14A nozzle does not close after shutdown

[vadupleix]

After I completed the flight and shut down my engines, I noticed that my right engine nozzle did not close. That happened after a normal dogfight, no engine problem/warning during the process, no light on the warning panel either. I did pull the MCB breaker. Wonder what could have caused this issue? Thanks

[bonesvf103]

That's normal for the F-14A. In a nutshell, when the right engine is shut down first, it is electrically held in place while electric power remains. When the left engine is shutdown, the hydraulic systems take longer to come offline than the generators and that cause the nozzle to be stuck open. It happens in the F-14B as well, but the nozzles are such that it's not as noticeable.

 

v6,

boNes

[bonesvf103]

In further detail, courtesy of Herr Anft:

 

The TF30's afterburner nozzles are regulated open or closed individually by each engine's afterburner fuel control system. The afterburner fuel control pumps are individually operated using the hydraulic pressure produced by the combined and flight hydraulic systems. The port engine powers the combined hydrualic system and the starboard engine powers the flight hydraulic system.

The Tomcat has a "weight on wheels" switch and a "weight off wheels" switch. When weight is "on wheels" (on deck) the nozzles are commanded open to reduce thrust produced by the engines to keep from blowing over ground personnel. When the weight is "off wheels" (airborne) the nozzles will close any time when being in "basic engine" from idle to military power (highest thrust without selecting afterburner) and will open up as afterburner is staged. This feature gives added thrust at idle when being airborne. The switches are mechanically operated by the main landing gear scissors assemblies, but need electrical power to function. When electrical power is taken off the jet completely, the aircraft will default to the weight off wheels condition where the nozzles close so that if there happened to be a total electrical failure airborne you would still have the same amount of thrust at idle that you always do airborne.

When the engine is shut down, the starboard engine is always shut down first. The reason why is because there is a bidirectional pump that has to be checked to ensure that if the starboard engine is lost in flight, the flight side hydraulics will still operate. Once it is ensured that it is working the bidirectional pump will be secured and the flight side hydraulics will go to zero and the afterburner fuel control on that side will no longer be powered because of the lack of hydraulics. Since the weight on wheels switch is still receiving power from the left generator, the starboard nozzle will be trapped open. When the port engine is secured the left generator drops off-line at approximately 55%, however the combined side hydraulics will still operate at 3000 psi for a short period of time as the engine continues to wind down. When the port engine is secured (power off) the nozzle closes because of loss of electrical power and residual fuel pressure through the fuel control to the nozzle actuator (see thumbnail below left).

 

v6,

boNes

[vadupleix]

In further detail, courtesy of Herr Anft:

 

 

v6,

boNes

 

Thank you, learned something interesting today.

[Victory205]

The F14A nozzles are powered by an AB hydraulic pump that uses AB fuel to actuate the nozzles. It's a bit more complex than the missive above, which errantly attributes nozzle power to the aircraft hydraulic system. Still, the result was that most of the time, shutdown resulted in one nozzle open, one closed.

 

The F14B's GE nozzles also use a separate pump, but they use engine oil as a medium for actuation.

[Wizard_03]

Are you supposed to shut the left engine down first? Or does it not matter?

[Victory205]

Right then left.

 

[RustBelt]

Yea it's due to you checking on Start up that the Transfer Pump can be driven by the Right engine, and on Shut down that it can be driven by the Left engine correct?

[Torbernite]

So should it be that left nozzle is kept open and right one closed, in a non-standard operation to wrongly shut down the left engine first? I see photos of both 14A and B/D showing that(links below). Also I heard that F110 will show the same asymmetric nozzles after shutdown but the closed one will gradually open later.

By the way in DCS the result is that both nozzles close.

 

 

http://www.anft.net/f-14/f14-photo-vf041-17.htm

http://www.anft.net/f-14/f14-detail-engine-02.htm

Edited March 8, 2021 by Torbernite

[fat creason]

The nozzles are commanded open when throttles are at IDLE and WOW is signal is detected. Pretty sure that if you shut down in the "incorrect" order, both engines will close their nozzles since the WOW circuit is only powered by one side. Can't remember which one at the moment.

Edited March 8, 2021 by fat creason

[Uxi]

DACO indicated because of the way the hydraulic pressure bled off the first engine shut down would go nozzles wide open while the second would close.

10 hours ago, Torbernite said:

So should it be that left nozzle is kept open and right one closed, in a non-standard operation to wrongly shut down the left engine first? I see photos of both 14A and B/D showing that(links below).

 

 

DACO page 40 shows left closed and right open.