Incorrect Nozzle Position?

According to Jell-O, a former F-18 pilot, the nozzle should be open when the throttle is on idle and it should close if you advance the throttle just a notch, without an increase in fuel flow.

 

This is from the Fighter Pilot Podcast episode 20. Now maybe it does not apply to the Lot 20 Hornet we have in DCS. I don't know... But at least it would be something worth checking with subject matter experts.

 

I have attached the audio down below. Please take a listen, Jell-O describes it pretty well.

 

Thanks.

 

EDIT: I didn't make it clear enough : the nozzle position in idle seems fine but it's when you start increasing the throttle that the behavior doesn't correspond with what Jell-O says. Right now in DCS when you advance the throttle the fuel flow increases right away and the nozzle does not start closing immediately.

f18 engine nozzle.zip

Edited August 7, 2018 by Nooch

I'm assuming you're referring to the "taxi nozzle", designed to increase thrust during taxi. I don't know as to whether this is a feature of the Lot 20 but it is a thing for a lot of aircraft.

According to a former F-18 pilot, the nozzle should be open when the throttle is on idle and it should close if you advance the throttle just a notch, without an increase in fuel flow.

 

This is from the Fighter Pilot Podcast episode 20. Now maybe it does not apply to the Lot 20 Hornet we have in DCS. I don't know... But at least it would be something worth checking with subject matter experts. I have attached the audio down below.

 

Thanks.

 

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No I am just referring to the standard engine nozzles. I have never heard of such a thing as a taxi nozzle.

Edited August 7, 2018 by Nooch

No I am just referring to the standard engine nozzles. I have never heard of such a thing as a taxi nozzle.

BlazingTrigger is referring to a nozzle position for taxiing, not a different nozzle. (Closing the nozzle increases thrust).

BlazingTrigger is referring to a nozzle position for taxiing, not a different nozzle. (Closing the nozzle increases thrust).

 

Oh ok, got it.

 

I'm assuming you're referring to the "taxi nozzle", designed to increase thrust during taxi. I don't know as to whether this is a feature of the Lot 20 but it is a thing for a lot of aircraft.

 

Here it's about keeping thrust to a minimum in order to avoid injuring the ground crew when you're sitting still on the deck and not asking for power. The F-18 does that by having its engine exhaust nozzles open when the throttles are on idle.

Edited August 7, 2018 by Nooch

Ground crew will always stay clear of efflux and it's pretty toasty and fast moving. The only reason they have it (at least on tornado) is to allow taxiing without using more fuel sitting at a higher engine setting.

 

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Is it "taxi nozzle?" I listened to that podcast as well, and Jell-O said that the nozzle opened up on idle to mitigate the possibility of blowing people/things off the deck .

Efflux when it's exiting the nozzle is at Mach 1 (around 1000mph due to the temp) it rapidly slows however it's still enough to blow a good few things around if not careful. The increase in the area of the jet pipe will reduce the force but anyone who works around jets knows to turn their back to the efflux as it passes as it's like being in a very strong wind.

Is it "taxi nozzle?" I listened to that podcast as well, and Jell-O said that the nozzle opened up on idle to mitigate the possibility of blowing people/things off the deck .

 

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The only reason they have it (at least on tornado) is to allow taxiing without using more fuel sitting at a higher engine setting.

You do know that the Tornados so called Taxi Nozzle has the exact opposite function? When engaged it increases the nozzle diameter over the normal full open position to decrease thrust even more so the aircraft does not accelerate while taxiing. In german, we call it Rollschubbegrenzung which literally means taxi thrust reduction system and that is what it does. The Tornados wheel brakes are really just for good look, completely undersized. It is one of the many extra functions the Tornado engine has and like the others of questionable usefulness. But I never heard of another engine with such a system.

According to Jell-O, a former F-18 pilot, the nozzle should be open when the throttle is on idle and it should close if you advance the throttle just a notch, without an increase in fuel flow.

 

This is from the Fighter Pilot Podcast episode 20. Now maybe it does not apply to the Lot 20 Hornet we have in DCS. I don't know... But at least it would be something worth checking with subject matter experts.

 

I have attached the audio down below. Please take a listen, Jell-O describes it pretty well.

 

Thanks.

 

That's exactly what it does. You seem to misunderstand him, however, close or open don't necessarily mean 100% closed or open. If you take a look at this chart you'll see that the ground idle is actually correct, it corresponds to the actual numbers in the NATOPS.

 

Keep in mind that the nozzles also control the turbine temperature, they must open or close in order to maintain a proper back pressure and temperature.

 

Apologies, it's been a couple of years since I've worked on Tornado, just got them back to front, apologies.

You do know that the Tornados so called Taxi Nozzle has the exact opposite function? When engaged it increases the nozzle diameter over the normal full open position to decrease thrust even more so the aircraft does not accelerate while taxiing. In german, we call it Rollschubbegrenzung which literally means taxi thrust reduction system and that is what it does. The Tornados wheel brakes are really just for good look, completely undersized. It is one of the many extra functions the Tornado engine has and like the others of questionable usefulness. But I never heard of another engine with such a system.

 

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apologies.

 

Haha, don't worry. Things can slip your mind quite fast. I know the feeling.

That's exactly what it does. You seem to misunderstand him, however, close or open don't necessarily mean 100% closed or open. If you take a look at this chart you'll see that the ground idle is actually correct, it corresponds to the actual numbers in the NATOPS.

 

Keep in mind that the nozzles also control the turbine temperature, they must open or close in order to maintain a proper back pressure and temperature.

 

I know, the idle position seems fine but the problem is there below

 

the nozzle should close if you advance the throttle just a notch, without an increase in fuel flow.

 

That's not how it is modelled in DCS right now. When you advance the throttle the fuel flow increases right away and the nozzle does not start closing immediately.

Edited August 7, 2018 by Nooch

I thought pretty much ever afterburning jet engine worked that way.

 

Yeah of course. But there is a normal operating range for the nozzle diameter. The Tornados RB199 engine has a special mode to open the nozzle even further. It can only be engaged on the ground. As I said it is a quite unique thing as far as I know and could have something to do with the weak brakes. While developing the engine for the Tornado they tried out many new things and in the end the engine is kind of over engineered.

Yeah of course. But there is a normal operating range for the nozzle diameter. The Tornados RB199 engine has a special mode to open the nozzle even further. It can only be engaged on the ground. As I said it is a quite unique thing as far as I know and could have something to do with the weak brakes. While developing the engine for the Tornado they tried out many new things and in the end the engine is kind of over engineered.

 

[memory on] Too true.. RCOVs on RAF batch 1-4 aircraft that had no indicator in the cockpit completely negating the benefit of having it because you didn’t know if it had operated..... so you always lost a gearbox with an engine failure despite the cross drive clutch operating.

Problem fixed for us in batch 7 jets about the the same time we got head up AP control panel to replace the killer AP panel buried in the cockpit.

 

However the RB199 meant you could accelerate like hot snot off a Teflon shovel at low level with its low bypass triple spool in combat power.

 

Nozzles to control afterburner ignition caused a few scary moments when shifting one into burner whilst plugged into the tanker. Bit of a thrust PIO just when you didn’t need it whilst IMC on a goose trail [memory off]

 

..... back to my cider now (and wondering why very few apply themselves to mastery of basic flying disciplines such as visual circuits and other mundane stuff such as Fast jet SOPs or proper IFR approach......but get all esoteric on case 1 carrier stuff) #run before walk :)

(...wondering why very few apply themselves to mastery of basic flying disciplines such as visual circuits and other mundane stuff such as Fast jet SOPs or proper IFR approach......but get all esoteric on case 1 carrier stuff) #run before walk :)

+1 :lol:

[memory on] Too true.. RCOVs on RAF batch 1-4 aircraft that had no indicator in the cockpit completely negating the benefit of having it because you didn’t know if it had operated..... so you always lost a gearbox with an engine failure despite the cross drive clutch operating.

 

Ah yes, on the ground they still confirm RCOV to Eng on the headset.

 

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