"thump" sound shortly after moving throttle to idle?

Hey, anyone know what exactly is causing that "thump" sound right after moving throttle to idle at 20% RPM ? :)

Engine Igniter(s) ?

Just tried a Nevada start.

No thump sound at 20%, though a little fluttering below that.... maybe a little surging of the JFS?

Up to 20% there is no fuel injected yet and only the low pressure compressor stages are turning. When you move the throttle it injects fuel and it may be simulating the initial combustion which then helps drive the high pressure stages of the engines. Or you could’ve knocked something on your desk! :)

Up to 20% there is no fuel injected yet and only the low pressure compressor stages are turning. When you move the throttle it injects fuel and it may be simulating the initial combustion which then helps drive the high pressure stages of the engines. Or you could’ve knocked something on your desk! :)

Both compressors (LP and HP) are turning. If not it would cause stagnation/stalls when fuel was introduce.

When you move the throttle it injects fuel and it may be simulating the initial combustion which then helps drive the high pressure stages of the engines. :)

ooooh, awesome! But wouldn't the thing that makes the low pressure compressor stages turning (Start 2 switch position) make some very loud noise aswell as I think quite some force is required to get the pressure stages running? (before fuel is injected)

ooooh, awesome! But wouldn't the thing that makes the low pressure compressor stages turning (Start 2 switch position) make some very loud noise aswell as I think quite some force is required to get the pressure stages running? (before fuel is injected)

It’s just compressed air. I worked on Nimrods in the RAF for 9 years and they used an APU designed for a car in the 1950s. It was incredibly noisy and would overheat to the point of almost going on fire after 5 mins.

https://en.wikipedia.org/wiki/Rover_JET1

The LP and HP stages are on separate shafts. The stagnation/stall is prevented by using bleed valves which allow air to escape during the start as the air flow is that powerful it can inhibit combustion.

No, bleed valve do not prevent stagnation on the F110-GE-129 AFAIK. PW engine have a bleed trap ( it has a different job, not preventing stall/stagnations), but we have here a GE engine in DCS.

As a matter of fact, in the Real life aircraft, the JFS, turn the engine thought the ADG, which turn the PTO, that turns the engine gear box, which turn the core (HP compressor) The LP compressor turn because the HP is turned by the JFS.

So, on start in the F-16, LP ( first 3 stages of compression and last 2 turbine) cannot turn unless HP ( correction, last 9 stages of compression and one turbine) is turning.

...

Guys, try the same engine off.

...

Guys, try the same engine off.

??? did, no sound at all... are you just trolling us? xD

It’s just compressed air. I worked on Nimrods in the RAF for 9 years and they used an APU designed for a car in the 1950s. It was incredibly noisy and would overheat to the point of almost going on fire after 5 mins.

 

https://en.wikipedia.org/wiki/Rover_JET1

The Viper is started by the Jet Fuel Starter (JFS), this is a small gas turbine engine and makes a hell of a noise. It produces around 400HP. At the moment you place the start switch to ST-I only one accumulator will open the JFS doors, and start to run the JFS up in RPM by a Hydraulic Start Motor. ST-II will use two accumulators to do this. Eventually fuel will be injected and the JFS will start. When it is running it will light up the run light.

Than the JFS will run the core engine (high pressure compressor and turbine) via clutches in the Accessory Drive Gearbox (ADG), the Power Take Off (PTO) shaft, the Engine gearbox and the towershaft. Because of the airflow the Fan and Low pressure turbine wil start to rotate as well.

Because compressors are really effective a gas turbine will not start very well without bleeding some high pressure air coming from the compressor. In the Pratt & Whitney it is not done via a bleed valve but via a bleed strap. I do not know how the GE works..but i think they do the same thing.

When the throttle is moved out of cutoff igintion and fuel is provided.

Once the Engine RPM is around 18% the Brake/JFS accumulators as they are called are starting to be refilled. When the RPM is around 50% the JFS automatically switches off (only on the ground).

Just took off the helmet and tried 2 more starts.

I'm not hearing anything.

The Viper is started by the Jet Fuel Starter (JFS), this is a small gas turbine engine and makes a hell of a noise. It produces around 400HP. At the moment you place the start switch to ST-I only one accumulator will open the JFS doors, and start to run the JFS up in RPM by a Hydraulic Start Motor. ST-II will use two accumulators to do this. Eventually fuel will be injected and the JFS will start. When it is running it will light up the run light.

 

Than the JFS will run the core engine (high pressure compressor and turbine) via clutches in the Accessory Drive Gearbox (ADG), the Power Take Off (PTO) shaft, the Engine gearbox and the towershaft. Because of the airflow the Fan and Low pressure turbine wil start to rotate as well.

 

Because compressors are really effective a gas turbine will not start very well without bleeding some high pressure air coming from the compressor. In the Pratt & Whitney it is not done via a bleed valve but via a bleed strap. I do not know how the GE works..but i think they do the same thing.

 

When the throttle is moved out of cutoff igintion and fuel is provided.

 

Once the Engine RPM is around 18% the Brake/JFS accumulators as they are called are starting to be refilled. When the RPM is around 50% the JFS automatically switches off (only on the ground).

Just to add to this

https://forums.eagle.ru/showpost.php?p=3904832&postcount=551

Just took off the helmet and tried 2 more starts.

I'm not hearing anything.

I don't hear anything either using open beta version 2.5.6.45915 in NTTR.

I'm not hearing anything.

I don't hear anything either using open beta version 2.5.6.45915 in NTTR.

u guys serious??? xD omggg here THIS SOUND (not canopy at start, I included that just to show how annoyed I am with DCS F-16 differing between a really short key-combination press and a key-combination press that is a LIIIITTLE bit longer)..... :glare::glare:

Also, any1 know why that ventilator (I guess it's a ventilator?) that turns on as soon as I turn the battery on sounds like it's gonna break any moment? (sounds like it' running since 2000 hours already or so xD that "clapping" noise)

(oh and pay extra attention to the lights-setup. Really cool boyz turn primary instr.+consl. lights to max. and deny ANY of the ugly flood-lights xD I see totally wrong light-setups on F-16 streams on Twitch WAY too often... none at all, most of the time, the streamers have a totally boring dark cockpit...)

I think you have a corrupt sound file?

I think you have a corrupt sound file?

What? are you being serious here? :huh: Which sound exactly, that "thump"?

(I repeated that thump in the end several times)

Yes, exactly that thumb. Try a repair.

If that doesn't fix it, remove all sound mods (if any) to verify a 3rd party isn't causing it.

What? are you being serious here? :huh: Which sound exactly, that "thump"?

(I repeated that thump in the end several times)

Yea, that doesn't sound like an intentional noise. Try a repair and as others have said, verify no 3rd party sounds are messing with anything. I believe that last update involved "encrypting" the sound files so It may have fumbled one.

did all of that, thump still there...

??? did, no sound at all... are you just trolling us? xD

Nope I am not trolling.

I (still) can't hear what you are talking about (on your video I just hear a loop with an increased volume), so I was initially wondering if you were talking about a possible throttle mechanical stop.

I think that suddenly loud sound loop is what he's interpreting as a "thump"

obviously I repeated the sound a few times for clarification (iirc I stated that on a page before in this thread)

Nope I am not trolling.

I (still) can't hear what you are talking about (on your video I just hear a loop with an increased volume), so I was initially wondering if you were talking about a possible throttle mechanical stop.

Then pls turn up your subwoofer (bass) or use a very good headset. it's a very deep frequency, I just checked with an app, it's ~60 Hz.

Did you try to rename your DCS folder in user/saved games to make sure there is nothing there messing with the sound? Repair wont touch that.