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Engine RPM jumping to max by itself after coldstart ... bug?


Frag

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Hey guys,

 

something happens to me a LOT and I am pretty sure that I could not be the only one who has this. I wonder if its a bug or I miss something.

 

- Coldstart

- Set battery ON.

- Set both Generator ON.

- Put both engine throttle to Idle.

- Order the crew chief to connect air supply.

- Order the crew chief to apply air supply (left engine)

- Start the left engine

 

At this point everything is fine...

 

- Order the crew chief to apply air supply (right engine)

- Start the right engine.

 

Sometimes, at this point ...the engine wont start for 15-20 seconds. I may have to click the start button again. And when it does that that ...the engine RPM will jump sky high to 100% ... throwing the plane into movement.

 

That thing happen to me so often that I now always ask the crew chief to place the wheel shock ...so the plane wont move if it happens. Also I carefully checked if the throttle handles move (thinking that it could be a controller issue with the axis) and no, the throttle handles are not moving at all.

 

Am I doing something wrong or its a known bug?


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Hey guys,

 

something happens to me a LOT and I am pretty sure that I could not be the only one who has this. I wonder if its a bug or I miss something.

 

- Coldstart

- Set battery ON.

- Set both Generator ON.

- Put both engine throttle to Idle.

- Order the crew chief to connect air supply.

- Order the crew chief to apply air supply (left engine)

- Start the left engine

 

At this point everything is fine...

 

- Order the crew chief to apply air supply (right engine)

- Start the right engine.

 

Sometimes, at this point ...the engine wont start for 15-20 seconds. I may have to click the start button again. And when it does that that ...the engine RPM will jump sky high to 100% ... throwing the plane into movement.

 

That thing happen to me so often that I now always ask the crew chief to place the wheel shock ...so the plane wont move if it happens. Also I carefully checked if the throttle handles move (thinking that it could be a controller issue with the axis) and no, the throttle handles are not moving at all.

 

Am I doing something wrong or its a known bug?

 

 

 

The engines shouldn’t go into idle until after or nearly the same time as pressing the start switch.

 

 

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Can you post a track? I think I have an idea whats wrong but Id like to confirm it beforehand...

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Can you post a track? I think I have an idea whats wrong but Id like to confirm it beforehand...

 

Sound good, I cannot reproduce at will ... but will post the track as soon as it happens. It happens to me a lot so should not be that long.

 

I will also check out what ricktoberfest told me to try.

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Yeah, when you move throttle from off to idle, it starts introducing fuel immediately (your fuel flow gauge will jump). So I'd say by the time you get to your right engine, when you ignite it, its full of fuel so has a "mini explosion" rather than a controlled ignition.

 

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I only fly multiplayer and I spend at least 75% of that time in the F5 and I have never seen this.

 

As numerous people in this thread have pointed out, with the F5's J85 engines (and essentially every other turbojet/turbofan engine until FADAC came around and changed some things on some types), you can start ignition at essentially any time in the start cycle before introducing fuel, but you can only move the throttle out of cutoff to start fuel flow once the engine reaches a certain RPM. Per TO 1F-5E-1, and as bun pointed out above, that is 10% for us . Introducing fuel prior to that minimum RPM or starting ignition after there is a bunch of fuel in the burner can is going to lead to a hot start or explosion that will require an inspection that will most likely reveal major if not catastrophic damage to the engine.

 

Like a lot of these issues, a track will immediately point out if it is a bug or not. And if it is happening in MP, DCS automatically saved your track...

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I haven't had this myself (and I've had the F-5 for years) but I have witnessed my friend fly off the taxiway into the grass a couple of times during startup - he's only had the F-5 since Christmas.

 

First time, I thought he'd done something stupid and I think he did too. Second time, there's something weird going on.

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Interesting. If it isn’t just constrained to engine start I am certainly more open to the idea that it could be a bug. Tracks will tell I suppose, I’ll definitely be paying more attention during startup and taxi now.

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Happened few days ago to me, twice on multiplayer, If it happens again I will remember to post the track here.

Both times, happened when starting the right engine, both throttles were at idle, but the right engine behaved like it was in pushed into AB right after start.

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Happens to me as well. I can’t recall the exact time in the startup process, seems to catch me off guard sometimes. I think it’s after asking the ground crew to apply air to the second engine, then the engine spools up and then at some point the throttle seems to increase to full power on its own and the jet rolls forward often getting stuck in the grass if starting from a hangar. I don’t have a track either.

 

What I’ve done to get around this is as the second engine spools up and the RPM stabilizes, I jiggle the throttle (now controlling both engines) slightly up and back down to idle. This seems to cancel the rapid (and seemingly on its own) ramp up of throttle. It’s almost like without that little jiggle, once the second engine spools up, the system treats the throttle like its at full power until you give some throttle input.

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I used to have this issue a lot, but since I started to set the throttle to Idle AFTER clicking Engine Start .... I did not reproduced the issue anymore.

 

So it seems that it will happen only if you set the throttle to Idle before clicking Start Engine.

 

For those who it happens as well, do you set the throttle to Idle before or after you click 'Start Engine'?

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This is why the procedure (written in the manual) is to hit the igniters BEFORE you add the gas.

 

Its really not surprising that your thrust would go through the roof after filling the engine with fuel then igniting it. Also really dangerous? The checklists were written with blood. So let's not reinvent the wheel on these things because it's possible the adverse effects are modeled . :-p

 

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