Start 1 vs Start 2?

[durka-durka]

What's the difference? Why should I use one over the other? Thanks.

[Raptor9]

The Jet Fuel Starter (JFS) is a small turbine engine that spools up the main F110 engine. Hydraulic pressure is routed through a hydraulic starter motor on the Jet Fuel Starter to get the JFS spooled up to speed, which in turn spools the main engine for the start sequence. The hydraulic pressure for starting the JFS is stored in a pair of hydraulic accumulators. When you press the switch to Start 1, you are using one of the accumulators to dump the contained hydraulic pressure into the JFS hydraulic starter to start it. If you use the Start 2 position, you are dumping both of the accumulators to start the JFS.

The difference being, if the start sequence fails or is aborted for some reason, you will have the second accumulator to attempt a second start if you use Start 1. If you use Start 2, in theory you only have one attempt to start.

Given these facts, as for why you would use Start 2, I'm sure there is a reason. I would imagine it would be determined on the environmental factors or maybe the type of fuel being used, but I don't have any real-world F-16 experience.

[Yurgon]

To add to what Raptor9 wrote, I think I read somewhere that Start 1 indeed requires certain conditions, I would assume outside air temperature, possibly not too much wind or something like that. In essence, pilots mostly don't bother because these conditions are somewhat rare, and there's no real downside to just always using Start 2.

[Raptor9]

I forgot to mention that once the main engine is started, the hydraulic accumulators are re-charged (which is important because my understanding is these also power the brakes), so if you shut down the engine following a full and successful engine start, you can still re-start it; even if you used Start 2.

[llOPPOTATOll]

On 11/16/2022 at 8:28 PM, Raptor9 said:

The difference being, if the start sequence fails or is aborted for some reason, you will have the second accumulator to attempt a second start if you use Start 1. If you use Start 2, in theory you only have one attempt to start.

Given these facts, as for why you would use Start 2, I'm sure there is a reason. I would imagine it would be determined on the environmental factors or maybe the type of fuel being used, but I don't have any real-world F-16 experience.

Start 1 should have a lower chance of working, so always use start 2.

Edited November 18, 2022 by llOPPOTATOll

[Falconeer]

4 hours ago, Raptor9 said:

I forgot to mention that once the main engine is started, the hydraulic accumulators are re-charged (which is important because my understanding is these also power the brakes), so if you shut down the engine following a full and successful engine start, you can still re-start it; even if you used Start 2.

Yes, they are also called "JFS-brake" accumulators

[Furiz]

Well if you think about it,

if you use Start1 and it fails you used 1 accumulator, so you are left with 1 again for the second attempt which will most likely result in a fail again, since use of only 1 failed the first time...

Therefore there is no logic in using only 1, better to use 2 and you are sure to start the engine, if using 2 fails then its not your fault and using only one in that case again would make no difference.

 

Edited November 17, 2022 by Furiz

[Dragon1-1]

From what I heard, the procedure for at least one non-US operator was to first use Start 1, then kick it into Start 2 if it's not turning fast enough. A single attempt doesn't necessarily use up the whole accumulator, so in practice, you still can do Start 2 if it's taken less than a few minutes of turning the engine over. Failure to ignite might come not only because there's insufficient JFS pressure, but also from, say, ignition problems, so two attempts with one accumulator each are useful, too. 

[LowGlow]

vor 16 Stunden schrieb llOPPOTATOll:

Start 1 has a much lower chance of working in dcs, so always use start 2.

Really? It never happened to me that start 1 would fail. Under which condition would that occur to you?

[durka-durka]

Thanks all for the thorough and easy-to-understand responses.  This helps a lot!  

[DrumminJ219]

For US, we use Start 2 all the time. Never met a viper pilot who used start 1, and it's taught to use start 2 from B-course on. 

[Spartan111sqn]

@Raptor9 Is simulated the discharg of Start 1 and 2?, I tried in flame out in flight in several timer, but it always work. I would like to perform the real re-start of the engine in flight with jstarts empty, also to charge the jstart with the windmill of the turbine. Is it simulated?

[Carbon715]

The short and sweet is start 2 for normal ops, start one of you have a JFS that might/or is prone to blow a start and it's not the end of the flying day. Reason being start 1 if you blow the start you have one more chance before the crew chief starts questioning his life choices for 5 minutes.

In the 80gs there is a theory of operation as to why exactly but I don't remember it enough to quote it right now.

Edited December 12, 2024 by Carbon715
Typo

[Cali]

If they both fail can we get the crew chiefs out there pumping it back up?

[Spartan111sqn]

But it is not simulated the discharg, you can swtich on anf off as many times as you want and for the duration you want, it is not well simulated.

 

@BIGNEWY will ED do it realistic?

[Sniper_1-1]

On 11/16/2022 at 5:28 PM, Raptor9 said:

The Jet Fuel Starter (JFS) is a small turbine engine that spools up the main F110 engine. Hydraulic pressure is routed through a hydraulic starter motor on the Jet Fuel Starter to get the JFS spooled up to speed, which in turn spools the main engine for the start sequence. The hydraulic pressure for starting the JFS is stored in a pair of hydraulic accumulators. When you press the switch to Start 1, you are using one of the accumulators to dump the contained hydraulic pressure into the JFS hydraulic starter to start it. If you use the Start 2 position, you are dumping both of the accumulators to start the JFS.

The difference being, if the start sequence fails or is aborted for some reason, you will have the second accumulator to attempt a second start if you use Start 1. If you use Start 2, in theory you only have one attempt to start.

Given these facts, as for why you would use Start 2, I'm sure there is a reason. I would imagine it would be determined on the environmental factors or maybe the type of fuel being used, but I don't have any real-world F-16 experience.

The reason for start 2 is because start 1 (half bottle) wasn’t able to hit the required rpm for a normal start, start 2 (full bottle) was able to achieve the required rpm. 

[Spartan111sqn]

On 12/25/2024 at 7:02 PM, Sniper_1-1 said:

The reason for start 2 is because start 1 (half bottle) wasn’t able to hit the required rpm for a normal start, start 2 (full bottle) was able to achieve the required rpm. 

yes, but the problem is that actually the bottle is infinity, you can use it as many times as you want.

[skywalker22]

 

 

[Sniper_1-1]

On 1/8/2025 at 1:41 PM, Spartan111sqn said:

yes, but the problem is that actually the bottle is infinity, you can use it as many times as you want.

Don’t know what u mean by infinity but in real life start 1 didn’t provide the engine with enough rpm to click it into a start mode that’s why modern procedures require start 2 

[Spartan111sqn]

15 hours ago, Sniper_1-1 said:

Don’t know what u mean by infinity but in real life start 1 didn’t provide the engine with enough rpm to click it into a start mode that’s why modern procedures require start 2 

how many uses of start2 can you have?, that's what I mean, try to switch on and off the engine several times, the start2 is infinite and in RL is not the case.

[Sniper_1-1]

7 hours ago, Spartan111sqn said:

how many uses of start2 can you have?, that's what I mean, try to switch on and off the engine several times, the start2 is infinite and in RL is not the case.

I see sorry for the confusion.

[void68]

Well, then why is there still a Start1 in RL? Wouldn't it be safer to erase / cover the imprint and change the switch to a simple OFF (ON)?

[itn]

2 hours ago, void68 said:

Well, then why is there still a Start1 in RL? Wouldn't it be safer to erase / cover the imprint and change the switch to a simple OFF (ON)?

In general you only change things for a good reason. The benefits have to outweigh the risks and costs associated. Changes cost time and money and usually cause more changes and costs in form of updated documentation and things like that.

In this case you would modify hundreds of Vipers in order to save some Crew Chief sweat in the likely quite rare occasion of a pilot accidentally using one instead of the two bottles to start, as standardized and trained for.

Other than that, don't know if there are some actual, hard reasons for keeping the panel as is. For example if it's used in some service/maintenance/checks.

[NytHawk]

3 hours ago, void68 said:

Well, then why is there still a Start1 in RL? Wouldn't it be safer to erase / cover the imprint and change the switch to a simple OFF (ON)?

33 minutes ago, itn said:

Other than that, don't know if there are some actual, hard reasons for keeping the panel as is. For example if it's used in some service/maintenance/checks.

The HAF manual states that the F100 powered Bl.52 can be started using any JFS position, while the F110 powered Bl.50 should be started using START 2.

All CCIP standard aircraft have high levels of cockpit commonality, and it has gone to the extent of sharing the JFS switch.

Edited January 14 by NytHawk