DCS Compressibility

[Coopes]

Oh, I get it. I thought the mach number was the top speed (in level flight) expressed as a mach number. This is why I'm not an aeronautical engineer.

So in layman's terms, the plane in the sim should be exhibiting some odd behaviour once passing M0.75 in a dive, but currently does not. Honestly that doesn't surprise me. Last time I flew the DCS Mustang, I managed to start the engine with both magnetos turned off, so it definitely has its issues...

Dont think you will manage that now

[Dave]

Dont think you will manage that now

Nope. Just checked and it still works:

[Coopes]

So what happens when you release the starter?
If the enginge stops, you have not really started it.

[Dave]

It keeps running. And as I explained to that guy in the comments - the starter motor is just that - a starter motor. It has no ignitor, that's what the magnetos are for. It is physically impossible to run the engine at 2,000 RPM as I was there just using the starter, without the magnetos. Much less TAKE OFF, FLY AROUND and then land again before realizing the mags aren't switched on.

edit: Just checked again, and killing the starter does kill the engine. First time I tried it I just flipped the switch cover thinking that would kill the switch too but it doesn't. It also turns out that the starter booster coil has an ignitor built into it, which explains the behaviour. I doubt you'd be able to run the engine (and fly with it) for 15+ minutes like I did, but sat on the ground for a minute or two during the starting process should be fine.

[Coopes]

It keeps running. And as I explained to that guy in the comments - the starter motor is just that - a starter motor. It has no ignitor, that's what the magnetos are for. It is physically impossible to run the engine at 2,000 RPM as I was there just using the starter, without the magnetos. Much less TAKE OFF, FLY AROUND and then land again before realizing the mags aren't switched on.

edit: Just checked again, and killing the starter does kill the engine. First time I tried it I just flipped the switch cover thinking that would kill the switch too but it doesn't. It also turns out that the starter booster coil has an ignitor built into it, which explains the behaviour. I doubt you'd be able to run the engine (and fly with it) for 15+ minutes like I did, but sat on the ground for a minute or two during the starting process should be fine.

I tried it. Without the magnetos engaged the engine was sluggish as hell. I took off just about and flew. The engine has no power at all.
So remember you magnetos if you want power lol

[Mauf]

At least you have to admit it's better than "Press I for engine on":P

[Dave]

Quite. If this was CloD we wouldn't even be having this conversation.

Edit: An aircraft mechanic acquaintance of mine who works on warbirds got in touch with me about an hour ago after watching the video, and told me that I was actually right to begin with. The starter does engage the booster coil, but that's not how the ignition system works (his words).

All I want to know is how deep this rabbit hole goes.

[IronJockel]

Quite. If this was CloD we wouldn't even be having this conversation.

Edit: An aircraft mechanic acquaintance of mine who works on warbirds got in touch with me about an hour ago after watching the video, and told me that I was actually right to begin with. The starter does engage the booster coil, but that's not how the ignition system works (his words).

All I want to know is how deep this rabbit hole goes.

Which one of the two?
I would like to hear Ed's statement on this.

[Dave]

He watched both... Sent me a message after I put up the second one saying I was right the first time around and started grumbling about keyboard warriors not knowing what they're talking about lol. He offered to explain in detail next time I was free - might take him up on it.

[Dave]

pretend quote just to get your attention

Here we go - got him to do a stream tech talk about it:

https://www.twitch.tv/aerosimgaming/v/102984455

He starts talking about the starter/ignition system at around the 2 hour mark.

TL;DR = You need the magnetos to sequence the sparking of the ignition in the correct cylinder firing order for the engine to start and continue to run. Without it, the booster coil just tries to spark every cylinder at once and it won't work. At least that's how I think it works... to be honest it's incredibly fucking complicated. But basically - yeah the way it's modeled in the DCS P-51 is wrong, and I was right the first time, entirely by accident.

TL;DR TL;DR = The magnetos do more than just spark the engines. You still need them to run the engine.

FWIW he also explains why he thinks people got it wrong in the first place, essentially by not understanding the technical manual properly (because they're not engineers and don't know how to read the manual correctly). If you've got the time it's worth watching - he points out other inaccuracies in things like the cooling system, temperature management and the start process itself.