Spitfire jumps forward on engine startup on P3Dv4.3

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bladerunner900
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Re: Spitfire jumps forward on engine startup on P3Dv4.3

Post bladerunner900 »

Daube wrote:What do you mean by "open throttle", how much % more or less ?
When I kill the engine for my test, the throttle is just open enough to maintain idle, so probably something around 10%. The engine runs and the plane doesn't move forward, I don't need to set the parking brakes.
And then I don't touch the throttle anymore. I just kill the engine with the mags, and set the mags back ON, then trigger the start switch.
Not sure the percentage, I tend to idle the engine by sound really. With fuel off at probably about 8 - 10% throttle. Brakes are on but as you say, she doesn't move at that low a setting. I wait for her to splutter then close the throttle completely. About 1 second later I kill the mags. Then, as I mentioned, the next time I select her for flight, I cycle the throttle open then closed, to make sure no throttle setting is carried over from the last flight.

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Nick - A2A
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Re: Spitfire jumps forward on engine startup on P3Dv4.3

Post Nick - A2A »

Hi Daube,

I've tried a few times to reproduce this and I'm afraid I can't: basically if I start up and shut down the Spit in the recommended manner, the tail stays firmly put, even with the parking brake engaged and the elevator in the neutral position.

To shut down, I reduce throttle to around 10-15% and then cut off the fuel cocks. When the engine starts to run rough, I pull the "slow running cut-out" (next to the primer) so you could try this instead of just killing the mags for more realistic operation. However, I don't think this will make any difference to the issue in question.

On startup, again I use a throttle setting of 10-15% and the aircraft stays where it's supposed to. RPM and boost needles don't even move off their pegs. It seems that in your case, the aircraft is detecting the throttle fully open, or significantly so in any case. Lewis's suggestion of trying without a throttle axis connected is a good one.

Thanks,
Nick

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Daube
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Re: Spitfire jumps forward on engine startup on P3Dv4.3

Post Daube »

I will try with the joystick unplugged. But don't you think it's strange that three people suffer from the exact same problem ? (Other two have a X-52, if I'm not mistaken).
If the sim would detect my throttle at fully open position during the second startup, wouldn't it move the throttle lever to 100% in the VC ?
And why would it detect the throttle at 100% on second startup, but not at idle when I kill the engine before the second attempt ?

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Daube
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Re: Spitfire jumps forward on engine startup on P3Dv4.3

Post Daube »

I just did the test, by unplugging my controller and trying the same sequences of start-kill-restart.
The problem occured again.
This time however, I could identify the logic of the event.

Basically, if I kill the engine with the slow-running cutoff switch, the plane doesn't jump on next start.
But if I kill the engine by simply switching the magnetos off, then it will jump forward.

More precisely, here is the exact sequence of things I did:
- start the plane normally, put it to idle without brakes. Final throttle position was 7% according to the tooltip in the VC. RPM lever was set to 0%.
- unplug the joystick
- kill the engine using only the slow-running cutoff
- wait for complete prop stop
- primer three times
- trigger start
- the engine starts and the plane doesn't move forward.
- set magnetos to OFF
- wait for complete prop stop
- set magnetos to ON
- reload cartridge
- primer three times
- trigger engine start
- engine starts and the plane goes forward.

So, for now, it seems the workaround is to kill the engine using ONLY the slow-running cutoff.
But that is just a workaround. The prop/engine shouldn't react like that, should it ?

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Nick - A2A
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Re: Spitfire jumps forward on engine startup on P3Dv4.3

Post Nick - A2A »

Okay, thanks for the info Daube. When I next get some spare time, I'll try these steps and see if I can reproduce the issue.

Not sure why you say using the slow running cut-off is "just a workaround" though? After all, it's there specifically to shut the engine down. You really shouldn't be killing the engine just by switching the mags to 'off'. Doing so leaves fuel in the carburettor and fuel lines.

Cheers,
Nick

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Jacques
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Spitfire jumps forward on engine startup on P3Dv4.3

Post Jacques »

Just for kicks I decided to try this, and shutting down with the magnetos only does result in the aircraft nosing over onto the prop on the next start.

Following the checklist for shutting down results in a good start every time.

Forgot to add its P3Dv4

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Daube
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Re: Spitfire jumps forward on engine startup on P3Dv4.3

Post Daube »

Nick - A2A wrote:Okay, thanks for the info Daube. When I next get some spare time, I'll try these steps and see if I can reproduce the issue.

Not sure why you say using the slow running cut-off is "just a workaround" though? After all, it's there specifically to shut the engine down. You really shouldn't be killing the engine just by switching the mags to 'off'. Doing so leaves fuel in the carburettor and fuel lines.

Cheers,
Nick
Because it's an Accusim plane. That's why :)

On non-Accusim planes, we have to follow the checklists blindly, else for example the engine would not start because I didn't close the canopy or I didn't switch the beacon light in the right sequence, or I didn't pump the primer the exact amount of times, etc... I hate that kind of stuff.

Accusim planes just "work". They don't follow the checklists, they follow the internal mechanical logic of the engine and the plane. It doesn't matter if you pumped the primer prior to switching your lights or the contrary. If the real engine would start, the Accusim engine would start. And if a mistake is made, the Accusim plane should react like the real plane would. That's precisely why I buy Accusim planes.

Now, in a real Spitfire, what would happen if I'd switch the engine OFF by setting the mags to OFF instead of using the slow-running cutoff ? Would the plane jump forward on subsequent start ?

Also, if we consider the problem itself (aircraft moving forward on startup), from a physics engine point of view, how can prop produce so much power when it's just starting to spin and it's not even at idle RPM yet ? To me, it looks like there's a small issue in the power calculations. I understand I'm not supposed to be in that situation normally... but "you're not supposed to do that" is invalid in the Accusim world, isn't it ;)

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Lewis - A2A
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Re: Spitfire jumps forward on engine startup on P3Dv4.3

Post Lewis - A2A »

Are you re-loading the aircraft between shut down and re-start?

How are you re-starting, manually or using shift + 3 auto start?

thanks,
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Daube
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Re: Spitfire jumps forward on engine startup on P3Dv4.3

Post Daube »

No, I don't reload the aircraft, I don't even touch any of the 2D panels. I just go right through the steps I described earlier in this topic.
Start is done manually everytime. I never use the autostart.
Auto C&D is set to ON, though.
To perform the steps, I used only the mouse. Joystick was unplugged as requested.

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Killratio
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Re: Spitfire jumps forward on engine startup on P3Dv4.3

Post Killratio »

Something must have changed from P3D 4.2 to 4.3 .

I am still using 4.2 and in the situation you describe, I am not getting the jump forward at all.
BTW, even though your procedure is contrary to the checklist, it is exactly how the Spitfire was shut down before the introduction of the SRCO.

The job of the slow running gear was to empty the fuel from the fuel lines and carb as much as possible. So you would shut off the fuel taps and run the engine slow, then when she started to run rough, shut off mags. This drained every possible bit of the system by keeping the engine going when it would normally quit (I think by propping up fuel pressure, I'd have to check).

The SRCO was introduced to override this system and let the engine quit WITH fuel in the lines even if the taps were closed. This aided restarting by leaving fuel in the system...exactly what you need in case of a scramble.

The SRCO, like the ABCOO were overrides, designed to bypass the named control, something people often forget, particularly in the case of the ABCOO where people often assume it was designed as a sort of War Emergency Power. That is how it ended up being used after 100 octane came in but it was not at all what the control was for.


So if anything, the Merlin should start quicker and more firmly if the SRCO has been used.. the opposite of what you are seeing in 4.3.

In any case, with brakes on and column back in the pit of your stomach (never should be any other way on the ground) and throttle at start position, the Spit should definitely not jump forward or tip. As said, I'm not seeing this in 4.2, so I wonder what LM have changed?
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Paughco
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Re: Spitfire jumps forward on engine startup on P3Dv4.3

Post Paughco »

Startups and shutdowns (and subsequent restarts) have never been a problem with my Spitfire MkIIa in P3Dv4. I check to make sure fuel and mags are on, generator is on, and then push open the throttle all the way and close it again to check the gear light. Then I follow the manual, which is to prime the engine (usually three shots) crack the throttle, open the starter cartridge cover, push it, then close the cover. The starter cartridge goes BOOM! and she lights right off. Oh yeah - chocks are out, and my feet are on the brakes, ready to come off, "just in case." Usually nothing does. I wish the tach showed low rpms better, but I carefully monitor and adjust throttle and watch the oil pressure and those critical temperatures. By now she's running smoothly. I let her warm up, then get the guys to hold the tail down while I stand on the brakes and run up to check mags and pitch. If it's a multiplayer flight (you really need to fly with us!) I do all this in preparation for our flight and then shut her down and wait. Shutdown procedure is again By The Book, which is let her idle, then pull the slow idle cut off ring. She shuts down. I turn off the mags, generator, and gas, and wait for the rest of the guys to show up. Restart is same as described earlier, except only one shot of prime. Or maybe I cheat and use Ctrl+E. Either way, easy on the throttle, and no parking brake. Never a problem.

My problem comes in keeping her lined up on the runway during takeoff! But that's a whole other story!

Seeya
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Lewis - A2A
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Re: Spitfire jumps forward on engine startup on P3Dv4.3

Post Lewis - A2A »

Okie dokie,

so you are shutting down, not closing the sim or reloading and just starting it up again right?

Just trying to get exact procedure you are doing to try and re-produce on one of my systems here.

thanks,
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Daube
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Re: Spitfire jumps forward on engine startup on P3Dv4.3

Post Daube »

Lewis - A2A wrote:Okie dokie,

so you are shutting down, not closing the sim or reloading and just starting it up again right?
Yes exactly :)
Just trying to get exact procedure you are doing to try and re-produce on one of my systems here.

thanks,
Lewis - A2A
Thank you Lewis, sorry for the trouble.

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bladerunner900
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Re: Spitfire jumps forward on engine startup on P3Dv4.3

Post bladerunner900 »

Jacques wrote:Just for kicks I decided to try this, and shutting down with the magnetos only does result in the aircraft nosing over onto the prop on the next start.

Following the checklist for shutting down results in a good start every time.

Forgot to add its P3Dv4

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Not for me. I have always shut fuel, run engine until she starts coughing, close the throttle and then kill the mags. Next start-up is no problem, although, I make sure to cycle the throttle open then closed first. The only time she noses over for me is if I re-load the Spit. after switching or shutting down the scenario with an open throttle. This is in P3D 4.3 by the way.

Steve.
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Lewis - A2A
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Re: Spitfire jumps forward on engine startup on P3Dv4.3

Post Lewis - A2A »

Daube can you please test with parking brakes.

I managed to re-produce the issue once so far, but found holding brakes kept it from jumping forward as a work around whilst the issue is looked into. Parking brakes are best, as in the platform (fsx and p3d) they tend to be more chocks than parking brake lol.

thanks,
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