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Old 12-03-2019, 06:43 PM   #1
grafspee
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Default P-51 cold start up

Now we know how p-51 engine behave in extreme weather
Can we have this in DCS ?

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Old 02-02-2020, 01:31 PM   #2
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And they say this is the most accurate P-51 out there, lol that is the dumbest thing i ever heard. Take a look at the A2A P51 with accusim, that is a very accurate model of it, and the engine behaves different in all sorts of climate changes. And if you don't do it after the book you will not be able to start the engine or you can damage the engine very easy. I wish they made there warbirds for DCS.
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Old 02-02-2020, 02:02 PM   #3
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I thought that the DCS P-51 and its engine performance was based on an actual aircraft. Miss Velma from the Fighter Collection.
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Old 02-02-2020, 03:23 PM   #4
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Yes cold start need love.
Magic_zach found out that if pilot move throttle too far prior to start up engine will kick back because ignition will be too early so electric starter will not manage to crank engine. Now you can start up with throttle wide open no problem which is impossible IRL.
Fact that cold start up isn't modeled properly cant get in the way of the engine and aircraft simulation. it is at very good level. both supercharger's and engine's modeling is outstanding imho
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Old 02-04-2020, 05:18 PM   #5
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... as well as the cold start model. It does have kickbacks, but the main reason of avoiding the early ignition is not the starter inability. Overall prop and engine inertia with starter assistance are able to pass top dead center (TDC) even with early ignition timing (before the TDC), but the piston rod will be stressed much more it is stressed at normal conditions.

As the slow model used for the engine start-up and shut-down truly simulates the cycle, timings and crankshaft-piston cinematics I can show the difference between normal start-up and abnormal start-up using simulation time histories.

The first graph represents the crankshaft total moment from the piston rods along with its angular speed. Electric motor having the same charachteristics as the real starter cranks the shaft (of course with the proper reduction gear). From 2 to 2.5 s the first two cylinders entered compression stroke and later another cylinders entered cold expansion stroke. Then, at t=2.9 the first combustion stroke appeared.
As the ignition moment is quite close to TDC the moment from the pistons is quite smooth, all gas potential is used in right rotational direction.

The second case is for a bit early ignition. Take a look at the kickback moment stricking a piston rod as the piston was trying to compress burning mixture. This kickback could not stop or even reverse the shaft but the series of preignited combustions caused slower acceleration.

The third case represents maximal preignition value. All effects are much more pronounced but the overall piston work before and after TDC is positive . The piston rods and bearings are hardly abused with strikes.
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Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів
There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.
Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me
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Old 02-04-2020, 05:25 PM   #6
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Thank you for your post
So are you saying that even with throttle at max kick back will not occur ?
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Old 02-04-2020, 06:35 PM   #7
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Quote:
Originally Posted by grafspee View Post
Thank you for your post
So are you saying that even with throttle at max kick back will not occur ?
It occurs. See lower angular speed after it.
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Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів
There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.
Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me
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Old 02-04-2020, 07:07 PM   #8
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Quote:
Originally Posted by Yo-Yo View Post
It occurs. See lower angular speed after it.
I can see slower angular speed but i was looking for reversed angular speed
check this nice kick back engine merlin 266
https://youtu.be/8OydGSADtYw?t=274
3 ignitions in row with reversed angular speed due to kick back.I doubt that throttle was w/o
I know his battery wasn't at 100% sure but war time batteries were't as good as modern one, + manual says that if possible use external power so i woudl agree that with external power starter would overcome kick back but not from battery alone.
And another thing DCS's starters are cranking engines quite faster then real one.
Check later in movie how fast engine come to stop at cut off.
Nice he talks about brakes which start creep at -3 lbs boost heh
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Old 02-04-2020, 08:37 PM   #9
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It can not be preignition. No signes of combustion. And it occurs rare. In DCS the battery is absolutely fresh. 146% of full charge .
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Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів
There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.
Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me
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Old 02-04-2020, 08:55 PM   #10
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Quote:
Originally Posted by Yo-Yo View Post
It can not be preignition. No signes of combustion. And it occurs rare. In DCS the battery is absolutely fresh. 146% of full charge .
What sign would you like to have ?? For me looks like combustion kick back all gases remain in side cylinder because starter keep pushing crank forward if not, only other explenation would be that starter just bouncing from peak compression point which would be even weaker then partial pre egnition.
Maybe you are right probably starter coil cutting out from voltage drop before peak compression
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