RPM/MP bouncing all over the place

[Nealius]

Track attached. 

 

Maybe I'm missing something in the startup, but I'm fairly certain I'm hitting the minimum necessary items. The engine runs rough with frequent RPM drops and MP spikes. It's worst at idle, but still major between idle and around 60% RPM. Above 60% RPM it's still running rough, but the spikes/dips aren't as large. The only time it's stable is above 700 MP or so, in-flight. After a 30 minute flight and landing, cutting to idle in the flare, the engine goes back to being a rusty go-cart found in an Alabama barn.  ]

 

Ran an Autostart to cross-check. I'm priming "to main line" without priming "to cylinders." However, if I skip the cylinder priming, shouldn't the fuel pressure gauge still read zero even if I primed "to main line?"

 

Yak.trk

Edited August 12, 2021 by Nealius

[Ramsay]

1 hour ago, Nealius said:

I'm priming "to main line" without priming "to cylinders." However, if I skip the cylinder priming, shouldn't the fuel pressure gauge still read zero even if I primed "to main line?"

No, the left position pressurizes the fuel system.

 

Quote

Priming
The primer is positioned on the upper right hand side of the front cockpit panel and has three positions, Left – Pressurizes the fuel system. Right, primes fuel into the engine. Upright is the Neutral position.
The general rule of thumb is to use one prime to the engine (Right hand position) for every 10°C below 100°C as indicated on the CHT. Up to a maximum of 9 primes.
When starting an engine from cold, the propeller should be pulled through for ½ a turn for each prime.
With a cold engine, at the moment of starting, it may be necessary to select the primer to the Right Hand position and add an extra 1 or 2 primes whilst the engine is firing

Warning: Over-priming my result in an engine fire. Should this occur, continue to crank the engine in order to smother the fire.

Pressurizing
Prior to starting pressurize the fuel system, by selecting the primer handle to the Left and pumping until the fuel pressure indicator shows 0.2 – 0.5 kg/cm.

Caution: Always return the primer to the upright Neutral position after starting. Failure to do so will result in the engine drawing fuel through the primer and running rough.

 

Edited August 12, 2021 by Ramsay
Add Yak-52 Fuel schematic

[Nealius]

Ah, one primes the engine, one pressurizes the system. Like a primer and wobble pump in one package. The nomenclature in the documentation is bizarre and misleading. "Prime main line" when it should be "pressurizing the system," and "prime cylinders" when it should be "prime the engine." Or more simply, "pressurize" vs. "prime."

[NineLine]

On 8/12/2021 at 9:04 AM, Nealius said:

I'm priming "to main line" without priming "to cylinders." However, if I skip the cylinder priming, shouldn't the fuel pressure gauge still read zero even if I primed "to main line?"

I'll ask.

[Ramsay]

On 9/2/2021 at 1:08 AM, NineLine said:

I'll ask.

 

Not sure why, the schematic shows the triple gauge is connected to main fuel line "main".

 

Pumping fuel to the "cylinders" is pumping fuel directly into the inlet manifold, i.e. IRL after each pump stroke the prop is rotated half-a-turn, none of which would show on the triple gauge as line pressure.

 

Whether a cold engine would start if the cylinders hadn't been "primed" is another question but we know the Yak-52 is missing it's failure modes ?

[Nealius]

12 hours ago, Ramsay said:

Whether a cold engine would start if the cylinders hadn't been "primed" is another question

 

Is this a thing? The cylinder priming requirement has confused me from the start because no other warbird in DCS requires this, including the other radials like Anton and Jug.

[Ramsay]

19 hours ago, Nealius said:

Is this a thing?

 

Yes, though like pre-start prop turning, a lot of things in DCS are glossed over / simplified.

 

A "typical" Yak-52 start up

 

 

Yak-52 cold starting at -3°C

 

 

The Mosquito will have you calling to the ground crew to work an external "priming" pump to start each engine.

 

I've no experience with aircraft but I've worked with several older engines from the 50's that required fuel squirted into their inlet manifolds as part of a normal starting procedure.

 

IIRC most had a fuel tank above the engine and were gravity feed, but perhaps one of them *might* have used a hand pump (it's a long time ago, so I really can't be sure).

 

Even today, products like "Easy Start" exist to assist cold weather starting

 

Edited September 4, 2021 by Ramsay
Add a more "typical" Yak-52 start up video

[Callsign112]

It would be nice if ED added the puff of smoke at startup, especially for the war birds.