Merlin negative G cutout too quick?

[IvanK]

Sternjaeger what would be your opinion on how much of a push or reduction in G would be required in an early Merlin to cause it to cough ?

At present a smooth (like doing your best IF technique) lowering of the nose to say 10 degrees nose down for a descent causes the engine to cough.

Originally Posted by IvanK

Sternjaeger what would be your opinion on how much of a push or reduction in G would be required in an early Merlin to cause it to cough ?

At present a smooth (like doing your best IF technique) lowering of the nose to say 10 degrees nose down for a descent causes the engine to cough.

IvanK it's no guesswork, you need a G-meter to determine it properly. A sustained 0G or a minimum negative G load (-0.1) are enough to interrupt the flow. Despite what our scientist friends here say, the mixture gets to the cylinder inlet almost instantaneously. As you know it's not like cylinders burn mixture all at the same time, so one cylinder not receiving enough mixture for a full detonation is enough for a cutout sometimes. Again, please guys provide me with a video and I will be able to tell you (in my humble opinion) if the effect is overmodelled or not.

[IvanK]

Here is a small video. Starts with throttle at idle then to max Boost.
Then a slow descent initiation with max Boost set.
I would be interested in your opinion on the RPM needle Bounce as well as the cough which starts about 19seconds in:

http://www.youtube.com/watch?v=Py7lfQUxgRA

I figure (based on experience) that the descent entry is less than 0.2g decrement on 1G i.e by estimation G is never getting less than +0.8G ... pretty slow entry and still it coughs

[doghous3]

Just to add to IvanK's vid.

Crusing speed with various moves to invoke this issue. Full realism.

http://www.youtube.com/watch?v=L7bxmmh0VzE

Dunno if it's just me, but the problem seems worse with engine heat realism off.. so that you can't control the rad. Prolly just me. *shrugs*

Hope the video helps anyway.

Originally Posted by IvanK

Here is a small video. Starts with throttle at idle then to max Boost.
Then a slow descent initiation with max Boost set.
I would be interested in your opinion on the RPM needle Bounce as well as the cough which starts about 19seconds in:

I figure (based on experience) that the descent entry is less than 0.2g decrement on 1G i.e by estimation G is never getting less than +0.8G ... pretty slow entry and still it coughs

regarding the needle bounce I think it's overmodelled. RPM gauges are connected by flex cable to a reduced gearbox attached on a specific slot on the back of the engine, so they're as accurate as it gets. You can get high frequency vibrations, but oscillations like that means that either your instrument is fooked or your engine is actually doing those oscillating RPM peaks (which is weird..).

[winny]

The problem in the Merlin carb was the fuel resevoir/float tank.
It's pretty much like the cistern on a toilet. With a float/valve system to refill

Fuel sit's in there and the supply to carb is taken from there. It's done purley by gravity. In negative G the fuel moves to the wrong end of the resevoir and so starves the engine.

Miss Shillings work around was a metal plate with a hole in it that slowed the liquid movement down. It didn't completely get rid of the Neg - G problem but it gave you more time before the fuel emptied from the resevoir

btw, I forgot to tell that my flying experience isn't with early Merlins, so de facto I have never had a cut out with the Merlin. I had it with other gravity fed machines (I once had a very hair raising experience with a Tiggie which left me falling down like a leaf with a dead engine..), but I asked one of the engineers this afternoon and he said that yes, power loss and cut out would be quite abrupt. As you probably know negative G or inverted flight is not recommended on a Merlin anyway because of its lubrication system configuration: you'd have oil coming up and messing up the cylinders and leaving the crankshaft dry. Another advantage that the DB engine had over the Merlin apparently.

A.

[II/JG54_Emil]

Originally Posted by Sternjaeger

btw, I forgot to tell that my flying experience isn't with early Merlins, so de facto I have never had a cut out with the Merlin. I had it with other gravity fed machines (I once had a very hair raising experience with a Tiggie which left me falling down like a leaf with a dead engine..), but I asked one of the engineers this afternoon and he said that yes, power loss and cut out would be quite abrupt. As you probably know negative G or inverted flight is not recommended on a Merlin anyway because of its lubrication system configuration: you'd have oil coming up and messing up the cylinders and leaving the crankshaft dry. Another advantage that the DB engine had over the Merlin apparently.

A.

Could you ask one of the engineers or the actual pilots if it is modeled good enough?

[Kurfürst]

Prolonged inverted was not allowed on the DB engined 109 either, for the same reason (lubrication system not prepeared for it)