Merlin negative G cutout too quick?

[klem]

Originally Posted by Sternjaeger

Bloody norah! nother engineer!

my humble knowledge comes from a thing called experience (in this specific case experience with Merlin and other aviation engines), which is something you can't learn on a manual or at university, but for the sake of science (and in order to pass my exams) I also had my fair share of theory books............

The G loads don't affect only the carburetor btw, but the inlet manifolds as well, so cutouts can be more or less abrupt. I haven't had the chance to fly the sim yet, maybe a video would help understanding better.

gosh, I would spend hours at the pub (or at the hangar with a pint) talking about this stuff mate lol

Sternjaeger, please don't take this the wrong way, I would really like to understand this and I know you will reply on the videos but can you tell me if you actually worked on Merlins (or just study them), did you ever experience or observe the negative G effect and do you feel that an engine that misfires in level flight would ever have made it onto the Spitfire?

The vast majority of us can only use three ways to assess this: Factual official reports (hard to find), common sense (would it ever have been fitted like that) and first hand reports in biographies which, in the dozen or so I have read including Geoffrey Quill, Alex Henshaw, Al Deer, Johnny Johnson etc, only ever refer to it when pushing over into an aggressive combat dive.

Can you also explain the part about it also affecting the inlet manifold please?

I'd be truly interested to know what you think.

[TheGrunch]

It's probably worth pointing out that Sternjaeger will never have experienced the Merlin engine at combat power or indeed emergency boost because unfortunately (or perhaps very fortunately, we don't want to destroy every Merlin on the planet ) no one does that anymore for practical reasons...this being the condition at which the cut-out is least severe in its onset.

Originally Posted by klem

Sternjaeger, please don't take this the wrong way, I would really like to understand this and I know you will reply on the videos but can you tell me if you actually worked on Merlins (or just study them), did you ever experience or observe the negative G effect and do you feel that an engine that misfires in level flight would ever have made it onto the Spitfire?

The vast majority of us can only use three ways to assess this: Factual official reports (hard to find), common sense (would it ever have been fitted like that) and first hand reports in biographies which, in the dozen or so I have read including Geoffrey Quill, Alex Henshaw, Al Deer, Johnny Johnson etc, only ever refer to it when pushing over into an aggressive combat dive.

Can you also explain the part about it also affecting the inlet manifold please?

I'd be truly interested to know what you think.

Klem, it's understandable and I'm well happy to explain things, so no worries!
My relatively modest knowledge of Merlins is because of my involvement with a warbirds association, I don't feel like giving too many info about it because I have had a lot of "new friends" approaching me more for my interests and luck than for anything else, so I hope you appreciate why I prefer to keep it confidential.

Anyway, I know three qualified engineers who work on pretty much any mark of Merlin ever produced, plus a pair of pilots who fly with them regularly. As you might understand, the wealth of information I have access to is pretty much blinding. Having said this, I prefer to keep things quite simple, mainly because not all of us are literate in engineering matters but still want to try and understand how things work.

Anyway, back to the topic, the videos I have seen seem show quite a jolly response, but then again if it's on full throttle they are quite spot on.

As a simple reference, the response to the negative G should be same or even less than the throttle response time.

Regarding the inlet manifolds, the answer is pretty easy: mixture, just like air or water, is a fluid, and as such is affected by gravity and G forces.

Check out this video, especially towards the end (and behold of the divine flying skills!) and see how fluids behave in the right situation.

http://www.youtube.com/watch?v=9ZBca...eature=related

now watch what happens to another kind of fluid (a more "organic" one) when under zero then negative G-load

http://www.youtube.com/watch?v=wbOU3l864H0

flying is a fun, fun thing ;0)

Originally Posted by TheGrunch

It's probably worth pointing out that Sternjaeger will never have experienced the Merlin engine at combat power or indeed emergency boost because unfortunately (or perhaps very fortunately, we don't want to destroy every Merlin on the planet ) no one does that anymore for practical reasons...this being the condition at which the cut-out is least severe in its onset.

I have experienced 100% throttle but not on take-off. It's highly not recommended to use full military power or 100% throttle anyway, again because of the components age concern.

A very quick but effective way to check the health of your engine is checking the lubricant oil for metal particles: they can be microscopic, but if found (often by means of special filters) they're a bad, bad sign.

There was a certain P-51 driver a couple of years ago who had the jolly habit to take off firewalling the throttle: needless to say the cylinder banks didn't want to know about it and an inflight engine failure followed, which fortunately happened close to landing.. the plane and pilot were ok, but the engine needed major (expensive) maintenance costs. Let's not forget that like any other liquid cooled engined, these monsters were meant to perform, not to last

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.

[TheGrunch]

Originally Posted by Sternjaeger

Let's not forget that like any other liquid cooled engined, these monsters were meant to perform, not to last

+1 ~20 hours for the Merlin III with the 100 octane fuel and +12lbs boost used.

[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)