[REPORTED] DCS. Spitfire mk IX. Excessive flight time inverted.

[Holbeach]

DCS bug report. Excessive time inverted. I don't know how long a Spitfire can fly inverted, but I doubt it's this long. 1min. 18secs. @ 2850 rpm 12 lb boost, or 1' 25'' @ 2650 rpm. Oil press./temp remain OK. Water OK. Fuel starvation eventually stops engine. No damage.

 

 

 

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[Holbeach]

I guess nobody knows.

 

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[humptydumpty]

What i noticed in the other aircrafts was a max of 10-12 seconds inverted b4 the engine went out , i guess 15 seconds is when the engine goes out. I haven't tried in the Spit but will do so hopefully later 2nite.

[Holbeach]

DCS bug report. Excessive time inverted. I don't know how long a Spitfire can fly inverted, but I doubt it's this long. 1min. 18secs. @ 2850 rpm 12 lb boost, or 1' 25'' @ 2650 rpm. Oil press./temp remain OK. Water OK. Fuel starvation eventually stops engine. No damage.

 

 

 

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I've had a couple of questions of concern cleared up for me, but this one is still hanging around.

 

How long can a Spitfire IX fly inverted?

 

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[Holbeach]

Sooooo!

 

How long can a Spitfire IX fly inverted?

 

1 min. 20 secs @ sea level?

 

Edited March 2, 2017 by Holbeach
Added picture.

[razo+r]

not so long, like 1 or 2 seconds due to the carburetor i guess

[flyco]

The DCS version of the Mk IX has an inverted fuel carburetor so the fuel flow continues at negative g. In earlier versions the engine cut within a second or two of negative g - hence the need to roll inverted to begin a sudden descent. The likely limits are going to be oil or fuel starvation, and the latter is going to depend on power settings - you will use any recuperator fuel faster at high settings.

 

I don't know whether any limit is laid down, there is not one quoted in Pilot's Notes, but it is certainly going to be for at least 10-30 seconds. You could slow-roll it and you will inevitably have 10 secs or more of negative g during that manoeuvre, if it is done properly.

 

I would check the oil pressure if you are going to fly inverted for a minute or more. When the engine cuts through fuel starvation, it will usually recover when positive g is re-applied. If you run the bearings dry, you risk a massive engine failure.

[Holbeach]

This is going to be the limiting factor for a Merlin engine -

 

"Inverted flying must be limited to 10 seconds because of loss of oil pressure and failure of scavenge pumps to operate in an inverted position".

 

This should happen -

Oil pressure should drop within a few seconds as scavenge pumps suck air.

Bearings are protected momentarily by an oil reservoir under the caps.

Irreversible engine damage will then start to occur.

Flight with oil pressure below 30 lb. is not permitted.

 

With our Spit, the oil pressure remains constant throughout the inverted period.

 

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[Holbeach]

Let's try a new approach.

 

Quote from a Merlin (P51) owner.

 

"The manual says not more than 10 sec of inverted flight to avoid oil starvation. It just seems to me than any time spent in neg g is not the best idea for a Merlin; if 11 sec will starve the engine for oil with possible damage, then it seems to me that even 5 sec is going to create an air bubble in the oil system and I don't want that in my Merlin that I paid for and that I am depending on for my safety and that of the plane"

 

Why doesn't the DCS Spitfire lose oil pressure, due to the scavenge pump sucking air, like it should?

 

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[Talisman_VR]

Let's try a new approach.

 

Quote from a Merlin (P51) owner.

 

"The manual says not more than 10 sec of inverted flight to avoid oil starvation. It just seems to me than any time spent in neg g is not the best idea for a Merlin; if 11 sec will starve the engine for oil with possible damage, then it seems to me that even 5 sec is going to create an air bubble in the oil system and I don't want that in my Merlin that I paid for and that I am depending on for my safety and that of the plane"

 

Why doesn't the DCS Spitfire lose oil pressure, due to the scavenge pump sucking air, like it should?

 

..

 

Alex Henshaw flight testing a MkV Spitfire at Castle Bromwich Birmingham 1941:

 

Happy landings,

[Holbeach]

Alex Henshaw flight testing a MkV Spitfire at Castle Bromwich Birmingham 1941:

 

Happy landings,

 

Thanks for the film.

 

Nobody doubts that the Spitfire can fly inverted, (it's cleared for 10 secs.) It's the time it can do it that's important.

I flew for 1 min 20 secs inverted at full power without damage.

The fact remains, that the oil pressure should drop to zero and it doesn't.

 

Without any feedback in these bug reports, we are non the wiser.

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[OnlyforDCS]

The DCS version of the Mk IX has an inverted fuel carburetor so the fuel flow continues at negative g. In earlier versions the engine cut within a second or two of negative g - hence the need to roll inverted to begin a sudden descent. The likely limits are going to be oil or fuel starvation, and the latter is going to depend on power settings - you will use any recuperator fuel faster at high settings.

 

 

This. The Spitfire IX fixed the defficiences of previous models, and can fly inverted for a significant amount of time. (Significantly higher than 10 seconds I believe, though that 1 minute is probably too much)

 

To the OP: What happens after that minute? Does the engine stall, cut out?

[blue_six]

To the OP: What happens after that minute? Does the engine stall, cut out?

Per the initial post by Holbeach, fuel starvation eventually stops the engine. In the video clip he's attached to his post, the low fuel pressure warning light comes on and the engine begins cutting out at approx. 1:25. Temps and pressures look to remain OK, and he reports no apparent engine damage as a consequence of this prolonged time in inverted flight.

[OnlyforDCS]

I guess I should have watched the video. Not sure about low oil pressure causing damage. Obviously the oil pumps would be pumping air, and the oil pressure would probably drop to zero indicated, but since the plane is flying inverted, most of the oil would flow right where it should be with the help of gravity, or am I wrong about this?

Edited April 27, 2017 by OnlyforDCS

[blue_six]

Obviously the oil pumps would be pumping air, and the oil pressure would probably drop to zero indicated, but since the plane is flying inverted, most of the oil would flow right where it should be with the help of gravity, or am I wrong about this?

For what it's worth, the Flight Operating Instructions and Pilot Training Manuals for the P-51D impose a limit of 10 seconds for inverted flight "because of loss of oil pressure and failure of the scavenge pumps to operate in an inverted position." The engines involved are the Packard Merlin V1650-3 and V-1650-7. Near as I can see, these are basically equivalent to the Merlin 61 and Merlin 66 respectively. I am inclined to support the OP's contention that it is unrealistic for our Spit to fly inverted for such prolonged durations, with no drop in oil pressure and no resulting engine damage.

 

 

blue six

[Holbeach]

A quick flight with the Spit shows that the oil pressure still remains constant when inverted, since I last checked it in 1.5.

 

 

This is incorrect. oil pressure should should drop to zero.

 

 

So is this a bug, or is this intended?

 

 

Without any feedback, it's not possible to know.

 

 

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[Holbeach]

It would be polite to have some sort of official feedback in this bug report, even if it's only bugger off.

 

 

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[NineLine]

I'm asking around, will get back to it when I hear something.

[Holbeach]

Thanks.

 

 

Some things to consider:-

 

 

Inverted flight at full power for 80secs will consume 3 gals petrol.

No loss of oil pressure when inverted, is also present on the P-51.

Loss of oil pressure will affect the CS prop.

Oil pressure reads 110 lb. in the spitfire. It should be 70 lb.

 

 

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[NineLine]

I tried the P-51 in sim, and it started starving for fuel after 28 seconds. This seems more correct, although as with the Spitfire, the oil pressure never changed. The Spitfire I was able to fly inverted for 3 mins before I started losing fuel pressure, and again, the oil pressure never changed.

 

So seems the Spit has two issues, and perhaps the P-51 has 1. I will report both, perhaps there is something about the oil system I dont understand, but the P-51 manual seems to state you should lose oil pressure.

 

What is odd to me is that the Mustang manual doesnt really mention any issues with flying inverted and fueling issues. Unless I am missing it. Not saying anything other than its weird its not mentioned that it would be starved for fuel after 30 seconds of flight ALTHOUGH, if you are restricted to 10 seconds due to the oil system, I guess the fuel system issues is moot...

 

Sorry for the thinking out loud in this post lol.

[Holbeach]

A few more points:-

 

 

 

The P-51 manual states that fuel is supplied in all flying conditions.

 

 

The plot thickens.

 

 

Incidentally, if you continue the glide in the Spit, inverted at about 2000 rpm, after the fuel has run out, the oil pressure will increase gradually to max, off the scale.

 

 

RR state that, the engine will run without oil pressure for some time, relying on residual oil in the bearing caps, before failure.

 

 

This will have been tested many times after battle damage, with pilots squeezing a few more miles towards home.

 

 

For the Mustang, oil pressure below 50 lb is not permitted and Mk9 30 lb. so maybe the fuel starvation problem, is assumed never to be reached.

 

 

 

The only thing that is certain. Oil pressure will drop in negative G.

 

 

 

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Edited August 12, 2018 by Holbeach

[NineLine]

Thanks, good points. I know Mr Grey told me the engine will quit flying inverted in the Spitfire for as long as being reported here, the fact that I went 3 mins seems super extreme. I would expect more of the same performance as the Mustang.

[DeepDrummer]

The oiling system is "Dry Sump" meaning there is no or little oil in the oil pan.

The scavenge pumps are at the front of this shallow oil pan.

There is also an accumulator which will continue to supply oil to the engine while inverted until the accumulator runs out. Likely about 10 seconds. The 109 is the same.

That is what needs to be determined.

How fast does the oil flow back out of the accumulator? How much oil does it hold?

Any engine will run without oil for a short time.

Is there a need to do that for more than 10 seconds?

The engine may not die in less than a minute but huge damage is being done once the accumulator runs out. This is a matter of some seconds.

[muehlema]

The Spitfire could not fly inverted very long as it would run out of fuel. The issue is from the carburetor float bowl. And no, the Bf109 was not having this issue as the germans added a direct fuel injection. This is Why the in BoB, the Bf109 was superior, just the german pilots were not up to speed.

 

https://en.wikipedia.org/wiki/Miss_Shilling%27s_orifice

[muehlema]

Btw, the Bf109 with the Mercedes-Benz engine has no dry sump ;)

http://kurfurst.org/Engine/DB60x/files/Flight_16April1942_DB601N_Engine.pdf

 

But bare in mind today, there are a lot of Buchon flying around as Bf109, which isn't really the same engine, neither shape or form.