Excellent IvanK,

now perhaps we can all stop guessing.

Lol they will stop guessing Klem, but they won't agree :p

Exactly. There is no need to guess. Pilots who fly float carburetor equipped aircraft have been telling your community from the beginning the effect is instantaneous.

The physics and science of a float carburetor fuel metering system supports their experience.

There is a reason why allied pilots complained about it and why German pilots equipped with direct injection fuel metered engines could bunt to escape. It speaks volumes for the realism of your game that players complain as well.

The effect is instantaneous upon the application of negative accelerations. The instrumentation used in the report backs that up very nicely within the accuracy of a mechanical dial gauge accelerometer.

The problem is when people try to interpret things they don't understand and push it as fact.

You can see that in many of the "home-made" graphs pushed around the flight sim community where the author of the graph did not understand such things as TAS, EAS, CAS, or IAS or density altitude effects.

Yep, its probably almost instantaneous when it hits 0.1G. A pilot that currently fies a float-carburreted MkI Hurricane has told us that he estimates a cutout at 0.3G after a second or two (some people might call that 'instantaneous'), possibly instantaneous at negative G.

It would be a brave or arrogant person that was prepared to argue with the Royal Aircraft Establishmnent (RAE) who had the aircraft/engines to make tests with ( we don't ) and the skills and instrumentation to determine the problem. Beatrice Shilling was working for the RAE when she came up with her 'orifice'.

I just wonder how much factual documentary evidence will be needed before people stop thinking the early Merlins farted every time the pilot hiccupped.

No probably to it, it is instantaneous. A Merlin engine sucks ~40-130 gallons per hour....there is not enough gas in the float bowl to fire the cylinders through one complete cycle.

Read the document again. Cut out occurs when it hits .9G on a mechanical dial gauge accelerometer. An acelerometer reads 1G at wings level or on the ground.

It only takes .1G of negative acceleration as measured on a mechanical dial gauge accelerometer to induce cut out.


That is 1/10th of a G...

By all means read that small amount of accelerations accurately on a dial gauge please.....

http://www.aircraftspruce.com/menus/...rs_falcon.html

The correct answer is "when the needle moves, cut out occurs...." That is what you see in the air with a float carburetor.

Crump, read again. It says at 0.9g negative acceleration and 0.1g instrument reading. Which means it will cut out fully when the measured acceleration reaches 0.1g (which may be different from the actual acceleration level experienced by plane and pilot).

The question is will the cut out appear in an on-off manner as we have now or will it be more a stepwise cut out as we had initially. My belief is that it will be rather a stepwise. With less g than level flight but with acceleration superiour to 0.1g the hydrostatic pressure in the lines and in the tank bottom will be less and my guess is that the engine will cough a little because of this.

Stormcrow is correct we have been down this very argument before. The cut commences at 0.1G.

A mechanical G meter/accelerometer used in Aviation uses 1G as its static reference. Sitting in your chair holding a G meter it would read 1G.

Here is a typical G meter as fitted in a YAK52 sitting on the ground the needle showing 1G.

http://img190.imageshack.us/img190/1...teryak521g.jpg

In cruising flight the aircraft is at 1G as the pilot progressively pushes forward the G decreases towards 0 G. The document states that a reduction of 0.9G. So the G meter would be reading 0.1G that's the needle just above the 0G mark as indicated in the graphic. As the document clearly states ..."i.e. at an accelerometer reading of less than 0.1g" ... or 9/10ths of G worth of Push ! or mathematically 1.0 - 0.9 = 0.1

I would though be a bit carefull with the number 0.1g. It may have read like that in the planes that were used to test this (nowhere is it mentioned to be Spitfires or Hurricanes so it could be any plane that had (which?) Merlin). It does not mean that at the location of the carburator it was 0.1g. And also the acceleration at the carburator in plane x will be different to the acceleration at the carburator in plane y even if the cockpit instruments reads the same acceleration for both planes. This is due to different location of carburator with respect to centre of gravity of the plane.

Yep aware of that. The same thing also applies inside the FM as to where the coders are taking their "G" from. The presumption is its at the c of G.... which is of course in a differrent location to the carbys themselves.

Unfortunately the RAE document refers to instrumented aircraft but doesn't state exactly the set up.

My guess is that a Russian 0.1g is the same as a British 0.1g (same unit and there is only one definition of the g-unit which is 9.81 m/s²).

On the gauge: The most straight forward thing would be that the gauge shows the acceleration at the CoG.

Yep every G meter I have used for the last 30 years uses 1G as a datum.

I have the entire document (lots of maths), there are is no list in the document as to the equipment being used. The term "G" is standard aviation terminology though. The snippet below comes from a comment in the covering letter to the document discussing testing methods used versus the nature of the original problem of G cut out in unmodified aeroplanes. Again the G used is unambiguous to me. The phenomenon occurring at "0.1 to 0g"

http://img405.imageshack.us/img405/3126/cvrletter.jpg

I will look through the second RAE doc that deals with the devices being tested to overcome the cutout (not very well either according to that document) to see if their are any equipment details in there.

Edit. The second document equipment list makes no mention of the Type of G meter used either. It simply lists the specific fuel system in each of the aircraft tested.

Of course you're right but don't forget that in flight the Pilot is the reference : he fly likes he feels and act in concordance.

So if it might be interesting for the engineer to get the true acceleration on the carb float, as a flight safety rule, it seems logical that they hve measured what a pilot would feel.

Yes but common car accelerometers are primarily used to determine lateral and longitudinal accelerations.
The Bob weight or whatever device is used sits at rest with 1G vertical but )g lateral and Longitudinal. Typically
these are used to determine braking effectiveness

http://img685.imageshack.us/img685/7007/cardecel.jpg

Motor transport investigators use both including vertical accelerations referenced to 1G.

:rolleyes:
http://forum.1cpublishing.eu/showpos...8&postcount=33

In your document it is said "were reported" and "feb 41"

If the date is of paramount importance for the time frame the fact that they are discussing "reported" fact and not "instrumented" let me think that the G-cut out were measured by a direct reading of a G meter or reading of a graph after the flight. The graphometer would hve been most presumably fixed inside the rear fuselage or otherwise just behind the pilot in place of the radio what makes it doubtful. As the rear fuselage option it less precise than a direct reading by the pilot (aft position) we can speculate that this were read or filmed (a Technic used by the Germans as I know).

Anyway the law of distribution of acceleration states that the Accel a point A (aA) equate Accel at a point b + ABxf(dAlpha/dt²) + AB f(d(Aplha²)dt)

where AB is the distance btw point A and B and alpha is the angle of rotation of the line AB in the plane of travel. D/dt is the time derivation and d/dt² is twice the time of derivation (d/dt(d/dt))

So let's say that
A is the carb float
B is the pilot

when the plane is traveling at cruise speed (300kph+) the radius of turn due to a 1 G push over is huge. Hence Alpha is really small. We can then neglate the third term in Alpha²

Regarding the second term, it translate the influence of the inertia gained wth the rotating mvmt around the CG during the push over. As the mass of the Carb float itself is supposedly far less than that of the entire plane ;) well we can say that if yes this term play it's part when studying the float, it won't have any influence in the value of the G read.

?
It is better if you do not want to teach me anything, especially if you do not understand what is the difference between the aircraft and automobiles accelerometer (vertical (1G) and horizontal (0G) installation). Should not be pompously, especially when talking about stupid things ...

For the document you are right, but unless I am wrong we discuss the carburator and its behaviour here so I think the acceleration at carburator location is interesting. That is why I said the cockpit reading cannot be transposed 1:1 to the acceleration experienced by the carburator.

My thesis is that the acceleration experienced by the carburator can be slightly different for different plane types even if pilot acceleration is equal due to distance differences between plane cog and carburator. I cannot tell however how big this difference could be (basically I do not want to make the calculation :-) ).

I understand the point you are making but I don't think the carburettor location is important. Well, except perhaps in my first point below.

It is unlikely that the accelerometer would be placed at the carburettor location unless they specifically wanted to look only at that issue. The accelerometer would have been used for other tests too. However if it were at the carburettor then, having accepted at what G level the cutout occurs, MG would have to decide how to simulate that in the FM design or calculate a reasonable estimate for their accelerometer wherever it may be located. Just following on from that, a 0.1G level at the carburrettor would be lower than in the cockpit or at the CoG due to the 'moment arm' point you are making so a cockpit or CoG G level could be say 0.15, 0.2, 0.3 -I'm not going to try to calculate it :)

More realistically, the Accelerometer would be at the pilot position or CoG. Now, I don't know where it is placed by convention but it is highly probable that the same convention was used back then as now and I would guess its the CoG. These were not the 'kite and string' guys of 1912, they were highly qualified experts who, among other things, had won the Schneider trophy and were no doubt sharing knowledge and conventions across the aviation world until a certain Mr Hitler turned nasty.

So, if we can accept say the CoG as the convention (I'm sure an aviation design expert will put me right if not) I will argue that the carburettor location does not matter because:-

It is the cutout itself that is being recorded and it is being recorded using the available instrument, the accelerometer at its conventional location. When the accelerometer is reading 0.1G the carburrettor may be at 0g or 0.05G or -0.5G but that in itself does not matter, the cutout is recorded when it happens and noted using the available accelerometer reference and that reference can be repated in the next aircraft etc.

There is one point to note and that does come back to the 'moment arm' issue. The moment arm (distance from carburettor to accelerometer) may be different in a Spitfire and a Hurricane so there could be minor differences in the cutout reading in the different aircraft but I think that would be quite small.

I understand what you want to say and I agree to it when it boils down to simulate ingame the thing.

I would like to know now if the cut out was an either on or off event with nothing in between.

Here is the drawing:
http://forum.1cpublishing.eu/attachm...1&d=1302878491

Is this pre- or post-modification?

As far as I understand the floater shall restrain fuel from flowing into to chamber when negative g's occur. That's above all in terms of function I can see.

Depending on the damping due to hinge friction my guess is that initially the floater will go up when one pushes the stick forward due to inertia that forces all objects to remain in the state they are until the forces get the better of them. So when it shortly gets up it will reduce the pressure loss at the reservoir entry by opening it. Hence more fuel will flow into the reservoir for a short time.

That design is post-production and covered in Viper2000's excellent post here:
http://forum.1cpublishing.eu/showpos...0&postcount=94
Especially read the pasted in section headed 'Appendix VI'

What is the function of the needle like thing? It doesn't seem to do anything. Also without the floater valve (K) what did the floater do?

Oops, I did read it wrong.

Does the document state the onset rate? Without that the information is interesting but useless.

Huge difference between .9 G at an onset rate of 25G a hour and 25G a second....

Yes cut out is a cut out.

The onset is depending on the Onset Rate...

At typical ROR acceleration onset rate of 6G/sec the Merlin as tested in the report cuts out in ~1/6 of a second.

In the cockpit, that would be instantaneous.

You know, all we are really concerned about is that:-

1. in a 'combat bunt' the engine cuts = LW happy
2. in a 'descent' that doesn't hit an extremely low or negative G the engine doesn't cut and we'd like it to be as close to reality as possible, which seems to be somewhere between 0.3G and 0.1G depending on who you believe = Allies happy because it isn't a pain in the a$$ to fly - because it wasn't. It was a dream to fly (see many Spitfire veteran pilot's interviews).

I'm not looking for a way around the 'combat bunt' problem. That was a reality and one I actually want to have to live with. As it is now the 'combat bunt' problem is there. I just think the normal 'descent' is porked because the cutout seems too sensitive. I have done a quick and dirty in FSX and by comparison it seems to cut in the region of 0.7G.

Now, if Luthier will just tell us what parameters he is using for the Merlin III/XII cutout and if they are close to the figures given by the RAE and a current MkI Hurricane pilot I will be happy and accept that CoD's representation is how it was. Even if the cutout parameters are too sensitive and are adjusted so the cutout isn't so sensitive, the LW guys still lose nothing in the combat sense. A severe bunt will still cut the engine.

Don't forget that in flight nobody likes to pull some neg G. It's more natural to roll and pull than simply push. It does not impact the way you can enjoy flying a spitfire

The G cut out being well documented by IvanK I don't see how we can disagree. With a bit of practice it comes naturally to avoid G in a fight (but obviously that nasty push over done by 109 still is difficult to match .. but wait that sounds historic ;) )

@Crumps : A G is a G what ever is the rate of sampling. or is there something that i didn't "Catch" ;)

G meters in cars are often used to test crash conditions and are way out of a G meter you can find in a plane (electric/mechanical device). I know that's not what Cheese is talking abt but I thought it had to be said.

"Does the document state the onset rate? Without that the information is interesting but useless.
Huge difference between .9 G at an onset rate of 25G a hour and 25G a second.... "

Neither of the two RAE documents have any data on G onset rates even in the Tabular results presented.

Well, unless I misunderstand my long-ago mechanics/physics classes, G is acceleration which is all about change of state versus time so 0.1G is 0.1G however fast you get there. So if a cutout occurs at 0.1G, that is where it cuts out. The 'onset' seems to me to be about how quickly you get to 0.1G and the only two things I can think of that 'onset' would affect is the perception of how 'sensitive' the cutout is - "blimey, if I really shove the stick it cuts out a lot quicker" - but still at the same G level and I suppose a slow onset might enable the carburettor to stay with it a little longer but are we splitting hairs?

Yes the onset rate is extremely important. Very rarely do you experience gradual onset rates in an airplane depending on the definition. That is why I asked IvanK about the onset rate information in the report.

Even wind gust will accelerate an airplane at Rapid Onset Rates:

http://law.justia.com/cfr/title14/14...1.3.164.7.html

That being said, GOR has a very broad definition and is generally defined in any study. It is the onset rate that tells us how much time it takes to reach a specified load factor.

GOR's definitions that I have seen range from .1G/sec to 4G/sec. That would range from ~ 9 seconds to .225 seconds before cut out.

No klem, the aceleration in this case is a fixed point but does not define the rate at which we reach that point. I think you should understand that airplanes arrive at that small a load factor very very quickly under the vast majority of flight conditions. Even transitioning from a climb to level flight will result in reaching that .9 load factor in less than a second unless a pilot makes a careful effort.

I would take you flying and you could watch the G-meter in my aircraft. When I reset it at the end of flight, it is generally ranging from ~(-)1.5G to (+)2.5 just in normal operations on a cross country trip.

Cut out will occur in a fraction of a second and is instantaneous from the pilots point of view.

I am sure you can see the distinct tactical disadvantage of a fighter trying to dogfight with a float carburetor fuel metering system.

Ok. They were probably just looking for the threshold on the test carburetor. Not all carbs will meet that same threshold, some will be better and others worse but it is a very good data point.

Combine it with typical onset rates and the tactical disadvantage becomes clearer.

Does the game model the longitudinal instability of the Spitfire, pre-stall, and post stall behaviors?

Do you guys have copy of the actual Spitfire Mk I POH?

I hve never thought abt that but if there is diff onset for G-meters it might be linked with what you want to measure.

For ex if wind gust is what you are seeking then the onset will be very small (less period -> high frequency). On the contrary if you are trying to evaluate pilot action on the plane, what you absolutely want not is to see some histerisys on your nice curves from the interferences of the wind gusts.

That said, I don't think it's a mater of discussion here. We have simply to assume that RR test-engineers knew what they were talking abt. And as they were certainly among the best in the world at the time well.... :rolleyes:


SO 0.9G wld be 0.9G corrected of any parasite accel ... If you add the fact that there is not atmospheric model in CoD until now (?) then ... :rolleyes:

By the way yes it was a disadvantage but pls remind that ALL the Fighters in the world at that time might HAVE HAD THE SAME PROB except those that had Fuel Injection in 1940. Let me guess they were German :D

If you run for the war earlier that's for sure you'd get some (unfair ?) advantages.

Si vs pacem etc... etc... :(

My guess is that they were some kind of piezoelectric (high frequency of the suspension system)). Take a look at Wiki to see how it works.

10k$ is a lot of money for a single one !

It is actually fortunate that GOR is so rare in flight. Human threshold for GLOC is much lower for GOR than ROR.

"Do you guys have copy of the actual Spitfire Mk I POH? "

Yes

Depending on required precision and response time, accelerometer implementations can vary. In some case you can get away even with simple weight+spring.

Ok, good.

Onset rate doesn't make much if any practical difference to the carburettor's behaviour because the determining factors are the geometry of the float chamber, the position of the float and the fuel flow rates into and out of the chamber, none of which are going to be a strong function of dg/dt.

As soon as the g level falls below about +0.1 indicated, the float stops floating properly, and the carburettor therefore stops metering. Exactly what reduced positive g will cause misbehaviour will depend upon the friction in the system and any slosh in the float chamber, leading to slight variation on a case by case basis; but this sort of detail is way beyond the scope of a simulation of this nature.

Much earlier in this thread I calculated the approximate subsequent chain of events for both the reduced positive and negative g cases.

In both cases, I would expect a lag between departure from 1 g flight and cut behaviour due to the volume of the float chamber, engine demand, and fuel pump delivery rate.

(For this reason, normal turbulence would seem quite unlikely to produce cut behaviour.)

Only if you want to the answer to the question "WHEN does cut out occur?"

Yes, it certainly will produce a cut out if the acceleration reaches the threshold.

Once again, in an engine consuming 100 gallons per hour, the tiny bit in the float bowl will not last a cycle....

Even in a lycoming consuming 9 gallons per hour, a cut out and rpm change can be heard in turbulence or any negative acceleration.

Where do think kids get the airplane engine noises, "WAAAA waaaaaaaa WWWAAAAAAA" when playing from?? :)

"Meeeep Mep MeeepMeeep " here in the country of thundering Renault engines (excluding F1 obviously) :rolleyes:

Regarding the cut out and turbulences : more consumption -> more flow -> higher capacity fuel pumps -> more fuel momentum -> less probability of a cutout from turbulences only

It seems as if some of us wld hve to compute the exact flow rates of the eng pump to end this debate

But definitively Crumpp is right for the Lynco.

Ok some Maths for the Boffins. Knock yourselves out guys :) Here are the Maths used in the design of the first attempt at the Negative G solution. The Source is the First document I referred to in previous posts. Note Its Merlin XX data.

http://img59.imageshack.us/img59/5658/vegcutfile.jpg

http://img546.imageshack.us/img546/5924/pg1t.jpg

http://img717.imageshack.us/img717/5898/pg2kb.jpg

http://img51.imageshack.us/img51/3451/pg3x.jpg

Thx IvanK for providing such a valuable source.

I understand there that CoD devs has alrdy really worked the point.

Considering that if the 0.2g was the design limit to sustain for the CutOut on the converted engine, the CutOut began much earlier on standard Merlin's (although obviously bellow 1G).

Doing a quick calculation (to be refined) I have a 0.017G as the min value for the cutout to begin in a non-modified eng with an assumed similar geometry (you need then to add the time that the 2nd carb chamber emptied it self of its remaining fuel - Vip as done that before - negligeable).

So am fully converting myself to Crumpp idea now. As a culprit of false assumption I condemn myself to run around my neighborhood both arms raised like wings and making loudly sputtering "WAAAA waaaaaaaa WWWAAAAAAA" engine noise.

lol!!

I don't think the devs have re-worked the G cutout in his patch, it 'feels' the same to me but if it has been reworked then that's that.

Not sure I follow what you mean regarding the 0.2G design threshold and the 0.017G cutout on unmodified engines but if the cutout on early engines was 0.1G it would make sense to have a design threshold (valve operation to prevent cutout) at a higher level so that it is already active before the 0.1G level is reached.

Sry the 0.017G theoretical value is the actual neg G you wld hve to push to experience a cutout on a non-modified Merlin. I mean that actual accel value wld be (1-0.017)G.

The doc is related to a redesign of the carb to allow at near zero G the engine to function properly. The 0G value is approximated as 0.2G in this computation as the way they ran the calculation, 0G was not permitted (see on top of pg 2 the ratio for the plumber calculation (counter-weight) - if G wld hve been 0 the ratio can't be calculated that way)

A new design had to be introduced latter for full neg G aerobatic which was not done on Uk produced Merlin as I can understand reading the extract of "A Merlin History" that was provided to us earlier.

Note also that the redesign involve an anti-vibration induced cutout device (a spring) that lead me to think that the Merlin encountered some vibration problem once fitted in fighter planes. My assumption goes for the Spitfire but only on the grounds of assumptions made on Sidney Cam's robust design.

This is probably a little bit irrelevant as it's a MkV, but it clearly shows what happens when the negative G cut outs occur.

If you watch and listen closley you can hear the engine misfire and see the smoke (especially when he's inverted). It happens quite a few times. Just thought it was interesting.

Alex Henshaw flight testing a MkV at Castle Bromwich 1941. (ignore the terrible acting bits!)

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

It is irrelevant at showing the effects of a float type carburetor. However it does clearly show that even "Miss Schillings" orifice and the SU pressure carburetor are still subject to effects from negative G. Only direct injection is immune.

Its not a MkV (no cannons) see wing detail at 0:21. Almost certainly a MkI.

One of the topics I discussed with Group Captain Peter Gilpin (who flew Spits for the entire war) was the introduction of the 'Ms Schillings orifice' and to what extent it solved the problem of neg G cutout. He told me that he could nose down and chase/attack without any problems.

See:

http://www.spitfireperformance.com/x4922.html

Mk Va's had rifle caliber machinegun armament just like the Mk I's.

Which has no bearing on the fact:

Does anyone else notice that it seems when you throw in the flaps on the Spit that you can put more Negative G load into it before the engine starts cutting out????

True. Sorry.

Many early MkV had MkI wings (and fuselages :rolleyes:)

Neg G is not near zero G. From the excellent source posted by IvanK (AAAH if all the doc posted on internet had the same trusty quality) , we can see that 0.2G was the design limit.

Neg G IMOHO would hve needed a MAJOR redesign of both the carburetor and the fuel supply line. The pumps are far from delivering a sufficient pressure differential). This would be interesting to investigate (both on historic doc and on Warbirds flying nowadays - ie are the Spitfire flying today fitted with US-made pumps ?)

I'm not sure of what was fitted to the aeroplane in the video but what I immediately noticed is that on an inverted flypast the engine spluttered, but not terribly, and maintained power. In game, even with minor moments of low/negative G the prop will grind to halt. So the question is really - what is fitted to this aeroplane?

I also notice the how easy it is to drive the Spit on the ground, never had that in game from any aeroplane. At Duxford the P51's waltz about at taxi but in 1946 they were far harder to move.

It was a positive G maneuver most likely and certainly did not have a float carboretor. AFAIK, Spitfires were not outfitted for inverted flight.

Float type carburetor's are not capable of inverted flight as fitted to the Merlin.

http://www.airspacemag.com/how-things-work/upside.html

The relative wind will drive the propeller and it will continue to spin. A CSP will act as huge airbrake immediately slowing the airplane down at a rapid pace until there is not enough wind to drive the propeller.

A fixed pitch propeller will slow the plane down at a much slower pace.

Something not completely related, but interesting non the less. This is a quote from sir Stanley Hooker, no doubt someone from here will be along to say he's wrong, and doesn't know what he's talking about, but hey:rolleyes:

Quoted from 'The Spitfire Story', by Alfred Price.

I think that in many of the maneuvers the throttle would have been cut back to reduce prop torque and aid control.

Yes. We shld not forget here that float carb was the norm at the time and pilots were used to fly that way.

Sir Stanley Hooker's quote in context is referring to a single point injection. It has nothing to do with direct injection.

Been away from the game for a little while.

Re: this issue, can spitfires still do a negative-G "outside" loop like they could in previous versions?

By this I mean push the stick forward and hold it there until the aircraft does a downward loop and comes back to normal flight? Because that used to be possible, and spitfire pilots were complaining even then about the negative-G "cutout" :rolleyes:

For sure the Hurri can't do that. ;)

Did you watch the video? I was referring to the video.

Indeed. Positive G maneuver? No way ...

That's what I thought. And it had power applied too otherwise there's no way it could retain height.

All I would like to know is if this was an injected engine or Ms Schillings Orifice

Looking at the video again the engine was not supplying power when inverted, it was windmilling with the occasional detonation. When he was inverted he was almost certainly bleeding airspeed as he went until he rolled right way up and the engine picked up - quite quickly too. Pretty sure its a carburettor not an injector.

The Mk.Va came with a float type carburettor. The Tilly orifice would only have an effect when flying at 12lb boost and 3000 rpm, if you did not do that, it was pretty much meaningless. If you did, however, the engine would continue to work under negative g just fine.

To me it sounds as if combustions stops during the inverted flight and the engine spools back up thereafter, which indicates the behaviour to be typical for a Merlin with a standard float type carburettor.

On the other hand the engine spools up quite nicely (though on a very rich mixture) immediately after returning to positive g's, so maybe a fuel flow restrictor (i.e. Tilly orifice) was in place. The Merlin handbook states up to 10 seconds of recovery after a neg g situation, which clearly isn't there.

The supercharger compresses the charge adiabatically.

In the isentropic case, (T2/T1) = (P2/P1)^((gamma-1)/gamma)

Isentropic Supercharger work = W*Cp*(T2-T1)

Actual Supercharger work = (Isentropic work)/(Isentropic Efficiency)

Reducing the temperature upstream of the supercharger therefore reduces the supercharger work at fixed supercharger efficiency, and therefore increases the overall efficiency of the machine.

Furthermore, because the supercharger temperature ratio is > 1, it follows that the the temperature reduction in the induction manifold will be correspondingly greater than that due to the evaporation of the fuel alone (though in this case the 25 K figure was measured in the induction manifold, the point is that you wouldn't actually get a 25 K temperature drop from direct fuel injection at TDC).

Which Merlin handbook are you referring to? Don't you mean Pilot's Notes General? Standard procedure for inverted flying was close the throttle to allow a smooth recovery.

Not a plane handbook / pilot notes, but a Merlin document, which I can't seem to find at the moment. Sorry.

Good point about closing the throttle, slipped my mind and it would indeed limit the problem, but the fuel pump would still flood the engine to some extend.

The throttle also had to be closed when negativ g cut out occured. IIRC Reason is that when the throttle remains opened and the fuel flow is restored the engine might overrev as power is regain so quickly that the CSP can't react quick enough.

Engine starves briefly at first and then gets flooded with fuel, because things get reversed: the more fuel you have in float chamber, the more fuel you get into it. Tilly orifice simply restricted fuel flow to amount engine needs at max power setting, so even when things are reversed, float chamber gets no more fuel than engine can burn (at max power setting). Lower the fuel usage (cut the throttle or lower the RPM), and Tilly orifice won't prevent the flooding anymore. Without orifice things are the same, except engine gets flooded even at max power setting.

Running engine at max RPM and open throttle softens the flooding by some extent, but recovering with same settings can indeed result in overrev. It is probably better to cut the throttle just before recovery and not the moment cut out occurs - this seems more optimal.

Rolling upside down is not a negative G maneuver, it is positive G. I do it sometimes the time in my plane.

Yes but...

if you cut throttle there's less air flow to suck the fuel out of the jet nozzle, so the engine does not get flooded as much. It's true what he said, it was recommended to cut throttle during neg g manoeuvres, in order to get the engine "get going earlier".

Throttle also had to be reduced and was not to be applied quickly due to low oil pressure in (longer) neg g manoeuvres.

http://www.austria-lustenau.info/for...s/facepalm.gif

Watch the video.

Well... they call it cold air intake with most of them being not so cold :rolleyes:

It works also with a turbocharger ;)

You didn't watch the video. It's not a roll, it's an inverted flypast. I don't see the prop windmill but regardless if I did this move in game it would most certainly cut out completely.

It is definately NOT a float carburetor then.

Its more a case of listening to the engine. It cuts to occasional firing.

ROFL that dog sure was at zero G's lol

Pls guys makes sure you are watching the video with sound tuned to max. There is no doubt that the engine is starving even if the pilot (excellent - hvn't read this until now) did throttle down.

A good surprise also is how the pilot over-quick the rudder when half rolling back to a normal attitude to add some positive G in the roll. I do that on CoD and it works perfectly. A real positive sign of how good this sim is !

I did watch the video. It is a cut scene from a movie that has nothing to do with reality.


I just checked the Mk I Operating Notes. Flying inverted is normal provided the engine is set up not to foul the aircraft with glycol and oil. It is done at high speed with the throttle closed and the pilot is instructed not to reopen the throttle until oil pressure is restored.

Why? As far as I know, the aircraft were original, and there was no CG in 1969...

So what?

Many original aircraft have been used in movies. These are real aircraft AND plenty of cut scenes with no CG either....

http://www.youtube.com/watch?v=l8wmyCcbnX0&NR=1

Crumpp, are you dure you're talking about the same movie? We've been discussing the film of Alex Henshaw flying an early MkVa:
http://forum.1cpublishing.eu/showpos...&postcount=152

It's Alex Henshaw, one of the chief Spitfire test pilots, flying a MkV in early 1941, at the Spitfire factory in Castle Bromwich. It's real.
It was filmed for the Americans to show how 'well' the British were getting on with the war. That's why the American guy is in it.

The flying is real, the Mk V has the 'orifice' fitted. If you listen carefully you'll notice that the engine does over-rev when the power comes back on.

Not sure about that. The RAE restrictor only works at full throttle.

To me it sounds like the pilot closes the throttle during the inverted flying and quickly opens it after it (which causes a slight overrev). There is no RAE restrictor needed in this conditions.

I did watch the video. It is a cut scene from a movie that has nothing to do with reality.

Was it a CGI flypast then?

You guys know there was lots of Hollywood trickery going on before computers were invented, right?

Doesn't have to be CG to be inaccurate.

There is nothing more sinister going on here than crummps partisanship. For some reason there's a selection of people with an axe to grind against the Spitfire and Crummp falls particularly into this particular sorry species.

The fact is if he had done ANY research on ANY of the readily available tomes of the Spitfire (the volumes by Alex Henshaw and Jeffrey Quill for one, both Spitfire pilots and people with a far more qualifed opinion on practical aerodynamics than Crummp I am sure) he will know that the various quotes he has selected are, as typical, cherry picked examples of well known and quickly corrected faults with the Spitfire.

1) Spitfire Stability in Pitch: The Spitfire was certainly not UNSTABLE in pitch but the stablity it did have was MARGINAL. Big difference. as long as the CofG was kept within limits then the a/c was perfectly safe. The issues that affected only Mk.V aircraft of vicious spin characteristics and some strcutural failures were as a result of Squadron a/c being poorly loaded and supermarine directives not being followed at squadron level regarding the loading of new equipment and pushing the CofG out of limits. Bob weights and eventually a redesigned elevator mass balance actually cured this. See Quills book.

2) I suggest he actually reads Henshaws description of his fairly standard aerobatic routine that he was regularly called on to display and is accurately described in his book, Sigh for a Merlin:

Though according to Crummp that couldn't possibly have happened could it?

Agenda boi much!?!?!

I, at least, see your agenda, Fenrir.

Crummp says that the spits/hurris are not outfitted for inverted flight!

That is 100% correct!

That doesn't say that said aircraft cannot endure inverted flight for a very limited time.

To be outfitted for inverted (neg g) flight the engine must get metered fuel AND oil-pressure during the inversion.

Afaik all piston drive AC during that time only could endure neg-g, some better than the others.

Many people do not know, but the DB 605 operating instructions also write, that prohibited the long inverted flight, because of the lubrication system.

I always was a bit astonished with the infinite inverted flight capabilities in old IL2...

Motor und Triebwerksanlage des Flugzeuges sind nicht zur Durchführung von Rückenflügen geeignet. Hingegen ist Motor und Triebwerksanlage geeignet für Kunstflug in jeder anderen Form, wo nur ganz kurzzeitige Rückenlagen in Verbindung mit anderen Flugfiguren vorkommen.

;)

No, he says it is a cut scene from a movie that has nothing to do with reality. That's not only outright wrong, it's bordering insanity.

I have it in Hungarian, but the same thing there written:
"Műrepülés: Ezzel a motortípussal rövid ideig bármilyen műrepülést végezhetünk, háton repülést is. Kivétel a kizárólag háton repülés, amelyre a motor kenőberendezése nem alkalmas."

:grin:

Kunstflug: Mit dem Motor können jede Art Kunstflugfiguren auch kurzzeitig in Rückenlage geflogen werden. Ausgenommen sind reine Rückenflüge, für die das Schmiersystem des Motors nicht eingerichtet ist.

:)

:rolleyes:

;)

Fair nuff.

Is that all??