The A2A Simulations Community

Hi A2A

Are you able to tell me what parameters you used for the Merlin III negative cutout, e.g. the actual negative or reduced positive G value, onset delay, recovery delay etc?

Can you also tell me what your sources were and if Dudley or anyone else has commented on whether it is realistic as currently modelled?

The reason I ask is it seems quite benign although that may well be correct.

Thanks

klem

Killratio is probably the best suited to answer this question, but I'll try anyways. The early Spitfires had a gravity fed carburetor. Negative G-forces starve the carb because the fuel is essentially "held back" in the line. Being upside down can cause the issue as well without positive g-force. This was fixed later by a lass who made a fitting which removed this problem. This was well documented and one of the advantages that the Germans used during the Battle of Britain and against these early Spitfires by quickly nosing over.

As for the data in regards to how this onsets, there are no exact parameters per say. Accu-Sim is working outside of the simulator and thus it measures the various factors like fuel flow, consumption, etc organically. It is all situational as to how it will react.

Interestingly enough, many of these planes also have gravity fed oil. Many of these planes if you hold them upside down for extended periods of time, it will cause the fuel pressure to drop as the oil sits at the top of the tank unable to feed properly. Naturally, that's a bad thing as you need your oil to keep your engine running smoothly. This I believe is also simulated.

That is my layperson's answer. I hope that helps bud.

[Edit, if you were not talking about the Wings of Power III Spitfire, I apologize]

_________________

Cody has just about covered the technical side but I'll add a couple of comments.

The cut-out IS fairly benign unless you hold negative G. All it does is interupt the flow of fuel slightly. If you stay under negative G then there are problems but only until the fuel starts to flow again as positive G comes back on.

The BIG problem with the cutout and the one that caused all the comment during the BoB and after was that the loss of power did not have to be great or long lasting, to see a high powered
Bf 109 pull quickly away in a dive. The Spitfire's acceleration was not huge to start with (at combat speeds) and to give up that power in a tail chase, even for a second, was decisive.

To get some idea of the effect, have a look at the openning scene for the Battle of Britain movie (and before anyone starts on about using movies as "reference"...... I'm talking actual physical effects) where the Hurricane does a slow roll. You can hear and see the effects of the negative cut out and a bit of black smoke. That is about as dramatic as it gets.

I know from flying aeros in gravity oil system aircraft that, as Cody said, the oil starvation is a big problem for engine longevity. It t6akes a little longer to happen (and to correct itself) than the carby.

Hope that helps.

Darryl

_________________

...Some say he never blinks, and that he roams around the woods at night foraging for Merlin parts...

Thanks for the replies guys.

It isn't a really big concern for me as I fly the Accusim Spitfires just for the pleasure of flying them, combat-type maneouvres aren't relevant, it was more out of curiosity. The Accusim Spits are in many ways looked on as a kind of benchmark by some people and there are some strong discussions 'in another place' about the G cutout levels in combat. The RAE test results in 1940 (which gave 0.1G as the cutout point) and the claimed short delays in onset would appear to make the Merlin III and Merlin XII Spitfires quite sensitive to reduced G levels, so I was just surprised at the 'high' level of negative G and onset delay before cutout in the Accusim Spitfire but as I say its not really a concern for me in this case.

Thanks again,

klem

As far as I know, that makes perfect sense and is simulated. Zero Gs is the absence of gravity, and .1 indicates as such. You are indeed starving the engine of fuel at .1, or at least it should, however that doesn't mean the engine won't run in that period of time, but you most certainly should have some degraded performance. I think you might be confusing the engine physically sounding down versus starving the engine of fuel. I'm not exactly sure any simulator has actually ran the physics (other than Accu-Sim) of what is happening here, as there is measured fuel being sloshed around the tank versus emulating it via math and/or tables.

I'm not familiar with said report, but I'm sure Killratio is.

_________________

Hi Darryl,
You wrote:"To get some idea of the effect, have a look at the openning scene for the Battle of Britain movie (and before anyone starts on about using movies as "reference"...... I'm talking actual physical effects) where the Hurricane does a slow roll. You can hear and see the effects of the negative cut out and a bit of black smoke. That is about as dramatic as it gets."

The Battle of Britain movie you're certainly meaning with Michael Caine was a masterpiece! it can always be used as reference, all the planes (exept the Stukas) were real and filmed in the air, special permission was needed to fly the German planes with swastickers over Spain, France and England (they were constantly chasing the weather!). The hangars which were bombed were really blown up! and the areas of East London they managed to use before they were to be destroyed for new housing projects.
There can never be a more accurate film about the Battle of Britain again!

Happy flights

M. Jordan

Hi Klem,
You wrote: "I fly the Accusim Spitfires just for the pleasure of flying them, combat-type maneouvres aren't relevant"

Me too! I generaly fly them as if I'm flying an old "museum piece" from one air show to another, but it is very difficult to resist a "Spitfire roll" so I'd like to hear more of a splutter sometimes!

Keep on "rolling"

M. Jordan

Guys,

Yes, I'm well aware of the report. The Accusim Spit may apear to be more benign than this would indicate and there is good reason for this...

FSX makes it very hard to put in some effects because of the weather. Wierd winds and inaccurate turbulence etc etc. As you have said, FSX is for flying, not combat and so is not so good at recreating some things that may appear in combat.

I have followed the "debate" in "the other place". One of the problems is obviously with the Spit cutting with turbulence. This simply should not happen.

THe concept of 0.1G is hard for non-aerobatic pilots to grasp. I have many times had passengers who have been scared and upset by what they have desrcibed as severe turbulence. This decsription is in most cases (and certainly from the Airlines passengers' point of view also) between +1.5 and +0.5G.nowhere near the Merlin "cut-out" level of +0.1.

Now to give you some idea, a normal airline 20-30deg bank turn causes a 1.1 to 1.2G acceleration which is enough to really feel the turn. A 60deg bank turn causes what most non-pilots and even MANY non-aerobatic pilots regard as an unpleasant G loading. It is actually only 2.0G. So you can see that to cut the Merlin out the change in force is equivalent to almost this (+1 G + 1G for a 60deg bank and only +1G (-) 0.9G to cut out.) Again to give some frame of reference, a large Roller Coaster is set up to give around 2G sustained force (momentary to about 5g but that is strictly momentary or everybody would be unconcious) and all those people "melting" and screaming are being subjected to the same as a 60deg bank turn or about the same degreeof force (but, of course in the opposite "direction") as is required to "cut" the Merlin.

Very hard to explain this to the coke swilling, all conqueuring, 9G monster, 300+ kill, 13 year old Doom Player set!!

From a flying simulation point of view the overall effect is what we are looking for, particularly in "unusual" regimes of flight, which is not necessarily provided by the strict figures. The Accusim Spit feels right because it takes an "effort" to apply negative G until the engine cuts out....and the engine will otherwise behave properly. So the excessive effects of turbulence in sim and the fact that it is not "unpleasant" to reduce to 0.1G in sim are mitigated against and the overall effect is, in my opinion, about reasonable. We have the luxury of not having to chase Bf 109's Of course normal flight figures MUST be adhered to rigidly as these are what the sim is (theoretically) designed for an these WILL give proper feel.

I have only ever once had a normally aspirated, standard carby engine "complain" about negative G (about -0.75) when we stayed there too long (my passenger panicked and grabbed my arm, making it hard to correct the situation!!). I have only ever maxed out at -3.0G in an outside loop and I can tell you, it is very unpleasant. I've never met a pilot (fighter pilots included) who liked neggies!! But give me +5.0G any day, +6.0G on Sundays and +6.5G on birthdays and Christmas..and I'd be happpy. As I am not a 5'5", no necked, chain smoking, high blood pressured, iron pumping, marvel (and I am told the best fighter pilots are), I'll pass on anything over 7G. But I digress!


best regards


Darryl



P.S.... Love that movie!! but I suspect the "roll" in BoB was done quite deliberately for the effect of the smoke....as a proper roll is a positive 1G manoeuvre and shouldn't ever cause cut-out when done properly...

_________________

...Some say he never blinks, and that he roams around the woods at night foraging for Merlin parts...

Hi Darryl,
You wrote: "Love that movie!! but I suspect the "roll" in BoB was done quite deliberately for the effect of the smoke"

I think you're right there!
I'm not trained in aerobatics so I can't imagine getting them right without a lot of practice, so I'd like to be "punished" for getting it wrong. This is exactly what I love about A2A planes, they "punish" me when I do something wrong (as the real thing would), so I know when I've got things right too! so I'd still like a "splutter" like the one on the BoB film

Happy flights

M. Jordan

Ok,

Let me have a detailed look at what the current modelling does and at what thresholds and then talk to Scott. I'd say the "smoke" is out because I think all the smoke effect places that FSX gives are used up. The threshold may be able to be lowered for the cut .. but I'm not a programmer so not sure how hard/long the work is that would be involved...all sorts of things can "break" when something is changed. I can neither confirm nor deny that they are busy with a certain "other" Accusim aircraft ATM

No promises!



Darryl

_________________

...Some say he never blinks, and that he roams around the woods at night foraging for Merlin parts...

I can neither confirm nor deny that they are busy with a certain "other" Accusim aircraft ATM

Hi Darryl,
Hmmm! Spitfire mk.V......Spitfire Mk.I & Mk.II update or......P-51.....
I couldn't say which I'm waiting for the most
Hopefuly all three at the same time!

Happy flights

M. Jordan

Hi Daryl,

many thanks for the explanation.

It not really important (to me) in the A2A Spit but if/when you talk to your guys I'd be interested to know what -ve G figure they have set for cutout - if thats how they've done it. I did 'borrow' the 2D' open' cockpit from WOP2 spitfire and added an accelerometer from the English Electric Lightning but I couldn't be sure of the cutout point, I seemed to be bunting under before it cut.

Anyway, I'm looking forward to the Accusim P51

Hi Darryl,
I've just been watching a DVD of The Battle of Britain Airshow at Duxford (yes the one with 16 Spitfires ) I noticed two spitfires doing a roll together one of them got it right, but the other spluttered and left a short trail of black smoke behind. It shows that even later Spitfires can splutter like in the Battle of Britain Movie if you don't get the roll right.

M. Jordan.

G'day Mate,

Yes, I believe Miss Tilly's oriface only really works well at high power settings (poor girl!!) and therefore a roll at normal type display settings could well be below the level that would prevent the cut out... Voila..smoke!!

D

_________________

...Some say he never blinks, and that he roams around the woods at night foraging for Merlin parts...