British FM killing the fun of the game for allied pilots.

[41Sqn_Banks]

Originally Posted by Kurfürst

Well the manual highlights that the elevator is so sensitive that the pilot can easily pull enough g-load to exceed the structural limitations and of the aircraft. It isn't so in the sim, no matter how crazy manouveres I tried in the Spit (ie. vertical dives at Vne) I simply couldn't break it.

It's incorrect and the stick/pitch behaviour should be fixed.

Also the aircraft seem to be rolling much faster at high speed than it should - 3 times as fast as I recall.

Personally I think this disharmony between the controls and senstitivity in pitch are one of the most curious ommitments from the Spitfire's FM. Simply to put, it is not flown like a Spitfire, 'with a light fingertip on the elevator and arm wrestling the ailerons' as pilots have put it.

Positive pitch stability for the Spitfire FM in the sim is also confirmed, as opposed to the real life longitudal pitch instability. This is, again, important for the flying experience: the very low stick force per g and slight instability meant that real Spit had to be handled with careful movements on the stick, and with routine aft-and-fore movements on the stick to prevent the aircraft to tighten up itself. I do not think this was particularly dangerous (though the low stick force per g had some safety risks, admitted by the manual), but it was characteristic of the Spitfire's handling.

+1

[swift]

Originally Posted by Kurfürst

Pure Glycol has about twice the boiling point of water but only about half the heat capacity (plus its an anti-freeze). So in effect the coolant (and engine!) temperatures are going to be much higher (since the coolant agent can carry away about half the heat), but I reckon it would boil much later. Hence why it is used in a mix with water. It would also explain why the Hurri I and Spit I overheats so fast.

Engine temperatures are a function of coolant capacity, coolant type, coolant circulation capacity and heat transfer capacity of the radiators. The amount of pressurization the cooling system also raises the boiling point.

What was the coolant capacity of the Spit and Hurri Mark Is, how many gallons/liters? Are there any cooling trials available for these aircraft?

how should something that was added to increase reliability increase the risk of overheating which would strongly reduce reliability? For me this is contradictory.

[Kurfürst]

Originally Posted by swift

how should something that was added to increase reliability increase the risk of overheating which would strongly reduce reliability? For me this is contradictory.

You seem to miss a detail - the temperature of the coolant agent is rather irrelevant, it can be of very high temperature, or even near/at/above boiling point as long as the temperature of the engine components are within permissable temperature limits. The two are not mutually exclusive. Yhe coolant may boil pretty quickly, be at very high temperature, what matters is the interaction between the coolant components and the coolant, of which the coolant's temperature is an indirect indication to the pilot about the engine component's temperature.

So say with a pure glycol coolant 140 degrees celsius may indicate that the engine compontents are about (iirc) 400 celsius, while when using pure water 90 degrees may indicate the very same, since water has a much higher heat transfer capacity (its more effective at carrying away heat).

I suppose they changed the coolant agent type to water-glycol mixture on later Merlins because they realised glycol alone simply cannot transfer heat fast enough, and by adding 70% water this increased greatly. This was usually the practice anyway, an 50-50 or 70/30 mix was generally used by everyone. The DB 601A had used 47% water, 50% glycol and 3% mixture of lubrication oil and water (1:2), which may explain why the DB powered planes do not overheat so easily compared the the all-glycol cooled Spitfire Mark I / Hurricane Mark I.

Coolant circulation may be also of important - the DB 601A circulated coolant for example at 65 000 liter / hour rate.

Glycol permitted higher coolant temperatures without the mix boiling away, and was an anti freeze too for higher altitudes (where temperatures can be easily at the -40 degrees celsius range).

[JtD]

Originally Posted by Kurfürst

What was the coolant capacity of the Spit and Hurri Mark Is, how many gallons/liters? Are there any cooling trials available for these aircraft?

Hurricane ~15 gallons, was tested in a climb with 2600rpm/6.25lb boost, result is that in English summer conditions (25°C at sea level) it can do this without overheating (oil & glycol).

[Glider]

Originally Posted by Kurfürst

Well the manual highlights that the elevator is so sensitive that the pilot can easily pull enough g-load to exceed the structural limitations and of the aircraft. It isn't so in the sim, no matter how crazy manouveres I tried in the Spit (ie. vertical dives at Vne) I simply couldn't break it.

It's incorrect and the stick/pitch behaviour should be fixed.

Also the aircraft seem to be rolling much faster at high speed than it should - 3 times as fast as I recall.

Personally I think this disharmony between the controls and senstitivity in pitch are one of the most curious ommitments from the Spitfire's FM. Simply to put, it is not flown like a Spitfire, 'with a light fingertip on the elevator and arm wrestling the ailerons' as pilots have put it.

Positive pitch stability for the Spitfire FM in the sim is also confirmed, as opposed to the real life longitudal pitch instability. This is, again, important for the flying experience: the very low stick force per g and slight instability meant that real Spit had to be handled with careful movements on the stick, and with routine aft-and-fore movements on the stick to prevent the aircraft to tighten up itself. I do not think this was particularly dangerous (though the low stick force per g had some safety risks, admitted by the manual), but it was characteristic of the Spitfire's handling.

I have already said that in a previous posting when I replied to the Crumps pilots notes

In a high speed dive it is possible to exceed the G limit, if you pull up too quickly.

So I don't see what the problem is. The only problem is the emphasis on it is easy. The pilots notes don't say that its easy, that say that it is very easy for the pilot to impose high load factors when looping, pulling out of dives or doing tight turns. Something any pilot of any airforce would agree. It then goes on to say that it is well within the pilots power to exceed 10G. If the Spitfire goes past 10G then you can expect the wings to come off.
I do not have any problem with the SIM breaking the wings off should the Spit exceed 10G

However its the how easy is it.
It depends on the individual but you would expect most pilots to lose consiousness at 7-8G and tunnel vision happens well before then. The Sim should show a tunnel vision effect at around 4G and a loss of consiousness at around say 8G.

All aircraft will have their break point whereas the effect on the pilot of the G forces is a constant and would apply to all.

In the real world it would be a rare pilot who delberately went past the point of consiousness it would have to be a real emergency, last throw of the dice situation. This would explain why it was rare to have an accident of this type.

The only situation I can see this happening is if the pilot yanked hard on the controls adn suddenly went through the passing out limit. Even here they would probably have a chance to ease off the controls as there are four stages, 1) a loss of colour vision, 2) tunnel vision 3) blacking out whilst stayng consious and then 4) passing out.

So to sum up, if the Pilot decides to go into a state of passing out and then the aircraft goes through its limits, you have a chance of things breaking up.

[JtD]

Blacking out takes time, damaging the airframe does not. There's no reasonable way to exceed the airframes limit in a sustained manoeuvre, however, in a sudden pull out, or due to buffeting with elbows not fixated, it may happen.
Put it as you want, personally I'd not agree with "dangerously low" control forces as propagated by some, nor do I agree that it was a none issue. The Spitfire II pilot notes had the paragraphs added in early 1940, after at least two fatal accidents due to wing failure had occurred and several Spitfires went to maintenance with bend wings. It wasn't a that rare thing to happen, but certainly Spitfires weren't falling from the sky as some here seem to believe. An extra warning was deemed necessary, as pilots transferring to Spitfire equipped units simply were not used to a feature like that. WRT elevator forces, I'd say that the Spitfires elevator forces were not sufficiently high to prevent accidents. Hence they were getting some attention.
Once more about longitudinal stability - the about neutral static stability of the Spitfire gave a lot of pitch reaction to little elevator movement. However, as opposed to what some claim here, the airframe would not self destruct given a bit of elevator input, as would be the case in a statically unstable aircraft. It was not necessary to pull back the stick to get a pitch up, and then push the stick forward to maintain controlled flight. A low static stability means that an aircraft needs a lot of time to settle around a new condition. This in turn means, that if you want a strong initial reaction, you'll have to pull back the stick like you would in a more stable aircraft, however, you'd end up at a lot more g. Or, you can pull back more gently and end up at the same g as a more stable aircraft, but you'd have a slower initial reaction. This leads to the pull - push routine an experience pilot would employ while putting the Spitfire through manoeuvres. Large deflection for a quick initial reaction, eased forward for moderate final loads. This is not critical at all, as the stick forces increase as the g load builds up. In a normally loaded Spitfire I, the pilot would still have to exert near 50 lbs of force to damage the airframe.
On to dynamic stability - short period oscillations were sufficiently damped by the Spitfire. Long period oscillations were not. This was however, typical for aircraft of that era, and opposed to what one poster claims, fighter aircraft of that time in general were no hands off aircraft. In fact, the Spitfire stability in long period oscillation is above average from what I've seen, much better than say a Hurricane. One of NACA's chief test engineers states that all fighter aircraft they tested were dynamically unstable in long period oscillations. They do not matter much to the pilot while flying, where they do matter is if the pilot's unconscious, and regains consciousness only to find himself in a steep spiral dive he can't get out of.
I'd recommend that instead of going over the same Spitfire chart time and again, try finding charts for other aircraft. This would certainly help to get the proper perspective, and maybe even an overall more accurate FM for many planes, not just the Spitfire. The focus of some on that plane is worrying.

[NZtyphoon]

Originally Posted by swift

how should something that was added to increase reliability increase the risk of overheating which would strongly reduce reliability? For me this is contradictory.

The biggest problem with using pure ethylene glycol as a coolant is that it is less effective at conducting heat than water so, as it circulates around the engine, it is less effective at keeping engine components cool. While the high strength alloys and other metals developed by the likes of Rolls-Royce for use in aero engines were able to withstand higher temperatures than earlier metals, components such as gaskets and oil seals were more likely to fail - early Merlin engines were renowned for their oil leaks. Head gasket failure in the middle of combat ops is no fun.

A second problem is that in its pure form Ethylene glycol is flammable, thus it was a hazard to use 100% glycol in combat aircraft. The Merlin II and III series had a normal coolant temperature of 90°, and 120°C emergency maximum - close to the flash point of glycol http://www.npi.gov.au/substances/eth...col/index.html Mixing glycol with water increases the flash point while preserving the anti-freeze, anti-corrosive properties of glycol.

Thus the Merlin XII and XX series (30% Glycol, 70% water) were able to run at higher temperatures 105° normal to 125° for climb, 1 hr maximum and 135° +12 lbs boost 5 minutes while the vulnerable gaskets and oil seals were less prone to failure.

I don't know why the British adopted 100% glycol, although I remember reading about it somewhere.

[NZtyphoon]

Originally Posted by JtD

Blacking out takes time, damaging the airframe does not. There's no reasonable way to exceed the airframes limit in a sustained manoeuvre, however, in a sudden pull out, or due to buffeting with elbows not fixated, it may happen.
Put it as you want, personally I'd not agree with "dangerously low" control forces as propagated by some, nor do I agree that it was a none issue. The Spitfire II pilot notes had the paragraphs added in early 1940, after at least two fatal accidents due to wing failure had occurred and several Spitfires went to maintenance with bend wings. It wasn't a that rare thing to happen, but certainly Spitfires weren't falling from the sky as some here seem to believe. An extra warning was deemed necessary, as pilots transferring to Spitfire equipped units simply were not used to a feature like that. WRT elevator forces, I'd say that the Spitfires elevator forces were not sufficiently high to prevent accidents. Hence they were getting some attention.
Once more about longitudinal stability - the about neutral static stability of the Spitfire gave a lot of pitch reaction to little elevator movement. However, as opposed to what some claim here, the airframe would not self destruct given a bit of elevator input, as would be the case in a statically unstable aircraft. It was not necessary to pull back the stick to get a pitch up, and then push the stick forward to maintain controlled flight. A low static stability means that an aircraft needs a lot of time to settle around a new condition. This in turn means, that if you want a strong initial reaction, you'll have to pull back the stick like you would in a more stable aircraft, however, you'd end up at a lot more g. Or, you can pull back more gently and end up at the same g as a more stable aircraft, but you'd have a slower initial reaction. This leads to the pull - push routine an experience pilot would employ while putting the Spitfire through manoeuvres. Large deflection for a quick initial reaction, eased forward for moderate final loads. This is not critical at all, as the stick forces increase as the g load builds up. In a normally loaded Spitfire I, the pilot would still have to exert near 50 lbs of force to damage the airframe.
On to dynamic stability - short period oscillations were sufficiently damped by the Spitfire. Long period oscillations were not. This was however, typical for aircraft of that era, and opposed to what one poster claims, fighter aircraft of that time in general were no hands off aircraft. In fact, the Spitfire stability in long period oscillation is above average from what I've seen, much better than say a Hurricane. One of NACA's chief test engineers states that all fighter aircraft they tested were dynamically unstable in long period oscillations. They do not matter much to the pilot while flying, where they do matter is if the pilot's unconscious, and regains consciousness only to find himself in a steep spiral dive he can't get out of.
I'd recommend that instead of going over the same Spitfire chart time and again, try finding charts for other aircraft. This would certainly help to get the proper perspective, and maybe even an overall more accurate FM for many planes, not just the Spitfire. The focus of some on that plane is worrying.

Excellent summary.

[robtek]

Originally Posted by JtD

........ It was not necessary to pull back the stick to get a pitch up, and then push the stick forward to maintain controlled flight. .......

And that is the point where you are wrong, according to the NACA - tests!

[JtD]

Originally Posted by robtek

And that is the point where you are wrong, according to the NACA - tests!

No, it's exactly what is stated in the NACA report.