Speed graphs for Spitfire and Hurricane

[Buchon]

Yeah, I mean there no boost control modeled, or at least properly, in-game now.

I think that they are working on it, if they made that performance line below of the Flight Test I think is because the properly Boost Control is coming.

[klem]

Originally Posted by Buchon

Yeah, I mean there no boost control modeled, or at least properly, in-game now.

I think that they are working on it, if they made that performance line below of the Flight Test I think is because the properly Boost Control is coming.

They made that line I added from B6's data by incorrectly amending the Spitfire FM. They need to make the Patch boost line align with the 6 1/4 lbs (thin pale blue) line. Then it will be modelled correctly for 87 Octane, +6 1/4lbs, 3 blade constant speed propeller, i.e. the Spitfire MkI we have now.

Its the +12lbs line achieved using 100 octane and boost cutout override that we hope they are working on because without it we don't have the BoB. We have "thank god they didn't come in November 1939".

[Buchon]

Well, this is how I see the problem (in Brits terminology)

The main problem is that the game´s FM haven´t Boost pressure changes modeled in yet.

So if you made your plane performance line over the blue line to obtain the Boost +6 1/4lbs performance (as is in pre-patch) then you will be over it always, even if cut the throttle and the needle is showing +2 1/4 psi.

The correct way is at the inverse, you should make the economic performance curve (+2 1/4 psi) and then add Boost pressure changes to the FM.

Then you have both performance lines, economic +2 1/4 psi and +6 1/4 psi.

If you watch carefully the B6 graph you´ll discover that it´s a economic performance curve (+2 1/4 psi), so my guess is that they are planing to add Boost pressure changes to the FM.

[fruitbat]

Originally Posted by Buchon

Well, this is how I see the problem (in Brits terminology)

The main problem is that the game´s FM haven´t Boost pressure changes modeled in yet.

So if you made your plane performance line over the blue line to obtain the Boost +6 1/4lbs performance (as is in pre-patch) then you will be over it always, even if cut the throttle and the needle is showing +2 1/4 psi.

The correct way is at inverse, you should make the economic performance curve (+2 1/4 psi) and then add Boost pressure changes to the FM.

Then you have both performance lines, economic +2 1/4 psi and +6 1/4 psi.

Unfortunately not, think what in Brit terminology is boost = ata.

the line B6 showed us is full speed as it is with ALL the other graphs, in a spit 1 with 87 octane fuel which happens to be 6 1/4 boost, and thats that, there is no 'Boost button', no gate to push through, full speed is just the throttle pushed all the way forward. There is nothing to be added to it at a later date.

when we are talking about boost, in this sense we do not mean what the old il2 used to call WEP.

[Buchon]

I know that there no Boost button but under a FM coding point of view the boost behavior is equal to WEP.

That´s because you should make overheating and damage for it so the best way is implement it in the code as is done with WEP.

[TheGrunch]

Originally Posted by Buchon

I know that there no Boost button but under a FM coding point of view the boost behavior is equal to WEP.

That´s because you should make overheating and damage for it so the best way is implement it in the code as is done with WEP.

When they say "boost" they just mean manifold pressure i.e. the throttle setting. The term doesn't always refer to any kind of emergency power. The overheating behaviour doesn't necessarily correspond between the aircraft capable of operating at +12lb/sq. in. and previous variants because different fuels were used. What was previously unsafe using 87 octane fuel would be achievable for limited periods and what was previously a 5 minute limit might then be a 15 minute limit, etc. Likewise there might be no changes to some of the operating limits. The devil is in the details. It's a struggle to find all the details because amendments to RAF Pilots' Notes and other such documents were often pasted on or clipped in as loose paper, and we usually only have scans or facsimiles of full editions to refer to.

[klem]

Originally Posted by Buchon

I know that there no Boost button but under a FM coding point of view the boost behavior is equal to WEP.

That´s because you should make overheating and damage for it so the best way is implement it in the code as is done with WEP.

"Boost" is alway present, its the manifold pressure, and is increased and decreased by the movement of the throttle, from below -4lbs (closed throttle) up to + 6 1/4 lbs at full throttle. There is a limit to the time +6 1/4lbs can be used otherwise damage results. This is already coded in.

The problem may be this: if we assume that the gauge reading of +6 1/4lbs is a true value, i.e. it truly represents the maximum manifold pressure, then there is something wrong in the conversion of the boost value to thrust and speed. I don't know how this is coded in CoD but its probably somewhere in the chain of formulas and values that convert throttle position to manifold pressure, manifold pressure to engine power output, rpm setting, propeller/thrust modelling, drag factors, atmospheric pressure, and probably other factors, to arrive at speed.

I assume several of these are the same for both Spitfire and Hurricane (same engine, same propeller) so it could be a common factor (engine modelling) and/or different aerodynamics for the two aircraft (they are both undermodelled at low altitude).

[macro]

Is there a graph for the spit IIa (real life, before and after patch lines)?

[camber]

Originally Posted by klem

The problem may be this: if we assume that the gauge reading of +6 1/4lbs is a true value, i.e. it truly represents the maximum manifold pressure, then there is something wrong in the conversion of the boost value to thrust and speed. I don't know how this is coded in CoD but its probably somewhere in the chain of formulas and values that convert throttle position to manifold pressure, manifold pressure to engine power output, rpm setting, propeller/thrust modelling, drag factors, atmospheric pressure, and probably other factors, to arrive at speed.

It's hard without knowing how the devs have configured their flight model formulae, but it seems likely to be as you say. Of course coding in this way makes it hard to calibrate to exact speed vs altitude (or any other) profile, as max speed (i.e where accelleration = 0) is at the termination of a chain of calculations where changes along the chain (to constants or altering the formulae themselves) can have unpredictable effects, and it may come down to laborious trial and error getting the two curves to match. Of course just getting the speed vs altitude curve right does not mean sim fidelity, for example if the plane accellerates in a non historical way to get there.

But we can compare along the chain where there is historical data, and currently boost is kind of right but the final speeds are wrong.

There are some problems with boost though, last night looking at the offline with cockpit off (apologies, I'm sure similar data has cropped up in many other threads):

Spits and Hurris have a boost controller (red cutout "off") that gives +5 1/4 to +5 1/2 psi minus boost cutout at 3000rpm full throttle. Boost drops as soon as the throttle is retarded, so CoD model is closest to the "variable datum" type of boost controller for all RAF aircraft. This should be +6 1/4 psi though.

Oddly, CoD boost increases to about right (+6.2 psi) when rpm is decreased to the 2600-2800 rpm range. From my reading this is incorrect, the boost controller should not be rpm dependant.

The Spit II with boost cutout activated (sea level; full throttle) achieves +9psi at 2600 rpm, +8psi at 3000 rpm (again the rpm-boost quirk). So the CoD Spit II acts most like a 100 octane conversion where the cutout was modified for +9 instead of +12 psi. At 3000rpm, the engine makes some distressed noises/ vibration but does not fail. Dropping rpm to 2600 rpm and/or putting mixture to weak smooths the engine. At sea level, boost cutout on, rad half open, weak mixture, 2600 rpm and +9 psi boost I could maintain 320 mph (IAS and TAS) for a full sortie. That is some serious speed (512 kmh)

The CoD Spit Ia/Hurri act (in boost characteristics) like 100 octane conversions where someone drilled the wrong size holes in error and gave tiny increments in boost. You can see the boost cutout effect in Hurri at 2600 rpm if you turn it off and on and watch the boost gauge(+6.2 to +6.4 psi), alhough I could not detect a speed difference. So you can't tell if the virtual tanks have 87 or 100 octane in them, it doesn't matter because the boost never gets high enough.

But getting the boost behaviour exactly right doesn't help much if the model does not pass the next check..that the boost combined with other inputs ends up producing overall performance in line with historical norms...which is more of a problem.

I didn't realise the Spit II could sit on 320 mph. Had an online sortie on ATAG, I just zigzagged up and down the channel on the wavetops at 320 mph, and started bouncing people from below. Fun, but not very historical I guess

camber

[camber]

Originally Posted by klem

They made that line I added from B6's data by incorrectly amending the Spitfire FM. They need to make the Patch boost line align with the 6 1/4 lbs (thin pale blue) line. Then it will be modelled correctly for 87 Octane, +6 1/4lbs, 3 blade constant speed propeller, i.e. the Spitfire MkI we have now.

Its the +12lbs line achieved using 100 octane and boost cutout override that we hope they are working on because without it we don't have the BoB. We have "thank god they didn't come in November 1939".

Klem, I agree totally.

So to summarise as I understand it, we currently have a Spit I that has low alt performance about right for boost controlled at +4 psi (although the gauge reads +6 1/4 psi, the correct boost setpoint for 87 octane). The new plots suggest that this performance might be degraded in the patch to about equivalent to if the boost controller setpoint was +2 1/4 psi. Of course this leaves aside that frontline BoB Spit Is had 100 octane and a modified boost control cutout that increased the boost setpoint to +12 psi, and we don't know if the devs have any plans to fix that.

B6 if this is correct, I don't think the Spit I will be useable in MP, it is almost unusable now.

Wouldn't it be cool if the Spit I and Hurricane boost cutout actually worked? Incidently this would tell us the octane number of the fuel in those virtual tanks.

If they are unmodified and running 87, pulling the cutout at full throttle on the deck would give an instant +17psi boost. The engine would make horrible noises, lose power and become damaged in short order. Sneaking the throttle up tells you the octane, if it starts making the predetonation plinking noise (that the game seems to model) at around +7psi, it is 87. +12 psi, it is 100 octane. Greater than that, it must be 150 octane (seems a bit unlikely ). Of course with 100 octane the boost cutout should have been virtually modified so that it is no longer a cutout, but instead controls boost at the higher +12 psi value.

The boost cutout in the Spit II is a bit strange, it just unlocks a bit more boost but clearly it has 87 octane inside as it starts to predetonate at around +7 psi.

EDIT INCORRECT STATEMENT with mixture/ rpm changes the Spit II will sit happily on +9 psi and go 320 mph IAS/TAS on the deck So it models 100 octane boost behaviour.

But if we have to have to use Spit Is and Hurris in their pre-Battle of France fuel configuration, the original (working) boost cutout would be fun! People would be using it to squeeze a little more power from their 87 octane but blowing up motors left right and centre. A bit arcade I know but I would love seeing it in MP. Perhaps a server side setting would be useful if you didn't want it ("crew chief secretly used extra thick wire on boost cutout after what happened last time" setting).

It is a problem that WEP configurations for combat edge carry little penalty if modelled correctly..because the problem is for the virtual erks or the next guy that flies your plane if problems are not addressed. Again most people would consider it arcade, but I would love to see that if you used combat concessions, you are that "next guy"...engine wear is accellerated over reality to "simulate" that effect. People would only use WEP configurations if they really thought their virtual life was in danger or interception was critical.

Well, you can dream,
camber

BTW Ramstein, great post on engine stuff