4.12m sneaky P-38 fm changes

[adsao1]

I just noticed p-38's compressibility issue above 650km/h is gone.
Plus there are some discrepancies between trim settings.
Is this work as designed or someone made a mistake?

[FC99]

I just noticed p-38's compressibility issue above 650km/h is gone.
Not really, compressibility issues bellow 0.63 Mach are gone.


Plus there are some discrepancies between trim settings.
What discrepancies? I don't remember any changes in P38 trim settings in 4.12.


Is this work as designed or someone made a mistake? Compressibility works as designed and for trim I can't say when I don't know what trim changes you are talking about.

[adsao1]

I did some test flights,it seems now you don't need to worry about compressibility ever if you fly below 7500m,really you could dive straight to the ground and never experience serious compressibility.
Starting from 10000m though,it does exhibit compressibility at around 8km,but even then when you get close to 4.5km,you can again control your plane.
Either
1.the compressibility effect is under-modelled,actually by using http://www.globalaircraft.org/converter.htm and compare against in game speed using open cockpit TAS gauge,i think it only get into uncontrollable dive above 0.8 mach.
2.or speed of sound is overestimated,yeah high precision mach number vs altitude/temperature is the thing that get classfied,and i'm totally a layman on this,but it can't be that far apart does it?
3.i just made a mistake in my assumption related to mach number because i'm a layman,but i tested in hot map(Coral Sea) and cold map(moscow),and it's all the same,below 4.5km you are immune,and not that pronounced above that.
4.or that the non-pronounced compressibility effect is modelled without considering every sim player can fly with joystick like they have hydraulic assists,and this game have not so accurate modelling of trims(actually much like a seperate low drag control surface,especially at low speeds,this solve the problem of uneven feels of moving main surface in opposite direction,exhibited if you simply model trim as main surface offset,but it can be exploited in certain situations where main surface should be too draggy to be usable.)

For trims,it looks like now trim is off by -3% compared to previous setting.
For 110% throttle Sea Level level flight with 50% fuel on Coral Sea Online map,
previously you need -23% trim,now you only need -20%,
For climbing at best climb rate speed,it was +15% trim previously,now it is +12% trim.
They have same max speed at sea level in 4.11 and 4.12.
It is a change for the better,now you don't get annoying pitch up when aiming using default trim,but i think this warrant a entry in change logs.

[FC99]

I did some test flights,it seems now you don't need to worry about compressibility ever if you fly below 7500m,really you could dive straight to the ground and never experience serious compressibility.
Starting from 10000m though,it does exhibit compressibility at around 8km,but even then when you get close to 4.5km,you can again control your plane.
That's basically how things should be. Compressibility was a problem at high altitudes only. Considering that Mach drag calculation is improved in 4.12 it is not surprising that there is less problems with compressibility at low altitudes simply because plane don't dive as fast as before.


Either
1.the compressibility effect is under-modelled,actually by using http://www.globalaircraft.org/converter.htm and compare against in game speed using open cockpit TAS gauge,i think it only get into uncontrollable dive above 0.8 mach.
2.or speed of sound is overestimated,yeah high precision mach number vs altitude/temperature is the thing that get classfied,and i'm totally a layman on this,but it can't be that far apart does it?
3.i just made a mistake in my assumption related to mach number because i'm a layman,but i tested in hot map(Coral Sea) and cold map(moscow),and it's all the same,below 4.5km you are immune,and not that pronounced above that.
4.or that the non-pronounced compressibility effect is modelled without considering every sim player can fly with joystick like they have hydraulic assists,and this game have not so accurate modelling of trims(actually much like a seperate low drag control surface,especially at low speeds,this solve the problem of uneven feels of moving main surface in opposite direction,exhibited if you simply model trim as main surface offset,but it can be exploited in certain situations where main surface should be too draggy to be usable.)

1. Model is fine on fundamental level, refinements are always possible.
2. Mach number is OK, nothing wrong with it, precision is actually increased in 4.12.
3. Don't know but it doesn't really matters.
4. Refinements are always possible.



For trims,it looks like now trim is off by -3% compared to previous setting.
For 110% throttle Sea Level level flight with 50% fuel on Coral Sea Online map,
previously you need -23% trim,now you only need -20%,
For climbing at best climb rate speed,it was +15% trim previously,now it is +12% trim.
They have same max speed at sea level in 4.11 and 4.12.
It is a change for the better,now you don't get annoying pitch up when aiming using default trim,but i think this warrant a entry in change logs.
AFAIK there were no changes in trim parameters, any possible difference in handling is result of something else.

[adsao1]

I mean dive from 7500m straight down all the way,and you at no time loss controllability,it does pitch down in relative terms but you still have good response on elevator main surface,and at no time is default trim pitching down in absolute term.
I can recover with 15% pitch up on elevator main surface from 940km/h TAS at 3000m(open-cockpit TAS gauge),way past mach 0.68,if it is truly modelled correctly,then it surely stretch my imagination a bit...
https://en.wikipedia.org/wiki/File:Compressibility010.png

[adsao1]

Start dive from 10000m,when at 6km with 360mph IAS,i do get very apparent compressibility,but dive from 7500m,when at 3km with 420mph IAS,i can still control it no problem.
IAS read from in-cockpit gauge,speedbar reading is higher.

[FC99]

Do you read my posts?

1. Model is fine on fundamental level, refinements are always possible.


BTW what is this sudden obsession with P38? It was wrong for years and now when it is more accurate you felt the need to "join" the forum and question its FM. Not that it is wrong to question the FM but the timing is interesting.

[adsao1]

Because i was in the process of testing trim and control settings for maximum maneuverability,after i become more conscious about certain factors after warthunder experience,pretty much power gaming really.
Then i just accidentally stumble upon p38 fm changes because a certain map on sov only have p51 and p38 on red side.
Then because i actually have something to discuss so i registered,and because sometime ago i bought il2 1946 on GOG.com,previously i did play pirated copy for a while because back then real shop selling real game mostly disappeared,and even if there is one,none have ages old games in stock.

Background aside,i did read your response fully,my conclusion is that mach number below 5km is a bit off,although algorithm might be improved,so it's a good start but right now the problem is one of tactical,simply that p38 won't experience any compressibility in real game sessions.

[FC99]

Background aside,i did read your response fully,my conclusion is that mach number below 5km is a bit off,although algorithm might be improved,so it's a good start but right now the problem is one of tactical,simply that p38 won't experience any compressibility in real game sessions.
Mach is fine, there is not much that can go wrong with it. I tested P38 after your first post and it can be affected by compressibility a bit more. In one of the next patches(4.13 most likely) its FM will be changed a little.

As for tactic, you can't expect compressibility at low altitudes, plane just can't fly fast enough to get into compressibility. If you are used to FM prior to 4.12 than just forget it, it was flawed on fundamental level and worked just the opposite of how things work in reality.

[adsao1]

OK,reenact within current model match following info pretty closely.
http://forums.ubi.com/showthread.php/465239-P38-Dives-Compressibility-Forums
So i guess it is mostly a hydraulic elevator for everyone problem..
You just don't need trims to recover.
Whether to implement further hinderance is a decision for developer.

[Fenrir]

Hi guys, just tested the 38 in QMB in a power dive from 7500m.

Whilst compressability (buffeting and heavy elevator effects) start at the requisite indicated airspeeds, the documented elevator ineffectiveness at this mach number is not apparent.

By all accounts in the prototype the elevators were at the focus point of shockwaves which made them useless and the aircraft would even begin to tuck under (start an outside loop) until denser air was reached and the Mach decrease. Given you were not a) going too fast and b) not going too steep at this point you could recover.

The new mach effects on the FM no longer appear to demonstrate this effect. Elevators, whilst still heavy, are effective and can be used to recover above the critical altitude. Similarly trim.

[horseback]

The P-38 prototype was a very different aircraft from the production aircraft. The earliest designs lacked the fillet between the wings and the fuselage/cockpit pod, and once those were installed the buffeting at high speeds was reduced somewhat, and as long as you followed the Do Not Exceed speeds at the designated altitudes, you were okay. Of course, at extreme altitudes the Lightning could exceed its DNE speed in level flight rather easily, which was the price you sometimes pay for being one of the first to get that high and that fast...

But all high performance aircraft of that era were subject to compression effects when they went past their critical Mach number--it's just that the P-38's number was a bit on the low side, due in part because the whole compression/critical Mach problem was not well understood when it was designed in the late 1930s.

In any case, if you could get the aircraft below 6200m or so before it broke, it would supposedly recover quite nicely in the thicker air.

cheers

horseback

[Cap'n Crunch]

Well, here's hoping those 4.13 changes will correct the combat flaps by increasing the flaps takeoff setting to 250 IAS. 10% flap isn't enough, the manual gives a 50% position for combat flap at 250. The current speed restriction on half flap sort of castrates it's high altitude maneuverability, in a big way.

[Woke Up Dead]

I tried some dives in QMB; the P-38 is definitely not a death-trap when diving steeply anymore, the 109 has also improved.

However, it appears that the 1941 MiG still suffers from heavy elevators at speeds above 500km/h. Am I wrong? If not, is this by design?