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 Post subject: Re: 109G14
PostPosted: Sat Aug 03, 2019 4:41 pm 
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I got asked about the Bf 109G-14's turning ability compared to the Spitfire XIVe with regards to wingloading and powerloading etc. I thought my answer could be of interest to other players as well, so posting it here. The next update will most probably see a slight induced dragco increase for all planes with slats (Bf 109's, La-5's, La-7's, MiG-3, Swordfish). Not a significant change for these planes, but should hopefully have the slats more realistically modeled.

------------------------

<S> sir!

Note that the Spitfire XIVe is the heaviest and worst turning Spit in the series. The Spitfire Vc and IXe will easily outturn the Bf 109G-14 in a prolonged turn fight between two equally skilled pilots, but the Bf 109G-14 and the Spitfire XIVe should be very closely matched. It's also quite a post war propaganda misconception that the Bf 109's weren't good turn fighters. They were actually great turn fighters, but were usually matched against the Spitfires and Hurricanes, and were as such often better off using boom n zoom tactics. And now on to the technical stuff... :)

The wingloading is not set as a parameter, but more a resultant from the flightmodel's current weight and liftco + max AoA. Pure wingloading wise at 100% fuel the Bf 109G-14 weighs 7325.2 lb vs the Spitfire XIVe's 8488 lb. The wing area is 173.3 sqft vs 242.1 sqft. As such we'd get a wingloading of 42.3 vs 35.1 in favour of the Spit XIVe. The wingloading is of course lowered if you have less fuel/ammo.

Wing area is not the sole factor determining the liftco though since the wing thickness ratio is important as well (and a few other factors). The Bf 109G-14 has an average wing thickness ratio of ~12.8% while the Spitfire has really thin wings at only ~11%. This is great for the Spitfire concerning drag and allows it a higher top speed compared to if it had as thick wings as the Bf 109G. Liftco wise though you could say that the Spitfire's wing area is only ~219 sqft relative to the Bf 109G-14 due to the Spitfire's thinner wings (I just ran some tests and calculations). As such the relative actual "wingloading" is rather 41.4 vs 38.8, still in favour of the Spitfire XIVe but not by as much.

What flips the coin though is the Bf 109 having slats. There is no code that models slats in Warbirds, but I've modeled the simulated max AoA gain from slats as close to realistic performance as possible, by studying data from ww2 stall tests of a La-5FN with and without slats, and I tried to rather be on the safe side as to not give to much liftco gain from slats. From my tests with slats simulated, the gain for the Bf 109G-14 is comparable to as if it had an actual wing area of ~212 sqft. As such the comparable "wingloading" between the Bf 109G-14 and Spitfire XIVe would rather be stated as 34.6 vs 38.8 relative to each other, in favour of the Bf 109G-14. As such due to slats and thicker wings, the Bf 109G-14 has a better max liftco vs weight compared to the Spitfire XIVe, and it should be able to win a turn fight against the Spit XIVe. Then the power/weight ratio comes into play though, which is generally in favour of the Spitfire XIVe, but at sea level the Bf 109G-14 has the better power/weight ratio. At WEP the Spit XIVe should be quite evenly matched to the Bf 109G-14 at altitudes above 2000 ft due to the power/weight ratio gap being larger, while the Bf 109G-14 should be better in a turn fight below 2000 ft. (Due to the DB 605 ASM engine having very high horsepowers at WEP up to 2000 ft). This is without combat flaps and with combat flaps the Bf 109G-14 should be the winner in a turn fight between these two, as the Spitfire XIVe doesn't have combat flaps. Note that this is before applying the negative drawbacks from having slats though.

Power/weight ratio (Bf 109G-14 vs Spitfire XIVe):
at Sea level: 0.242 vs 0.241
at 12000 ft: 0.207 vs 0.240

Also note that the Spitfire LF IXe quite easily wins a prolonged turn fight against the Bf 109G-14 between two equally skilled pilots, owing to the IXe's lighter weight compared to the Spitfire XIVe, but the Bf 109G-14 can be dangerous in the first few laps of a turn fight even against a Spitfire LF IXe.

Now there is a drawback with slats as they increase the drag and induced drag when deployed. This will cause an increased energy bleed in a turn fight. The turn radius is not so much affected by this side-effect, nor is the instant turn rate while there is excess energy to bleed, but the sustained turn rate is definitely affected negatively. Iv'e actually been pondering for some time wether I've modeled these drawbacks realistically or with to light negative effects. It's often better to be on the safe side but I've felt that the negative effects should be slighly larger. I've ran some more in depth tests this last week and from these concluded that an increase in the amount of induced drag penalty would be advisable. I've studyied ww2 turning tests conducted between early Spitfires vs Bf 109E's, and also German turning tests between the adversaries. I've tested the Spitfire I vs Mirlox flying the Bf 109E-4, with him starting on the tail of my Spitfire I. Turning at full WEP and the best of our abilities, it required me 4 laps to reverse the positions and get on his tail, which shows the Spitfire I is definitely the superior turn fighter. In real ww2 trials though it required only around 3 laps for the Spitfire to get on the tail of the Bf 109E when performing the same test. I'm thinking of increasing the induced drag penalty for slats slightly for all planes using slats, not just the Bf 109's, for the next update, but still want to run more tests to conclude it would be a more realistic setting. With my planned change the relative turn performance between a Spitfire I and Bf 109E would be very close to ww2 trial reports. The Bf 109's and La-5, La-7 etc would see a slight decrease to their sustained turn performance, although quite small with the turn rate increased by ~0.4 sec/lap, so it shouldn't affect these fighters potential by to much, but would be a step in making them closer to real life performance. With this change the turn performance between the Spitfire XIVe and Bf 109G-14 would be a close call for sure. The Oswald factor (Wing efficiency factor / induced drag factor) for the Bf 109G-14 would then be 0.741 (previously 0.791) while the Spitfires have a factor of 0.910, which means quite a lot more induced dragco vs liftco for the Bf 109G-14 when pulling G's in a turn.


Here is also some engine data that was used when programming the DB 605 ASM engine of the Bf 109G-14. The numbers are most likely under min RAM conditions.


Image

Image


Cheers!
/Robert


Last edited by Robert on Wed Aug 07, 2019 9:25 pm, edited 2 times in total.

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 Post subject: Re: 109G14
PostPosted: Mon Aug 05, 2019 4:11 pm 
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I did some turning tests for fun, since asked why the G-14 could turn at 14.1 sec per lap, when ww2 trials indicate 22-23 sec/lap. My turn tests were at sea level at only 50% fuel, while ww2 trials usually were at 12000 ft with more fuel. This makes several seconds per lap difference since the air is thinner the higher up you go, and more fuel means more weight. I also turn at max WEP setting, while sometimes in real life tests they used military power (less hp/weight ratio means worse turn rate). Below is a turn test of the Bf 109G-14 flightmodel when turned at sea level vs 12 000 ft, at 75% fuel. At 12 000 ft the turn performance is quite close to the 22-23 sec/lap data from real life tests.


Image


Below is also a turning test I just made at 12 000 ft, 75% fuel, between the adversaries of the Battle of Britain. I hope someone finds it interesting :). The Bf 109E-4Aa holds a really nice turn radius thanks to the high max AoA from using slats, but can't match the Hurricane and Spitfire in the turn rate. The Hurricane also has a high max AoA with it's thick wings. The Spitfire is quite close to the Hurricane I in turn rate even though it has really thin wings compared to the Hurricane. This is thanks to it's eliptical wings and thus low induced dragco, but the Spit holds a larger radius due to the low energy bleed. Having a good turn rate is more important than holding a lower average speed in the turn though, so the eliptical wing is a good thing and the Spit would not have been able to match the Hurricane's turn rate as well with a more square wing shape that resulted in a larger induced dragco. With the quite narrow turn radius the Bf 109E-4 can be dangerous in the first lap of a turn fight against a Spitfire as it can keep inside the Spit's radius for a while, but the Spitfire should easily get on the Messerschmitt's tail in any prolonged turn fight if the pilots are of equal skill.


Image


Cheers!
/Robert


Last edited by Robert on Mon Aug 12, 2019 10:50 am, edited 1 time in total.

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 Post subject: Re: 109G14
PostPosted: Sun Aug 11, 2019 10:02 am 
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Oops, I typed incorrect numbers for the turn test results of the Spitfire above. It has now been corrected.


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 Post subject: Re: 109G14
PostPosted: Sun Aug 11, 2019 9:53 pm 
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Thanks for all the testing and effort Robert! Well done!

What are you using for the Max Coefficient of lift for the Spitfire XIV. THe american tests inaccurately measured it in the SPitv, as you may already know. (I think I submitted the RAE document refuting it and giving the correct number years ago when I was more actively involved in the FM team.)


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 Post subject: Re: 109G14
PostPosted: Mon Aug 12, 2019 7:16 am 
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Thank you, sir!
The flightmodels are set for power ON stall speed, which is usually 7-11 mph below power OFF stall speed (also depending on how much manifold pressure you use). The code doesn't account for the air blown over the wings by the airscrew, so the liftco has to be set higher to simulate the determined power ON stall speed. In the game the power OFF and ON stall speeds are the same, due to the code, whereas in real life they vary. As such the liftco used probably doesn't match normal liftco data that only focuses on the wing's liftco without counting the air blown from the propeller. When determining the stall speed one firstly checks for ww2 data available, but usually has to calculate it based on wing area/weight/max AoA etc, since ww2 stall speed trial data is often very arbitrary and varies greatly from different trials of the same airplane. The data can give a good guideline though, and sometimes can be quite precise like the P-39 stall data from NACA. Sometimes the ww2 stall data is just completely whack, like the Pilot Manual of the F6F-5 stating a stall speed of 71 mph (62 knots). This must be due to instrument errors since it's quite illogical that the F6F-5 would have a lower stall speed than an A6M Zero. (Wingload of 37.2 vs 23.0).

Below is the in game power ON stall speeds for the Spitfires and Messerschmitts. If you check ww2 trial data the Spitfire I and Bf 109E-4 had quite the same stall speeds in real life, so the Spit and Schmitt series should be quite historical in game relative to each other.


Image - Image


P.S. I'm redoing the turn tests for all the fighters, now at 12 000 ft and 75% fuel. I will use this data for the Vehicle info instead of the sea level turn tests for the next update. This should give data that is more similar to the ww2 turn data available, which was usually from mid altitude trials. Just takes a bit of time since it requires a 5 minute test per fighter for all 99 fighters :D .


<S>
/Robert


Last edited by Robert on Tue Aug 13, 2019 7:16 pm, edited 2 times in total.

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 Post subject: Re: 109G14
PostPosted: Tue Aug 13, 2019 4:32 pm 
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Posts: 158
Sounds good Robert!


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 Post subject: Re: 109G14
PostPosted: Tue Aug 13, 2019 10:29 pm 
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Posts: 158
I think the POH for the Hellcat confused MPH and knots per hour.
My data sources are aligned with 72.9 KNOTS power on and about 78=79 KNOTS power off. That's 15 percent higher, and inline with what one would expect from the wing loading.
finn
Robert wrote:
Thank you, sir!
The flightmodels are set for power ON stall speed, which is usually 7-11 mph below power OFF stall speed (also depending on how much manifold pressure you use). The code doesn't account for the air blown over the wings by the airscrew, so the liftco has to be set higher to simulate the determined power ON stall speed. In the game the power OFF and ON stall speeds are the same, due to the code, whereas in real life they vary. As such the liftco used probably doesn't match normal liftco data that only focuses on the wing's liftco without counting the air blown from the propeller. When determining the stall speed one firstly checks for ww2 data available, but usually has to calculate it based on wing area/weight/max AoA etc, since ww2 stall speed trial data is often very arbitrary and varies greatly from different trials of the same airplane. The data can give a good guideline though, and sometimes can be quite precise like the P-39 stall data from NACA. Sometimes the ww2 stall data is just completely whack, like the Pilot Manual of the F6F-5 stating a stall speed of 71 mph (62 knots). This must be due to instrument errors since it's quite illogical that the F6F-5 would have a lower stall speed than an A6M Zero. (Wingload of 37.2 vs 23.0).

Below is the in game power ON stall speeds for the Spitfires and Messerschmitts. If you check ww2 trial data the Spitfire I and Bf 109E-4 had quite the same stall speeds in real life, so the Spit and Schmitt series should be quite historical in game relative to each other.


Image - Image


P.S. I'm redoing the turn tests for all the fighters, now at 12 000 ft and 75% fuel. I will use this data for the Vehicle info instead of the sea level turn tests for the next update. This should give data that is more similar to the ww2 turn data available, which was usually from mid altitude trials. Just takes a bit of time since it requires a 5 minute test per fighter for all 99 fighters :D .


<S>
/Robert


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 Post subject: Re: 109G14
PostPosted: Wed Aug 14, 2019 2:02 pm 
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Posts: 158
Pakrat wrote:
Please dont mess with the trim autorepeat. It has already been desensitized and any more would severely alter the way many pilots fly. Leave it alone!

The auto trim key is like a cheat code for the realistic FM.
It shouldn’t be available on any plane.
Finn


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 Post subject: Re: 109G14
PostPosted: Wed Aug 14, 2019 7:38 pm 
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Posts: 158
Bollock, this deserves its own thread. Could you re-post it separately? I'd love to see this happen.
finn


bollok wrote:
The cooling effect of MW50 allowed "higher boosts" to be used without detonation.
IIRC. The Bf109 could run MW50 for up to 10 mins at a time and had enough water reserves for 20 min total use.

In the same way, 150 grade fuel which the allies used late war in EUROPE worked in the same manner.
The additional cooling effect allowed higher boosts to be used without detonation.

Hence why I think the +18lb boost level on the Spitfire XIV should be re-instated as BST2 (with+ 21lbs as BST3).

If the spitfire xiv was safe to run at +21lbs for 5 mins WEP, it should be good for say 7.5 mins at +18lbs before engine overheats.

If you know anything about how the throttle body worked on a spitfire, you would realise that they were fully automatic.
As you increase the engine REVS with the throttle lever it automatically increases the pre-determined BOOST to match.

UNLIKE many American planes where you had to MANUALLY adjust engine RPM and BOOST!

Image


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 Post subject: Re: 109G14
PostPosted: Thu Aug 15, 2019 10:26 am 
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I have good data on the Griffon engine so shouldn't be a problem to program that. Question is will it be of a large enough benefit to the player, or will it make the boost system for the Spitfire XIV more clunky, resulting in people accidentally choosing boost3 instead of 100% and overheat their engines more frequently? +18 lbs for 7.5 min is 200 hp less for nearly the same heat build-up penalty compared to +21 lbs for 5 minutes.

What is the exact reason why one would want less hp in a fight at almost the same heat build-up penalty, and also having to handle 3 boost stages instead of 2 boost stages? In what way would it benefit you? If the benefits outweigh the drawbacks then I can of course implement it for the next update. Maybe should make a voting poll?


Image


Also after two weeks of turning tests I've finally finished clocking the sustained turn rate and radius for all 100 fighters at 12 000 ft, 75% fuel, no flaps. I will add this to each fighter's Vehicle Info data for the coming FL2073 update :-).


Image
Image


<S>
/Robert


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