Jump to content


  • Content Count

  • Joined

  • Last visited

Everything posted by Holtzauge

  1. I'll say no more on the subject but truly intriguing that you have the experience to be able to make that parallell. 😉
  2. Pre-ordered BON. The developers of this excellent sim deserve all the help they can get. Especially looking forward to the Spitfire Mk14! 😍
  3. OK, that chart was interesting: Even if the figure is for an F4U with quite a different wing planform the principle I was after should be present there as well but it looks like the partial span flap effect on the lift gradient is less than I expected which then would not explain why there seems to be such a large change in pitch attitude when changing speeds in-game with the P-47 with flaps down......
  4. I just had a look at the last chart you posted JtD and having given it some thought here is a theory of why you get a slightly different lift slope for the case with flaps deployed in-game: I would expect the game to use some sort of bound vortex panel model and this has the advantage that it captures the wings 3d effects. Now I’m focusing on the lift slope in your figures, i.e. the dCl/dalfa, and if you take the wing 3d effects into account, there is a large discontinuity in the lift at the flap joint when they are deployed. This results in a large vortex shed there which induces changed aoa’s in both the outer and middle panel. Another way of looking at this is that your effective aspect ratio goes down when you deploy flaps. The easiest way to visualize this is to consider the aoa when the outer panels are just unloaded meaning all lift is generated by the middle part which then in effect becomes a wing with a very short span. Of course it’s a bit more complicated than that since the outer panels will still work a bit like horizontal winglets but the idea still captures the first order effects I think. From aerodynamic theory we know that the lift slope dCL/dalfa is a function of aspect ratio so I would expect the lift slope to be lower with flaps meaning you need larger changes in attitude when speed is changed , i.e. just like your measurement´s in BoX shows. Thoughts?
  5. Just sent a PM with the BMW801D thrust figure attached: I guess you already have the "Widerstansdaten von Flugzeugen" table with aerodynamic data? If not I can PM that as well. If you compare the static thrust in that table for the Fw-190 A8 (1836 Kp) with the figure I just sent you, you can see that the averaged thrust line they have drawn into the diagram hits ca 1836 Kp at q=0 Kp/m**2. This leads me to suspect that the figure I sent you is reliable and that the drawn line is used for T/O calculations and the like. Interestingly, in the figure the "actual" thrust line is much lower initially and then getting higher as the plane begins to move, probably due to the prop being unable to absorb all the power until some forward speed is gained. Anyway, whats interesting is how low the actual forward thrust is, i.e. the prop efficiency, at lower speeds.
  6. Neat analysis JtD! Very interesting to see that BOX is actually overestimating the drag due to flaps for the Fw-190A8. However, since it seems that turn rate a lower speeds is overestimated (at least for the P-47) this would indicate that thrust is being overestimated. As a happy coincidence, I actually happen to have a figure showing thrust as a function of dynamic pressure for the BMW801D at 1800 Ps. Alas it is just a figure and I don't know the provenance so its difficult to judge how reliable it is but its the best I've got. IIRC then you did a test with the P-47 earlier at 240 km/h IAS and if I read of the thrust at q=272 Kp/m**2 (240 km/h IAS at SL) I get a thrust of around 1400 Kp. By my estimate that corresponds to a prop efficiency of around 0.69. This is pretty low and I would not be surprised if the prop efficiency used in BOX at that speed is higher. For the Fw-190A8 at 4400 Kg I get a best SL turn time of 21.8 s at 240 Km/h IAS with 60 deg flap in my C++ simulation. Going faster or slower than that increases it, e.g. at 220 Km/h IAS it goes up to around 24 s and at 260 km/h IAS to around 22.5 s. Maybe someone can volunteer and do some tests in-game with 60 deg flap full fuel load and see what SL turn times you get at 240 km/h IAS and then going faster and slower than that to get some more data points? Addendum: The C++ numbers above are for 1,42 ata boost.
  7. Maybe the P-47 is even more exceptional than the other BOX planes but I think the low speed performance is in general better than IRL in BOX and as has been pointed out above, it’s not totally clear if it’s a flap or thrust issue. Speaking for the latter, the legacy Maddox Il-2 had an issue with prop efficiency at low speeds that was quite marked since you could fly much slower than best climb speed and climb just as well. This was tuned and got very much better but my gut feeling is that it is still a bit better than it should be. Also, I had a long discussion with a developer about the P-51’s prop efficiency in the DCS forum a few years ago and the early Me-109 K4 there could really hang on its prop before this was tuned. Moving back to BOX, I remember with fondness Monostripzebra’s slow speed videos (unfortunately removed from YouTube) showing Il-2’s helicoptering onto Stalingrad rooftops and P-40’s and I-16’s prophanging STOL-like takeoffs and landings, bouncing up and down on runways at crazy aoa’s etc. So it seems it’s difficult to get the low speed handling and performance right in flight simulators in general and not just in BOX. OTOH this is hardly surprising: Considering theoretical aerodynamics and flight mechanics I would say that if you were to draw a diagram with modelling difficulty on the y-axes and speed on the x-axis you will get a so-called bathtub curve: High on the ends and lower in the middle. Why? Well on the high end you have compressibility effects: Subsonic drag rise, Mach tuck and buffeting etc. while on the low end you get larger and larger regions with major flow separation affecting both lift and drag and in addition, prop efficiency is very difficult to predict. Personally I have spent a lot of tuning effort on both ends of the “bathtub” in my C++ model and while I can afford the luxury of waiting while the numbers are being crunched this is for obvious reasons not an option in BOX where everything needs to be calculated within ms. So maybe there is a limit to what can be done here but without knowing any details about the exact nature of the BOX modelling I’m guessing these parts (high and low speed characteristics) have some sort of script overlay on the basic (I’m guessing panel based) FM. As an example, I would be very surprised if the FM models the Mach tuck effect by modelling a shock wave gradually developing in the inner wing section leading to a flow separation which in turn reduces the downwash on the stabilizer/elevator leading to a nose-down pitching moment. I would rather guess that it is some sort of rule overlay on the basic FM just as I’m assuming that the stick forces, control column shaking and aileron falling off due to flutter have all not been modelled in detail but are rather rule based meaning they can be tuned. I would guess that this also applies to the low end range of speed so that it should in theory be possible to tune the in-game prop/lift/flap efficiency somewhat. Of course it’s difficult to deliver solid proof that some of the slow speed antics we see today in-game are not also possible IRL but I have to admit that there are some video clips like those Monostripezebra posted that I find hard to accept as being possible to replicate IRL. That being said I agree with YIPPEE that the most import thing is to get the relative speed, climb and turn rate between the planes right but here my impression is that BOX has made great strides lately so this does not stick out as a big issue anymore as far as I can tell. In addition, now that the AI are far better behaving and have been weaned of their propensity for prophanging with full flaps all the time I think the low end speed handling is of less importance but OTOH I sympathize with the MP players where I can only guess that whatever low speed “exploits” there are will be found and used so I’m all for a tuning of this and based on the input in this thread so far a guess on my part is that a reduction in slow speed propeller efficiency and maybe also the wing/flap lift & drag would be a step in the right direction.
  8. OK, well I get 21.1 s at 212 Km/h so close enough. 😉 BTW: Did you try going faster? For me the corner speed is around 240 Km/h which was why I posted the 18.2 s because that was the lowest turn time I got.
  9. @Voyager & @Legioneod: I have the P-47 D-30 modeled and at sea level with 65" boost 45 deg flap I get 18.2 s for a 360 deg turn at @ 242 Km/h assuming about 50% fuel (ca 12000 lb) so it looks like the Thunderbolt should turn pretty well at low speed if you drop the flaps and don't carry a full fuel load. That being said I have done no tests myself so I don't know how the P-47 is behaving in-game but I have seen complaints. What kind of turn times are people getting in-game then that they think are too good?
  10. Finally got the P-38 J Lightning modeled in C++. Here are results for stationary turn rate: Time to do a 360 degree turn at weight 7332 Kg (16149 lb): No flap: 20.6 s @ 339 Km/h Combat (8 deg) flap: 19.3 s @ 319 km/h 45 degree flap: 16.8 s @ 270 Km/h So quite close to the numbers in the turn time charts JtD posted earlier and also quite in line with the in-game 45 degree flap turn test as well. So as far as I can see the current BOBP modeling seems close and the Lightning with 45 degrees Fowler flap should turn quite fast with a small radius. Question is do you want to go there? However, if you do find yourself at low speed in a knife fight it certainly looks like the Lightning delivers!
  11. Have not checked all the numbers but that table fails a simple sanity check: Just look at the turn times given for the Me-109K4 and Spitfire Mk14 at 6000m: The table lists the K4 at 31.2 and the Mk14 at 39.0 s, i.e. the K4's turn time according to the table in that book is 20% FASTER than the Mk14 when in fact it should be about 10 % SLOWER. As Oleg Maddox once said about another title: "Close that book and never open it again".........
  12. Don't know if the wing profile shown in airfoiltools.com for the Tempest is correct but if it is then 1.75 seems like a huge stretch: Granted airfoiltools only shows Clmax up to Re=1E6 but for a Hawker Tempest profile it gives only 1.25 as Clmax. Looking at the profile this seems reasonable: It is basically a symmetrical airfoil with a small camber and in addition, the leading edge radius is small neither of which is going to help the high aoa characteristics. In addition, the Clmax=1.25 is for a 2D profile and if you consider that the 3D wing has a spanwize lift distribution and also counting the relatively ineffective wing area in the fuselage you usually end up with a significantly lower number. As an example, a 3D Clmax of 1.35 for a wing profile listed at 1.5 or higher for 2D , e.g. the popular NACA230-series, would be reasonable. Applying that factor on the Tempests 2D Clmax of 1.25 yields a 3D Clmax of 1.13. So as things stand now my assumption of a Clmax=1.35 for the Tempest in the charts I posted above seems optimistic..... Link to Tempest profile data at airfoiltools.com
  13. Good summary unreasonable and I agree it would be good to ask the devs to look into this but I'm AFK for a week now hunting Moose so I was hoping someone else could carry the torch!
  14. OK so this is in line with what I got as well in the C++ simulation with Clmax=1.75. Reducing Clmax to 1.35 gives 15.4 deg/s at 235 Km/h.
  15. It did not show in my simulations either (using 1.35 or 1.75) in terms of getting a better turn rate figure. What it did do was to extend the speed range in which I could get the max turn rate down to really low numbers. Have you tried going slower? Like at 250 Km/h IAS SL? What turn rate do you get at those speeds?
  16. At full fuel load I get sea level climb rates of 23.3 m/s for G14 at 1.7 ata and 27.7 m/s for Mk9 at +25 boost in the C++ simulation. At 50% fuel it goes up to 25.0 m/s and 29.9 m/s respectively. So to me Il-2 seems a bit optimistic but I can't see that the Mk9 stands out in any way. However, as I recall it this has always been the case with Il-2 but on the positive side most planes have higher than historical rates so the important issue of the relative performance is maintained to some extent anyway (Maybe with the exception of the G14 sea level climb rate which at 27.5 m/s looks rather optimistic).
  17. OK, so basically identical results. I use Clmax=1.35 for the Tempest in the C++ model. Well if that is the Clmax clean wing then 1.75 is way to high. With some angle on the flap then sure but clean wing no way. Probably has to do with the IAS position error just like on the P-40 and Spitfire and the manual stating what you would see in the cockpit and not the actual calibrated speed. I recall some rather heated forum discussions about this (position error being a thing or not at stall speeds) a while back......
  18. Tempest Mk5 turn performance simulated in my C++ program yields these results at +11 boost sea level +15 deg C standard atmospheric conditions: W=5221 Kg best turn speed 293 Km/h gives turn rate 19.8 deg/s W=4974 Kg (400 l fuel) best turn speed 299 Km/h gives turn rate 20.8 deg/s @-=PHX=-SuperEtendard, Do you think you could test the Tempest in-game like you did the other planes for a comparison? I think it was mentioned that the in-game Tempest currently has a Clmax of 1.75 modeled? Just out of curiosity and since the effect of Clmax has been discussed I did a run with this and while the best turn rate does not go up that much it turns out that you can keep a very high stationary turnrate down to very low speeds, all the way down to 230 Km/h in fact, which reduces the turn radius by a lot and gives you the option to cut a very tight corner inside someone's turn without loosing speed: W=4974 Kg (400 l fuel) and Clmax=1.75 best turnrate pretty flat at 21.7 deg/s from 290 Km/h all the way down to 230 Km/h.
  19. Sure, IIRC I have both +9 and +11 boost modeled so if you give me the weight I can do it after work today.
  20. OK, so here are the numbers for sea level I get in my C++ simulation. I use standard atmosphere 15 deg C and IIRC then you use the autumn map right? If that is so then we are comparing same conditions. I'm really surprised with how good Il-2 is: My C++ simulations run pretty quick (takes 5-10 s to get the numbers on i7 4 core 3.4 GHz) but in BoB all this is being done in real time so once again we can see what a good simulator this is! The level of accuracy is simply outstanding. When I started off doing these comparisons between my C++ models and the state of the art flight simulators more than 10 years ago the level of accuracy was nowhere near as good as this is. We can be very happy with what we are getting for our money. I post both the results for the speeds you tested at and also what the simulation thinks are the optimum speeds for best turnrate. For the K-4 at the same 3361 Kg, 1.8 ata: 280 Km/h 18.1 degrees/s, at 310 Km/h 19.3 degrees/s Bf 109 G-14 3266 Kg (400 liters of fuel) 1.7 ata: 280 Km/h 18,7 degrees/s, at 300 Km/h 20.0 degrees/s P-51D-15 4343 Kg (690 liters of fuel) at 67": 280 Km/h 17,2 degrees/s, at 273 Km/h 17.3 degrees/s P-51D-15 4170 Kg (450 liters of fuel) at 75": 280 Km/h 19,0 degrees/s, at 286 Km/h 19.2 degrees/s
  21. OK, thanks for the info. I can't run the numbers today but tomorrow evening after work CET I will do a simulation with those numbers and see how that pans out. I think the comparison I did was originally to compare the Dora and Pony and that the K4 was added later at full fuel load which is more like 296 Kg according to Kennblatt but without the MW50 which adds another 63 Kg for a total of 359 Kg which is close but not quite 388 Kg the rationale for which now escapes me 5 years later......
  22. OK, interesting that the P-51 is better. How much fuel (%) did you use in the test? Is there a way to get the exact weights you had in test (all up) because that is what I use in the simulation. Both Clmax and power can get you a higher sustained turnrate: If you take any of the figures I posted above, increasing Clmax translates the left hand part of the curve up to the left, i.e. better turnrate at lower speeds (right hand curve stays in place) while keeping Clmax constant and getting more power keeps the left hand part of the curve in place while the right hand part gets moved up to the right, i.e. higher turn rate at higher speed. So the plane is at Clmax at the apex of the curve.
  23. Gotta love the latest release and especially the P-51 which is absolutely lovely and my new favourite ride! Anyway, concerning the relative turn rate between the different planes it’s a lot to do about the assumed boost and weight of course and IMHO the Pony should not be penalized for a high internal fuel capacity so I assumed the same fuel load for the Me-109K4 and P-51D in the attached C++ simulation chart I did a few years back. As can be seen, even at full internal fuel and even at 1.8 ata the K4 beats a Pony with a similar amount of fuel. Also interesting is how much better the K4 is at 8 Km. IIRC then if you decrease the P-51 down to 67” boost (i.e. translate the right hand part of the P-51 curve down at bit) then the C++ simulation indicates that the Dora and Pony are pretty evenly matched in terms of turn rate but the P-51 will do it at a lower speed than the Dora. However, when it comes to the stationary turn rate the K4 should have a slight advantage even at 1.8 ata so at 1.98 ata the difference will be even bigger with the right hand part of the K4 curve translated up to the right.
  24. My hat is off to the developers! What a fantastic update! The Tempest and P-38 are really nice but the P-51 is my new favourite no question. And the new pilot physics: Have to admit I was sceptical at first when it was announced but it’s simply great. Especially taken in combination with the new AI behaviour (no more prop-hanging AI!) and that the AI are also affected by blackouts. Then, to top it off 150 octane options for the Pony and Spitfire Mk9! Absolutely fantastic release!!!
  25. Have no fear: I have it on good authority that both cows and moustaches will be modeled!
  • Create New...