Jump to content


  • Content Count

  • Joined

  • Last visited

Community Reputation

730 Excellent

1 Follower

About Holtzauge

  • Rank

Profile Information

  • Gender
    Not Telling

Recent Profile Visitors

1161 profile views
  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?
  • Create New...