Pilum

Yes, the climb rates you posted above seem a bit on the high side. This is the climb rates I get out of my C++ simulation from sea level to 3 km altitude: Engine and power setting? Valid choises: 3 = Junkers Jumo 213A Start und Notleist mit Mw50 3 Alt(Km) v true(Km/h) v ind(Km/h) climb(m/s) climb (fpm) 0.00 298.74 298.74 22.65 4470.28 0.10 299.83 298.44 22.60 4461.40 0.20 300.94 298.14 22.55 4450.97 0.30 302.07 297.84 22.51 4442.17 0.40 303.21 297.54 22.45 4431.09 0.50 304.37 297.25 22.40 4421.08 0.60 305.55 296.95 22.34 4409.50 0.70 306.75 296.65 22.29 4399.58 0.80 307.97 296.35 22.23 4388.08 0.90 309.21 296.05 22.18 4378.26 1.00 310.46 295.75 22.13 4366.85 1.10 311.63 295.45 22.08 4356.93 1.20 312.81 295.15 22.02 4345.40 1.30 314.02 294.86 21.97 4335.58 1.40 315.24 294.56 21.91 4324.13 1.50 316.48 294.26 21.68 4279.53 1.60 317.74 293.96 21.34 4212.49 1.70 319.02 293.66 21.00 4145.47 1.80 320.33 293.36 20.79 4103.06 1.90 321.65 293.06 20.63 4071.60 2.00 323.00 292.76 20.53 4052.40 2.10 324.24 292.47 20.46 4038.63 2.20 325.51 292.17 20.38 4023.18 2.30 326.79 291.87 20.31 4007.78 2.40 328.09 291.57 20.25 3996.30 2.50 329.42 291.27 20.20 3985.89 2.60 330.77 290.97 20.13 3973.76 2.70 332.14 290.67 20.08 3963.46 2.80 333.53 290.37 20.03 3953.23 2.90 334.95 290.08 19.97 3941.26 3.00 336.39 289.78 19.92 3931.14 EDIT: Sorry for the formatting, will post a figure next time..... Concerning speed: I get 686 Km/h or 426 mph 13 k altitude and 688 Km/h at 26 k altitude so not much deviation there......

OK, that's good to know but again, maybe the plane was clinically dead before that? API through engine casing causing major oil leak, radiator and/or coolant circuit out of action? All these thing would kill the plane but it would take time. If you pour in 130 hits in a very short time it's difficult to know exactly how this is modeled and when you killed the plane IMHO. Another thing that is strange is how few times the pilot got killed in the tracks you posted: I would expect it to be pretty unhealthy to sit like that and take 130 rounds API from dead astern since the API core from a 50-cal should have no trouble punching through back- and headrest armour. This is of course unless the DCS model is so advanced that it models the rounds starting to tumble due to penetrating fuselage and hitting radio and other equipment before reaching the pilot's armour :P

OK, good to hear that you agree about the expected difference in climb rate. I plan to do some more tests later this week to see if I get similar results as in the tracks I posted in the OP. Concerning how I estimated climb rates I have two methods for this: One is using a C++ program I developed which can calculate speed, climb, turn, dive and acceleration performance etc. and another simpler Excel spreadsheet for ballpark calculations. I post data from the spreadsheet below so you can see what assumptions I made for the 175 mph case. I could not paste in the table but I think you can see the assumptions made in the text anyway. Granted, Specific Excess Power (SEP) climb rate is only valid for small climb angles which is not really true for WW2 fighters but it is close enough to get the ballpark numbers for comparisons I think, at least to compare relative performance between 120 and 175 mph climb speeds. P51D Mustang Mass (Kg) 4445 Span (m) 11.26 Wing area (m*2) 21.79 Cdo 0.0176 Aspect ratio A 5.818614 Pi 3.141593 Cdi 0.01972 Cl 0.537017 Oswald factor e 0.8 Mach 0.229142 vTAS (m/s) 78 a (m/s) 340.4 ra (Kg/m*3) 1.225 q (N) 3726.45 loadfactor n 1 g (Kgm/s*2) 9.81 Propellerefficiency n 0.8 Engine power (hp) 1670 Tprop (N) 12606.36 Texhaust (N) 681.6327 Ttotal(N) 13287.99 D (N) 3030.397 IAS (m/s) 78 SEP climb estimate (m/s) 18.34845 SEP climb estimate (fpm) 3611.899 Propeller diameter (m) 3.39 engine rpm 3000 reduction ratio 2.088 Propeller rps 23.94636 Propeller advance ratio J=v(n*D) 0.96085 Cp=P(ra*n^2*D^5) 0.163208

Yep, and be sure to only shoot a few rounds and wait to see the effects before adding more. One thing that would be really interesting would be to to shoot a few rounds in the P-51 radiator on full open from behind and wait and see. Will the engine seize after a period of time or won't it? Maybe a job for the cowling Mg131 mounted close to the sight line in a close formation flight :smilewink:

Ok, that is interesting and if you don't use tables but actually calculate the efficiency from blade theory then that is certainly impressive, especially if you manage to capture the reduced Cl/Cd ratio that results due to the higher disk loading in a way that approaches the NACA measured data :thumbup: Concerning my tests, I simply clocked the values between altitudes in Tacview so I may be off there and I'll do a few more and post some results later this week for verification. Based on a reduction of prop efficiency from 80.4% to 68.5% in DCS I would expect to see a dramatic reduction in climb rate then between using 175 and 120 mph. Do you agree and what would be your estimate? My climb rate estimate was in the order of 2900 fps at 120 mph and 3600 fps at 175 mph. So here there is a substantial difference. Is this in line with what we should expect to see in DCS as well? i.e. a reduction in climb rate of around 20%?

Good that you took the time to do this! :thumbup: For me it was an eyeopener to see the difference between AI and player damage model. Based on the AI statistics where in many cases 100+ hits are needed to bring down the AI and it almost always either fails catastrophically or continues to fly forever as a sieve, the player model seems impressive. I have two observations after looking at the tracks: The one being that it still seems to take 100-130 rounds to make the Dora fail catastrophically in most tracks. The other being that in the few tracks where you manouver away and it took longer, the kill hit count went down to 40 and 50 in a couple of cases. Now my thinking is that the Dora may already be dead after a few tens of hits in many of the tracks but because the fire keeps pouring in in most tracks we will never know. So a better test of what it takes to kill a Dora with 50-cal would IMHO be to give it a few short bursts, not only from 6 O'clock but also in deflection angles. To me it looked like the engine was registering hits and the engine did quit after some time which would be expected in most cases as well I think since it's probably that in many cases it's the engine auxillaries that die and this takes some time (like in track 20). If this would bring us down to the previously estimated 20 rounds for a kill I don't know and that may be a stretch but the way the rounds keep coming in in many tracks kind of clouds the issue IMHO because the engine may be dead due to leaking oil or coolant and before that shows will take time and hitting with 100 + rounds in a short time may hide this. One final observation: One thing that did not come up (except the obvious empennage failures in the externals) was text messages in the debrief stating control failure due to control wire or linkage shot away which I would at least have expected in some tracks. Is this there or is it missing?

Just did two tests from standstill in Dora: Test 1: Full thrust with brakes on, released brakes when tail starts to lift then full rudder left. Result: A complete 180 after 10 m run no damage :smilewink: Test 2: Full thrust with brakes on, released brakes when tail starts to lift then full rudder right. Result: Quite a bit slower due to the slipstream rotation which the rudder has to overcome but still a 180 to the right albeit ending up nose down with ruined prop after a short run this time. Conclusion: Since forward speed basically zero, rudder force must be due to propwash. So I don't know what the coloured streamers in the OP are supposed to show but there is certainly propwash modelled and I for one can't see the problem......

Well actually prop efficiency is not that much reduced at 800 TAS (At least not in my C++ simulation): This of course depends on altitude but I made a simulation diving from 500 Km/h TAS 20 deg dive from 9 Km alt and reached 800 Km/h TAS at 7.5 Km alt at which time the prop tip M=1.08 which is not too bad and prop efficiency is actually quite good at 0.8. However, a little later at 875 Km/h TAS at 5.7 Km alt the tip speed is up to M=1.11 and here the efficiency has dropped dramatically to 0.75. So things happen rather fast at these speeds..... I don't get why the Dora should be so much worse? I get about the same results for the Dora with the same initial conditions. Why would the Dora's prop efficiency drop so low as 65% at 800 Km/h TAS?

OK, so to take an example and to be more specific and use some real numbers: I'm assuming the following: Altitude: sea level ( Using 0 Km altitude as an example to show the delta in climb rate. Results concerning the delta in climb rate due to reduction of prop efficiency due to lower advance ratio (J) and higher Power loading coefficient (Cp) are in the same order at 1-2 Km altitude) P51D data assumed: Power P: 1670 Hp at 3000 rpm @ sea level Weight W: 4445 Kg Prop dia D: 3.36 m Activity factor AF=112 Prop reduction ratio: 2.088 Prop rps n: 3000/(2.088*60)=23.95 rps Advance ratio J=v/(n*D) Power loading coefficient (used in NACA report) Cp=P/(ra*n^3*D^5) =0.16 So using these numbers to estimate climb performance assuming prop efficiency is reduced according to NACA wartime report “The selection of propellers for high thrust at low speeds” (WR-L-483) figure 10 for Cp=0.2 for the 4 to 6 blade curve: J=0.96 at 175 mph gives prop efficiency circa 0.8 J=0.67 at 120 mph gives prop efficiency circa 0.67 The reason for using an interpolation between the 4-6 blade curve in figure 10 is that the report is for blades with AF=90 and not like the P51 D which has AF=112. Note that according to the report author, it is perfectly reasonable to equate a larger number of thinner blades to fewer wider blades (third paragraph page 13 “Concluding remarks”). So five blades 5X90=450 solidity can be assumed to be equal to four blades 4x112=448. At 120 mph (54 m/s) with prop efficiency assumed 0.67 : Climb rate circa 14.74 m/s (2902 fpm) At 175 mph (78 m/s) with prop efficiency assumed 0.8 : Climb rate circa 18.35 m/s (3612 fpm) Comparison of climb performance with prop efficiency assumed constant at 0.8: At 120 mph (54 m/s) with prop efficiency assumed 0.8 : Climb rate circa 18.41 m/s (3624 fpm) At 175 mph (78 m/s) with prop efficiency assumed 0.8 : Climb rate circa 18.35 m/s (3612 fpm) So here there is not much of a difference with this assumption. This is also what seems to be the case in DCS, i.e. there is not much of a difference if one chooses to climb at 120 or 175 mph IAS which could be an indication that the prop efficiency is assumed to be the same at both speeds? Is this the case or how is a prop efficiency at low speed modeled in DCS? Link at NASA NTRS for report WR-L-483: http://ntrs.nasa.gov/search.jsp?R=19930093644&hterms=wartime+report+483&qs=N%3D0%26Ntk%3DAll%26Ntt%3Dwartime%2520report%2520483%26Ntx%3Dmode%2520matchallpartial%26Nm%3D123

Sorry for not replying earlier but I'm on vacation so I don't have access to my computer and consequently I can't check up either the advance ratio or prop efficiency in a high speed dive. However, as soon as I tire of Grecian wine and sun I'll post some numbers :smilewink:

Well I'm totally with you on the authenticity part and I have read quite a bit about the time period as well and again, if you are looking for authenticity then you should fly against the Me109G6 because that was the ride most LW pilots had at hand at the time. I have not had a chance to think about what kind of boost would be appropriate for the P-47 but it may well be as you say that in this case a high boost version is needed to "balance" the sim experience. However, that being said I fail to see the P-47 being better than the Dora in all aspects because of increased boost because the Dora will at least turn better and probably climb better as well. The Dora should also be better down low but due to the turbo supercharger the P-47 will be better at altitude and also dive better. Again, there is some kind of balance here. However, give the Pony 75" boost and the B4 Dora is doomed because it has nada in the toolbox: It will be slower, turns worse, not dive as well and have poorer climb.

Could not help noticing there has been a Pony boost inflation and we are now at 75" not 72" :smilewink: Jokes aside, while I respect the majority of the arguments put forward for 75" boost since appropriate fuels seems to have been available at the time period the sim depicts, I can't help being a bit cynical and hear "I want all the advantages I can get when playing this sim" when I read some of the post pointing towards "historical accuracy". The Me262 was brought up as an example why we should learn to live with superior performance and not talk about balance. Now IMHO the Me262 is actually a poor example because there is actually an element of balance here that makes this setup interesting to fly in a sim: While the Me262 is superior in speed, it has no chance in the turn. As some of the previous posts pointed out in a very good way this can actually make for some interesting situations because it is pretty difficult to shoot down a Pony that is aware that you are there and pass after pass makes a slight jinx when you are are about to fire. So this is actually an interesting sim scenario where there is an element of balance since it's an extreme energy fighter versus an (in comparison) extreme angles fighter. Now exchange that for a 75" Pony against B4&MW50 Dora and have the Pony attacking. Just how exactly will this fight become interesting? Even if we start with energy parity what can the Dora do? Climb? No Turn? No Extend? No Dive? No. Going from sea level to ceiling, exactly where is the Dora supposed to have parity or an advantage? However, as pointed out before, in the current setup one is doing better down low, the other at altitude, ergo an element of balance making this sim fun to fly. The 75" Pony will simply have both the angles and energy advantage. Period. In addition, if we compare the current 67" Pony to the current Dora the small turn rate advantage the Pony has now will with 75" boost become much bigger since the added power will enable the Pony to drag it's lower wing loaded wing around quicker making turning a no contest. In the context of a sim I think interesting to fly is pretty much synonymous with balance and that was the point I was trying to make in my previous post. However, if 75" is enabled as an option then by all means if what rocks your boat is to have both angles and energy advantage then enable it and go on your turkey shoot. BTW: Since it seems to be so popular to have "options" then why not model a C3 & MW50 Dora as well? By the same argument, if you don't like it then you don't have to enable it. For those looking for historical accuracy, it would have been better to have the numerically more prevalent Me109G6 in DCS, some with gunpods and the majority with 1.3 ata boost and no 1.4 ata Notleistung enabled. In addition, to mirror the proficiency state of the majority of late war LW pilots set the AI on "Average" and you're good to go!

I don't think the 72" should be added to the Pony. Why? For balance! I know balance is a dirty word and if it comes to tweaking the IRL performance for any aircraft in DCS then I'm totally against it. I agree that getting as close to the IRL performance as possible is the goal and this also seems to be DCS view. Kudos to them. However, what I'm for is plane set balance. Here I think DCS have struck just the right balance: You have two aircraft, the B4&MW50 Dora and the 67" Pony for which the IRL performance is pretty close. However, one happens to be better at altitude and the other at low level. The alternative? If you take a 72 " Pony and start checking in the boxes (speed, climb and turnrate etc.) you will find that it will dominate the Dora from sea level to service ceiling. Will this make flying in the DCS fun and interesting? No, at least not for me. I can see the objections coming: "But the Pony did fly with 72"!" This is historically correct! True, but this will make for a very dull experience unless Pony pilots don't like challenges and want Doras served on a platter. So while I'm totally for historically accurate FM and abhor changing FM to balance a sim, I'm totally for balancing the plane set. What I mean is that you have to choose a plane set that is suitably matched: Both the Hurricane and the Me109K4 flew in 1944. Would modelling both make for an interesting matchup in a sim? I rest my case. It is here in this aspect that I think DCS has struck the perfect balance with the B4&MW50 Dora and the 67" Pony. One is slighly better down low, the other up high. No one dominates.

Completely agree. It may take one or it may take a lot. It all depends on where you hit. However, the question is how should it look if you start collecting statistics? Right now it seems that the average amount of 50-cal needed are in the order of 100 instead of 20. So IMHO a (min, average max) distribution of what it should take to down the Fw-190 should look something like (1, 20, 50) rather than (20, 100,200) with the "1" being the head shot you mentioned. Interesting and plausible observation and yes, I'm not sure I've seen 13 mm hits in the statistics, only 20 mm but OTOH I usually chicken out via the escape button after a few hits because I have been more interested in dealing out punishment than receiving it so far but maybe I should let the AI hose me down to get some 20 mm statistics as well. OTOH the fw-190 AI seems rather reluctant to fire even though they are in a favourable position...... If the P-51 can absorb on average 15-30 20 mm shells then I think we need to redesignate the P-51 from Flugzeug to Panzerkampfwagen :smilewink: So based on the statistics, it looks like the current damage model is off by about the same margin both for HMG and cannon, i.e by a factor of 5 which at least would make it "balanced". However it for sure looks like this could do with a workover if thing are to be more realistic and that is if I understood it correct the intentions with the DCS WW2 modules? In addition why does it always have to end catastrophically with wings falling off and the rest burning intensely with exterior showing the hallmarks of having been hit by a missile fragmentation warhead? Whatever happened to engine seizure due to AP in the engine block, engine seizure due to radiator shot, pure structural failure like tail aileron, rudder or stabilizer falling off, no visible damage only non-manouvering due to dead pilot? Huge explosion due to lucky shot etc. etc. What is the developers view on this? Anyone?

Funny how differently one can read a text. I actually think they acknowledge the ducks are in a row but that the line may not be perfectly straight :) I notice you selectively highlight this: "Where it does have an effect, it is generally to boost the scores of high-capacity HE shells while reducing those of lower-velocity AP cannon shells and AP bullets, which is validated by the Luftwaffe's decision to focus on chemical rather than kinetic energy in developing their aircraft weapons." While avoiding the main message that preceeds it: "In conclusion, while it is admitted that some elements of the calculations – especially concerning the relative weighting given to kinetic and chemical damage – are open to criticism, in practical terms the results stand up quite well. Changing the method of calculation affects some scores but has surprisingly little effect on the overall 'order of merit' of the destructiveness rankings" So some elements are open to criticism BUT the analysis stands up quite well and changing the method calculation has surprisingly little effect! In addition how shall the developers use your criteria "I have opinion, which is based on memoirs, that steady 1-2s burst with 6x.50 was enough for a kill."? Is it enough to close your eyes, get a 1-2 burst off to get a kill? How many of those bullets need to strike? No one is contesting (at least not me) that cannon are better than HMG. I actually prefer to fly using German armament but if STATISTICALLY around 100 strikes of M2 are needed then this seems strange. To get back on a constructive track, some sort of scoring system and relative destructive power between different loads needs to be implemented. The best I've seen so far is a circa 3.5 ratio between 151/20 and M2 but I'm open to constructive input. On the other hand maybe the damage model for 151/20 is off by the same margin? Will be interesting to see if there is the same scale factor for the 20 mm loadout and if STATISTICALLY significantly more than 5 rounds are needed to down a fighter sized target. Then it will be a general problem and not just related to the M2 rounds.

A perfectly valid question and this is a good diagram: First of all the Pony is limited to min 23 deg pitch AFAIK and taking this as an example (although we can do so only to show the principle) , if the advance ratio (J) in the picture goes to 0.5, then if we had this propeller we would get a prop efficiency of only 0.6 as opposed to the optimum 0.85 because pitch lower than 25 deg was not possible even to set. This illustrates the problem but note this diagram is only valid for a certain design and power loading and it would look different depending on the number of blades, blade size, profile and disc loading, i.e. what is the air density and what is the power being absorbed. The problem in case of the Pony is that it may not even be possible to go to 23 pitch because the prop may not be able to absorb this power: By that I mean that if you fed the WEP power into the prop at 23 deg pitch it may overrev and go beyond 3000 rpm. So how to solve that? Well you increase the pitch which would result in a higher blade aOa. So taking another example, say we have J=1. Looking in the diagram we would want to set pitch 25 deg and get 0.85% prop efficiency. However, say the constant speed governor needs to go to 35 deg pitch to absorb the power and limit the revs to 3000 rpm. Then the prop efficiency is reduced to around 0.72. So again, the question is how is the propeller modeled in DCS? At low J values and high disc loadings like climbing at slow speeds like 120 mph, is the prop efficiency still the same as at 175 mph or is it reduced? If so by how much and how is it modeled in the prop hanging scenario?

Ok, so in your opinion, what is a reasonable relative between M2 and MG151/20? I have Gustin/Williams book "Flying Guns of WW2" and IMHO they seems to have their ducks in a row. What sources do you want to cite?

Granted, I have only flown DCS a few days now and mostly looked at climb performance but I think you have a valid point here: In the few tracks I've collected so far and analyzed the hit count it seems on the high side. Usually due to the hanging props antics I nail the AI in a few deflection passes when they are presenting the upper side in a vertical deflection shot so whatever is hit of the vitals are not going to be armour protected. Even so, doing the hit counts it's like OP says: needing 50-100 or even more is not uncommon. I also agree with the analysis: German WW2 analysis indicate twenty 20 mm hits needed to down a "Boeing". IIRC then the estimate was that about a quarter of that was needed to down a fighter. Emanuel Gustin and Anthony Williams have a power table in the link has the rifle calibre 7.92X57 referenced as 1 in destructive power. They then access both the 0.5" M2 (12.7x99) and the MG151/20 (20x82) in terms of destructive power based on chemical and kinetic energy and come up with a power factor of 4.6 and 16 respectively, i.e. about a factor 3.5. So doing the maths and assuming five 20 mm rounds needed, it should take about 18 M2 rounds to down a fighter: 5*(16/4.6)= 17.4 Of course, all of this depends on where you hit and 18 hits on the wing will not do, but on the other hand 18 in the engine, radiator, fuel tanks and pilot etc will. So statistically, looking at tracks it seems reasonable that the average should land up in the twenties and not the hundreds :music_whistling:

Again, the primary problem as I see it is not in the absolute values as such but that the DCS propeller modelling seems to be too optimistic when the prop blade load is high, i.e. when the disc loading is high in combination with low prop advance ratios such as when WEP is applied at low speed. Even if it's hard for human pilots to hang on the prop like the AI due to control issues in DCS, it's still perfectly possible to control the P51 at 120 mph which was the speed I did the tests at. The point here is should the prop efficiency degradation if you are slowing down to 120 mph IAS in a dogfight be 5 or 20-25%? I think it should be the latter. IMHO this also is a central issue in getting the sim as close to IRL performance as possible. If this is off, it will unrealistically favour those who fly in DCS using TnB verusus those who BnZ. Both the Pony and the Dora were as we know designed for the latter. Propeller design is always a compromize between climb and speed characteristics: This can also be seen in WW2 NACA and German reports where prop designs are sometimes referred to as a climb or speed prop design. A climb prop will have a high activity factor (blade area/disc area) and relatively thick blades and camber to enhance high Cl operation. The high speed prop on the other hand will have a relatively thin blades and less camber to avoid compressibility problems due to the high prop tip speeds WW2 fighters had. So how do you get the best compromize? Well you build in enough thickness and camber in the blades so that climb does not suffer too much. This means that you are operating on the higher end Cl (aOa) in the climb case, just before your profile drag starts to become excessive. In this way you have as thin a blade as you can get away with which will postpone compressibility effects and consequently give you good high speed performance as well. So as long as you keep an IAS that is in line with the design in your climb you are fine. Now the problem that happens if you go to a lower IAS is that to absorb the power from the engine the prop blade aOa (not to be confused with pitch) has to increase to maintain RPM. This increses the prop blade loading outside what it was designed for and the drag of the blade increases a lot meaning you are expending torque to overcome the increased blade drag which is not helping your climb. As I said before, my suspicion is that the DCS prop modelling is too optimistic here and that this effect (blade efficiency decreasing at high aOa) in the sim is not as large as it should be. At least that is what the 5% reduction in climb rate and prop hanging antics indicate to me. Again, it would be good if someone involved in testing or design of the prop modelling in DCS could comment on this.

I'm assuming a constant speed prop and that the revs are maintained at 3000 rpm in the C++ simulation. I went back and checked my track and I did notice that that USARStarkey has a point and I do have a bit of a zoom initially and that was a bit sloppy but I guess anyone can reproduce the climb test and make up their own opinion of how 120 compares to 175 mph IAS climb. To me 120 mph climb rate seems to optimistic and I for sure think the prop hanging you can do today seems weird.

True, but I start off at 500 m and zoom to reduce speed but by the time I reach 1000 m I believe I'm pretty stabilized. So the actual measurement is from 24 s into the track until 1 min 29 s, that's where 1 min 5 s comes from.

I actually bought DCS for the jet modules initially but now with the coming addition of the Fw-190 D9 I decided to get the P-51D module and try it out to see how this sim fares in comparison to other WW2 flight sims. First of all let me say I'm impressed by this simulation. I have over the years tried a number of different flight sims and my impression of the P-51D flight modelling in DCS so far is favourable. That being said there is one thing I have noticed that IMHO sticks out and that is the low speed behavior: I started noticing this since the AI hang on the propeller in a way that looked really strange. This brings back memories of the early versions of IL-2 in which it was also possible to hang by the prop in low speed scenarios. In DCS this property does not seem to be limited to the AI only because when I started to explore the low speed regime myself I found that this was also part of the player flight model. My suspicion is that the low speed propeller efficiency modelling, or more precisely the low advance ratio (J=v/(N*D)), modelling is a bit on the optimistic side. To test if this was true, I set up a test scenario to test climb rates at different speeds. As the benchmark, I set climb at 61" 2700 rpm with 175 mph IAS. I then did another test with 120 mph IAS. I took the climb time from 1 to2 Km altitude out of TACVIEW and got climb time 1 min 2 s and 1 min 5 s respectively. Both tests with 9542 lb initial weight. (Track files attached) Note that the difference in climb time in DCS is just 5%. I believe that this is to low. Granted, I don't have climb charts for the P51 showing the climb rate as a function of IAS but based on IRL data of other aircraft this should be more bell shaped with the climb rate being lower at both the higher and lower IAS speeds. IMHO it looks like this is true in DCS for speeds higher than the optimum climb speed but that the climb speed does not suffer as much as it should when going as low as 120 mph. (BTW: the reason I did not do 67" 3000 rpm test in DCS is because cooling is insufficient and I blew the engine in the 120 mph IAS climb scenario). I have over the years developed a C++ simulation program that I have tinkered with and which gives rather good correlation in most cases and which I use to evaluate different flight sims from a performance perspective. However, I don't have the Packard Merlin 1650-7 boost 61" 2700 rpm case modelled so I had to compare the WEP 67" 3000 rpm case. With this boost I get climb times from 1 to 2 Km at 1 min 2 s for 175 mph and 1 min 16 s for 120 mph, i.e. a difference of 23% at 9542 lb weight. In addition, looking at tracks in general, it looks like this issue affects both the P51D and Fw190D9 and IMHO the low speed helicopter antics of the AI currently looks weird. So I would be interested to hear the developers view on this and if they agree that the low speed propeller efficiency modelling right now is a bit on the optimistic side and if they have any plans to address this? Pilum aka Holtzauge Tacview-120mph.txt.zip Tacview-175mph.txt.zip