Pilum

OK, good info! :thumbup: So there seems to be quite some weight of evidence supporting that the rudder became stiff at high speed as well then.

To be honest, I have not read through the entire thread but I don’t think it is as simple as a Newtonian physics analysis looking at the rocket, rail and exhaust plume balance in isolation because the exhaust plume will introduce a ”source” of high speed flow medium being generated in close proximity to the wing. This will change the flow field both behind and (since the flow is subsonic) in front of the wing. So since the flow field will changes around the wing this will most likely produce some up- or downward translational and pitching forces as well as either an acceleration or retarding horizontal force on the plane even if the rocket/rail/exhaust gases were in perfect balance. The question of exactly how large or significant this effect would be would probably best be judged by experiments or CFD but IMHO it is not possible to judge purely by reasoning. :)

British test pilot Eric Brown had the following to say (Source: Royal Air Force yearbook article ”Four of the finest” from 1975, page 23) about the Me109 G6 he flew in 1944: ”Another inherent shortcoming was the lack of any rudder trimming device, necessitating the application of moderate right rudder during climb and considerable left rudder during a dive. Thus, although Gustav pilots tended to use a bunt into a steep dive as an escape manouvre during dogfights, they had some very heavy rudder and elevator control forces to contend with as speed built up” I’m usually sceptical to single source pilot qoutes but since Brown was a respected test pilot and during his career flew many different types of aircraft to access their flight characteristics, the quote above does indeed support the view that both the rudder and elevator in unison should become more heavy at high speeds.

You know what Yo-Yo? I think Echo38’s post above was dead on and a good summary of where things stand and would have been a good point to end the debate. However, now you introduce new unfounded claims that ” If you take a look at this tabs comparing to full functional trimmer tabs, you can see that they have much less length along the stab chord and the much less length along the span (much, less area). So, as it was written above these tabs are not for RETRIMMING the airplane in the way a pilot wants, but only to compensate any manufacturing deviation form the standard.” Based on what evidence? How can you ”see” this? I don’t agree and here the argument is being rehashed again and not by me and then topped off with the Parthian arrow ”There are always some people who always know better”. Well, I agree to this only it seems applicable to more than one person in the debate. So I think we will just have to agree to disagree on this one.

Apparently this bears repeating: The current DCS Me109K4 adjustable tailplane trim range may well be correct for a certain elevator trim tab angle. So the Me109G6 Klaus Plasa flies may well mirror the Me109K4 in DCS with the trim tab set at a certain angle. However, the point is that the Me109K4 elevator was equipped with a trim tab that allowed the trim range of the adjustable tailplane to be moved and what we are asking for is that this tab be adjusted slightly to allow the tailplane trim range to a more nose heavy range that is all. Again, a DCS pilot controlled option would be nice but a change of the elevator hinge moment coefficient mimicking a tab adjustment upwards would be OK as well. :)

So now we need to prove that an adjustment of the elevator trim tab would have the effect that the 109 became more nose heavy? Maybe the 109 is special in this case? Any other plane would react as expected but we need to prove this specifically for the 109? Or is it the K4 that is special so we need data for that? Where is the goalpost? As explained before, the trim tab is a basic aerodynamic trim device. Either you believe a trim tab can change trim or you don’t. Take the DCS 109 K4 and max it out and see how much you need to change the elevator angle to trim out. Go external. You can barely see the delta in elevator angle. So the change in elevator angle the trim tab has to generate is minimal. Frankly, questioning that a trim tab could do this is like questioning that moving the elevator will have an effect on pitch or that turning a steering wheel on a car will make it change direction. I have never driven a 1965 Mini Cooper but still I believe turning the steering wheel on a 1965 Mini Cooper will make it turn. Can I prove it? No. I don’t have the data. I don’t think I can find the data. However, maybe I can find some data on another car. However, since I cannot find data on the 1965 Mini Cooper a valid standpoint would be that the 1965 Mini Cooper does not respond to steering wheel inputs? Give me a break…..:doh:

You know what? You keep bringing up that some of the devs do this for a living and that they have access to former WW2 pilots. Well, I have seen former WW2 pilots on Discovery CH say some pretty weird stuff and the devs sometimes have some interesting ideas and explanations as well as witnessed in the exhaust thrust discussions we have had earlier. None of us are fault free. In addition, some of us here in the forum have a pretty solid background in aerodynamics, both in terms of education and work experience and some of us have also worked in the aeronautical industry for a living. So IMHO what is redundant is your implication that we don't understand the issue and should "read the thread". In addition, if you had a basic understanding of how a trim tab works you would not call it magical. It is in fact a pretty simple and powerful trim device one you understand how it works :)

Concerning the trim problem this is IMHO a no-brainer: No pilot IRL would fly around in a plane that was not in trim if you could avoid it: The first thing you would do on landing your 109 as currently implemented in DCS would be to adjust the tab slightly up to move the adjustable elevator trim range to a suitable range. So if we don’t get a game controlled tab, just introduce a constant to the elevator hinge moment coefficient. This would be the equivalent of setting the tab at a slight angle. This would not only eliminate all the discussion in the forum but also be more realistic since no pilot will fly around holding a constant forward pressure on the stick if he can avoid it by adjusting a tab. Period. This type of adjustment was done all the time on these types of aircraft because no two elevators, ailerons or rudders were the same due to production issues. Usually the actual structure underneath the fabric was wood or sheet metal and an ever so small cusp or angle on the trailing edge translates to a significant hinge moment which the tab can and was used to compensate for. If there is no tab there are other methods: For example on the Spitfire the same effect was achieved on the ailerons by doping a piece of string on the trailing edge to balance the plane in roll. Legend has it that some test pilots after a while became so adept at judging needed trim that they would on landing not only be able to tell the riggers where to apply the string but also how long the piece of string should be :) On the issue if something is wrong or not I think I’ll pass on that one because based on experience this always seems to be such a sore point. But to sum up: No pilot will willingly fly around in a plane that cannot be trimmed if it can be avoided and since the IRL 109 had the tab it makes sense to use it also ingame in DCS. Sorry to be so blunt but should this discussion really require more than 30 pages and that some people who have a valid point are belittled because they may perhaps be a bit off on the technical description of the problem?

The problem with metal covering on control surfaces compared to fabric is that the control surface needs to be balanced around the hinge to avoid flutter problems. Given that most of the control surface is behind the hinge line this means that a large amount of weight (e.g. lead) needs to be added forward of the hinge line to balance which leads to the complete control surface being much, much heavier than just the difference in weight between the metal and fabric coverings.

Here is a link to a quite comprehensive guide to ECM & ECCM. I know it’s in Swedish but it has some nice explanatory pictures and you can always copy text and run it through Google translate. I tried and while the English grammar sucks it’s still understandable.:smilewink: I agree with Edddie that while the exact inner workings and algorithms used in ECM and ECCM are closely guarded secrets the internet provides sufficient info to build a much better model than we have today in DCS. The current ECM model in DCS is bluntly put WW2 technology: Broad band noise jamming. In addition, the burn- through distance is IMHO way to far out. Especially since even a post-WW2 noise jammer would most likely be more of a cover pulse jammer and consequently the burn- through distance would be much closer. The book also gives some hints as to how jamming should look on the scope: Instead of the single noise jamming bearing we get today in DCS, multiple bearings, false targtes etc would be more appropriate. The book also mentions things like towed decoys, cross-eye jamming, illumination of chaff by active jamming, DRFM techniques etc. so really there is quite a lot to go on. It also mentions ECCM techniques, like noise jamming triangulation via data link or even passive triangulation by a lone aircraft. Today the radar model we have in DCS is also based on guesswork: Detection distances, susceptibility to beaming, chaff, look down angle etc. so there is no reason really not to do the same type of assumtions and model ECM based on a guesstimate as well. So really, if there was an ambition to improve the ECM & ECCM modelling in DCS this could be done quite nicely based on open sources and, like Dr Strangelove would have put it, it only requires the will to do it! http://www.google.se/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CCEQFjAA&url=http%3A%2F%2Fwww.luftvarn.se%2Fhot%2Ftklv.pdf&ei=7wR0VdiYBqOlygOPyYJw&usg=AFQjCNHu_m72ky0zG8pLQDssDbHJWtUFrQ&bvm=bv.95039771,d.bGQ

Well OK, I always assumed 1800 hp because the K4 Kennblatt said 1800 hp but if we assume 1850 hp then I agree 24 m/s sounds good!

But using the thin brown line in your own figure in post #8 this shows a climb rate of 23.5 m/s at 1800 hp which agrees with my calculation Yo-Yo :)

Well I think it is a weak statistical argument: If you look at the trend line for the 109 (thin brown line) this is drawn based on a scatter of data points at 1300 hp and then just one point at 1450 hp. Now if the point at 1450 hp was just a teeney-weeney bit higher or lower then the result at 1800 hp (i.e. the K4 DB605D at 1.8 ata) would be impacted significantly. So any error on the part 1450 hp value has a huge impact on the results. Hardly a sound statistical foundation surely? OTOH, if you read off the Me109 climb rate at 1800 hp in Yo-Yo's figure in post #8 you get 23.5 m/s which I can only agree with ;)

+1 :)

Too bad you don't see sights like these any more.......

I agree completely! I just wanted to temper expectations about the flight performance because sometimes people think that a canard is so great because it provides an upforce and not a downforce like you have on a tail configuration when in fact the upforce you get on the canard is cancelled by the resulting downwash on the wing and the trimmable Clmax you can get out of a canard configuration is as a rule lower than a tail configuration. But now I'm beginning to sound like Ridder...:music_whistling: But yes, I think it would be nice to have a Viggen. As an opponent I guess an AJ would be the best choise because setting up Mig-21bis against a JA-37 "David" seems rather unfair :)

Yo-Yo: I don’t think I quite follow your logic in this thread: On the one hand we are to dismiss the calculated results from Messerschmitt and Focke-Wulf because they were calculated and not based on flight test. However, you yourself now do a calculation to shows trends that coincide with your viewpoint that the climb rates in DCS are now correctly modeled. Is that not a double standard? In addition, I don’t think you can make the sort of simplifications you do in your method of calculation: In post #1 you claim: ”The second simplification is that we intentionally neglect exhaust thrust and radiator drag. First of all, at climb they have opposite signes and approximately equal”. Where did you come up with that? Where is the proof that it is so? I’m not at all convinced you can make such simplifications and in fact I think I think the very reason you get the results you do proves the point. But if we are to treat this scientifically, If you claim that you can neglect these since they cancel out then the onus is on you not me to prove it is so. I summed up my arguments about what I think the climb rate should be for both the K4 and the Dora and my method of calculation here so no need to reiterate that: http://forums.eagle.ru/showpost.php?p=2398986&postcount=3 Regarding the trend chart you posted in post #8, I in fact compiled a similar figure showing the climb rate for the Me109 with different power to weight ratios (P/W) about a year ago which I have attached below. Granted, this compilation is for 2 Km altitude but translating this to the sea level then the climb rate target for the K4 at 1.8 ata should IMHO be around 23.3 m/s not the 25-26 m/s which seems to be the currently targeted climb rate in DCS. So to sum up: Sorry, but I’m more inclined to trust the Messerchmitt and Focke-Wulf calculations rather than your calculation as outlined in post #1 above. Especially since they agree so well with my own calculations. :)

I would love to see the Viggen as well but do not have too inflated expectations concerning the flight performance! :smilewink: True, Viggen has good low speed characteristics which has always been a SWAF requirement due to the dispersed road basing system planned for times of conflict and this has also given the Viggen good momentaneous turn performance. However, the stationary turn performance is poor. This is due to the Viggen being a very stable design so the canard is highly loaded which creates a lot of drag, especially in turns. So since the Viggen will make only ONE very tight turn before you are out of E, make it count! So yes, having the Viggen would be great but the true strength of the Viggen does not rest on flight performance but on the aircraft’s systems such as the radar, ECM, data link and that it was tied into a good integrated control system which gave the pilot very good situational awareness. However, while I have been impressed by the DCS FM, the ECM modeling in DCS leaves much to be desired to put it mildly..... Putting a canard on a plane is no magic bullet and the Swedish aeronautical community has always been split on the subject . SAAB’s choise of a canard configuration for the JAS39 Gripen was in fact vociferously opposed in the early 80’s by one of, if not the best aerodynamicist in Sweden, Professor Sven-Olof Ridder.

So far only in flight sim forums under user name Holtzauge (I originaly registered in DCS for the jet part and missile flight modeling which is why it's Pilum here). Recently I also posted some stuff in another contemporary flight sim forum (no names :music_whistling:) but unlike DCS where we can have these interesting FM discussions, the devs there seem to put it mildly not very interested in a dialogue which is why DCS IMHO is the best flight sim environment right now. When it comes to publishing, yes well one can dream and when I retire I plan to do something but that alas is still some years away.:(

Well, concerning accuracy, I have the same experience with my model: In the beginning (about 10 years ago), the assumptions I made and parameter settings I had in my C++ simulations did not always match IRL data so well. This was partly due to parameter settings but also due to that some effects which turned out to be important were not included in the beginning. However, simulation being an iterative process, this was ironed out and the number of lines of code grew. Consequently, when I today add a new plane, I just add the basic input parameters and the results tab well with IRL data from the start. Like you, I am pleasently surprised that when new data arrives that I did not have before, this usually confirms my modelling based on the limited set of input parameters I had when I did the modelling. As an example, one aircraft I modeled based on the only data I had at the time (speed and climb) turned out to have the same acceleration and turn performance as measured in flight tests. Another example is actually the K4: I did the basic modelling based on climb and speed data. Then later on I got hold of diagram data calculated by Messerschmitt for the momentaneous turn performance of a K4 at 6 Km altitude which was quite close to my estimate. So in the same sense as you are reassured by the A-10 data, I have over the years been reassured by the correlation between my results and the IRL data I have gathered so this is the basis why I think I’m pretty close in my estimates now for the Dora and K4. On the subject of data from the 30’ and 40’ we seem to have different opinions: I think most calculated data by respectable firms is pretty close. At least the calculated engineering data that is unadjusted by marketing and management in order to secure contracts. So if anything, the calculated estimates you see will most likely be on the high, not low end if they have received TLC from marketing and management. This is why I doubt the calculated K4 and Dora climb data by Messerschmitt and Focke-Wulf we have discussed previously would be on the low end. Getting back to wartime calculated engineering data: I have the greatest confidence in their estimates: It is the same here: Just because we have computers and CFD today does not make us more accurate: As the saying goes in simulation: crap in gives crap out so it all depends on the tuning. So a 10% deviation may be just as applicable to CFD or in flight tests due to measurement errors as for calculations. I believe you can get very good results using the slide rules and nomogram engineers used at the time. Again, it all depends on the assumptions and simplifications you make in your calculations and I have a humble view here: The guys that did the diagrams and figures we today post were professionals in their field and they did this on a daily basis and they did it for a living. So I think we should be very careful before we dismiss data from the 30´and 40's just because it was calculated. And before someone post a calculation from the 40’ that is obviously wrong to prove I’m wrong, I am again talking about a judicious compilation of data to find the mean, i.e filtering out outliers, be they flight measurements or calculations. Finally, sorry for teasing: But if you are convinced that the engineers back then compensated for atmospheric effects and even aircraft mass without mentioning it why would they treat exhaust thrust any different? Because performance results without exhaust thrust mean NOTHING! :smilewink:

No, you have it backwards: I agree with the first part: That over the years it has become clear that we disagree on a lot of issues. However, I think we draw very different conclusions from this fact and what the problem might be. :smilewink: Anyway, if you have anything constructive to contribute then post it but please spare us your analysis of who understands what because that will lead nowhere.

Just want to clear up some confusion: When I referenced other sims as high end I mean in terms of ambition: They explicitly targeted historical accuracy and in that ambition they strove to get as close to IRL performance as possible and I can't recall any of then defending figures that were far away from historical data that's all. Some people here seem to think that just because one is using a more advanced FM this means it is inherently more accurate and therefore whatever results it produces must be right which is wrong. At least if the issue is the measurable climb rate and climb times like we have been discussing here. Whatever computer simulation you have, this is a model of reality and is parameter controlled and a FM is no exception and it will give no better model of reality than the tuning it receives. So a CFD FM could be way off while a good old scripted 6DOF FM can peg down basic flight performance much better. It all depends on the parameter settings..... I currently make a living running simulations in the telecom industry so I'm quite familiar with the issue and as a collegue of mine (who has a doctorate in Physics) jokingly puts it "Tell me what results you want and I will simulate it". :smilewink: Jokes aside: Good to know the climb rate is being tuned and let's see what we get!

Beginning with the propeller modelling, I use two different methods, both of which certainly handle propeller solidity and also account for efficiency as a function of disc loading, advance ratio and tip Mach effects. One of which I have described in detail here: http://forums.eagle.ru/showthread.php?t=127918&highlight=propeller First of all I don’t think my calculations are pessimistic: I have modeled more than 20 aircraft over the period of 10 years and tuned this continously based on IRL data. The reason I think I get pretty close is simply that the results I get out of the simulations usually tab pretty well with historical data. When I say historical data, I mean an average of the data available. I tend to trust data like Allied pilot’s notes of pilot operating charts and German Kenblatts rather than individual flight tests. Why? Simply because tests even at the best of times data have a normal variance around a mean. There area also measurement errors, data taken at different tempertures etc. In addition, using individual tests opens up the field to cherry-picking, both high and low outliers depending on the agenda. So yes, IMHO you can rely on tests but then you have to compile a statistically significant number, convert them all to the same weight, power, standard atmosphere, ensure that they include position error and Mach corrections etc. etc. Getting back to the Me109K4: To me 25-26 m/s at 1.8 ata is too optimistic based on my modelling. True, there is not much IRL data to go on here either but I have modelled Steig & Kampfflesitung climb rates as well and they tab well with Kennblatt data on the K4. I also get quite close to the climb times here which are good indicators since they integrate the climb rates and any large deviations is bound to come up here. Here the DCS FM model seems too optimistic since both the K4 and Dora have way to good climb times compared IRL data. In addition, while DCS may be the latest and best simulator, I think there has been a general consensus about what figures to target in earlier high end siumulators like IL-2, Aces High etc. and while these may not have as an advanced FM as DCS, I have respect for their developers and the tuning they have performed over the years. To the best of my knowledge these developers have roughly the same opinion as me as to what the IRL figures to target should be and to me it looks like DCS as it is currently tuned a bit too optimistically when it comes to climb performance. How optimistic? Well I believe that my simulation numbers below are closer to IRL performance: Sea level climb rate Fw190D9 at 1.8 ata MW50 W=4270 Kg around 22.5 m/s http://forums.eagle.ru/showpost.php?p=2347279&postcount=64 Sea level climb rate Me109K4 at 1.8 ata MW50 at W=3362 Kg around 23.3 m/s http://forums.eagle.ru/showpost.php?p=2397641&postcount=9 I’m not saying I have to be right. You can of course continue to claim that my figures are too pessimistic. However, you appeal to my common sense and I will do the same to you: What is more plausible? All previous high end flight sims targeting the wrong figures (which generally agree with mine) and IRL data from firms like Focke-Wulf and Messerschmitt not containing exhaust thrust and making no mention of it even though we both agree it has a significant impact on performance? Or is the current modelling of the K4 and Dora in DCS simply too optimistic? Which is more plausible? Finally, please note that this input is done with the best intentions and should not be interpreted as criticism: DCS is IMHO the best WW2 flight sim out there. I'm just trying to provide input which I believe will make it even better :)

Time will tell, time will tell :)

Well, I guess that is a goal we all can agree to! Can't wait to see what a historically correct Spitfire Mk9 climbs like though:music_whistling: