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LLv24_Vilppi

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About LLv24_Vilppi

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    Tokyo, Japan
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    Classical Martial Arts, NLP, Machine Learning, Education, Photography, Music, Physics / Science in general :)
  1. I think you misquoted a bit my misquotation :D The fault lies in me of course as I was the one who initially made the whole topic quite a lot murkier. But if I'm allowed to continue in the off-topic a bit, what I meant is that the weight increase does affect the TOP speed (i.e. the speed that the plane can achieve with maximum thrust, as limited by the engine) in level flight. How significant this is, is -- as noted by others -- the real question here. And as Klaus noted, the shape of the plane does change (I was making an oversimplification there) due to the needed trimming of the elevators (or the whole tail wing) for the speed and weight balance. I believe that when designing an aeroplane, these are questions on optimising the qualities of the plane for its purpose (fuel economy, speed, stability, etc). And like you noted, for racing planes it makes sense to get the best lift-drag ratio to the higher speeds, but this does not change the fact that if the plane is made heavier at that point it does need more lift to fly, and more lift with the same wings mean more drag, right? And if the engine can't create any more thrust to overcome that increase, the speed will drop. Again, if this increase in drag is the most significant thing and how big of a relative impact it has, depends on the plane design.
  2. Ah, re-reading the thread now I see I kind of jumped the gun and misquoted you by taking that one sentence out of context (sorry for that). While I stand by what I said (and looking at your post, I don't think we even disagree), my comment wasn't really relevant to Fern's original question. The original discussion was about the relative difference between planes and the overall significance of the effect that weight has against top speed, and as Klaus and others explained, there are other (possibly more significant) factors included than the one I commented on.
  3. I'll get back to this once I'm sober, but just a quick remark on this exact sentence: The sentence indeed seems correct. But, the heavier plane also needs a better weight to power ratio to make into that same optimal speed. Hence, what happens with the same maximum power output (in which we achieve the maximum speed) when the mass of the plane increases?
  4. Is that really true? I know it is true in vacuum, when no other forces are acting on the object, but how about in the case of an aeroplane? Classic mechanics: F=ma. In case of aeroplane flying on constant altitude the lift needs to be equal to G, or in other words F_l-G=0. That means that as G=mg, F_l (lift) needs to change accordingly to the mass of the flying object (hopefully an identified one), as g is constant. And how does a plane that does not change its shape create more lift? By increasing AoA. And if a plane increases AoA, it also increases drag. I do believe this is pretty much high school physics, at least in the Finnish educational system. And if I'm wrong or rude, I'll apologise tomorrow. It's just the booze and frustration talking.
  5. Um, I'm sorry I must be more drunk than I thought (not the first time that's happened, mind you), but is this then only about whether the developers used the term "E(nergy) retention"? I also thought that we are talking about how the sim works. What benefit would that information about use of the term bring to the accuracy of the simulation?
  6. Oh, then I've rather misunderstood. But I'd like to think you'd forgive me as in the end this is exactly the forum about the math behind the sim.
  7. I think he's talking.. and then I read your next post: Exactly (and that's why I wrote that I don't disagree with you). But during simulation one DOES need to make these predictions as the players are not going to restrict themselves to the conditions that the published, limited empirical tests give results to. Yes, if the flight model does result in similar energy state after a similar kind of manoeuvre in the simulation as the empirical results show, one can verify that something's been done right, but that doesn't guarantee that everything else is right. After that it comes down to understanding how robust the model is. In practice, quite often, the more robust one tries to make the model, the less accurate it usually is (compared to the empirical data), and vice versa, the more accurate one tries to make the model, the less robust it usually is. And going back to what I believe Venturi is trying to say (sorry mate, not trying to put words into your mouth, so please correct me if I'm wrong), in order to create a robust and accurate model one would need to be able to grasp the highly complex and chaotic nature of turbulence and other related phenomena. Again, this all being said, I don't know how robust the best computationally feasible models (for commercial combat flight sim) for aerodynamics are, so I can't comment on this exact topic, but I can see what Venturi is trying to say. I might be a bit incoherent in the text above, as it is rather late in Tokyo at the moment, and I am rather drunk. I'll try to edit and fix it to more coherent text tomorrow, but for the meanwhile, give a benefit of doubt
  8. This does not conflict with anything that has been said by JG13_opcode, and this is not a comment directed to him, but just to be pedantic, the energy of an isolated system does not change. An aircraft is of course not an isolated system, but loses energy by interacting with the material it is travelling through. For you who haven't studied the matter deeply: it's called air. In my case it may contain sometimes bullets, tree branches, and occasionally intermix with dirt and water, but those cases should be handled separately. If I'm allowed to play an English to English interpreter just a little bit here, I think that what Venturi is trying to say is that while you can clearly calculate the energy difference between the two points, you also need to know exactly how much chemical energy was transferred into kinetic energy and in what efficiency by the engine in order to know how much energy was lost during a manoeuvre. If the balance between the engine performance during the manoeuvre and the loss of energy is not correct, this might cause some unwanted behaviour in the flight model. How significant this might be, I cannot tell.. That being said, engine performance in different flight regimes must be a well studied problem, and there must be quite good models for that. And while we do not know exactly how the energy was lost during each exact point of time during the manoeuvre (this doesn't seem like a trivial problem), the total energy lost is then of course easily calculated. So, how critical this is for simulation is definitely arguable. Just as a closing note, there is an old maxim which I've learned to cherish: "all models are wrong, but some are useful". Even F=ma isn't strictly speaking correct. We just usually can ignore the effects of general relativity in WWII context, as I believe the error won't be that significant even with the REALLY FAST Me-262 In simulation it is always also a balance between computational complexity (keeping those frame rates up) and accuracy and of course trying to match the performance with multiple, sometimes conflicting sources.
  9. I think this is a fallacy. The claim is not against that the recommended engine limits are different from the documents (this would honestly be a silly argument). The claim is that the regulations were not always followed by the pilots and there indeed seems to exist historical documentation supporting this fact. What that historical evidence cannot provide us is quantifiable data. I.e. how long and how much abuse the engines could withstand in field conditions. What objective sources (or even anecdotes) has anyone provide to support the fact that rules and regulations were always strictly followed by everyone during missions in WWII? To be honest, I would even go so far as to say that this stand is not falsifiable at all and therefore moot. Sheer amount of attached documents does not mean that a person's claims are correct. Don't let that fool you. Read the actual documents and see what the people who wrote those reports are ACTUALLY saying, without any assumptions or extrapolating what they MIGHT be saying based on your own opinion.
  10. I'd say that with the Allison Engineer's letter, the interviews and (auto)biographical information, including Greg's answer there is enough materials to make a strong case to present it to the devs to allow the P-40 engine to run longer and with higher MP. The problem here is that there are no formal tests on what should be the actual times for the engine modes (or have I missed something), so in the end it is up to the devs to decide if they want to stick to the official manuals as a policy to leave any guess work out, or if they would include this kind of information in the game. Here's a suggested draft, feel free to fill out any facts as they have appeared in this discussion and edit. Let's see if we can make a community created letter to the developers: -- Item: P-40 Allison Engine (V-1710-39) performance Currently in the game, the engine limits for the P-40 are as follows: [insert the limits here] There are several anecdotal references that point to the fact that these limits were not observed strictly during combat, without any catastrophic effects to the engine: [placeholders] 1) Russian pilot NN states in his memoirs... [a book reference] 2) In the interview ..... [magazine / URL reference] 3) GregP, the ? of Planes of Fame museum [some biographical information about Greg] states that.... [Link to the original discussion between GregP and Venturi]. 4) ... To corroborate the above anecdotes and interviews, there is an official letter from a Allison Engineer to the Commanding General of the Army Airforces Materiel Center, dated December 12th, 1942, where he confirms these reports of using the V-1710-39 engine above its recommended levels for prolonged periods without immediate detrimental effects. [Link / attachment of the letter] While we were unable to find any formal test data to show how long the engine can be run with different MP and RMP, we believe the above evidence shows that de facto the engines were run with higher settings during combat operations than their de jure limitations given in the manual without immediate detrimental effect. We request that the current P-40 engine limits in the game are re-evaluated in the light of the above evidence to allow more correct historical operation of the plane in the game. Signed, Richard A Nixon [or list of community members who are willing to sign this, or whoever sends it] -- I would suggest NOT giving any suggestions on what the times and the levels should be, but to let the devs figure it out themselves. We engineers can be petty and have our nerdish pride if someone comes and tells us how to do our work I also suggest we do not elaborate or write out too much on the materials to keep the suggestion short, a reference should be enough. Like I said, in the end we can only provide the evidence and present it in logical manner. The final decision lies with the devs and managers of Il-2: BoS/BoM in terms of where they want to take their product. Or they come back with a counter argument which we can then further discuss. EDIT: The Allison engineer's letter wasn't internal as I initially wrote, but addressed to the Commanding General of the Army Airforces Materiel Center.
  11. Sorry, are you referring to this thread: http://forum.il2sturmovik.com/topic/14420-reasons-why-i-severely-lowered-my-bos-flight-time-lately-bos/ I don't think it was shown anywhere conclusively that the gear change is indeed triggered by change in density. In fact, the reply from the developers was that the supercharger gear change is correctly modelled using static pressure: http://forum.il2sturmovik.com/topic/14420-reasons-why-i-severely-lowered-my-bos-flight-time-lately-bos/?p=229775 Or are you referring to another thread or post?
  12. Here's a relatively easy to understand article about aileron design: http://faculty.dwc.edu/sadraey/Aileron%20Design.pdf I'm not qualified to judge how accurate the model is (seems to omit at least the effect of wing torsion, so I wonder if it has other simplifications also), but at least the mathematics seem pretty easy to follow. Would you have a source for this? The article I linked above and quick Google search seems to suggest the opposite. Plus some people seem to say that fluttering (due to wing tip vortices) is a possible problem with ailerons extending to the tip of the wings (I believe these were RC people discussing the matter, so I have no idea how pronounced this problem is in bigger, heavier planes). I'd be curious to learn more.
  13. JtD, what's your intuition / educated guess / knowledge on this? Is the acceleration to the steady rate indeed that instatenous in reality (and if not, why wouldn't the report take it into account)? I.e. how big role does inertia, for example, play in all this? I honestly have no intuition at all behind this as I've never calculated anything similar, but the acceleration seems mighty fast to me. Assuming that Ze_Hairy's results are correct, just taking in to account the constant acceleration from the 0.5 sec time to given aileron deflection gives following results: 100 deg/s -> ~107 deg/s 110 deg/s -> ~119 deg/s 120 deg/s -> ~131 deg/s 130 deg/s -> ~143 deg/s Calculated as: 360 deg / ((360 deg / p) - 0.25 s) Where p is the average roll rate over 360 degrees reported by Ze_Hairy. I.e. Ze_Hairy's plot would be somewhat closer to the RAE given values, but still quite far off taking into account the acceleration as it is stated in the RAE report. Of course there are several factors in play, such as accuracy of the test (no disrespect meant at all towards Ze_Hairy here, that's just how experiments are), how BoS models the stick forces and delay to equivalent aileron deflection (i.e. is it even comparable with the RAE settings), are my calculations correct, etc.
  14. No, they are not. You got a "range" of values, minimum being 72.5 and maximum 79, with completely ignoring units. You may now have the last word as I will try hard to keep this as the last reply to you about this matter.
  15. Thanks again. Then we are indeed reading the same paper and interpreting it the same way.
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