Crump Posted May 27, 2016 Posted May 27, 2016 Unless they were using different weights, but that would make things pointless. I agree with that assumption. It is not an assumption...it is a fact. If you read the reports TASGI used standard methodology on all of these testing. An assumption would be the VVS and TASGI were stupid and did not conform to aircraft performance standard thereby producing completely useless information.
Crump Posted May 27, 2016 Posted May 27, 2016 Fact - the assertion or statement of a thing done or existing; Assumption - the act of taking for granted, or supposing a thing without proof; https://www.psychologytoday.com/blog/your-career-in-counseling/201110/facts-and-assumptions-what-is-the-difference-and-does-it Because you cannot look at the units and math, JtD, too realize those facts does not make it an assumption nor does implying that the conclusion is based on assumption make you appear any smarter. It is a fact the speed, weight, and power is the same as the quotient is the same. It is also NOT an assumption that a given amount of power will produce a give velocity in aircraft performance.
Crump Posted May 27, 2016 Posted May 27, 2016 BTW, JtD... You could have simply asked politely instead of posting your original statement of "fact" about my "assumptions'! I would have been happy to discuss it and despite your "assumptions" about me....recognize that I am fallible and open to locating and correcting error.
JtD Posted May 27, 2016 Posted May 27, 2016 Alll within ~1% of 510Kph using 1.2ata @ 2300U/min....Assumption, not fact. Wrong, in fact. At sea level FW-190A5 Handbuch says 505kph IAS at sea levelAll this data is TAS. As for your original assumption, please see attachment, from a transcription of the test report.
Crump Posted May 27, 2016 Posted May 27, 2016 (edited) All this data is TAS. It could be because of some simple facts they teach you in school JtD. EAS = TAS at sea level..... CAS = EAS at sea level... So, you can call it TAS or you can call it EAS or you can call it CAS!! All are correct but since our quotient is the same and the turn performance is at 1000 meters, it is EAS. Again, something they teach you in school. from a transcription of the test report. The transcription is wrong. 1. That does not match Vmax for 1.35 ata and is well beyond the normal variation. However, it clearly matches 1.2ata performance. The VVS report I have is not a transcription, clearly list's power in two different locations and clearly defines the continuous power as 1.2ata.... So.... Which makes more sense and is a fact. The transcription error that would have to make an assumption that the FW-190 data used by the VVS was WAAAAYYY off.... Or somebody simply wrote the power in the wrong spot and the VVS FW-190 conforms to the original power settings listed in the report!! Well the POH says 510kph EAS or TAS if you like....at sea level. 505 kph IAS + 5kph PEC = 510kph CAS = 510kph EAS = 510kph TAS at sea level. Ta Da!! Now not only does the POH say that 510kph EAS is achieved at 1.2 ata @ 2300U/min It gives great agreement with every other Focke Wulf document showing 1.2ata performance!! It is within 1%! Again, it is a fact in aircraft performance that a given amount of power will produce a given amount of performance. The quotient is the same in both charts. If the quotient was different....the Vmax would be different.... That means the weight and power are the same as the quotient is the same..... That is simply a fact. Edited May 27, 2016 by Crump
Crump Posted May 27, 2016 Posted May 27, 2016 The original uses the term "nominal power", JtD. I think your author thought nominal power was 1.35ata and not 1.27ata....
Irgendjemand Posted May 27, 2016 Posted May 27, 2016 LOL.. Thank you!! I already have one though. I do not think they could afford me! The more they should apprechiate your help and actually use it. I hope they might do.
JtD Posted May 27, 2016 Posted May 27, 2016 (edited) If this rambling* is your way of saying thank you - you're welcome. If not, I can't be bothered to waste more of my time. *Position error is irrelevant for EAS & CAS, you stated the data was IAS and it still is TAS. Simple as that, no need for page-filling posts. Edited May 27, 2016 by JtD
Crump Posted May 27, 2016 Posted May 27, 2016 I hope it helps! It is fun for me to "play detective" on some of these old reports.
Crump Posted May 28, 2016 Posted May 28, 2016 *Position error is irrelevant for EAS & CAS. This is signature worthy. By definition (google it) Calibrated Airspeed is Indicated airspeed corrected for position and instrument error. Equivalent Airspeed is CAS corrected for Compressibility. Explain how position error is irrelevant to CAS and EAS? On the rest of it I can see how you would be confused after the previous post going into some depth explaining how it it is EAS and the other five times 510 kph was mentioned how one typo of IAS would completely throw out the baby with the bath water and destroy your mind. It is TAS at sea level. We seem to have a hard time understanding that TAS = EAS only at sea level. Since the quotient is the same in our turn performance at 1000meters altitude....it is a fact that EAS is used.
JtD Posted May 28, 2016 Posted May 28, 2016 Explain how position error is irrelevant to CAS and EAS?Because it's already been corrected for.
Crump Posted May 28, 2016 Posted May 28, 2016 Because it's already been corrected for. Ohhh.... So obviously you did not read anything I wrote and just made an "assumption". Boy it sucks when people do that especially just to mouth off at their own "smartness" http://forum.il2sturmovik.com/topic/21001-fw-190/?p=360639 505kph IAS @ sea level using 1.2ata = 505kph IAS + 5kph PEC = 510 kph CAS = 510kph EAS = 510 kph TAS @ sea level Problem is it is not smart JtD. Pages of discussion would have been avoided if you had just know what the quotient is telling us. LOL 1. Go look at any FW-190A5 level speed chart and see what the power setting required to achieve a Vmax of 510kph. 2. The quotient is the same in both charts. If the quotient was different....the Vmax would be different..... http://forum.il2sturmovik.com/topic/21001-fw-190/?p=360555 The first reply to you should have been the end of the discussion because you were wrong in concluding "assumptions" had been made when the quotient verifies the physics as fact.
JtD Posted May 28, 2016 Posted May 28, 2016 Look Crump, the figures in the handbook are TAS. No matter how many red herrings, strawmans or whatevers you want to throw out, if you want to perform another sing and dance routine or stand on your head and laugh silly. They're TAS. End of story.Frankly, the misinformation you keep posting hidden among all the fog you keep throwing up will just lead to the following. If Han or whichever dev happens to see your posts he'll just take this as a reconfirmation that everyone in this community is an idiot, which is a bad thing. Real issues will then never get their attention. If folks who lack the proper education believe what you write, they will consider the developers a bunch of idiots because allegedly they keep making stupid mistakes, which is a bad thing, too. Not to mention, theses guys will be damaged for life having a load of nonsense floating around in their head. Clearly not a good thing, either. Therefore, your posts are damaging this community damaging the product damaging the relation between the devs and the community. This makes your posts a constant violation of forum rule 17. I'm certain the moderators and admins will not let this slide forever, especially considering that folks have recently been banned for less. In the meantime, however, you can expect me to at least point out the largest fallacies you're producing. Deal with it like an adult, or don't, I don't care. And just to repeat the issues at hand: The handbook figures are not IAS. 510 in Soviet tests was not reached at 1.2/2300 max. continuous power. Fw190 test results in sea level top speed vary more than 1%. I will have no problem repeating this until it sinks in. Thank you for your attention. 5
JtD Posted May 28, 2016 Posted May 28, 2016 (edited) Prove what exactly? That the handbook figures are not IAS? You think there's a chance for a Fw190 to achieve 650 km/h IAS at 6km, giving it a top speed of 900km/h? Use your common sense, man. That the Russian did not test at 1.2/2300? Given that it's not easy to come by, I've already provided the relevant snippet of a test report transcription. What's missing is any sort of proof for 1.2/2300. That the speeds varied by more than 1%? Feel free to look up tests, there are literally dozens available at http://www.wwiiaircraftperformance.org. Permitted contract speed tolerance was +/-3%. For a reason. What documents "he has" have impressed you so much? The ones that do not show that the speed is IAS? The ones that do not show that the Soviets tested at 1.2/2300? The ones that are no test reports? Edited May 28, 2016 by JtD 1
Brano Posted May 31, 2016 Posted May 31, 2016 It is not an assumption...it is a fact. If you read the reports TASGI used standard methodology on all of these testing. An assumption would be the VVS and TASGI were stupid and did not conform to aircraft performance standard thereby producing completely useless information. ...TsAGI or in original ЦАГИ
1CGS LukeFF Posted May 31, 2016 1CGS Posted May 31, 2016 Fw 190 You posted a video - how quaint. What is your point?
MiloMorai Posted May 31, 2016 Posted May 31, 2016 What better thread to put the video in than one titled 'Fw190' as this thread is.
L3Pl4K Posted May 31, 2016 Posted May 31, 2016 I post this in the Fockewulf Horror stuff, maybe this is a better topic. How good is the 190 nosedive performance compared to the real world performance. If i read this, Bf109 F4 vs. FW190 A2/ The A3 has a reliable and slightly more powerful engine, http://www.beim-zeug...35-5178712EEA61 Page 3 paragrah b: Google translate The comparisons were with combat power, about 20% of orbital inclination and flown via a respective difference in altitude of 2000m. It was found that the Fw 190 A2 in all heights won several hundred meters ahead. The steeper and more plunged longer was, was all the greater this advantage. However, also in this case, the slower is the Fw190 A2 on their speed limit displays as the Bf109. Me and ema33ig make a dive test from 4000m to groundlevel. The 190 fly with Kampfleistung nearly its topspeed. The 109 was 100m behind the 190, with same speed. On groundlevel the109 was next to the 190. At first glance it looks like, the 190 could not gain several hundred meters lead. Maybe someone with more experience, could investigate/eplain
RAY-EU Posted June 1, 2016 Posted June 1, 2016 The FW 190 A3 was better fighter more manubrable , better roll rate , speed and climb than the Spitfires MKV that was better than The Bf 109 F4 and G2 . With the FW 190 A3 we can not dogfight with Soviet planes or do 2 or 3 turns or you do not have exit with front shoots , and in that ways the victories and sucsesfull was for the FW190 A3 in il2 BOS is the oposite . Remenber that The rate victories Lutwafe vs Soviets were 25 : 1 ; so One Germany plane destroyed for 25 soviet planes destroyed So they have to ballance the Game but for that way it does not make to be a Historic Real Simulator
1CGS LukeFF Posted June 1, 2016 1CGS Posted June 1, 2016 So they have to ballance the Game but for that way it does not make to be a Historic Real Simulator
LLv24_Zami Posted June 1, 2016 Posted June 1, 2016 So they have to ballance the Game but for that way it does not make to be a Historic Real Simulator I think that Fw-190 is not 100% accurate as it is now but that is not true.
Crump Posted June 1, 2016 Posted June 1, 2016 LOL...original ЦАГИ.... Since the "bonfire of the vanities" of a few posters threatens to cast a disparaging light on a very good data point aligning power, weight, and measured performance I thought it might be time to repost some of these very factual "assumptions"! First of all, let's do a recap. The important conclusion is highlighted in red: Turn performance from VVS testing: 23.2 seconds to turn 360 degrees. The horizontal axis is the quotient of the wing loading and the sea level top speed. (They are extrapolating from EAS) Using the top level speed as measured by the VVS of 510kph: We can do some quick math based on a wing are of 18.3 M^2 to arrive at a weight of 3995Kg for the VVS FW-190A5. That equals a clean configuration full wing weapon FW-190A5 normal fighter variant with natural petroleum AVGAS. The Vmax at sea level of 510kph corresponds to Dauerleistung or maximum continuous power which equals 1.2 ata at 2300 U/min or ~1360hp. First question we need to answer is what power setting was used? Well basic physics tells us that the same amount of force on the same mass object will produce the same acceleration. That acceleration will reach zero at the same point. In other words, you exert the same amount of power on the same airplane under the same conditions.....you are going to get the same airspeed!! Pretty simple stuff. It is not an assumption but rather just a basic fact of physics. TSAGI very nicely spells out all the power ratings they used in their testing of the FW-190A4. I understand they got a replacement engine from a captured Do-217 bombers making their engine a BMW801A series. That is an assumption but nonetheless, their power settings match the BMW801A series engine and not the BMW801D2 found exclusively in the FW-190A4. TSAGI power settings for the FW-190A4: 1.27ata at 2400U/min or ~1380 HP at 510kph (That equals the engines static FTH 1460 HP characteristics at 510 kph RAM conditions at sea level) Now let's look at the measured turn performance conditions of the TSAGI FW-190A4: The key fact is the altitude of 1000 meters! This turn performance occurs at altitude and the FW-190 achieves ~23 seconds to complete a 360 degree turn at 1000 meters. Altitude changes and power changes will effect that turn performance. Now let's look at the FW-190A5 airspeed at sea level. Again, we have 510kph exactly matching the FW-190A4! It also does 510 kph at sea level! Not surprising...it the same amount of power...1460 STATIC PS @ FTH ! So, in order to achieve ~510 kph Vmax we need ~1380 PS input in an FW-190A series.... Well that checks with Focke Wulf's FW-190A5 data: 510 kph - 505kph Handbuch Speed = 5 kph / 510 kph = ..9% or less than a 1% difference 517 kph - 510 = 7 kph / 510 kph = 1/3% difference Both are well within the 3% level speed variation for a Focke Wulf and fit normal aircraft performance variation. Therefore they give good agreement and are considered the same thing. It is a fact that our 510 kph Vmax occurs at sea level at a power setting of 1360HP. Once more since our quotient of (weight/wing area) / Vmax is the same in both figure 26 and figure 27 we can conclude for a fact that our weight, wing area, and Speed matches for both data points. If our speed equals the same, then our power equals the same. If our turn time performance matches the 1000 meter data point the only conclusion can be that the turn performance represents 1000 meters altitude. It is a fact that equivalent airspeed equals true airspeed at sea level. However, at 1000 meters our true airspeed changes at the reciprocal of the square root of the density ratio for those atmospheric conditions. Since our quotient does not change and still represents 510 kph.....the only airspeed it can be at any other altitude besides sea level that is the same as TAS at sea level....is equivalent airspeed by definition. All the data cross checks and agrees under these conditions of weight, power, and equivalent airspeed. 1
ZachariasX Posted June 1, 2016 Posted June 1, 2016 Reading through the "ramblings" (of all parties involved) I think there is some good info here. If one takes the "I stop breathing until the other believes me" factor out of it, the arguments are not that far apart. Thank you Luke for keeping this open (and restraining yourself, sometimes even on the second attempt ) Ah, simple math... Felix qui potuit rerum cognocscere causas! And if things get hot: Major e longinquo reverentia. Z 1
Crump Posted June 2, 2016 Posted June 2, 2016 Felix qui potuit rerum cognocscere causas! That is sigworthy...in a good way!!
JtD Posted June 2, 2016 Posted June 2, 2016 (edited) Are you now seriously suggesting that the power output of a BMW801C/A at combat power equals that of the BMW801D at max. cont. power at sea level? If you take the ram @500 @sea level figure of 1390 of the C/A engine, you'd have to take the same figure from a similar source for the D, which is 1260. Or, simpler but less accurate, static FTH figures for both, which are 1460 and 1370. Instead, you're comparing a 1370 static FTH apple with an 1380 rammed sea level orange. Again, you are misleading people. --- Just to summarize for the bypassing reader. Crump's arguing that the Soviet turn time figures were being achieved at ~1300hp. He builds his case on linking half a dozen documents, the last one of which contains the figure he's looking for. I'm arguing that the Soviet turn time figures were achieved at ~1400hp. Because a Soviet test report says so. This is relevant to the question what happens to sustained turn time at higher power settings, up to 1700hp. Basically Crumps approach gives a free 1s improvement, which imo is not there. Maybe it still doesn't sound like much, but it will give you the wing guns for free, performance-wise. Edited June 2, 2016 by JtD
ZachariasX Posted June 2, 2016 Posted June 2, 2016 If you take the ram @500 @sea level figure of 1390 of the C/A engine Sorry for being slow, but That is an assumption but nonetheless, their power settings match the BMW801A series engine and not the BMW801D2 found exclusively in the FW-190A4. we are somehow taking the differences on the two power plants into consideration. I'm trying to understand how. Not having sekrit documents from ЦАГИ at hand, I will have to resort to what we have here or there. Crump has detailed that a FW-190 does fairly exactly 510 km/h at sea level, given ANY powerplant of same dimension and weight producing 1370 hp at sea level. Right? (Nothing is trivial here.) Looking there for instance, 510 km/h seems a very precise speed reference for an A4 in combat configuration travelling with Kampfleistung. A tolerated 3% variation seems indeed enough to cover any engeneer's ass over at Focke Wulf back then. Crump: The semantics to describe power make me ask again: Kampfleistung would equal 1520 hp in the manual page you posted just above? As I understand you (and JtT thnx for summarizing) it would do so at 1370 hp? Many tests here are tather consistent about stating speed at Kampfleistung, for instance here (last page). Then it is safe to say the Russians would also have used Kampfleistung to get 510 km/h at sea level, right? In that case 1520 hp @ sea level? It is impressive that the A-5 is a lot faster according in the chart you posted. How come? I mean, given the airframes are fairly similar, I would deduce from that chart that höchstzlässige Dauerleistung @ 2300 rpm and 1.2 ata would suddenly be significantly higher in an aircraft that differs only in mild variations of the airframe? The chart you posted doesn't have the speed compressibiity adjusted. How would it look if it was? Can it explain the difference? Z
Brano Posted June 2, 2016 Posted June 2, 2016 Extracts from soviet document Crump declares as TsAGI,is in real NII VVS document about german aircrafts edition 1944. For those interested,it is: НАУЧНО - ИСПЫТАТЕЛЬНЫЙ ИНСТИТУТ ВВС КРАСНОЙ АРМИИ НЕМЕЦКИЕ САМОЛЕТЫ Под редакцией инженер-полковника П.В. Рудинцева НКАП * СССР ГОСУДАРСТВЕННОЕ ИЗДАТЕЛЬСТОВО ОБОРОННОЙ ПРОМЫШЛЕННОСТИ Москва 1944 http://www.airpages.ru/mn/fw190_01.shtml 1
Crump Posted June 2, 2016 Posted June 2, 2016 Extracts from soviet document Crump declares as TsAGI, Brano... Fig 26 and Fig 27 are from the history of TSAGI. TSAGI is as I understand it, an organization very similar to Rechlin, the NACA, or the RAE. It is the organization responsible for gathering, maintaining, and distributing aeronautical knowledge to support the aviation authority.
Brano Posted June 2, 2016 Posted June 2, 2016 I just pointed at source you used in your post. NII VVS was military research and test center were all domestic and foreign aircrafts were tested. TsAGI was/is civil scientific institution focused at research of aerodynamics as a field of science. Not testing military aircrafts as such. If there were requests from OKBs to help them with improvements of their aircrafts aerodynamics properties, TsAGI obliged by using its brainpower and wind tunnels to suggest best way how to achieve it. Or if NII VVS asked for some specific wind tunnel tests. Same way there was /is separate scientific institute focused on aircraft power units TsIAM to help engine constructors in their work. If you want to make argument using Soviet documents, you need particular NII VVS test reports for given aircraft. Those are documents used by developers of this game. Source you used is mere "know your enemy" encyclopedia issued by NKAP editor for use within VVS.
Crump Posted June 2, 2016 Posted June 2, 2016 Then it is safe to say the Russians would also have used Kampfleistung to get 510 km/h at sea level, right? In that case 1520 hp @ sea level? For the BMW801A they did use Kampfleistung. For the BMW801D2, the equivalent power is Dauerleistung. The BMW801D2 has a higher Brake Mean Effective Pressure than the BMW801A/C. I just pointed at source you used in your post. NII VVS was military research and test center were all domestic and foreign aircrafts were tested. TsAGI was/is civil scientific institution focused at research of aerodynamics as a field of science. Not testing military aircrafts as such. If there were requests from OKBs to help them with improvements of their aircrafts aerodynamics properties, TsAGI obliged by using its brainpower and wind tunnels to suggest best way how to achieve it. Or if NII VVS asked for some specific wind tunnel tests. Same way there was /is separate scientific institute focused on aircraft power units TsIAM to help engine constructors in their work.If you want to make argument using Soviet documents, you need particular NII VVS test reports for given aircraft. Those are documents used by developers of this game. Source you used is mere "know your enemy" encyclopedia issued by NKAP editor for use within VVS. Thank You Brano!
Crump Posted June 2, 2016 Posted June 2, 2016 Then it is safe to say the Russians would also have used Kampfleistung to get 510 km/h at sea level, right? In that case 1520 hp @ sea level? The power characteristics are different due to the higher BMEP of the BMW801D2. t is impressive that the A-5 is a lot faster according in the chart you posted. 517 kph - 510 = 7 kph / 510 kph = 1.3% difference In terms of aerodynamics, they are the same. The chart you posted doesn't have the speed compressibiity adjusted. How would it look if it was? Can it explain the difference? Actually, that chart does have an expression of compressibility. Compressible aerodynamics were a new frontier for engineers during World War II. There several theories and the differences could be dramatic. That is one reason why I use EAS and a modern universal compressibility expression for compressibility. 6. An additional airspeed and altimeter installation error was found to exist at altitude and was evidently dependent upon Mach's number. If this error in the airspeed and altimeter is neglected, an error in true speed of as great as 13 M.P.H. in level flight at 30,000 ft. may result. http://www.wwiiaircraftperformance.org/mustang/p51b-12093.html It is not just a problem for Focke Wulf and you have to be careful to ensure the compressibility error is universal in application from the same theory. It is an effect of the environment and not the aircraft. All aircraft at the same speed and atmospheric conditions will have the same compressibility error. By taking sea level TAS or Indicated airspeed and using EAS to determine all your altitude airspeed, you eliminate any errors due to atmospherics and compressibility. All you are left with is the instrument and position error of the initial indicated airspeed. The margin of error becomes much smaller.
Crump Posted June 2, 2016 Posted June 2, 2016 That pressure coefficient over compressibility tells us that at low angles of attack, the error is not as large while at high angles of attack.....it is significant.
ZachariasX Posted June 2, 2016 Posted June 2, 2016 For the BMW801A they did use Kampfleistung. For the BMW801D2, the equivalent power is Dauerleistung. The BMW801D2 has a higher Brake Mean Effective Pressure than the BMW801A/C. Ok, good to know. So then the Russians would be expected to have reached 510 km/h at sea level with the 1370 hp as stated in the manual page you posted. There it also says tha Vmax for höchstzulässige Dauerleistung (I suppose 1.2 ata?) would give 505 km/h (TAS, right?) at sea level. With 1730 hp at 1.42 ata I would get 560 km/h (TAS) at sea level according to that manual. Correct? So far, so good. But why are they so slow when they test it here: Here, they fly the 190 A-4 with Kampfleistung. The entire pile of documents on the A-4 says like that. Starnge enough, now we have the Russian documents matching the power/speed chart you posted. What is wrong here? It says on the document you posted that these speeds are not adjusted for compressinility effect. This for sure must must be TAS, but how did they get to that? Or CAS? Would that make sense? TAS? "uncalibrated" TAS (whatever that is)? Using this, if velocities were CAS, then the 512 km/h would become 525 km/h TAS at 15°C in ISA athmosphere at seal level. Still a bit slow? I find it very condusing, having on one side all these velocities, abbreviations, while little effort is done on sorting the data we have. Also in the documents, they put in little effort on what they really did. Poor style. For them back then, it was obvious. But it's not. Now we seem to be lacking some information to repeat their experiments and have to find that again. The science is not that hard. Getting some order in what we have is. It would also quench some arguments. Z
ZachariasX Posted June 2, 2016 Posted June 2, 2016 By taking sea level TAS or Indicated airspeed and using EAS to determine all your altitude airspeed, you eliminate any errors due to atmospherics and compressibility. All you are left with is the instrument and position error of the initial indicated airspeed. The margin of error becomes much smaller. You were, faster. Thnx. AFAIR in Lerche's book, he mentioned that at Rechlin, they measured speeds also with the theodolite from the ground, making the plane fly certain distances forth and back, making it some sort of "normalized ground speed", eliminating any problems associated with the instrument on the plane. I will chack that again. So it is really not trivial where the number we have in those docs were made up.
Crump Posted June 2, 2016 Posted June 2, 2016 So it is really not trivial where the number we have in those docs were made up. They all just have to agree within the engineers percentage variation. If they do not, then start looking for a problem or a different airplane configuration. The airplanes vary slightly in performance mainly due to mass production engines vary slightly in their power output and airframes have slight variation in the gaps/sealing/finish of their construction.
Crump Posted June 2, 2016 Posted June 2, 2016 What is wrong here? It says on the document you posted that these speeds are not adjusted for compressinility effect. This for sure must must be TAS, but how did they get to that? Or CAS? Would that make sense? TAS? "uncalibrated" TAS (whatever that is)? In the FW-190A5 curve, the gap between the two curves represents the uncorrected and corrected airspeed. It can be very confusing. Focke Wulf did not always apply ANY correction to their airspeed. For one thing, it does not matter to the pilot. He only has ONE airspeed indicator to reference anyway. In their internal engineering documents and some of the flight testing, they do apply a PEC correction as well as what is called "The Standard Means of Evaluation" to achieve True Airspeed. Other times they have a compressibility correction applied. I think as the war went on, they benefited from some of the RLM research into compressible aerodynamics and simply incorporated the latest knowledge of the time. That is another reason why I stopped paying much attention to their listed speeds at altitude. It is just too easy and more accurate to use EAS and the power available at that altitude to predict performance. Thnx. AFAIR in Lerche's book, he mentioned that at Rechlin, they measured speeds also with the theodolite from the ground, making the plane fly certain distances forth and back, making it some sort of "normalized ground speed", eliminating any problems associated with the instrument on the plane. I will chack that again. That is a very common and established technique for constructing a Position Error Curve in an aircraft. It is used today.
Crump Posted June 2, 2016 Posted June 2, 2016 Using this, if velocities were CAS, then the 512 km/h would become 525 km/h TAS at 15°C in ISA athmosphere at seal level. Still a bit slow? There is no compressibility correct applied at sea level. That is standard. Here is a modern compressibility correction chart. Notice at sea level, the compressibility correction is always zero on a standard day. That is the "calibration" point and sets the playing field level. Only Position and Instrument error are accounted for to establish that calibration point.
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