Gripen,
Posting an extract from Perkins & Hage, only provides further evidence that the efficiency factor is indeed a factor and not a constant, if it were a constant, they would have called it that, and used it as a constant, but they don’t, they acknowledge it as it is, and every aero engineer since has accepted it as such. Nobody, since its conception has ever treated it as a constant… until you came along! LOL!
As for your wind tunnel data, Professor Wood says in his paper:
Originally stated by Professor Wood
Performance estimates based on model test results are unsatisfactory because of the large and uncertain corrections necessary to make the results correspond to the free flight of a full sized airplane.
He is referring to the fact that model tests involving fluid forces never completely represent the full scale condition because of practical limits on the control of the variables involved. For example, the density and viscosity of the fluid are controllable only within narrow limits depending on the range of pressures and temperatures within the test apparatus, and they can vary significantly. Most model tests involve errors relating to Reynolds number, Mach number surface irregularities and roughness, turbulence, and interference effects. Infact, before and during WWII the attempts to correct for differences in turbulence effects between wind tunnels and free air proved so inaccurate that full scale flight testing was widely considered to be essential for anything other than preliminary design. These considerations make the data you have, based on wind tunnel tests made on scale models during the period in questions, almost entirely useless, and lead to conclusions that are not only invalid, but in your case, actually fly in the face of accepted aerodynamic theory.
Hardly surprising, but since you have no formal aerodynamics training, you wouldn’t have been expected to know any of this, you probably only picked up a copy of Perkins and Hage when you saw Badboy’s post as quoted here:
Originally posted by Badboy
There are a large number of sources that clearly state the relationship between the efficiency factor and Aspect Ratio (AR) and several of them also provide graphs of e against AR, examples include:
Principles of Aerodynamics, by Dwinnell, page 144.
Airplane Performance Stability and Control, by Perkins & Hage, page 73.
Elements of Practical Aerodynamics, by Jones, page 73.
Some others publications have multiple curves in order to include taper ratio. A readily available source, for which you can also obtain software, is:
Aerodynamics Aeronautics and Flight Mechanics, by McCormick, page 172.
In this thread:
http://www.hitechcreations.com/forums/showthread.php?threadid=128143&referrerid=4117Because from that point forward you appear to have clued up slightly, however, you still seem to be determined to rely on specious data. The quotes above from Professor Wood, explain why he used full scale flight tests to obtain his data. It explain why, in 1949 four years after WWII, Perkins & Hage were still calling Oswald’s discovery, an Efficiency Factor, not a Constant!
If you want anyone to take your wind tunnel data seriously, you need to post a lot more information about it, for example, the method of supporting the model and the control of associated turbulent flow problems, and the degree of detail in the model, for example were details such as the radiator details, intakes, pitot heads, radio masts, airspeed and air temperatute booms, antenna, guns or gun ports, gun and ammunition door and hatches included on the model? Were any other measures taken to simulate discontinuities in those locations? What corrections were made for Mach number and dynamic pressure calibration? What corrections were made for Reynold’s number? Was the static pressure survey in the tunnel conducted with multiple booms and how were local air disturbances handled? What corrections were made to the Mach number and aerodynamic coefficients for the blockage factor due to the model? What corrections were made to the angle of attack and drag coefficients due to the presence of the tunnel walls? Those are the sort of details you need to be discussing, along with some very self critical estimates of the size of the error bars involved. That was enough to cause Wood to say:
Originally stated by Professor Wood
Performance estimates based on model test results are unsatisfactory because of the large and uncertain corrections necessary to make the results correspond to the free flight of a full sized airplane.
When he conducted his tests, and concluded that e was not constant. Dr Raymer published his empirical method based on NADC data from 1966 in his book on aircraft design in 1999, and he still considered that e was not constant… The reason is that those men are professional aerodynamic engineers, with vast experience and high standing in their fields… You on the other hand are a game player using specious data to win an argument in a silly thread.
So, why don’t you stop pretending to know more than you do, instead of making grossly incorrect statements about a subject you are clearly struggling to pick up as you go along? You would make much better progress by asking genuine questions, instead of acting as though you actually already know what you are talking about, while making absurd claims. Your approach is more befitting a clown than someone with a genuine interest in the subject and a real desire to learn.
Please, give up your silly claims, or compile them with the proper transparency and rigour of a serious academic exposition and publish your findings… Put up, or shut up!
Dweeb
