• Ivan's Avatar
    Yesterday, 07:41
    Hello Aleatorylamp, In regards to being able to adjust Directional and Lateral Static Trim, I have no working solution. In regards to being able to compensate for a Counter Rotating propeller, we have a pretty good working solution to this in another thread on this forum: The Lockheed P-38 Lightning - Design Study had a pretty similar problem to address. My solution there which probably is technically incorrect but has no side bad effects that I have seen thus far is to move the opposite rotating propeller LEFT. In the case of the P-38, it was moved outward by around 20 inches, but for your Giant, I doubt it will be exactly the same. I decided to respond here because I believe the subject may be of general interest.
    1101 replies | 64713 view(s)
  • Ivan's Avatar
    March 23rd, 2015, 07:54
    My son happens to be working on Algebraic Functions in school and I showed him a couple tools I had used to work on the Table 512 template. We didn't actually get into the exact result and I don't know if he would even recognise the results in my spreadsheet, but he at least has the basis now to get to the same place. All of these computer tools and the Internet simply didn't exist when I was doing the same things in school. Now I just have to get him to WANT to figure out what I am doing..... That is a much harder task because Los Santos and Liberty City are much more appealing to him in comparison to plotting curves on a spreadsheet. "So what the heck does your spreadsheet have to do with playing Combat Flight Simulator???" He would much rather pilot a Pod Racer through a...
    1101 replies | 64713 view(s)
  • Ivan's Avatar
    March 22nd, 2015, 11:26
    Have you actually tuned the engine RPM setting in the AIR file? You should not be exceeding the RPM limit under normal flight conditions. As for what exactly is happening when RPM is too low but HP is correct or HP and Climb are too high if RPM is correct, I would actually need to test it myself to see what is happening. I have already told you the way I would do the tuning, so there is no other information I can give that is new. Please check your post in the area regarding Compression Ratio.... The numbers that are listed do not make sense. My guess is that with the difference in HP and RPM between the two engines, you will need to do some tuning in the propeller tables.
    1101 replies | 64713 view(s)
  • Ivan's Avatar
    March 20th, 2015, 13:05
    Hello Aleatorylamp, Thanks for the offer. It IS appreciated, but probably won't do me much good at the moment. First of all, the extent of testing varies quite a bit depending on how much information I really need. For example, the Me 109E Trop that was done a little while back had only the amount of testing necessary to give it the handling I THOUGHT a 109E should have and the basic straight line performance, climb rate and ceiling. This meant that I only did speed tests at 500 feet and around 15,000 feet (?). (I can't remember the exact altitude but it was wherever the engine power started to fall off.) On this test, I am guessing I will be doing speed runs with notes on propeller pitch and thrust EVERY 2,500 feet. There may be the need to record more numbers when things...
    1101 replies | 64713 view(s)
  • Ivan's Avatar
    March 19th, 2015, 16:44
    Thanks for the offer Aleatorylamp. I don't think this is a task that I can delegate though, especially not with the first try at Propeller Tables. I suspect testing this time will be a bit different from my usual protocol. My plan (very subject to change) is this for now: Gather enough information for a data sheet on the Kawasaki Ki-61-Id. I MIGHT already have this but can't tell right this moment because any data and references would be on the HDD for my dead laptop. (It would also help if I could remember where the notebook is that contains all my old test record sheets.)
    1101 replies | 64713 view(s)
  • Ivan's Avatar
    March 16th, 2015, 14:51
    Glad it all worked out for you. It does look cool from the screenshots. I have also made some progress with the Propeller Tables. Hopefully there will be something worth flight testing shortly. The candidate for flight testing is a Ki-61-Id that has been waiting its turn in the paint booth for years. - Ivan.
    1101 replies | 64713 view(s)
  • Ivan's Avatar
    March 13th, 2015, 17:49
    Hello Aleatorylamp, Please do check your email. I found something very old that might be useful to you. Regarding Tom Goodrick and Rabbijah Guder: I don't believe I have seen anything recent from either of them. To me this means that their work and observations about AIR files was done at a time when there was much less knowledge available. A lot of their conclusions although logical for the evidence available at the time is no longer valid as we find out more about the structure and contents of AIR files. Another problem is that the AirEd.ini and FDECtrl.txt files which listed the "known" fields in the AIR file had much less content than they do now. That means that quite a lot of the AIR file was "invisible" to them. That is why I suggested doing a hex dump of the actual...
    1101 replies | 64713 view(s)
  • Ivan's Avatar
    March 13th, 2015, 00:37
    I bet the actual aircraft builders would much rather have a self energizing perpetual motion propeller instead. I know *I* would prefer a real aeroplane that could fly around the planet with a single gallon of avgas. If you send me both good and broken AIR files, I am sure a hex dump could find the difference. If I could find my old program, it could tell in a minute or two what record the error was in as well. - Ivan.
    1101 replies | 64713 view(s)
  • Ivan's Avatar
    March 12th, 2015, 21:24
    Silly question, but if a side-by-side comparison of two AIR files isn't difficult, then why not figure out what was Broken in the AIR file and fix it rather than throw it away and start over? I find it to be tedious and very error prone to compare long files. That is why I prefer to let machines do the text searches and matching for me. By the way, Just a few minutes ago, I generated my first spreadsheet calculated Propeller Power Coefficient Table (512). Though the curves are programmatically generated, the adjustments to curve parameters need to be entered by hand. Actually only the positive values are tuned so easily. The negative side is also formula generated, but the formula is not easily tuned. Now I just need to build a matching Propeller Efficiency Table (511) to test....
    1101 replies | 64713 view(s)
  • Ivan's Avatar
    March 11th, 2015, 08:15
    A quick patch to prevent the perpetual motion effects in the Mustang's Propeller is not hard to do. Attached are screenshots showing the Power Coefficient Table and the Revised Propeller Efficiency Table. The thing to look for is that at no point should the efficiency be non-zero when the power coefficient is negative. The revised Table 511 does not quite satisfy that requirement, but the overlaps are very small and hopefully transient enough not to cause problems. The bigger issue is still that the maximum advance ratio is still too low. Consider that with the current efficiency table, the propeller efficiency does not change above 400 MPH and I believe that some of the values there are a bit too high. At this point, the limitations are that it is difficult to generate a...
    1101 replies | 64713 view(s)
  • Ivan's Avatar
    March 11th, 2015, 07:58
    Hello Aleatorylamp, Glad you are satisfied with how the Giant flies. I have never been completely satisfied with any of the flight models I have worked on and most of the time it is because of handling issues rather than straight line performance. I just quit messing when I have exhausted what I "know" how to do or when it is likely I will mess things up more than fix things. Way back when I was heavily into writing utilities to use for CFS Development, I wrote a short little C program to generate all the possible fuel tanks in an AIR file that did nothing else. It gave me a reliable source to copy records for fuel tanks for a new AIR file. FDE would not do the copying but AirEd would. From there, since I pretty much understood the structure of the AIR file if not the...
    1101 replies | 64713 view(s)
  • Ivan's Avatar
    March 9th, 2015, 16:19
    Actually, as we were discussing in email, the Simulator is pretty good for the time. The stock AIR files however are not so good and this is just one more example to prove my point. Notice though that I have been tuning AIR files literally for years and have not found this issue until now. Then again, I didn't really understand the tables or examine them in detail until now either. So.... As goofy as these Propeller Tables are, they are part of the AIR file for every aeroplane project I have ever released. THAT fact is the "Now What?" I am still trying to figure out how to go about building my own tables. Doing them by hand isn't hard, but tuning them afterward is annoying. I want a spreadsheet that will let me do most of the calculations I need for the fine tuning. I...
    1101 replies | 64713 view(s)
  • Ivan's Avatar
    March 9th, 2015, 15:52
    First of all, Regarding the Giant.... You already know enough to tune this beast because it is now pretty much where we originally started. If your maximum power is achieved at too low an altitude (even 400 feet too low), just increase the boost a tiny bit. I would strongly suggest you try out the original boost setting I used on the first 14 foot propeller I sent to you. After you get your peak power at the right altitude, you can tune it down a bit with the Friction / Engine Efficiency. Once you get that, then if necessary, you adjust the Propeller Power Coefficient to get it to lug a bit to reduce power lower and higher than the 4300 feet critical altitude. To reset your speed, Use Propeller Efficiency.... Same cycle one more time....
    1101 replies | 64713 view(s)
  • Ivan's Avatar
    March 9th, 2015, 05:07
    Last night I decided to test whether I was correct in my understanding of how the numbers in Table 511 and Table 512 interacted by conducting a simple speed run at 500 feet. The first test was with a stock P-51D AIR file: Without WEP Pitch - 39 degrees Power - 1376 HP RPM - 3000 Speed - 334 MPH With WEP
    1101 replies | 64713 view(s)
  • Ivan's Avatar
    March 9th, 2015, 04:44
    Hello Aleatorylamp, What you are describing is what is actually SUPPOSED to happen. The Constant Speed Unit regulates the Engine RPM and adjusts it to the RPM set by the pilot. It does this by making the pitch more coarse (higher degrees pitch) if the RPMs are too high and makes the pitch more fine (lower degrees pitch) if the RPMs are too low. At some point, you hit the mechanical limits that limit the range of pitch settings on the propeller. The P-51D has quite a wide pitch range at 23 degrees Minimum to 65 degrees Maximum. The reason for this exploration to begin with was that I was finding that the propellers on a couple of my aeroplane projects were unable to maintain RPM at lower airspeeds (Advance Ratios). I already knew I needed to adjust the Propeller Power...
    1101 replies | 64713 view(s)
  • Ivan's Avatar
    March 8th, 2015, 11:43
    Here again are the Tables 511 and 512 for the stock P-51D Mustang. Also attached is a Propeller Efficiency Graph calculated using Vortex Theory. For this exploration, I will use a Propeller Pitch Angle of 25 degrees because it is within the operating range of the P-51D. Note that the Vortex Theory Graph shows that Efficiency drops to Zero at just below J=1.3. This is happening because the relative air flow to the Propeller means that at any forward speed above J=1.3, the AoA of the blade is negative. Next, note that Table 512 shows that the power absorbed by the propeller drops to zero at slightly above J=1.2. So far, so good. Things here are more or less consistent.
    1101 replies | 64713 view(s)
  • Ivan's Avatar
    March 8th, 2015, 11:09
    The results from looking at Tables 511 and 512 didn't seem logical. I was wondering if perhaps the numbers we interpret to be Advance Ratio were actually 1/2 Advance Ratio or something else that would mean that these Tables were specifying settings at a much higher speed than it appeared. The next step was how to set up a test that would "prove" that the value we interpret as advance ratio really was that AND to confirm that I had not calculated Advance Ratio incorrectly. (It is a very simple formula but who knows?) As a test, I took a copy of my Kawasaki Ki-61-Id (the original version without the latest propeller modifications) and used AirEd to change all of the propeller efficiencies above J=1.0 to be Zero. The column for J=1.2 was also reset to be J=1.05. So.... This fancy...
    1101 replies | 64713 view(s)
  • Ivan's Avatar
    March 8th, 2015, 10:44
    Hello Aleatorylamp, I am certain that other folks have figured this out long before now, but to me this is new. Hopefully no one minds my posts and probable missteps as I explore this area for the first time. The numbers you are posting for your Giant imply that nothing significant is being changed in the flight model other than giving the ability to fine tune the Propeller parameters. Obviously you figured out that the varying interval works as well. I did one more test yesterday that also results in the same conclusion. - Ivan.
    1101 replies | 64713 view(s)
  • Ivan's Avatar
    March 6th, 2015, 07:57
    Last night I did a bit of tuning to Table 512 for my Kawasaki Ki-61-Id. The results are a bit interesting to say the least and I will need to do some more changes before this graph is useable. First, I was able to adjust the propeller so that it now reaches full 2500 RPM below 150 MPH. It is only 145 MPH which isn't much but then again, I only changed the values by 3-5% just for testing. Idle speed is a bit higher 465 RPM instead of 450 RPM. I have no doubt I can drop a bit more with no great issues. Unfortunately I could not resist "fixing" the curves that were so strange looking so now the general propeller pitch is quite a bit more coarse in normal flight. The worst result though was to change the value for 45 degrees pitch at J=2.4.
    1101 replies | 64713 view(s)
  • Ivan's Avatar
    March 5th, 2015, 12:58
    Hello Aleatorylamp, Actually the total number of columns would remain the same, but the intervals might be closer. As an example if the Advance Ratio were incremented by 0.1 between columns instead of 0.2, you would only go from J=0.0 to J=1.2 This seems to be quite sufficient for the Giant and similar machines: J=1.2 would mean a forward speed of around 275 MPH which the Giant and its brethren are not likely to reach, at least not in one piece.
    1101 replies | 64713 view(s)
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