OK, thanks. Iīll test the columns to see what speeds are proper.
Your 4-engined Mitchell .air file sounds most intriguing, even if only just to get by for the visual model!
Yes I fully understand what you say as regards to your plans, both as regards the Messerschmitt 262, as well as the sequence of steps to proceed with for the Orionīs turboprop CFS .air file conversion. No hurry, no problem!
I translated one of the NASA Experimenterīs Handbook speed columns into mph - corresponding to 110000 lbs weight, as I was getting about 125000 lbs for a fully tanked, crewed aircraft with no bomb/missile payload.
From S.L. to 30000 ft the max. continuous speed values converted from Kt to Mph are:
345, 385, 397, 408, 421, 433, 446, 454, 450, 447, 439, 425, and 404 mph.
I wasnīt using the 30000 ft. line because the plane didnīt really hold the altitude with 125000 lbs weight, which is not really surprising.
I was also thinking along the lines that the only way to get more speed at altitude was to tamper with the propeller graphs, but didnīt dare! I remember your comment very early on when we were tuning the Zeppelin Staaken engines, that moving the propeller table columns to the left by two positions would increase efficiency and thrust. Maybe I will dare now... It could be interesting... just for kicks!
As an approximation, I expect the calculated thrust values would be based on the estimate a few days ago, that added the propeller thrust and exhaust thrust, the latter being more or less constant with altitude, as opposed to the former.
I was looking over the NASA speed table for the Orion yesterday.
I am actually more interested in the 90,000 pound or 95,000 pound columns because they give maximum level performance.
The first thing worth noting is that maximum is only 404 knots while the Orion should be good or 411 knots.
The question here is now to make the correction for a target speed. I DO want maximum speed as per specifications.
I do believe that the propeller tables are the key to this AIR file.
Until I create the rest of the AIR and DP files, I cannot get a good feel for what the propeller tables should be.
As I commented earlier, I really don't have an interest in the Orion, but it does offer an interesting learning opportunity as far as AIR files go.
Hopefully we will get there eventually.
Today I have a young guest staying at my house. My nephew wanted to get away from all the tension over at my mom's house, so he came over last night. Guess I should go make some breakfast.
Baked beans on toast with a fried egg and sausages, or also bacon and eggs make a nice English breakfast if itīs cold... In hot weather I suppose corn flakes with cold milk, sugar, cinammon and sliced bananas will do! Anyway, itīs nice to have youngsters around the house sometimes.
As regards the Orionīs performance tables on the NASA handbook: 404 Kt (464.9 mph) would be with maximum-continuous on the turbines, and that will probably mean 97% N1 power, if the Orionīs turbines are similar to the usual, normal turbines...
Then, the 411 Kt (472.9 mph) maximum take-off power would be under maximum throttle setting, perhaps 104 or 105% N1.
I have to investigate a little which % of N1 power is correct for the 5-minute maximum on these turbines.
In general, it is apparently often over 100%, but will depend on the manufacturer.
So, the good news is, that your conviction about the propeller tables, once finely tuned with proper research and development, means that a CFS .air file can provide a satisfactory turboprop engine. That will ge great!
A correct .air file for the rest of the plane, as a starting point for a more meticulous kind of investigation, is of course also a must. In my case Iīm afraid I can only arrive at approximations, due to my more limited knowledge on the subject.
Then, I think I made a mistake in my memory with shifting the propeller table columns to increase thrust and eficiency. This is just for an approximate try to improve this aspect. I remember starting on the right, so columns are to be shifted 2 positions to the right, not to the left! My memory is getting worse... but my age is getting better...
Even if the Orion in itself is not really interesting for you, Iīm glad that it has aspects that do attract your interest. In my case, I find the different kinds of aircraft engines and their differing performances fascinating, and I will thankfully be able to follow your study on the subject with interest whenever you decide to start with it.
Update:
As regards the "approximate" adjustments to the propeller tables that I was trying, or going to try: I used AAM because of its visual display, but to be honest, it is all very much over my head and I donīt really understand what or how it is to be done, so Iīm afraid Iīll desist for the moment. Not to worry, however, there are other tasks awaiting attention!
Cheers,
Aleatorylamp
Last edited by aleatorylamp; July 25th, 2016 at 12:51.
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