S77th-GOYA Posted December 16, 2007 Posted December 16, 2007 Does that kinda answer your question, Goya? :D Ummm.... maybe? :smilewink: If I'm being dense here, I apologize. Even taking into account a factor of the time-limited-pursuit giving an advantage to the 95% trimmed F-15, there still exists differences. And you are still saying I am extrapolating data when I am not. I am using data from the graphs. Perhaps you see a problem in using the STD -10C data and if so, please explain why. For the purposes of demonstration, please refer to this blow up from the charts: Highlighted is an altitude of 36K and a speed of M2.3, the speed at which the time-pursuit-limited portion of both graphs begins. A. The graph shows that that speed/altitude is within the flight envelope of the 95% trimmed plane on a STD -10C day. B. The graph shows that that speed/altitude is NOT within the flight envelope of the 102% trimmed plane on a STD -10C day because of ops limit. C. The time-pursuit-limited portion of the 102% graph never comes into play at that speed/altitude because it is outside the flight envelope. The difference is small but it is plainly there. If anyone sees any errors in any of that, please point them out.
Frostie Posted December 17, 2007 Posted December 17, 2007 I think the only thing this proves is that you can't 100% rely on hand drawn graphs. I can clearly see the error is created by a marginal error in pencil line drawing and also the error is increased by the diffferent angle produced from (34000ft to 42000ft on the 95%) compared to the angle produced from (34000ft to 45000ft on the 102%) I think 'estimates' is more appropriate. "[51☭] FROSTIE" #55 'Red 5'. Lord Flashheart 51st PVO "Bisons" - 100 KIAP Regiment Fastest MiG pilot in the world - TCR'10 https://100kiap.org
Rhen Posted December 17, 2007 Posted December 17, 2007 Ummm.... maybe? :smilewink: If I'm being dense here, I apologize. Even taking into account a factor of the time-limited-pursuit giving an advantage to the 95% trimmed F-15, there still exists differences. The difference you're referring to is STILL the time limit on the engine. Everything in the hash-lined region is the time limit. This time limit is MORE RESTRICTIVE for the 102% engine since the temps that the engine's running at are higher, thus the slope of the ops limited area is greater for the 102% engine vs the 95% engine. And you are still saying I am extrapolating data when I am not. I am using data from the graphs. Perhaps you see a problem in using the STD -10C data and if so, please explain why. Just because you're using graphed data doesn't make it extrapolated!:D The reason for use of the vanilla STD Day data is that the entire curve is, more or less, within the confines of the envelope. There, we can see that at 45,000ft, the F-15 trimmed at 102% can stay pretty darn close to M2.3 all day long without any limitations while the F-15 trimmed to 95% can only hope to make M2.07, proving the aircraft generating more thrust is the one trimmed to a higher percentage of FTIT, right? I mean, after all, as a pilot, all I want to know is how quick can I get to a speed at a given altitude and when do I run into the ops limit/structural/whatever - brick wall. For the purposes of demonstration, please refer to this blow up from the charts: Highlighted is an altitude of 36K and a speed of M2.3, the speed at which the time-pursuit-limited portion of both graphs begins. A. The graph shows that that speed/altitude is within the flight envelope of the 95% trimmed plane on a STD -10C day. Actually where you have the mark is STD -7C day. The actual mark at 36K would have to be EXTRAPOLATED! :smilewink::P B. The graph shows that that speed/altitude is NOT within the flight envelope of the 102% trimmed plane on a STD -10C day because of ops limit. Quite true. C. The time-pursuit-limited portion of the 102% graph never comes into play at that speed/altitude because it is outside the flight envelope. Here's where you're wrong - The time-limited portion of the 102% graph is responsible for the slope of the curve changing at 34K. It's slope is greater for the 102% trimmed engine; thus the time-limit (ops limit) comes into play and restricts - to a greater extent than the 95% trimmed engine - the mach number that can be achieved. While the 102% trimmed engine can accelerate the Eagle faster and to a higher mach number, near the edge of the envelope it will also hit the "brick wall" faster than it would normally because it's operating at a higher FTIT. The difference is small but it is plainly there. You're right, and Frost1e's pointed out why: ...the diffferent angle produced from (34000ft to 42000ft on the 95%) compared to the angle produced from (34000ft to 45000ft on the 102%) ...which is due to the time-limited nature of operating a hotter engine. Clear as mud?:smilewink::smartass: 1
S77th-GOYA Posted December 17, 2007 Posted December 17, 2007 Clear as mud? Just one part: Why does the ops limit line for the 102% graph change PRIOR to reaching the cross hatched, time limited portion of the envelope? If it changed AT the threshold of the time limited portion, it would make perfect sense. Please just tell me it is because of sloppy graph making so I can shut up about this. :D And not to start a whole new process but since this graph only deals with max thrust, would I be correct in assuming that the 102% F-15 might eliminate its time-limit penalty by lowering burner to 2nd or 3rd stage instead of 5th stage and still match (or better) the performance of the 95% F-15? And what is the difference between the time-limits at the threshold and ops limit? Meaning, for example, do I have 10 minutes if I'm barely into the time-limt portion of the envelope and only 1 minute at the ops limit?
Pilotasso Posted December 17, 2007 Posted December 17, 2007 I think the only thing this proves is that you can't 100% rely on hand drawn graphs. I can clearly see the error is created by a marginal error in pencil line drawing and also the error is increased by the diffferent angle produced from (34000ft to 42000ft on the 95%) compared to the angle produced from (34000ft to 45000ft on the 102%) I think 'estimates' is more appropriate. :huh: Pencil? These graphs are old sure but as far as I am concerned computers were already printing these 30 years ago, not Fred Flinstone. If copying it distorted the graph then it would also distort the grid equaly, dont you think? ;) And yes, its not only the F-15 that needs fix, Mig and Su-27 need also, the mig more than the SU though. .
Frostie Posted December 17, 2007 Posted December 17, 2007 Pencil : a narrow set of lines, light rays, or the like, diverging from or converging to a point:D "[51☭] FROSTIE" #55 'Red 5'. Lord Flashheart 51st PVO "Bisons" - 100 KIAP Regiment Fastest MiG pilot in the world - TCR'10 https://100kiap.org
S77th-GOYA Posted December 17, 2007 Posted December 17, 2007 These graphs are old sure but as far as I am concerned computers were already printing these 30 years ago... I tried to overlay one graph on the other and the gridlines didn't match up in places. That may account for some discrepancies.
Rhen Posted December 18, 2007 Posted December 18, 2007 Just one part: Why does the ops limit line for the 102% graph change PRIOR to reaching the cross hatched, time limited portion of the envelope? If it changed AT the threshold of the time limited portion, it would make perfect sense. Ok, at M2.25, things start to change regarding the inlet pressures and the FTIT. This causes a new portion of the aircraft/engine envelope to develop. This happens at 34K at M2.25. The slope of this line increases with increasing FTIT - as in an engine operating with less margin (102%). Please just tell me it is because of sloppy graph making so I can shut up about this. :D Sorry, not a sloppy graph, just one scanned poorly. I've got a hard copy of the F-15-1 and it's easier to read, but that pesky line's still there! And not to start a whole new process but since this graph only deals with max thrust, would I be correct in assuming that the 102% F-15 might eliminate its time-limit penalty by lowering burner to 2nd or 3rd stage instead of 5th stage and still match (or better) the performance of the 95% F-15? That's pretty theoretical - as a pilot... (here we go again :smilewink:) I'm only interested in how fast I can go and how quickly I can do it without bending the jet. While you can eliminate some of the temperature perturbations in the data, compressibility is still a factor once you start crossing mach numbers above a certain value. Then you start to get into a backflow problem with the pressures from the afterburner section interfering with the N1 fan. And what is the difference between the time-limits at the threshold and ops limit? Meaning, for example, do I have 10 minutes if I'm barely into the time-limt portion of the envelope and only 1 minute at the ops limit? Time/temperature/airframe/structural limits are ALL ops limits. These are what we call - "PASS THIS LINE, THERE BE DRAGONS." If you value your aircraft or your hide, you trespass these lines at your peril. The risk/benefit ratio has to be worth it. You can also take the "hashed lines" as being inside a secondary envelope, that's time limited. Past the point of safety, or beyond the limits of the envelope, you've just changed hats from fighter pilot to test pilot. Just one question for you... Is this still a MADDOG thread? :smilewink:
IvanK Posted December 18, 2007 Posted December 18, 2007 Hear hear lets talk about Missiles not engine limits !
S77th-GOYA Posted December 18, 2007 Posted December 18, 2007 Is this still a MADDOG thread? :smilewink: Sure, I was just borrowing it. Here you go guys, have it back. Thanks, Rhen.
Yeniceri Posted December 18, 2007 Author Posted December 18, 2007 please, go on guys.. This thread is more educating than my highschool.. :thumbup: [sIGPIC]http://i201.photobucket.com/albums/aa200/misikci/41-imza-1.jpg[/sIGPIC] "To infinity...and beyond!.." SIM-MOD Modeler TURK!
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