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#1
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max altitude and Mach 1 Now With Charts
"Boomer" wrote...
the first chart is an F-16 (it SAYS F-15 but a look at the stats tells you otherwise) Notice that it's Max altitude comes BEFORE Mach1. the second chart is for an SU-30, it also reaches max alt BEFORE Mach1. the third chart should be a F-4 vs MiG-21 notice these planes reach max alt well AFTER Mach 1 Curiosity killed the cat, and I'm gonna find out why! From a non-aerodynamicist's point of view, there are several factors at play. Any one of them may be limiting at a specific airspeed/altitude combination. The short answer is that the airplane is optimized for subsonic flight (because it spends 99%+ of its life below Mach 1), so max altitude will be attained at a subsonic speed. Looking at the F-15 chart, because it is the "cleanest": Below approx 38,000', max airspeed is placarded at 800 KCAS (for discussion purposes, roughly equal to 800 KIAS). That is a structural airframe limitation, and the engine might be able to push it faster until it falls apart. At the left side of the curve is Max Lift, or stall speed, and will equate to a roughly constant Max Lift or "Stall" Angle of Attack. If you go any slower, you start going down. At approx 60,000' and Mach 0.95, you hit the peak of the envelope -- max lift, max thrust, max drag. There is only one speed where the engine can produce enough thrust to maintain altitude, and that is at Max Lift AoA. When the airplane is transonic (here, above Mach 0.95), drag increases significantly, before dropping off again at approx. Mach 1.05. The only way to go faster if you start at 60K and .95 is to descend and accelerate. At the same time, engine thrust is likely decreasing as the intake ramps and exhaust nozzles are not controlling the airflow to and from the engines perfectly. As the ramps and nozzles start re-configuring, thrust falls off somewhat. By the time the thrust has recovered at Mach 1.05, drag is starting to increase again, so the engine thrust limits performance up to Mach 1.4. At that speed and approx 57,000', any further climb causes thrust to decrease to the point where altitude and airspeed cannot be maintained. |
#2
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Were you able to see that charts I attached? Because my post with the charts
hasn't shown up on my system yet, I have NO idea why grrrr. -- Curiosity killed the cat, and I'm gonna find out why! "John R Weiss" wrote in message news:3wbpc.50585$iF6.4560150@attbi_s02... "Boomer" wrote... the first chart is an F-16 (it SAYS F-15 but a look at the stats tells you otherwise) Notice that it's Max altitude comes BEFORE Mach1. the second chart is for an SU-30, it also reaches max alt BEFORE Mach1. the third chart should be a F-4 vs MiG-21 notice these planes reach max alt well AFTER Mach 1 Curiosity killed the cat, and I'm gonna find out why! From a non-aerodynamicist's point of view, there are several factors at play. Any one of them may be limiting at a specific airspeed/altitude combination. The short answer is that the airplane is optimized for subsonic flight (because it spends 99%+ of its life below Mach 1), so max altitude will be attained at a subsonic speed. Looking at the F-15 chart, because it is the "cleanest": Below approx 38,000', max airspeed is placarded at 800 KCAS (for discussion purposes, roughly equal to 800 KIAS). That is a structural airframe limitation, and the engine might be able to push it faster until it falls apart. At the left side of the curve is Max Lift, or stall speed, and will equate to a roughly constant Max Lift or "Stall" Angle of Attack. If you go any slower, you start going down. At approx 60,000' and Mach 0.95, you hit the peak of the envelope -- max lift, max thrust, max drag. There is only one speed where the engine can produce enough thrust to maintain altitude, and that is at Max Lift AoA. When the airplane is transonic (here, above Mach 0.95), drag increases significantly, before dropping off again at approx. Mach 1.05. The only way to go faster if you start at 60K and .95 is to descend and accelerate. At the same time, engine thrust is likely decreasing as the intake ramps and exhaust nozzles are not controlling the airflow to and from the engines perfectly. As the ramps and nozzles start re-configuring, thrust falls off somewhat. By the time the thrust has recovered at Mach 1.05, drag is starting to increase again, so the engine thrust limits performance up to Mach 1.4. At that speed and approx 57,000', any further climb causes thrust to decrease to the point where altitude and airspeed cannot be maintained. |
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"Boomer" wrote...
Were you able to see that charts I attached? Umm, yes... That's why I commented on them... |
#4
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thanks it still hasnt shown here.
-- Curiosity killed the cat, and I'm gonna find out why! "John R Weiss" wrote in message news:CIgpc.50861$536.8780260@attbi_s03... "Boomer" wrote... Were you able to see that charts I attached? Umm, yes... That's why I commented on them... |
#5
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In article ,
"Boomer" writes: Were you able to see that charts I attached? Because my post with the charts hasn't shown up on my system yet, I have NO idea why grrrr. I wouldn't mind seeing them, but my news servers filter out binary (image) posts sent to non-binary groups. If teh charts are on the Web, may I ask that you post the URLs for them? If not, give a shout & we'll arrange for you to E-Mail them. -- Pete Stickney A strong conviction that something must be done is the parent of many bad measures. -- Daniel Webster |
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#7
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btw, if anyone else wants to see them just send the same message.
-- Curiosity killed the cat, and I'm gonna find out why! "Peter Stickney" wrote in message ... In article , "Boomer" writes: Were you able to see that charts I attached? Because my post with the charts hasn't shown up on my system yet, I have NO idea why grrrr. I wouldn't mind seeing them, but my news servers filter out binary (image) posts sent to non-binary groups. If teh charts are on the Web, may I ask that you post the URLs for them? If not, give a shout & we'll arrange for you to E-Mail them. -- Pete Stickney A strong conviction that something must be done is the parent of many bad measures. -- Daniel Webster |
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