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(Fact Check needed)Is F-16C largely over-performing than F-14B in the two-cycle BFM engagements in the real life?


Sonoda Umi

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You should have enough authority to compensate for an engine failure high supersonic flight. The problem is that things happen so fast that neither SAS nor the pilot have enough time to react. Thats what happened to an SR-71. One of the inlet cones failed at Mach 3 instantly killing the engine. The resulting yaw moment immedietly turned the aircraft around and the airflow ripped it to pieces. The pilot didnt even have time to pull the handle and was thrown out of the cockpit with his seat and magically survived. 
Sure, but that thing was flying at 80 thousand feet and have the engines very far apart, even when compared to the F-14.

Also the reaction time of pilot or SAS should not be a factor as the vertical stabilizer itself should keep the jet flying true. It's the reason you can keep your feet on the floor when you're fast.

Anyway, I've never heard that stability issues were the reason for the Tomcat's speed limits. I would very much like to read about it.
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The engine centerlines are close to 3 METERS apart. meaning 1.5 Meters from CL and they each make at speed around 124.5 kN of force. The vertical stabs would have to be something like 3 times as large to maintain directional stability with a torque moment like that. Even with control input on the rudder it's a significant rotation when theres 124.5 kN on one side of the CG and basically 0 minus the drag of air blowing through the dead engine's fan bypass on the other side. 

You don't build a fighter to have single engine directional stability at speeds it can't reach with one engine.

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The engine centerlines are close to 3 METERS apart. meaning 1.5 Meters from CL and they each make at speed around 124.5 kN of force. The vertical stabs would have to be something like 3 times as large to maintain directional stability with a torque moment like that. Even with control input on the rudder it's a significant rotation when theres 124.5 kN on one side of the CG and basically 0 minus the drag of air blowing through the dead engine's fan bypass on the other side. 
You don't build a fighter to have single engine directional stability at speeds it can't reach with one engine.
So stabilizer area was sufficient below Mach 1.88, but above Mach 1.88 it needed to be 3 times larger?

Also, the stabs compensating for a 200 kNm torque doesn't sound unreasonable to me. They are the size of F-16 wings, and the F-14 is also equipped with ventral fins of considerable size.

I've googled this speed limit and found the following explanations:

-Intake ramp was set in a fixed position
-Stability
-Afterburner spray bar structural limitations

These can't all be true. Is there any open official documentation on this issue?
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The Stab force doesn't need to be "Sufficient" at just under 1.88M. But the directional divergence won't break the plane below 1.88M.
Sounds like the sort of thing that would be related to calibrated airspeed rather than Mach.

Have you seen any source material for this or is it just speculation?
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Mach limits exist separate from CAS limits for a reason.  Shockwave interactions around the bodies passing through the air behave very differently and have pressure gradients that you can't account for with a simple CAS number.

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Mach limits exist separate from CAS limits for a reason.  Shockwave interactions around the bodies passing through the air behave very differently and have pressure gradients that you can't account for with a simple CAS number.
I know, but to me it is obvious that a departure from controlled flight will result in a rapid unplanned disassembly at Mach numbers far below 1.88. Especially at low altitude (high CAS).
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You aren't thinking about Shockwave interactions with yaw angles then.  The low altitude high pressure regimes have comparatively blunt or non existent Shockwave that are less likely to impact the airframe at a given yaw angle

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You aren't thinking about Shockwave interactions with yaw angles then.  The low altitude high pressure regimes have comparatively blunt or non existent Shockwave that are less likely to impact the airframe at a given yaw angle
Do you have a reference that discusses this issue with regards to the F-14?
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1 hour ago, Katj said:

Do you have a reference that discusses this issue with regards to the F-14?

My Aerospace Engineering degree.  The fact of the matter is that you can find sources that cite directional stability with a single engine operating as the reason for a lower Mach limit.  As you pointed out, when Mach is the limiter (not CAS) you are not dealing with maximum dynamic pressure.  So if raw dynamic pressure isn't the issue, then what is and how is it related to Mach number?  Deductive reasoning leads me to either shockwave interactions and/or aeroelastic twist (exacerbated by the pressure differentials from the supersonic flow).   

FWIW, the SR-71 cruised at ~300KCAS, didn't stop one from disintegrating at Mach 3.  Q (dynamic pressure) isn't everything.  Mach matters.

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28 minutes ago, Spurts said:

 

FWIW, the SR-71 cruised at ~300KCAS, didn't stop one from disintegrating at Mach 3.  Q (dynamic pressure) isn't everything.  Mach matters.

 

If my calculator's not wrong, the SR-71's typical cruise speed was about 800 KCAS.  Nb. the charts are all in KEAS, and the compressibility correction for ~Mach 3.2 @ ~80k feet on an ISA standard day is going to be pretty significant.  Unless I'm missing something, in which case hand me some shells to load my footgun.

 

 

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10 hours ago, cheezit said:

 

If my calculator's not wrong, the SR-71's typical cruise speed was about 800 KCAS.  Nb. the charts are all in KEAS, and the compressibility correction for ~Mach 3.2 @ ~80k feet on an ISA standard day is going to be pretty significant.  Unless I'm missing something, in which case hand me some shells to load my footgun.

 

 

You have to calculate true airspeed from indicated from that altitude, then calculate mach from the TAS at 80,000 ft. Thats where ~300kias equals ~mach 3

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Interesting.  When I plugged the numbers from the SR-71 charts into AeroToolbox, the Mach number for 350 KEAS @ 80k feet matched the Mach number on the Air Force's chart from the SR-71 flight manual, and the TAS was obviously correct for the Mach number and altitude; seeing this, I thought that they had to be using the equation for supersonic flow.  Maybe I'll try calculating by hand and submitting a patch to AeroToolbox if I can figure out what's going wrong (I assume everything on that page is done browser-side in JS so source shouldn't be too hard to track down).

 

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quick admission, I was referring to KEAS not KCAS, since KEAS is representative of the speed needed at sea level to have the same pressure.  So many aircraft I have had to deal with professionally used a CAS/Mach limit that it was stuck in my head.  But it is KEAS that is relevant to our discussion of pressure on an airframe.  Also, we are vastly off topic.. 

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