Do fighter jets have a Vne?

I'm vaguely remembering a story about some sort of g limit horn on maybe an F15? Guys would just pull until they heard the horn maybe? And some incident involving entering the wrong exterior load into the computer to processes load limits for the flight controls?

Stories from long ago for sure.

Yes, there are definitely G limits that can be exceeded. The OWS does compute G limits based on current configuration, airspeed, weight, etc, and uses accelerometers all over the aircraft to determine that.

The OWS both displays "max available G" real time in the HUD, and also generates a set of tones when current G approaches those computed limits.
 
So are you able to bug the VNE for a given configuration, or just brief and be aware of the a/s and G limits?
Does aerodynamics affect which pylons you can put a given device on?

The G limits are computed real time and displayed, but max speeds are not displayed or bugged.

Again, I've had the Eagle running all out, full burner, unloaded acceleration....starting over the Mach up in the 30s, and pushing the nose over to accelerate as fast as I can get it....and still not gotten close to max Mach or KCAS.

External stores configurations are tested, approved, and listed in the airplane's weapon manual. Different configurations have different operations limitations.
 
I think that the answer to Beas's real question (based on Hacker's last post) is "yes there is a max speed that the aircraft is designed for" but it doesn't really matter because you can't realistically get to it (at least in some fighters). After all, I'm pretty sure if you got the airplane up to Mach 93.86 the wings would fall off (or melt off). So there HAS to be a maximum allowable speed for any aircraft... but that doesn't necessarily mean it's important. If you can't get to it anyway... who cares what it is?
 
So, yeah, there is a Vne and the OWS tells you what it is..

But, it's NOT a "Vne", although a limitation it may be!

§ 23.1505 Airspeed limitations.

(a) The never-exceed speed V NEmust be established so that it is—

(1) Not less than 0.9 times the minimum value of V Dallowed under §23.335; and

(2) Not more than the lesser of—

(i) 0.9 V Destablished under §23.335; or

(ii) 0.9 times the maximum speed shown under §23.251.

(b) The maximum structural cruising speed V NOmust be established so that it is—

(1) Not less than the minimum value of V Callowed under §23.335; and

(2) Not more than the lesser of—

(i) V Cestablished under §23.335; or

(ii) 0.89 V NEestablished under paragraph (a) of this section.

(c) Paragraphs (a) and (b) of this section do not apply to turbine airplanes or to airplanes for which a design diving speed V D /M Dis established under §23.335(b)(4). For those airplanes, a maximum operating limit speed ( V MO /M MO-airspeed or Mach number, whichever is critical at a particular altitude) must be established as a speed that may not be deliberately exceeded in any regime of flight (climb, cruise, or descent) unless a higher speed is authorized for flight test or pilot training operations. V MO /M MOmust be established so that it is not greater than the design cruising speed V C /M Cand so that it is sufficiently below V D /M Dand the maximum speed shown under §23.251 to make it highly improbable that the latter speeds will be inadvertently exceeded in operations. The speed margin between V MO /M MOand V D /M Dor the maximum speed shown under §23.251 may not be less than the speed margin established between V C /M Cand V D /M Dunder §23.335(b), or the speed margin found necessary in the flight test conducted under §23.253.

§ 23.335 Design airspeeds.

Except as provided in paragraph (a)(4) of this section, the selected design airspeeds are equivalent airspeeds (EAS).

(a) Design cruising speed, V C.For V Cthe following apply:

(1) Where W/S′=wing loading at the design maximum takeoff weight, Vc(in knots) may not be less than—

(i) 33 √(W/S) (for normal, utility, and commuter category airplanes);

(ii) 36 √(W/S) (for acrobatic category airplanes).

(2) For values of W/S more than 20, the multiplying factors may be decreased linearly with W/S to a value of 28.6 where W/S =100.

(3) V Cneed not be more than 0.9 V Hat sea level.

(4) At altitudes where an M Dis established, a cruising speed M Climited by compressibility may be selected.

(b) Design dive speed V D.For V D,the following apply:

(1) V D/MDmay not be less than 1.25 V C/MC; and

(2) With V C min,the required minimum design cruising speed, V D(in knots) may not be less than—

(i) 1.40 V c min(for normal and commuter category airplanes);

(ii) 1.50 V C min(for utility category airplanes); and

(iii) 1.55 V C min(for acrobatic category airplanes).

(3) For values of W/S more than 20, the multiplying factors in paragraph (b)(2) of this section may be decreased linearly with W/S to a value of 1.35 where W/S =100.

(4) Compliance with paragraphs (b)(1) and (2) of this section need not be shown if V D /M Dis selected so that the minimum speed margin between V C /M Cand V D /M Dis the greater of the following:

(i) The speed increase resulting when, from the initial condition of stabilized flight at V C /M C,the airplane is assumed to be upset, flown for 20 seconds along a flight path 7.5° below the initial path, and then pulled up with a load factor of 1.5 (0.5 g. acceleration increment). At least 75 percent maximum continuous power for reciprocating engines, and maximum cruising power for turbines, or, if less, the power required for V C/ M Cfor both kinds of engines, must be assumed until the pullup is initiated, at which point power reduction and pilot-controlled drag devices may be used; and either—

(ii) Mach 0.05 for normal, utility, and acrobatic category airplanes (at altitudes where MDis established); or

(iii) Mach 0.07 for commuter category airplanes (at altitudes where MDis established) unless a rational analysis, including the effects of automatic systems, is used to determine a lower margin. If a rational analysis is used, the minimum speed margin must be enough to provide for atmospheric variations (such as horizontal gusts), and the penetration of jet streams or cold fronts), instrument errors, airframe production variations, and must not be less than Mach 0.05.

(c) Design maneuvering speed V A.For V A,the following applies:

(1) V Amay not be less than V S√ n where—

(i) V Sis a computed stalling speed with flaps retracted at the design weight, normally based on the maximum airplane normal force coefficients, C NA ; and

(ii) n is the limit maneuvering load factor used in design

(2) The value of V Aneed not exceed the value of V Cused in design.

(d) Design speed for maximum gust intensity, V B. For VB, the following apply:

(1) VBmay not be less than the speed determined by the intersection of the line representing the maximum positive lift, CNMAX, and the line representing the rough air gust velocity on the gust V-n diagram, or VS1√ ng, whichever is less, where:

(i) ngthe positive airplane gust load factor due to gust, at speed VC(in accordance with §23.341), and at the particular weight under consideration; and

(ii) VS1is the stalling speed with the flaps retracted at the particular weight under consideration.

(2) VBneed not be greater than VC.
 
Again, I've had the Eagle running all out, full burner, unloaded acceleration....starting over the Mach up in the 30s, and pushing the nose over to accelerate as fast as I can get it....and still not gotten close to max Mach or KCAS.

2 questions.

What's the fastest you got it to go?

What's the max mach/CAS?

Interesting discussion. It seems odd that you can have a plane descending with full power and not be able to reach any sort of structural limit speed. Is the speed simply that high, or do you guys need bigger engines (which I doubt)?
 
2 questions.

What's the fastest you got it to go?

What's the max mach/CAS?

Interesting discussion. It seems odd that you can have a plane descending with full power and not be able to reach any sort of structural limit speed. Is the speed simply that high, or do you guys need bigger engines (which I doubt)?

The F-15E has a lot of parasite drag, so that's the real reason. If there were none of the external hardpoints, pods, etc, hanging from it, I could get it a lot faster.

The max airspeeds vary by altitude, weight, etc. It's a curved line on a chart. I don't have it in front of me, so I can't tell you what it is. Just to give some perspective, it's greater than Mach 2 and 700 KCAS.

In general, though, the structural limit at 1.0G is greater than when the airspeed attainable on a stock configured aircraft when thrust=drag and it won't accelerate anymore.
 
Thanks.

So parasite drag is the real enemy. What about newer, cleaner designs like the F18 and the F22? Do they encounter the same type of problems?
 
The Hornet is advertised as 1.8 mach for the maximum speed. The best I ever got was 1.4 in a jet with only pylons, nothing hanging on them, and starting at about FL410. In the Super Hornet, the best I ever got is about 1.2, and that was without the inboard pylons installed and only a single centerline tank. For those that don't know, the E and F models have their inboard pylons canted a couple degrees, for what the engineers thought was going to be needed for bomb separation, but is actually only a permanent speed brake. A slicked off Super will preform pretty well, with less than a full bag of gas, you can get airborne in about 1,000 feet. The Hornet has a G limiter as well, due to the folding wings the max G is 7.5, but if you are smooth with your pull, you can see higher than that without popping a code for overstress which requires an inspection.

A combat loaded jet will be a pig and is not going to go very fast until you jettison everything and that can get expensive quickly. As far as all of the formulas and rules posted, I have no idea what you are talking about, I just push the "I believe" button and go fly, there is way too much other stuff to know and I cannot waste any brain capacity worrying about the aerodynamics and physics of it.
 
. As far as all of the formulas and rules posted, I have no idea what you are talking about, I just push the "I believe" button and go fly, there is way too much other stuff to know and I cannot waste any brain capacity worrying about the aerodynamics and physics of it.

What Ive been trying to tell people in the CFI Forum here for a long time. There's "need to know" information, and there's "nice to know" information.
 
I've only seen like 1.2 going downhill, single bubble, in full blower, and I started out mid 30's.....probably could have gone faster had I been more aggressively nose low, but out over the water, I don't have the cajones to do that. The Hornet is quite a draggy jet; one of the techniques we use to accelerate quickly is a quick unload which will clean up the LEF's and TEF's which dig way down in maneuvering/loaded flight, and will really slow us down. Not really a factor in a mach run, but just speaking to the general drag associated with the airframe. To add to C-182's very informative post, we also can hit the paddle switch on the stick in a pinch to exceed the G limiter by a certain amount, but this would certainly result in an overstress and I've never done it.
 
As far as all of the formulas and rules posted, I have no idea what you are talking about, I just push the "I believe" button and go fly, there is way too much other stuff to know and I cannot waste any brain capacity worrying about the aerodynamics and physics of it.

b b b b b buuut the interview gouge for american eagle airlines says I need to know advanced aerodynamics before they issue me epaulets!
 
What Ive been trying to tell people in the CFI Forum here for a long time. There's "need to know" information, and there's "nice to know" information.

Only trouble is that much of what many consider "nice to know" can save your life in a pinch.
 
Only trouble is that much of what many consider "nice to know" can save your life in a pinch.

True, and situation dependant. In my former business, the times it would help you were far outweighed by the times it could kill you if your mind was spending any brain bytes on it.
 
The F-15E has a lot of parasite drag, so that's the real reason. If there were none of the external hardpoints, pods, etc, hanging from it, I could get it a lot faster.

The max airspeeds vary by altitude, weight, etc. It's a curved line on a chart. I don't have it in front of me, so I can't tell you what it is. Just to give some perspective, it's greater than Mach 2 and 700 KCAS.

In general, though, the structural limit at 1.0G is greater than when the airspeed attainable on a stock configured aircraft when thrust=drag and it won't accelerate anymore.


From your post (and others), it seems that Vne is a bit of a dumbing down of the factors involved in general aviation (I never got a c-172 up to Mach 2--tried--but the best I could do with a 40 knot tailwind was 170 kph).

Behind Vne is our beloved Load Factor and I am thinking that is the key point; or am I missing something?

Awesome post, btw
 
btw,

Thanks to all you pros who put up with people like me.


I read your replies and get humbled very quickly.

thanks so much.
 
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