From an engineering point of view, really,another reason you want your plane to be able to go Mach 2 is for the same two reasons your conventional Toyota sedan is capable of speeds ludicrously higher than you should ever drive it:
Because in order for it to work well at a more commonly needed speed, it needs to be able to go faster than that. If you conclude your plane will need to go Mach 1.2, having Mach 1.2 be its absolutely maximum speed is a terrible idea, for the same reason that having your Camry’s top speed by 78 MPH; you do not want to regularly operate the machine at the limits of its capability and
It’s also a matter of ACCELERATION, not just top speed. The same power than will push a Fighting Falcon to Mach 2 is the power that gets it from a cruising speed to an attack speed, or that will enable it to quickly recover speed after executive a maneuvre that sapped a lot of its airspeed.
On the first the B-58, though a bomber not a fighter, had a Mach ~2 top speed specifically because it was believed the capability of then standard Soviet S-75 (aka SA-2) SAM system was significantly lower against a target that fast than a subsonic one, besides making it a difficult target for slower Soviet interceptors which had already appeared and around as fast as the MiG-21 which appeared about the same time as the B-58. But, even under that assumption about system capabilities the number of home defense Soviet SAM sites increased into dense zones at least in western USSR where the B-58 could practically reach, and the B-58’s endurance was only marginal even assuming the a/c would only have to dash briefly through limited SAM coverage areas. This is mainly why the program was cut back. The a/c then adopted low altitude tactics like other SAC bombers but in that situation was just another subsonic penetrator but with low endurance and payload. So it didn’t serve for long.
But now and for a long time M 2, at the medium altitudes where it’s practical, isn’t fast enough to help much against later generation heavy SAM’s.
On the second theme this is absolutely true of an a/c like say the F-16. It was designed with lots of thrust in the transonic range so it could accelerate rapidly from cruise to transonic, pull lots of sustained g’s (pulling 7 g’s the wings are producing ~7 times as much induced drag as in level flight at the same speed, assuming the lift/drag ratio as good), and climb like hell. The ability to barely reach M 2 is basically a byproduct of that, not a design goal. The F-16 has a fixed geometry inlet optimized for the transonic range, which loses efficiency above around M 1.6 unlike the variable geometry inlets in the F-15 which can be optimized for higher Mach.
For example the early, light, F-16A Block 15 could reach Mach 2.05 around 36k ft with static thrust of 23,830lbs at combat weight 19,169 lbs, clean but for a pair of wingtip AIM-9’s, thrust/weight ratio 1.24. As noted above the max official speed of F-15C with 4 AIM-7 otherwise clean was Mach 2.34 with 46,900lbs static engine thrust at combat weight 38,982, 1.20 ratio (declassified official stats). The main reason was the F-15’s variable geometry engine inlets. A speed significantly above M 2 was still a design goal in itself in the F-15’s case.
The eye watering ‘energy maneuverability’ of the early lightweight F-16A was also at pretty low altitudes besides lower speed. It could only sustain 7g’s up to a little more than 10k ft, had 45k ft/min climb rate at that altitude (~15 times a good climb rate for a WWII fighter), top speed at 10k ft ~M 1.4. The ability to barely exceed M 2 was over a narrow range of much higher altitudes where sustained g and climb rate were much lower.
B-58 actually had good endurance compared to anything except a long-range heavy bomber. But while its endurance was definitely an issue vs a B-52, I don’t think the B-58 was phased out early mainly because of “marginal” endurance. Rather it had numerous issues. Of the 116 constructed, 26 crashed in accidents.
Re the other statements about Mach 1.8+, etc, remember air drag increases as the square of velocity. So while Mach 2 is only 10% faster than Mach 1.8, it entails 24% more drag. Also aerodynamic heating increases as roughly the cube of velocity, so small increases in speed produce large increases in airframe heating.
To help answer the OP question of under what circumstances would [Mach 2] actually be needed in a fighter, we can try to examine history. IOW to answer “why would you do it”, ask “has it ever been done by a fighter in a true tactical situation”.
Throughout all military aviation history, has there ever been Mach 2 flight by any production pure fighter plane from any country in a tactical situation? Comprehensive data is difficult to find but in general I think the answer might be no, at least for “pure” fighters.
Interceptors are an interesting grey area, because there would possibly be a more rational need for Mach 2 on that mission type. However purpose-built interceptors are no longer constructed, for the most part. The Mig-25 is sometimes listed as a “fighter” and it definitely flew Mach 2 on a regular basis. But it’s really an interceptor.
The F-106 was a purpose-built interceptor which was later sometimes used as an air-to-air fighter. It was designed to reach Mach 2 and carried internal weapons which helped. To show the difference between its “nameplate” max Mach 2.3 and the real world, the F-106 apparently only reached this on one occasion for a speed record attempt. It reached Mach 2.31 over a short 11 mile course, and this resulted in paint burned off leading edges, canopy panels deformed from heating and the engine was ruined. Source: F-106 Delta Dart Illustrated, by Lou Drendel.
I don’t have the reference but I read a detailed account of an F-104 pilot who reached Mach 2. It wasn’t combat but a ferry flight. He described how rare and difficult it was to achieve. At Mach 2 the plane was very sensitive in pitch and he accidentally zoom climbed over 60,000 ft and the engine nearly flamed out which would have probably resulted in loss of aircraft. He felt fortunate to survive.
I have read some articles recently postulating that with the arrival of supersonic “cruise” missiles fast interceptors might make a comeback. Like the MiG41.
Yes that is the main reason the B-58 had such a short service life. Lots of planes crashed alot back then. The B-58 just didn’t have anything compelling in the way of range/range payload once forced to adopt low altitude subsonic tactics. And the planning had to be changed to that because it didn’t have the endurance at Mach 2 to
pass through the greatly thickened belts of V-75 (SA-2) missile sites sprouting up in the 1960’s. Originally the idea was to quickly dash through limited areas of V-75 coverage where it was assumed (this wasn’t confirmed obviously in real combat) that M2 speed would seriously degrade the capability of that system, besides the then-new deception repeater electronic countermeasures the B-58 was one of the first a/c to carry (and other models of that general type of ECM did prove effective against the fire control radars of V-75 in Vietnam).
Consider the then-secret, subsequently declassified, ‘Standard A/c Characteristics’ document of the B-58A compiled in 1959. The specification for ‘basic mission’ was at a radius of 3910 nm with ‘combat zone speed’ of 1147 kts (ie ~M2) at around 58k ft, but maintained for only the last 100nm in and out. Obviously 3910nm is much farther than B-58 CONUS bases to the USSR, that’s where aerial refueling and/or staging through bases in Western Europe would come in. But graphs in the booklet show that assuming the a/c had to dash at M2 for 500nm in and out, the total radius shrank to only 1700nm. And by the early 60’s an a/c might have to fly that far pretty continuously within range of V-75 sites contrary to earlier expectations. That’s what undid the original concept of the B-58, leaving it just another low altitude subsonic penetrator, but with far inferior range/payload in that mission profile compared to the B-52.
Even in terms of quick googling, your own first link says:
“Major General John McConnell, SAC’s Director of Plans, declared that his command was interested in the development of the B-58 as a future weapon system but not for the SAC inventory. McConnell called the B-58 a “short-legged plane,” adding that “as long as Russia (and not Canada) remained the enemy, range was important.” The B-58’s range limitations would haunt it throughout its operational life.”
In the 1950’s high speed interceptors were built to counter the threat of nuclear bombers. High altitude aircraft were built to fly above the ceiling of intercepting jets and air to air missiles. And high speed bombers like the B-58 and the B-70 were a response to the increasing speed of intercepting aircraft.
With the shift to ICBM’s as the primary mode of nuclear attack, high speed interceptors became somewhat obsolete. The Soviets developed surface to air missile technology in the late 1950’s, obsoleting the high altitude, high speed bomber. After Gary Powers was shot down in his U2 over Cuba, altitude was no longer considered safe Planes like the Avro Arrow became obsolete, and other high-speed interceptors like the F-104 were transitioned to other roles, with mixed success.
Now we focus on stealth, terrain hugging and manoeverability instead of raw speed and altitude for survivability. There are still reasons for high-speed flight as mentioned above, but high mach speed is generally not the primary requirement for jet fighters.
Another thought: the us military was probably thinking primarily about offense when they specced out the last couple generations of fighters. Since you can’t defend against ICBMs with fighters and the us Homeland is geographically protected, offense is a solid defense. Instead of intercepting enemy fighters, bomb their airfields.
Anyways, on offense, you want the enemy to have as little warning of your attack as possible. So either you use extremely fast aircraft, minimizing warning time, or you use stealthy aircraft.
Both fast and stealthy aircraft are still vulnerable to being shot down at close ranges. (radar can work against stealth at close range or there are other sensors like IR).
The absolute top speed of a given aircraft is just that. Presumably, the faster the absolute top speed the fast the other speeds, as well. Things like climb speed, speed loaded out etc. Its like saying the top speed of the new Corvette is 250 MPH or whatever. It can reach that speed but no one is expected to drive it like that (except under controlled conditions) If you build something to go fast, the question of “Just how fast CAN it go?” will always be there. Its bragging.
It’s true some sources mention the alleged B-58 short range as a reason for its phaseout, in particular the book “Rearming for the Cold War 1945-1960”.
However a review other literature doesn’t consistently show range was the primary decision criteria, but rather one of several. This is also common sense - the B-58 was essentially replaced in SAC by the FB-111 which also had range limitations and also required significant air-to-air refueling. The FB-111 served in SAC from about 1970 to 1991.
Obviously the FB-111 had terrain-following radar which helped low altitude penetration and the B-58 did not, but the B-58 was capable of the low-level mission. In one practice bombing mission the B-58 flew two hours (about 1,200 mi) at 0.92 mach at altitudes from 200 ft to 500 ft AGL (Source: “The B-58 Blunder” by George Holt, Jr).
Like the B-52, the B-58 required structural inspection, repair or upgrades for the new low altitude mission. Those were completed in 1967. By contrast the F-111 was designed at the outset for the low altitude mission.
The B-58 was a complex aircraft and would have required further upgrades for newer weapon systems. In 1965 the decision was made to replace the B-58 with the FB-111 which had roughly similar range but terrain following radar, better integration with newer systems, and was projected to have less eccentric (ie safer) flying characteristics. This proved true as the FB-111 had a very low loss rate.
True, though Major Rudolf Anderson managed to get shot down over Cuba in a U-2 as well, during the Cuban Missile Crisis.
joema, why did the FB-111 have a lower accident rate than the F-111 tactical models? Fewer combat missions? Fewer low-level training missions in bad weather? It seems like they would have similar non-combat loss rates.
EDIT: thanks for the cites and info on the B-58 and others, guys. This thread has been a treat to read.
Uh, yeah. And I meant to say 1960. No idea why I conflated that with the Cuban missile crisis. Probably because they are often mentioned together in stories about that era of the cold war.
I don’t have the specifics and actually I don’t think the F-111 non-combat loss rate was very high, either. I didn’t mean FB-111 vs the F-111 only that the FB-111 had a low loss rate in general and especially compared to the B-58, B-47, etc.
There is a book which lists some of these details but I don’t have it: “One-Eleven Down: F-111 Crashes and Combat Losses” by Steven Hyre.
Back to the OP question of need to go Mach 2, there is some interesting data on this NASA page. It supposedly lists the max mach capability of various fighters at optimal altitudes. Many fighters in a clean configuration can theoretically briefly reach Mach 2 from an aerodynamic standpoint. But in real world tactical situations I doubt this is ever done. There is some doubt whether it has ever been done for a pure fighter in a tactical situation: Quest for Performance: the Evolution of Modern Aircraft - NASA Technical Reports Server (NTRS)
You might liken the perceived vs actual use of Mach 2 to the perceived vs actual rate of “gun kills” in air-to-air fighter combat. Surely among all the all air forces around the world this must happen a lot. However apparently the last “gun kill” by any fighter from any nation in air-to-air combat was about 1988: https://csbaonline.org/uploads/documents/Air-to-Air-Report-.pdf
Because it only does one thing well and that’s fly mach 3 at 85,000 feet.
It doesn’t climb well and turning takes a ridiculously long time.
It’s also a hanger queen and not something you get up in the air with 2 minutes of warning.
Cudos to engineer_comp_geek for getting it right. It was built off the A-12. The changes they made in the chines by the nose changed the stability of the plane so they had to add stabilizer underneath and it folded for landing.
Interesting fact, it was built with Russian titanium that was acquired by phony CIA companies buying it for other reasons.
