BACK TO BASICS: SPEED



Welcome to "Back to Basics"; an ongoing series in which we will attempt to "get back to basics".  Each week (or so) we will examine one crucial aspect of a fighter and how the fighters vying for Canada's FFCP compare.  

What makes a fighter aircraft...  A fighter?  

The ability to carry offensive weapons is the primary factor, obviously.  So is detection equipment, maneuverability, range, and (recently) stealth.  What really excites our inner 12-year-old when it comes to fighters, however, is speed.  

It is a fair assessment.  What good are weapons if you cannot catch up to your target?  A long-range fighter bristling with weapons, sensors, and lots of fuel ends up to be a middling platform without the speed to put it all in play.

Since conception, fighter development has focused on speed.  Speed is not only makes a fighter deadly but acts as its greatest defense.  Speed allows a fighter to intercept enemy bombers and catch ground targets off guard.  Speed helps a fighter evade enemy fighters and missiles.  

In fighter maneuvers, kinetic energy is paramount.  For those of us forgetful of high-school physics, kinetic energy is simply speed + altitude.  Altitude is important because it can quickly be converted into speed (up to 9.8 meters per second per second) in a dive.  

For fighter pilots speed is life, and altitude is life insurance.  

YF-12, the SR-71's missile-toting brother.
During the early Cold War years of the 50s and 60s, fighters began to get faster and faster.  Propellers were cast aside for increasingly more powerful jet engines.  The sound barrier was broken.  A greater understanding of aerodynamics and improved manufacturing methods allowed for sleeker shapes.  Soon, fighters were capable of flying faster than the twice the speed of sound.  Some designs even approached Mach 3.  Some even surpassed it.  

There was a brief period when speed appeared to be the ultimate trump card.  Mach 2 seemed to be a prerequisite for fighters like the F-104 and MiG-21.  Even bombers like the B-58 Hustler and Tu-22M could reach twice the speed of sound.  Soon, the Mach 3 XB-70 Valkyrie bomber took flight with equally fast interceptors like the MiG-25, YF-12, and XF-108 Rapier ready to give chase.  

Mach 3 turns out to be just as difficult a barrier as Mach 1, however.  Possibly more so.  At speeds that high, air friction heats up most metals to the point of melting.  Stronger materials, like titanium, can be used; but they are much more expensive and difficult to fabricate with then steel and aluminum.  Going beyond Mach 3 also requires different engine technology, as the typical turbojet engine simply cannot function without some clever wizardry.  

When speeds approach hypersonic, the challenge goes up exponentially as superheated metal interacts with fuel, turbulent air, and destructive harmonics conspire to shake things apart.  Here, be dragons.  

Fighter designs have lost that loving feeling for the need for speed.  

Just as aerospace engineers were tackling the difficulties associated with high airspeeds, missile development was becoming increasingly advanced.  Exceedingly fast aircraft suffered from a major weakness; no matter how fast you made an aircraft, it was easier and cheaper to make a missile that could fly faster.  

Compare a fighter to a missile.  The fighter is far heavier, needs to take-off and land, fly at different speeds and altitudes, and also must take care of the squishy bits in the cockpit.  The missile, on the other hand, is a relatively simple, disposable object that weighs several hundred pounds.  Many also have the advantage of getting a "boost" by being launched by an aircraft, booster rocket, or similar.  

As missile guidance technology improved, less emphasis was placed on fighter speeds.  This led to modern fighters actually becoming slower than the fighters they replaced.  Modern doctrine would seem to be to let the missile do most of the work.

Modern fighters still need to be fast, however.  The faster the fighter, the faster it can intercept potential threats, enter and egress contested airspace, or position itself over the battlefield.  In an encounter between two opposing aircraft, the faster of the two will have better control over whether and/or how they engage or retreat.  Speed is still a powerful defense against enemy fire, especially when combined with maneuverability.  Offensively, that same speed is just as important.  Remember kinetic energy?  A fast, high flying fighter will bestow that same kinetic energy on any missile it fires.  This means a missile fired at 40,000 feet and Mach 1 will end up flying faster and much further than the same missile shot at sea level and stationary.  

Legendary "Fourth generation" fighters like the F-15 and Su-27 combined speed and maneuverability to become more deadly than fighters that lived on speed alone.  Newer fighters, like the Typhoon and F-22 Raptor, take an even more holistic approach, adding increasingly more advanced stealth, radar and missile technology to go along with speeds in excess of Mach 2.  

For modern fighters, speed is not as important as it once was...  But it is still important. 

So how do the FFCP fighters compare?


F/A-18 Super Hornet
The Super Hornet is by no means a sluggish aircraft.  No aircraft that can break the sound barrier can be dismissed as "slow".  However, compared to other fighter aircraft (including the F-14 Tomcat that preceded it) the F/A18E/F could be classified as "underwhelming".

When first revealed, the Super Hornet was classified as having the same Mach 1.8 top speed as the "legacy" F/A-18 Hornet.  The classic Hornet was slightly slower than contemporaries like the F-14 (Mach 2.34), F-15 (Mach 2.5), and F-16 (Mach 2.05).  Of course, those numbers are based on a "clean" aircraft flying at optimum altitude and full afterburner, so take them with a grain of salt.

With the Super Hornet, that "grain" of salt turns into a giant boulder.  It has become rather infamous for its canted pylons that drastically increase drag at high speeds.  Increased drag means slower speeds and reduced range.  That reduced range necessitates additional fuel carried in external tanks which results in even more increased drag.

Thankfully, the latest "Block III" upgrades address this issue somewhat.  By adding conformal fuel tanks, the "Advanced Super Hornet" greatly increases its fuel capacity while adding only a minimal amount of drag.  Boeing now lists the Super Hornet's top speed at a slightly lower Mach 1.6, but it will likely see faster "real world" speeds than before.

Unfortunately for the Super Hornet, it has the distinction of being the slowest contender in the FFCP.


F-35 Lightning II
On paper, the F-35A Lightning II shares the same Mach 1.6 top speed as the Super Hornet.  Some decry the JSF for being slower than many of its predecessors but the F-35's "real world" top speed is faster than it would initially seem.

As mentioned before, most fighters' "top speed" is reached in an aerodynamically clean state:  Minimal weapons (if any) and no external fuel tanks.  Needless to say, a fighter with barely any weapons and very little fuel is of little use for anything except getting into the record books.  The F-35 bucks this trend by carrying sufficient amounts of fuel and weapons internally.

Impressively, the JSF can carry up to two AMRAAMs and two 2,000lb JDAMs internally.  That can be switched to four AMRAAMs (soon to be six) for A2A (air-to-air) mission.  The F-35A also carries a substantial amount of fuel internally.  Both A and C variants store fuel in the space that occupies the lift fan in the STOVL B variant.  This gives a "clean" F-35 similar range to older fighters loaded with external tanks.

Even with external weapons, the F-35 will be less draggy and likely be faster than a similarly loaded up Super Hornet.  One cannot overemphasize the advantage of having less external pylons to drag around.

It would be remiss not to mention the issues some F-35s have at higher speeds.  During testing, it was found that supersonic speeds at high altitudes would "blister" the stealth coating on the horizontal tails and tail boom.  This issue seems to be specific to the B and C variants, and not the A model on offer to Canada.

Saab JAS-39C (not "E", sorry)

With a listed top speed of Mach 2, the Saab Gripen is easily the fastest of the three fighters competing to replace the CF-18.  The JAS-39E is also the only remaining FFCP contender capable of supercruise.  This seems rather counterintuitive, as it is also the least powerful.

The Gripen has, literally, one half of the Super Hornet's power.  Its svelte airframe houses a single GE F414 turbofan (22,000 lb of thrust) whereas two are found in the F/A-18E/F.  The F-35 almost matches the Super Hornet with its massive single Pratt & Whitney F135 (43,000 lb of thrust).

So how does the Gripen manage to outrun fighters with double the power?  A combination of simple Newtonian physics and more complicated fluid dynamics.  At about 8 metric tonnes, the Gripen is substantially lighter than the 13 tonne JSF and 14 tonne Super Hornet.  Its smaller, canard-delta design also happens to be aerodynamically optimized for high speeds.  Great attention was paid to the area rule and achieving minimal drag.

By contrast, the other two fighters rely mostly on brute force to break the sound barrier.  The Super Hornet's design required several compromises necessitated by its need for carrier landings and commonality with the "legacy" F/A-18.  The JSF's aerodynamics required even more compromises still, having to work around stealth and commonality with both a carrier and STOVL version.

The Gripen's fleet-footedness comes with two major caveats, however.

First of all, the Gripen E has not completed all of its testing.  The numbers that Saab have published were achieved by the "Gripen NG" test aircraft.  Minor differences between the "NG" and "E" versions of the Gripen may result in downgrading those performance numbers.  The difference would likely be minor, however.

Second, the same physics that enable the Gripen to outrun the other planes in "clean" form will conspire against it as its load-out increases.  While a few air-to-air missiles would have little effect, 10,000 pounds worth of payload will likely have much more effect on the Gripen than it would the other two.

 The Gripen is the sleek sports car while the other two act more like SUVs.  With a light load, the advantage is clear.  Once you start adding baggage...   "You're gonna carry that weight."

X-15.  The record holder.
Speed is not all-important to a fighter.  If it were, modern fighters would look more like the X-15 or X-43.  Make no mistake, however, SPEED IS IMPORTANT.  Exactly how important depends on the mission, but the faster fighter will always be preferable when all else is equal.  The faster a fighter is, the more it will be able to dictate the terms of engagement and the more kinetic energy it will impart on its weapons.

For Canada, where distances are great and airbases are few and far between, speed is definitely a must.




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