BACK TO BASICS: MANEUVERABILITY



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. 

Is there anything more thrilling than watching a fighter jet pull impossibly tight turns, loops, and rolls at mind-boggling speeds?  Maybe a few things come to mind, but not many.  Not a single person watched TOP GUN for its romantic subplot.  

Fighter maneuverability does more than excite people at airshows and make a star out of Tom Cruise.  For the kill-or-be-killed world of fighter combat, agility is requisite for survival.  Like speed, a fighter with superior maneuverability will have better control over the engagement.  A fighter without speed and agility is more likely to become the hunted instead of the hunter.  


The purpose of fighter maneuvers is simple:  Position your fighter so that it is in the firing range and arc of your weapons whilst keeping your aircraft away from theirs.



While simple in theory, basic fighter maneuvers are a complex subject.  There is more to it than a simple barrel roll.  The air, after all, is a three-dimensional space in which to maneuver in.  In this space, the aircraft themselves need to follow the rules of physics.  A maneuvering aircraft is constantly at odds with momentum, gravity, and air friction. 

On top of all that, there are the aircraft and pilot's own physical limitations.   Violent maneuvers cause extreme stress on both the airframe and the pilot.  For many modern fighters, flight software limits maximum turning speed, either to keep the aircraft in one piece or to keep the pilot from blacking out due to G-LOC (g-force induced loss of consciousness).  

It is a testament to modern jet fighters that their limits far exceed that of mortal men (and women).  As the aircraft changes direction, its centrifugal force (measured in Gs) can far exceed that of the earth's gravity.  Fighter pilots need to be fitted for a G-suit that uses air bladders to squeeze blood from the lower extremities towards the body and head.  A pilot can also utilize the "Anti-G Straining Maneuver" to combat the effects.  Without these, the pilot's brain would soon be starved of blood and oxygen (hypoxia), causing tunnel vision and possibly unconsciousness.  The opposite effect happens during a violent "pitch down" maneuvers and too much blood rushes into the brain, causing a "red out".  Even with preventive measures, high-G maneuvers can only be maintained for a short time.  
Part of the allure of UCAVs (unmanned combat aerial vehicles) is that they have the freedom to exceed the limits of a human pilot.  

It ain't just for air shows
How well an aircraft maneuvers depends on how well it can overcome the forces affecting it.  During steady flight, an aircraft has to overcome the both force of gravity and the force of drag.  Lift (produced by the wings) overcomes gravity while thrust (produced by the engines) overcomes drag.  While simple in theory, there are countless variables in play.  The faster an aircraft goes, the more drag it produces.  Higher altitudes mean less drag as the air gets thinner.  Thinner air also means less lift, however.  An aircraft's overall design must maintain a balancing act to provide optimum performance.

This is easy for something like a jetliner, it merely has to take off, cruise at an efficient speed and altitude, then land.  This is why jetliners all pretty much look the same.  A fighter needs to be much more versatile.  It may be tasked with reaching supersonic speed, maneuver violently during combat, then fly slow enough to land on an aircraft carrier.  This requires compromises as aircraft engineers prioritize one factor over another.  An aircraft that stable at slow speeds may not be stable at high speeds.

Modern aircraft design does have the advantage of "fly-by-wire".  Instead of being directly under the control of a pilot, an aircraft utilizes computers to interpret the pilot's inputs.  This flight control software (FCS) can make multiple calculations per second, enabling constant, minute adjustments.  This frees up designers to utilize relaxed stability designs that would be nearly impossible to fly by human hand alone.  The advantage here is that, being relatively unstable, the aircraft is much more willing to change direction at a moment's notice.

Relaxed stability designs, combined with high thrust-to-weight ratios and wings capable of providing massive amounts of lift, result in fighter aircraft that can seemingly violate the laws of physics.


Pugachev's Cobra Maneuver. 

While maneuverability in general can be described as getting the aircraft to move as the pilot wishes, it is much more difficult to give a hard and fast rating.  An aircraft's handling characteristics is a much more subjective subject than speed or payload.  There are plenty of subtleties at play; everything from the general weight distribution of the aircraft to the fine-tuning of the FCS.

What we can measure is how each aircraft deals with fighting the forces of momentum.  For those of you rusty on high-school level physics, this means how well it can accelerate in any given direction using its thrust and lift.

For our purposes here, we will concentrate on the more obvious and objective ratings of each candidate in Canada's FFCP.  We will leave a true "seat of the pants" evaluation to the pilots of these aircraft.

This includes:

  • THRUST-TO-WEIGHT RATIO (more thrust = more better)
  • WING LOADING (the less weight per total wing area the better)
  • g-LIMIT (the maximum turning force)
  • SIZE (less mass and bulk is always easier to move)
  • GENERAL AIRCRAFT DESIGN (what design aspects favor or hinder maneuverability)



Of the three aircraft vying to replace the CF-18 Hornet, only the Super Hornet could be seen as a downgrade in maneuverability.  This is not to say that the F/A-18E/F is a clumsy or awkward aircraft, it just (barely) fails to meet the exceptional handling characteristics of aircraft it is derived from.  It is still a better aircraft in almost every metric.

The Super Hornet is an upscaled Hornet, and it it shows with performance numbers nearly identical to its progenitor.  Thrust-to-weight ratio (0.93) is the lowest of the three contenders and just slightly lower than the CF-18's 0.96.  Its wing loading (456kg/m2) is slightly worse than the legacy Hornet, while its g-limit is slightly better (7.6 vs 7.5)

While the Super Hornet looks superficially identical to the CF-18, it is a much larger aircraft.  Roughly the size of an F-15, the F/A-18E/F pushes the boundaries of what can be considered a "medium" sized fighter.  Out of the three FFCP contenders, it is the largest and heaviest at 14.5 tonnes empty.

As far as general design, the "Rhino" is nearly identical to the CF-18.  This design is rightly praised for its low speed, "high alpha" handling characteristics.  Being a carrier-based fighter, the Super Hornet's literally lives or dies on its ability to land on a boat.  It does this quite well thanks to its signature leading edge extensions (LEX) providing extra lift and canted tail-fins providing extra control at high angles-of-attack (AoA).

Unfortunately, the same cannot be said about the Super Hornet's high-speed handling characteristics.  As it approaches the speed of sound (transonic) its design produces excessive drag.  While certainly not terrible, the compromises baked into its design keep it from approaching greatness.  Such is the cost of versatility.

The Super Hornet is akin to a pick-up truck.  Plenty of power and versatility, but it will always have to contend with its bulk.



Despite rumors to the contrary, the F-35A is a fine-handling plane.

No, it is not as maneuverable as the F-16 it intends to replace.  This is disappointing, but should be seen more as an accolade for the F-16; one of most agile fighters ever developed.  The JSF was meant to benchmark the (legacy) F/A-18, a task it succeeds at.

The F-35A actually has an impressive thrust-to-weight ratio (1.07 "loaded' with 50% fuel).  It also exceeds both versions of the F/A-18 g-limits (9.0).  Unfortunately, it is let down by its rather stubby wings that provide 526kg/m2 of wing loading.

Size-wise, the JSF is slightly smaller than the CF-18.  Looks can be be deceiving, however.  It is a much bulkier aircraft with an empty weight of 13.3 tonnes compared to the legacy Hornet's 10.4.  This, despite the F-35A's lack of carrier-specific gear, and more modern design and materials.

Where the F-35 suffers is in its general design layout.  Required to replace multiple aircraft in multiple roles, the JSF requires a great many compromises.  Its short, stubby wings are predicated by its STOVL variant, as is its "hunchback" and engine placement.  The placement of its wings, tails and elevators pay homage to its carrier variant; which, like the the F/A-18, requires low-speed stability.  Add stealth to the mix and things get even more complicated.  Stealth designs are rarely aerodynamically efficient.   While some may tout the JSF's internal weapon storage as enabling the F-35 to always fly "clean", the truth is not so simple.  Building an airframe around two large boxes with doors that open at supersonic speeds requires a monstrous amount of reinforcement.  In simple engineering terms:  "Holes can be heavy".  

The fact that the F-35 flies as well as it does is a testament to the skill of its designers.  It  lacks the sleekness of the F-16 or the aerodynamic trickery of the F/A-18.  Instead, the JSF relies on sheer brute force to get the job done.  The JSF can only be described as "sleek" in the same way as a minivan.  It might have plenty of power and cargo space, but it would not be your first choice for a spirited drive.


This one is really no contest.

The Saab Gripen has two major advantages when it comes to maneuverability.  First of all is down to the simple laws of physics; smaller and lighter means less momentum and therefore less energy needed to change position.  Also, its designers never had to accommodate the needs of a carrier version, a STOVL version, or stealth.  Their benchmark was the Su-27, an aircraft legendary for its handling capabilities.

The older Gripen A,B,C, and D models were already known as a "supermaneuverable" fighter.  The new E/F models continue the tradition with an improved (1.04) thrust-to-weight ratio while keeping its wing loading (283kg/m2) and g-limits the same.  Despite being slightly heavier than older models, the E utilizes slightly larger wings and a much more powerful engine than its predecessors.

Compared to other fighters in its class, the Gripen is pint-sized.  Some would argue that it does not even qualify as a medium fighter, being only 8 tonnes empty.  Dwarfed by the Super Hornet, the Gripen is actually much closer in size to the CF-5 than it is the CF-18...  Despite exceeding the CF-18's capabilities in almost every way except maximum payload.

The Gripen's does not only use its smaller size to its advantage.  Its delta wings provide it with enormous amounts of lift at high speeds.  Normally, delta-wing layouts are not optimal for lower speeds, but the Gripen counter-acts this by utilizing close-coupled canards.  These canards add lift and help divert airflow over the wings during high-alpha maneuvers, allowing for near-STOL capabilities while maintaining the advantages of a delta wing.  The Gripen also utilizes a tail-heavy design that both reduces drag and induces a constant "pitch up" tendency that increases instability (a desired trait in a fighter).

The Gripen's small size and uncompromising design make it far and away the best-handling plane out of the three FFCP candidates.  Imagine it as the small sports sedan when everyone else is piloting crossovers and trucks.

CF-18 at "high alpha"
There are some who may wish to downplay the need for maneuverability in this age of advanced missiles.  The argument could be made that an aircraft's survivability is much more dependent on advanced countermeasures and stealth rather than "turning-and-burning".  This may be partly true, but the same argument was made years ago, leading to harsh lessons over the skies of Vietnam.

An entire "generation" of fighter aircraft was birthed by the need to regain an edge in maneuverability.  No matter how advanced the missile, it is always best fired "on the enemy's six".  The only way to do that, is outmaneuver them.

[NOTE:  IT HAS COME TO MY ATTENTION THAT SOME OF THE NUMBERS PRESENTED FOR THE GRIPEN E ARE IN FACT FOR THE "GRIPEN NG" DEMONSTRATOR.  THE NG LACKS CERTAIN EQUIPMENT AND IS ABOUT 800KG HEAVIER, MAKING FOR WORSE T/W RATIO AND WING LOADING NUMBERS.  THIS WOULD NOT CHANGE MY RANKING OF THE AIRCRAFT, HOWEVER.]

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