BACK TO BASICS: RANGE

Rutan Voyager (All around the world without refueling)
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. 

No matter how capable a fighter aircraft may be, it is of little value if it cannot get to where it needs to be.  While this fact may seem obvious, many fighter comparisons seem to either gloss over an aircraft's range or ignore it entirely.  One could make the argument that, in the age of aerial refueling, an aircraft's maximum range is no longer a priority.  Maybe so, but that assumes ample resources will be available; something that is not always the case.  

Perhaps one of the reasons a fighter aircraft's range is often overlooked is because there is never a clear-cut answer.  Unlike top speed or g-limits, which have a clear "maximum" number; an aircraft's range often comes down to "it depends".  

CP-107 Argus (up to 31 hours of flight on a single tank!)

An aircraft's ability to travel a certain distance depends on an overwhelming amount of factors.  Weight, aerodynamics, engine efficiency, and amount of fuel carried are the most obvious factors, but these only brush the surface.  External factors like altitude, wind speed, and even ambient temperature also play an important role.  Add to this the behavior of the aircraft itself (speed, maneuvering, payload, etc) and predicting an aircraft's range becomes a "best guess" type of affair.  

Typically, long-ranged aircraft follow a certain pattern; fuel efficient engines that provide just enough power, lots of fuel, and long, thin wings that provide optimum lift-to-drag.  

Unfortunately, fighter designs are not the most fuel efficient.  High powered engines (with afterburners), weapon storage, and aerodynamics optimized for high speed maneuvers all conspire to make the aircraft decidedly inefficient.  

Thankfully, there is a fix for that:  Add more gas.  


Adding fuel to a P-51.

Specifically, add the ability to carry more fuel.   This is done by simply adding external tanks.  

First used in the Spanish Civil War and seeing widespread use in World War II, external fuel tanks could add a substantial amount of fuel to an aircraft.  Unfortunately, these did so at the cost of additional weight and drag.  They also had a detrimental effect on the aircraft's handling, increasing the moment of inertia.  Thankfully, these tanks were designed to be released if needed; hence the term DROP TANKS.  An aircraft could take off, utilize the fuel in its drop tanks, jettison them, then carry out the rest of the mission unimpeded.

Despite their large, bulky appearance, drop tanks themselves are relatively lightweight.  Constructed of lightweight aluminum, fiberglass, or even paper; it is the fuel inside that imposes the majority of the weight penalty, not the tank itself.  The tanks still impose a harsh aerodynamic penalty, however. They also increase an aircraft radar cross section (RCS).   External tanks also need to be specifically designed and tested to be approved for supersonic flight.  These tanks also reduce a fighter's payload capacity, having to be mounted on an external pylon.  

Another method of adding fuel (and range) to a fighter aircraft are conformal fuel tanks (CFTs).  These external tanks allow a fighter to carry additional fuel in large, blister-like tanks attached to the fuselage.  Unlike drop tanks, CFTs do not require mounting on a weapon pylon.  They also impose far less aerodynamic drag.  Unlike the more generic drop tanks, CFTs require specifically designed tanks attached to CFT-compatible aircraft; making them far more expensive to implement.  They are also impossible to jettison while in flight.

The good news is that CFTs and drop tanks can be used on the same aircraft, increasing range even further.  

F-22 jettisoning its tanks

For our purposes here, we will mostly ignore the various external factors (weather, airspeed, etc) that influence an aircraft's range.  Instead we will concentrate more on the specifics of each aircraft.  These include:

  • Ferry Range:  This is the maximum distance a fighter can travel safely at a cruising speed.  This does not include any combat maneuvers or significant payload.  It may also be equipped with all the fuel it could carry via drop tanks or CFTs.
  • Combat Radius:  This is the distance a fighter can travel from its base, engage in a combat operation, and return home.  Combat radius can vary greatly depending on the type of mission, altitude, and payload.  An air-to-ground mission carrying heavy bombs at low altitudes would be far less than an air-to-air intercept with missiles and extra tanks.  
  • Fuel Capacity:  The ability to carry more fuel is always preferable.  The more options, the better.  
F-35A Lightning II


Putting the F-35 in last place for range is incredibly misleading.  It is NOT a short range aircraft.  What it lacks, however, is options.  

One of the design goals of the JSF was to achieve similar ranges as its predecessors WITHOUT the need for external tanks.  At this, it exceeds expectations.  The F-35A's combat radius of almost 1,093km just about doubles that of the CF-18's 537km, despite the JSF's lack of external tanks.  It carries over 8 tonnes of fuel internally.  This is an incredible achievement, all things considered.

Unfortunately, the insistence that the JSF carry all of its fuel internally limits it somewhat.  Its ferry range of 2,200km is almost exactly double its combat radius.  This is because there are no options to carry fuel externally.  With external tanks, the CF-18 can greatly surpass the F-35's ferry range, able to fly 3,330km.  For now or the foreseeable future, the JSF lacks the ability to carry external tanks in either drop tank or CFT form.  External drop tanks were initially planned, but these plans were dropped thanks to separation issues.  This may change in the future, but doing so would require additional development.

It also must be noted that the F-35's impressive range numbers stem from carrying weapons internally, allowing a "clean" configuration.   No doubt these numbers would drop substantially when additional weapons are mounted on the wings (ie: "beast mode).  Anything more than the 4-6 internal weapons would see sharp decrease in range.  

Compounding the F-35A's range issues for Canada is its aerial refueling system.  Designed around the USAF-preferred "flying boom", the F-35A is not compatible with the RCAF's "probe-and-drogue" tankers.  This means that any potential CF-35 would need to either land to refuel or depend on non-RCAF assets to lengthen its reach.  



Gripen E drop tank testing


The JAS 39 Gripen usually gets dismissed as a short-range fighter.  This is true for the older A/B/C/D variants.  Saab addressed this for the newer Gripen E/F models, adding an additional 40% internal fuel as well as the ability to carry more fuel externally.  

Even with the extra 40%, the Gripen E carries a relatively scant 3.4 tonnes of fuel internally.  Compare this to the 8 tonnes carried by the JSF or the 6.7 tonnes carried by the Super Hornet and one might think the Gripen still lacks for range.  These numbers can be misleading however.  Being a smaller and lighter fighter means that the Gripen goes further on each liter of fuel.  Saab claims a combat radius of 1,500km with an impressive 4,000km ferry range.  This greatly exceeds both that of the CF-18 and the F-35A.  The caveat here is that these numbers are provided without details.  More than likely, they are "best case" scenarios with minimal weapon loads and maximum external fuel carriage.  Loading up a Gripen with heavier weapons would likely decrease these numbers greatly.  

Unfortunately, the Gripen lacks any sort of CFT option.  It does have the option of carrying either 300 or 450 gallon tanks under its wings or fuselage.  It also comes equipped with a probe-and-drogue aerial refueling system, fully compatible with Canada's aerial refueling tanker fleet.  

Altogether, the Gripen E/F offers up an impressive amount of range...  If one is not too insistent on a heavy payload.  


Super Hornet Block III with CFTs and a hybrid belly tank.

The Super Hornet was meant to have far greater range than the legacy Hornet.  It easily met those expectations.  For its Block III configuration, it goes even further.  Compared to the other fighters, it easily wins any range comparison.  It does so not based solely on numbers, but also on the amount options available to it to increase its already impressive range.  

Superficially (see what I did there?) the Super Hornet does not seem that impressive.  It cannot carry as much fuel internally as the F-35 (6.7 tonnes vs. 8).  Nor does it match the F-35A's combat radius (722km vs 1,239).  This may be a bit misleading, however.  The F-35's combat radius (which happens to be almost half of its ferry range) seems to suggest flying out with minimal air-to-air armament shooting, then returning to base.  The Super Hornet's 722km combat radius is listed as an "interdiction" mission, climbing to high altitude, diving low to engage a ground target, then climbing back up to high altitude.

The Super Hornet's ferry range of 3,330km (equal to the CF-18) does not suggest a greatly improved range, but this number is for older versions of the Super Hornet.  The Super Hornet on offer to Canada, the Block III, will likely have much improved range thanks to its conformal fuel tanks.  With these tanks, the Rhino's combat radius may increase an additional 200km.  These tanks not only allow the Super Hornet to carry more fuel externally, they help diminish the effect of its infamous canted pylons.  These pylons are now free to carry more aerodynamically efficient missiles.

The Block III Super Hornet also utilizes a novel ventral tank that incorporates an IRST sensor.  Holding an extra 330 gallons of fuel in and of itself, a Super Hornet equipped with this plus CFTs would have little need to mount any additional fuel under its wings...  Although still capable.  

Not only is the Super Hornet compatible with Canada's current aerial refueling assets, but it could become part of those assets itself.  Capable of "buddy" refueling, the Super Hornet can see its range get extended even further.  While a Super Hornet will never replace a dedicated tanker, it can help "top up" a fellow fighter after take off; giving it just a little bit more range.  


Not the "kill" markings a pilot wants to get...

Range is kind of a big deal for a Canadian fighter aircraft.  That much is obvious.  

We live in a big, mostly unpopulated nation.  Part of a Canadian fighter's mission will be to travail these wide open spaces.  Another part of their mission will be to engage in operations overseas.  Neither of these operations are feasible with "puddle-jumpers".  

Luckily, all three fighters offer some sort of upgrade to the CF-18 when it comes to range.  Of the three, only the F-35 displays a worse ferry range, a problem easily solved by logistics...  But that is another issue for another post...



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