Thursday, July 3, 2014

Range anxiety.

Artist's rendering of F-35Bs operating from HMS Queen Elizabeth.

Remember that F-35B flyby hoped for the HMS Queen Elizabeth's naming ceremony?  It is not going to happen.  You can thank the JSF's recent history of spontaneous combustion, combined with a 36-hour turnaround time for that.  Appearances at the Royal International Air Tattoo and Farnborough Air Show are still scheduled.  First, the F-35Bs will have to contend with a mandatory inspection before being given U.K. flight clearance.  There is also the matter of tropical storm Arthur possibly mucking things up as well.

With all the anxiety and hand-wringing involved in the JSF's upcoming transatlantic trip, I thought it would be a good time to examine the F-35's range.

"Dang it!"
Range anxiety.  Most of us have felt it.  That feeling you get when you hear a "ding" emanate from your car's dashboard, accompanied by lit up gas pump icon.  This feeling can range from minor annoyance when your driving around town, to sheer panic when you are traveling an unknown highway with no idea where the next gas station might be.  Or maybe you are just broke.  Either way, the worst case scenario is that your car sputters to a halt, and you have to either call roadside assistance or start walking.

In an aircraft, running out of fuel is more than an inconvenience.  Without fuel, even the most advanced jet fighter becomes a simple glider...  And then possibly a crater.

Thankfully, there are plenty of ways to extend an aircraft's fuel capacity and range.

P-51D Mustang drop tank
First used in the Spanish Civil War, the idea of an additional, expendable fuel tank mounted to an aircraft became mainstream in during WWII.  Drop tanks were indeed crucial in enabling the legendary P-51 Mustang to escort bombers deep into enemy territory.  Since then, external fuel tanks have been mounted to fighter aircraft just as often as missiles and bombs.

External fuel tanks can add a great deal of range to a multirole fighter.  This enables it to increase its combat radius or prolong its loiter time.  The extra fuel can also help offset the extra juice needed to carry a large bomb load.  Less glamorously, sometimes extra fuel is needed simply increase the aircraft's ferry range, enabling it to reach a far away station without the need for refueling.

All this extra range comes at a price.  External fuel tanks add a great deal of weight and drag to an aircraft, decreasing the aircraft's performance while increasing that aircraft's fuel demands.  They also take up room on an aircraft's weapons pylons, reducing the amount of missile and bombs able to be carried.  Some external tanks cannot even go supersonic.

CF-18 with three external tanks.
Under some conditions, external tanks are pretty much a necessity.  Given Canada's geographic size and how dispersed its military bases are, external tanks are pretty much mandatory equipment of the CF-18 Hornet.  If you have seen a CF-18 in the wild, there is a pretty good chance it had at least one drop tank.  If not, it was probably a demonstrator at an air show.

The F/A-18, of which the CF-18 is a variant, was never meant to be a long range fighter.  In its natural habitat, the USN, the Hornet was a light "jack of all trades" serving alongside two more specialized designs.  Long range interception duties were meant to be handled by the USN's F-14 Tomcat, and Long range strike missions were carried out by the A-6 Prowler.

Thankfully, all of the potential CF-18 replacements have substantially superior ranges to the Hornet.  No matter which aircraft Canada eventually selects, it is certain that it will fly further than our current fleet without external tanks.

But what if we need to fly further?

For that, external tanks are still an option for all the jets...  With one exception.


All models of the F-35 have a large space just aft of the cockpit.  For the STOVL F-35B, this space is reserved for the lift-fan.  With no need for a lift-fan, the CTOL F-35A and CATOBAR F-35C are able to utilize this space for fuel.  As you can see in the illustration above, this accounts for over 4,000lb of extra fuel for the F-35A compared to the F-35B.  Because of this, literature for the F-35A often touts the fact that the JSF can match the range of legacy fighters like the F-16 and F/A-18 even when the latter have external tanks.

If a clean F-35A can match the range of a tanked up CF-18, then a F-35A with external tanks must be able to go substantially further, right?

About that...



Early F-35 information portrayed the JSF as capable of carrying up to two bowling pin shaped 426-gallon wing tanks.  The F-35's inboard wing pylons are "wet", so it only makes sense that external fuel tanks would be available.  The odd shape was adopted as traditional spindle shaped tanks were found to have "separation issues" (i.e. crashed into the plane when jettisoned).

Wind tunnel testing revealed that changing shape of the tanks did not fix the problem completely however.


As of now, there are no definite plans to add external fuel tanks to the F-35.  There are rumors that Israel may choose to design and build some, but no F-35 customer currently requires them (i.e. nobody wants to pay for their development).

Where the JSF is currently suffering from a lack of external fuel options, the other fighter aircraft available may soon have a wealth of options.

Eurofighter Typhoon
Dassault Rafale
F/A-18 Super Hornet
Already capable of mounting external fuel tanks, other fighter manufacturers have tried to do themselves one better by studying the feasibility of adding conformal fuel tanks (CFTs).  These tanks, looking like blisters on the upper fuselage, enable plenty of extra fuel storage while adding only minimal drag and radar cross section.  They also free up the pylons for weapons storage.  If need be, CFTs can be utilized with traditional drop tanks, enabling even further extended range.

While the Gripen NG has not seen any CFTs yet, they will be possibly looked at in the future.  There is not really a rush however; changes made to the Gripen NG's fuselage and wing enable a 40% greater fuel capacity than the legacy Gripen models.  Saab is also working on larger, 450 gallon tanks to extend the Gripen's range even further.  These developments squash one of the Gripen's main criticisms, its lack of range.

F-15E with unmounted CFTs, formerly known as "FAST packs".
As for the F-15SE, additional fuel storage is made possible by utilizing space in its conformal weapon bays, as well as the traditional CFTs used by the F-15E Strike Eagle.

It could be argued that an aircraft's maximum range with external tanks is not relevant when aerial refueling is available.  In a perfect world, maybe, but aerial refueling brings its own challenges and limitations.  Not the least of which is:  What type?

F-35A refueling via a "flying boom" method.
Much has been said about the F-35A's incompatibility with Canada's current aerial refueling infrastructure, the CC-150(T) Polaris.  The F-35A uses the "flying boom" method of aerial refueling, while Canada's Polaris and CF-18s use a "probe and drogue" method.  Solutions to this seem simple enough:

  1. "Canadianize" the F-35A to utilize probe-and-drogue.
  2. Purchase either the F-35B or F-35C instead (both use probe-and-drogue).
  3. Make do without a sovereign aerial refueling capability until time comes for a CC-150 replacement.  
Unfortunately, each and every one of these options would add both cost and complexity to a fighter program already notoriously over budget and behind schedule.  
  1. A "Canadianized" F-35A (CF-35CA?) would require additional cost and testing.  It would also reduce the commonality benefits a CF-35 would have with the rest of the global F-35 fleet.  
  2. Both the F-35B and F-35C are significantly more expensive than the F-35A.  They also have reduced performance due to higher weight.
  3. Likely the most attractive option, Canada can rely on USAF tanker assets or private firms to provide aerial refueling.  When the time comes, we simply replace our current CC-150 fleet with a tanker capable of supporting boom-style refueling.  This would likely be either the Boeing KC-46 Pegasus or Airbus A330 MRTT.

Airbus A330 MRTT (notice the flying boom and the drogues)
New tankers would increase our current capability.  Both the KC-46 and the A330 MRTT are available with both flying boom and probe and drogue compatibility.  This gives them the flexibility to refuel just about any aircraft in our inventory, current and future.  Currently, Canada lacks the ability to perform aerial refueling for its CC-17 Globemaster IIIs and C-130 Hercules.  Purchasing new tankers would also give Canada another resource to contribute towards coalition actions as well.

Then again, purchasing new aerial tankers could be problematic given Canada's recent defense procurement history.  The KC-46 has a unit cost of almost $300 million, and its selection by the USAF over the A330 MRTT was controversial.

The question that needs to be asked is fairly simple:  How badly does Canada need a "boom" style tanker?

CC-150 refueling pod.
Both the CC-150 Polaris (based on the Airbus A310) and its predecessor, the CC-137 (based on the Boeing 707) were straight-forward conversions of existing commercial airliners.  By comparison, specialized tankers like the KC-46 require a "ground up" build to accommodate the large and heavy boom.

There is an interesting proposal, found here, to incorporate Bombardier's new C-Series passenger jet as the basis for a new MRTT (multi-role tanker transport) as well as the basis for a CP-140 Aurora replacement.  This proposal could be extremely promising, not to mention politically rewarding.

CC-137 and CF-18
Probe and drogue style has its benefits.  It is a smaller and simpler system.  As such, it is much easier to incorporate into existing aircraft.  It allows for "buddy" refueling systems, allowing multirole fighters to become aerial refueling assets themselves.  Refueling pods can be added or removed as needed adding flexibility.

CC-130H(T) ready to refuel CF-18s.
With the addition of probe-and-drogue refueling pods, even Canada's fleet of CC-130 Hercules can become an aerial tanker resource.

So with all the flexibility and simplicity of probe-and-drogue refueling, why do aircraft manufacturers bother with the flying boom system?

B-52 Stratofortress refuels
The single biggest benefit to flying boom style refueling is speed.  Able to pump over 1,000 gallons per minute, the flying boom pretty much a necessity for larger, long range aircraft like heavy transports and strategic bombers.  This is why it is the USAF's preferred method.  With heavyweights like the B-52 and C-5, probe-and-drogue style refueling would take a LOT longer.  Smaller aircraft, like fighters, cannot take advantage of this however, and fuel must be transferred slower.

Would the addition of a boom-style aerial tanker really help the RCAF?  It would, but the difference would be negligible.  While both the CC-17 and CC-130 are compatible, both are already long-range aircraft (5,000kms for the CC-130J, up to 10,000km for the C-17) making in-flight refueling of little use for most flights.  The the CC-17 also makes up a rather small fleet of only 4.

By contrast, fighter aircraft would likely be the biggest users of aerial refueling.  With shorter ranges along with the need to deploy just about anywhere in the world as part of a coalition, the ability to carry lots of fuel and be refueled is imperative.

In a country as big as Canada, with a NATO commitment that sees the majority of our fighter deployments overseas, range is not just a luxury for Canada's next fighter, it is a necessity.  A combat aircraft is of little use if it cannot get to where it needs to be.

With no current provisions for external tanks and an incompatibility with Canada's aerial tankers, one has to wonder if the F-35 is up for the task.



5 comments:

  1. Again, Doug, very well done.......

    ReplyDelete
  2. Most other nations use the same method of aerial refueling as we do, so do we match the US or our NATO friends. Go with the friends and US Navy. The other method that I like for canada is the fighter to fighter refuelling like the super hornet does.
    Doug this is one of the reasons I like the Rafale - range. As indicated Want a coffee?on the chart I sent from India's jet fighter competition. The F15 and the Rafale have the right range for Canada. As far as the F35 if that is the way Canada goes, you have to get the A because it is the only one with a gun.

    Great article by the way!

    ReplyDelete
  3. Although the F35 Jonestown Strike Fighter has had
    a few awkward looking adherents, one can only hope there never comes a time when
    Canadian taxpayers are force drinking the Koolaid with these pious
    imbeciles.

    ReplyDelete
  4. Don't panic. all they need to do is to install an arrested cable and a couple of tennis courts to take off from there Super Hornets and Growlers.

    "Rietz told HT at Lemoore, which holds half of the US Navy’s striking power in the Pacific, “In our simulation, we discovered that not only could the Super Hornet take-off from a ski-jump, but could do so with a significant weapons load.” Landing the Super Hornet on the Gorshkov would pose no problem since the warship comes equipped with an arrester cable. The 16 MiG-29K fighters that will come with the Gorshkov will land using this “trap” method."

    http://publication.samachar.com/pub_article.php?id=1909638&navname=General%20&moreurl=http://publication.samachar.com/hindustantimes/general/hindustantimes.php&homeurl=http://www.samachar.com

    https://www.youtube.com/watch?v=pz2Cl3TnRyM

    https://www.youtube.com/watch?v=_9NGLvc7eLM

    ReplyDelete

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