As the Navy is forced to get more service out of its F-18 Hornets, here’s a bit of simple technology that could add a surprising amount of capability to existing Super Hornets: conformal fuel tanks (CFT). The nice thing about the CFTs is that they don’t need to be
|Super Hornet Conformal Fuel Tanks Atop Wing and Fuselage|
hung from pylons which use up available hardpoint attachments. Instead, they are bolted to the airframe along the upper wing and fuselage.
“The CFTs sit atop the upper fuselage on either side of the central spine and run 24 ft. in length from the aft cockpit to the leading edge of each vertical tail. At 4.3 ft. wide at the broadest point, the CFTs hug the upper fuselage surface, rising to a maximum height of only 1.8 ft. just forward of the wing leading edge.” (1)
Just for fun, using the maximum dimensions gives an internal tank volume of
24 ft x 4.3 ft x 1.8 ft = 186 cu.ft. = 1389 gal = 9445 lbs (6.8 lbs per gal of JP-5)
For a pair of tanks, that gives 2778 gal or 18,890 lbs.
Using more realistic average dimensions gives an internal tank volume of
24 ft x 3.5 ft x 1 ft = 84 cu.ft. = 628 gal = 4270 lbs
For a pair of tanks, that gives 1256 gal or 8540 lbs.
In point of fact, the CFT’s are reported to carry 3500 lbs of fuel per tank (2) which agrees reasonably closely with our estimate of 4270 lbs. So, 3500 lbs it appears to be.
The tanks apparently produce a slight decrease in overall drag.
“We knew it was essentially a zero-drag configuration and, although there was no content in the tanks, we could measure drag through fuel flow. We actually saw a little better performance, as it improves transonic transition.” (1)
“The CFTs add no drag to the aircraft at subsonic speed; at transonic or supersonic speeds they produce less drag than a centerline fuel tank …” (4)
The tanks weigh 870 lbs each, empty (1) and add 260 nm to the aircraft’s range and 130 nm to its combat radius for a total combat radius of 700 nm (3). Combat radius claims are always suspect but that CFT’s add to the radius without using up hardpoints or requiring external fuel tanks is a significant benefit.
The tanks can be retrofitted to existing aircraft.
“The CFT … is designed to be retrofittable for new-build aircraft. “The intent is to be able to install it in a shift,” says Walke [Bob Walke, Northrop Grumman F/A-18 programs director and chief engineer]. The CFT bolts onto the structure at three attachment points per side, which are designed to keep loads isolated from the rest of the structure and vice versa.” (1)
Development of the tanks was rapid.
“Northrop says the prototype units went from “napkin to first flight” in just 10 months. “The effort began in 2010 with low-level trade study work until 2012, when the decision was made to make a prototype happen quickly,” says Walke. Following a go-ahead in September 2012, the tank design was completed in January 2013, assembly began in May, delivery started in early July and flight tests on a leased F/A-18 were underway in August.” (1)
CFT’s supposedly offer a decrease in overall signature, enhancing stealth.
“The conformal fuel tanks are aerodynamically designed to help the F/A-18 have a lower detectability or signature. Boeing officials have said the conformal fuel tanks reduce the signature of the aircraft by over 50 percent.” (2)
“Enhancements to the aircraft’s radar cross section, including the EWP [enclosed weapons pod], produced a 50-percent improvement in its frontal low-observable (LO) signature.” (4)
I’ve read reports that suggest that the Super Hornet is the third most stealthy aircraft in the
inventory behind the F-22 and F-35. I don’t know if that’s true and I’ve been
unable to confirm it. US
|Conformal Fuel Tanks|
So, a simple CFT adds range, decreases drag, decreases overall signature, can be retrofitted to existing Super Hornets, and is production ready (1). Honestly, this improvement seems like a no-brainer. I’m unsure why the Navy hasn’t moved forward with this.
(1)Aviation Week website, “Upgrade Of F/A-18 Fuel Tank Gains Ground -
Conformal fuel tank attracts Navy interest as part of possible Super Hornet upgrade”, Guy Norris,
Dec 16, 2013,
(2)Military.com website, “Navy Tests Stealth-Like Features for Super Hornet”, Kris Osborn,
(3)Global Aerospace Solutions Website, “The F/A-18 Advanced Super Hornet”, James Wynbrandt, date unspecified,
(4)ainonline website, “Boeing Pitches ‘Advanced Super Hornet’ For Future Threats”, Bill Carey,