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 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, 15-Jul-2014 ,
http://www.military.com/daily-news/2014/07/15/navy-tests-stealth-like-features-for-super-hornet.html
(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, 15-Nov-2013 ,
Increased weight leads to greater tanking requirement for the same range and it degrades manoeuvrability.
ReplyDeleteProbably worth it, but nothing is free
?????? Didn't get any of that. How does extra fuel lead to greater tanking requirement? How does it degrade maneuverability?
DeleteI too am unclear about the greater tanking requirement. I didn't think you could refuel non internal tanks?
DeleteThe cost in maneuverability is real, I'm sure, but I think more questions need to be answered. Like, if we delete the centerline tank is the reduction in maneuverability closer to a wash?
If we can't, and there is a real reduction in maneuverability, does it matter? Because with its limited range it would seem like an SH pilot would want to avoid the merge anyway.
I realize you may not be able to avoid it, but I think that the increase in range is a greater mission priority for these planes than the decrease in maneuverability. Unless the CFT's turn them into F-104's.
"How does extra fuel lead to greater tanking requirement?"
Delete"I too am unclear about the greater tanking requirement. I didn't think you could refuel non internal tanks? "
The F18 has a maximum weight it can take off with.
If you bolt on 1740lbs of fuel tanks, that extra weight has to come from somewhere.
And the only real place it can come from, is fuel.
So, you launch with 1740lbs less of fuel, and then are tankered to the brim, a normal load, plus the 1740lbs you launched short, plus the 7000lbs to fill the tanks.
A lot more tankers
Its less of a problem for ground based fighters, who have much longer airstrips to take off from, and much bigger tankers.
"How does it degrade maneuverability?"
Extra weight, the advantage of drop tanks is that they can be dropped once they are empty, you cant drop conformals, you have to drag them around during a fight or a landing. Again, not a huge problem, the F18s shouldnt be dog fighting and I'm guessing the max return weight has been sorted.
At the end of the day, the conformals are decreasing the drag and RCS, the F18 wasnt shaped that way in the first place for a reason.
The concept behind these tanks is that they can eliminate the need for wing/fuselage tanks. That may, or may not, result in a decrease in weight.
DeleteThe extra fuel and slightly decreased drag results in greater range and thus, less need for tanking, not more.
As far as maneuverability, nothing I read described any impact, good or bad, on maneuverability other than stating that the aircraft could engage in A2A maneuvers without having to drop tanks - a decided advantage.
Yep, once the fuel is consumed, they become a deadweight, and unlike drop tanks, they cannot be jettisoned. In a dogfight, a fighter aircraft would jettison drop tanks for maximum performance. That said, conformal tanks only add a fraction of the drag so perhaps overall a better option.
DeleteAgree with Trt though - the Super Hornet is no dogfighter.
"the Super Hornet is no dogfighter"
DeleteNo one has claimed it is! This is what you get when you try to build disparate functions into a single platform (hey, someone should do a post on that!). You get a platform that is a compromised, and generally a poor one, for each incorporated function.
The super hornet weighs 32,000lbs empty
DeleteIt has a max takeoff weight of 66,000lbs, considerably less on a carrier launch.
Adding CFTs adds to the Hornet weight, but doesnt increase the take off weight.
That change can only be countered by taking off with fewer arms, or less fuel.
If you take off with less fuel, you need more tankers to take off with you and refuel you.
Its the take off weight that drives it in my understanding.
"As far as maneuverability, nothing I read described any impact, good or bad, on maneuverability other than stating that the aircraft could engage in A2A maneuvers without having to drop tanks - a decided advantage."
The advantage of drop tanks if that they can be dropped.
CFTs cant.
A CFT free F18 will be 1700lbs lighter all else equal, which means it can turn quicker, accelerate quicker, ect.
Some of the comments are quoting incorrect fuel capacity and structural weight figures for the CFTs.
DeleteAn earlier article at Aviation Week makes it clear that the 3500 lb figure is the combined capacity of both CFTs.
I haven't been able to find a similarly unambiguous statement about structural weight. However, it is very likely that the figure of 870 lb is the total weight for both tanks. Why? (1) This figure is always quoted as the weight of the "tanks" (plural) along with the 3500 lb fuel capacity figure, which we know to be the total capacity. There is little reason to quote the weight of a single tank as a drawback of the system when the CFTs can only be used in pairs (unlike drop tanks). (2) Combined, the CFTs for Block 50/52+ F-16s weigh 900-1000 lb and carry 3056 lb of fuel (both figures per the flight manual). These are similar in shape to those of the Super Hornet and also about 24 ft in length. Hence, an increase of around 83% in structural weight for only 15% more fuel (assuming 870 lb per tank) does not seem plausible.
By comparison, a centerline 480 gal tank weighs 381 lb and carries 3216 lb of fuel. The impact on maximum speed with typical air-to-air loadouts is already small. The reduction is less than 2% at military thrust (high subsonic) and around 6-7% at maximum thrust (supersonic). (These numbers come from the level flight envelope figure in the flight manual.)
Hence, the claim in the linked article of "very little" drag for the CFTs between Mach 0.6 and 0.84 is plausible. There is also an unambiguous claim (attributed to a Boeing manager) that "the performance [with CFTs] is better than a clean aircraft in transonic or supersonic operations." Boeing engineers have probably been able to reduce supersonic wave drag by selecting the dimensions of the tanks to smooth out the area distribution of the whole aircraft. (It certainly does not follow from "basic aerodynamics", as implied elsewhere in the replies, that such improvements are impossible.)
I wondered about that and was unable to find a clear statement one way or the other. My best interpretation of what I read indicated that the weights and capacities were for each tank. That's why I presented the max and average tank capacity calculations. The average for one tank agreed pretty well with the 3500 lb figure, hence my acceptance of 3500 as a per tank value. I'm more than willing to modify my thinking on that if you can cite a definitive source. Of course, the change in values does not affect the conclusions in any way!
DeleteFind a source and help us!
The combined fuel capacity is certainly 3500 lb (1750 lb per tank). From the linked article: "The objective tanks, being developed with funding from and to be built by Northrop Grumman, would weight 870 lb. and the two together would carry 3,500 lb. of fuel, 500 lb. more than the CFTs envisioned only a few years ago in the International Roadmap."
DeleteI have scoured the internet for a similar statement about the structural weight and just can't find it.
You are quite right about it not changing the conclusions, other than to make the arguments about bring-back weight and fatigue life even less relevant.
Here is an official slide show containing some information not found in other sources.
That seems like a very small amount of fuel per tank - around 260 gal each. That is so far off from my average calc that it makes me question whether it really is 3500 lb for two tanks. Well, no matter.
DeleteThanks for the link to the slides. There's some good information in them.
You're right.
DeleteYour average dimensions leading to 84 cu ft look about right to me. If you assume that 85% of internal volume is usable for self-sealing bladders and then deduct a further 10% to account for the volume of the bladders themselves, you wind up with around 64 cu ft or 3300 lb of usable fuel. (According to Raymer's book on aircraft conceptual design, 85% of total internal volume is typically usable for fuel in the fuselage, while 92% is typical for the wings. Assume, somewhat conservatively, that CFT storage is about as efficient as wing storage. Self-sealing bladders impose a further 10% penalty.) Where do you lose the other 1650 lb? It doesn't make any sense.
"Yep, once the fuel is consumed, they become a deadweight, and unlike drop tanks, they cannot be jettisoned. In a dogfight, a fighter aircraft would jettison drop tanks for maximum performance."
DeleteI'm pretty sure that nowadays the SH never drops that centerline tank; especially with IRST hooked to it.
I'm curious as to the claim tha the SH can't dogfight? Maybe its not on top of the latest designs, but everything I've read about the SH make it at least able to hold its own. For WVR I've read it has excellent low speed maneuverability; not F-16 like, but not bad either. It also has JHMCS and AIM 9X for HOBS shots.
DeleteFrom BVR it can carry the AMRAAM, and has very good avionics linked the the nice AESA radar, as well as some front aspect stealth.
People write about it as if its a garbage truck carrying missiles.
Now, admittedly, my sources are difficult; I'm either reading accounts of pilots, stuff off of F-16.net, or things from Boeing. But never have I read that the SuperHornet is a complete dud in air combat.
"Yep, once the fuel is consumed, they become a deadweight, and unlike drop tanks, they cannot be jettisoned. In a dogfight, a fighter aircraft would jettison drop tanks for maximum performance."
Delete"I'm pretty sure that nowadays the SH never drops that centerline tank; especially with IRST hooked to it."
One of the challenges in running a blog and opening it up for comments is that many of the commenters focus on trivial, nearly irrelevant points - some just to argue, some just like to point out problems, no matter how small. The challenge for me is to keep the discussions from veering off into irrelevant or trivial side issues. Much of this drop tank discussion has, unfortunately been of that nature. I need to do a better job of guiding the discussion.
One of the issues is that various people are equating the conformal tanks to drop tanks and then concluding that they are flawed in various ways. This completely misses the main point of conformal tanks. THEY ARE NOT DROP TANKS!!!! They will not be dropped. If installed, they are a permanent part of the aircraft just like the wings, tail, fuselage, cockpit, and internal fuel tanks.
Conformal fuel tanks are just bigger internal fuel tanks that the aircraft now has for the rest of its life. As a permanent addition to the aircraft, they may be worth it or they may not but to compare a CFT to a drop tank is nonsensical. That's like comparing a drop tank to the nose gear. We can drop the tank for A2A combat but we can't drop the nose gear, therefore, the nose gear is inferior to the drop tank. Nonsensical.
The CFT either justifies its permanent addition along with arrestor hooks, landing gear, internal tanks, oxygen supply systems, and everything else that's permanently on an aircraft or it doesn't.
The main justification for a CFT is that it increases the aircraft's range which is the Hornet's most serious shortcoming. That it does so without increasing drag is a bonus. That it does so while significantly reducing the aircraft's signature is a tremendous bonus. That it may, in some scenarios, eliminate the need for drop tanks is an occasional bonus. That it increases the weight of the aircraft which decreases dogfighting performance is a negative. And so on. My assessment is that the gains far outweigh the negatives.
It's far too easy to get caught up in debates about irrelevant points and I need to do a better job of preventing that.
"I'm curious as to the claim tha the SH can't dogfight?"
DeleteFew of us, and I'm not one, can evaluate an aircraft's actual dogfighting performance. For what it's worth, here's my assessment.
Compared to our own inventory, the F-22, F-35, F-15, and F-16 are all superior dogfighters. That makes the F-18 the worst of our own aircraft. My guess about enemy aircraft (and none of us know anything about these!) is that the MiG-29 and Su-Flanker family are superior. The Chinese J-20 and J-31 are probably superior just because they're newer and have a degree of stealth.
Thus, the F-18 does not rank highly among the world's dogfighting aircraft.
Of course, this does not take into account pilot training and capabilities.
Pure speculation!
Anyone want to differ?
This comment has been removed by the author.
DeleteI suppose, before I get myself in too deeply, I'll try to define things a bit.
DeleteWhen I hear 'X isn't a dogfighter' it makes it sounds as if 'X cannot dogfight effectively'. That is what I'm arguing against.
I'll grant you that the Superhornet is likely the least capable dogfighter in our arsenal. However, that's a pretty good stable, and it doesn't mean that the SuperHornet can't effectively dogfight.
I've read articles from F-16 pilots who were very wary when tangling with Hornets. They felt they had the superior aircraft, but it wasn't a F-8 Bearcat vs. Brewster Buffalo difference.
The F-18 *was* designed to fight at the merge. It can do so. I guess my argument is that it can even do so effectively.
Would a SuperHornet pilot much prefer to shoot at a MiG from far away with AMRAAMS? I bet! But if he has to he could engage the Fulcrum and have a very realistic chance of winning.
The SuperHornet has serious limitations, no question. And I much would have preferred the Navy went with purpose built aircraft. But its almost become a meme to harsh the SuperHornet.
But, again, from what I've read, the Superhornet isn't a sitting duck either.
Now, all this is just based on the technical capabilities of the jet, in one configuration. Everything changes based on how the aircraft are configured, pilot training and experience, etc.
A well trained SuperHornet pilot vs. a nube in a Flanker may tip the balance.
And given that SuperHornets are often burdened down for attack as bomb trucks, its unlikely that they'll be all that effective in A2A most of the time.
But all that is true of any airframe.
Let me put it this way; to borrow from your 3rd offset strategy post.
Would it be better to have CV's with limited amounts of F-35's, whose pilots will have limited training time due to the cost of the planes plus the cost/ flight hour of running them? Or would it be better to have a ton of SuperHornets (if you could fix the range issue) where the pilots can train and fly all the time?
You didn't ask about numbers, you asked about dogfighting. Pick a question and stick to it!
DeleteYou know my opinion about numbers. Quantity makes up for a LOT of quality.
Back to dogfighting, if the Hornet ranks last among all the aircraft I mentioned then it's not a dogfighter. That doesn't mean that it can't win a fight, just that it's the least likely of all of them to win. That's what you get when you try to build a multi-function aircraft - it can't do any of its jobs well. All of the aircraft I mentioned, with the exception of the F-35, were built as pure fighters. They have since been given secondary strike capabilities but they were built for A2A. That's what I keep harping on about multi-function being the path to losing in combat.
The jury is still out on the F-35 as a dogfighter. If it can be effective it will be because its stealth and sensor fusing is everything the proponents wished for. If not, it won't be a good dogfighter. We've already seen that its combat flight characteristics are nothing special or even sub-par - again, not surprising for a multi-function aircraft.
While the length of the tanks are 24 feet, the wet length is 18.7 feet. Slides 9 and 10 of the preso that Anonymous submitted yesterday has an exploded view of the tank and its dimensions. Given there are internal forms/frames, some sections in the wet area might be blocked off reducing the amount of fuel it can carry.
Delete"if the Hornet ranks last among all the aircraft I mentioned then it's not a dogfighter."
DeleteI'm sorry CNO, I just don't get that argument.
Its like saying
Corvette; Nissan GTR; Honda 2000.
Of those 3, the Honda 2000 is least likely to win in any sort of race, ergo its not a sports car.
Of course its a sports car. It was designed as a sports car. It was built as a sports car. It has all the attributes of a sports car. In its time, it was a great sports car. It just doesn't do it as well as the other two. Given the right circumstances, it is still competitive.
Declining ability does not equal a change in basic form.
And, as I said, while you may have less capability in the SuperHornet vs. say an F-16, the F-16 driver isn't going to treat you like he would a MiG-21.
Fine. Call the Hornet a dogfighter. Call it a vacuum cleaner. Call it a tree. Call it whatever you want. It's the least likely to win a dogfight against contemporary fighters. Sure, it could probably win against a MiG-21 or a Fokker Triplane and if we fight a country equipped primarily with those aircraft then we're in great shape. On the other hand, if we fight a country equipped with MiG-29, Su-XX, J-20, J-31, PAK-FA, then our dogfighter is going to lose most of the time.
DeleteUltimately, this is a matter of semantic labeling and has no practical meaning and, therefore, is of no interest to me. Call it what you wish and move on.
"While the length of the tanks are 24 feet, the wet length is 18.7 feet. Slides 9 and 10 of the preso that Anonymous submitted yesterday has an exploded view of the tank and its dimensions. Given there are internal forms/frames, some sections in the wet area might be blocked off reducing the amount of fuel it can carry."
DeleteSo, do the calculation and tell us what you get.
"On the other hand, if we fight a country equipped with MiG-29, Su-XX, J-20, J-31, PAK-FA, then our dogfighter is going to lose most of the time."
DeleteI guess that's my point. We don't know that its going to lose 'most of the time'. It may be 50%. I'm not convinced it doesn't come out winning against the Fulcrum more often than not.
This isn't just semantics. Its about capability, manufacturability, cost, and numbers.
The future of the Navy is, right now:
SuperHornet. F-35C. No dedicated tankers. No S3.
Even if we wanted, we cannot have another Navy fighter other than the F-35C or the SuperHornet. There are no other plants making any other navalized fighter. Congress won't buy a foreign design.
I don't like it. It Stinks. But it is the objective reality.
The F-35C is expensive to buy and fly.
The SuperHornet isnt.
If the SuperHornet, as a Gen 4+ fighter, has a 25% chance of winning against its opponents and no hope of expansion, then we should start divesting ourselves of it now and hope for the best with the F-35C.
If, however, the SuperHornet has a 50% chance, against those planes, or even a 40% chance that we can expand through better avionics and weapons, then we should seriously consider keeping it, buying it in numbers, training up on it, and dump the F-35C while we try for something else.
That is the utmost in practicality. I'm sorry if you disagree. I'll leave it there for now.
Sounds like a very good idea. Of course, there are very few totally new ideas: the "slipper tanks" fitted to British and German aircraft in WWII were conformal tanks and had several advantages, though of course they didn't affect transonic performance or stealth. If Wikipedia is accurate, conformal tanks have been fitted already to F-15C and Es, F-16 C,D,E and F, the Israeli F-161, and the Taiwanese F-KC-1; and have been tested on the Chengdu J-10, Rafale and Typhoon. I share your bafflement at the USN's delay in improving the Super Hornet. But then, there are quite a few things about the USN (and other navies) I find baffling.
ReplyDeleteNever said it was a new idea! It's an old idea that would appear to be long overdue.
DeleteIt takes fuel to move fuel! Adding fuel makes the aircraft heavier, so it burns a bit more fuel per mile to fly. This is why passenger jets rarely tank up fully, they just fly with what they need for each leg.
DeleteAnd it must increase drag, that is basic aerodynamics. You got something sticking out the sides! However, it may be that the tanks provider more lift that offsets the increased drag. If that is the case, then say so.
I'd rather them look at mounting 2-4 Tomahawk cruise missiles on an F/A-18, to give a carrier another 1000 miles of strike radius.
"And it must increase drag, that is basic aerodynamics. You got something sticking out the sides"
DeleteNot necessarily, if they shape it to minimise drag.
Yes, they are shaped to minimize the increased drag. If you mount something on the top of your car, it increases drag because pushes against air, no matter how you shape it, there is still increased drag, because something is there! Even a radio antenna on a car increases drag.
Delete"And it must increase drag, that is basic aerodynamics. You got something sticking out the sides! However, it may be that the tanks provider more lift that offsets the increased drag."
DeleteDid you read the post and the referenced links? There was a slight overall decrease in drag.
The tanks have no impact on lift other than, possibly, some slight effect due to eddies and pressures.
"no matter how you shape it, there is still increased drag,"
DeleteRead the post and the articles.
CNOps: I never meant to imply you said it was a new idea, but my question is: since this is not at all a new idea, and other US aircraft and aircraft in other countries (including China) have been using it for some time, why has it taken the USN so long to apply it to the SuperHornet?
DeleteThat's the question I posed in the post. I have no idea why the Navy has passed on this.
DeleteConformal fuel tanks have been around since WW2, possible before.
Delete"And it must increase drag, that is basic aerodynamics. You got something sticking out the sides! However, it may be that the tanks provider more lift that offsets the increased drag."
Agree with this. There will be a penalty in drag, although probably very small.
Perhaps yes, the tanks do provide some lift - enough to offset the extra drag so that the L/D ratio is slightly improved. Hard to say without flight test data being made public for analysis.
I'm very skeptical of this claim for that reason.
I still think that the Super Hornet needs conformal fuel tanks and that overall, the benefits exceed the drawbacks, but I'm naturally skeptical of manufacturer claims here. We really need the test data to be published for us to get a full picture.
"There will be a penalty in drag"
DeleteRead the post and associated links. There was an overall slight decrease in drag. The claim is based on fuel flow data. The decrease is likely due to the elimination of the centerline fuel tank although that is not made clear in the linked articles.
I see no way conformal tanks can provide lift when mounted on the top side of the wings other than by a very minor impact on pressure profiles. None of the articles claimed any lift.
Here is an example of F-16s with CFTs:
Deletehttp://foxtrotalpha.jalopnik.com/why-dont-new-u-s-air-force-f-16s-use-these-futuristic-1712746714
There is a modest penalty in drag; 12%, which is not huge, but it is still there. I have no proof, and won't without flight data, but I suspect that there will be a comparable penalty on the Super Hornet.
Again, it's a necessary upgrade, but it's not without its drawbacks.
Read the post and links!
DeleteIt seems to me that people are confusing drag with something else. Drag decreases top speed while weight decreases acceleration.
Delete"Read the post and associated links. There was an overall slight decrease in drag. The claim is based on fuel flow data. The decrease is likely due to the elimination of the centerline fuel tank although that is not made clear in the linked articles."
DeleteBut, your post states, “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 …”
The conformal fuel tanks appear to add drag at transonic and supersonic speeds, but the added drag is less than that produced from the centerline tank.
As for fuel consumption, any added weight (fuel or structure) over the baseline design will decrease fuel consumption. Given these are conformal fuel tanks that don't have the drag penalty of the centerline or wing mounted tanks, the decrease in fuel consumption is much less.
I meant to say that added weight increases the fuel consumption rate and that the increase in that rate with CFT's is less than that from centerline or wing mounted tanks.
DeleteIn your opinion, will it decrease survivability to the aircraft or require additional modifications to operate off a carrier?
ReplyDeleteAs stated in the post, it appears to improve overall stealth and, therefore, survivability. I can think of no modifications to operate such a Hornet from a carrier.
DeleteIs the landing struts and arresting gear able to withstand that increase in weight?
Delete"Is the landing struts and arresting gear able to withstand that increase in weight?"
DeleteYou tell me. Think about what you know (Wiki has all the data you need) about take off weights, weapon weights, max weights, etc. Analyze and answer your own question. Tell me what you conclude.
Using specs listed on Wikipedia, it stats safe bring back weight is 9k lb for munitions and fuel. Using your realistic specs of 8.5k lb of additional fuel, and disregarding high fuel or munition usage, thats wasteful from a economic standpoint that could be used to save fuel or munitions.
DeleteInterestingly, I believe thats the reason the navy didn't pursue conformal tanks. According to one website I've read, increasing bring back weight became official navy policy with the increase in munitions cost in the late 80's.
http://www.airvectors.net/avhorn_2.html
OK, you got a start on the question. Now what does a carrier aircraft actually bring back? This is a bit less common knowledge. Ideally, an aircraft would use the last drop of gas as they catch a wire. In practice, they bring back a minimum of fuel (the amount needed to land plus a safety factor) which is why there are overhead/recovery tankers always in the air, in case they bolter a few times and run low on fuel. So, they're not going to bring back 7000 lbs (that's the actual number versus my guesstimated number which allowed me to check the claim) of unused fuel. They'll likely land with empty conformal tanks and nearly empty internal tanks. So, the additional bringback due to the conformal tanks is 870 lbs per tank for a total of 1740 lbs, the weight of two empty conformal tanks.
DeleteNow, the idea is that the conformal tanks will replace one or more of the drop tanks so the net bringback will be less than 1740 lbs. In fact, depending on the configuration, conformal tanks may allow an increased bringback (I don't know what drop tanks weigh, off hand).
So, no, it seems highly unlikely that bringback was the reason why the Navy did not pursue conformal tanks.
A more likely reason for not pursuing conformal tanks is that they didn't want to enhance the Hornet to the point where people would start to question the need for the F-35.
My ideal, (relatively) affordable SuperHornet would have the EPE's and the CFT's, coupled with deleting the outward cant on the one weapons hardpoint (Can you remove it entirely if the plane is doing CAP?). To get that, if possible, I'd stop retrofitting old C's and buy new build E's. You'd have to find a bit more money, but I have a sinking feeling that SLEP'ing those old C's is going to end up costing alot more than we think due to their age and wear, and by the time the maintenance depots get through their backlog we'll have some SLEP'd, old C's with their very limited range.
ReplyDeleteBarring all that, the CFT's, if they can go on the existing SH fleet, are, as you say, no brainers. Anything to increase the range of these birds.
A SH with a 700nm combat range, AIM-120D's, and its good set of avionics isn't a bad aircraft, and may well be the best option we have for carrier flight decks in the immediate and near to mid term future.
Two questions:
A) Is it retro-fittable to existing inventory?
"is designed to be retrofittable for new-build aircraft."
B) Are your ranges, etc. with the deletion of the centerline fuel tank on the SH? Deleting that could give the SH's some help with drag reduction. But it would also delete the IRST, which is maybe what is giving the Navy some hesitation? (I personally think they should find another IRST solution and ditch the centerline if they can, but that's just me).
I don't know to what extent it can be retrofitted beyond the statement in the post. I'm pretty sure it can't go on the legacy Hornets, at least not in its current form.
DeleteYes, the ranges assume the deletion of the centerline fuel tank. The IRST could easily become a simple pod, I would think.
There have been many proposed offerings to help with that, and I'm surprised that the Navy's solution was the tank mounted IRST.
DeleteBoeing has offered an easily swap-able/removable internal IRST for the nose, and the UASF has had very cheap and easy results with just slapping a Sniper pod to F-16s and slaving them to the radar.
I've read (I'll have to look it up) that the reason for the centerline tank IRST was that they kept having it masked from other locations, and that there was something on the nose from preventing it from going there MiG style.
DeleteHowever, from what I've read of IRST, and given the SH's likely opponents in the near to mid term, I think the range is more valuable even if they have to partially mask it.
Right now I think that IRST is a very, very important technology. It is passive. The US is considerably behind Europe in this regard.
DeleteThere is nothing like PIRATE IRST here in North America. That's a big problem for air superiority.
The development of QWIP IRST should be a huge priority, and should be included in any air superiority fighter.
"The development of QWIP IRST should be a huge priority"
DeleteGive us a gazillion dollars and 30 years and I guarantee we can develop an average IRST.
In that case, then, just buy the one from the European nations. PIRATE or something similar. They already exist and are on modern fighter aircraft.
DeleteThe Russians are also working on their own QWIP IRST system, the OLS 50.
This comment has been removed by the author.
DeleteThese days any and all promotional material from any defense contractor should be taken with a very large chunk of salt.
ReplyDeleteThat said, even if only half of the info on it is true, it would still be worth it for the navy to get on board with most, if not all of the proposed "Advanced Super Hornet" upgrades offered by Boeing.
Although the conformal fuel tanks will greatly increase maintenance time (since they would need to be removed completely just to get to an underlying access panel), it would still be worth it to have the increase in range for the oft-maligned short range of the Hornet.
Another proposed upgrade that I am surprised the Navy hasn't been frothing at the mouth for is the improved weapon pylons. The current Super Hornet pylon configuration has them canted at an angle, which imposes serious drag and eats up fuel economy (by orders of magnitude more when laden with any store) acting like mini-airbrakes installed across the length of the wing. It has been a major criticism of the airframe since it was adopted, with Boeing only doing so because of being rushed to meet deadlines, and that being the only solution to safe store separation.
Boeing has since offered to install non-canted pylons that are less aerodynamically challenged that offer safe stores separation. That one upgrade alone should help the Super Hornet not to be such a slouch in the range, acceleration, and fuel consumption regimes, and might even help to improve the overall top speed.
There is that - I am skeptical as I said of the idea that they reduce drag. I would like to see the flight data without and with conformal fuel tanks.
DeleteIt's not a miracle solution, but given the weaknesses of the SH, it is probably a net benefit.
There are other inherent problems with the Super Hornet. To try to mitigate the wing drop issue (never 100% eliminated), they dropped performance further.
IMO these days, the USN exists to enrich the defense industry above all else.
I think that we're maybe getting a bit ahead of ourselves. Sure, its not perfect. I don't think anyone claims it would be. But it would stand a chance at making the jet better at its main job; and likely expose the CV to less risk by allowing it more flexibility.
DeleteNow testing would have to be done in a real world environment to see if its worth it, but I'm a bit surprised at the skepticism ("there are drawbacks...") .
If there's one thing I'm learning, there are drawbacks to *everything* when making a fighter jet. Large size for more fuel? Increased drag. Larger wing for less wing loading? increase drag. More internal fuel? Gotta hoist it so you need a bigger engine. Smaller size? Less fuel/payload. Smaller radar? Likely won't work as well. Bigger radar? Heavier. Stealth? Expensive. Non stealth? Light up like a Christmas tree...
No free lunches.
The SH is what we have, and it has a (severe, to my mind) lack of range. This could help. Yes, of course it would have costs, but at least on some of the jets it would be, as Alt says, a net gain.
"Boeing has since offered to install non-canted pylons that are less aerodynamically challenged that offer safe stores separation. That one upgrade alone should help the Super Hornet not to be such a slouch in the range, acceleration, and fuel consumption regimes, and might even help to improve the overall top speed."
ReplyDeleteI've never seen that. Do you have a reference? I'd love to read it.
Add the CFT's and eliminate the canted pylons and you have a decent bang for your buck.
You know, I hope I'm not having a bit of foot-in mouth syndrome as I can't seem to find any documents on it. A shame since I seem to recall a good amount of details on it, and I swear multiple sources were commenting on it at one point.
DeleteI seem to recall that Boeing had developed/conceived it long before the "Advanced Super Hornet" proposal, and may have been done during the development of the Super itself, but that the Navy flat-out refused to bite, as it would extend development time and increase cost for what was ultimately a massive oversight (see f*ck-up) by Boeing in development.
Though form what I heard, the solution may have been related to installing larger, more powerful ejectors on the pylons as well as making the pylons longer themselves.
But till I can find some documents, it's all hearsay, so I'll be on the lookout and post back once I find it.
That would be awesome. The SH has some major drawbacks (range, the pylons) that were fine in the 90's early 2000's when it was developed, or at least livable. But now I think we need to eek as much out of it as we can. Its not going away.
DeleteGrendel, your sources were likely thinking of the "PACER" concept. According to a 1999 AIAA ASME conference paper (written by Boeing employees) entitled "F/A-18E/F Weapons Separation Flowfield Improvement": "The Pneumatically Actuated Constrained Ejection Rack (PACER) was developed to provide additional store yaw constraint during the 6-inch ejection stroke. This constraint was obtained by integrating the bomb rack captive carry store restraint system (swaybraces) into the bomb rack ejection system (pistons). The PACER uses pneumatics in place of the more conventional pyrotechnics devices. The pneumatic system allows the ejector force characteristics of the PACER to be tailored to duplicate almost any bomb rack, including the F/A-18E/F BRU-32."
DeleteA prototype was constructed, and flight tests were conducted with an F/A-18C "using a MK-84LD separating from the midboard pylon next to an inboard 330 gallon external fuel tank." Results "showed that the PACER improved store separation distances for all flight test conditions." Additionally, a dynamic ground test was performed to assess the ability of the PACER to control store yaw, and "[e]xtrapolating the F/A-18C results to the F/A-18E through the use of the dynamic ground test data indicated that the PACER could also improve the store trajectories for the F/A-18E. However, the results of the ground test indicated the PACER reduced pitch and yaw levels, not through physical restraint, but through an increased ejection force and a more efficient stroke."
PACER was one of several concepts included in a 1995-1996 trade study addressing stores separation issues. The remainder were drawn from an earlier concept screening test involving a (seemingly exhaustive) list of aerodynamic fixes that could potentially address separation problems without requiring a major redesign. (Such problems were observed during earlier transonic wind tunnel tests conducted at 10% scale.) The aerodynamic fixes surviving to enter the trade study were "pylon toe" and "pylon doors", each to be used in conjunction with a new release sequence. The pylon toe option was selected after weighing the costs and risks associated with each of the proposed solutions. The increased drag was partially offset by the inclusion of a drag reduction fairing on the trailing edge of each pylon.
And there you have it, our contemporary Super Hornet! (In fact, further modifications were required to address "wing drop"/"abrupt wing stall" issues while maneuvering at transonic speeds and during powered approach conditions.)
I have heard nothing about further development of the PACER concept. A test article was (circa 2004) to be used in a sled test connected with the HIFEX (High-Frequency Excitation Active Flow Control for High-Speed Weapon Release) program.
Very nice PACER summary. Thanks for presenting that.
DeleteUgggghhhh. We didn't do it?? I wonder if it really had a chance at working. Not sure what the 'reduced pitch and yaw' levels might mean.
DeleteI think that may have been just what I was thinking of. Thanks, Anon!
DeleteAs someone above alluded to it isn't just about the added fuel but the aero and structural penaltys that come with it. I would imagine they add stress to the center barrel structure reducing service life.
ReplyDeleteThat said its worth a look. Any improvement helps if it can improve the strike range. Maybe the E model could become the fighter version without the conformal tanks and the F model the attack birds with them.
"I would imagine they add stress to the center barrel structure reducing service life."
DeleteI've seen nothing to indicate that. Here's what one of the referenced links has to say,
"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."
Nothing about this indicates the presence of additional stress sufficient to reduce service life.
Roger that, I am sure they did their due diligence to make that statement but as a system there is always a penalty and more weight always means more stress. Just Luke the 5 wet tanker configuration induces MRE these tanks will also do the same. That is why we test in all configurations with instrumentation ashore and embarked against the FEM of a standard SH.
DeleteLike I said, its worth investigating, it just needs a rigorous vetting. There are no panacea fixes for elementary tech challenges like this.
Combat maneuverability is arguably in the "top three" most important metrics for a fighter and *any* external fuel tank, not to mention overlarge internal tanks) is a hit on maneuverability.
DeleteThat said, clearly there are mission considerations that may make these tanks not just acceptable, but critical.
GAB
My guess is that there will probably be G restrictions and perhaps a somewhat reduced structural life.
DeleteNet it is still very needed for the Super Hornet, but yeah, we should be aware of the drawbacks.
One can probably make the same argument that weapons will reduce structural life. However, the whole point of a combat aircraft is to deliver weapons so any impact they might have on structural life is just something to be gladly accepted. So, too, with conformal tanks if they can help in carrying out the mission of weapons delivery.
DeleteIf all we want is an aircraft that never ages then we need to park them in some zero-g environment and never use them.
There is no evidence that they will impose any significant pre-mature structural deterioration. Yes, it is reasonable to assume that some slight degree of deterioration may occur but the incremental contribution is likely undetectable in the context of overall airframe aging.
The final analysis is these aircraft exist to deliver weapons and CFTs seem like a very useful aide in that mission.
It's mostly the heavier stuff that really affects structural life.
DeleteBombs, drop fuel tanks, and perhaps very heavy sensors. Air to air missiles for shooting down fighter aircraft don't weight that much (they cannot as they must be agile to kill fighter aircraft). Long range anti-bomber missiles though tend to be heavier.
I'd consider the effect of air to air missiles to be low and not far from flying "clean" versus bombs, and extra fuel tanks which are quite heavy. They have to be for their warheads and for fuel capacity.
I don't know where you're getting this whole structural life effect thing. An aircraft is designed to handle whatever stresses it encounters whether it's cats and traps or weapons carry. The weapons and their pylons are designed to handle the weights and stresses. The aircraft doesn't somehow lose life if it loads weapons. An aircraft doesn't have a certain number of times it can carry a weapon. The design life of the aircraft includes carrying weapons of whatever weight is appropriate.
DeleteCFTs are not going to reduce the life of an aircraft.
High G maneuvers and heavy loads invariably affect structural lifespan.
DeleteThere are reasons why older airframes in air forces around the world have G restrictions. The more you use an aircraft or the harder you use it, the faster it will wear out. That's just the reality.
I consider it necessary to subject pilots to high g training, especially for air to air as it simulates real combat. Does it wear out the fighter aircraft faster? For sure. Is it worth it? For sure.
CFTs are not a miracle solution. They do improve fuel fraction for sure, but they are not without their drawbacks. The reason why I'm pointing this out is because you make it sound like CFTs are going to be a free lunch for the F-18. There's never a free lunch.
I should mention that I'm pro CFT, but I think that we should be aware that there are drawbacks.
DeleteIt's like everything else. I'm pro bomber interceptor (a passive, delta winged Su-27 like aircraft), but it's not without it's drawbacks as well. I just see it as the best option amongst the possible choices for a specific role.
My problem with comments, in general, is when they get into irrelevant minutiae. If some detail has absolutely no bearing on the topic then the comment has no worth other than as trivia.
DeleteI look at CFT's, or any item, in the larger context of its impact on a platform's role and ability to execute missions. Certainly, if there are serious and significant flaws, they need to be discussed and weighed in the balance. However, if we get bogged down in discussing the pro's and con's of one type of screw versus another (to make up an example), that's pointless.
If the use of a CFT causes a 0.05% decrease in airframe service life, who cares? If it causes a 50% decrease, then, yes, we care a lot. Unless you or someone can offer some supporting data, I consider CFT impact on airframe life to be miniscule and irrelevant given that we hang all kinds of other stuff off the fuselage and wings and aren't concerned about airframe life. That suggests to me, in the absence of data, that this is a non-issue - possibly theoretically true but in practical terms, irrelevant.
I'm trying to raise the level of discussion, in general, and getting bogged down in minutiae does not further that goal.
It would be interesting to see how conformal fuel tanks could be integrated onto the Growler to either add increase its fuel load or replace the external fuel tanks. Increasing the Growler's ability to stay in the air longer to certainly worth a look.
ReplyDeleteThe referenced links indicate that the conformal tanks can be added to the Growler and will, in addition to the range gain, open the "visible" paths for the various pods by removing the fuel tanks that restricted their field of view.
DeleteDiscussion:
ReplyDeletehttp://www.janes.com/article/63291/advances-in-stealth-range-expected-under-ngad?utm_source=Sailthru&utm_medium=email&utm_campaign=Military%20EBB%208-31-16&utm_term=Editorial%20-%20Military%20-%20Early%20Bird%20Brief
b2:
ReplyDeleteI think that the article is interesting. I now, I think, prefer more native range to dedicated mission tanking, if I had to choose.
I do notice that its the next generation 'Air Dominance' fighter, that they are tasking to the ground attack role too. I wonder how they are going to split that baby; make it BVR almost exclusively in A2A and concentrate more on A2G, or concentrate more on A2A and handle A2G secondarily.
All in all, I like the concentration on range. I think some decent level of stealth is going to be needed (and one thing I do like about the F-35 is that the skins do seem to be durable). I'm not a fan of unmanned at this point.
But overall, given our acquisition/economic environment I'm wondering if NGAD will ever get built.
If you are assuming level flight (No combat air maneuvering) fighting opponents like we have been fighting for the last 30 years, i.e. utterly incompetent, then conformal tanks are a slam dunk.
ReplyDeleteBut as as per previous comments you do not get something for nothing. Adding to the width and thickness around the fuselage will heavily impact a plane's aerodynamics once you start combat air maneuvering - adding lots of drag and much faster loss of energy, etc.
Also being that they are not droppable, as are drop tanks, you will go into a fight carrying at the minimum the extra weight of the tanks, but also whatever fuel is in the tanks.
The bottomlline is that the reason fighters were not originally designed to have a thicker fuselage to carry more fuel is that doing so significantly affects their ability to execute combat air maneuvers.
So if we can count on world of leisurely BVR type engagements against incompetent opponents they totally make sense. Or if the multi-role fighter originally designed to be a decent air-to-air fighter will be primarily focused on ground attack missions with other planes doing air superiority I guess they can make sense.