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May 31, 2004

A Crazy Idea for a Boring Day

It's a slow news day and everyone's got memorial day pretty well covered, so just to fill in with something here's a silly idea I had.

There has been considerable debate at many levels about the aircraft mix being flown by the Navy. We’ve retired the A-6 and A-7, and soon the F-14’s are also going the way of the dodo bird. That will leave the Navy with little aside from the F-18 to cover the majority of combat roles that naval aviation may be tasked to provide. Fortunately the F-18 is great aircraft, but it does lack a bit of range, and that's what's worrying some people. Here’s a basic rundown on the history of the problem, and an insane solution I’d like to suggest.

Background

During the Vietnam era the Navy was flying the F-4 Phantom, A-6 Intruder, and the A-7 Corsair II. The F-4 was replaced by the F-14 Tomcat, which could essentially do the job of four F-4’s. When Congress asked the Navy why they couldn’t just buy four times as many F-4’s instead of the F-14s, given that the F-14 cost more than four times as much as the F-4, the Navy replied that they would need four times as many aircraft carriers to provide sufficient parking space. So the Navy got the F-14.

f4A-6
                     F-4 Phantom                                 A-6 Intruder

a7e_corsair
                     A-7 Corsair II

So for over a decade the Navy flew the F-14, the A-6, and the A-7. The A-7 was getting long in the tooth, and the Navy looked at the Northrop YF-17 which had lost the Air Force lightweight fighter competition to the F-16. The YF-17 looked like the better option to the Navy since it was a twin engine fighter, something they greatly prefer for their operations. The Navy needed a slightly larger aircraft with a longer range, so the YF-17 was scaled up to create the F/A-18 Hornet, a combination fighter and attack aircraft, its chief advantages being high performance compared to the A-7 and low cost compared to the F-14. So through the 80’s we flew a mix of F-14s, A-6s, A-7s, and F-18s.

f-14f18
                    F-14 Tomcat                                      F/A-18 Hornet

Then we retired the A-7, so the Navy flew the F-14, A-6, and F/A-18, with the F-14 handling the long range intercepts, the A-6 handling the long range deep strike mission, and the F/A-18 handling combat and attack missions closer in, or further out with the help of refueling tankers. But the A-6 is a purely subsonic aircraft, and although blessed with long range and payload (comparable to a B-17 in most respects aside from speed) it’s not sufficiently survivable against opposition offered by modern fighters, and the A-6s were getting very old and expensive to maintain. To update the fleet’s capabilities the Navy pursued an aircraft called the A-12, which was to be a long range replacement for the A-6 with stealth capabilities, much like a smaller version of the B-2 bomber. However, the A-12 program hit financial and development problems and crashed and burned like an F-105 (the Thud) hit by ground fire, ending in ugly lawsuits, and leaving the Navy without an equivalent replacement or upgrade to the A-6. Despite many cries of protest, the A-6 was finally retired from service in 1990’s.

This left the Navy with a small gap in long range bombing capabilities, which distressed some in the Navy, but there was no way to get another totally new attack aircraft through Congress. Many argued that with the Soviet Union gone the Navy air role would likely involve littoral combat near the coasts of unstable third world countries, and that the capabilities of an aircraft like the A-6 would probably not be required. The Navy did receive proposals to convert existing F-14Ds into long-range attack aircraft, since the F-14 had plenty of undeveloped potential in the air-to-ground role. By adding extra hard points for bombs the F-14 can be used like a mini B-1 bomber, and could be further optimized for such a role if the Navy felt the need for long-range deep strike was sufficiently important. However, the F-14s are also quite old, and the resulting maintenance problems would limit such a solution to a stop-gap lasting no longer than the F-14’s existing airframes, which are flying with quite a bit of fatigue on them.

The solution chosen by the Navy was to increase the range and payload of the F/A-18 by building a new and bigger F-18, called the F/A-18E Super Hornet. The F-18E was an absolutely ingenious way to sidestep the decade of development most new aircraft designs demand while still providing a good degree of certainty that it would fulfill its requirements, which it has. The Navy is buying very large numbers of the new F/A-18E, which has about 25% more thrust and wing area than the F/A-18. The F/A-18E has had some teething problems, but compared to most new aircraft development it has gone very smoothly. Still, whereas the F/A-18A and C had about a 360 nm combat radius for a strike mission, the F/A-18E in comparison still only has about a 520 nm combat radius. This is a little over half that of the A-6, but of course the A-6 can’t defend the carrier against air attack or maintain air superiority. The A-6 also can't carry its full weapons load at these ranges. The F-18E does have a very versatile weapons load-out, and actually looks rather favorable in comparison to the A-6 in such regards. Here are some further arguments in the Super Hornet's favor.

Along comes 9/11 and we find the Navy using the F-14s as long range bombers in Afghanistan, refueling them once in route and having them strike targets all the way into the north of the country. The smaller F/A-18, however, could only fly as far as Kabul while carrying half the F-14’s bomb load. We again needed those old A-6s for the specialized role requiring payload and long range. The F-14s were filling in admirably, but we only have about 150 of them left, and those are slated for retirement. They are just too old to keep flying without major rework. This will leave the Navy in an interesting predicament, as the carrier decks will have almost nothing but F/A-18’s and F/A-18E’s. Some in the Navy take this lack of range so seriously that they have suggested making every fourth or fifth F-18E into a special F-18E tanker to refuel all the other F-18Es. Apparently the need to retain the deep strike capability is viewed as quite important in naval circles, or they wouldn’t be suggesting such fixes. And their backs are against the wall because they

The Problem

So now to get to the heart of the problem, which is that the F/A-18 has about twice the thrust of the older A-6, and the F/A-18E far more, but can’t match it for both payload and range because of the F-18's small thin wing, which is designed for supersonic combat performance. The limitation certainly isn’t thrust, since the Super Hornet has well over twice the thrust of the older A-6. The wing area would have to change to get the heavy payload and range out of the F/A-18. Yet we can't change the wing on the Hornets without seriously compromising its performance in other areas of the flight envelope. The choice of a wing is a compromise, and a wing that optimizes one aspect of performance will be de-optimizing others. So we're going to have to get clever if we're to squeeze more out of the Super Hornet.

The Tomcat doesn't have much more thrust than the Super Hornet, but it uses the interesting aeronautical trick of having a sweep-wing. With the wings extended, the F-14 has a broad wingspan, and a large wingspan reduces induced drag. Induced drag is the drag component which comes from those vortexes rolling off the tips, which is why sailplanes always have such slender, broad wings. The crucial term is span loading, meaning the load divided by the wingspan, in pounds per foot or other units. But there are other benefits to variable geometry. When swept, the chord, relative to the airstream, is longer from lead edge to trail edge, and so even though the wing retains the same thickness, it is relatively much thinner with respect to the chord, meaning the air doesn't have to get around that thickness quite so abruptly. So the span and area not only reduce, but the apparent thickness of the airfoil section reduces too. On top of all that, of course, the wing becomes swept which helps in supersonic flight.

So if you put all this together you get one of the reasons why the Tomcat could cruise all the way to northern Afghanistan carrying a large bomb load. To also get supersonic performance the Tomcat’s wings sweep back, so in effect the Tomcat is using a set of different wings to meet the different roles, which is a very nice trick. It can be optimized in flight for a couple different areas of the flight envelope.

An Odd Aerodynamic Trick for the Hornets.

There’s no way to pull a similar trick on the Hornets, or is there? Obviously we can’t really touch the design of the Hornets without seriously degrading supersonic combat performance, yet an airliner-style subsonic wing would better optimize it for the long-range deep strike missions. Instead of replacing its existing wing with another one, which isn’t feasible, how about attaching a second wing to hard points underneath and converting the F-18 to a temporary biplane? The idea would be to increase the lift so the Hornet can get massively greater payloads into the air, and then use the aid of the second wing to cruise out to the target with a long range subsonic mission profile just like the A-6. Once nearing the target, or in any situation that warrants, the second wing is dropped just like an external fuel tank and we’re back to having a full performance F/A-18 rolling in on a mission.

In essence, the extra wing would be dropped immediately prior to maneuvering into the strike phase of the mission. This leaves the F-18 fully loaded with fuel and weapons while at the target end of the mission, as if the F-18 just took off fully loaded very close to the target area, having merely to complete the strike and then make the long flight back home to the carrier.

So suppose we design a detachable wing for the F/A-18 having about the same wing area as the existing wing. The wing doesn’t need any control surfaces and can even be designed for only a 3G limit like a commercial transport, since the idea is to simply convert the F/A-18 into a temporary long range transport on the outbound leg of a strike mission. We're making it a temporary transport plane. The extra fuel for the outbound leg is in the thick new wing, which is attached to hard points that are already plumbed for external fuel tanks anyway, so hopefully no design changes at all are required to the aircraft. We’re just attaching a really bizarre drop tank to a hard-point that’s already designed to withstand some pretty tremendous forces. The only change to the aircraft might be some software updates to tell the fight computer that it the flight envelope is restricted with the extra wing, along with some extra parameters to reflect the aircraft's altered aerodynamics.

Lift

Let’s look at what would a second wing do for the lift. The limiting factor on an aircraft’s maximum weight is of course the lift from the wing. The wing’s lift is given by the formula L=1/2*rho*S*Cl*V2. In English units L is lift (in pounds of force), rho is air density (0.002378 slugs/cubic foot at sea level), S is the wing area (in square feet), Cl is the coefficient of lift (more about that later, but it usually runs between +-1.2 or so, more as you add flaps and slats), and V is the velocity in feet per second. The Hornet has a wing area of 400 square feet (500 square feet for the Super Hornet), so at sea level and 200 mph (283.3 fps) with a lift coefficient of 1.0 the wing provides 40,922 lbs of force. At a given altitude and velocity, the only way to lift more weight is to either increase the coefficient of lift or increase the wing area. We’re doubling the wing area, but losing a little bit of the gains to interference effects between the two wings.

If we go through some old NACA tables from the 1930’s we can get a pretty good estimate of what such a configuration could provide. At maximum load the F-18E wingtip is 7.8 feet off the deck, so if we put the lower wing within two feet of the deck we could get a gap of about 5.5 feet or so, which is about half the average chord (distance from the front to the back of a wing) of an F-18E. So the Gap/Chord ratio is approximately 0.5. The camber (bend) of the F-18 wing is adjustable, so my numbers here will be a bit crude, but it looks like the biplane configuration should work fine with a maximum wing loading of about 110 lbs/sq foot, slightly less than the 126 lbs/sq foot of the monoplane configuration. If I get a bit conservative and say it will lift 100 to 110 lbs/sq foot then the total lift is increased by 58% to 74%. That gives us a huge increase in maximum takeoff weight. And almost all of that weight is bombs and fuel, probably fuel given the limits on existing hard points.

Drag

Don’t worry too much about the drag because the Hornets have thrust to spare to provide supersonic performance; plus we’re burning fuel that it couldn’t have otherwise carried anyway. In addition, for the same span and load a biplane actually has less induced drag than a monoplane, since each wing is working at a far lower coefficient of lift. The reason we went to monoplanes is that by slightly increasing the monoplanes' wingspan its induced drag can be lowered to the same level as the biplane, and without all the interference and struts and such. Biplanes are great for lifting things but tend to have a high parasitic drag, and when our chief limitation was on thrust and our chief goal was speed, the biplane was a bad choice. In this case we’ve got thrust to spare, a deck area limitation on wingspan, no particular speed requirement, and our chief goal is payload. Since the wing is dropped as soon as its drawbacks outweigh its benefits, its addition is simply a plus.

Stress

However, we need to make sure the wings worst case lift and drag won’t overstress the mounting pylons and other such questions. If we’re running at a coefficient of lift of 1.2 on the lower wing, it’s induced drag coefficient is given approximately by CL2/(pi*AspectRatio), where aspect ratio is the wingspan divided by the average chord, or distance from leading edge to trailing edge. Sailplanes have huge aspect ratios, often 12:1 or more, whereas stubby fighters have very small ones. Anyway, for a Super Hornet at a maximum launch weight of 65,900 lbs and 155 kts, the lift coefficient is at 1.6, which is extremely high. The induced drag on its 500 sq foot wing will be around 9,600 lbs. The total drag won't nearly double this. The steam catapult currently in use starts off with about a 6 G acceleration, lessening as the launch progresses. The central fuel tank holds 480 gallons, or about 3200 lbs. So the force on the pylon during a catapult shot could peak at about 20,000 lbs. So the center pylon looks strong enough to handle the drag component.

The lift component may present serious stress problems, since the lift from the wing might exceed what a single pylon is designed for to withstand in compression. For example, if 40,000 pounds of force where on just the central pylon, the load would be equivalent to that 3200 pound central fuel tank while the aircraft pulled 12 G's negative. And this is the load when the aircraft is at 1G, not the 3G limit for a transport aircraft. So the force needs to be more distributed, possibly across the central pylon and two outboard pylons, which unfortunately would reduce the weapons load. And this still means that at 3 G's all three pylons are still likely overstressed. A better place to carry the load would be having the second wing apply force to the existing landing gear location, which is already strong enough to support the entire aircraft while slamming into the carrier deck. However this might mean the landing gear would have to remain down to allow an attachment or load bearing contact that can't be transmitted through the landing gear doors. But if you leave the gear down the aerodynamics are horrible and you can't drop the wing without snagging the gear. The airframe around the gear is possible strong enough to withstand the force if it was presented as a distributed load, which would have to be investigated structurally.

In short, the pylons can take the drag but possibly not the lift. The gear locations can certainly take the lift if there's a way to transfer the forces in this area, but this area is also the most difficult part of the design. It might be possible to pull this off, it might not. So of course this whole idea is contingent on a big "maybe".

Payload

Currently the maximum weight of the F/18 is around twice the empty weight. A second wing allows us to up the maximum weight by somewhere from 50% to 75%. Even at 58% this means the actual payload of the F-18 (maximum weight minus empty weight) more than doubles, with a maximum weight now at 104,000 lbs instead of about 64,000. Since we’re merely taking off with this weight the wheels and landing gear should handle it, since they are designed for slamming into a carrier deck, even though we’ve likely exceeded their design loads, which include these landing loads. The catapult might be a limitation, since a fully loaded Tomcat only weighs 72,000 lbs, however we’re replacing all the steam catapults with 2 Megawatt linear motors capable of launching a 100,000 lb aircraft at 200 knots. So let’s assume the new design is flyable and launchable.

Range

Since the Super Hornet can already conduct a strike missions over a 500 nm radius in a high-lo-lo-high mission, the plane is already flying 1000 nm on existing internal and external fuel, while carrying a load of ordnance on the outbound leg. Since the extra wing will provide the fuel for the outbound leg, and the payload is dropped on the target, the radius of strike missions should increase to around 1000 nm, doubling the strike radius and getting us four times the area of coverage as we’d otherwise have with an all F-18 deck. And if you really got crazy you might try hanging about 40,000 lbs of bombs off of it instead of fuel, thought I can’t think of a particular target where they’d need to be doing this. But it’s nice to know the capability might be there, if the challenges of providing all the extra hardpoints can be overcome, although at some point you're simply carrying more external ordnance than aerodynamically wise.

Storage and Design

The extra drop-wings could be stuffed into any nook and cranny on the carrier, and need only be used if the Navy finds itself with a target that’s otherwise outside the normal range of the Hornets, so they certainly wouldn’t be used for common missions. They’re just an expedient enhancement useful in a limited range of situations where the target is outside the new range of a carrier strike. Design them to be simple, cheap, and overbuilt, since carefully optimizing them would only result in allowing the F-18 to fly out so far that it couldn’t make it back. We’re basically talking about a crappy WW-II or Korean War era wing, probably with no moveable surfaces. Ideally a prototype experiment would be designed by graduate students on laptops and put together by a guy named Bud with a Miller welder. As long as the program doesn’t become an F/A-18 enhancement requiring thousands of engineer hours and simply remains a bizarre drop tank experiment it should be cheap as dirt to develop, as aviation equipment goes. As an added bonus, not all the drop tanks need to be full sized, since a wide variety of mission capabilities can be toyed with. Some could be full span, some merely the width of the Hornet's folded span for easier set up on a packed carrier deck. All types of configurations are possible, and since the wings are throw aways there’s not much reason not to try out a multitude of different designs, exploring the limits of low-cost throw-away construction.

Since this is for a naval application dropping large wings isn't a problem, since they're falling into the ocean instead of on people's houses. A standard external fuel tank has a pretty predictable impact point when you drop it, unlike a fluttering wing, which may be yet another reason, aside from cost, that this bizarre method hasn't been used before. The Navy faces a greater logistical problem with heavy refueling tankers, and just increasing aircraft range might have greater relative benefits for them as opposed to the Air Force.

Drawbacks

There are a host of drawbacks to the idea. Interference drag will likely be fairly high, though as previously noted we have thrust to spare and we're burning fuel that otherwise couldn't be carried. Other drawbacks to fielding such a drop tank are having the people on deck wheeling around large wings in high winds, a recipe for disaster if the wing isn’t mated to a heavy cart. You also have to have a release mechanism which must shift the wing to a negative angle of attack for release, otherwise you'd "release" it but the plane would just keep sitting on the wing, since the wing is still providing positive lift. The release mechanism is probably the most critical component, since as long as you can immediately jettison the wing and the extra payload it allowed, you’re still well within the flight envelope of the unassisted F-18 and recovery from any problem should be fairly simple.

F18EgearThe other major drawback is trying to figure out how to make a drop wing not interfere with the landing gear while still having some structural integrity. The biggest risk comes at takeoff when the gear is down and the wing can't be jettisoned without risking snagging the gear. Other drawbacks are that everyone might laugh at the idea of using a biplane, and having flying scarves come back in fashion. There's also the cost involved, since a refueling tanker doesn't involve disposing of a wing, however cheaply it's built.

Normally crazy ideas like this are immediately rejected, since an ugly but cheap performance enhancement to an existing aircraft is often used as justification to cancel funding on a new aircraft far more suited to the specific role that's being addressed by the proposed enhancement. However in this case there’s no hint that a new long range attack aircraft will be forthcoming, since even the future F-35 lacks the combination of long range and payload. That's why they call it an 'F' instead of a 'B' or an 'A'. There's also a need to have the long range bomber role filled, and this might allow the Hornets to act a bit more like a medium bomber that automatically converts back to a fighter halfway through the mission. Another way to think about it is that it's merely using the staging concept common to rocketry, and the aircraft drops a wing and a tank instead of an engine and a tank. In either event, there's some advantages to the idea, but I really have doubts as to whether anyone would go for such a strange configuration.

The final question is what to name such an odd idea. Obviously you wouldn’t want to call it a biplane lest other services laugh at it. Maybe X-wing or I-wing would be more fitting. Nevertheless, the final name is almost a certainty. During the Vietnam era when the Navy was flying Grumman A-6 Intruders and Douglas A-1 Skyraiders they called them the “Spud” and a “Spad”. The Spad of course was a WW-I biplane, and it rhymes with “Spud”, which is a good comparison between the front end of an A-6 and a potato. Given that the piston-engine plane was nicknamed the “Spad”, in reference to a previous bi-plane, a Super Hornet in this bizarre biplane launch configuration would inevitably be called the “Super-Spad”.

skyraider_02f18bipe
                A-1 Skyraider "Spad"                   F/A-18E "Super Spad"

And that's my stupid idea for the day. Maybe tomorrow I'll note that a biplane on a space shuttle would mean that the lower wing has all the heat absorbing tiles while the upper wing is spared from most of the heat of re-entry. You might be able to double wing area while not increasing the weight as much as with a monoplane that has twice the bottom area, and thus about twice the heat shield weight. I haven't crunched through the math on that one, though, and it might be a non-starter.

May 31, 2004 in Science | Permalink

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Comments

You would be better off mounting the second wing ABOVE the normal wing. The Brits had above drop tanks and missile carriage for the English Electric Lightning, with no apparent problems.

This would allow the same undercarriage and hard points to be retained. It would also allow roughly the same angle of attack to be used for a carrier approach. The only change being a hard point with fuel transfer capability on the top of the airfoil.

When the second wing needed to be jettisoned, natural aerodynamic lift will carry it up and away. You may even be able to retain it while trapping aboard a carrier.

Right now the Navy along with the Air Force and Marines are wrapped up in the F-35 WonderFighter program, but I think this latest project will fall to the Congressional budget axe.

Suggest it to the Navy's Material Command with info copies to the Chief of Naval Operations. The worst they can say is "no."

Rich

Posted by: Rich at May 31, 2004 9:33:52 PM

A couple of problems leap to mind, other than the ones you mention above.

1) You're assuming that adding the second wing automatically means that you get to double the available payload. I'm not an Aeronautical Engineer (or, for that matter, ANY kind of engineer, other than model railroad), but I've gotta figure that the biplane would still be around if it gave that sort of performance boost.

2) You don't seem to mention (or perhaps I miss it) what happens when the add-on wing DOESN'T jettison, or jettisons incorrectly.

2a) If it doesn't jettison, you've got to land this beasty back on a carrier at a high rate of descent, then an incredibly high brake rate (the "carrier landing as controlled crash" school). Think launching the plane is hard?

2b)If it's a two-piece wing (one wing piece under or over each "real" wing), suddenly you've got inequal lift and instant roll. If it's a one-piece and it jettisons on "one side" only, you've got at BEST a crippled plane (as the 2nd wing rips free from the attached side, then flaps and smacks its way down the fuselage), at worst a dead one (and don't say it's got a foolproof jettison device... we'll come up with a better fool).

2c) Adjunct to having a top-mounted wing, what would it do to the ejection properties of the pilot seat, if anything?

There have got to be other problems that I haven't thought of. Is it possible? Maybe. Is it worthwhile? Probably not. Maybe easier to just redesign the F/A-18's wing and have ANOTHER version, this one specifically designed for heavy lifting and long-range stuff (including tanking).

Rich, your comment about the Lightning's above-wing hardpoints is correct, but please note there are a lot of other planes with top-mounted tanks/weapons/what-have-you, the Jaguar and (if my memory serves) one version of the Mirage. It's not as common, mostly because you can't put bombs up there (probably the most common payload), but there's probably no penalty to putting something on top of the wing, as opposed to below, as long as you design for it.

Of course, the whole Electric Lightning looked a little... well, hinky, though, what with the engines being stacked on top of one another and the top-mounted missiles. MOVED like a bat outta hell, though.

Posted by: Wonderduck at May 31, 2004 10:29:24 PM

Oh, I'm not saying you get twice the lift, but biplane interference is pretty well understood and dependent on the gap ratio. If I was truly doubling the lift I could get 130,000 lbs in the air.

Biplanes were around a long time because they do allow a structurally easier way to get the required wing area, and at slower speeds it takes more wing to lift a given payload.

Jettisoning the wing is actually no more complicated than dropping a bomb once you get it to a neutral or negative angle of attack, and if all else fails you could go to slight negative G's and just use the existing bomb release mechanisms. And a faulty bomb release can already cause the loss of an aircraft.

You can't modify the existing wing on an F-18 to get dramatically increased range and payload because then it becomes a subsonic wing and you no longer have a supersonic fighter. If we wanted a purely subsonic plane we wouldn't have gone to all the enormous trouble of making them supersonic in the first place. If we were going this route we wouldn't have gotten rid of the A-6s.


Posted by: George Turner at May 31, 2004 11:02:56 PM

Sure we would have. The A-6, though a marvelous aircraft, was wearing out fast. A new airframe would allow you to work 50 years of improvements into the design (example: big-honking drum computers vs teeny tiny black boxes; stealth; better/more powerful targeting systems) You have a choice: retool a construction line for a 1950s era airframe (albeit a fantastic one), or build a new airplane altogether.

Which would Congress prefer? Heck, which would the NAVY prefer? If you said "build a new airplane" you get a gold star.

Oh, and if we're going to all the trouble to put a biplane wing on a F/A-18, who's to say you COULDN'T redesign a single-wing for a high-speed/high-load combination? Heck, if they can put a delta on a F-16, or make a pure superiority fighter like the F-15 into the world's greatest attack aircraft, why not?

Back to jettisonning the extra wing; yes, I'm aware that a bad drop of a bomb can cost you airplane. I submit that it IS more difficult than dropping a single bomb, simply because of the SIMULTANEOUS requirement of releasing two or more locking points. Again, assuming only two locking points, they both have to work, successfully, at the exact same time, or the airplane gets bent. With two bombs, if one doesn't drop, well, at least the wing doesn't automatically fall off. How long a delay is allowable, structurally, before too much damage is done? Navy aircraft get beaten up just landing, sooner or later. Adding another variable into the equasion seems to be asking for trouble.

Existing mechanisms for dropping bombs are not just mechanical clamps. Many also use (literally) shotgun shells to kick the bomb off the wing, according to references I have around here. I assume thats to help with clearing the wing/hardpoint. POSITIVE Gs help, too (they pull the bomb DOWN. You'd use negative Gs if the munitions are on top of the wing). You'd probably need a higher level of precision for the release mechanism of the biplane wing, to prevent damage. At what point does the whole thing become too complex to go to sea (with all THAT entails)?

Why stop at two? Why not three and paint all the planes red while you're at it?

Posted by: Wonderduck at Jun 1, 2004 12:00:41 AM

Finally got two brain cells to rub together, and came up with the following.

1: In WWII both we and the Brits had what they called "slip wing" projects to enable modern fighters to be reliably catapulted from Merchant Marine vessels carrying supplies to England and Russia. The Brits were modifying their older Hawker Hurricanes and we were experimenting with the Grumman Wildcat (which the Brits also used as the Martlet.) We were trying to negate the German high altitude recon FW-200's which were spotting convoys for the U-Boat wolf packs. The results were kind of inconclusive, as what finally worked was our possession of an Enigma machine which allowed us to read their codes and harrass the subs directly.

2: Remember, the Super Hornet is a compromise of a compromise. The design started out as the Northrop YF-17, which lost to the F-16. The Navy scaled it up and called it the McDonnell Douglas F-18. Later they hung bombs on it and called it the F/A-18, because the A-7E engine problems (Allison version of the Rolls Royce Spey) forced an earlier retirement of the Corsair II than planned. They scaled it up again for the Boeing Super Hornet. The problem being that you usually cannot do direct scale ups without encountering problems. If what I've been reading is true, the Super Hornet already has severe drag problems carrying external stores.

3: For the assymetrical wing drop problem, I have two words. Explosive Bolts. They are cheap and reliable, and have been used in aviation for quite a while. It's proven technology.

4: Wonderduck's suggestion (?) about painting them all red, only works for the Carrier due out next April. the USS Barnum and Bailey. You've heard of it. The Navy's environmentally friendly carrier, powered by baking soda.

Rich

Posted by: Rich at Jun 1, 2004 1:08:46 AM

My apologies George. I shouldn't have gone into the F-18 genesis as you had covered it pretty throughly above.

I always have had problems with RTFQ.

Rich

Posted by: Rich at Jun 1, 2004 1:15:28 AM

I think a better idea whould be a redesign of the A-6 to allow supersonic flight up to about Mach 1.3 and with enough internal volume to allow the different versions to be produced with minimum basic changes. Bomber, Electronic Jammer, Tanker, Missile Carrier for Fleet Defence, and VIP Transport.

The Air Force would probably buy the Jammer after having tried to do it with a two man crew (the EF-111 Spark Vark.)

Rich

Posted by: Rich at Jun 1, 2004 1:29:06 AM

One other thing, the Poles, before the breakup of the Soviet Bloc, designed and flew a jet engined biplane crop duster. I have the specs in one of my books, I just can't seem to find the book.

Rich

Posted by: Rich at Jun 1, 2004 1:41:35 AM

Wonderduck,

They tried going with an all new airframe, the A-12, and the project crashed and burned. That left them with the F-18 and a need, so they upscaled it.

If you put a much bigger wing on the F-18 you increase the supersonic drag, and it's already got a few drag problems. You could try turning it into a different airplane. If you go with a delta wing like the Eurofighter Typhoon which has similar thrust to the F-18E you get a fighter with a max takeoff weight of only 46,480 lbs and a combat radius of only 560 miles. Our Super Hornets already do better than that for getting weight off the deck with less wing area.

But our decks will be covered in Super Hornets as built. They are great in a dogfight and we don't want to give up that performance. There's not a supersonic wing that's going to turn them into a long range bomber without drastically harming other areas of the flight envelope. It would be nice if we could, but that's not in the cards, much less getting Congress to fork over even more money for it.

And there wasn't anything in the F-15 that prevented it from being an attack aircraft except philosophy, ie "Not a pound for air to ground," and it's range on internal fuel is less than the F-16. Col Boyd, who was in charge of the F-16 program, made sure of that because the several Air Force generals, who were certain they could kill off the little runway defender program, never bothered to check the numbers on its internal fuel capacity as a percent of gross weight.

The drop wing idea has flaws, but it's also an idea that can succeed or fail without sucking up enormous R&D dollars.

Posted by: George Turner at Jun 1, 2004 1:58:45 AM

Nice points, Rich.

The Hawker link was nice, too. I'm favoring the low wing configuration for a couple reasons.

The F/A-18 is a high wing fighter, and it would makke sense to install "the wing that is not there." For an F-4 it would make far more sense to try and put a wing on top.

If you did try to put a wing up top the release problems are simpler but you have the thrust way underneath much of the drag. Maybe not a killer but not that great.

You'd have to add lots of load points to attach it. It would also have to clear the vertical stabs, along with its mounting mechanisms, which might not be trivial when the pilot hits the panic button. Underneath and rearward the Hornets are clear.

Can you imagine a crew trying to install a high wing on a Hornet on a carrier deck? Most of the plane is "No Step", and we don't really have cranes running around. It pretty much has to get loaded like a bizarre piece of ordnance or nobody is doing it.

Posted by: George Turner at Jun 1, 2004 3:44:20 AM

George, yes, I know about the A-12, too. I'm saying that this time they can maybe design an aircraft that ISN'T riddled with 200% cost overruns, graft, criminal proceedings, and lawsuits out the ying-yang. Unless you want to say that we can never, ever, try and design a Navy attack craft again because of it?

Saying the A-12 was a failed design is one of the biggest understatements ever. Heck of a story though.

Posted by: Wonderduck at Jun 1, 2004 9:09:59 AM

The reasons I favor the high wing approach are as follows.

When you mount the wing low, you affect the angle of attack during the approach and landing on the carrier. On approach, Naval pilots fly a constant angle of attack (they call it "Flying the Ball") and vary the thrust as required. A second wing, mounted low, would require two sets of flying responses, which means an accident waiting to happen. Remember there is a lot of air moving down the deck of a carrier, and the direction changes very abruptly (it becomes a down draft) as soon as it leaves the carrier. A high mounted second wing minimizes those required changes.

The top wing, not requiring hardpoints for weapons carriage and release can be much simpler and lighter in internal structure. It's ONLY jobs are to provide lift and store fuel. If you put the wing under the present wing, you have to add hard points for weapons carraige, complicating the structure.

Since the top wing is already providing lift, use that lift to jettison the wing prior to combat. A low mounted secondary wing will require forcing the airplane into a regime where lift is no longer being provided, then get rid of the wing. To a pilot, that is a definite no no. Especially in combat.

Pilot ejection with the top wing in place does need to be looked at. The fins are already splayed outward, but I think the current ejection envelope allows the pilot to clear them with ease. The problem could be downwash from the top wing forcing the seat and pilot into a new, lower trajectory that doesn't clear the fins. The solution could be a more powerful rocket for the seat, forcing a higher trajectory. Another problem could be the placement of the top wing over the cockpit. If the section immediately over the cockpit were not metal and had no structural beams in the area, the pilot coud eject through the wing, the way having been cleared by the canopy.

Just some random thoughts.

Rich

Posted by: Rich at Jun 1, 2004 11:15:24 AM

Does the Joint Strike Fighter not solve these issues? I don't know what the range is on that thing.

Posted by: Calliope at Jun 1, 2004 11:45:15 AM

Calliope, the Joint Strike Fighter/F-35 will be one of the most expensive programs in aviation history. They are trying to design a fighter for three separate missions by designing three separate variations of an airplane. I predict it will be canned by Congress as too expensive.

We tried this once before with the F-111 in the sixties in the TFX program. McNamara tried to force the Navy to accept the F-111B, which couldn't even reliably land on a carrier deck, but the Navy rebelled. The Navy finally turned to Grumman and got the F-14 which has served them well.

Now, they could go to Boeing and get their JSF entry, but that airplane was pretty much a dog. The Lockheed/Martin design wiped the floor with the Boeing plane. That leaves Northrop/Grumman and Raytheon, and Raytheon doesn't do fighters.

The Air Force soldiered on with their F-111, eventually fixing the intake problems it had, and it became their "Supersonic A-6." The TFX program itself has always been viewed as a failure primarily because of the F-111B debacle.

What we are discussing here is a CHEAP way to modify or redesign a existing aircraft design to increase it's mission envelope to allow it to be effective for a couple of more decades. All other Navy fighters and bombers are pretty old and worn out. Carrier duty is very hard on airplanes and after about 5 years or so, they start exhibiting age, fatigue and corrosion problems. Pretty soon, the F/A-18 will be the only carrier aircraft they have left.

Rich

Posted by: Rich at Jun 1, 2004 1:36:20 PM

BTW, George, I resent the slap at the F-105 in the middle of your piece. I spent two tours in SE Asia when we were sending them up North as a avionics tech. I've also worked on the F-4, A-7, AC-130 and F-15. Sure the F-105 had it's combat design flaws, but so does every other aircraft.

The F-105 was the ONLY fighter that could get down in the weeds and go supersonic. The Mig 21 airframe shook itself to pieces (some actually did exactly that), the F-4B shook its crew to pieces (stout bird, but too much wing area,) the Crusader wouldn't go supersonic that low. Only two aircraft even had a chance and they were both on our side. One was the F-111A and the other was the Navy's RA-5C Vigilante (a brilliant aircraft design crippled by an idiotic weapons delivery system.)

I have great respect for the F-105, and if the tooling hadn't been destroyed by DOD, we would have had many more of them. BTW, the same thing has happened to the A-10 program.

Rich

Posted by: Rich at Jun 1, 2004 1:56:20 PM

While I'm thinking of it George, replacing, removing or intalling a secondary wing, regardless of mounting position, on the flight deck will be darn near impossible unless the carrier has almost no wind across the deck.

All such operations would have to be done on the hangar deck and the plane returned to the flight deck.

Rich

Posted by: Rich at Jun 1, 2004 2:09:23 PM

/wave

I'm an old AWG10A F4 missile control system tech Rich. (Not Vietnam era though, 82-86)

As far as I'm concerned we have to suck it up and buy the JSF whether its expensive or not. I can't believe it when people bitch about a defense program that costs a few billion dollars when we toss money down the drain on fruit fly studies and crap like that. Far better to make the investment we have to make to maintain our advantage in air power. I can remember when other countries made planes that could shoot ours down. Now they run rather than fight. That's worth a few hundred billion over a few years to me. Its the most important thing we do with our money.

Posted by: Calliope at Jun 1, 2004 4:14:50 PM

Rich, alas, George was just calling the Thud it's own nickname from Vietnam! And why was it called that? Because that's the sound it made when it flew (supersonic or otherwise) into the ground.

Fantastic as an interceptor, yes. As a ground attack plane though, it was an accident waiting to happen: one book I have (at home, I'll look it up after work) says that over HALF of the constructed 105s ever made ended up imitating a dart.

Maybe we can convert the new version of the COD plane to tanker/support?

Posted by: Wonderduck at Jun 1, 2004 5:14:43 PM

Sorry about the snide F-105 remark, Rich. They were a good airplane but not quite redundant enough. Interestingly they use exactly the same airfoil as the Hornet, and I imagine that leading edge root extensions would really up an F-105's turning performance. But the point about having too much wing area for low-level supersonic flight is a good one. Turbulence beats you to death when high speed, thick air, and a big wing turn slight changes in angle of attack into massive forces and thus accelerations. Of course this also means that instead of the "hog", the "ground hog" you get called the "super ground hog", although if you go for a big slow wing like the A-10 they just call you a "wart hog".

I love the A-10's, btw.

And Calliope, one of the odd reasons I'm writing the "Space Fleet" post is that we're starting to get really good at lasers. We can already shoot down sidewinders, aircraft, and artillery shells, and if we can do it you can be some enemy 15 years down the road will have some French or Chinese built laser air-defense system. Since our planes are all lightweight aluminum and filled with fuel they're very vulnerable, and such systems might severely impact our air superiority. So some of what I'm toying with in the "Space Fleet" posts might apply to taking out such potential air defenses. I'm really fond of the grazing angle nosecone (hope that works out) that looks backwards to maintain its alignment on the beam.

Posted by: George Turner at Jun 1, 2004 6:13:04 PM

The only thing i see that would work when attacking is flying really, really low. But than you get in the "why did they build a wall here" so the number of returning sorties would be low so manned plans are out.
For airsuperiority over enemy territory i think you could use lasers in the air (mountaintops, planes, etc.) who are over the horizon from the ground but not from the air


ps. hitting a satelity from earth with a laser isn't that hard so the question what to do against laserfire in space seems to be opportune but with the added problem that you have use a lot more energy from earth than you could from space.

Posted by: carl at Jun 1, 2004 8:54:30 PM

I wasn't really THAT ticked off about the F-105 comment.

I heard all the early "Thud" jokes at McConnell in 63. Then we had a bird crash (hydraulic failure) in a Kansas field, and I was one of the ones to go pick up the pieces. Very depressing duty.

The weaknesses of the F-105 were three.

One, the internal bomb bay (yes, it had one) was used to carry an extra fuel tank, which was right in the line of fire from anyone with a AK-47.

Two, right above that fuel tank were hydraulic lines grouped closely together, so if you hit one, you probably hit them all.

And third, was lack of cooling airflow around the P&W J-75 engine which caused intermittant engine explosions. This last is what happened to the Thunderbird F-105 lost over the Golden Gate Bridge in California.

The F-105 inherited the Wild Weasel mission when the F-100 was retired. They had those old birds loaded down with so much gear, bombs and missiles, it was a wonder they got off the ground. They even brought back the F-105B from the boneyard to try to fill the demands for aircraft. Finally the airframes just wore out.

After a brief flirtation with F-4's, the Wild Weasel mission was finally given to the F-16, where it remains today.

Posted by: Rich at Jun 1, 2004 9:25:31 PM

Wonderduck, the F-105 flew the majority of its missions before the Air Force got the F-4 in any significant numbers. That we left about half of them littering the countryside around Hanoi is understandable, considering the layered missile and gun defences and the lack of top cover. Where was the Navy? They had their own problems with Haiphong Harbor. At least they were able to provide top cover to their A-4 and A-6 attack jets with first the F-8 Crusader, then the early F-4 Phantom. The Air Force brought over the F-104, and the F-102, but neither had the range to even reach Hanoi, much less provide top cover. So the F-105's went in naked, and paid the price.

Regardless of what the Republic brochure said, the F-105 was never really an interceptor. It's primary mission was delivery of a nuclear bomb in Europe. That's why it was designed with an internal bomb bay. The mission profile was for a low level supersonic ingress to the target, pop up and deliver the bomb, and (hopefully) get out of Dodge by flying low level back out.

In fact, in the last years of service with the Georgia ANG, they were so old and laden down with Wild Weasel equipment that most couldn't fly above 35,000 ft.

It was an airplane that tried to fill mission requirements with inadequate numbers. But Lord, how it tried. It will always have a special place in my heart, along with my first muscle car, and first firearm, and various other firsts.

Rich

Posted by: Rich at Jun 1, 2004 9:51:55 PM

We are about 25 years away from having a true laser defense system. When that happens, a lot of old and not so old airliners are going to get suddenly yanked out of the civilian boneyard around Mojave airport and get commissioned as LF-747's and LF-10's (they could unstead use the AL prefix like the prototype 747 they are now testing,) and wind up in military markings. Why use airliners? Because you need to haul around a lot of support equipment, such as storage capacitors in order to be effective and you need the range for loiter time.

I'm not sure they have solved the atmospheric scatter problem well enough to enable a Earth to LEO defense system. Most demontrated ranges are much shorter than that, but then I'm not privy to the test results from any tests.

Rich

Posted by: Rich at Jun 1, 2004 11:30:26 PM

Not sure about that Rich. The Airborne Laser is coming along, we're putting a multi-megawatt one on the AC-130 and soon a coule-hundred kilowatt model on the F-22. The Air Force is also getting good at hitting satellites, though right now they're just lighting them up with a narrow beam. There are certainly pushing the "rubber" mirrors to the limits. The AC-130 COIL laser is designed for a 20 mile range, which would be a pretty good radius for a ground based system.

Posted by: George Turner at Jun 1, 2004 11:47:46 PM

In response in an earlier comment: I hope you dont expect the guy to go into all the design details, he just came up with an idea and for someone that has to write an article I dont think its bad at all.

The device that ejects the wings can be made fool proof, and probably with devices so simple a kid could understand watching transformer cartoons. Also, a procedure to eject them safely could be made so that they would not hit any part of the aircraft. One way is through using negative G's. I have an experience with this concept because I fly an L-39 with my father, and this is only a subsonic jet. The power available to produce the ammount of G force to eject the wings away from the aircraft is minimal and the F-18 is capable.

For an L-39 that doesn't have hot seats (ejection system), this concept must be used in the case of an emergency. The Seats would be detached then after going up into what seems like part of a loop, a sudden rotation either direction and then pushing the stick forward would eject you. Non-hot canopys would be ejected the same way.

Now, stupid idea? no. possible? yeah. practical? maybe not.

Posted by: Chris Battle at Jun 13, 2004 2:11:48 AM