F-111B Colossal Weight Improvement Program

This assessment is based on a 1/50th scale model in the Grumman History Archives on Long Island and a three-page summary of Grumman's CWIP (Colossal Weight Improvement Program) study provided to General Dynamics.

The empty weight proposed for the F-111 was even more optimistic than usual in winner-take-all paper competitions. As is customary, Grumman and General Dynamics initiated a two-pronged F-111B weight reduction study effort, the Super Weight Improvement Program and the Colossal Weight Improvement Program, even before first flight. Roughly speaking, the ground rules for the SWIP were to reduce the weight but not significantly depart from the design and mission requirements. The CWIP allowed a great deal more flexibility, basically tossing out anything imposed only by the Air Force low-altitude strike mission and preferences like the crew escape capsule.

For the CWIP configuration, Grumman engineers deleted the bomb bay and escape capsule and reduced the volume required for the main landing gear by not allowing for the large high-flotation tires required for operation from unprepared fields. That enabled them to shorten the forward fuselage by about five feet. The shorter forward fuselage presumably allowed them to delete the ventral fins, with the original vertical fin now adequate for directional stability even at high angles of attack. However, the horizontal stabilizers were slightly increased in size, presumably for improved low-speed handling qualities for the carrier approach.

All six Phoenix missiles were now carried on the fuselage, four semi-submerged and two on short pylons on the lower sides of the fuselage. This arrangement eliminated both the wing pylons and swivel mechanisms required to keep the missiles aligned when the wings were swept. I haven't yet found any information on the main landing gear configuration change required by putting two missiles on the centerline of the belly, but presumably it resembled that on either the Grumman F11F Tiger or the North American A3J Vigilante.

The center fuselage with the engine inlets and wing mounting structure were basically unchanged except for the main landing gear bay. The wings were also unchanged. The engines appear to have been moved forward by about two feet to restore the center of gravity after the nose was shortened.

Although the canopy appears to be bulged upwards, my preliminary assessment is that the visibility over the nose was no better than it was on the original F-111B, which was determined to be unsatisfactory. However, the lower weight would have resulted in a lower angle of attack for the same lift, possibly providing the same over-the-nose visibility improvement as the raised cockpit that was eventually required.

The government program team elected to incorporate most if not all of the SWIP changes in the 12th F-111A and the 4th F-111B. The CWIP specification changes stayed on the drawing board until Grumman was able to apply them to what became the F-14.

One if by Land, Two if by Sea

“One if by land, and two if by sea.” That line from Longfellow’s poem commemorating Paul Revere’s famous ride in 1775 was one of the justifications used by the Navy in 1976 to select the twin-engine McDonnell F-18 over the single-engine F-16 for its VFAX program. Some viewed it as dissembling on the Navy's part since the desirability, much less necessity, for twin-engine carrier-based aircraft had not been very evident up until then. In fact, although single-engine airplanes were in the minority in the air wings at the time, that was a relatively recent change from past practice. A year earlier there was still an air wing aboard Hancock (CV-19) that was almost entirely comprised of single-engine aircraft. Now, of course, there are no single-engine airplanes in the carrier air wings.

The major benefit of twins, the capability to return to base after an engine failure, was initially problematic for a carrier-based airplane. The pilots approached power-on in level flight at the lowest safe speed and minimum altitude, cutting the engine just when the airplane would settle onto the deck. This was essentially the same technique used for a short-field landing ashore, where it assured a touchdown very close to the approach end of the runway, allowing the maximum distance for stopping.

The pilot of a twin-engine propeller-driven airplane with one engine inoperative had to take into account the minimum control speed in that situation. Since the engines were almost always placed out on the wing, when one failed the other produced a significant turning moment which had to be counteracted by the rudder. Since rudder effectiveness varied with airspeed, at some point the pilot could no longer stop the airplane from turning with the engine at full power. What’s worse, the turning generated a roll because of the difference in the lift on the wing on the outside of the turn versus the one moving slower on the inside. Since the ailerons also lost effectiveness with decreasing airspeed, a loss of control in roll would result as well if the engine power was not immediately reduced.

Unfortunately, the minimum-control speed at the power required to climb with the gear and flaps down was almost certainly higher than the required approach speed dictated by arresting gear, which made a successful wave-off an iffy proposition.

The tyranny of minimum-control speed was also imposed on an airplane taking off, but it was more draconian at sea than ashore. If the pilot taking off from a runway lost an engine while still below minimum-control speed, he would simply close the throttle on the good engine and reject the takeoff. The outcome varied with the length of the runway and if it came to that, the landscape beyond its end, but was rarely as dire as faced by the pilot of an airplane less than one hundred feet above the sea after being launched from an aircraft carrier at less than the minimum-control speed with full power on the operating engine. If he reduced power on it engine to maintain control, he almost certainly would not have enough for level flight, much less to climb or accelerate to a speed at which he could use all the power available.

Having a second engine was therefore not as good a deal for a pilot flying from an aircraft carrier as it was for one flying from an airport. Although it enabled one to divert to a land base or get back to friendly ships and ditch if an engine was lost in flight, it doubled the risk of an engine failure during a critical, albeit short, time during takeoff and landing. Twin-engine airplanes also tended to be bigger than singles whereas compactness was a virtue on an aircraft carrier.

Nevertheless, there were benefits beyond the ability to continue flight after an engine failure. The easy way to improve the performance of fighter airplanes is to incorporate more powerful engines in new or existing designs. Increasing power in piston engines basically meant adding more and/or bigger cylinders and supercharging. By the late 1930s, the engine manufacturers were beginning to approach the limits of existing technology and incremental horsepower increases were resulting in increasingly smaller increases in speed and greater engine complexity. The obvious next step was the twin-engine fighter, a doubling of power available without requiring the time and expense of a new engine development.

The U.S. Navy solicited proposals for a twin-engine carrier-based fighter in 1937 but none of the submittals were deemed to be acceptable. In 1938, the Navy had Lockheed modify an Electra Junior to have a fixed tricycle landing gear and tail hook. It was designated XJO-3 and delivered in October 1938. On 30 August 1939, Navy pilots made 11 takeoffs and landings from Lexington (CV-2) to evaluate it from both twin engine and tricycle landing gear standpoints.

In parallel with this research program, the 1938 competition for a new fighter was opened to both single and twin-engine designs. This time, the Grumman design number G-34 was considered worthy of evaluation by the Navy as the XF5F along with single-engine designs from Vought, the XF4U-1 powered by the big new P&W R-2800; and Bell, offering a derivative of the Army Air Forces P-39, the XFL-1.

The XF5F, probably in consideration of the one-engine-inoperative requirement, had the engines mounted as far inboard as possible and twin vertical fins, one in each engine’s slipstream. One-engine-inoperative wave offs were evaluated at altitude: "(A wave-off) might be accomplished (on one engine) provided the airspeed is about 80 knots or more and no more the 1/2 power on the operative engine were used." The "proper" approach speed based on stall speed, however, was defined as about 74 knots.

In spite of having as much or a little more installed horsepower than the XF4U, the XF5F was slower and couldn’t climb as high although its rate of climb through 20,000 feet was essentially the same. As a result, the Navy elected to proceed with the F4U for development and production. Nevertheless, the Bureau of Aeronautics continued to be interested in a twin-engine carrier-based fighter. On 30 June 1941, Grumman received a contract for the two XF6Fs and two XF7Fs. The F7F program suffered from the priority on F6F Hellcat development but the prototype Tigercat finally flew for the first time on 3 November 1943.

As soon as Grumman test pilots flew the XF7F-1, they realized that it did not have a big enough fin and rudder for an acceptable minimum control speed in the event of an engine failure on takeoff or a wave-off. Design of a bigger fin and rudder was initiated and introduced on the F7F-3. Although all models of the F7F were carrier qualified, the likelihood of and/or concern about a successful single-engine wave-off must have been low as there was no description of the technique for a single-engine carrier landing in the flight manual. In any event, the Tigercat never deployed with an air group on a carrier, probably due to its size as much as anything else.

One of the Navy’s first carrier-based jets, the McDonnell FD-1 Phantom was a twin, mainly because the Westinghouse-provided engine wasn’t very big. It grew to become the F2H Banshee, the first twin-engine airplane to regularly deploy on carriers. Two of its contemporaries, the Douglas F3D Skyknight and the North American AJ Savage, were also multi-engined. The AJ had three engines, two turning propellers and a jet. Like the F7F Tigercat, the Skynight was primarily operated by the Marines and made very few deployments. The Savage did deploy because of its critical mission of long-range nuclear strike, but because of its size, it generally was held in readiness at nearby Naval air stations during a carrier’s deployment. These jets were less limited from a minimum control speed standpoint in the event of a one-engine-inoperative situation than previous twin-engine propeller-driven airplanes because the engines were located close to the centerline; the AJs were slightly better off if one of its piston engines failed because the jet engine was located on its centerline.

However, North American was concerned about minimum control speed as evidenced by the size of the AJ’s original fin and rudder, made even bigger because carrier basing necessitated a fairly short airplane. Unfortunately, the rudder proved to be too big for high speed flight and resulted in a fatal accident when it broke the tail off in a flight test maneuver. The empennage was redesigned to increase the size of the fin, reduce the size of the rudder, and delete the dihedral in the horizontal stabilizer.

The lack of U.S. Navy concern about engine failures in the late 1940s was evident by the initiation of single-engine airplane programs, the Douglas F4D Skyray and the McDonnell F3H Demon, to replace the twin-engine all-weather Banshee. It was still true in 1958, when the Navy had to choose between the single-engine Vought F8U-3 and the twin-engine McDonnell F4H. The safety record of twin versus single-engine airplanes was examined and determined to not be a deciding factor. In fact, the only twin-engine airplane in the deployed carrier air groups at the time was the Douglas A3D Skywarrior, which had two engines because it was too big to be powered by only one. The F4H was selected because it had a dedicated radar operator, not because it had two engines.

The Navy did regularly deploy one twin-engine propeller-driven airplane at sea for more than two decades beginning in the mid-1950s on axial deck carriers, in part because Grumman had learned a lot about operating twin-engine airplanes from aircraft carriers with the F7F program. Its S2F (S-2) was as short-coupled as carrier airplanes get, so in order to size the rudder both for the single engine takeoff and wave-off condition and—relatively speaking—high-speed flight, it had a two-piece rudder. Up and away, the forward portion of the rudder was just used for directional trim and only the aft portion of the rudder moved with the rudder pedals. For takeoffs and landings, the forward and aft portions of the rudder could be selected to move as a unit, doubling the width of the rudder and reducing the S2F's  minimum control speed to one suitable for carrier launches and wave-offs.

The introduction of steam catapults, angled decks, and descending, constant angle of attack approaches also reduced the degree of difficulty of one-engine-inoperative takeoffs and landings.

By the time Grumman engineers designed the F-14, they felt confident enough in their handling qualities analysis to widely separate its engines to provide a "tunnel" where two of the big Phoenix missiles could be carried side-by-side.

However, minimum control speed would still prove fatal to the unwary: Hultgreen Crash

Finally, click HERE for a great tale of how a second engine and a naval aviator saved an airplane...

Blog Index

See July 2010 for an index of blog entries 1-99.

Barriers and Barricades, One More Time

I recently read an excellent history of a carrier-based airplane but noted that the author, in the captions, did not bother to differentiate between barriers and barricades. It is a minor quibble, but the nomenclature is specific and illustrates a two-step set of changes to carrier-deck equipment forced by the introduction of jet airplanes, one element of which was retained on angled-deck carriers.

Barrier

Davis Barrier

The configuration of the Davis barrier changed over time but the principal remained the same.

Barricade

The original barrier was introduced at the very beginning of carrier operations to stop an airplane when its tail hook had missed all the arresting wires. First one steel cable and then two were strung across the deck about three feet high at each barrier station. They were attached to stanchions which could be folded down to place the cables on the deck so airplanes could taxi past the barriers. An operator was stationed at each barrier to raise and lower it.

The steel cable barriers were very effective.

Unfortunately, the original barriers were not safe to use to stop airplanes with nose landing gears and to some extent, with twin-engine airplanes. The steel cables would wipe out the nose landing gear, raising the potential for the cables on the next barrier forward to slice the canopy off the airplane, and with it the pilot's head.

There was also the potential on a twin-engine propeller-driven airplane for the nose gear to pull the cable forward, allowing a propeller to hit it an angle and cut it, rather than skip off of it and past it. A tightly stretched steel cable when cut could wreak all kinds of havoc, not to mention not stopping the airplane.

The Davis barrier solved those problems by having the cables laying flat on the deck. A canvas strap was strung across the deck about three feet up using the same stanchions used for the original barrier. When the airplane's nose gear (or a "retractable barrier guard" in front of the windscreen if the nose gear had collapsed) hit the horizontal strap, vertical straps between it and the cables pulled them up off the deck to engage the main landing gear, thereby stopping the airplane. There were about six or so barriers on a carrier, so some were rigged for props and some for jets. They could also be reconfigured or replaced fairly quickly. Four barriers are shown in the following picture, two prop (lying on the deck) and two jet/AJ, i.e. Davis, one that has been activated but didn't snag the main landing gear because the jet had hooked a late wire so was going too slowly (barrier operators were cautioned not to drop their barriers too quickly) and the other in the ready position.

The Davis barrier worked acceptably after some development, although it was recognized that if the airplane were going too fast when it hit the Davis barrier, the cables might not be pulled up high enough, fast enough so they didn't get above the main landing gear tires and snag the landing gear struts before the main landing gear had passed by. There was also a problem with the steel cables being cut by airplane appendages at the higher landing speed of jets as well as pilots defeating the purpose of the barrier with a late and unsuccessful wave off as pictured above. After a few incidents in the fleet with jets not being stopped by the Davis barrier, a really big canvas net hung from scaled-up barrier stanchions was introduced as the last-chance layer of protection for the men and aircraft forward of the landing area. This was the barricade.

With the advent of the angled deck, barriers were no longer required. However, the barricade was still necessary if a jet had a landing gear or tail hook problem and couldn't land ashore. It is only rigged when required and the deck crews periodically practice erecting it on short notice and in only a few minutes.

XF2D-1/F2H-1/F2H-2 Fuel System

Today I read an article in an English modeling magazine by a well-known aviation history author who repeated the error that the F2H-2 fuselage was longer than the F2H-1's, whereas the length increase actually occurred between the XF2D-1 and the F2D-1 (F2H-1). I decided to fix that on Wikipedia as a public service. In the process of doing so, I also fact-checked statements about the fuel capacities of the three airplanes. That's when I discovered that I had only resolved part of the length error that continues to be promulgated.

At the time of the XF2D-1 mockup review, its Standard Aircraft Characteristics (SAC) chart dated 1 May 1945  lists the fuel capacity as 510 gallons internal plus a 345 gallon external tank. Unfortunately, there were no drawings on this SAC chart. However, the length was given as 38' 9.5". The external tank was probably similar to the one provided for the FD-1 (FH-1) as shown here in November 1948.

A month later, an addendum page was added providing the "effect of mock-up changes on XF2D-1 preliminary data sheets dated 1 May 1945": "Subsequent to the distribution of the XF2D-1 data sheets, mock-up board recommendations revised the fuel system to eliminate the external droppable tank and provide instead an increase in internal protected fuel capacity from 510 to 847 gallons."

The XF2D-1 SAC chart dated 1 June 1946 shows an overall length of 38' 11.5", an increase of only two inches. The total internal-fuel capacity shown is the required 848 gallons, including the two tanks in the stub wings that presumably was 90 gallons of the more than 300-gallon increase required. I would guess that the fuselage was deepened from the mock-up configuration to provide most of the rest.

Note that there are three large fuselage tanks, again similar to the FD/FH fuel system configuration.

According to the SAC charts, the F2H-1 internal fuel capacity was increased by only 29 gallons over that of the XF2D-1. What's a little confusing is that the 1 April 1948 F2H-1 SAC chart page for Armament & Tanks is identical to the one above for the XF2D, almost certainly an error in compiling the SAC chart since the correct fuel quantity of 877 gallons is listed on its Page 1. (Each tank has a small but different capacity, with the largest difference being the aft tank at 223 gallons instead of 198.) Another oddity is that this SAC chart lists 200-gallon tip tanks for the F2H-1, whereas it's clear from the Pilot's Handbook for the F2H-1 dated 1 October 1949 and the F2H-2 SAC dated 1 November 1949 that the F2H-1 did not have provisions for tip tanks. Note that the F2H-2 SAC page for Armament & Tanks once again uses the XF2D artwork although it has been updated to show the -2 tip tanks and label each fuselage fuel tank with its correct volume without changing the size or shape of the tanks from the original XF2D illustration.

Not withstanding all that, the revelation to me is that the increase in fuel system capacity does not account for all or even most of the fuselage length increase ahead of the engine inlets between the prototype XF2D and the production F2D (F2H). A net increase of 31 gallons in the three fuselage tanks (the wing stub tanks were reduced in capacity by one gallon each) requires a net increase in length of the tanks of only about five inches, not 12. The remainder may have resulted from the need for additional interior volume for equipment and/or the desire to increase the fineness ratio of the fuselage and canopy to reduce drag. A center-of-gravity correction can't be ruled out, either.

A-12, The Gift That Keeps On Giving, IV

The Supreme Court has agreed to hear part of the A-12 appeal by Boeing and General Dynamics. (See here, here, and here for the background; the case status is provided here.) Note that they are limiting their review to the Fifth Amendment issues and not reviewing the termination for default issue.

Sep 28 2010 Petition GRANTED limited to Question 2 presented by the petition. The petition for a writ of certiorari in No. 09-1298 is granted limited to Question 1 presented by the petition. The cases are consolidated and a total of one hour is allotted for oral argument.

09-1302 BOEING COMPANY V. UNITED STATES
DECISION BELOW: 567 F.3d 1340
LOWER COURT CASE NUMBER: 2007-5111, 2007-5131
QUESTION PRESENTED:
1. Whether the Due Process Clause of the Fifth Amendment permits an appellate court to adopt a new legal rule, inconsistent with its own prior ruling in the same case, and then apply it retroactively to the record established in the trial court pursuant to the prior ruling, without remanding to afford the parties the opportunity to prove their case under the new rule. 2. Whether the Due Process Clause of the Fifth Amendment permits the Government to maintain a claim while simultaneously asserting the state secrets privilege to bar presentation of a prima facie valid defense to that claim. 3. Whether the Government may terminate a government contract for default on the ground that a contractor has failed to make adequate progress toward timely completion of that contract where the Government has not set a valid deadline for completing the contract.
CONSOLIDATED WITH 09-1298 FOR ONE HOUR ORAL ARGUMENT
09-1298 LIMITED TO QUESTION 1
09-1302 LIMITED TO QUESTION 2
CERT. GRANTED 9/28/2010

The 27 Charlie

Some ship guys who know a lot about aircraft carriers don’t know all that much about carrier-based airplanes. Similarly, some carrier-based airplane enthusiasts are likely to be equally ignorant about aircraft carriers in spite of their best efforts, as in my case.

For example, I have sometimes referred to any angled-deck Essex/Ticonderoga-class* carrier as a 27 Charlie. The nickname comes from the SCB (Ship Characteristic Board) design number for a set of Essex-class carrier modifications that began to be defined in the late 1940s, when the Navy realized that a major upgrade program was needed to allow them to operate jets, which had to be launched and recovered at higher speeds, and larger attack aircraft.

While doing some fact checking for my Skyhawk book for Specialty Press, including trying to figure out why a hangar-deck illustration appeared to show two starboard deck edge elevators on an Essex-class carrier (see here), I discovered that I was in error. As it turns out, the SCB 27 modifications added more powerful catapults and arresting gear, a reinforced flight deck, larger centerline elevators with additional lift capability, a new island, and an increase in the aviation gasoline storage capacity, among other things,  but not the angled deck or starboard deck edge elevator. The first nine modified were 27As with the new H-8 hydraulic catapult and the final six were 27Cs (hence the Charley nickname) with the even newer and more powerful C-11 steam catapult, the most significant difference between the two upgrades. The nine 27As and three of the six 27Cs were completed and placed into service as axial deck carriers; the addition of the angled deck was accomplished in a subsequent overhaul period. (Only one SCB 27 carrier, Lake Champlain, did not eventually receive the angled deck.)

Not, strictly speaking, a 27 Charlie (Kearsarge)

A 27 Charlie (Ticonderoga)

(Note that the shape of the forward elevator and the aft location of the starboard elevator mark it as a 27 Charlie but an Essex-class carrier with a rectangular forward elevator and the starboard elevator located more forward might also be one of the 27 Charlies.)

In short, of the 15 (including Antietam) Essex/Ticonderoga-class carriers with angled decks, there were only six 27 Charlies: Intrepid (CVA-11), Ticonderoga (CVA-14), Lexington (CVA-16), Hancock (CVA-19), Bon Homme Richard (CVA-31), and Shangri La (CVA-38).

The last three (Intrepid, Ticonderoga, and Hancock) of the six 27Cs modification were completed with the angled flight deck, so-called hurricane bow, and a starboard deck edge elevator replacing the aft centerline elevator. These modifications were the major part of SCB 125, which was then applied all but two of the carriers updated by SCB 27A and 27C. (These three were also unique in that the starboard deck edge elevator was located farther aft than on the other three 27Cs or any of the 27As subsequently modified in accordance with SCB 125, hence the hangar deck illustration mentioned above showing two locations for that elevator.)

The 27 Charlies are also distinguished by a 70-foot long forward elevator. However, the three modified at Puget Sound (Lexington, Hancock, and Shangri La) were originally completed with the standard SCB 27 54-foot forward elevator for some reason, with the 70-foot version being retrofitted at some point.

More than half of the angled-deck Essex-class carriers were therefore 27 Alphas plus the SCB 125 changes. One, Antietam (CVA-36), was neither a 27A or C but it was modified with an angled deck for an evaluation, which resulted in SCB 125. The starboard deck edge elevator was not incorporated. Antietam was eventually relegated to a training role.

Strictly speaking, it is not even correct that all angle-deck carriers with steam catapults were 27 Charlies. The first carrier to be modified in accordance with SCB 27A, Oriskany (CVA-34), had its hydraulic catapults replaced with steam catapults in the late 1950s when the angled deck was finally added to it. This was the unique SCB 125A configuration. From a capability standpoint, it was equivalent to the other 27 Charlies.

For much, much more on the subject of the development and description of U.S. Navy aircraft carriers, I recommend Dr. Norman Friedman's excellent U.S. Aircraft Carriers: An Illustrated Design History, Naval Institute Press, 1983, ISBN 0-87021-739-9.

* The most significant difference between the so-called Essex and Ticonderoga classes, if I understand correctly, is that the Ticonderoga-class had the upper part of the bow extended slightly to accommodate a second quad 40 mm cannon emplacement just in front of and below the flight deck. This gives rise to the categorization of short hull (Essex) versus long hull (Ticonderoga) ships; they were the same length at the waterline and the flight decks were essentially the same size.