By Tommy H. Thomason

Wednesday, March 30, 2011

I hate it when that happens

However, one of the benefits of writing to a blog is that I can readily correct errors and add new information. As an example, I've been fixing errors in the Grumman sto-wing entry off and on all this afternoon. So if you read it earlier today, you might want to look at it again...

If you have a specific request

If you have a specific request rather than a compliment, correction, or addition pertinent to the topic, it's best that you send me an email rather than submit it as a comment on one of the entries. My email address is tommythomason@sbcglobal.net.

Grumman Sto-Wing Redux

Click HERE to see a summary of Grumman's innovative wing-fold concept that it called the sto-wing.

Pat Donahue wrote to ask me how the aileron control mechanism spanned the large gap created when the wing was folded alongside the fuselage. He had looked at the wing-fold area of the F6F at the National Naval Aviation Museum at Pensacola without being able to determine how it was done.

 Uhh - that's a good question. As it turns out, Grumman created three different ways to do it, although the original one, on the F4F Wildcat, appears to be the only one that was used on more than one Grumman design. (Click on the images for a bigger picture.)

In the closeup of the area encircled in green on the first picture, you'll see a rod coming out of the wing stub that pushes/pulls on a bellcrank that has two contact points on it on either side of its pivot point. If you then look at the inboard end of the outboard wing section in about the same location, you'll see another bellcrank that has an upper and lower arm connected by two small flat plates that correspond to the contact points on the bellcrank mounted on the wing stub. It's hard to see, but the left side (aft side when the wing is in the flight position) of this bellcrank is attached to a rod that disappears into the outer wing panel.

In other words, the ailerons are disconnected at the fold joint when the wings fold down and aft. When the wing is in the flight position, the two bellcranks have come together as a unit so the push/pull tube in the wing stub is pushing and pulling on the push/pull tube in the outer wing panel.

This would seem 1) difficult to rig without loss motion or overload of the bellcranks in compression and 2) to require some means of restraining the ailerons when the wings were folded. Perhaps in recognition of these drawbacks, Grumman used a different concept on each of its next two designs.

The TBF took me a while to figure out, although the mechanism is hidden in plain sight, right where Pat thought it should be, at the wing panel pivot axis.

The Grumman Archives came to my rescue with a maintenance manual. The TBF aileron control system changed from a push-pull mechanism to a cable system in vicinity of the fold joint. Two pairs of pulleys located at the pivot axis were used to transfer the motion across the fold joint This illustration depicts the pulleys on the right wing when the wings are spread:
One pair was mounted on the outer wing panel and the other on the wing fold actuator link, with the cables crossing between the two pairs so as to not introduce any slack or tension in the cables in the folding process. All that is visible are the pulleys and cables under the link that the two wing-fold hydraulic actuators are attached to. The following illustration shows the right wing pivot axis with the wings folded, looking inboard. Note that the transition between the two sets of pulleys is on the wing pivot axis.

For the F6F Hellcat, a link between two bellcranks was used to span the gap between wing stub and outer wing panel when the latter was folded back. The bellcrank in the wing stub and one in the outer wing panel were cleverly shaped and positioned so that when the wings were folded, the control stick imparted little or no motion to the ailerons. (Note that the outboard end of the gap-spanning link was positioned on the wing pivot axis.) Left wing folded:
Wing Spread:

The two concepts that did not break the connection between control stick and the ailerons when the wings were folded would appear to be more desirable, particularly the approach used on the F6F, but Grumman and/or the Navy thought otherwise for some reason. Grumman reverted to the original concept used on the F4F for its subsequent designs incorporating the sto-wing: the AF Guardian, WF (E-1) Tracer, and E-2 Hawkeye.

Monday, March 21, 2011

Steam Catapult Development

As part of the British development and qualification of the steam catapult, a platform containing the hardware was added on top of the flight deck of HMS Perseus.


After catapulting deadloads at dockside in mid-1951 in initial development tests, the carrier proceeded to at-sea trials in the outer Firth of Forth, beginning with deadloads and then the catapulting of six surplus, unpiloted Seafire 47s which had the wings removed at the fold joint and just enough fuel for start, warm-up, and the launch. One reportedly took umbrage at being sacrificed in even a worthy cause and managed to climb and turn back toward the ship before crashing into the sea short of the carrier. A video survives of the testing (the Seafires were not, as stated, radio controlled):

http://www.britishpathe.com/record.php?id=29482

Perseus was subsequently sent to the U.S. for demonstrations of the steam catapult in February 1952, first dockside at the Philadelphia Navy yard and then at sea. The steam catapult allowed the successful launch of a Douglas F3D Skyknight with a 10-knot tailwind. The existing Navy hydraulic catapult required a 30-knot headwind for the same airplane weight. The Navy immediately began planning to require steam catapults in its new aircraft carriers and retrofit existing carriers that had enough service life remaining to justify the conversion. As a result, bigger airplanes with higher performance could now be carrier-based.

Westinghouse: From Hero to Zero

Who would have thought that a company that didn’t even know what a jet engine was (Westinghouse) and one that had never developed a carrier-based airplane (McDonnell) could have succeeded in producing a fully operational carrier-based jet fighter on the first try during World War II? But the more experience engine and airplane manufacturers were too involved in production contracts and more conventional development programs, so the Navy gave them the assignment.

The Army got the plans for the Whittle engine, which was actually running in England, and gave them to General Electric. The Army then contracted with Bell Aircraft, an experienced airplane manufacturer, to design a land-based jet fighter using two of those engines. The resulting P-59 was, by all accounts, a dog.


Westinghouse created its engine from scratch with no outside assistance due to the secrecy imposed. It had an axial-flow compressor, which was the future, instead of the centrifugal compressor used in the Whittle engine, a dead end from the standpoint of increasing thrust significantly. The original Yankee engine, only 19 inches in diameter, worked well enough to demonstrate that the configuration was sound. One was flown under an FG-1 Corsair at NATC Patuxent River beginning in January 1944.


After development and qualification, two flight-rated versions of the Yankee powered the Navy's first jet fighter, the McDonnell XFD-1 Phantom. It became the J30.
The Phantom incorporated all the features necessary for carrier-basing: strong landing gear, folding wings, catapult/holdback hooks, and the tail hook. It was armed with four .50 caliber machine guns. One squadron operated it briefly, including carrier qualification, but the FD lacked range, cockpit pressurization (necessary for comfortable operation at the altitudes jet airplanes operated most efficiently), and an ejection seat. This required a bigger, heavier airplane requiring a more powerful engine.

So Westinghouse scaled up the 19-inch diameter engine to 24 inches for more thrust.  It was subsequently designated the J34. It powered the McDonnell F2D Banshee and the Douglas F3D Skyknight (which necessitated the change of the McDonnell designation from D to H; the original Phantom became the FH and the Banshee, F2H). And also the Vought F7U-1 Cutlass, with the addition of a government-furnished afterburner that was subsequently provided by Westinghouse.

The Navy needed still bigger, more capable jet fighters so it held a competition for an even more powerful engine. Picking Westinghouse to scale its engine up again as the J40 must have seemed like a no-brainer. Originally, the J40-WE-6 was to power the A3D Skywarrior and the J40-WE-8, which was essentially the -6 with a Westinghouse-developed afterburner added, was to provide the thrust for the Douglas F4D Skyray, the McDonnell F3H Demon, and the Grumman F10F Jaguar. See Paul Christiansen's comment below for the subsequent changes in dash number.
For much, much more on the J40 program, see Paul Christiansen's excellent monograph:
It's available on Amazon.

 Fair warning: it's detailed, technical, and comprehensive even by my standards, a blow-by-blow description of the engine and its development. There is relatively limited discussion of the airplanes it powered and the difficulties it caused in their development. For that however, you can read my much less detailed and technical books, Naval Air Superiority and Strike from the Sea.

Unfortunately, Westinghouse, which had been so successful up until then, failed miserably with the new engine as well as the electronic fuel control for the engine and afterburners. Development problems delayed the availability of the Navy's new fighters and long-range jet bomber, first by putting Westinghouse well being behind schedule on deliveries of engines for flight test and then by it not being able to qualify the engine for production at the necessary thrust, requiring Douglas and McDonnell to substitute other engines for the J40.

Westinghouse was not fully responsible for the Cutlass program problems. Vought was in part at fault for the cancellation of F7U-1 production because it wound up significantly overweight; however, availability of a satisfactory afterburner for the proven J34 contributed to program delays and a lack of enthusiasm for the airplane. Vought and the Navy attempted to address the weight problem with the J46 that was based on the J34 and developed concurrently with the J40. It was almost as disappointing but the F7U-3 was produced and deployed, albeit with a J46 of lower thrust and higher fuel consumption than planned, insuring that the F7U-3 Cutlass would forever be known as "gutless" and be replaced by other fighters as soon as possible.

Although production and support of the J34 continued, Westinghouse eventually exited the aircraft engine business.

Where did Westinghouse go wrong? One theory is the early successes did not result in a problem-solving culture within the engine division. Another is that the company did not continue to invest in technology and innovation like P&W and General Electric did. For example, to improve compression ratio for better thrust to weight and lower specific fuel consumption without incurring compressor stalls, P&W developed the two-spool engine and General Electric, the variable inlet guide vane concept. Westinghouse just kept scaling up the basic design, which eventually proved inadequate to the task.