U.S. Navy Aircraft History

By Tommy H. Thomason

Sunday, March 29, 2015

New A3D/A-3 Skywarrior Monograph

If you have any interest in Whales, naval aviation, or the Vietnam War, you should buy this book. While the title seems to limit it to the Vietnam War, Rick also summarizes the airplane's origin story and post-Vietnam career. For more of what it includes and some five-star reviews by people who know what they're talking about, look it up on Amazon.

Wednesday, March 25, 2015

Happy Birthday, Vought F8U Crusader

On 25 March 1955, the Vought F8U-1 flew for the first time. I almost missed joining the celebration. For an excellent and well-illustrated example, see here: http://voughtworks.blogspot.com/2015/03/xf8u-1-crusader-at-60-part-v.html

The milestone was even more significant because it included breaking the sound barrier. First flights are usually planned to minimize risk, with the primary objective being photos, not envelope expansion. And in this case, supersonic flight was not only not a sure thing but the ability to do so, somewhat of a concern.

Richard Whitcomb of NACA experimented in early 1952 with reducing transonic drag by what he described as the area rule. The concept was that an airplane's total cross-section (area), including the wings and empennage, needed to smoothly increase and then decrease along its length. Because even a swept wing resulted in a fairly abrupt increase in cross section, that meant that the fuselage cross section had to decrease to compensate. He published a confidential paper on his theory and wind tunnel test results in September 1952.

Grumman engineers had already postulated the same theory and applied it to a fighter design study in late 1951. Note the distinctive fuselage "Coke-bottle" shape.*

The unsolicited proposal included the following illustration, clearly a representation of the area rule:

Convair was in the process of designing a new delta-wing fighter, the F-102, for the Air Force in 1952. Their wind tunnel testing indicated a significant drag problem at transonic speed that proved to be correct in flight test in 1954. As a result, they had to delay flight test and production in order to reshape the fuselage in accordance with area ruling to reduce drag.
 The delta wing created a large peak in the overall cross section near the wing's trailing edge that had to be offset by indenting the fuselage and adding bulges aft of the wing to more smoothly taper down the cross section.

Vought won the 1952 competition for a Navy day fighter with an innovative design that included a variable-incidence wing. It did not take into account area ruling, which at that point was still a theory backed up by wind tunnel test of notional models.

The Navy awarded Vought a contract for the F8U in mid-1953 and encouraged the company to consider incorporating the area rule. After careful consideration and evaluation of its wind-tunnel test predictions, Vought was not inclined to do so. The necessary shaping of the fuselage cross-section was onerous from a weight and manufacturing cost standpoint; it also affected the internal volume needed for fuel. NACA tentatively agreed that the high fineness ratio of the F8U and its relatively thin wings probably sufficed from an area-rule standpoint.

In late 1953 and early 1954, however, the results of NACA wind-tunnel and rocket-propelled F8U model testing at transonic and supersonic speeds indicated that drag was likely to be higher than Vought had projected.
 From Joe Chambers' excellent monograph: http://www.nasa.gov/pdf/483000main_ModelingFlight.pdf

Vought began to take the problem seriously and define changes to take area rule into account, but like Convair, successfully lobbied to not make major changes in the prototype in order to fly on schedule. According to a NACA memo, these would be evaluated in wind-tunnel test with the intent  of incorporating them in production at ship #75.

Before first flight Vought was able to sharpen the forward fuselage by extending the nose cone about three inches (it had become shorter and more bulbous than shown on the mockup), reducing the size of the canopy, and incorporating a sharper inlet lip.
(It's not clear when the cannon were relocated aft; that may have occurred before the area rule improvements, possibly for weight and balance.)

The aft fuselage was reshaped and extended as well to smooth the decrease in cross section.
As it turned out, the NACA test results were pessimistic and these initial changes proved to be all that were necessary, along with the fact that the combination of long slender forward fuselage of the F8U, lack of bubble canopy, and the close coupling of the empennage to the wing resulted in a shape not far from the ideal one. The additional changes were cancelled.

Vought management and engineering must have been greatly relieved, particularly after Convair's struggle with the F-102's excessive drag. Ironically, the competition, Grumman's beautifully area-ruled F11F Tiger that resulted from its 1951 design study, lacked both performance (it had a less powerful engine) and also enough internal fuel, unlike the F8U. (Also see http://thanlont.blogspot.com/2009/02/area-rule.html)

Vought learned its lesson about area rule, however. When incorporating the camera installation in the photo-reconnaissance variant, F8U-1P, it was taken into account. See http://tailspintopics.blogspot.com/2013/12/photo-gator.html

* A "Coke bottle" shape is aptly descriptive to those of us of a certain age:

Sunday, February 22, 2015

Swept-Wing Tip Skid

Bob Sikkel called my attention to a detail on the McDonnell F3H-2 Demon that I hadn't noticed before, a post-mounted blivet out on the underside of the wingtip. I found excellent pictures of it in Don Hinton's walk-around photos of the F3H-2 at the National Museum of Naval Aviation in Pensacola.

Note that the "saucer" of the skid itself is clearly intended to be readily replaceable.

It's a definite oddity, since I don't remember anything like it on other Navy swept-wing jets. I was familiar with the XF3H-1 originally having a much longer version of it.

However, that skid disappeared from the XF3Hs when the wing was changed to move the ailerons inboard.

Nevertheless, a very short tip skid turns out to have been incorporated on the ill-fated production F3H-1.

And it is present on the F3H-2 wingtip in almost every picture of it with sufficient resolution to discern it. It is identified in a F3H maintenance-manual illustration as the "wing tip skid". (Thanks to a Royal, a volunteer at the Emil Buehler Library at the National Naval Aviation Museum, for finding that for me.)

So what was that all about? The only other evidence of a similar device is on a circa 1946 Douglas predesign three-view of its D571-1, the predecessor to the F4D Skyray.
I haven't seen any evidence of one on either the F4D mockup or XF4D prototypes.

The Navy was nervous about the approach-speed handling qualities of a swept-wing carrier-based airplane so they contracted with Bell for a swept-wing conversion of its P-63, designated the L-39, in 1946. (Also see http://thanlont.blogspot.com/2011/04/bell-l-39-wing-sweep-evaluation.html)
There's no evidence of tip skids on it or any mention in the flight test evaluation of the need for them.

If there was a concern at the Bureau of Aeronautics about swept-wing tip contact with the deck/runway, it didn't reach Vought or was ignored in 1945 when it was proposing what became the F7U Cutlass. There is no evidence of a tip skid in any of the proposal documents or the mockup or the XF7Us themselves.

Similarly, the earliest swept-wing studies at Grumman in 1947 don't feature tip skids and they weren't on the XF10F mockup, which was constructed about the same time as the McDonnell proposals for the F3H in 1948.

My guess is that the tip skid was required on the F3H because of the minimal ground clearance of the tip when the tail skid made contact, even when the wings were level.
(Yes, that is a Mk 7 on the fuselage pylon.)

There was no assurance that the wings would be level in a tip back situation, particularly in the event of a barricade arrestment.

Hence the need for a tip skid on the F3H.

Thursday, February 5, 2015

Goodyear F2G Corsair: Kamikaze Killer?

The F2G was a Corsair developed by Goodyear and powered by the Pratt & Whitney R-4360, a four-row, 28-cylinder radial engine instead of the R-2800, two-row, 18-cylinder engine of the stock Corsair, roughly a 50% increase in horsepower.

It is usually written that the F2G was created to counter the Kamikaze tactic that the Japanese introduced in the Pacific, first recognized in October 1944. If so, someone was prescient, since the decision to install an R-4360 in the Corsair had been made well before that. Pratt & Whitney used two F4U-1s for R-4360 for engine testing. The first one was for ground runs only, which began in May 1943. The second first flew on 12 September 1943.This picture was taken to illustrate the difference between the R-4360 configuration (referred to as F4U-1 WM for Wasp Major) and the R-2800 one:

Goodyear got a contract in March 1944 for 418 F2G-1s and 10 F2G-2s. The -2s were to be fully carrier-basing compatible. Don Armstrong flew the first FG modified with the R-4360 on 26 August 1944. So strictly speaking, the F2G's raison d'etre was not to counter the Kamikaze tactic, at least not originally. (My tongue-in-cheek explanation is that someone in BuAer wondered how fast a Corsair would go when powered by the humongous R-4360.) The F2G apparently was really intended to be supplied to shore-based Marine squadrons, as almost all of the order was for the -1 that didn't have a tail hook or powered folding wings.

In any event, only 10 F2Gs—five land-based -1s like BuNo 88454 in the first picture and five carrier-capable -2s—were built along with several Corsairs modified for flight test of the configuration. The Navy had elected to equip itself with the Grumman F8F Bearcat instead.

One XF2G was flown with a lower aspect-ratio vertical fin that replaced the side area lost by the change to the upper aft fuselage to accommodate the bubble canopy. (The rudder was not changed.)

Goodyear decided instead to add a 12-inch plug to the bottom of the fin, which also provided for the addition of an auxiliary rudder for additional yaw-control power during a waveoff or go-around at low speed.
The auxiliary rudder deflected 12.5 degrees right when the flaps were more than 30 degrees down. (Full flaps was 50 degrees; recommended takeoff flaps was 20 degrees.) The main rudder deflected 7 more degrees to the right than to the left.

Note that the picture on the left is an early F2G-1, which were delivered without a tail hook; the picture on the right is an F2G-2.

Sunday, January 11, 2015

The Breaks of Naval Air

This is an eBook. If you don't have one of the eBook-devices (Kindle, Nook, etc.), the latest Apple operating system, Yosemite, allows you to download eBooks to a Mac via iBooks. If you aren't acquainted with Youthly Puresome, it's worth the modest price to become so. If you are, now you can have his entire oeuvre at your fingertips, including some material that hasn't been published. Note that this blurb is from iBooks; it is also available on Amazon (Google "Woodul Amazon").

Note that the correct title is The Breaks of Naval Air; you can see the actual cover and enjoy more from Youthly Puresome on Woodul's blog here: http://youthlypuresome.com/

I'd write a review but I can't do better than Barrett Tillman's on Amazon:

Thursday, January 8, 2015

Shoulder Harness

Although it seems hard to believe, carrier pilots were only restrained by a seat belt up until about mid 1942. One mark (literally) that might distinguish a carrier pilot before then was the impression of a dent in his forehead from striking the gunsight or instrument panel coming in a barrier crash or ditching. Probably as a result of increased incidents of that kind that wartime operations produced, at least one air group added upper-body restraints to the cockpits of their airplanes. BuAer subsequently made that official, as described in the 15 June 1943 issue of Naval Aviation News. Note for example that it lists a retrofit to the SBD-3/4s but not SBD-5s, which suggests that the latter (the first of which was delivered in April 1943) came off the production line with shoulder harness.

The gun sight statement suggests one reason why something so obviously beneficial in a crash wasn't implemented before then.  The prewar sight in both fighters and dive bombers required the pilot to lean forward.

And also to use his plotting board.

Tuesday, December 9, 2014

Aircraft Pictorial 7: F4U-1 Corsair Vol. 1

Dana Bell's long awaited monograph on the F4U-1 Corsair is finally available. There are many books and articles available on the F4U. I can say, because I have a goodly number of them in my collection, that none are quite as deeply researched or as sharply focused as this one is. It is a relatively slim volume, only 72 pages between the soft covers, but every page has a photo or illustration of interest, many of the former in color. I am very pleased to write that it contains information and facts about the Corsair of which I was previously unaware and should be taken as gospel, based on the depths that Dana has plumbed at the National Air and Space Museum and the National Archives. Most notable are these two: there was officially no F4U-1A and the cause for the Navy not deploying Corsairs on carriers initially was not due to unsatisfactory deck landing characteristics. (One proof Dana cites for the latter is an evaluation aboard Woverine that concluded it was very easy to land aboard; I may have missed Dana's mention of it but that carrier was one of the two converted side-wheeler excursion ships plying Lake Michigan as training carriers: it was not only short, it was slow.)

Some things this excellent volume is not: a compendium of war stories, list of squadron assignments, tables of performance attributes, or overall operational history. All that is available elsewhere. What it is: a detailed and well-illustrated document that describes the configuration, configuration changes, and color schemes (internal and external) of the so-called "Birdcage" Corsair during its initial flight test and operational usage, both U.S. and U. K. (Volume 2 will, Dana promises, cover the raised cockpit F4U-1, aka F4U-1A.) As such this work will not appeal to everyone, as fascinating as it is to me. If you are a Corsair fan, however, almost every page contains something of interest that you probably didn't know and likely is mentioned in no other Corsair reference.

For example, a picture of the early 20-gallon (your car's gas tank probably has less capacity) oil tank mentions that a larger tank was substituted to account for oil consumption on longer missions when greater endurance was provided by the addition of external tanks; however, a decal was placed on the larger tank to advise the ground crew not to fill it with more than 20 gallons of oil when external tanks weren't fitted in order to minimize weight. A revelation was the reason for the almost standard application of tape externally to the panel lines around the fuselage fuel tank. It turns out that it was to keep spilled gasoline out of the interior of the fuselage aft of the firewall when the tank was being filled because the result was sometimes a fire.

If Dana hadn't thoughtfully sent me a copy, I would have been first in line to purchase one based on his previous work and personal knowledge of his research diligence and insistence on the use of primary-source documents.