Approach Lights Redux

It's surprising how often something new shows up for something old. I wrote about approach lights here: http://thanlont.blogspot.com/2012/04/night-carrier-landings-in-beginning.html

It was just brought to my attention that the F-4 had a green light on the left side of the fuselage that the LSO could use at night to determine roll attitude when he could not see the position light on the right wingtip, e.g. if the Phantom was turning left for lineup. It can be seen in this picture just below the crossbar in the A in NAVY. It looks like it is at the same waterline as the left-wingtip position light. I'm surprised that it is flush rather than protruding like a similar one is on the E-2.

The picture is cropped from a walkaround by Howard Mason of an F-4J on the Prime Portal website here: http://www.primeportal.net/hangar/howard_mason/f-4j_155563/

And Now for Something Completely Different

While doing research for my book on the development of U.S. Navy carrier-based jet fighters, I came across a cryptic reference to a proposed rocket-propelled interceptor.

I dismissed it out of hand although the Germans had not. In World War II, they developed the cannon-armed Me 163 interceptor that was rocket powered and had very high performance. One of the first aviation books that I remember reading as a preteen was Rocket Fighter by Mano Ziegler, a WW II Luftwaffe pilot who flew it.  Although legend has it that the Komet was more dangerous for its pilot than the B-17 crews that he was attacking, it was reportedly easy to fly and phenomenally fast for the time. The main problem was its fuel, C-Stoff (57% methanol/ 30% hydrazine/ 13% water), and oxidizer, T-Stoff (80% concentrated hydrogen peroxide / 20% oxoyquinoline. The combination was hypergolic, meaning it ignited just from being mixed, without the need for an ignition source. The Germans developed a process for safely fueling the Komet but a crash on takeoff or landing (particularly from the rough-and-ready fields available) was likely to result in an explosion or fire.

It turns out that the rocket-propelled interceptor proposal was a paper dated 8 June 1950 that was written by a U.S Navy officer, Commander Robert C. Truax, who was also literally a rocket scientist. It was a summary description and analysis promoting the development of a destroyer-based, rocket-powered interceptor.  In this case, furfuryl alcohol was the fuel and  nitric acid was the oxidizer. A small engine was provided for services and cruise;  a much larger one provided the thrust and control for vertical takeoff and acceleration.

In Truax's mission scenario, the interceptor would be launched vertically from the fantail of a picket ship, in this case a Gearing-class destroyer that would carry five of the aircraft.

After a flight profile measured in minutes, it would descend by parachute to the sea, from which it would be recovered to be prepared for its next mission.

 The range depended on the profile flown, ranging from zero ballistic (70 nm) to full ballistic (150 nm). Top speed was about Mach 4.

(Note that the full ballistic profile meant a recovery about 80 nautical miles from the launch point for a straight-out mission.)

An AN/APS-25 radar was to be used to locate and navigate toward the incoming bombers. 1,500 lbs of the 13,000 lbs gross weight was allocated to the weapons, which were yet to be defined. Aerial mines detonated by proximity fuses were one possibility.

In his paper, Truax noted that significant experience had been gained since the war with liquid-fuel rockets, including over 200 flights of the Bell X-1 with a rocket as its sole power plant. The Douglas D-558-2 was about to fly with a rocket engine. The smaller rocket engine in his design was one in development under contract to the Navy.

Although far-fetched, Truax's proposition received formal consideration at the Navy’s Bureau of Aeronautics and garnered at least one letter of support. However, even if the Korean War hadn’t become a distraction shortly thereafter, it seems very unlikely that the Navy would have taken any action on his rocket-powered interceptor after BuAer's review.

Truax retired from the Navy in 1959 as a Captain and went on to a career at Aerojet, after which he founded his own company, Truax Engineering. Among other things, he designed the Skycycle X-2 for Evel Knievel’s Grand Canyon jump. For more on Truax, see http://en.wikipedia.org/wiki/Robert_Truax .

F7U-1 Cutlass

My long overdue monograph on the F7U-1 Cutlass for Steve Ginter's Naval Fighters series is finally done and at the printer.

It is available from Amazon: http://www.amazon.com/dp/0984611479 , Sprue Brothers, Specialty Press, and Steve Ginter himself (http://www.ginterbooks.com/NAVAL/NAVAL.htm).

I guarantee that it has pictures and illustrations that you haven't seen before.

The F7U-1 was ahead of its time in many ways.

(Swept national insignia wasn't authorized until March 1955.)

Rogue markings were indicative of much more audacious decisions that resulted in F7U-1 development falling well behind schedule and the production program being terminated. I hope you agree that I've done its story justice.

Waving Them Aboard - The LSO

I did a very brief summary of Landing Signal Officer (LSO) history and responsibility here: http://thanlont.blogspot.com/2009/05/waving-them-aboard.html  This is an expanded discussion that is limited to landings on axial-deck carriers.

The LSO was a very early innovation in the development of aircraft carrier operations. He stood on a platform on the aft port side of the ship and visually coached the pilot of the approaching airplane into position for a successful landing or directed him to go around for another try.

According to legend, the first LSO was CDR Ken Whiting, the executive officer of Langley, the U.S. Navy's first aircraft carrier. He reportedly watched many of the first landings from what would become the LSO position and eventually grabbed two white sailor's hats to make his corrections more visible. Standardized signals and the creation of the LSO's paddles followed in short order.

To land on an axial deck carrier, the U.S. Navy pilots approached as for a short field landing, "dragging" the airplane in a speed just above stall and a constant altitude only about 20 to 30 feet (wheel height) above the deck. Upon receiving the "cut" signal from the LSO, the pilot closed the throttle, which resulted in an immediate descent onto the deck in the midst of the landing wires.

The pilot first had to get to the start of the "groove", which was where the LSO's coaching began. At the risk of oversimplifying, the groove began a few hundred yards (less for propeller-driven airplanes) behind the ship, where the pilot had completed his turn from his base leg and was lined up and on speed at approach altitude in level flight. At this point, the LSO's signals were visible and he began coaching the pilot as to height, airspeed, and line up in that order of priority. Those signals were advisory in nature relative to the two mandatory ones, which were the cut and the waveoff. Given the speed of the aircraft, there was only a few seconds for coaching and correcting before the LSO had to give the pilot either the cut or the waveoff signal. These were the basic signals:

There were several more, as illustrated in this article from Naval Aviation News in 1945:

Note that these were the "Day" signals. I haven't yet found a description of the corresponding "Night" signals.

The "slant" or "tighten turn" were used to coach the pilot as to line up, since—particularly with the F4U Corsair—the groove might well begin while the pilot was still turning to line up with the carrier. If the LSO thought that the pilot was in the process of making a good approach, he might therefore be given a Roger signal even while in the turn.

A wave off wasn't necessarily indicative of a poor approach. In order to bring all the airplanes in as quickly as possible, the interval between them left little margin for a problem getting one out of the landing area. A wave off might therefore result from a foul deck.

The LSO might also realize that the deck movement, which he could feel before the pilot could see it, was out of sync with the airplane's ability to settle into the landing area without being long (deck descending) or  touching down too hard (deck rising).

There were also variations in the LSO signals, possibly unofficial and specific to an Air Group. For example, these are the ones that Frank Bon used to wave AD Skyraiders in 1955:

Note the addition of the angling approach signal, which meant that the pilot was coming in at an angle to the axial deck rather than turning to line up with it. That may be the signal that this LSO is giving the pilot of the F9F Cougar during field landing practice or he may have stopped waving and commenced to relocate himself farther stage right. (The caption given with one instance of this picture's publication that he's giving a cut signal, which is clearly not the case.)

This is a good illustration of the cut signal:

Note that jets had to be cut farther out than the propeller-driven airplanes because they did not lose speed and settle as quickly:

The student LSO, who was invariably a Naval aviator, had to become well acquainted with what a good approach looked like, both in altitude and speed, from the LSO's viewpoint. With jets, angle of attack was the better indicator of the proper approach speed since the speed varied with weight (which could be significantly different due to the jet's much higher fuel burn) and the angle of attack did not. Early on, jets were marked with stripes, first on the nose and then on the vertical fin, to provide an angle of attack reference based on which stripe a certain part of the airplane, like the horizontal tail, was aligned with.

Getting the picture mean watching many landings waved by an experienced LSO. (The Brits also had the trainee LSO practice with experienced pilots who were unlikely to be misled by LSO judgment errors.) At first, the neophyte LSO would only be qualified to work with one type of aircraft. Over time, he might gain enough experience to bring other types aboard.

The paddles used were traditionally hand-made by the LSO himself. As a result, there was significant variation, for example round vs. square or oval.

The LSO initially wore the usual working uniform.

Whatever that might be.

When the higher speed of jets required that the LSO be visible from a greater distance, standard flight suits were modified to provided a more obvious indication of the relationship of the LSO's body and his arms.

 The requirement for all-weather and night landings increased the need for better visibility of the LSO. This was initially provided by a suit with stripes and paddles that fluoresced with black light but that was soon replaced with a lighted suit and paddles as shown here.

A readily available example of the activity on the LSO platform is provided by the excellent movie, Bridges at Toko-Ri.

F8F Safety Tips—It Seemed Like a Good Idea at the Time

Much of this post was taken from Naval Fighter Number Eighty: Grumman F8F Bearcat, an excellent monograph on the Navy's last and arguably best propeller-driven fighter from the standpoint of air superiority.*

It is available directly from Steve Ginter (http://www.ginterbooks.com/NAVAL/NF80.htm), Sprue Brothers (http://store.spruebrothers.com/), or Amazon books.

In 1943, Grumman engineering was struggling to meet the weight goal for their new high-performance air-superiority fighter that was intended to replace the F6F Hellcat. In the process, they came up with a gimmick that would have been expected from their across-the-Sound rivals, Vought, but not from what was fondly referred to as the Grumman Iron Works.

The primary structural design requirement is specified as a limit load in gs at a design gross weight.  For fighters, the design gross weight was approximately the same as the combat weight, which was the operating weight (empty weight plus trapped fuel/oil, fixed armament, pilot, removable equipment, and other odds and ends) plus bullets and 60% of internal fuel. Application of the limit load was not to result in a permanent deformation of the structure. There was also an ultimate load requirement, which was expressed as a percentage of limit load, below which the structure might be permanently bent but would not break. If it was subjected to something greater than ultimate load the designer was no longer responsible for what happened.

At the time, according to Corky Meyer,  a longtime Grumman test pilot and one of the coauthors of the monograph, the limit load requirement was 7.5 gs and the ultimate load almost twice that, 13 gs. To minimize weight, the Grumman innovation was to have the outboard three feet of the wing, including that portion of the aileron, break off at 9 gs, which would allow the remaining, less-leveraged wing structure to sustain an ultimate load of 13 gs. The weight savings was 230 lbs, a significant reduction for an airplane with an empty weight of only 7,600 lbs.

The weak link, so to speak, was just outboard of middle hinge of the aileron so adequate roll control would still be available in the event that both tips broke off, which was the expectation. The concept was successfully tested in flight using an F4F Wildcat modified with breakaway wingtips. F8F flight tests were subsequently accomplished by Corky himself to include landings with only one wingtip broken off to demonstrate controllablity in the asymmetric condition. Demonstrated and proven, the safety tip was standard on production Bearcats.

It also worked in service, with pilots even landing on carriers after they had parted company with their wingtips by overloading their airplanes. "I made a wide gentle pass—had 100 knots at the 90-degree point. The pass felt very little different, just a little fast. The landing was normal with quite a bit more shock on catching the wire."

There were, however, fatal crashes associated with the breakaway of only one wingtip. One was a Blue Angel who failed to pull out of the downward finish to a Cuban 8 at an airshow in September 1946. Another was during pullout from a dive-bombing run. The resulting sudden roll reduced the effectiveness of a pullout to less than that needed to avoid hitting the ground.** That only one wingtip came off instead of both was ascribed to variation in manufacturing tolerance (size of rivet holes, clamp-up load, skin thickness, etc) in the structure and a difference in the weakening over time of the weak-link structure in each wing caused by carrier landings and buffet during high-g maneuvers.

The response was to add a ballistic backup to the weak link to insure that both tips came off at the same time. Primacord (a thin plastic tube filled with explosive) and a microswitch were added to the break point and the installations on each wing were connected electrically. If the microswitch opened on one wing, indicating that the wingtip had separated, a circuit would close to detonate the Primacord on the other wing, insuring that its wingtip separated as well.  Corky demonstrated the removal of one wingtip ballistically in flight.

If there was understandable nervousness about bombs embedded in aircraft structure, it wasn't enough to insure that adequate safety measures were established or observed although the installation was identified with a red line on at least some Bearcats.

 Capt Paul Anderson collection via Jan van Waarde

It was therefore probably inevitable that a short circuit during maintenance on an F8F caused the wing tip to separate, killing a sailor. According to the Flight Manual "it has not been possible to make and maintain a continuously reliable installation of the explosive wing-tip-shedding device in service airplanes." The result was an airframe change in early 1949 to delete the Primacord installation and eliminate the weak link with a structural beef-up of the wing.

* A somewhat different story of the genesis of the Bearcat than the one provided by Corky in his monograph can be read here: http://thanlont.blogspot.com/2011/02/conception-of-f8f-bearcat.html

** Contrary to what you might think, the loss of lift from the wing tip was usually accompanied by a net increase in lift from the rest of the wing rather than a decrease. The nose-down pitching moment of the wing was reduced by the loss of the wing area but the nose-up pitching moment of the horizontal tail remained the same, resulting in an increase in the angle of attack of the wing at the amount of aft stick when the tips came off. If the increase didn't exceed the angle of attack for stall, lift would therefore increase.

Westinghouse Redux

All this time, I had misidentified the jet engine under the F4U at Patuxent River in 1944 as the Westinghouse 9.5-inch engine instead of its original 19-inch Yankee engine. I'm not sure why I didn't compare it more closely to the airplane's tires to establish its diameter. However, it's clear to me now that it was the bigger Yankee engine so I've revised the post accordingly: http://thanlont.blogspot.com/2011/03/from-hero-to-zero.html

Baby Steps for the Tip of the Spear

One of the U.S. Navy's first airplanes was a swept-wing biplane with no horizontal tail. Burgess was a U.S. shipbuilding company that got into the airplane business in 1910. Beginning with Curtiss and Wright designs, it built airplanes under license for several years. It also bought a manufacturing license for the Dunne D.8 that was developed by John Dunne in England. The Navy bought at least a few as the Burgess-Dunne AH-7 in 1914.

NA 80-G-452496

The sweep of the wing was obviously not for speed but to move the pitch control surface far enough aft of the center of gravity to provide sufficient pitching moment for control of angle of attack.

At least one was fitted with bomb racks, one under each wing as evidenced in this picture taken at Pensacola in September 1916.

 NA 80-G-463263

The bomb looks almost home made...