Tag Archives: naval aviation

A Quick History of US Navy Flight Deck Tractors

Aircraft carriers have limited deck space in which to position and move aircraft on the flight deck. This is where a rather unsung workhorse of US Naval Aviation come into its own. To move these aircraft around, the Navy uses flight deck tractors.

Flight deck tractors first started to make an appearance on flight decks during the intense Pacific campaigns of World War 2. It was discovered that man-handling aircraft to position them for flight operations took too much time. The first integration of the flight deck tractor was actually just a plain old US Army Willy Jeep:

Here's a Willy's Jeep towing a Grumman Avenger during World War 2.

Here’s a Willy’s Jeep towing a Grumman Avenger during World War 2.

The tow tractors also became necessary because of the increased weight of aircraft like the SBDs, Grumman Avenger and Hellcat. Willy’s Jeeps served as aircraft tractors on fleet carriers (Yorktown and Essex classes) as well as on smaller ships (Independence, Bogue, Sangamon, Casablanca classes) till the end of the war.

At the same time the US Navy adopted the Clarktor 6 Tractor which was already in use with the USAAF. The Clarktor 6 was based on a pre-war commercial tractor design. These tractors were in use on Lexington, Essex and Midway class carriers till the mid-1950s:

Here's a Clarktor 6 towing a newly built F2H-1 Banshee at the McDonnell factory in St. Louis, MO.

Here’s a Clarktor 6 towing a newly built F2H-1 Banshee at the McDonnell factory in St. Louis, MO.

The BNO-40 flight deck tractor was also based on a pre-war commercial design that entered US Navy service in 1943. These tractors served on most USN carriers, including veterans like USS Enterprise (CV-6), Essex and Midway class attack carriers, Independence class light carriers and even the smaller Bogue, Sangamon, Casablanca and Commencement Bay class escort ships. By the mid-1950S these tractors also service with the French Navy aboard the R96 La Fayette (ex USS Langley) and R97 Bois Belleau (ex USS Belleau Wood):

BNO-40 flight deck tractors aboard the USS Ticonderoga CV-14 during Okinawa operations.

BNO-40 flight deck tractors aboard the USS Ticonderoga CV-14 during Okinawa operations.

The introduction of jet aircraft to US Navy flight decks in the 1950s posed a whole new set of problems with flight deck tractors. The US Navy introduced the MD-1 flight deck tractor which was the first equipped with a gas turbine unit to assist in starting the modern jet powered aircraft. For this reason they become known by the name “huffer.” Huffers served on the served on Essex / Oriskany, Midway and Forrestal / Kitty Hawk class carriers of the U.S. Navy until mid 1960s. They were also used by the Royal Canadian Navy aboard the HMCS Bonaventure:

Here's an MD-1 with an A-4 Skyhawk.

Here’s an MD-1 with an A-4 Skyhawk.

Introduced in the early 1960s, the MD-3 tow tractor was the first purpose-built flight deck tractor. Introduced in the 1960’s the MD-3 featured a low profile to fit under the nose of modern naval aircraft. To cope with the larger size of aircraft at the time, the MD-3 was also larger and heavier than its predecessors. The MD-3 also featured a gas-turbine starter but also space of a fire extinguisher. The MD-3 served on all US Navy carriers (all classes included the CVN-68 class) and amphibious assault ships of the era:

Here an MD-3A tows an S-3A Viking from VS-28 aboard the USS Forrestal (CV-59).

Here an MD-3A tows an S-3A Viking from VS-28 aboard the USS Forrestal (CV-59).

The current flight deck tractor found on all aircraft carriers and amphibs is the A/S-32A-31A. Introduced in the 1990’s, the -31a looks like the MD-3 but is longer as it has a new starter unit and contains a place to stow equipment. The -31A is powered by a 3 stroke diesel engine, an automatic transmission. Although rear wheel driven the -31A has power assisted steering up front:

Here's an A/S32A-31A tow tracor on the aircraft carrier flight deck.

Here’s an A/S32A-31A tow tracor on the aircraft carrier flight deck.

The newer SD-2 is a version of the A/S32A-32A designed specifically for use in the aircraft hangar deck. Due to the even more restricted space below the SD-2 has a castoring wheel that enables to fit aircraft into the tighter spaces found on the hangar deck. The SD-2 also does not need to tow bar as the aircraft are handled by an attached brace on the tractor that fits into the nosegear:

SD-2 tow tracor on the flight deck.

SD-2 tow tracor on the flight deck.

Tow tractors enable carriers and other aircraft operating ships to rapidly reposition aircraft to facilitate a rapid tempo of flight operations. Keeping in mind, IYAOYAS, tow tractors and their aviation bosun mates enable that ordinance to be on target in a timely manner. As with other member of the Naval Aviation team,  They give creditibilty to US Naval power.

6 Comments

Filed under Defense, navy, planes, ships

The Humble Trader keeps on CODdin’

Carrier Onboard Delivery, that is, the use of planes to provide logistical support to aircraft carriers, has been around pretty much as long as there have been carriers. The first dedicated COD aircraft was the TBM-3R, a modified Grumman Avenger with its armament removed, bomb bay sealed, and provisions for carrying passengers, mail, and cargo. But by the early 1950s, the Avenger CODs were getting old and tired, and their limited payload and range was also an issue. So Grumman devised a COD version of their highly successful S2F Tracker airplane. The wings, engine and empennage were the same, but the fuselage was somewhat deeper, looking for all the world like a pregnant Tracker. Originally designated TF-1, it was named the Trader, and first flew in 1955. Eighty-three were built, and would support the fleet until 1984. It was the last radial engine powered plane in the fleet.

File:Grumman C-1 flying side view.jpg

C-1A Trader

In the mid 1960s, Grumman would similarly adapt their E-2 Hawkeye wing, engine and empennage to a new, larger fuselage to produce the C-2 Greyhound COD, which first complemented, and later replaced the Trader in service. The Greyhound continues to support the COD mission to this day. 

File:C-2A DN-SC-89-09037.JPEG

C-2A Greyhound

Now a 60 year old design, out of service for over thirty years, you’d think the Trader’s story has come to a close. But wait, there’s more!

When France retired its aircraft carrier Foch in favor of the nuclear carrier Charles De Gaulle, Brazil bought Foch to replace its previous aircraft carrier, Minas Gerais*, and renamed her Sao Paulo. The Brazilians also bought Kuwait’s surplus A-4KU Skyhawks. Designated AF-1 in Brazilian service, these are excellent carrier aircraft, but they lack range.

Back in 2010, Brazil announced plans to purchase four C-1A Traders, and refurbish them for use as COD aircraft. The planes are in very rough shape.

Basically, the framework and sheetmetal are to be saved, and everything else, the engines, hydraulics, wiring, instruments and avionics will be brought up to 21st century standards. As an aside, re-engining S-2 Trackers with turboprop engines is a fairly standard modification, one that even CalFires has done with its S-2T tanker fleet.

The program has been somewhat stalled for the last four years, but finally, this week, Brazil signed a contract with Elbit Systems of America to perform the work. In addition to restoring them to flight and modernizing them, Elbit will add a refueling package to enable the Traders to refuel the Navy’s Skyhawks.

Elbit Systems of America, LLC, a subsidiary of Elbit Systems Ltd., announced today that it received a directed subcontract from the Brazilian Navy to upgrade four Grumman C-1A aircraft. The prime contract is held by Marsh Aviation Company of Mesa, Arizona. The subcontract, valued at $106 million, will be performed by Elbit Systems of America over a five-year period.

The upgrade work will be performed in San Antonio, Texas, at the facilities of M7 Aerospace, an Elbit Systems of America subsidiary, under the supervision of Brazilian Navy officers who are currently deployed to San Antonio. When upgraded, the Grumman C-1A aircraft will be designated as KC-2 COD/AAR (Carrier Onboard Delivery/Air-to-Air Refueling) aircraft, for the ultimate use on the Brazilian Navy’s aircraft carrier, the NAe São Paulo. AEL Sistemas S.A., Elbit Systems’ Brazilian subsidiary, located in Porto Alegre, Brazil, will provide in-country contractor logistic support services for the program as a subcontractor to Elbit Systems of America.

The planes should start being delivered about 2018. It’s amazing just how much Grumman got right with their design. Sixty years old, and it makes more sense to refurbish these planes than to attempt to convert some other or to design a new one for the role.

4 Comments

Filed under navy, planes

F/A-18E/F Super Hornet and IRST

In February 2014, the aircrew of an F/A-18 Super Hornet carrying the Navy’s infrared search and track (IRST) system, inspects the aircraft before the first flight with the pod at Edwards Air Force Base, Calif. IRST reached a critical milestone Dec. 2, authorizing low-rate initial production of the sensor pod system. (Photo courtesy Lockheed Martin)

In February 2014, the aircrew of an F/A-18 Super Hornet carrying the Navy’s infrared search and track (IRST) system, inspects the aircraft before the first flight with the pod at Edwards Air Force Base, Calif. IRST reached a critical milestone Dec. 2, authorizing low-rate initial production of the sensor pod system. (Photo courtesy Lockheed Martin)

Kind of “behind the power curve” on this but Lockheed Martin had achieved “Milestone C” for the IRST-21 flight tested aboard a US Navy F/A-18F Super Hornet.  As I understand it milestone C, pending approval, would be the before the IRST is approved for low-rate initial production. See the confusing figure below:

dafaq?

Dafaq?

Yeah I know that we attempt to clarify things here but I’m not even going to attempt to talk about the DoD acquisition process (that’s what the comment section is for) so my intent here is to give you “the big picture” as to exactly where the IRST-21 is in terms of being fleet deployed.

Lockheed Martin's IRST-21.

Lockheed Martin’s IRST-21.

The Lockheed Martin IRST is a self contained passive infrared sensor that’s designed to search air-to-air targets. Again the sensor is passive, meaning it doesn’t emit detectable signals that could give away the platform’s presence to the enemy. The IRST-21 on the Super Hornet is installed on the nose of the aircraft’s centerline fuel tank can be integrated into other tactical airborne platforms.

See the brochure here:

Investment in IRSTs really isn’t new they’ve been around for quite a while but it speaks to the threat that’s out there even with stealth aircraft being used by potential adversaries.

Oh yeah and this too <cough, cough>:

The AN/AXX-1 TCS (televison camera system) is left and the IRST is right on the F-14D Tomcat.

The AN/AXX-1 TCS (televison camera system) is left and the IRST is right on the F-14D Tomcat.

Just sayin’ baby :)

3 Comments

Filed under ARMY TRAINING

On the back side of the power curve, and other oddities of the carrier approach.

Piggybacking on Spill’s post on the S-3, I should mention that he and I discussed Direct Lift Control quite a bit the other day.

DLC is used on several different aircraft. And while there are various ways of achieving the effect (the F-35C apparently programs the flaps) let’s take a look at the F-14 Tomcat’s version.

On a carrier approach, you have to balance several issues simultaneously. Airspeed, angle of attack and attitude, and lineup.

Lineup is the left or right displacement of the aircraft from the extended centerline of the landing area. Now, since the landing area of a carrier is canted to port 8-10 degrees, and the ship is moving forward, lineup is never static for the approaching aircraft. The landing area appears to be continuously crawling to the right. So a series of corrections for lineup have to be made throughout the approach. The amount of correction varies due to the variances in just how much ambient wind there is, and the actual speed of the carrier through the water.

Airspeed is critical as well. The lift generated by the wings of a plane is directly related to the speed of the plane, obviously. Similarly, attitude, that is, the amount of nose up pitch, and angle of attack, are critical with respect to the rate of descent. The two are related. AoA is very roughly the angle at which the wings are biting in the air. Obviously, attitude is related to this. But so is airspeed.

Changing any one of the three, airspeed, attitude, or angle of attack changes the other two factors. Given that precision needed for a successful carrier approach, that places an enormous workload on the aviator. And so, tools to reduce that workload are prized.

Here’s the other odd thing. You’d expect airspeed on an approach to be controlled by the throttle, and the angle of attack to be controlled by the control stick. In fact, it’s just the opposite.

When a carrier jet settles into the groove for its final approach, jet is supposed to be at a given airspeed (generally about 130 knots, but varying by type), and a specific angle of attack (again, varying by type) and at a specific rate of descent (again, varying by type, but aligning with the standard 3.5 degree glideslope used on a carrier approach). The jet would ideally maintain this slight nose up attitude all the way to touchdown. There’s no “flare” to stop the rate of descent just before touchdown.

When in this approach configuration, the jet is said to be on the back side of the power curve.  You normally think of jets, pull back on the stick, the nose goes up, and the plane climbs, right? On the back side of the power curve, the increase in induced drag from the increase in angle of attack actually causes the plane to slow down, and in fact, increase the rate of descent! Pushing the stick forward lowers the nose, increases the speed, and reduces the rate of descent.

In the cockpit of every carrier jet, there’s a quick visual aid to tell the pilot his angle of attack- the AoA indexer. What it is really telling the pilot is if he is fast or slow.  The pilot simply cannot glance down to his airspeed indicator. Even in HUD equipped aircraft, an AoA indexer is a faster way of imparting information to the pilot than a digital airspeed indication).

If you’re slow, pitch the nose down slightly. If you’re fast, pitch the nose up slightly. Helpfully, the “arrows” point the way you should go. If you’re seeing the green donut, you’re on speed. While the picture shows all three symbols illuminated, in operation, only one would show (or on some, two, for instance red and green, indicating slightly slow).

Having this tool to show his airspeed, the carrier aviator also needs information on his glideslope. As noted, there’s a notional 3.5 degree glideslope reaching from the ideal touchdown spot aft into space along the approach path. To give the pilot a visual reference, mounted on the port side of the carrier is “the meatball.” The IFOLS, or Improved Fresnel lens Optical Landing System shines a beam of light along that 3.5 degree slope. That beam is centered between datum lights that show the proper glide slope. If a pilot is high, the “ball” climbs above the datum lights. If the pilot is low, the ball sinks. Sink to far and the datum lights turn red, because landing short on a carrier approach means smacking into the aft end of the carrier.

When you hear Maverick at three quarters of a mile, call the ball, that’s what he’s seeing- confirming to the Landing Signal Officer that he in fact sees the IFOLS.

If our intrepid aviator is on speed, but a bit high, he would squeeze off just a touch of power. That increases the rate of descent. As he approaches the correct glideslope, he’d add on a bit of power. If our aviator is low, he would goose the throttles a bit, and then pull off a bit before climbing through the glideslope.

The problem is, it’s very rare to only have to make one correction. Instead, our aviator would end up having to jockey the throttle virtually to touchdown. All while trying to maintain the perfect speed, attitude, and angle of attack.

So back to DLC. If there is a way to suddenly increase or decrease the rate of descent, without having to jockey the throttles, that’s a boon. And that’s what DLC does.

On the F-14, on carrier approach, the spoilers were partially deployed. That inefficient use of the wing raised approach speed by about 10 knots. That’s the downside. On the plus side, if our aviator is high on his approach, simply using a thumbwheel on the control column allows him to add a bit more spoiler deployment. That instantaneously increases the rate of descent. Coming to the proper glideslope, releasing the thumbwheel puts the spoilers back in the default position, and instantaneously puts the Tomcat back to the normal rate of descent. The converse is also at work. Low? A little thumbwheel lowers the spoilers, increasing the efficiency of the wing, and decreasing the rate of descent.

Spill also mentioned the poor response time of the S-3’s engines at approach power. The lower the power a jet engine is producing, the lower its RPM. Inertia being what it is, it takes time for jet engines to spool up to produce more power.

For this reason, most carrier jets fly the approach with their speed brakes deployed. The higher drag means they need considerably more power to maintain their approach speed. That higher RPM also tends to improve throttle response times, as there is less inertia to overcome. If also means that if a pilot suddenly needs quite a bit more airspeed, all he has to do is pull in the speed brakes.

When Spill and I first talked about DLC, I was a bit surprised to learn one of the very first uses of it was on the Lockheed L-1011 TriStar jetliner. Apparently, it was rather highly thought of by the crews.

4 Comments

Filed under planes

S-3 Viking Flight Quality Improvement Program

DN-SC-05-07440

Lockheed S-3 Viking

The Lockheed S-3 Viking was a carrier borne antisubmarine aircraft that entered service with the US Navy 1974 and ended it’s front line service in 2009.

The War Hoover (as it’s known due to the sound of it’s engines) was one the few carrier borne aircraft from Lockheed and as such they partnered with Ling-Temco-Vought (LTV) who had a long line of success of building carrier based aircraft. Lockheed put LTV’s experience in the S-3 to work as it uses the main landing gear from the F-8/A-7 stable of Vought carrier based aircraft.

Before all naval aircraft enter service they all undergo testing to evaluate how they handle when coming aboard the carrier for landing and how they behave when launched from the carrier’s catapult. The testing for the S-3, conducted in 1973 was no different. The case study of the S-3 illustrates the design complexity that all naval aircraft undergo to safely operate from the carrier environment.

1371151836545

Vikings from VS-21 “Fighting Redtails” aboard an aircraft carrier. Note the wing fold for stowage aboard the carrier.

The S-3 has a high aspect ratio wing the aircraft makes for a good glider and large turbofan engines that have 22:11 bypass ratio big that don’t respond to power changes quickly. Now you have an aircraft that uses low engine power to maintain position on the glide slope (with very low RPM on the engines). Not a huge problem on land but on a ship:

“If all the sudden your starting a settle coming into the carrier, you add power” to regain altitude, but nothing happens because of the delay in getting the engines to respond. “Then you find yourself sitting there looking at the ramp,” the wall of steel below the deck of the carrier. Hitting the ramp means dying. “In fact I almost hit the ramp” when testing the S-3 on the carrier, Webb said. “The combination of a very clean and very slow power response was a major problem.”

S-3 Viking 9.5 Engines

An S-3B illustrates how the engines are tilted 9.5 degress from the aircraft longitudinal axis.

Another problem was the S-3 would pitch up when power was added and pitch down when power was reduced. This was because the thrust line of the engines was below the center of gravity of the aircraft. This always placed the aircraft “out of trim” whenever a change to power was made. The remaining problem was that during simulation, Lockheed didn’t account for the burble of air coming from island and flowing across the landing area. Lockheed assumed the flow was horizontal behind the carrier.

“This gust responsiveness makes it considerably more difficult to bring aboard under wind conditions which create a strong ‘burble’ of distrubed air behind the carrier. In fact the aircraft failed its initial carrier suitability testing largely due to its gust responsiveness”

After additional flight testing, Lockheed implemented a number fixes to address these problems. The first was called “thrust trim compensation.” Whenever the pilot increased or decreased power, the elevators would automatically down or up to neutralize the pitching. “With that fix, a pilot trying to stay on glide slope while coming in to trap “does not have to fight the pitch with power all the time.””

Viking Pitch Trim System

The S-3 Viking’s Pitch Trim System as schemtically illustrated from the S-3 NATOPS Manual.

Another fix was applied to the S-3 spoilers. A spoilers is a control surface at the top of the wing, hinged on the wing’s leading edge. The spoiler is designed to disrupt or “spoil” the airflow on the top of the wing to dump lift. Normally, in the S-3, the spoilers are activated one wing at a time with movement of the stick left or right to assist the ailerons in control of the aircraft’s roll. With the press of a button the spoilers on the S-3 rise on both wings simultaneously. This allowed the pilot to reduce lift and descend faster without the pilot having to pull back on the throttles to reduce power. This “direct lift control” meant that the pilot could keep the engines at a relatively high power and not back to the unsafe “low-rpm” low power regime. The pilot needs the engines to main at a high power level in case he needs go around and try for another landing.

Viking DLC

An S-3 on launch from a carrier. You can see the DLC spoilers on the upper surface of the wings just forward of the flaps (seen in red and captured mid retraction).

These improvements took almost 10 years to apply and were collectively known as the FQIP (Flight Quality Improvement Program) Mod. The S-3 eventually became a very successful carrier borne aircraft and had a reputation the fleet as being an aircraft with relatively benign carrier landing characteristics. The Viking FQIP is one of many example of the performence constraints that naval aircraft must operate in.

S-3 Viking on the landing rollout after catching a wire.

S-3 Viking on the landing rollout after catching a wire.

Sources:

Flying the Edge by George C Wilson.

World Airpower Journal Volume 34 Autumn/Falll 1998.

S-3 Viking NATOPS.

3 Comments

Filed under navy

The BBC’s 1964 Masterpiece “The Great War”

Of all the events of the Twentieth Century, it is the First World War that has had the most dramatic and longest-lasting impact on the psyche of Western civilization, more so than all the events that followed.   For anyone with an abiding interest in that war, the 1964 BBC documentary The Great War is an invaluable reference to understanding.  Narrated by Sir Michael Redgrave, the 26-part documentary is a superbly-crafted work.  The tenor of the broadcasts reflects the erosion of the naïve hopes of the warring parties in 1914 into the grim fatalism that the years of slaughter evoked, and the upheaval that would ultimately topple the crowned heads of Germany, Russia, Austria-Hungary, and Serbia.  BBC producers make excellent use of voice to read the actual words of the key participants such as Edward Grey, Bethmann-Hollweg, Conrad von Hotzendorf, Joffre, Haig, Falkenhayn, and others.  The series features remarkable and little-seen motion footage of the world of 1914-18, including the civilians, the politicians, the armies, and the great battles of that war.   The battle footage heavily emphasizes the two great killers of that war (in inverse order), the machine gun, and modern breech-loading recoil-dampened artillery.

Of note also are the poignant, and sometimes extremely moving, interviews with the participants of events of the great tragedy.  Some had been in the thick of the fighting, others young subalterns or staff officers at the sleeve of the decision-makers.   Most remarkably, the BBC managed to produce a documentary about momentous events that changed the world and yet also managed to allow the viewer insight into the inestimable human tragedy that these events summoned.   At the time of the release of The Great War, those events were closer in time to the audience than the beginning of the Vietnam War is to our contemporary world.   The twenty-six episodes are around forty minutes each.  Worth every second of the time spent.

Oh, and as the credits roll at the end of each episode, one can spot the name of a very young (19 years old) contributor named Max Hastings.

3 Comments

Filed under Air Force, armor, army, Around the web, Artillery, Defense, doctrine, gaza, guns, history, infantry, iraq, islam, israel, logistics, marines, navy, planes, Politics, Syria, veterans, war, weapons

Cold War Naval Ops on Iceland

Warbirds News has some very interesting photographs detailing US Navy operations in Iceland during the 1960s:

One of VW-11′s Lockheed WV-2 Super Constellations at Ernest Harmon AFB.

One of VW-11′s Lockheed WV-2 Super Constellations at Ernest Harmon AFB.

From contributor Will Tate:

In November, 1963, after boot camp and Aviation Electronics school, I arrived at my new command, VW-11 (AEWRON Eleven). The squadron’s home port was Naval Air Station Argentia in Newfoundland, Canada. However, to maintain readiness for the ever-present Soviet bomber threat, the twenty man crews for our EC-121K Super Constellation AWACs aircraft spent two weeks out of every month deployed to a forward base; Naval Air Station Keflavik in Iceland. Our role was to augment the Distant Early Warning Line, or DEW Line for short. The DEW Line comprised a series of radar stations spanning the northern rim of the Americas out over the North Atlantic to the Faroe Islands. Along with other units, our squadron helped form an Airborne Early Warning (AEW) barrier in the Denmark Straits between Greenland and Iceland, and another barrier between Iceland and the United Kingdom. The DEW Line’s land-based radar stations throughout Alaska, Canada and Greenland were thusly joined with an unbroken link to stations in Iceland and England. The Navy’s AEW barriers would fill the over-water gaps round-the-clock for the next three years. While at NAS Keflavik, I was able to observe and photograph Navy and NATO aircraft operating from base.

There’s interesting photographs here of classic naval aircraft.

Comments Off on Cold War Naval Ops on Iceland

Filed under ARMY TRAINING