S-3 Viking Flight Quality Improvement Program

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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.

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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.

Maritime Domain Lessons from MH370

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I’ve been laying low on social media concerning MH370 (in addtion to the personal reasons). Seems like everywhere I go someone is going to ask me “what do you think happened to the aircraft?” or better yet, “how can you lose an airplane”).  I haven’t been able to go out for the past couple of weeks without being asked just once about MH370.

Frankly before we have evidence, I have no idea. The first and foremost point I try to make is that the ocean is a BIG place. To those of you on the coasts this isn’t new but those of us (here in flyover country) without exposure to the maritime domain, I think really don’t concieve just how BIG the ocean really is.

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All the black area is ocean!

It’s not enough to be told in school that combined the oceans cover 2/3 of the surface of the planet. Below is a picture of the USS Harry S. Truman, a Nimitz Class nuclear powered aircraft carrier. There are amongst the largest movable man-made objects on the planet. According to Wikipedia the Nimitz class ships measure 1,092 feet overall and have flight decks that measure about 4.5 acres.

That's a HUGE ship!
That’s a HUGE ship!

The Truman seems immense when compared to the buildings in the background! But let’s take another look at the Nimitz class seen in the vastness of the ocean:

Or is it? There are 3 Nimitz class aircraft carriers here.
Or is it?

I know quite a few Naval Aviators that tell me the same thing about their first arrested landing and that’s, “it looked so small” and indeed it does.

Let’s go to MH370. MH370 is a Boeing 777-200ER twin turbofan powered aircraft carrying about 250 passengers. The -200ER has a length of 209ft 1in and a wingspan of 199ft 11in.

The 777 less than 1/5th the length of the Nimitz Class aircraft carrier. Keeping that in mind you can see the problem finding the aircraft in the vast ocean, let alone any wreackage (and that’s not even taking ocean currents, weather, etc into account).

That's a big airplane! A Malaysian Airlines 777-200ER.
That’s a big airplane! A Malaysian Airlines 777-200ER.

Hopefully, this will give you an idea about just how easy it is to lose what we perceive as large objects in the vast ocean. It’s the proverbial needle in a haystack.

Look at all that ocean.
Look at all that ocean.

The vast ocean makes MH370 hard to find, also makes it easy to hide a Carrier Strike Group (CSG). That brings me to an interesting article over at the Naval War College Review: “Maritime Deception and Concealment.”

The uninformed reader might think that in the age of global satellite converage it would be diffcult to hide a Carrier Strike Group (CSG) in the ocean but this isn’t the case. CSGs can undertake active and passive measures to deny an enemy the ability to target them.

Passive measures can include EMCON:

The most commonly practiced maritime tactic is emission control (EMCON). Maritime forces typically restrict their radio frequency (RF) emissions and configure shipboard systems to limit acoustic emissions when operatinf in contested areas; platforms tasked with active sensor searches in support of forces in EMCON are positioned so that the former’s emissions do not reveal the latter’s general location. As repeatedly demonstrated by the US Navy against the Soviet Ocean Surveillance System (SOSS) during the Cold War, EMCON measures can severaly constrain if not eliminate the usefulness of wide area passive sonar and RF direction-finding or electronic intelligence (ELINT) sensors for surveillance and reconnaissance. EMCON does not necessarily imply complete silence; highly directional line-of-sight communications and difficult-to-intercept “middleman” relays (satellites or aircraft) can provide critical command and coordination links. Even so, it does represent a deep cut to the force’s normally avaiable bandwidth. Effective EMCON therefore requires decentralized doctrine that embraces unit-level initiative in executing the forces commander’s intentions, as well as preplanned and frequently practiced responses to foreseeable situations.

Even weather can be used to limit the effectiveness of different deployed sensors:

Sufficiently dense haze and cloud cover reduces vulnerability to infrared (IR) and visual-band electro-optical (EO) sensors. Precipitation similarly reduces EO/IR sensor effectiveness and, depending on wavelength and clutter rejection capabilities, sometimes radar as well. Atmospheric layering can cause radar emissions to be so refracted as to render nearby surface units and aircraft undetectable. Highly variable diurnal ionospheric conditions can likewise degrade shore-based over-the-horizon-backscatter (OTH-B) radars. Heavy seas, however unconfortable for crews, increase the background clutter OTH-B radars must sift through, as well as the ambient noise that complicates passive sonar search.

I highly recommend reading the entire article. Learn about how a CSG can sometimes easily delay dectection by an enemy. Think about the different factors and limitations of various sensors and environmental factors effect tactics employed in a wartime search. All these factors are also applicable to a peacetime search and rescue/recovery.

Many of these limitations apply  to the non-combat SAR environment as well and that’s the lesson that I come away with from MH370.

 

 

China Begins Building Second Carrier

Actually, it’s their first domestically built carrier. Their first is a refurbished ex-Soviet carrier.

It will be interesting to see what the differences in the configuration are between Liaoning and the second carrier.

The speculation is that it too will use the “ski ramp” method for launching aircraft. Unlike US carrier with steam catapults, the ski ramp system is much simpler, but also limits the weapons and fuel any jet can launch with. China has worked closely with Brazil (which operates a carrier with steam catapults) so they should have access to the technology. And steam catapults are hardly new. They’ve been around for 60 years. Steam catapults may not be the easiest technology to master, but it is a rather straightforward engineering challenge.

We in the US think of our aircraft carriers almost exclusively in terms of power projection. From Korea, through Vietnam, Desert Storm and the wars in Iraq and Afghanistan, the role of the carrier has been to sit off the enemy coast and send attacks ashore.

But China’s stated strategy is one of Anti-Access/Area Denial (A2AD). That is, they are structuring their forces and doctrine to deny us the ability to conduct operations in certain areas, or make them prohibitively expensive in lives and political support.

If the follow on carriers in Chinese service do use a ski ramp, that would effectively limit their fighters to a loadout of a modest number of air-to-air missiles, and a decent internal fuel load. So if Chinese carriers cannot reasonably be expected to perform War At Sea Anti-Surface Warfare (ASuW) attacks on our carrier groups, what is their possible doctrine?

Here’s my theory, based solely on PIOMA:

A Chinese carrier battle group of one or two carriers and escorts is intended to provide local air superiority over itself, and execute limited challenges to air superiority over our carrier forces.

China wouldn’t even have to secure air superiority over our carrier group, but instead, merely make credible challenges from time to time, while avoiding being destroyed.

It doesn’t take a lot of credible threat to one of our carriers before a large portion of the sorties generated have to be devoted solely to Combat Air Patrols (CAP) over the carrier for self protection. Indeed, the political consequences of losing a carrier, or even having one badly damaged, would tend to make force protection the first imperative for any US Navy operation. To say our current Navy is rather risk averse is to put it mildly.

And so, with a majority of the sorties of this notional carrier task force devoted to protecting itself, it has essentially become a self-licking ice cream cone. The carrier exists to provide air cover to the fleet, which the fleet is there to support carrier operations. See what I mean?

What do you think?