CVN 72 - Abe Lincoln

These photos were taken while working for NKF Engineering in 1992. I was on the Aircraft Carrier 'Abe Lincoln' (CVN-72) for 6 days while at sea off the California coast. Air operations were conducted around the clock during that time - mainly as qualification/re-qualification for pilots needing to obtain a carrier landing rating, or to keep it current.


I was on the ship to collect vibration data from the 'arresting engines', which stop the aircraft on landing. Think of a 30 foot long hydraulic cylinder (similar to a very long automobile lift in a service station) that is oriented horizontally with multiple pulley sheaves on each end. A large steel cable passes through the sheaves and runs to the carrier deck. The hydraulic cylinder begins at a fully extended position. After an aircraft snags a landing cable, the cable compresses the hydraulic cylinder (making it shorter in length). The hydraulic fluid in the cylinder passes through a controlled orifice which decreases in size as the cylinder compresses. This also has an additional setting for the size of the aircraft, with smaller orifices for larger weights. There are 4 cables on deck that an aircraft may hook on to. Each of these has an arresting engine connected to it.


A problem had arisen on one carrier that had sheave bearings installed that were not properly heat treated, and they had failed prematurely. The question was whether other carriers also had these defective bearings. Considerable time and effort (estimated $50k in 1992 dollars) was required to disassemble and replace the bearings in an engine. 'Condition Monitoring' uses vibration data to determine if there are 'pits' in bearing races, which are an indicator of impending failure. By noting the rotational speed and comparing intermittent vibration spikes to the speed, it is possible to identify pits because they generate a brief vibration pulse every time a ball/roller encounters one. My instrumentation consisted of an optical sensor and a mark on the side of a pulley, and accelerometers mounted inside of the pulley shaft . During my week onboard I collected data from multiple engines. (Later processing showed no significant signs of deterioration, so the bearings were not changed until the next normal overhaul period, thus saving considerable expense).


During this period a couple of crew members I had become acquainted with took me on deck while operations were on-going. I was on deck next to the arresting cables as aircraft landed, and between the catapults as they took off. It was one of those lifetime memorable experiences!


Some interesting points:


  • Video cameras are mounted on the stern, looking directly up the landing path. Hundreds of monitors are installed all over the ship, and landing approaches were watched (and commented on!) by many. These was no hope that a bad approach would not be noticed!
  • The F-14's and F-18's were landing at well over 100 mph, but from the high angles of attack and the wobbly motion at that speed, I had the impression they were just barely hanging in the air
  • Even with a good approach, there is no guarantee the hook will snag an arresting cable. Therefore, the moment the wheels touch the deck the pilot goes to full throttle in preparation to take off again.
  • The cables that the aircraft hook snags are heavier than the ones that pass through the arresting engines. A count is made on the number of catches that each cable makes, and after a fixed number of catches (I think perhaps 100), the cable is immediately replaced, a process that takes only a few minutes.
  • Near the end of my stay, ordance (bombs, etc) was transferred off the carrier in preparation for an extended port stay. It was transferred to USS Mt Hood  by cables and Chinook helicopters.

Even though I have served in the military, I was still impressed by the precision of operations onboard an aircraft carrier. It requires 100's of people working simultaneously to conduct air operations. Planes land, are unhooked and moved in quick succession on one part of the deck, while only a few yards away planes are also taking off. Any one person failing to do their job properly could result in major difficulties or disaster. Yet, after a few days it all seems to be 'routine'.


My final thrill for this trip was to be catapulted off the carrier on a COD (Carrier Onboard Delivery) flight. These are propellor aircraft which haul mail, personnel. With no windows there was nothing to see, but it was still quite a thrill. All passengers are strapped in with full harnesses and given instructions for body position during takeoff. The g-force was quite impressive, but it was over in an instant.

Nimitz-class aircraft carrier USS Abraham Lincoln (CVN 72) - this was the ship I spent a week on in 1992
190130-N-PW716-1312 ATLANTIC OCEAN (Jan. 30, 2019) The Nimitz-class aircraft carrier USS Abraham Lincoln (CVN 72) transits the Atlantic Ocean during a strait transit exercise. Abraham Lincoln is underway conducting a composite training unit exercise with Carrier Strike Group (CSG) 12. (U.S. Navy photo by Mass Communication Specialist 3rd Class Clint Davis/Released)
Small Target
There are 4 arresting cables that cover a fairly small area of the deck. If they miss hooking one of the cables they have to continue flying and try again
Caught it!
The hook has grabbed a cable - the hook is horizontal and the cable is stretched out behind it, being pulled out of the Arresting Engines which increase force until the plane stops. Meanwhile, the pilot has gone to full throttle as soon as his wheels hit the deck, in case he misses a cable and has to fly off again.
Incoming
Right at the edge of stall, they are still over 100 mpg
Still Dragging
This aircraft has not yet hooked a cable - the tail hook is still dragging on the deck - but there is still another cable ahead that it can hook.
View from the stern, below the flight deck
There are video cameras at the back edge of the flight deck that broadcast into nearly every living space on the ship. They are aimed to look right up the ideal flight path, and at any time many on the ship are watching. They know if you are high or low, and are commenting on whether you are blowing it or not.
Barely flying
At the end of the approach they are barely flying, high angle of attack and wobbling as if they are barely in control
COD (Carrier Onboard Delivery) Landing
COD Flights shuffle mail, personnel and supplies. When I was catapulted off the deck at the end of my stay it was on board one of these planes.
Not So Pretty Up Close
Compared to say, sleek Blue Angels aircraft, actual in-service ones are not nearly so glamorous looking. Flat and dingy gray paint with greasy hand prints and stains.
Replacing a Cable
Records are kept of the number of landings for each of the 4 cables. When that number reaches 100, the cable is immediately replaced, even in the middle of landing operations. The part that is replaced is just a section that the tail hooks grab, and it is a thoroughly practiced and efficient operation, accomplished in a very short time. You can see two other arresting cables to the left and one to the right of the one being replaced
Available Space is Efficiently Used
Landing operations are like clockwork - wings are being folded even as the plane is taxiing away from the landing zone, then moved to a space where it is loaded aboard an elevator to the storage hangar below.
Close Quarters
All available space is utilized
Final Stop
Every available bit of the runway is used to bring a plane to a stop - the pilot is looking at the edge of the deck at the end of the landing
Go Around!
This one did not hook a cable. As soon as the wheels touch the deck pilots go to full throttle. At that point they have either hooked a cable, or are beginning their takeoff to go around for another try. If they were successful in hooking a cable, they are at full throttle when they come to a stop, otherwise they are accelerating to achieve flying speed. Because the tail hook did not snag a cable, it is dragging on the deck - the shower of sparks from the hook dragging across the rough surface is visible under the tail of the plane.
Yours Truly
A friendly Crew Chief dressed me up and took me on deck to witness flight operations up close. Double hearing protection - first the foam plugs in the ear canals, then the ear muffs/head set over those. Still very loud. It was an amazing experience to be so close to fighter jets landing and being launched!
Up Close!
You can't get much closer than this - controlled violence
Oops
Another go around that missed the hook
Barely Flying
At this stage of the landing they are wobbling with large control movements, seeming to barely be hanging in the air, although at over 100 mph!
Launch
While planes are landing on the aft/left side of the deck, others are taking off on the forward/right side of the deck. The plane on the left is about half way through being launched by the catapult
Barely Flying
Even with the catapult assist, they are on the lower end of flying speed at the end of the launch - usually they drop a little bit off the end of the deck while they are building more speed
Full Operations
The plane at the left has just landed and unhooked from the arresting cable, and is now clearing the landing zone for the next plane. The plane on the left catapult is running up its engines with a blast deflector raised out of the deck behind it - it will be taking off very shortly. The COD plane on the right is getting into position, its wings are still folded.
COD Flight Launching
Winds unfolded and taking off
Clockwork
Dropping the hook after landing on the left, two getting ready to launch
On Deck!
When my friendly Crew Chief took me on deck, it was not only to witness landings, but also to take me the catapults. It was a hazardous place, I could often feel the Chief's grip on the back of my vest, pulling me this way or pushing me that way to keep me safe.
Hooking Up
Checking the connection to the catapult
Question Mark Vapor Trail
Not my photo, but it shows what I saw while on deck, but did not get a photo of. When a plane went to full throttle, the low pressure at the inlet formed this odd question mark-shaped vapor trail from the bottom of the inlet to the deck. It was very spooky - making it obvious how much air was flowing. It was not a place you wanted to get any closer to!!
Launch!
Full throttle and catapult assist - heading down the deck. The dome in the deck is where the Launch Officer lives - he is the one who pushes the catapult button.
The Elevator
A large portion of the area under the flight deck is the hangar. An elevator takes planes between levels. Currently the elevator is at deck level. When it comes to hangar level planes enter and exit through this opening
Bottom of Elevator
Looking up at the bottom of the elevator
Rescue Chopper
Whenever flight operations are being conducted, a rescue helicopter is hovering nearby, ready to rescue any pilots who end up in the water
Hangar Deck
It was too dark for an old film camera to be able to capture very well. This is a huge space.
Police Call
During pauses in operations there would be police calls to scour the deck for even the smallest things that could get sucked into a jet engine. All four arresting cables are visible on the deck
Arresting Cable Connection
A fairly closeup view of an Arresting Cable connection, just to the left of the circular white area. The cable that disappears into the deck is part of the Arresting Engine, and is pulled out as the plane travels down the runway. The slightly smaller cable to the left is the short section that the tail hook snags. It is replaced every 100 landings. The metal coupling is a quick connect fitting, allowing cables to be switched very quickly.
Catapult Area Maintenance
The Launch Officers bubble is on the right
Off Loading
At the end of the current flight operations the CVN 72 was scheduled for maintenance time in port. All ordnance (bombs, etc) was first off-loaded while at sea, so none would be taken into port. Cables were strung between the carrier and an ammunition transport ship (USS Mt Hood - since decommissioned: USS Mt Hood AE-29 ) on a parallel course. A couple of bombs are visible as they are ferried between the ships.
Off Loading
In addition to the items riding across on cables, Chinook helicopters ferried loads between decks.
Officer's Quarters
I was privileged to have on board accommodations in the Officer's Quarters. Not exactly spacious, but far more so than for the enlisted guys.
The Arresting Engines
An operator walks between two Arresting Engines. In the foreground to the left is a weight selector valve, which is set to the anticipated weight of the approaching aircraft. This valve controls the pressure of a hydraulic cylinder which is designed to stop all aircraft in the same distance, regardless of weight
Arresting Engine Diagram
Most of what happens is below deck. A large hydraulic cylinder with sheaves on both ends starts at full extension.  The cable from the deck passes through the sheaves for multiple loops.  As the aircraft hooks the cable and pulls it onto the deck, the cylinder is compressed.  A control valve that is set for the aircraft's weight is progressively closed as the cylinder is compressed, resulting in the same stopping distance for aircraft of different weights.  Image credit:  www.nature.com/ figure
Control Valve
A closer look at the control valve. There is an operator for each engine, and each engine's valve must be set for every approaching aircraft
Fixed End of the Arresting Engine
Referring to the earlier diagram, these are the two sheaves at the fixed end of the engine. The ends of the hollow axles for both sheaves are visible. The numerous small tubes surrounding each hollow shaft opening provide bearing lubrication. Some of the multiple loops of cable are also visible.
Cables and Sheaves
The number of cable loops and diameter of the sheaves can be seen here.
Vibration Measurement
Accelerometers were installed inside the hollow shaft measured vibration in order to evaluate the condition of the ball bearings. Any wear in the form of pitting of the balls or races would show up as vibration at certain frequencies
Optical Sensor
The small bracket with wires attached is an optical sensor that was part of my test instrumentation. It is used to measure the rotation speed of the sheaves.
Optical Sensor Trigger
The black square on the edge of the shiny sheave was the trigger for the optical sensor. It provided a change in signal every time it passed the sensor, which could be used to calculate the rotation speed throughout the event.
Oil Coating
Even though the sheaves became covered in red oil/grease, the black mark was still able to provide enough change in optical reflection to make measurements
Spare Engine
Spare parts are good!
Friendly Crew Chief
This is the guy who took me on deck during operations (and often kept a firm grip on me to make sure I didn't get into dangerous places)
Another view of the CVN 72 in Puget Sound
BREMERTON, Wash. (Jan. 13, 2010) The aircraft carrier USS Abraham Lincoln (CVN 72) transits Puget Sound. Abraham Lincoln has been pier side at Puget Sound Naval Shipyard for nine months undergoing a complete overhaul during a planned incremental availability. Abraham Lincoln will soon undergo sea trials for an upcoming deployment. (U.S. Navy photo by Wendy Hallmark/Released)
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