Nimitz Class Aircraft Carrier Antennas - Up or Out?

prokofi5

Hi,

  I'm currently working on Italeri's USS Theodore Roosevelt, but I'm trying to figure out the antennas all around the flight deck.  I see in some references that they are oriented straight up and in others they are pointed outwards.  Are they repositioned during flight operations or something?  Also, if that's the case would it be all or some of the antennas that are moved?

Thanks for your time.

During flight ops (which is 24 hours a day 7 days a week) the antennas are extended as to keep them from getting clipped by the wings of aircraft as they are launching (all moveable antennas are on the foreward section of the flight deck). And at port they are raised.

We also raised them when heavy seas were expected.

subfixer

We also raised them when heavy seas were expected.

Don't you pretty much mean a Hurricane or Typhoon? Because a 30-40ft swell would hardly phase a carrier.

 You don't have to be in a storm to get the heavy seas of one. I have seen solid green water go across the flight deck (60 feet from the waterline) and have seen the crests hit the pilot house windows without actually being in a storm. This was in the Pacific on the Ranger, a Forrestal class supercarrier. I was in several storms out there, but we avoided direct contact with typhoons by going around the actual storm center. 40 foot waves are common at sea in rough weather and I have seen seas that were 90 feet high (at least) from trough to crest in some situations. Although the ride on a carrier in heavy seas isn't the thrill ride that you experience on a destroyer, (I was a crewman on the USS Theodore E. Chandler, DD-717, for a little while, too) it will still literally rock your world.

  I was in a hurricane in April, 1976, in the Gulf of Mexico on the Lexington. We had to recover bodies from an oil rig that foundered while under tow. That wasn't so bad for an Essex class carrier, but it was still a little hairy because the old boat groaned a lot. Especially at the expansion joint where our berthing was located. We had to strap ourselves down in our racks for that one.

 The waves will hit the hull so hard that the boom of the impact will shake some equipment from their mountings. We lost our berthing compartment TV in one storm from the shock of a wave hitting the hull from a weird angle. In conclusion; if the waves are going to be bad enough to curtail flight ops, the antennaes are raised.

Mikeym_us

Because a 30-40ft swell would hardly phase a carrier.

It's not the size of the swell, it's what causes the swell.

Round numbers, the side area of a CVN is about 900 x 35, or over 31,000 square feet of area for winds to push against.

Using q = 0.00256*V² A 30 mph wind (26 kts) exerts 2.304 psf, or about 71,000 pounds over that 31,000 sf, which is enough to impart motion.

30 mph is only Beaufort 6, 10'/3m waves. 

But, the other thing to remember is that, as a ship rolls, those antennae are along way out around the axis of rotation, bringing the tips closer to rising wave tops.  Add in the flex in the antenna structure, it would be easy enough to roll them into a moderate sea, and seawater has an annoying habit of keeping things like that.  Which gets the sparkies all cranky carrying away either send or receive conductors.  The hinge mechanisms do not take kindly to unexpected lateral movements, either.

A CVN is a huge object; but oceans are far far far larger, and have been smugly bemused by the vanities of we mere humans.

CapnMac82

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A CVN is a huge object; but oceans are far far far larger, and have been smugly bemused by the vanities of we mere humans.

Hear! Hear!

CapnMac82

 

Mikeym_us:

Because a 30-40ft swell would hardly phase a carrier.

 

It's not the size of the swell, it's what causes the swell.

Round numbers, the side area of a CVN is about 900 x 35, or over 31,000 square feet of area for winds to push against.

Using q = 0.00256*V² A 30 mph wind (26 kts) exerts 2.304 psf, or about 71,000 pounds over that 31,000 sf, which is enough to impart motion.

30 mph is only Beaufort 6, 10'/3m waves. 

But, the other thing to remember is that, as a ship rolls, those antennae are along way out around the axis of rotation, bringing the tips closer to rising wave tops.  Add in the flex in the antenna structure, it would be easy enough to roll them into a moderate sea, and seawater has an annoying habit of keeping things like that.  Which gets the sparkies all cranky carrying away either send or receive conductors.  The hinge mechanisms do not take kindly to unexpected lateral movements, either.

A CVN is a huge object; but oceans are far far far larger, and have been smugly bemused by the vanities of we mere humans.

An Aggie engineer!    Well done!

EdGrune

An Aggie engineer!    Well done!

Well, between the legal requirements in architecture for lateral forces, and one too many classes on principals of ship stability (and more than a fair bit of ocean experience), a person can learn a thing or two over a half-century.

A forty story building is a pretty massive thing, and seemingly uncaring of mere wind.  Yet, we discovered down in Galveston after Hurricane Alica, that we needed to adjust just how "bendy" buildings near the shore need to be. 

Which made being aboard USS Anchorage a contrast, being about 45 "stories" long (if with a better turning radius than most of the buildings on the Strand<g>)