Stupid Questions about Naval Aviation (Part 3)

[Recovering LSO]

@Hopeful Hoya hoya On a four wire ship, the nominal hook to ramp clearance (how much the hook clears the back of the ship by) is about 14 feet. On a three wire ship, the hook to ramp clearance is reduced to something closer to 12 feet. Those numbers are based on an aircraft that is on-speed, on centerline, and glideslope.

 

[kejo]

On 77, we have four arresting gear engines, with up to three wires configured at any given time. From the fantail forward, 1, 2, 3, and 3A. 3 and 3A are interchangable for use with the barricade, whereas "legacy" systems use a separate, #5/barricade-only engine.

Reasons for the change, at least from a systems perspective, include cost savings, space savings, and raw statistics. Apparently, studies determined that four wires was one too many...or at least, unnecessary. The introduction of the ARC (Advanced Recovery Control) system greatly improved overall arresting gear reliability, and was also a likely driver towards the three wire configuration.

 

[Hopeful Hoya]

Very cool, thank you for the info gentlemen.

 

[nittany03]

Even on four wire boats it's common for one or more wires to be missing at any given time for numerous reasons.

Every cross-deck pendant has a finite lifespan; you'll often see them gathered over by the LSO platform after they're used up. I want to say 125 traps, but it's been awhile since I stood Pri-Fly observer. There's a screen in Pri-Fly which tracks, among other things, the trap count on each engine for the maintenance of various and sundry parts of the arresting gear system. IIRC, they'll also strip the wire when any other part of that engine is broken, so no one can trap on it.

 

[ea6bflyr]

IIRC, they'll also strip the wire when any other part of that engine is broken, so no one can trap on it.

If they do it wrong, this happens. IIRC, they stripped the wrong wire then locked the correct engine, which 102 trapped on. I believe it was the first Super Hornet F-Model ejection.

 

[AllAmerican75]

@Hopeful Hoya hoya On a four wire ship, the nominal hook to ramp clearance (how much the hook clears the back of the ship by) is about 14 feet. On a three wire ship, the hook to ramp clearance is reduced to something closer to 12 feet. Those numbers are based on an aircraft that is on-speed, on centerline, and glideslope.

Wait, wait, wait. Don't you want more hook-to-ramp clearance, rather than less?

 

[nittany03]

Wait, wait, wait. Don't you want more hook-to-ramp clearance, rather than less?

You want whatever it takes to put the hook point at the targeted spot on the flight deck on-speed and on centerline, ever so slightly above the middle of a 3.5 degree glidepath. If the loss of that hook-to-ramp distance would have been a showstopper, I'm sure NAVAIR and the test guys would have had something to say about it along the way. I'll defer to the Paddles mafia for details.

 

[Recovering LSO]

Wait, wait, wait. Don't you want more hook-to-ramp clearance, rather than less?

To an extent. But if you agree that the three (or four) arresting wires aren't moving - i.e., their location is fixed - than increasing the H/R clearance, BUT still putting the hook in the spaghetti would require, as Nittany pointed out, more than a 3.5 degree g/s and in turn greater rates of decent. Beyond the scope of this conversation, but you can adjust up to a 4 deg g/s, but generally there should be quite a bit of wind.

 

[Hopeful Hoya]

To an extent. But if you agree that the three (or four) arresting wires aren't moving - i.e., their location is fixed - than increasing the H/R clearance, BUT still putting the hook in the spaghetti would require, as Nittany pointed out, more than a 3.5 degree g/s and in turn greater rates of decent. Beyond the scope of this conversation, but you can adjust up to a 4 deg g/s, but generally there should be quite a bit of wind.

And I'm guessing that 4 deg g/s landings come with an increased amount of wear and tear on the airframe, hence the 3.5 degree norm?

 

[nittany03]

And I'm guessing that 4 deg g/s landings come with an increased amount of wear and tear on the airframe, hence the 3.5 degree norm?

Among other things, they can compensate for higher than normal winds. Perceived glideslope is 3 degrees as seen by the aircrew. 3.5 degree actual glideslope takes into account wind and boat movement; i.e. as the boat moves forward, it turns a displayed 3.5 degree glideslope into the aircraft actually flying a 3 degree glideslope through the air. If the relative wind is too high, Paddles shifts glideslope up to a max of 4 degrees as to maintain the perceived 3 degree glideslope. As RLSO said, steeper actual glideslope == more VSI == more airframe wear.

If the lens is broken or the environment is out of spec for it due to winds or ship movement (long story short, the ball is gyrostabilized and has limits), Paddles rigs what is known as MOVLAS (Manually Operated Visual Landing Aid System). In its simplest form, it's a bunch of light bulbs which bolt on top of the Fresnel lens, use its datums, and allow the LSO to show the pilot whatever ball indication he/she wants the pilot to see, with the expectation that the pilot will fly it just like a normal ball. All the pilot needs to do is fly the ball like normal, and Paddles can directly wave him/her aboard. You can also bolt the MOVLAS on a couple other places with its own datums and waveoff/cut lights, but generally no one likes this because it monkeys with your scan.

Edit: MOVLAS is also referred to sometimes as the "green machine." If a pilot does what Paddles says and is reasonably on parameters during a MOVLAS recovery, they're pretty much guaranteed to get an "OK," which is a green puck on the greenie board, and usually a nice little GPA bump for that line period.

 

[Recovering LSO]

And I'm guessing that 4 deg g/s landings come with an increased amount of wear and tear on the airframe, hence the 3.5 degree norm?

If you're commanding 4 deg with the IFLOLS, then you most likely have quite a bit of wind over the deck that helps with closure rates and VSI. MOVLAS, as Nittany pointed, can result in a 1 degree (gulp....) or a 10 degree (double gulp....) glideslope - it all depends on what Paddles is showing, and in turn asking of the pilot. Certain pitching deck conditions (look at 46 sec mark for an idea of how much the ramp was moving up and down), might mean an apparent 6 deg glideslope is prudent - and depending on the urgency/op environment, CAG and CAGMO might just have to accept the cost of 903s and 904s (codes the jet shits out to troubleshooters to tell them it had a hard landing).

 

[Hopeful Hoya]

Very interesting, is the MOVLAS something that is used quite often (i.e. do you usually experience that many severe pitching decks during a cruise)?

 

[nittany03]

Very interesting, is the MOVLAS something that is used quite often (i.e. do you usually experience that many severe pitching decks during a cruise)?

You see it from time to time. It's not just for a pitching deck. It also is used if the IFLOLS is flat-out broken, which happens now and then. That's the other reason behind MOVLAS stations 2 and 3 (the ones not bolted to the IFLOLS). Get people back aboard even in the event of battle damage taking out the IFLOLS.

My air wing also planned a MOVLAS recovery every so often for no other reason than to let everyone practice. They did that enough times that, regardless of the vagaries of scheduling, everyone would see it now and then. It's when it's not on the air plan, and you hear "99 Barbwires, MOVLAS recovery, MOVLAS recovery" over the controlling freq that you go "hmm."

 

[Hopeful Hoya]

If you're looking on a per-aircraft basis, the relevant numbers can be found here:

http://en.wikipedia.org/wiki/List_of_active_United_States_military_aircraft#Navy

Not sure about community sizes in terms of NAs/NFOs though.

 

[Uncle Fester]

Hopefully this question isn't too "stupid" haha:

What would you guys say is the split between the various flying communities in the navy? E-2 vs Helo vs Hornet etc.

Someone asked me this today and I had no clue. My guess would be something like:
35% Helo
35% Fighter
15% P-8
15% E-2

Do you mean numbers of airplanes, or proportion of pilots/FOs/NACs? And if the latter, do you mean people actually assigned to a squadron and actively flying, or who came from those communities whether actively flying or not?