The Super COD

[nagpaw]

I alluded to working on this paint on another thread, but I'm bringing the subject over here to stay on subject. Here's what I'm working on, and I need some help from the experts...

The DC-9 was proposed as a "Super COD" near the end of the Vietnam War. I'm using the Sky Simulations DC-9-20. It's not perfectly accurate, as the proposed COD Nine had numerous structural modifications, including a lengthened (and extendable) nose gear and no thrust reversers, but it's close enough for me! Keep in mind that the paint is definitely an early work in progress.

At about 93 feet, the Nine's wing span is 13 feet wider than the C-2 Greyhound. That's 6.5 feet either side. I'm using the basic FSX:A carrier here. Without modification, the Nine fits on the boat. Apparently the wing-fold system was scrapped after it was assumed the aircraft would only be aboard for 30 minutes at the most.

The Nine would likely have required a nearly clear after deck for landing. Aircraft parked along the deck edges are really close to the wingtips.

She's stable all the way to the deck, and I might have nailed a three or four wire on this pass. Apparently the deck landing weight would have been limited to 75,000 pounds. I used Flaps 50 for landing with an approach spped of about 110 knots.

Boltering might be exciting. A positive rotation is required nearing the deck edge. It doesn't take much sink off the deck to put the right wingtip into the port side catwalk.



So here's my questions and asks...

1) The pilot's eye height on the Nine would be significantly higher and further ahead of the main gear than other carrier aircraft. How would that affect use of the optical landing system? I'm afraid that following the normal glidepath would likely put the main gear into the ramp. Is the glidepath adjustable for different aircraft? If so, is that capability available in FSX?

2) I'd love to add a launch bar and tailhook to the aircraft.cfg. I've read the FSDeveloper Wiki and understand the basics, but I'm not sure how to calculate the exact geometry. I took a best guess, and failed miserably Can anyone provide some guidance...or even just figure it out for me?

Thanks for any help, guys!

 

[Mike71]

So here's my questions and asks...

1) The pilot's eye height on the Nine would be significantly higher and further ahead of the main gear than other carrier aircraft. How would that affect use of the optical landing system? I'm afraid that following the normal glidepath would likely put the main gear into the ramp. Is the glidepath adjustable for different aircraft? If so, is that capability available in FSX?

Thanks for any help, guys!

Eye to MLG is not an issue - hook to eye value is. That is the controlling issue. The FLOLS roll angle is adjusted for the "hook to eye": vertical distance so that the hook point passes a nominal 14.7 feet above the ramp on a perfect pass, on speed (AoA). This was the case with earlier large deck carriers before they went to three wires, etc. It is likely somewhat different now (hook to ramp value).

SOOooo - in th end, A C-9 pilot's eye may cross the ramp much higher than a C-2 pilot's eye, but the hook point for both would clear by the same distance and touch down at the same point on the deck on a perfect, on speed (AoA value) pass. AOA controls body angle, which controls hook to eye; it all falls into place when done "the Navy way".

As an additional note ,the wing span would dictate more of a problem wrt bad lineup. A C-9 would likely land last - CODs usually do, because they are somewhat cumbersome to deal with at the beginning of a recovery. However, a C-9 would be worrisome because at the end of a recovery you have a lot of airplanes nose up to the foul lines along the landing area. Off center engagements would be really disastrous - their bad enough with a C-2 or E-2.

 

[nagpaw]

Mike71,

Thanks for the great information! I fiddled with my numbers for launch_assist and tailhook intermittently all day before I finally found the problem, and I feel pretty stupid. I was using a carrier that wasn't configured to carrier operations. Duh. So I reinstalled AICarriers.net and went back to work.

Good news? I think I have numbers that are close. And you're absolutely correct: following the ball works just fine!

So, would anyone out there with the Sky Simulations DC-9 be willing to try the numbers out? You'll need to modify the DC-9-20 aircraft.cfg thusly...

1) Comment out the existing [Tailhook] section.
2) Add the following text at the end of the file:

[launch_assistance]
launch_bar_pivot=-10.15, 0.0, 4.45
launch_bar_lug=-10.15, 0.0, -5.75

[tailhook]
tailhook_length=4.5
tailhook_position=-70.78, 0.0, -3.0


The only problems I'm having right now are:

1) With the nose gear attached to the catapult shuttle, the tailcone extends through the JBD. That's probably a fault of the FSX carrier model being geometrically inaccurate, but that may have been an issue with the real aircraft. I'll try installing a better model and see.

2) The airplane seems to stop pretty quickly, even at the maximum landing weight of 75,000 pounds. There's the .cfg entry "cable_force_adjust" that I haven't fiddled with. Maybe that's it?

3) The Sky Sim -20 model has airstairs that are toggled with the tailhook command. Anyone know if there's a way to stop that from happening? As it is, once you get on the deck, the stairs extend.

 

[Mike71]

Mike71,

Thanks for the great information! ----

1) With the nose gear attached to the catapult shuttle, the tailcone extends through the JBD. That's probably a fault of the FSX carrier model being geometrically inaccurate, but that may have been an issue with the real aircraft. I'll try installing a better model and see.

2) The airplane seems to stop pretty quickly, even at the maximum landing weight of 75,000 pounds. There's the .cfg entry "cable_force_adjust" that I haven't fiddled with. Maybe that's it?-----

Glad you have grasped the concept. However, though I have used AI Carriers quite a bit, I am no FS CV designer. I do not think that these fine models adjust the FLOLS roll angle as in real life. In real life, the glide slope stays at a constant angle in relation to the deck (called "basic angle"), and adjusting the roll angle raises or lowers that path vertically, parallel to the basic angle path, which adjusts for individual hook to eye distance. The basic angle is hardly ever changed - typically only for the rare barricade engagement or a badly pitching deck, but that would likely result in LSO's using MOVLAS.

I'm not surprised about the JBD issue. Real ones had a center panel that could be lowered when launching the overly long A-3, leaving the outboard ones behind the engines up. However if that would not work with a DC-9 with high, tail mounted engines they may have planned to launch it with a clear deck aft of it, likely from Cat#1.

Stopping quickly?? Not in real life. Arresting gear is designed to be at a constant runout of about 310 feet for any airplane when set for it's max landing weight. (Big deck carriers; ESSEX class 27C's were only about 200 feet!).

The AG will attempt to do this no matter what the actual conditions are; the only feedback the AG engine has is how far the followup mechanism is set for each type of plane (the Constant Runout Valve, or "CRV"). If a plane is too overweight or too fast, the plane and AG will suffer, but a lot of "slop" is available. Worst case is a heavy, fast landing that can "tube lock" the AG and the cross deck pendant will break. because the AG engine piston has traveled as far as it can within its cylinder and locks up and gets damaged. Think of pushing the plunger of a hypodermic needle down as far and as hard as you can until it empties - eventually the glass cylinder would break. The AG engine is really just a huge hypo needle with the ability to adjust the size of the hole in the actual needle to allow different flow rates out of the hole, and ultimately to gradually close down that hole to bring the gear to a stop.

An airplane that is light or slow on engagement will still pull the wire out the nominal distance, but just run out at a relatively slower rate because the AG engine is set for a greater resistance than needed. It is always set for "max trap weight".

The Officer of the Deck, Air Boss, and LSO's all shoot for 25 knots wind over deck. This is the nominal goal and accounts for the most critical airplane, the E-2 fuselage / hook limits (at least in my day up to the 90's). If 25 knots cannot be achieved, LSOs are more vigilant with waveoffs for fast approaches, burble effect ,etc.

Accounting for unusual situations such as flap issues, it is much easier and standard to adjust WOD, especially for a nuke - more speed - no problem! Each aircraft has a set of Recovery Bulletins with required settings, speeds, etc for such conditions. LSOs and Air Bosses have them readily at hand and confer as to the best solution for problems. Non standard flap conditions may also require adjustment of the roll angle to adjust for the non-standard body angle / AoA for a non standard flap setting.

Remember - the ultimate goal is for the hook point to cross the ramp at a standard height and touch down in the middle of the cross deck pendant pattern. That is why on 4-wire carriers the target was the 3-wire: the hook touchdown target is right in between the 2 and 3 wire.

As far a I can tell, FS carrier ops are based on a fixed glide slope basic angle, no roll angle. I do not know about AG constant runout distance. There are people here who do know the answer though.

 

[PhantomTweak]

2) The airplane seems to stop pretty quickly, even at the maximum landing weight of 75,000 pounds. There's the .cfg entry "cable_force_adjust" that I haven't fiddled with. Maybe that's it?

Yes, that's the one.
Try lowering to 0.75. If still to abrupt, lower it a tenth. 0.65, for example. You want it set to where the nose gear stops a little short of the end of the deck. Enough to turn back onto the rest of the carrier, if you see my meaning.
Another possibility, and this is useful if the plane veers too easily to one side or another when it catches the wire as well, is to move the hook's longitudinal position rearward some. Use 10 foot increments, and shorten to zero in on the correct setting. The farther aft it is, the less it will veer in an off-centerline trap. You don't want TOO much, or it will allow the plane to run off the end of the deck. And never veer off centerline, no matter where on the wires it catches, left/right. The below settings were the result of studying the NATOPS for the plane and the ship's air-ops, as well as a lot of research into just how far off a Hornet CAN land without tipping over.

For example, the FSDT F/A-18C tailhook section is

[tailhook]tailhook_length = 6.34//6.85
tailhook_position = -79.0, 0, 1.5//-49.0, 0, 2.5//-49.453, 0, 1.556
cable_force_adjust = 1.74

Note the longitudinal position. The Hornet isn't anywhere close to that long, but that's where we had to set it, or it would veer off and nose over/wing over at the slightest bit off off-centerline. It took some experimentation, but this is what I eventually wound up with. Same for the Cable Force Adjust. With the tailhook positioned that far aft, and given the plane's max landing weight, WOD requirement (35 kts) according to the NATOPS, and so forth, this is what it had to be.

Note that the settings in the aircraft.cfg do NOT affect the visual model in the least. Not these sections. Yes, the contact point section can change where the plane sits on, above, or in the surface of the airport, but that's a completely different animal.

Finally, make sure that the three contact point settings that control how the landing gear behave,
//9 Static Compression (feet, 0=rigid) //10 Max/Static Compression Ratio
//11 Damping Ratio (0=Undamped, 1=Critically Damped)
are set correctly for the landings on a carrier.
Remember that landings on a carrier means flying the plane down onto the deck. NO flare. Keep the same AOA, speeed, and sink rate, all the way down to where the wheels actually contact the deck. Navy planes don't flare for landing. The landing gear has to be sturdy enough, and have the capability of taking a much greater load, and flex rate, at touch-down.

BTW, since most of the carriers available for FSX steam at 25 Kts, I always set a wind of 10 kts over the angle deck. The speed the carriers steam CAN be changed, but it requires changing the sim.cfg file. And it must be calculated. Much easier to just add wind down the angle deck as required.

Hope all my babbling is slightly helpful...
Pat☺