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Stern Conversion Turning Room


Horns

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I was looking at a 2002 version of the CNATRA P-825 document (part of a kindle book so I can't link it), and I noticed that it said "Following extensive, and often dangerous, flight testing, we pushed the T-39N to the edge of  the envelope and concluded that 20,000 feet (roughly 3 1/2 nm) is the ideal amount of turning  room for the reattack intercept. As you can imagine, the T-39N will need more lateral  displacement than high performance fighters".

The 2014 and 2017 revision of P-825 (p110) doesn't talk about the amount of turning room required by a particular aircraft, but instead it talks about the "40K lateral separation goal", and in the excellent video Spiceman made on F-14B Intercept Geometry he refers to this as a number quoted for the F/A-18 and says that it makes sense for the Tomcat.

There must be some big difference between what's being spoken of in each text, but I'm new to intercept geometry and I just can't see it. Could anyone hazard a guess at why these values are so different? Both talk about arriving at this LS at 10 nm with the goal of arriving in the bogey's rear quarter, so  I think they're talking about the same maneuver. Can anyone enighten me?

I'm trying to figure this out for use in the F-14, that's why I placed it here.

 

 EDIT: I want to be clear that I was not and am not suggesting Spiceman was wrong. I believed the numbers given by him and the relevant documents were correct, my question was only meant to ask ‘what am I missing?’. For transparency, this edit was added after lunaticfringe’s reply and my response to him.


Edited by Horns
Clarifying Question

 

 

Modules: [A-10C] [AJS 37] [AV8B N/A] [F-5E] [F-14] [F/A-18C] [FC3] [Ka-50] [M-2000C] [Mig-21 bis] [NTTR] [PG] [SC]

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A T-39N Saberliner versus an F-14 or F/A-18?  One has no weapons, whereas two do.  One is stressed to, perhaps, 3G and a cruising speed of 450 knots, whereas two are stressed to 7G and can blast around at 550 knots without breaking a sweat.  And one has negligible radar capability and integration to the crew to maintain good positional tracking on a visual intercept conversion, whereas the other two are solid.  

The Saberliner is performing a slower intercept, thus its turn circle is smaller, even at a substantially lower available G.  The Hornet or Tomcat starting its conversion turn is going to be coming in hotter, and so while it can get away with more G to maintain that pure pursuit turn (nose on, looking for the bandit to be on the bandit's 3/9 at 90 degrees), it's also going to have a larger turn circle.  Thus, the lateral separation has to be bigger to make it "fit". 

The keys of what makes a training platform pull a maneuver well are different than the tactical airframe. In certain situations of speed and altitude the F-14 or F/A-18 could perform a closer conversion, but it's of marginal utility and generally asks for trouble (the danger part), whether inadvertent (collision) or hostile intent.  


Edited by lunaticfringe
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6 hours ago, lunaticfringe said:

A T-39N Saberliner versus an F-14 or F/A-18?  One has no weapons, whereas two do.  One is stressed to, perhaps, 3G and a cruising speed of 450 knots, whereas two are stressed to 7G and can blast around at 550 knots without breaking a sweat.  And one has negligible radar capability and integration to the crew to maintain good positional tracking on a visual intercept conversion, whereas the other two are solid.  

The Saberliner is performing a slower intercept, thus its turn circle is smaller, even at a substantially lower available G.  The Hornet or Tomcat starting its conversion turn is going to be coming in hotter, and so while it can get away with more G to maintain that pure pursuit turn (nose on, looking for the bandit to be on the bandit's 3/9 at 90 degrees), it's also going to have a larger turn circle.  Thus, the lateral separation has to be bigger to make it "fit". 

The keys of what makes a training platform pull a maneuver well are different than the tactical airframe. In certain situations of speed and altitude the F-14 or F/A-18 could perform a closer conversion, but it's of marginal utility and generally asks for trouble (the danger part), whether inadvertent (collision) or hostile intent.  

 

Thanks, that explains it perfectly. When the older document mentioned the T-39 needing more displacement than ‘high performance’ fighters I hadn’t considered that would only be true within similar speed regimes and conditions, which is obvious now you say it. Much appreciated.

 

 

Modules: [A-10C] [AJS 37] [AV8B N/A] [F-5E] [F-14] [F/A-18C] [FC3] [Ka-50] [M-2000C] [Mig-21 bis] [NTTR] [PG] [SC]

Intel i7-12700F, Nvidia GTX 3080, MSI MPG Z690 Carbon WiFi, 32GB DDR4 @ 1600 MHz, SteelSeries Apex Pro, Razer Basilisk 3

VKB Gunfighter 3 w/ F-14 grip, Thrustmaster Warthog throttle, Thrustmaster MFD Cougars x2, MFG Crosswind,

DSD Flight Series button controller, XK-24, Oculus Rift (HM-A)

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I'd suggest taking those books (and even the 2008 edition) with a grain of salt: each uses a different platform, and therefore many parameters change.

They are a spectacular source to build the forma mentis, but they are too elementary and academic in many aspects. For instance, to recognise a bogey jinking in altitude, the trainee should use the elevation strobe. I mean, yeah, it works, but when you translate it to DCS you have more tools available, often more direct and immediate.

IIRC the F-4 sets the DT→CT to build circa 7nm, back to the 40k ft of LS goal then (or vice versa, since the F-4 is older 🙂 ).

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Cheers, good point and will do. I was reading the older version of the doc because the F-14 was still in the fleet then (unlike the newer ones where the F/A-18s were the only fighters remaining) so I hoped that they might share values that were relevant to the Tomcat, but they just seemed to referenced the trainer aircraft instead. As you say, it provides an opportunity to learn to apply the tools the aircraft provides to solve these problems, so it's not all bad 🙂 

 

 

Modules: [A-10C] [AJS 37] [AV8B N/A] [F-5E] [F-14] [F/A-18C] [FC3] [Ka-50] [M-2000C] [Mig-21 bis] [NTTR] [PG] [SC]

Intel i7-12700F, Nvidia GTX 3080, MSI MPG Z690 Carbon WiFi, 32GB DDR4 @ 1600 MHz, SteelSeries Apex Pro, Razer Basilisk 3

VKB Gunfighter 3 w/ F-14 grip, Thrustmaster Warthog throttle, Thrustmaster MFD Cougars x2, MFG Crosswind,

DSD Flight Series button controller, XK-24, Oculus Rift (HM-A)

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Yep, it does help a lot, no matter the fact that it was written for the "elementary school" on the T-39 🙂

In fact, it teaches much more than the 2017 versions. For instance, the relations between the angles, how the BDHI is the coolest piece of equipment you can desire, and how the five Cuts can be used to describe a manoeuvre or a scenario, and the effects they have on the LS (the 2017 version says that the cut is not used anymore - which is fair for modern aircraft). It also teaches you some neat relations, like the CCC formulas, in case you don't have the TID track to immediately find the Collision Bearing. And there's a lot more!

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full_tiny.png

"Cogito, ergo RIO"
Virtual Backseaters Volume I: F-14 Radar Intercept Officer - Fifth Public Draft
Virtual Backseaters Volume II: F-4E Weapon Systems Officer - Internal Draft WIP

Phantom Phamiliarisation Video Series | F-4E/F-14 Kneeboard Pack

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