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On a T-38 Talon on static display at a museum, I spotted a trio of aerodynamically shaped devices located aft of the vertical tail and between the engine aftbodies fore of the nozzles, as shown in the photos. If these are vortex generators (VGs), what in the world are they doing there where there's no aerodynamic surface aft of them for the energized vortices to flow over? Could they be some other sort of protuberance, such as antennae for some system on the aircraft?

from the aft end from the side, looking over the top of the engine aftbody/nozzle

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  • $\begingroup$ Can you tell us what museum? I've looked through Google images of T-38 tails and none that I've seen have the same "fins" on the back. It would help to know what variant of the T-38 you are photographing, maybe even a tail number. $\endgroup$ – Ron Beyer Aug 16 '16 at 3:14
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    $\begingroup$ The aircraft in question is 58-1192 (picture), an YT-38A, which is one of the first prototypes of the T-38. $\endgroup$ – Jordy Aug 16 '16 at 6:39
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    $\begingroup$ There doesn't have to be any aerodynamic surfaces for it to act on, but there is something else that may benefit from having vortices created there - the end of the aircraft. The drag created from the bound airflow coming off the fuselage and lower tailplane at that point may be reduced by disturbing the airflow at the point where the drag increases - in this case, where the aircraft ends. $\endgroup$ – Moo Aug 16 '16 at 17:49
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    $\begingroup$ @UnrecognizedFallingObject they may have changed something further forward on the fuselage, which changed the airflow over that part of the aircraft, reducing the need for the vortex generators, or any number of things :) $\endgroup$ – Moo Aug 16 '16 at 18:08
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    $\begingroup$ My car has small protrusions around some of the windows that creates a disturbance to prevent low-frequency oscillations when the windows are cracked or open. The sun roof has a particularly interesting 'comb' that pops up. You can actually pull it down with your fingers and experience the weird pressure oscillation it prevents! Since this is right next to a very un-streamlined feature on the fuselage, I can imagine it serves some similar purpose. $\endgroup$ – Daniel Oct 15 '16 at 16:02
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There are a couple of possibilities, both out of the T-38 Flight Operations Manual.

It's a nozzle for a smoke generator. This was an option on the T-38 airplane to generate a smoke trail behind the aircraft for training purposes.

If possible, inquire if that aircraft was an AT-38B. Those aircraft apparently had an optional 'ballast box' in that region, which I'm assuming was some sort of a counterweight placed there in conjunction with the bomb racks for practice bombs and other range equipment.

As to the vortex generators? Who knows!

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    $\begingroup$ Hi Carlo, I agree they probably have to do with smoke. I would guess the opening below the three vanes is for smoke, and the three VGs keep the separated flow between the engine nozzles down so the smoke trail stays more coherent. Just a guess, though. $\endgroup$ – Peter Kämpf Aug 16 '16 at 6:40
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Several of the aircraft I have worked on have vortex generators just a head of the fuel dump area, especially if they're near the exhaust. Those do appear to be right about the fuel dump on that aircraft.

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  • $\begingroup$ Interesting -- did the T-38 ever have support for dumping fuel though? $\endgroup$ – UnrecognizedFallingObject Oct 20 '16 at 22:09
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    $\begingroup$ I believe the fuel dump vent was on the vertical fin right above the rudder on a T-38. $\endgroup$ – Carlo Felicione Oct 21 '16 at 4:41

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