# Trim Drag Question



## Zipper730 (Aug 28, 2020)

I was told a tailed-delta had advantages over a tailless delta at low speed and transonic speed, but inferior at supersonic speed. While some of the lower end of the performance envelope seems to owe to the ability to use flaps: The transonic area seems to have revolved around trim-drag. I've heard conflicting information over the years regarding pitch-control and maneuverability while supersonic on tailed-aircraft.

This leads me to wonder why there's lower trim-drag on tailless aircraft versus tailed aircraft: As best I understand it...

Transonic: Tailed design is more effective because...
The tailplane is further aft than on tailless design (i.e. delta) and can exert more leverage over pitch.

Supersonic: Tailless design is more effective because...
Elevons do not have their leading-edge into the airflow, where as a tail does, so you get lower shockwave intensity owing to the lack of the stagnation zone (it seems pretty much any surface, however sharp it seems, is blunt if you look at it close enough).

Now, I might be wrong here but, if I'm correct: Does the increased shockwave reduce the control-power of the stabilator below the effectiveness of the elevon? Or does it just add drag from the stagnation zone?



 davparlr
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 drgondog
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 FLYBOYJ
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 Shortround6
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 XBe02Drvr


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## MIflyer (Aug 28, 2020)

I don't know, but here is an interesting bit of data.

The F-106A has an automatic trim enhancement system that transfers fuel between tanks to help trim the aircraft when it gets just past Mach 1. There's a device I worked on that senses the ratio between total pressure (static plus ram pressure) and static pressure and I think when it gets to something like 1.14 it throws a switch and transfers fuel between tanks to correct for the aft movement of the center of pressure that accompanies going through the sound barrier. This improves the aircraft's acceleration by taking care of the trim change for the pilot. Working on that device led to me deriving an equation for one of the very few times in my engineering career. I filled the blackboard in the boss's office with my calculations - and then sheepishly realized that I already knew the answer and did not need to do all that.

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## Zipper730 (Aug 28, 2020)

MIflyer said:


> The F-106A has an automatic trim enhancement system that transfers fuel between tanks to help trim the aircraft


That, I actually know about. For some missions, IIRC, the transfer tanks were actually loaded since the fuel in them would be burned up fast, and once supersonic, the fuel control system would just move fuel from the main tanks to the transfer tanks and keep doing that until the correct CG was met, then it would burn as normal.


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