So here is what I used:

1) Download Massimo Taccoli’s FS2002 X-15 (x15c.zip)
2) Drag and drop the X-15c folder with all contents to your simobjects/Misc directory.
3) Delete or hide the “Panel” and “Sound” folder, aircraft.cfg and X-15c.air files.
4) Create a sim.cfg file in the X-15c folder with the following entry

[fltsim.0]
title=X-15c
model=
texture=

[General]
category=GroundVehicle

[contact_points]
destroy_on_impact=1

[EFFECTS]
wake=fx_wake
water=fx_spray
dirt=fx_tchdrt
concrete=fx_sparks
touchdown=fx_tchdwn

[DesignSpecs]
max_speed_mph =4520
acceleration_constants = 50000.4, -20.4     //Time constant (effects responsiveness), and max G acceleration
deceleration_constants = 50000.4, -20.4     //Time constant (effects responsiveness), and max G acceleration

5) Add the following to the weapon section of the B-52 CSWeapon.xml

       <Weapon>
           <Gun>X-15c</Gun>
           <Shell>X-15c</Shell>
           <Unlimited>0</Unlimited>
           <Station name="RightWingInner" params="5.5,2,-4,0,0.087,0,6" />
           <Mode name="SINGL" setshots="1" shotrate="1" sequence="1" reset="0" />
           <DefaultMode>SINGL</DefaultMode>
       </Weapon>

6) Add the following to the gun section of the B-52 CSWeapon.xml


       <Gun>
           <Type>RocketLauncher</Type>
           <Name>X-15c</Name>
           <Desc>X-15c Air launched test vehicle</Desc>
           <HudString>X-15c</HudString>
           <Pix />
           <ConeAngle>0.005</ConeAngle>
           <TargetRange>2500</TargetRange>
           <MaxGForce>10</MaxGForce>
           <Delay>0</Delay>
           <FxFire />
           <Sound name="..\..\..\Captain_Sim\Weapon\Sound\csweapon_rocket2.wav" gain="4.0" />
           <Shell>
               <Name>X-15c</Name>
               <Desc>X-15c Air launched test vehicle</Desc>
               <HudString>X-15c</HudString>
               <Pix />
               <Container>X-15c</Container>
               <FxWake>csweapon_ai_smoke_mid</FxWake>
               <Weight>15420</Weight>
               <TargetWeight>10000</TargetWeight>
               <Lifetime>60.0</Lifetime>
               <CtrLifetime>60.0</CtrLifetime>
               <Efficiency>0.3</Efficiency>
               <RadiusRatio>1.0</RadiusRatio>
               <DragCoeff>0.04</DragCoeff>
               <OpArea>0.004</OpArea>
               <GravCoeff>-0.12</GravCoeff>
               <InitSpeed>0</InitSpeed>
               <EngThrust>313000</EngThrust>
               <ThrustDuration>60</ThrustDuration>
           </Shell>
       </Gun>

7) Test it out, it is in the Rocket section the weapons, there are 6 shots so you can get a good look at it.

There are  currently 2 bugs:
1)The landing gear. Sometimes it is out, sometimes not. I don’t know why
2) Sometimes it auto destructs on launch. I don’t know why. I guess that’s why I’m flying the launch vehicle and not the X-15.

Let me know how it works out.

--Dan