Stock Whiplash/NERV SSTM , Astrojet Citation

[AeroGav]

https://kerbalx.com/AeroGav/Astrojet-Citation

5 Kerbals. 2200 dv in orbit.  Inline clamp o tron. Vernier engines, fly by wire hub.  Able to horizontally land on Minmus and Duna.

This project arose from two inspirations.   The  first was a design sent to  me by Bewing.  It still shares the basic layout , but you could say I stretched it a bit

Spoiler

 

Original ship

 

The other was a project of mine to try and achieve the best possible handling for manual control.  I wanted to avoid CG shifts as fuel burns off, without relying on any fuel balancer mods and keeping draggy struts to a minimum.

When running off jet engines , this is easy - just balance the number of tanks fore and aft of CG, so the centre of mass does't move.    However, the NERVs, like all rocket engines do their best to mess your spaceplane up.  First, they refuse to take from wing tanks, strake tanks, in fact anything radially attached and not of their own stack.  Second, from all the tanks they can access, they drain the front most first before working backwards, messing with your CG.  So , there is only one fuel tank on the same stack as the NERV , a mark 1 liquid fuel fuselage (400fuel), and i arranged things so the midpoint of this tank is exactly on our CG.  Since this ain't enough fuel to go to orbit, I ran a fuel line to the largest available tank - the Fat 455 airplane wing  (600 fuel), and arranged this to be over our CG too.

Spoiler

 

The first thing I had to do was find out where the CoM of the wing itself lay.  This was a process of trial and error,  moving the wing back and forth until i found the location where emptying or filling the wing tank would have no effect on the vehicle's CoM.   It turns out the wing's CoM lies halfway between the rear spar and the trailing edge.   You'll notice that placing the wing in such a way is going put our CoL too far forward.  I had to add substantial lifting surfaces to the rear to correct for this. 

 

 

 

 

After all the effort i put into balancing the plane,  I at this time discovered Mechjeb.   It takes a lot of the stress away and makes trying different flight profiles very repeatable.   In between the physics bug that makes all aircraft, however stable, gradually roll to one side or other, and the the lack of joystick support, it is impossible to fly smoothly, hold the desired pitch angle with single degree accuracty AND make rapid pitch changes when going through sound barrier/speed run etc.    

Here's some video of me flying to space with Mechjeb.     Having found the optimum pitch angles etc with autopilot, it should be possible to make a manually controlled flight that gets quite close to this using pitch trim adjustments - with the proviso it'd probably be better not to attempt the kind of manuvers i make around the transonic region, and just hold constant 4-6 degree pitch, using the NERV to boost us through it.

 

The jet's party piece is horizontal landing -

The pure SSTO version of this craft can reach Duna, aerocapture/brake (20km or above), land, take off to orbit, but probably not finish the burn to return to Kerbin.  It has a docking port so you can refuel it in orbit of Kerbin or Duna.  It is unlikely to be able to aerocapture Kerbin on the return leg, due to low heat tolerance parts.

I have now developed the "Citation X",  a no-holds barred version of this ship that includes Panther jet booster pods and has the ability to shed the Rapier (note, if your destination is Laythe you might want to hang on to that!).https://kerbalx.com/AeroGav/Astrojet-Citation-X 3700dv in kerbin orbit.

Spoiler

 

 

 

Edited May 15, 2016 by AeroGav

[Redshift OTF]

Wow, great job there. It looks difficult to get into orbit but then to have a good amount of DeltaV to use in space you have to be on the edge of getting enough height and speed for the Whiplashes to work. @Rune is good at ultra-efficient SSTO's so he might be able to give you some optimisation tips.

[AeroGav]

Redshift -  I suppose I've had a lot of practice when designing it but I don't think it's difficult to just get to orbit if that's all you are trying to do.    There is so much spare fuel you'd have to mess up badly to not get to there.  If you don't use enough nose up trim and don't throttle back you can overheat it (done that),  and if you pitch up too much you'll loose delta V.    For manual flight i'd just say use pitch trim for 3 degrees gradually increasing to 5 or 6 by supersonic,  toggle on the nukes at sound barrier briefly,  lock in SAS at 25km.   There's a decent margin between thrust and drag once the nukes kick in.

[Redshift OTF]

Oh I can see by your second video you also have Rapiers. I thought you only had one Whiplash! Lol. That would be a challenge. I guess it is more user friendly than I first thought. Good job.

[AeroGav]

2 minutes ago, Redshift OTF said:

Oh I can see by your second video you also have Rapiers. I thought you only had one Whiplash! Lol. That would be a challenge. I guess it is more user friendly than I first thought. Good job.

Nope sorry ! No RAPIERs lol (i was just rambling in my text bubbles) .  Just one Whiplash and 2 Nukes.   It's a Toyota Prius, not a Chevrolet Camaro.   Well, I guess ease of use is about having a decent margin between running out of fuel on one hand,  and stagnating because you dont have enough power on the other.  And not melting.  I'd rather not talk about the last one.

[Redshift OTF]

Well this is impressive then! How much does the plane weigh? My only other thought is that wouldn't you end up using more fuel trying to get the plane in orbit compared to if you used 2 Whiplashes?

[AeroGav]

8 minutes ago, Redshift OTF said:

Well this is impressive then! How much does the plane weigh? My only other thought is that wouldn't you end up using more fuel trying to get the plane in orbit compared to if you used 2 Whiplashes?

30 Tons, so we're close to the limit of what one airbreather can do.   One Whiplash engine gets me up to Mach 3 and 19.5km before i have to light the nukes.  Mach 3 is the speed at which the Whiplash makes max power, if you go faster the thrust starts to tail off.  However, the atmosphere also starts getting thin very quickly, thrust halves with every 2km in height, so you wouldn't gain that much more from bringing another engine.   Bear in mind , the Whiplash weighs 1.8 Tons and the current empty weight is about 14.5 Ton,  so the dead weight will hurt our delta v.

The Citation X variant uses a Rapier, which produces more thrust at high speed but less down low.  As a result the gains you make from being faster/higher before starting the nukes,  are offset by the worse isp and weaker thrust subsonic, we waste more fuel down low.   That's why it has a nice set of panthers boosters on wing pods :-)