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S-32 complete, now for an upgrade!


JetGoFast
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Firstly I would like to give my thanks to @swjr-swis and @Snark for the multitude of suggestions on my little journey.

Thank you!

Now,

After taking in the advice given by those fine gentlemen(or ladies) I have constructed this-

These are screenshots of several versions of the plane I made.

The first iteration, S-32, was too unstable so I added vertical stabilizers and shifted the canards forward and the ailerons back. 

S-32.2 had issues with heat so I added the nose cones to act as an ablative heatshield. I also added heat sinks for the engines and the nose cones.

S-32.3, I added batteries at first because the craft was running out of electricity too fast from the heatsinks. After another test or two, I added that third engine to put her over 1700 m/s.

The next issue to be addressed is how to eke out more power from the Rapier engine. When that is done I need a new method of dealing with the temperature without sacrificing aerodynamics.

 

Would any of you kind fellas have some suggestions to help me achieve my dream of being the fastest air-breathing jet around?

 

Many thanks,    -guy

 

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3 hours ago, JetGoFast said:

The next issue to be addressed is how to eke out more power from the Rapier engine. When that is done I need a new method of dealing with the temperature without sacrificing aerodynamics.

I haven't looked at the screenshots to deduct if you have already done this, but what if you replaced the fuel tanks the RAPIERs are mounted on with the intercooler parts (can't remember their names)? They also suck in air, so they would act as a second air intake and would increase the power of the RAPIERs.

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7 hours ago, JetGoFast said:

Would any of you kind fellas have some suggestions to help me achieve my dream of being the fastest air-breathing jet around?

Looks great!  :)

This is pretty minor, but that pointy 0.625m section you've got up there on the nose,

MnRScEG.png

...I'd suggest getting rid of it.  Given the way KSP aerodynamics work, I believe that it accomplishes nothing but adding some drag.  (Hopefully a fairly small amount of drag, since it's only 0.625m and has a pointy front, but it will be non-zero, and getting rid of it would eliminate that smidgen.)

 

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1 hour ago, Snark said:

...I'd suggest getting rid of it.  Given the way KSP aerodynamics work, I believe that it accomplishes nothing but adding some drag.  (Hopefully a fairly small amount of drag, since it's only 0.625m and has a pointy front, but it will be non-zero, and getting rid of it would eliminate that smidgen.)

I agree with @Snark. Not so much due to drag - the RAPIER brings enough thrust to overcome that tiny extra bit - but because you can achieve the same thermal protection effect with a much smaller and lighter part: the linear RCS port. Attach it radially to the cockpit, then rotate it properly and offset it right in front of the cockpit nose. KSP does account for the wake, so you will notice the cockpit takes longer to heat up with just that one simple and lightweight trick.

 

9 hours ago, JetGoFast said:

S-32.2 had issues with heat so I added the nose cones to act as an ablative heatshield.

Ablation is a real effect in KSP, but not with just any part; you would have to use actual heatshields that include the ablator resource. You can find those in the thermal section. They can help keep heat away from less hardy parts, and ablation works even when they're not facing the air directly. They also have a very high temp tolerance and are configured to transfer heat more slowly. A good place for them is right behind 1.25m nosecones, for example. Just don't face them 'bare' into the wind (unless its at the bottom of a command pod on a reentry from space), they're very draggy by design.

 

9 hours ago, JetGoFast said:

I also added heat sinks for the engines and the nose cones.

Three things to keep in mind when using heatsinks/radiators to cool in-atmosphere:

  • They only draw heat away from the part they are directly attached to, and the parts attached to that (so at most one part 'away').
  • You need to ensure they are not directly in the airstream - radiators by nature are just as good at soaking up heat as they are at radiating, so they need to be 'behind' other parts in the airstream to prevent them from having the exact opposite effect from what you want. Even then, as you speed up and the surrounding air heats up, they will become less efficient.
  • They are unfortunately very draggy parts, even in their most optimum orientation. So their use will always be a compromise - whatever cooling they can achieve will come at a cost in top speed.

 

9 hours ago, JetGoFast said:

S-32.3, I added batteries at first because the craft was running out of electricity too fast from the heatsinks.

If you add a bit of Oxidizer to your tanks, doesn't need to be much, you could use a fuel cell for the power generation. The fuel cell will double as battery. Remember to activate it.

 

Other than the above, keep in mind that while flying higher does help to lower drag and heat, it also lowers the total thrust of your RAPIERs. If you really want to get the utmost out of them, you literally need to face the heat and fly lower! But yes, first make sure your craft is dealing with the high temps you are already seeing.

Fine-looking craft so far.

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Put small nosecones (0.625 m) on the empty construction nodes at the back of the rapier engines, with KSP's aerodynamic model this will be more aerodynamic - yes the end where the flames are coming out, trust me, as long as you take the small ones, it should be fine. I do that on almost every rapier SSTO.

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5 hours ago, s_gamer101 said:

Put small nosecones (0.625 m) on the empty construction nodes at the back of the rapier engines, with KSP's aerodynamic model this will be more aerodynamic - yes the end where the flames are coming out, trust me, as long as you take the small ones, it should be fine.

A small nosecone will remove a small bit of drag, but if you're already doing this, might as well go all the way: use a 1.25m part to get the full drag-saving effect. The round nosecone works, but the circular intake is quite effective as well. Just offset it inward so it won't block the exhaust and you're good.

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Two tips here, first using the inline cockpit then the MK2 to 1.25 meter fuel tank should give better heat handling, you should also be able to run on one shock cone you can put in front. 
Another option is to put an 1.25 m fairing in front as they can handle plenty of heat. 

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