SweetJet: Reaching Mach 3 (966 m/s) [0.15 STOCK]

[Cezary]

I\'ve been playing around with the different engine types in KSP 0.15 and I decided to build a super sonic jet. For those of you not familiar with the speed of sound, it is roughly 340 m/s at sea level and goes down as the air gets colder and altitude gets higher. By my rough estimation, the velocity required for Mach 1 at 15,000 - 20,000 meters (on Kerbin, not Earth) is 322 m/s. Mach 3 would therefore be 966 m/s.

If you think about it, reaching that kind of velocity is easy. We\'ve all done it before using rockets. It\'s even possible to go that fast in the atmosphere with enough thrust. So where lies the challenge? I\'m glad you asked.

Here\'s the criteria for my super sonic jet:

• 
  [li]No cheating (use Space Plane parts only)[/li]
  [li]Takeoff and land horizontally[/li]
  [li]No decoupling boosters (every original part has to be attached during Mach 3)[/li]
  [li]Completely reusable (no detaching landing gear, etc...)[/li]
  [li]Balanced for atmospheric flight AND high-altitude speed attempt[/li]
  

Easy, easy, easy, easy, um... what?

Step five is the tricky part. A poorly designed jet will pull up or down on you, even with ASAS turned on. The balance of your plane depends not only on lift surfaces like your wings, but also on engine location and power. Even if you manage to place all of your components such that your plane flies straight at sea level, higher altitudes provide less lift and less air for your engines. So what do you do?

I designed the awesomely named SweetJet to balance both at sea level and at 15 - 20km altitudes. The trick is that it\'s not perfectly balanced between those altitudes. At sea level, the wings and canards combined with the main engines provide a smooth ride that begins to pull upwards the higher you go. This is mainly because the engines gain thrust faster that the wings lose lift in the thinner air. Rather than the basic jet engines, I chose the TurboJets for their ability to get me to 15km.

Once high enough, the Toroidal Aerospike Rocket activates and in conjunction with the TurboJets propels the craft up to Mach 3. The high-altitude 'nose up' behaviour is corrected by the position of the rocket engine and the jet becomes balanced yet again. I highly advise to keep the altitude under 20 km as the air becomes too thin for the control surfaces to keep the jet steady.

Once the Rocket runs dry, you should descend to 12 km and fly your plane to the nearest landing zone. I tested the SweetJet by rotating it 180 degrees so that I would be over land instead of water.

*** Ship download link ***

1062 m/s = Mach 3.3

[Guest]

TBH, the aerospike rocket is not a spaceplane part, but a rocket engine. It\'s balanced for 'space' tanks.

[Tim_Barrett]

To it under 1km. Cry. :

[Cezary]

TBH, the aerospike rocket is not a spaceplane part, but a rocket engine. It\'s balanced for 'space' tanks.

Whoopsie. I assumed it was for space planes since it\'s new for 0.15 and the manufacturer is C7.

[Guest]

It sure does look the part, but all it\'s stats are comparable with rocket engines. It\'s actually the most powerful stock engine, with much more thrust than old ones.

[Ted]

I\'m going to attempt to reach ~700m/s without the aerospike.

I shall post the results, I doubt it will be a long flight though

[xclusiv8]

I\'m going to attempt to reach ~700m/s without the aerospike.

I shall post the results, I doubt it will be a long flight though

Looking forward to your results =D I\'ve been trying to achieve that myself =)

So far i max out at 632m/s @ 15km

Edit: I made it =D This jet is the best ive made so far. It was so stable that i could just drop from 15000m to 0 without loosing control. Just before the ground it was going around 30m/s and it didn\'t crash =D. AMAZING!

[Ted]

Finally reached 701m/s on air breathing engines, it was around 15,000m. Ran out of fuel just as I reached it.

I actually had two other full tanks of fuel on board, the engines just weren\'t wired correctly in order to use the fuel.

Also, I reckon with a bit of tweaking I could get it to 750m/s as one of the engines broke off during take-off.

Flight log:

(I pretty much span out of control once the engines turned off and I tried to manoeuvre, the plane was very back-heavy)

The monstrosity of jet engines that got me to that velocity:

(This is about 10 seconds before I hit 701m/s.)

[xclusiv8]

Finally reached 701m/s on air breathing engines, it was around 15,000m. Ran out of fuel just as I reached it.

I actually had two other full tanks of fuel on board, the engines just weren\'t wired correctly in order to use the fuel.

Also, I reckon with a bit of tweaking I could get it to 750m/s as one of the engines broke off during take-off.

Flight log:

(I pretty much span out of control once the engines turned off and I tried to manoeuvre, the plane was very back-heavy)

The monstrosity of jet engines that got me to that velocity:

(This is about 10 seconds before I hit 701m/s.)

Try using less engines =) I achived 726m/s with two engines =) Check my post higher up.

[sal_vager]

Surely the 'space' part of 'spaceplane' requires rocket engines, making all 4 rocket engines usable, just try using either jet engine at 70km+.

[Cezary]

Alright... I managed to hit 726 m/s using just 2 TurboJets. Using 5 tanks of fuel, the plane, named Floater, flew 700km North from the KSC before coasting down just short of the polar ice cap.

***

Ship Download Link ***

[Tim_Barrett]

Did anyone see my above post? There is very little drag to the full atmosphere below. Everyone should do under 1km for comparable results if this becomes a challenge.

[Ted]

Did anyone see my above post? There is very little drag to the full atmosphere below. Everyone should do under 1km for comparable results if this becomes a challenge.

Shall give this a go.

This time with less engines as well

Edit: I can\'t quite get above ~250m/s. :\'(

I shall try some other designs tomorrow.

[Tim_Barrett]

Shall give this a go.

This time with less engines as well

A long time ago I got really fast (1.1km/s?) under 1000m with this ancient jet, but I have to re-do everything with all of the new game features.

[thec0w]

hmm kinda wanna have a go at this. Is using mechjeb ok just for the sake of not having to babysit the plane quite so intently? I think I have one that does 850 m/s or so using everything else stock besides mechjeb. Though when i have more time i could probably do it without and give it a 100% stock go i suppose