Let's Go Hypersonic! [Help Needed]

[Selrahc4040]

Hey all, I'm not much for introductions, so let's get straight into the thick of it.

I recently got back into KSP; specifically the in-atmosphere portion, and I've been interested in seeing exactly how fast I can get a plane to go. With a little bit of effort, I started out with this beauty:

http://i.imgur.com/MZYUUKZ.png

She functioned GREAT, up until Mach 4, when the Ram Intakes started to fail. So, in the spirit of KSP, I thought "MOAR INTAKES". Ten Minutes later, I get this:

http://i.imgur.com/tKi5dWI.png

But, for some reason, the Scoop Air Intakes don't work as I had understood them to. More Speed = More Air Intake, correct? Not really. As I was nearing Mach 2, I could see that the Scoop Intakes were getting next to useless, only bringing in .01 air per. What am I doing wrong? Can any of the intakes function past Mach 4? Do I just need even MOAR intakes? Thanks in advance!

(Note: The goal here is to eventually go Hypersonic, or Mach 6)

(Also, if someone can tell me how to embed images, I'd be much obliged.)

Edited November 17, 2013 by Selrahc4040

[[ Jeremy ]]

Ram air intakes are the best ones suited for high altitude / high speed flight, whreas the radial scoops are good for low altitude flying. The best you can do is just MOAR RAM AIR INTAKES!

[Selrahc4040]

MOAR RAM AIR INTAKES!

But I only have the one space on the end of each engine Nacelle. Maybe Have in-line air intakes? Or can I have separate air intake nacelles powering the engines?

[Geschosskopf]

You can stick air intakes all along the wing leading edge using Cubic Octagonal Struts. If you want to look less kluged, put twin or triple stack adaptors on the fronts of your fuel tanks and then fill them up with intakes.

[NeMeSiS]

But I only have the one space on the end of each engine Nacelle.

Put a bicoupler at the end of it, and you have double the space.

[Selrahc4040]

Wow, never thought of that! Thanks for the advice. One question though: Can they even function at Mach 4+? (1360 m/ps)

[arq]

Max speed is based on intake/mass ratio, assuming that you can get up high enough to hit flameout. More intakes means flying higher, which means less drag and flying faster.

Reading the 'intake air' stat is imprecise for the entire vessel and especially so for individual intakes.

As others have suggested, the ram intakes are the best option. People like to clip them together in long lines of alternating intakes and cubic struts.

[rpayne88]

How much altitude were you gaining? If you wind up at high altitude, no amount of intakes will work.

[arq]

Wow, never thought of that! Thanks for the advice. One question though: Can they even function at Mach 4+? (1360 m/ps)

The turbojets can technically go up to nearly 2400m/s, though thrust starts falling rapidly above 2000m/s (but at this point it hardly matters because your throttle is so low because of the thin air). But this is nearly impossible to do below about 45km.

Your plane is rather big. It would be easier for you if you started with something smaller. Also, I think you have more fuel than you really need.

[Selrahc4040]

Your plane is rather big. It would be easier for you if you started with something smaller. Also, I think you have more fuel than you really need.

Go big or go home.

[Selrahc4040]

How much altitude were you gaining? If you wind up at high altitude, no amount of intakes will work.

I don't recall my exact altitude, but I was about halfway through the second bar of atmosphere.

[el_coyoto]

More Speed = More Air Intake, correct?

This is true if you fly level (with 0 m/s vertical speed).

The problem might be the altitude you reached, in which the increase of speed didn't compensate the decrease of air pressure because you are still climbing "fast" (let's remember that air pressure drops exponentially, so a small increase in altitude may result in a big drop of pressure).

I'm not an excellent SSTO pilot and sometimes it takes me time to get it right, but I try to gather as much speed as possible when I've left the densest part of the atmosphere. I try to limit my vertical speed to ~50 m/s or so, trying to balance the "more speed/more air vs more altitude/less air to breathe vs less air/less throttle" equation.

Being a mod user, I find Kerbal Engineer a useful tool in that case, with its ability to display (among others) V-Speed and the CraftVelocity / TerminalVelocity ratio.

So, long story short : yes, more intakes never hurt!

Good luck on your hypersonic aircraft!

[Selrahc4040]

Thanks for the link! It'll definitely come in handy.

[700NitroXpress]

A good technique is to put the long spike things in the aerodynamics tab on the plane and then attach a air intake to those like what I have shown in the first picture. The spikes can be placed in the middle of the wings and clip into the plane naturally. The air intakes on them will fuel all of the engines and allow your plane to operate in excess of 30,000 meters and above 2100 m/s.

This plane didn't start loosing engine power until it was over 28,000 meters, you could cruise at full power at that altitude.

Edited November 18, 2013 by 700NitroXpress

[Selrahc4040]

Impressive stuff, there! Thanks!

[numerobis]

I recommend reading the Machingbird thread in the challenges forum, to get tips. You can definitely exceed 2km/s below 30km; you just need a rated TWR of 2 (which, at 2km/s, is actually just TWR 1, since thrust falls off) -- that's roughly terminal velocity at that altitude. To be at full throttle at 30km you need about 8 ram intakes per turbojet.

At low altitude, awash with air, you need engines to make you move. At high altitude, engines are an impediment: they're heavy and don't change your max throttle, which depends only on how much air you can get.

[UmbralRaptor]

I'd say that the main problem with the original design is TWR. replace the forward cockpit with a ram intake, and the center engine with a turbojet, and things should go better.

In general, less is more. Though sometimes intake spam gives fun results.

(With 1 ram intake it would probably get 1600 - 1700 m/s. With 3-5, it could get one of those fun 75 x 30 km orbits when going east. This is just for fun.)

[Hodo]

I build my craft for use in FAR and DRE so they handle pretty close to what you expect out of a real aircraft. I found when doing a little research both here on these forums and around the web that the attitude of "MOAR INTAKES" is completely backwards when trying to fast. Intakes = Drag = Slower craft.

So I came up with this which is the fastest aircraft that is built in FAR in the Maching Bird Challenge.

As you can see it has 2 ram intakes. And it topped out at 2175m/s at a low altitude of 24.9km. I can break that if I used B9 parts and easily gone 2200+m/s at 29-34km. But I was using stock parts, which quite frankly are inadequate.

Then I had this... for the Airline challenge.

Javascript is disabled. View full album

Again not a lot of intakes on that thing, yet it cruised at 1700m/s around the world.

Then there is my Emergency Crew recovery vehicle, the SP-103 Jackal

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5 intakes, 4 jet engine 1 rocket. Top speed in atmosphere 2290m/s.

[barrenwaste]

You can put ram air intakes all over your ship and it will work. I like a more streamlined and convential look, though. You can get that by clipping. No, you don't need the dev console to clip. The key to clipping is the small cubic strut. Zoom in until you can see inside of a piece on your plane. You can snap a cubic strut anywhere inside that you could outside of the piece. Using this set up you can create "trees" of ram air intakes to put on the nose of your plane. This allows you to design your plane normal sized but have atomic engines running through your fuel tanks. Here is a link to my Pelican SSTO. I encourage you to download it, take it apart, and see how it ticks.

The link to the forum post of the KC-9 Pelican. The post has the download link for the spaceplane.

http://forum.kerbalspaceprogram.com/threads/57914-KC-12-Pelican-8-Kerbal-SSTO?highlight=pelican