SSTO intake stacking questions

[kinnison]

I am starting to build my own Hybrid SSTO with small payload, or a hitchhicker for increased crew capacity and ability to reach the Mun or Minmus (not necessarily to land)

My initial design has a centerline Turbojet, a NERVA on either side, and another pair of Turbos on each side outside the NERVAs all in a line. I can get a ground TWR of over 3 at ground level, and thinking of letting the outside Turbojets flameout and going as high or far as i can with the center-line turbojet before achieving and circulizing LKO with the NERVAs (TWR of .3)

Should i think about staking intakes, or can I get away with just several intakes on the front of the craft?

Is stacking intakes cosmetic or effective? And do they have to be exposed to the leading edge of a craft to work?

[Tank Buddy]

Yes, stacking does allow you to get more intake air. I would assume that you would want to face them towards the prograde marker at high altitudes. Really, you don't need too many intakes, as long as you can reach a sufficient speed at the allowed altitude, and your NERVAs can take over. Just add MOAR if you aren't getting the speed/altitude you want. But don't overdo it. If push comes to shove, you may have to ditch your design if you can't get into orbit with enough fuel. Also, pics would help. Use BB code: Furthermore, you can just edit your first post and add the pics there.

Edited February 3, 2014 by Tank Buddy

[Claw]

As Tank Buddy said, stacking will get you more intake air but isn't always necessary. I usually use around 3 intakes, but have plenty of space planes that only use 1 intake.

You do want it to be pointed toward your prograde marker, but sometimes your prograde marker can be significantly below the level axis of your craft. So for looks, most people just place the intakes pointing straight forward on their aircraft. You cannot place it facing backward and get air intake. Also, if put your aircraft in extreme pitch maneuvers, you can risk premature flameout at altitude.

Here is one example of stacking intakes that isn't a complete eyesore.

Also realize that any intakes you have will feed whichever engines are running. So for example, say you have three intakes and three TurboJets you have a 1:1 ratio. If you shutdown the two outboard TurboJets, you will end up with three intakes feeding one engine (3:1 ratio). Depending on the weight of your plane, you might not need three engines to begin with. You can get 12+ tons into LKO pretty easily on 1 TurboJet.

Hope that helps.

[kinnison]

so what is a good ratio of ram intakes to to turbojets?

[thiosk]

i had no idea you could stack them like that. i've been using side boosters and quad couplers.

[Clockwork_werewolf]

Yea this is what is called air hogging. Each of those air intakes is attached to its own Cubic Octagonal Strut and then the strut is attached to the beam. if you do this and have between 8-15 air intakes per engine you find you can turbo jet up to very high speeds and heights. I have seen someone get an AP of 100k with only a turbo jet, 12 air intakes a tank and a probe core. They had no rocket engine so their PE was still within the atmosphere but I think you see the point. Some players consider this cheating and others think that it is acceptable as the game allows this (just).

[Claw]

There is no strict definition for "air hogging."

I generally use Round 3 intakes per turbojet, but I also have designs that use 1 intake per turbojet. Some people use 15 or more.

I also have a manned space plane that reaches an AP of 200k with only two radial mount (scoop) intakes and can circularize out there.

Air hogging just makes this easier to fly, even though there is no definition. So "air hog" if you want. Don't if you don't want to. And mounting them with cubic struts does not automatically mean you air hog.

I have also used side booster and quad couplers. Whatever I looks good at the time.

It's a game, have fun with it.

[Clockwork_werewolf]

I think if you have two or more air vents all clipping into each other in a way that could never exist in real life, that counts as air hogging.

I think if you add 4 air intakes for one engine but use a quad stack facing forwards to mount them this is not air hogging.

The difference is whether it could work in real life. People use the quad struts because they are very light where as quad couplers are half a ton.

For the optimal air engine power use 12-15 air intakes per engine.

I have been very careful to not state my opinion on whether to air hog or not.

I want to be clear it is a game and have fun how ever you like

[kinnison]

Thanks for the info, this will help

[Claw]

True, but in real life I can make the compression section longer with more stages, and it's all within a single compressor stack. That's more realistic than having a wall of four thinner compressors.

KSP doesn't allow users to create longer compressor sections in a single part, so the only option is to use more intakes. Also, on a lot of high performance airplanes, the intake and compressor sections are inside the airplane, not hanging off the side or pasted to the nose (i.e. clipped). The front portion of the intake is out of the body, but the diverters and compressor are internal.

Edited February 4, 2014 by Claw

[Clockwork_werewolf]

Good point, I never though of it that way.

I do know that two normal turbo jets with two compressors were able to get a jet fighter to 34k up in the real world so the idea is not off. I'm my opinion the normal air rams should have 8 times the air intake area and weigh about 0.2 to 0.6 tons. The extra weight is because otherwise people would still add 4 rams per engine and get 32 intake per engine. At 0.6 tons a ram adding two rams would be almost as heavy as another engine and 4 rams would be heavyer making it a decision to take one two or three rams per engine not just a matter of fitting them on.

[Jouni]

I do know that two normal turbo jets with two compressors were able to get a jet fighter to 34k up in the real world so the idea is not off.

34 km in Earth's atmosphere is only something like 22 km in Kerbin's atmosphere, because of different scale heights.

[Clockwork_werewolf]

true but this was with a one intake per engine craft that was not designed for the specific purpose of high altitude flying. I still feel rams are too weak and too light.

[Jouni]

Whatever the ram intakes are, they are definitely not too weak. The top airspeed of this thing with two turbojets, two ram intakes, and start mass of around 15 tonnes, is at least 1750 m/s at around 28 km:

The craft has to use part of the thrust to counter gravity, and it still almost reaches Mach 6. That's quite close to (or perhaps even past) the speed, where real-word ramjets become very inefficient and start breaking down. So assuming that turbojets with ram intakes are actually supposed to simulate ramjets (that can somehow operate below 200 m/s), the performance is pretty much as it should be. On the other hand, if they are supposed to simulate real-world turbojets or turbofans, they are far more powerful than their inspirations.

[Claw]

Yeah, RAMs and TurboJets actually seem pretty powerful now that I've gotten used to working with them. Stacking intakes certainly makes the TurboJets last a lot longer, but I see the primary benefit in that it just makes it easier to fly for those who don't want to (or can't) deal with the extra hand flying. Since it's just a game, I like the simplicity of the current mechanics.

Although I still stack intakes for multi engine setups to help deal with asymmetric thrust, but still only around 3:1 intake to engine ratio.

[Clockwork_werewolf]

So I decided to use some air hogging to show how over powered it is. This silly thing has 1600 more liquid fuel than it should because it is only the second version (the first didn't have enough trust to leave the launch pad). It's got a science lab despite being in sandbox. It has a hitch hiker module for no reason. It has 750 Mono despite having no thrusters. It has four of each science experiment (except the mat lab because I couldn't be bothered). It carried a full orange tank into orbit.

It has one of each type of docking port.

It is very badly designed.

It has got to the mun.

[Claw]

Haha. You also have quite a few engines on there. Almost looks like you wasted space on having wings.

Stacking huge amounts of intakes is pretty overpowered. But to be honest, I still like the simplicity of the mechanics. I'm not really offended if someone wants to build something like you just demoed. In fact, it looks kind of cool.

[Clockwork_werewolf]

Almost looks like you wasted space on having wings

I think I put 12 stacks of 12 intakes on the whole ship and that's not counting the normal end intakes. I had enough room for the wings, and needed them for control in the atmo this thing had amind of its own. The intake stacks would wobble about like snakes and slowly pull the ting off center.

I don't mind people doing this, it's a fun sandbox game after all. I just think it shows something isn't quite balanced right when most people stuff 12 objects inside of each other and a way that glitches and snakes but is considered normal. Imagine if an MMO had a way of walking though a wall into a negative space and out again to bypass a difficult boss and get loot. Almost everyone would do it and it would be considered a normal part of the game but that doesn't mean it shouldn't be fixed.