Air intakes backwards and shielded from air drag

[Sharpy]

How would air intakes backwards and shielded from air drag perform?

(or more specifically, in a situation of "flight backwards")?

The idea is to use a ramjet-powered lander. A little too big for any reasonable number of parachutes; the ramjets would provide most of atmospheric braking in the final descent/touchdown phase, but their air intakes are oriented upwards, against the direction of descent, and shielded by the elements they are mounted above. How would they perform?

Edited June 10, 2015 by Sharpy

[Mic_n]

Just to make sure and get it out of the way: the only place that'd work is Kerbin itself or Laythe, those are the only atmospheres jets will operate..

Air intakes pointing retrograde don't work, though.. or.. are exceedingly limited in their effectiveness... anyone who's ever had a spaceplane tumbling out of control at high speed and altitude can attest to the engines cutting out and coming back on as it spins retro- and prograde.

For your purposes though.. remember that the intakes and engines are totally separate parts and need not be connected. Intakeair is a global resource provided to the craft as a whole, and consumed from that whole by the engines. There's no reason you couldn't mount an air intake to one node of a bi-coupler and an engine to the other to use for braking if you wanted to.

I can't imagine a scenario where you'd actually want to use that, though. Even without airbrakes, you should be able to aerobrake with your lifting surfaces to a pretty huge degree, and in your final descent, parachutes are absolutely going to outperform engines for that purpose weight by weight..

[Wanderfound]

Backwards-facing intakes will suck less air than properly oriented ones, but it's not really a problem in this application; you'll only be needing them at relatively low altitudes, anyway. Turbojet landers with up-facing intakes work just fine:

[Sharpy]

Even without airbrakes, you should be able to aerobrake with your lifting surfaces to a pretty huge degree, and in your final descent, parachutes are absolutely going to outperform engines for that purpose weight by weight..

In my final-final descent the engines will outperform the parachutes. I definitely plan to use the parachute to slow and stabilize the descent, but this thing being so big, it will be the last 40m/s or so of speed to lose; the difference between crashing and a touchdown.

And yes, I plan it for Laythe exactly.

[n0xiety]

Here is a trick that not many people knows. Use rapier engine and place a shock cone at the back of the rapier. Now this will normally block the rapier engine thrust. What you need to do is to clip the shock cone untill you can't see the white part at the side of shockcone. Do not clip more, there is a really small window of error. Now what this will do is to reduce your tail drag and at the same time give you a bit more air while increasing the stability of your plane. Now i know what you are thinking. You are adding more mass how can it increase performance. Try it with the 2 rocket launch test if you like to and you will see the huge diffrence even with the added mass the rapierspike engine one will go alot faster.

Just so you know if you are planning on efficieny use rapiers. Rapiers are much more effcient than turboram. Rapier can reach higher than turboram = less drag and give more thrust at higher speeds 1400m/s+ making it more efficient for long flights.

Edited June 10, 2015 by n0xiety

[Red Iron Crown]

Just so you know if you are planning on efficieny use rapiers. Rapiers are much more effcient than turboram. Rapier can reach higher than turboram = less drag and give more thrust at higher speeds 1400m/s+ making it more efficient for long flights.

Depends how you're defining efficiency. Turbojets only use 80% of the fuel that the RAPIER uses for the same level of thrust, if you don't need the higher speed that the RAPIER can hit then the turbojet is usually the better choice.

[n0xiety]

Depends how you're defining efficiency. Turbojets only use 80% of the fuel that the RAPIER uses for the same level of thrust, if you don't need the higher speed that the RAPIER can hit then the turbojet is usually the better choice.

Well last couple of days i have been trying to create a plane that can circumnavigate kerbin 7 times. To this point ı reached 6 circumnavigations and found out that it is impossible to do this with the turboramjet simply because you cannot reach really high altitudes and still be able to go fast enough to be efficient. I made it so the plane can fly at 27k+ altitude with 1450m/s+ which gets faster as the fuel gets consumed. At this altitude plane uses 0.09 fuel/s after takeoff. It becomes so efficient at the 6th circumnavigation that it only uses 0.05 fuel/s reaching 28.5k altitude and going more than 1500m/s.

[Red Iron Crown]

How does higher speed make it more efficient? Drag increasing with the square of velocity would seem to imply that slower planes are more fuel efficient, but maybe I'm missing something.

[Wanderfound]

Well last couple of days i have been trying to create a plane that can circumnavigate kerbin 7 times. To this point ı reached 6 circumnavigations and found out that it is impossible to do this with the turboramjet simply because you cannot reach really high altitudes and still be able to go fast enough to be efficient. I made it so the plane can fly at 27k+ altitude with 1450m/s+ which gets faster as the fuel gets consumed. At this altitude plane uses 0.09 fuel/s after takeoff. It becomes so efficient at the 6th circumnavigation that it only uses 0.05 fuel/s reaching 28.5k altitude and going more than 1500m/s.

If you're trying to do a fuel-efficient jet circumnavigation of Kerbin, you don't do it by flying level at Mach 5. You want to imitate the Silbervogel; a ballistic climb to the edge of space followed by a succession of "bounces" off the lower atmosphere, with the engine completely throttled off 90% of the time.

That's another one that works better in FAR than stock, though.

[n0xiety]

If you're trying to do a fuel-efficient jet circumnavigation of Kerbin, you don't do it by flying level at Mach 5. You want to imitate the Silbervogel; a ballistic climb to the edge of space followed by a succession of "bounces" off the lower atmosphere, with the engine completely throttled off 90% of the time.

That's another one that works better in FAR than stock, though.

I am doing it for the circumnavigation challenge which has a requirement. I know that atmosphere hopping is alot more efficient but the thing is rule says i can't pass 30k altitude.

How does higher speed make it more efficient? Drag increasing with the square of velocity would seem to imply that slower planes are more fuel efficient, but maybe I'm missing something.

I have no idea how but rapier becomes more efficient as you gain speed at very high altitudes. There is like more than %100 fuel consumption change between going at 25k against going at 27k altitude for rapier. On top of this you don't even loose much speed going from 25k to 27k. If i was going with 1550m/s at 25k i can go 1450m/s at 27k but use maybe less than half the fuel i am using at 25k altitude.

You get more air as you go faster. Sure you are going to tell me that you get more drag as you go faster on top of more air but i just feel like drag and air gained from intakes are not changing accordingly to each other at different altitudes. It doesn't feel scaled. Maybe its how the rapier reacts to pressure. Maybe its just KSP drag model that still needs fixing.

Edited June 10, 2015 by n0xiety