High Altitude Atmospheric Spaceplanes?

[DreadZombie]

Hi,

If this has been asked before please delete this thread, but, I couldn't find anything.

No matter what I try, I seem to always have the same problem with spaceplanes. I get to around 16km-19km and I get jet flame outs. I add more intakes, change jet engine types, all that I can think of, and I get no luck.

How do you build your high altitude atmospheric Spaceplanes? What tips can you offer?

[rodion]

I always thought the old key to this was just to add excessive amounts of intakes so the engines could continue to function due to the sheer amount of air available to the craft (the infamous school of airhogging/intake spamming). If even that isn't working for you, I don't know what you could be doing wrong.

[briansun1]

larger wings and more intakes + throttling down at high altitudes or turning some engines off will help

[DreadZombie]

I always thought the old key to this was just to add excessive amounts of intakes

When you say excessive, what engine to intake ratio (roughly) do you mean?

[UmbralRaptor]

When you say excessive, what engine to intake ratio (roughly) do you mean?

I'd say at least 4 ram intakes per turbojet engine. Going for 8-12 would make things easier.

[Captain Sierra]

No it wouldn't. That intake ratio is more than acceptable. THe problem is your flight profile. Can you elaborate on what it is currently?

[DreadZombie]

Can you elaborate on what it is currently?

Currently I take off and slowly raise my prograde vector by slowly edging the nose up further by a few degrees each time. So I'll basically be climbing at the max angle that I can still accelerate at, until I'm at a height that is just under the spaceplanes limit (which so far has been roughly 10-13km). Then I tend to level out so I'm flying relatively flat.

[arq]

I was messing around with this exact thing earlier. With 5 intakes and 1 turbojet, I could fly a plane up to 47km and over 2100m/s. Bear in mind that aircraft in these situations are absurdly unmaneuverable. Still, with less than 400 fuel (and some very sloppy flying) I circumnavigated Kerbin twice in 78 minutes, and could have been a touch faster yet.

I did a few things I did to help this along. I mounted vertical stabilizers well-behind the CoM. to keep it stable. I angled up both the wings and horizontal stabilizer 30deg, so that they would provide maximum lift when I was flying straight-and-level (air intakes lose air as they spin away from forward). However, this made it fly very awkwardly in thick air (it would point about 20deg below the horizon, which meant landing needed to be very slow), so that was a little bit of a challenge.

The trick is to keep backing off the throttle as then engine flames out (this is why it is good to have just a single engine, or at least have an odd number and make sure that the center one will be the one to flame out). When I was up above 45km, I was at maybe 4% thrust.

Note, however, that you aren't missing much above 25km. 'Planes' up there act more like rockets (and certainly can't maneuver) because of the high speed necessary to keep air going through the engine.

Less is often more, in this case. My ship was under 4t after I had burned out all the fuel. The main thing that determines max altitude is your intake/mass ratio. In air-starved environments, air is thrust and (as always) mass is drag. If it still won't go high enough, try bigger wings. At 45km, my engine was delivering maybe 6kN of thrust. More engines would just add drag, which would slow it down.

[Pariah89]

This is the best tutorial out there, how to build them and how to fly them.

Helped me big time.

http://forum.kerbalspaceprogram.com/threads/39141-Tutorial-How-to-make-your-first-SSTO?highlight=ssto+tutorial

[lammatt]

a lower rate of climb helps.

you basically want to get to ~1.5km/s (orbit) before switching to rocket, because you need a ~2.2km/s for a 75x75km circular orbit and you probably need ~1-1.2km/s of dV to get from 1.5km/s to 2.2km/s

the lower the rate of climb, the more time you can buy for your plane to accelerate before the jet flames out.

also, lowering the thrust when the intakes are getting low helps too,

you should start throttling down a bit at around 0.2 intake and then at ~0.12 intake, you should be running both the rockets and the jets at fairly low thrust

and when the jets die, throttle the rockets back to the max and pitch up a little (or not, depending on the altitude you are at).

-----------------

my experience is,

the number of intakes doesnt really matter (of cos spamming intakes make it A LOT easier) as long as you manage to get to ~1.5km/s (orbit) and have ~1km/s rocket dV left, you will definitely be going to space.

---

another tip is,

for planes, the smaller it is, the easier it flies.

try to take a look of the stock Aeris 4A, and note it's parameters,

mass, jet thrust, rocket thrust,rocket dV

the Aeris 4A is a good start for flying/building planes, you can get into a 100X100km orbit with it with some fuel left.

(tho' you may want to tweak the wings a bit as the stock tends to flip if your maneuvers arent too gentle)

Edited September 30, 2013 by lammatt

[Monger]

From my experience, there are two cases we have to distinguish here: a plane that "only" flies at very high altitudes (let's say, 60km), and space planes that actually achieve orbital velocity. Unfortunately, the two designs are very different.

For the first one (which I assume you are trying to do), there are a few simple rules:

- One jet engine usually suffices

- Avoid flameout by throttling down

- Spam Air intakes, at least four per engine. The circular jet Intakes are better than the side-mounted one

- Reduce weight and drag. You don't need that much fuel, and take a close look at the lift/drag ratio each wing and flap has.

- Add wings until you can lift easily, but not more.

Space planes, are a very own chapter, and should be discussed separately, I think. Due to their higher payload they are usually unable to maintain such a high flight profile.

Edited September 30, 2013 by Monger