How to attain very high-altitude flight with air-breathing engines.

[SSgt Baloo]

Someone in another thread mentioned than it is possible to get up to nearly 30 km with air breathing engines in KSP 1.0. Does anyone have any tips for how to fly at high altitudes with air-breathing engines, for someone stuck with 1.0 (bought mine from Amazon *head-desk*)? I can get up to about 17 km before the Rapiers shut off. I know it must be difficult, but how is it done?

[Starhawk]

Hello SSgt Baloo, and welcome to the forum!

The Rapier can operate up to an altitude of about 29500 m in air-breathing mode.
This is the extreme limit, however, and as altitude increases toward that limit, thrust decreases.

If air-breathing mode cuts out at 17 km, it sounds like you don't have enough air intakes.

I have no idea how purchases from Amazon work, but you should upgrade to 1.0.5.

Happy landings!

[eddiew]

Given the problems with the Amazon distribution of KSP, I think it'd be worth contacting the support team here. Might be able to sort you out with a 'proper' version

Or just buy it again on Steam. Can always copy your save files over ^^

[SSgt Baloo]

This has been an ongoing problem with Amazon since the release, and I only discovered it after I made my purchase. Eventually I'm gonna have to buy it from Steam, but until I've exhausted the possibilities, even this "defective" copy is good for me to learn how to do things. I'm sticking to Science mode and Sandbox mode for now, until I understand what the objectives are and how to achieve them. Landing on the moon is difficult, but getting there with enough resources to return? That can be even more difficult to sort out.

Edited December 16, 2015 by SSgt Baloo

[AeroGav]

If sustained air breathing flight at 29.5km is your goal, these things will help -

1.  Fly at mach 3.7 above 20km,  this is the mach number where RAPIER gives most thrust, which will help offset the loss of thrust as the air gets thinner.

2.  Adding more RAPIERs will also offset the loss of thrust with altitude,  but that also means more drag nodes for engine nacelles and the mass of the rapier itself.  Other aspects of performance (ie. payload mass fraction, delta v) will suffer if you take this too far

3.  Adding lots of wing.   Optimum lift drag ratio occurs at 2degrees AoA subsonic and about 5 degrees hypersonic, most space planes have to use significantly larger angle of attack to get sufficient lift at these altitudes, so they suffer excess lift induced drag.   If you're planning to fly air breathing at 29.5km, your RAPIERs will be only be making a tiny amount of thrust at this point, so you need to avoid this lift induced drag problem.    If you construct your super size wing from Big-S Delta and Big-S strake sections, they can double up as liquid fuel tanks for your RAPIER and NERV engines.

The drawback to adding lots of wing is that your plane may become too draggy to beat the sound barrier at sea level.  You may want to climb subsonic to 10-14km before going through the sound barrier, which makes the whole process take a fair bit longer.

[SSgt Baloo]

I've been experimenting. I've been trying to build a drone capable of circumnavigating Kerbin on a single tank of fuel. I've been experimenting with "porpoising". When the rapier cuts out due to lack of air, I turn it prograde and shut the intakes to reduce drag. Then I reopen the intakes as it drops through 30,000 meters, get it to re-light, and then accelerate until it has enough speed to pull up before burning up, and climbs above the altitude it can breath again. Lather rinse, repeat.

So far I've made it a bit more than halfway around before burning something critical up. "Well, shoot! I was using those wings." 

[Wanderfound]

The other factor: are you after sustained level flight at high altitudes, or efficient circumnavigation?

For sustained level flight, you want lots of wing area and a very gradual climb. For efficient circumnavigation, you want minimal wings and a Silbervogel technique: zoom climb (i.e. gather speed at low altitude, then pitch up into a steep climb that takes you above your level-flight ceiling) to a suborbital altitude, then circumnavigate the planet in a series of "bounces" off the atmosphere, with your engines powered up only in the troughs of the bounce.

Edit to add: just noticed the post above. Keep the nose a few degrees above prograde, so that your bounce bottoms out at a higher altitude. You may also find it useful to stick one of the small curved radiators on top of your fuselage near the wings.

Edited December 22, 2015 by Wanderfound

[SSgt Baloo]

On 12/22/2015 at 11:00 PM, Wanderfound said:

Edit to add: just noticed the post above. Keep the nose a few degrees above prograde, so that your bounce bottoms out at a higher altitude. You may also find it useful to stick one of the small curved radiators on top of your fuselage near the wings.

Radiators?

Also: Update. I have re-purchased KSP* (this time, through Steam) and so I should have no difficulty with updates, except that I don't see any of the new stuff that's supposed to come with 1.05. About how long after you download KSP does it update itself?

* Edited to correct order.

 

Edited January 11, 2016 by SSgt Baloo

[cephalo]

I think it tells you the version on the intro screen. A lot of the stuff is subtle other than the new parts in the VAB.

[SSgt Baloo]

Spotted the new bits. The tiny jet engine is perfect for some of my more simple ideas. I'm still trying to figure out how to convincingly model pioneer airplanes that were more open framework with wings attached than anything else.

[SSgt Baloo]

Enough things have changed that Munar missions are off until I can master launching without also incinerating all my parachutes.