Can I make Turbojet engines burn out at the same time?

[Cypherwraith]

Alright, so I've been experimenting with SSTO designs. I've gotten an SSTO into orbit before, but only when there was a single Turbojet engine at the center of my design. Whenever I have more than one, one of the engines burns out from lack of intake air before the other, causing it to spin uncontrollably (the yaw, not the pitch) and go into a death dive.

Two questions then:

Is it possible to make two turbojets run out of intake air simultaneously? (If not, is there some sort of chart that can tell me at what altitude my intake air will run out based on how many intakes I have per turbojet?)

and

How do you regain control of pitch, yaw, and roll when you're in a death dive?

--EDIT--

I'm glad to report that adding a third turbojet engine directly behind the CoM gave me enough time to throttle back before burning out. The mechjeb method works just as well. Thanks for all of the input!

Edited August 21, 2013 by Cypherwraith

[MiniMatt]

Assign jet engines to an action group in construction, then toggle them off manually just prior to flameout (keep an eye on the intake air resource).

As for regaining control.... prayer sometimes works

[numerobis]

(If not, is there some sort of chart that can tell me at what altitude my intake air will run out based on how many intakes I have per turbojet?)

You can use the mechjeb throttle control, which automatically throttles back to prevent jet flameouts if you ask it to. Or, 1 intake per jet => 21km if you can get going fast enough, and from there, every time you triple the number of intakes (or reduce your throttle by a factor of three) you get about 5km extra ceiling.

[Johnno]

Open your resources tab during flight and keep an eye on your intake air. In the VAB/SPH you can look at the engines and each engine will have a set flameout point (think it's 0.10). If you're using two jets then when your intake air hits 0.20 you're at danger of flameout. The lower your throttle the lower the risk of flameout.

You can also look at your intakes individually to see how much air they have, I think if any single one goes to zero before you close it you'll flameout. I haven't confirmed this 100% but the way I fly is once my intake air hits 0.20 (with two jets) I monitor my individual intakes, if I for example have 10 intakes they'll have 0.02 each, once I find one that's at 0.01 I know that soon I'll be out of air and hit up my rocket engine. Works for me at least but I'm sure others fly differently.

[annallia]

As others have said, use the action groups to shut off your jet engines/turn on your rocket.

If you really want to let them burn out I would say try fuel balancer and balance the air intakes, the few times I have done this it seemed that both engines, or in one poorly designed (poor alden the test pilot...) all 6 of the engines flamed out not quite at the same time but in fast enough succession that it only turned my plane not put it into a spin.

[SRV Ron]

Since it is difficult to monitor which engine will flame out first, it is best, as others have stated, to have an action group that shuts them all down prior to a flame out occurring. Otherwise, you can fly a single engine to flame out without causing an uncontrollable spin. That condition can be just as fatal for real multi engine hypersonic high altitude aircraft such as the SR-71 Blackbird.

[Eric S]

As I understand it, the last engine placed will be the first to flame out. If you place the last engine centered behind the CoM, when it flames out, you'll have a warning that you need to deal with it, either by throttling down or shutting down engines. Unfortunately, you need three engines to take advantage of this.

[ThatNoob]

You could use just engine and abuse intakes.and make orbit with ION DRIVES!(Idea from Macey Dean)

[Tollazor]

If you are into making SSTO Spaceplanes, I highly recommend installing the FAR mod. I spent lots of time making SSTO Spaceplanes with Stock and after installing FAR I found it to be far more satisfying and you can more realistic planes.

As for the crazy spin out, I find switching off SAS, cutting all engines and oscillating your control surfaces until you are falling straightish then firing up your jet engines helps to recover. When I say oscillating, I mean that you only apply your control when you are facing vaguly the direction you want, then stopping whilst you spin around to that point again. Eventually you regain control, you have about 20,000km to do so

[maccollo]

The only way to get a symmetrical burnout is to have one engine lined up with the Com. If you put that one on first it will always be the first to go.

If you can't have an engine at the center the best you can do is to have action groups ready to respond. However the first thing you should do is not to turn of the engines.

Jet engines will still produce power a few seconds after you turn them off, so if you try to do that in order to recover quickly from a potential spin out you're basically boned. Instead, set up an action group to toggle the air intakes. At altitudes where you can suffer from burnouts this will kill the thrust instantly, making it possible to recover.

[ChevronTango]

Eventually you regain control, you have about 20,000km to do so

20,000 km? WOW! I wanna know what spaceplane your using. Where can I get one.

But that aside its a balancing act between height, speed, lift and drag always. I use mechjeb to control the flight as not only does the throttle control prevent this vary senario, the MechJeb Advanced SAS when set to surface can maintain a constant heading pitch and roll which makes flights dead easy and further helps to prevent such problems as flameout induced flatspins.

[numerobis]

Open your resources tab during flight and keep an eye on your intake air. In the VAB/SPH you can look at the engines and each engine will have a set flameout point (think it's 0.10)

It's about 0.075 at full throttle for the relevant altitudes, so you can throttle back when it hits 0.07 -- but only usually. There are ways (which I don't fully understand) to thwart that, and have the resources tab readout give lower numbers. The more reliable method is to right-click on an intake, see the flow in units per second, multiply by the number of intakes and divide by the number of jets.

You need substantially more air per engine at the surface, and substantially less from 2 km-15 km, but this isn't usually an issue.

[Tiron]

Basically, what happens is this: Intakeair is (extremely unrealistically) automatically routed throughout the craft. So when one engine flames out, all the Intakeair that it was using automatically redirects to the remaining engines, keeping them alive.

There's really only three ways to deal with it:

1.) Have a Center Engine that flames out first.

2.) Manually disable the engines before they flame out via Action Group

3.) Cut the throttle to reduce the intakeair requirements to a level that prevents flameouts.

The last is hard to do manually. Mechjeb 2 will do it automatically, although it's far from perfect at it.

[Sauron]

20,000 km? WOW! I wanna know what spaceplane your using. Where can I get one.

But that aside its a balancing act between height, speed, lift and drag always. I use mechjeb to control the flight as not only does the throttle control prevent this vary senario, the MechJeb Advanced SAS when set to surface can maintain a constant heading pitch and roll which makes flights dead easy and further helps to prevent such problems as flameout induced flatspins.

Uhh...

A 1:1 intake ratio will get you to 20 km (a very little bit lower, strictly speaking) without any babying of the throttle.

[Anton P. Nym]

A 1:1 intake ratio will get you to 20 km (a very little bit lower, strictly speaking) without any babying of the throttle.

Yes, it'll get you to 20 000m but it won't get you to 20 000km. (Chevron's having fun with typos.)

-- Steve

[Sauron]

Egg on my face for replying to quotes without any context Oopsie!

[numerobis]

Mechjeb 2 will do it automatically, although it's far from perfect at it.

Can you reproduce a problem? If so, PM me a bug report. I've seen it screw up but not reproducibly: whenever I look carefully, it works flawlessly.

[Tiron]

Can you reproduce a problem? If so, PM me a bug report. I've seen it screw up but not reproducibly: whenever I look carefully, it works flawlessly.

Well, it's better than it was, last time I checked, but it still sometimes flames out if you're climbing too hard, particularly if you try to cut the safety margin to get more thrust out of it. After some goading in the K-Prize thread I've tried to find a way to use just the jets to go higher, and have consistentently failed, and usually end up in at least a partial spin at least once if I push it high enough, even on 5% margin (which seems to reduce the thrust too much to make it really work, or maybe I just don't have enough period, I don't know.)

[numerobis]

There's no modeling of spin down time, so that's what the margin is about: if you climb fast, you need to throttle back fast.

I have on rare occasion noticed a flat spin when the navball is on orbit speed rather than surface speed. I'm completely confused about why that would matter.

As far as I know, it hasn't changed at all, so it shouldn't have improved.