Plane design (newb)

[Giygus]

I have started to mess around with Career mode, and felt I needed a plane to help get some science points and complete a few survey contracts.  The problem is, once this plane gets up to about 12K, it starts to slow way down, preventing the plane from climbing higher.  I did skim through the tutorial here (the one with the funky hand drawn pictures and outdated drag info) but I saw nothing on this issue specifically.  The wings are set up as the tutorial suggested: front ones for pitch, rear ones for rotation, and tail fin for turning.

So far, my tech tree (vanilla) is only unlocked through the 45 sci. cost level, every thing else costs 90.  I have yet to do any orbital science experiments, nor did I visit most Kerbal biomes, so I may be able to push to another unlock before I try for the Mun science.

Thanks for any tips!

Here are a couple of pictures:

 

[Newnard]

Do your engines actually flame out? Because as you go higher up, your air intakes get less efficient and you might be starving the engines for intake air. Spamming more and bigger air intakes onto your craft wherever they fit sometimes helps with that particular issue.

[Nich]

10km (33,000 ft) is about the limit for junos wheesles and goliaths.  Nice plane

[Giygus]

6 minutes ago, Newnard said:

Do your engines actually flame out?...

I do not believe so.  I thought maybe the issue would be lack of oxygen at that height...but..

8 minutes ago, Nich said:

10km (33,000 ft) is about the limit for junos wheesles and goliaths...

...I guess that is it.  So I just need better tech it would seem.

[Hodari]

8 minutes ago, Nich said:

10km (33,000 ft) is about the limit for junos wheesles and goliaths.  Nice plane

Yeah, it's worth noting that this is around the altitude most commercial aircraft will fly at too.

[Nich]

If you need more for a survey strap an LFO engine on and use that to kick it up higher.

[GDJ]

1) Nice plane! Great way to start.
2) Yeah, like others have already said, 10,000 metres is pretty much it for Juno's, Weasley's, and Goliaths. You may be able to squeak it to 12,000 metres, but the plane's design and balance has to be dead perfect. Also it will take a long time to sneak up from 9500 to 12,000. 5 to 10 m/s vertical velocity. Up in the thin air wings are your friend, and do your best to get your velocity up as high as possible.
3) The engines may not flame out, but they will produce so little thrust that they might as well be off. The sweet spot for these engines seems to be between 5000 and 8000 metres.
4) Yeah, I have to agree with Nich on the LFO engine. It will definitely help getting your plane up to ideal velocity at higher altitudes, and if you get going fast enough the engines may get a small boost in thrust. You don't need big LFO engines, but a pair of tiny ones will do the trick.

Edited March 15, 2016 by GDJ

[AeroGav]

My best effort was about Mach 1.3 at 12km on 10 (!) Juno engines.   Wheesly's and Goliaths are actually worse than Juno for speed / alt.  

That's a very decent little plane but if you don't mind me saying, the back end is a bit on the lardy side.  Meaning you have a very draggy open node at the rear of the fuselage, creating a source of flat plate drag.   Put a nose cone on it, or tail connector, something pointy.   If you press F12 in flight you'll see where the drag is coming from in your design.

Alternatively,  attach a nice little "terrier" engine.    They're considered low thrust upper stage engines but the Junos are only putting out 10kn each at those altitudes,   the Terrier's 60kn is plenty enough to send you upstairs.  It's also light (0.5 ton ) and very efficient.  Up at 10km you're practically getting the vacuum rating of the rocket, it's awful sea level performance won't matter.

[AeroGav]

Like  I said,  a single Terrier is plenty powerful enough for an LFO engine.   Your thrust doesn't need to equal your weight because you are an airplane - at optimum angle of attack (2deg) you're getting a lift/drag ratio of 20:1.   So long as you don't have weight equal to more than 20 times your thrust in other words, it is possible to climb.

I've done a very low tech space plane before with 10 Junos and 1 terrier.  Just barely scrapes into orbit.   I jettison the landing gear after takeoff, jettison the junos when they flame out and ditch it in the water near KSC on return. And yes i'm also attaching tail cones to the front and rear nodes of the fuselage then offsetting them so the engine can still exhaust, to minimise drag.

 

 

Re intake spam - please don't , that's just extra weight and drag since 1.05 or even earlier.

There's a config file in the game directory for each  engine that specifies how rapidly thrust tails off with increasing altitude and there is nothing you can do about this.  It also describes the flameout altitude which again is fixed,  and also how quickly thrust is gained with increasing speed, what speed peak thrust is reached and then how quickly power tails off as you go still faster.       The Juno is actually the best high speed engine till you get the Panther,  it maxes out at 1.3mach and looses thrust more slowly than the Goliath and Wheesly as height is gained, but the downside is it's less efficient.  And tiny.

If you do have insufficient intakes for the number of engines,  this manifests as the engine cutting out and restarting multiple times per second (spluttering/surging)  possibly with different engines on different sides of the vehicle cutting in and out at different times, causing a snaking/weaving motion.  Unmistakeable if it happens,  but if it's not then there's nothing to be gained by more intakes.

 

edit - yes there are 14 engines on the first pic, but it didn't help me get any higher than with 10 or 12.  Call that an unsuccesful variant.

Edited March 16, 2016 by AeroGav

[Newnard]

1 hour ago, AeroGav said:

Re intake spam - please don't , that's just extra weight and drag since 1.05 or even earlier.

There's a config file in the game directory for each  engine that specifies how rapidly thrust tails off with increasing altitude and there is nothing you can do about this.  It also describes the flameout altitude which again is fixed,  and also how quickly thrust is gained with increasing speed, what speed peak thrust is reached and then how quickly power tails off as you go still faster.

...

If you do have insufficient intakes for the number of engines,  this manifests as the engine cutting out and restarting multiple times per second (spluttering/surging)  possibly with different engines on different sides of the vehicle cutting in and out at different times, causing a snaking/weaving motion.  Unmistakeable if it happens,  but if it's not then there's nothing to be gained by more intakes.

Thanks AeroGav for the education, and apologies to all for suggesting intake spam.