low tech space plane

[steuben]

I'm trying to build a low tech space plane, not necessarily ssto, but as close as possible, for kerbal rescue.

I've got all tier 3 research done, general construction, aviation, and aerodynamics researched. I think I may need to do supersonic flight and advanced rocketry.

can it be done? what directions should I think of in terms of design?

 

 

 

[GoSlash27]

steuben,

 If you're at tier 3, then air breathing really isn't practical.

 I'd recommend sticking with rocket power. Vertical takeoff is more efficient. You can build a practical SSTO using any of the engines you've unlocked thus far.

I think you may have overheating problems with the landing gear on reentry. The fixed ones have low temperature tolerance.

Good luck!

-Slashy

[cephalo]

You need to go really fast to get to orbital speed. I haven't tried the panther yet, but it might be helpful in reducing the needed rocket fuel, but since the afterburner mode is inefficient, I can't say if it's better than full rockets. I can tell you it will be more challenging than building a normal high-tech spaceplane, which already takes some practice, because you have to build it right and fly it right. If you've already done that, it might be a fun challenge, but at mid tech there are better ways to accomplish the mission.

If you want a cheap way of rescueing Kerbals from LKO, you might find it a lot easier to build ssto recoverable rockets. 

[steuben]

the tier is arbitrary. it just happens to be where I started my design work.  I'm aiming for the lowest/least tech possible.

I've hacked up a career save with enough science and funds to overflow to negative amounts.

I think I may have to bring in the panther as well as the 909

[Snark]

With the tech nodes you've described, you only have the low-speed jet engines (Juno, Wheesley), which can't get over Mach 1.  You can use them to lift a ship up to 10 km or so, but not much higher than that, which means you'll need to use rocket engines for nearly all of your dV, which in turn means that your jet engines will just be dead weight for 90%+ of the dV to orbit.

In other words, they're more trouble than they're worth.  If you can unlock Supersonic Flight, then you get the Panther, which makes a spaceplane much more possible (still not ideal, the Whiplash would be best, but it's doable with the Panther).

Is there some particular reason you want to build a spaceplane?  i.e. is your reason practical, or is it just "I want to do a plane because I like planes"?  If you're just doing a kerbal rescue from LKO, you really don't need a plane-- a very simple conventional rocket will do it.  You can build a rocket for only around 8000 funds or so that will retrieve a kerbal from LKO without a problem.  Yes, the percentage recovered would be a little lower than for a spaceplane, but it will be much simpler to build and operate, and in any case the cost of the rocket is only a small fraction of the reward you get for rescuing the kerbal, so it easily pays for itself many times over.  Honestly, I'd suggest just going with a rocket.

If you really want to do spaceplanes, they're a lot easier if you wait until you have a bit more tech.

[GoSlash27]

10 minutes ago, steuben said:

the tier is arbitrary. it just happens to be where I started my design work.  I'm aiming for the lowest/least tech possible.

I've hacked up a career save with enough science and funds to overflow to negative amounts.

I think I may have to bring in the panther as well as the 909

The Panther and LV-909 make practical spaceplanes workable. Nowhere near the payload fraction you can get from the Whiplash, but still good enough to get the job done.

Best,

-Slashy

[cephalo]

After looking at the stats, it looks like the panther is very efficient without the after burner, and just as efficient as the whiplash with the after burner on and almost as fast and 2/3 the weight. It might work well actually.

[GoSlash27]

cephalo,

 It works, but not what I'd call "well". My first 1.05 spaceplane design was a Panther/ Terrier. It only gets 2t payload per engine, which is pretty dismal. The Whiplash can get 8 and the RAPIER over 10.

 It's the "almost as fast" part that shoots it in the leg. You have to make up the speed/ altitude difference on rocket power and that means a lot more fuel and oxidizer than the other designs.

 But as I said, it does work.

Best,

-Slashy

 

Edited December 24, 2015 by GoSlash27

[AeroGav]

If you're doing low tech spaceplane for the hell of it,  you can get there with Junos and a terrier.  Note that "Spaceplane" does not  necessarily mean  SSTO,   as it is with my design - the staging is set thus

Stage 1 - Fire up all the Junos

Stage 2 - After liftoff, punch off the fixed landing gear, don't want their weight and drag.  We'll be landing in the water, or in very small pieces.

Stage 3 - The Juno reach peak thrust at 1.3 mach, which corresponds to the low point in the drag after the transonic drag spike.   With this number of Juno it should be possible to reach 1.3 mach and 12km before she stops climbing, then press SPACE again to start the Terrier.

Stage 4 -  At around 17KM the Juno will flame out.   At this point I use a radial decoupler to separate them, their intakes and fuel tanks from the wing.  Since we're no longer  targeting 1.3 as their "max thrust " airspeed, i just fly to constant AoA now on  the Terrier.

 

 

 

Sorry about the poor screenshots, but here it is on the ground and in orbit.    As you can see , virtually no payload/delta v capability remaining.   You could probably do the mission cheaper with a disposable rocket, than you could by throwing all those Junos away.

PS the ground screenshot is of an experimental version with 7 Junos on each wing, but it didn't let me climb any higher airbreathing than with 6 per wing.

PPS in the second screenshot i'm going to have a problem soon , because i didn't research solar panels yet.....

[Evanitis]

I had great fun with low-tech spaceplanes before - though I started my relevant career save in 1.0.4. I didn't have those fun little new engines, so I taken a Whiplash test mission to never complete, while only having Mk 1 structural parts. The most I managed to construct is this munar biome-hopper / Duna craft.

It's definately an SSTO, and almost everything on it lands that isn't considered payload. Except those wings on the front, but no one will notice that. It has 3.5k dV on LKO, and a whopping 7 terriers for the silliest suicide burns.

About building hints... I feel it's impossible to fully separate lifting parts from a considerably sized payload on this tech level. Disposable wings help here. Of course you don't need nearly as much for LKO rescues, but why stop there? Last time I checked, even some stock planes could do recues well enough.

Compared to sane SSTOs, the only extra difficulty here is that the wet/dry CoM/CoL should be aligned not just for the whole craft, but for the separated lifter part too, in order to land it.

Edited December 26, 2015 by Evanitis

[Wanderfound]

You need at least Panthers (and preferably Whiplashes) to build a useful airbreathing SSTO spaceplane. But if you care more about the spaceplane than the SSTO part, dump the jets entirely and build it as a reentry glider. Perhaps something like this:

 

 

http://s1378.photobucket.com/user/craigmotbey/Kerbal/Beta/Kerbodyne%20Showroom/Sidewinder/story

 

That one probably uses higher tech than you'd like, but a similar concept based on lower-tech boosters should be doable. And, if you wanted, you could even stick a Juno or two onto it just to make cruising back to base a bit easier.

Edited December 26, 2015 by Wanderfound

[AeroGav]

On 24/12/2015 at 6:48 PM, AeroGav said:

 

.

As a said in the previous post, this design ditches it's jet engines , intakes and jet fuel tanks when they flame out, it even dumps it's undercarriage after takeoff.    I did try taking things one step further, and putting the wings and control surfaces on decouplers/structural pylons (i had a contract to test one, at this point).

However, separating the wings at 40km caused me to not make orbit.    The terrier didn't have the thrust weight ratio to stop us falling back into the atmosphere, without the wings being there.    I did however, blow the wings off for my munar/minmus explorer at 60km.   

Pressed the space bar and they were out of sight in seconds... upwards.

[Wanderfound]

I did see that you'd already tried some multistage designs; the point I wanted to raise is that it's easier to do one of those if you abandon jets entirely and launch with a much steeper profile than is typical for a spaceplane (notice that the apoapsis is already at 85km in the pic where I'm dropping the wingtip boosters?). If you're circularising on a very low TWR engine, you need to give yourself time to do it, and you can't afford to hang around in the draggy  bits of the atmosphere.

Staged airbreathing can be made to work, but it's usually harder to do one of those than a conventional airbreathing SSTO. You can get fairly extreme ΔV out of them though:

 

Vertical-launch oxidising reentry gliders are much easier to get right than one of those, however, especially if you're going low-tech.

Edited December 26, 2015 by Wanderfound

[AeroGav]

That's an awesome design Wander,  I did a much less ambitious one in my current career game (with Whiplash engines).      

Whilst it's economically bonkers, I don't think staged airbreathing is that hard...   at least compared to getting to orbit single stage on low tech, where the margins or razor thin.    Separating two airplanes in flight and having both remain controllable is hard, but what's so clever about blowing the wings off above the atmosphere?  Engine dropping is just a case of making sure your engine pods are over the CG so it doesn't move around afterward.

For me, I find building large, tall rockets that stay controllable harder, but i've been flying flight sims since 8 bit days and it kind of comes naturally, wheras gravity turns etc. still feel weird.

Two more (non, shedding, single staged whiplash spaceplanes met it in orbit to refuel the thing and also deliver the service bay which contained more science instruments)

Then it taxied over the surface of Minmus,  visiting every biome, and came back to Kerbin orbit with almost 3k science.

I've now refuelled it again and it's currently doing the same thing on the Mun,  trying hard to flip over...

 

[ForScience6686]

I managed to build my first ssto space pane last night using 2 Panthers and a swivel.  Was surprised it actually made orbit, nor much fuel to spare but with more practice flying it I should be able to squeeze some dv out.

I've got a question, would it be better to get into a steeper climb and ignite the rocket sooner, or build slightly more speed at a low aoa. I am thinking I had better results with the higher vertical speed to escape the atmosphere sooner.  I can barely get to 800 m/s on the Panthers once at altitude at about 5 degrees.

 

[AeroGav]

6 hours ago, ForScience6686 said:

I managed to build my first ssto space pane last night using 2 Panthers and a swivel.  Was surprised it actually made orbit, nor much fuel to spare but with more practice flying it I should be able to squeeze some dv out.

I've got a question, would it be better to get into a steeper climb and ignite the rocket sooner, or build slightly more speed at a low aoa. I am thinking I had better results with the higher vertical speed to escape the atmosphere sooner.  I can barely get to 800 m/s on the Panthers once at altitude at about 5 degrees.

 

I am very impressed ,  normally people learn to make spaceplanes in Sandbox, with all the high tech goodness, even then they can struggle.

Panthers produce max thrust at mach 2.5, then quickly fall off.   My strategy is to get up to mach 2.5 (preferably not below 15km to avoid premature heat buildup) ... which is about 750m/sec i think (Kerbal engineer converts for you...)  and after that stop accelerating and use any surplus thrust to climb.   When the climb rate dies down to negligible i light the rocket.  Make a note of your angle of attack during this phase.    Angle of attack is the difference between where your nose is pointed (the orange -W-) and the prograde marker (yellow circle).   Optimum lift drag is 2 degrees angle of attack @ subsonic ,  5 degrees at orbital velocities.    So you're hoping to see something in this range.  If you need more angle of attack @ mach 2.5 and these altitudes, then you don't have enough wing.

In rocket mode ,  ideally i just try to fly at up to 5 degrees angle of attack and gradually get higher and faster, over time, the aircraft's weight is increasingly supported by the centrifugal force of hurtling round the planet, rather than wing lift, but it's a gradual transition.  I use kerbal engineer plugin to display Apoapsis on the HUD, when that exceeds 70km i shut down and coast the rest of the way up,  circularise above the atmosphere...  heck why am i trying to tell you this?  I'm sure you were a good rocket pilot before trying your hand at planes.  I came at it the other way, and have only recently learned how to not make egg-shaped orbits.

The Terrier is a better engine for this than the Swivel, if you can get a contract to test one.    Higher ISP and less weight.   Less thrust, but you're an airplane and you don't need massive TWR. 

1 Rocket  and 2 Panthers?   Sounds like an engine dropper design to me.   Putting the panthers on wing pods makes it very easy to drop them, their intakes and their fuel when they flame out, and not muck up the plane's handling.   I'd probably attach a tail cone to the back of the rocket engine though, then offset it forwards till you can barely see the very tip buried deep inside the engine, so that it still makes thrust.  Engine nozzles are VERY draggy, this little exploit lets you have the best of both worlds.

In this pic you can just see the tip of the tail cone buried in my Terrier nozzle!

 

If you're making a full re-use design,  I'd go with one panther and one terrier ,   attach the Panther to the back of the terrier, and offset it forwards so both can thrust at the same time without blocking each other.   That way your aircraft only gets the drag from one engine nozzle (the panther, since it is rearmost, the drag from the terrier won't count as it isn't "at the back" as far as the game is concerned) throughout its flight.

 

[ForScience6686]

I'm not a fan of clipping like you describe aero.  And I was quite impressed it made orbit.  My design does not drop engines, and I tried with the terrier but it didn't have the power needed.  It's planned to be completely reusable and can only rescue or drop off at the station.  I plan to refit it for Sat deployment, but I'll have to devise a method of getting the satellites to the island runway and loaded in.  Space-K has purchased the island airbase and will be taking over low orbit duties as they advance their fleet.  They will only use  ksc for new construction and repairs.

[GoSlash27]

ForScience6686,

I recommend 2 Terriers for each Panther or 1 Poodle per pair of Panthers. Both should already be unlocked by the time you get the Panther.

Best,

-Slashy

[ForScience6686]

You know I did not try the two terrier setup, that should give me the power plus better efficiency.  As well as less hazardous with shorter engine hangingoff the back.  Looks like I will making more changes to it tonight.  Thanks for the idea slash.