Mini challenge - fix the Stearwing D45

[AeroGav]

Remember that interesting stock spaceplane with the engine staging design, forward swept wings and unique two-class passenger accommodation system?

Sadly it was removed from the game in 1.1.0 being unable to make orbit without mods.

Edit - links to original craft file here https://www.dropbox.com/s/w3byc0jlofmv5dc/Stearwing D45.craft?dl=0

and here http://www.antiwindowscatalog.com/media/ksp/StearwingD45.craft.zip

thanks @Gordon Fecyk and @swjr-swis

 

 

So, has anyone tried to fix up this design?  What can it do,  and how close to the original appearance were you able to keep?

This is what I came up with.    

https://kerbalx.com/AeroGav/Stearwing-D45N

Economy class passengers now benefit from cabin lighting, an RTG based heating system, and a reaction wheel powered seat vibro-massage function to help ward off DVT.  However, we've had to start charging for Pretzels.

I'm starting to see a pattern with my designs.  Most people fix stuff with "moar boosters".    With me it seems to be a case of "moar nukes, moar wings, moar cones!"

Despite the forward swept wings, it looks not much like the original i'm afraid.  Look at all that fuel though, on nuke engines this thing can go places..

 

    

 

 

Edited December 7, 2016 by AeroGav
link to original craft

[Jestersage]

AeroGav, please post the link to the two stock d45 on KerbalX (and are there any difference between them?).

Side note: what is the original performance?

[AeroGav]

1 hour ago, Jestersage said:

AeroGav, please post the link to the two stock d45 on KerbalX (and are there any difference between them?).

Side note: what is the original performance?

I've added a link to the one I found on KerbalX .  I think the uploader made a few changes but only by adding stuff to cargo bay, the external appearance matches picture on wiki.

As for performance of original ship, I never got round to flying it when 1.05 was installed so I don't know, but i'd be very surprised if it can do more than reach low orbit.  Certainly not reach Minmus or Mun.    The wiki says it was removed from game due to no longer even being able to get to orbit under 1.1.0, and actually if you search the forum there are a lot of complaint threads about this craft from 1.05 and earlier, with folks being told to just use something different.

Mine appears to have the Delta V to do a return trip to Minmus.   It could potentially get to Duna but i don't think you'd be coming home.

[Beetlecat]

I love this idea!

It was one of the things that felt like a challenge to fly that we *could* if only it could be figured out. Obviously changes to the game/atmosphere/etc. render it a bit impossible. I like your new craft, but it winds up being a bit *too* altered from the original to simply be a fixed design. More like a MKII? 

Maybe some simple fixes like they could do in the shop: adjusting fuel load, canards, swapping engines, adding engine pods, etc.?

[swjr-swis]

8 hours ago, AeroGav said:

If anyone has the 1.05 stock version with no mods somewhere, I would appreciate if they share a link !

I have put a copy of the 1.0.5 version from a pure stock install on my dropbox: https://www.dropbox.com/s/w3byc0jlofmv5dc/Stearwing D45.craft?dl=0

 

[Gordon Fecyk]

If no one found the 1.0.5 craft, I found it in a 1.0.5 copy I kept. I made it available here:

http://www.antiwindowscatalog.com/media/ksp/StearwingD45.craft.zip

There are three craft files. The .original is the file from 1.0.5 saved by KSP 1.1.3 before converting it to the .craft with 1.1.3 compatible settings. I then attempted to make it work in FAR by adding nose spikes, tail planes, and an extra nose cone on the cockpit. Damned thing kept overheating if I tried flying it 'almost to orbital speed' as the description says, but I lose thrust above 20 km and can't seem to exceed 1 km/s otherwise.

If nothing else, it seems to fly stable with FAR, though you need to turn DPCR off and climb in a hurry on takeoff.

[Update from yesterday] I took a look at the new D45-N from AeroGav. Beautiful bit of construction there, but I'm having a devil of a time maintaining pitch after ditching the single Ramjet because the craft wants to pitch up rapidly! That might be an artifact of my trying to load the craft in 1.2.1 when it was saved in 1.2.2. Managed to get into orbit once only, but didn't have enough fuel for anything but a return trip.

After a few hours of experience on that, I went back to the little hack job I did in 1.1.3 for FAR. Maybe I learned something on AeroGav's D45-N, because I was able to take the older hack job into orbit on the first attempt! Don't have time to try landing it, but there seemed to be enough fuel for the Terriers that, say I missed my re-entry target, I might be able to limp the rest of the way to the runway. The trick with the hack job was to risk very high dynamic pressure and climb at full throttle quickly, with enough pitch upward that the Terriers stand a chance of completing orbit and still avoid overheating the cabin.

--

 

Edited December 8, 2016 by Gordon Fecyk
Added some flight experience

[AeroGav]

4 hours ago, Gordon Fecyk said:

If no one found the 1.0.5 craft, I found it in a 1.0.5 copy I kept. I made it available here:

http://www.antiwindowscatalog.com/media/ksp/StearwingD45.craft.zip

There are three craft files. The .original is the file from 1.0.5 saved by KSP 1.1.3 before converting it to the .craft with 1.1.3 compatible settings. I then attempted to make it work in FAR by adding nose spikes, tail planes, and an extra nose cone on the cockpit. Damned thing kept overheating if I tried flying it 'almost to orbital speed' as the description says, but I lose thrust above 20 km and can't seem to exceed 1 km/s otherwise.

If nothing else, it seems to fly stable with FAR, though you need to turn DPCR off and climb in a hurry on takeoff.

--

 

Yeah I got carried away with my mod,  and changed too many things.   Stock craft tend to have simple clean lines with stuff snapped on at regular angles not tweaked and non-overlapping wing segments.     Though this thing is a bit of  a kludge tbh,  and makes you wonder how hard you should try to deliberately gimp a spacecraft by making it look like something that doesn't work.

Minimum changes to make orbit - 

• get rid of the radially attached crud - ladders, 4 way thrusters, fuel lines, place-anywhere linear rcs
• inline cockpit must go, it is broken. The current heating model, that takes account of bow wave separation penalises cockpits that form the very front of the craft
• angle the wings up a few degrees to reduce the drag from mk2 fuselage .
• OMG Squad, really - NONE of the items in the cargo bay are shielded by it due to being incorrectly attached.   The drag model treats them all as being radially hung off the outside of the ship,  as will the re-entry heating.   That's just shoddy.

 

If you do all of this and can actually make orbit,  then perhaps the Stearwing makes sense as a lower tech crew transport (RAPIER not available in career mode).    If you really want it to be able to make sense vs a pure rapier, pure SSTO design then you need nukes and to give it interplanetary capability.

If you're doing that, you probably want wet wings and will surely have to rearrange stuff to balance CG with those heavy old nukes.  And you need more wings to get enough lift with those heavy nukes onboard - my redesign weighs 50% more than the original.

[swjr-swis]

15 hours ago, AeroGav said:

So, has anyone tried to fix up this design?  What can it do,  and how close to the original appearance were you able to keep?

I gave it a shot: https://www.dropbox.com/s/ix0sqitbcp1jkiz/Stearwing D45 fixed1.craft?dl=0

I tried first to keep it almost intact, but I found it horrible to fly, I really disliked the idea of dropping the jets (I may want those when coming back from orbit), the angled tail fins kept messing with the controls, the intakes kept knocking off parts when sliding off, all kinds of heat, drag and rigidity issues.... I quickly lost all incentive to try and keep that contraption.

So, I rebuilt it almost from scratch and I did a lot of things different, but I think I managed to keep very close to the original appearance, and it's now LKO and reentry capable in 1.2.1, with ample RCS for docking maneuvres, and LF to spare to find a landing spot after reentry.

Terrier+Whiplash replaced by Nerv+RAPIER, only the mk0 tanks drop now, less intakes placed on the Mk2 edges, doubled up on the wings and control surfaces to create enough lift, replaced the short LFO Mk2 tank by a long LF one, removed all oxidizer from the bicoupler, replaced all vernors and RCS by 3x 6-way linear ports, reordered all Mk2 parts (had to redo the entire cargo bay content to do so), added Mk2 drone core, repositioned gear, repositioned all wings and control surfaces, added a small RCS tank, and added some panels so the antenna, solar panels and docking port can be used without 'exposing' the passenger section to space. Ladder and front gear have been attached further back on the fuselage and then offset to the cockpit, to minimize the nr of parts that bleed heat to the cockpit; that and the front RCS ports allow the cockpit to survive ascent and reentry.

I really just wanted to rip out the regular unfueled wing sections and use fueled Big-S rakes instead, much like what you did, but that changes the look a lot.

[AeroGav]

Alright, continuing with the step-by-step rebuild,  I removed the radial "crud", attached the contents of the cargo bay correctly so that it is now on the inside of the ship - shows up "shielded".   None of these things change the appearance.   However the cockpit will still explode, so I changed to inline.  

The next picture shows how much this changes the appearance - do you think it's already "no longer a Stearwing"?   Also in this picture i separated off the jet engines and external fuel tanks to see how the CoM and CoL look when the thing has staged :

These days I'd never design something with the CoL so far aft of CoM.     The thing is, under jet power, our top speed is limited by the velocity curve of the Whiplash.   

The fuel is also "free" , coming from the external tanks, and any that you don't use is discarded when you stage.  However flight under rocket mode is going to directly affect your delta V, so this is what we should optimise for.  Contrary to popular opinion, aerodynamics do not go out the window as soon as you start the rocket engines.  It is still an airplane, and the transition from lift cancelling out 100% of gravity to the centrifugal force of hurtling around the planet cancelling gravity is  a gradual one.  Lift drag ratio makes all the difference here, though the stock Stearwing actually has a near 1:1 TWR when staged, so it will be less sensitive to bad aerodynamics.

So, how do we get our CoM and CoL closer, so as not to get brutal trim drag ?    The wings would have to slide ridiculously far forward, so instead i tried strakes.  Canards would probably have more visual impact, though they might make it less susceptible to trim drag when having a very aft CoL -

Trouble is i think its already starting to look more like a DreamChaser than a Stearwing.

Because the CoL is now close to CoM,   I had to put some wings on the jet section so that it won't be unstable with the weight of them 

At the end of all this, I had a "Eureka!" moment and thought why the hell don't i just replace those Terriers with NERVs.  That would bring the CoM aft, making it less important to futz around with the CoL.

Going nuclear means increasing the engine mass of the orbiter form 1 tons to 6.  But it reduces our fuel burn by a factor of over 2.3.   Unfortunately the stock vessel only carries 6 tons of fuel to start with, so we need to add a lot more fuel, and make this a longer legged vessel,  for the nukes to actually make sense.

 

[AeroGav]

27 minutes ago, swjr-swis said:

I really disliked the idea of dropping the jets (I may want those when coming back from orbit),

I don't really find I miss the jets coming in to land.  I tried to make a tutorial video explaining how you can adjust your glide during re-entry to hit KSC every time.    

If you are still concerned about muffing the re-entry, well a juno or two is enough to limp in with your tail between your legs, but honestly who has the patience and fuel to make a long atmospheric flight back if you came down far from KSC?  I just land wherever i am and take the financial hit on the low recovery %.

I think the main issue with the engine staging rationale is that the Whiplash's thrust multiplier drops to 3 by mach 4.5 (1350 m/s), whereas the  RAPIER stays above that out to mach 5.5 (1650 m/s). .

Because orbital velocity is 2300 or so, the RAPIER version only needs to add another 650 m/s delta-v to get there, the Whiplash needs 950 m/s to make low kerbin orbit.   True, the staged version only carries 1 ton of engines to orbit (two terriers)  while an SSTO would have four tons if using dual RAPIER, also the Delta V of the Terrier is over 10% better.     So why not use RAPIERs as your disposable engines and get the best of both worlds?  Cost, that's why  - the RAPIER is three times as expensive.

I suppose if you're going beyond LKO, the lower dry mass of the two stage design can overcome the  disadvantage of it's lower starting velocity.  But the Stearwing doesn't have the delta v to do this,   that means swapping to nukes as i did with my first entry, a staged whiplash/nerv interplanetary ship.

37 minutes ago, swjr-swis said:

replaced all vernors and RCS by 3x 6-way linear ports

Well, the first problem is, if the Stearwing cannot dock to anything, why does it need RCS?  Reaction wheels are lower drag and never run out of propellant.   My version had an an inline clamp-o-tron.   So, the next question is, can't the orbital object it docks to, which does not need to be aerodynamic, be the thing with the translation ability, and just have the plane passively wait to be docked to?  If the answer is still "no, the spaceplane must be able to translate, to dock to an immobile station via it's clamp-o-tron", then  putting ports on the docking bay means they generate no drag till out of the atmosphere and the cargo doors are open.

Second, if you are going to have RCS, I figured the Vernor's aren't a bad choice.  They use up Oxidizer, which your craft has ample unused tankage for , which saves having to add extra mono tanks.  And they are strong enough to act as lift engines for horizontal landings on Duna / Minmus etc.

[swjr-swis]

I was mostly trying to keep the original appearance while still getting it to orbit and back with as much functionality as possible, since that seemed to be what you asked for specifically:

17 hours ago, AeroGav said:

So, has anyone tried to fix up this design?  What can it do,  and how close to the original appearance were you able to keep?

Considering the wording of the challenge, I am a little disappointed that in your assessment the look wasn't factored at all. There are many many things I would do differently for a spaceplane, if trying to keep the appearance of the original had not been a criterium.

 

16 minutes ago, AeroGav said:

Well, the first problem is, if the Stearwing cannot dock to anything, why does it need RCS?

Because it can in fact dock. LKO rendezvous and docking is almost the only thing it's good for. It retains the Jr docking port on the underside of the panel floor of the cargo bay, like the original. If you check the RCS ports, you'll notice they are set to work only for translation, leaving the reaction wheels to do what they do best. Reaching LKO with 120+ LF and 95 units of mono offers good margin for rendezvous and docking.

 

28 minutes ago, AeroGav said:

putting ports on the docking bay means they generate no drag till out of the atmosphere and the cargo doors are open.

True, and I might've looked at moving RCS into the cargo bay if it had been absolutely necessary. But the drag of the RCS ports does not prevent the craft from easily making LKO, and placing them outside provides the beneficial side-effect of pushing the heat bow slightly ahead of the cockpit, which means I can keep the original cockpit.

 

34 minutes ago, AeroGav said:

Second, if you are going to have RCS, I figured the Vernor's aren't a bad choice.  They use up Oxidizer, which your craft has ample unused tankage for , which saves having to add extra mono tanks.  And they are strong enough to act as lift engines for horizontal landings on Duna / Minmus etc.

The oxidizer space left on this version is just there because of the bicoupler; stock offers no LF-only alternative. Adding almost any oxidizer to that part -just to fuel vernors- quickly unbalances the plane when returning low or empty of LF causing it to spin, and requires rather extreme counter-measures that affect the original appearance more than I was aiming for. Additionally, I saved more mass removing the vernors and oxidizer than I added with the mono tank and RCS - in fact I can add another almost full tank of mono with what I saved. And since this craft gets nowhere near to leaving Kerbin SoI, any changes aimed at landings on other bodies is pointless.

 

Btw, I noticed just now that by using the bicoupler that was in the original 1.0.5 craft, it kept its original tank sizes, which are significantly smaller than they are now (135/165 vs 180/220). Makes me wonder what other values and modules are wrongly translated when importing a craft from older to current versions...

[AeroGav]

6 minutes ago, swjr-swis said:

I was mostly trying to keep the original appearance while still getting it to orbit and back with as much functionality as possible, since that seemed to be what you asked for specifically:

Considering the wording of the challenge, I am a little disappointed that in your assessment the look wasn't factored at all. There are many many things I would do differently for a spaceplane, if trying to keep the appearance of the original had not been a criterium.

 

Sorry that post wasn't meant as a critique of your design at all, I was still discussing the issues with the stock aircraft, but you'd drawn attention to something else to consider.   Yes,  your version does retain the look pretty well so congrats on that.     I wasn't really planning to be the "judge" , i think if there was to be some kind of scoring system it should be based on votes.

[swjr-swis]

3 minutes ago, AeroGav said:

I wasn't really planning to be the "judge" , i think if there was to be some kind of scoring system it should be based on votes.

No worries, I answered the challenge just to see what I could do within the given constraints, it was an interesting problem and quite relevant to me right now since I'm trying to get myself motivated to rebuild several of my older craft. My 'disappointment' stemmed just from being left wondering if I had met that particular part of your challenge. All's well.

The tank size difference set me to thinking though: the stock craft should probably be rebuilt entirely from scratch first, and move from there, to prevent any import artifacts from obscuring the real issues. Which also tells me reworking my older craft may be a lot more work than I care for, if I'm going to have to watch for clues of import errors that the game doesn't warn us about.

[AeroGav]

5 minutes ago, swjr-swis said:

No worries, I answered the challenge just to see what I could do within the given constraints, it was an interesting problem and quite relevant to me right now since I'm trying to get myself motivated to rebuild several of my older craft. My 'disappointment' stemmed just from being left wondering if I had met that particular part of your challenge. All's well.

The tank size difference set me to thinking though: the stock craft should probably be rebuilt entirely from scratch first, and move from there, to prevent any import artifacts from obscuring the real issues. Which also tells me reworking my older craft may be a lot more work than I care for, if I'm going to have to watch for clues of import errors that the game doesn't warn us about.

The tank underfilling caught me out too, but I assumed the original designer of the stock craft had intentionally underfilled it to correct a weight/balance issue or because it simply had no need for extra fuel on stage 2.

I'm working on another design, but when i get 5 minutes i'll maybe post a summary board of what the community has come up with, pics from your ship etc.

Edited December 7, 2016 by AeroGav

[AeroGav]

 

Ok, after creating this "Dreamchaser Stearwing" -

I came up with the idea of using nukes instead of terriers, so that their weight allows me to put the wings as far back as they are on the stock craft. However,  I could not find a legit way to squeeze more than 3 tons of liquid fuel onto the thing, having 6 tons of engines to burn 3 tons of fuel seemed like madness.   But after checking the total weight, minus jet engines , it hit me - do we actually need two nukes?

Concerned that people might struggle with the low TWR, i put the two aft translating vernier engines outside the cargo bay so we can get a  24kn boost from them added onto the 60kn off the NERV.    The drop tanks consist of 3 oscar b as well as some size 0 LF.   These give 88 seconds of RCS assist at the start of the close cycle burn.  The internal oxidizer tanks are locked so there will still be some for docking.

@swjr-swis raised the issue of not having any air breathing engines after re-entry.  I decided to put a Junos on the fixed mk0 fuel tanks either side of the fuselage.

Despite my fears of low TWR,  it actually "only" takes 12-13 minutes from engine start to MECO.   If it was a clean sheet design, i'd want more wing than that - lack of lift meant it stayed deeper in the atmosphere to higher speeds than i'd like, leading to increased drag and higher temperatures (a heat bar appears on the shock cone, towards the end, but no danger).

Unfortunately, after reaching a 100km orbit we only had 850dV or so.  That's a fair bit, but a couple of hundred short of what it would take to reach Minmus.   I guess our low airbreathing top speed (1100 on a single whiplash) and the fact we can only fit 4 tons of fuel on something with a dry mass of 12tons is what really hurts us.

I guess we can toss out those Junos - after return from Minmus you're hardly going to have much fuel anyway - and i can try tweaking the drop tanks, fewer Oscar Bs and more size 0.   But I've got my doubts..

On the bright side, operating economics are way better than the stock craft.  We are only  throwing away one engine at 2200 kredits and  instead of two, and we keep the air intake, wheras the stock ship throws away 8 ramp intakes at 900 kredits each....

[AeroGav]

6 hours ago, AeroGav said:

Unfortunately, after reaching a 100km orbit we only had 850dV or so.  That's a fair bit, but a couple of hundred short of what it would take to reach Minmus.   I guess our low airbreathing top speed (1100 on a single whiplash) and the fact we can only fit 4 tons of fuel on something with a dry mass of 12tons is what really hurts us.

https://kerbalx.com/AeroGav/Stearwing-D45N-Lite

Well, I put this plane on a diet.      Normally it's low on my list of priorities for a spaceplane.   The process usually starts

1. decide on the propulsion

2. get as much lift/drag ratio as possible

3. check the fuel fraction

But now that i've run out of options, i started removing stuff.   The Junos had to go, as did the mk2 clamp-o-tron - it now gets the junior port in the cargo bay floor it had when stock.   This means the port is now slightly recessed rather than sticking out, and also Kerbonauts stuck in coach class have a significant trip hazard between the middle row of seats. But any port in a storm, as they say in the navy, so it'll do.

I kept the two Verniers that thrust downwards in case anyone ever needs a horizontal landing offworld, but replaced the other verniers with a single linear RCS thruster for each axis, being 50kg lighter each.  Since these other thrusters use monoprop, you'll have to load the cockpit's supply up if you're planning to be docking.

I added another mk 0 to the external tanks, which really is the limit or you'll have the thing looking like a jousting knight.  

Finally, I realised the insanity of burning lf/o in a vernier engine at 260 ISP for RCS assist.  Instead, each of the external tanks has a spark engine on the back , with a whopping 320 ISP and 20kn each.

These changes reduced the dry mass about 10%, which by my calculations would only give it 950 dV in LKO.   I made two test flights however, both of which reached 100km orbit with more than 1700dV!

The one thing i am pondering now is why an OSCAR-B tank is less than 1/3 the size of a mk0, yet manages to fit in 18 units of LF and 22 O, vs 50 LF only for the mk0.   Must be some form of liquid compression technology I'm not aware of.

 

 Economy Cabin - looking aft , cargo doors open

Economy Cabin - facing forward , doors shut.

Edited December 7, 2016 by AeroGav

[Gordon Fecyk]

17 hours ago, AeroGav said:

Well, I put this plane on a diet.

I tried flying your D45-N Lite last night on KSP 1.2.1. I had to edit the craft file version to make it load, figuring parts didn't change any in 1.2.2.

How am I supposed to fly this without flipping out of control after Ramjet separation? Either the Sparks or some other component is making the craft pitch up dramatically after separation, and then I lose a third of my speed to drag before recovering and then reverting to launch. I can only reach 1 km/s somewhere between 18 and 20 km up flying horizontally, if I'm lucky.

--

[AeroGav]

2 hours ago, Gordon Fecyk said:

I tried flying your D45-N Lite last night on KSP 1.2.1. I had to edit the craft file version to make it load, figuring parts didn't change any in 1.2.2.

How am I supposed to fly this without flipping out of control after Ramjet separation? Either the Sparks or some other component is making the craft pitch up dramatically after separation, and then I lose a third of my speed to drag before recovering and then reverting to launch. I can only reach 1 km/s somewhere between 18 and 20 km up flying horizontally, if I'm lucky.

--

Hmm.  With SAS off and no control input it settles to a 3 degree negative AoA with the engine still present,   after decoupling this becomes two or three degrees nose up with power off, and about 5 or 6 nose up with power on.

I designed this to fly with SAS set to Prograde hold during the most critical phases of flight .  Like this, the nose-down before separation is only about half a degree AoA,  after separation it becomes about 1.5 degrees nose up, then when the Spark engines burn out it becomes pretty neutral.

The thing is, mk2 fuselage drag is severe when you more than about half a degree or so off prograde, that is why i designed it to fly on Prograde hold.   You can't hand fly with anything like that accuracy.  

Other than putting some instructions up, i'm not sure what else i can do.   I can't move the external tanks  up to be more in line with centre of mass because i'd have to put them out on the wing tips to not interfere with the wing - that's too much of a visual change.

With prograde set the pitch change is fairly small and helps transition you automatically from speedrun mode to the climb for orbit.

Edit - OK,  i will try fine tuning the angle of the wings attached to the whiplash engine so there is no power-off trim change.  

Angling the Spark engines downward to thrust through the centre of mass required angles over 20 degrees, which must make for large cosine losses.   I think that's because they are not very far behind the centre of mass, but quite a long way below it.

I have made a version with the external tanks out on the wing tips.  Because of dihedral that puts them at the height they need to be to be inline with CoM.   To stop it looking like a trident ,  i changed the mk0's for Oscar B's which are much smaller for the same liquid capacity.  And i discovered, 20% of the drag.   I used Configurable containers to change the contents from 18 LF /  22 OX to  32 LF and 8 OX.    If you download that craft, you get the modded tank capacity even on an unmodded install, but it's hardly a very "stockalike" approach !

edit - the one with the wing tip tanks is here, it is more stable i agree.

http://pastebin.com/Yd9SfEi0

What else can i do?  make it into a high wing design i guess,  but the original craft had a mid mounted wings.  Well, something's got to give.

Edited December 8, 2016 by AeroGav

[Gordon Fecyk]

1 hour ago, AeroGav said:

I designed this to fly with SAS set to Prograde hold during the most critical phases of flight .  Like this, the nose-down before separation is only about half a degree AoA,  after separation it becomes about 1.5 degrees nose up, then when the Spark engines burn out it becomes pretty neutral.

OK, I'll check my flight profile again. Thanks for the pointers. That also explains why you turned off the gimbals on the Spark engines.

This confirms what I saw during my flights though: Prograde was a few degrees higher than my basic SAS hold at takeoff, so I'd keep it there and climb gently until prograde drifted closer to my nose. If I flew prograde on ascent, it would climb too quickly and lose speed before reaching thin enough air. So at some point I'd have to switch SAS to prograde, and I just need to learn when to do that.

--

[AeroGav]

3 minutes ago, Gordon Fecyk said:

OK, I'll check my flight profile again. Thanks for the pointers. That also explains why you turned off the gimbals on the Spark engines.

This confirms what I saw during my flights though: Prograde was a few degrees higher than my basic SAS hold at takeoff, so I'd keep it there and climb gently until prograde drifted closer to my nose. If I flew prograde on ascent, it would climb too quickly and lose speed before reaching thin enough air. So at some point I'd have to switch SAS to prograde, and I just need to learn when to do that.

--

The wings are angled upwards so even when the body of the plane is following prograde they are making lift.  At high speed and low altitude this can cause it to pull up into a climb if you stay Prograde.  If you set stability hold (SAS) to try keep prograde at the same climb angle, it ends up flying nose-low, which is  ok but does cause extra drag.

From what I recall,  the best bet is to set SAS stability hold on the runway, so it maintains the 3 degree nose up attitude it has resting on the gear.  That way it will fly itself off.  At 100 m/s set Prograde hold. If the plane tries to climb steeper than 20 degrees it's probably best to lock the nose angle with SAS.  That will cause the nose to fall below prograde slightly until you've climbed to thinner air.. once it's returned back to prograde or started to rise above it, swap back to Prograde hold again.

Once above 6km this calms down a bit.

These climb/descend cycles are called  Phugoids

https://en.wikipedia.org/wiki/Phugoid

aircraft do them when held to a constant angle of attack.  Unless really severe though, they're probably best left to do their own thing.

If the plane jumps above flameout height and you're going less than 1100, i'd just wait for it to come back down and relight.  At some point it'll pick enough speed to be ready for staging.

After going supersonic, it zoom climbed to 25km and is now on the way back down.  

[Val]

Here's my entry.

I tried to keep it reasonably close to the original and even kept the 2 stage design. But I did remake the RCS and removed the Vernors. And rebalanced it a bit so it's easier to control when reentering and landing.

Gets to orbit with just over 500 m/s dV when flown using my recommended Ascent Profile.

Craft, Instructions and more pictures

The landing speed is as low as 35 m/s so it's easy to land in terrain.

[SHiftER2O]

10 minutes ago, Val said:

Here's my entry....

I think you just won the challenge

[AeroGav]

@Gordon Fecyk did you have any more luck with my plane?

Do you think the one i put on kerbal x is better or do you prefer the "beta" one i shared on Pastebin with the wing tip fuel tanks (looks like an F104 now !)

 

[Gordon Fecyk]

1 hour ago, AeroGav said:

Do you think the one i put on kerbal x is better or do you prefer the "beta" one i shared on Pastebin with the wing tip fuel tanks (looks like an F104 now !)

What am I supposed to do with the Pastebin content? It doesn't have the headers of a craft file. Or this an appendix to the D45-N Lite? I tried both of these approaches and KSP 1.2.1 wouldn't even show my craft list.

In any case, with your advice I got to orbit on the D45-N Lite in one attempt, this time with 443 / 860 LF left at 95 km. Game is currently paused so I could write this. Ended up getting to 22 km, Ramjet lost thrust but didn't flame out. Craft descended back to about 15 km but then had enough air for another push to orbit. Stayed prograde through most of that, though I was getting nervous when I was approaching 14 km on the descent and pulled up at least to level pitch.

Also got nervous at about 32 km when I was losing altitude again; is this the phugoid behaviour you linked to? I saw this at 12 km on Thrimm's LTS Dove under Ferram Aerospace; thing was oscillating between 11.5 and 12.5 km or something, and I'd lose and gain airspeed. Though it was stable enough I could turn SAS off and just set trim, then use 4x physics warp.

About to see how far I can go with 440 LF, then see about landing. Much better, now that I know how to fly this bird.

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[AeroGav]

7 minutes ago, Gordon Fecyk said:

What am I supposed to do with the Pastebin content? It doesn't have the headers of a craft file. Or this an appendix to the D45-N Lite? I tried both of these approaches and KSP 1.2.1 wouldn't even show my craft list.

 

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the pastebin link is a webpage that looks a bit like notepad (shows the content of the craft file) but there should be a "get" button above it, which downloads the file.   By default, it saves it with the .TXT file extension  which the game won't realise is a craft file.   If you rename it to .craft it should then work.  Can't remember if you have to change something in folder options in windows to do that, default behaviour of windows escapes me.

Yeah I let the aircraft dip in and out of the atmosphere until i'm going 1100 at least, after that i'd just stage it next time it's passing over 22km.  If you let it dip in more times you might get more delta v, or you might just waste fuel, or blow up from overheating.

I reckon you can get to Minmus with 440. I haven't tested this feature yet, but i kept the Verniers and a smidgen of oxidizer in the hope of pulling one of these off -

 Might cost a bit less fuel than the usual tail sitter, plus there's the style points.