3 NERV Spaceplane with 2 droppable panthers > 4700dV

[AeroGav]

One for career mode ?  Tier 7 tech space plane that can launch from Tier 2 Runway and Hanger, can be researched with Tier 2 R&D facility.   In fact,  I have deliberately excluded any items that are not on a prerequisite tech node for the Panther or NERV engines.

https://kerbalx.com/AeroGav/Kranker

Flight envelope here, as reported by Kerbal Wind Tunnel.  Note, KWT does not at the time of writing take account of orbital free fall effect, so at mach 4 and upwards it cruises a lot higher than indicated.  It is useful for showing best way to beat sound barrier however and it indicates that the craft would probably make orbit in fully re usable mode, even if you don't activate the final stage and punch off the jets.

Chart on left is for jet power only.  Middle chart is performance with NERVs active,  right picture is with jet stage separated.

Flight tips 

The airplane's wings are angled up and will make lift even if the nose is on prograde.   It also flies a degree or two above prograde even when prograde hold is set, and the nose rises a few degrees further if SAS is taken off completely.

You can more aggressively force  the nose down by activating Orbit mode on the Navball while in Prograde Hold mode, since this makes the airplane attempt to point its nose at the horizon, rather than the prograde marker, which is likely climbing.

Abort action group toggles nukes.   Jettison the jet engines once their tanks empty.  Once you've lit the nukes,  stay on Prograde Hold mode and keep Navball in Surface mode until passing over 70km.

 

[TheFlyingKerman]

How dose the re-entry profile of this SSTO look like?

[AeroGav]

1 hour ago, TheFlyingKerman said:

How dose the re-entry profile of this SSTO look like?

Before anyone shouts at us,  remember it is NOT an SSTO - the jet engines are on decouplers,  and the value of the discarded components comes to 7150 Kerbucks,   though he orbiter itself still has a value of 52,819 Kerbucks after staging and empty of fuel.

As regards re-entry,   if you leave SAS set to Prograde in surface mode it will, because of high lift drag ratio,  keep skipping off the atmosphere and will end up much further downrange than you think.   In fact if you retro burn to an AP of 35km you are likely to come down at this point - after gliding round the entire planet one more time.

To get back in a reasonable timeframe (and without cooking our Kerbals unnecessarily) ,  i'd say use the desert on the continent west of the space centre as your aim point, and retro burn until the blue trajectory line shows you will impact the ground in the middle of the desert.    Come in with the nose pitched at 5 degrees above prograde,   and watch your trajectory from the map mode screen (but keep the navball visible so you can see if the plane is doing anything silly).   As you get down  below 45km the atmosphere should start to bite and the blue line moves downrange.  If you think you might be undershooting,  go to prograde hold mode for a better glide rate, if you think you're overshooting, pitch up aggressively.    Of course you can also use the engines but that's cheating.

 

[TheFlyingKerman]

I am mainly concerned with the crewed parts overheating. That 4700 dv would be enough for going to Dres orbit and return, but is this thing supposed to crash into the Kerbin atmosphere at 3500m/s?

Edited October 21, 2018 by TheFlyingKerman

[AeroGav]

11 hours ago, TheFlyingKerman said:

I am mainly concerned with the crewed parts overheating. That 4700 dv would be enough for going to Dres orbit and return, but is this thing supposed to crash into the Kerbin atmosphere at 3500m/s?

I got home from work tonight and used hyperedit to put it orbit of dres, then forced a kerbin encounter by dumb retro burning from full tanks, ended up going into  kerbin at 4700.   A more realsitic encounter would have lower speeds,  jool return is normally 3800 to 4000 and i normally need to retro burn 500 or more dv on a mk3 

Now, the more you retro burn and slow down before hitting the atmosphere, the lower your periapsis can be and not blow up , which in turn means you can brake more.  So retro burn before aero brake.   I kept save scumming till i found the max speed that enables me to get captured by the kerbin system

with a velocity of 3700 m/s when entering the atmosphere, i could go no lower than 48.6km and after passing through the atmosphere,  we were still on an escape trajectory from kerbin.   At 3600,  we could drop down to 47km and the drag built up and built up,  holding radial out with max roll to spin stabilize us ,   we ended up with a 3 million km apoapsis in the kerbin system after the aerobrake.

So your options would be 

1.  Add an inline clamp o tron to refuel the ship in orbit before setting out for Dres,  ans do the needed retro burn

2.  Do a clever gravity assist off Duna or the Mun.   This is beyond my skill and could add many years to the mission

3.  Accept you wont capture kerbin system on 1st pass,  orbit the sun a few times and the next encounter with Kerbin will be easier.  This also takes a lot of skill and can add decades to the mission

4.  Put a 1.25m heat shield between the nose cone and the cockpit,  and a decoupler in front of the heat shield.    When re-entry is your goal,  decouple the nose cone, exposing the heat shield, and come in prograde,  let the heat shield do its job         Just realised this won't work.   The wings will still explode.   In short term, high intensity heat scenarios like this,  they aren't much tougher than the cockpit.   - it's down to the max skin heat.     The mk1 crew parts have low tolerance for internal heat,  which is due to prelonged, less intense exposure.

 

To be honest i never considered you'd want to go to Dres.     I just built this as a demo of what's possible with this tech level.   In my career games i'm usually still on minmus at this point.      A craft like this might get used for 

• Going to the Mun and driving over the surface biomes
• Visiting Mun and Minmus in same mission - some tourists ask for this
• Gilly
• Duna,   this craft is VERY suited to flying around there and getting thermometer / barometer readings from the biomes in its lower atmosphere.   If you unlock stronger landing gear,  perhaps some verner lift thrusters or some drag chutes,  you could actually land with this plane

 

EDIT -  On second thoughts,   are you wanting me to design a mk2 cargo bay spaceplane based off panther and nerv tech ?   How many cargo bays long does it need to be, if you'd prefer to use it to lob a capsule at places like Dres instead?

Edited October 21, 2018 by AeroGav

[TheFlyingKerman]

Never mind, it just looks like the plane has enough dV for this mission.

In my experience cargo SSTO's are indeed more flexible. 2 CG-04 sections with 2.5t payload would be useful, 3 sections with 3.5t payload would be good. My landers are unusually light and small, though.

 

[Aeroboi]

A few pointers from me about overheating which I tested extensively.

The Mk1 cockpits can all be protected against this to some degree by using wings on it. You can attach something like a main wing to the Mk1 cockpit and then move it to a desired spot on the spaceplane. This way you can have the attachment points of all wing pieces on the most heat intolerant part like a Mk 1 cockpit. Wings are basically radiators

It also works when not directly attached but better when you do. To easily move parts far away from there parent part I use the Editor extensions redux mod by linuxgurugamer. This is a mod I can't play without, even stock

Also, if you place a small heatshield without ablator vertically on top of a stack you can extend the heat resistance of the part below it like a nosecone for instance. Sometimes by many hundred degrees...

The overheat ceiling also is determined by the other parts like type of nosecone or if there is more then one end cap protecting the Mk 1 cockpit or any other heat intolerant part that is the first within the stack. Heat tends to bleed through so having multiple parts protecting a cockpit can help also. Usually nothing so drastic is required, but maybe people can use this. You can test by reading active part temperatures to see where there is heat bleeding using the Thermal UI interface within the debug menu. Heat bleeding would be a part behind another part (in the cross section of the front part "nosecone") that still gets most of the heat effect.

Sometimes a critical temp of let's say 2.000K is achieved at a higher speed then in another case. Using a better thermal nosecone or other part there in between often means that part is able to stay cooler and less heat will bleed through. Sometimes placing the Mk 1 cockpit aft instead of fwt on the fuselage allows it to go a lot faster because the bow shock of the other parts at the front lessen the heat load on parts that are less heat resistant.

Max temperature is also reached based on the orientation of a part against the plasma stream. I'm not sure how it works in KSP at all or what's the story with Mk 1 but since the glass canopy is supposedly less heat resistant I would expect it melts under negative pitch.

[Zosma Procyon]

Aren't Nervs a little heavy for an STO spaceplan? I've never used them in that application.

[AeroGav]

On 10/22/2018 at 11:11 AM, TheFlyingKerman said:

n my experience cargo SSTO's are indeed more flexible. 2 CG-04 sections with 2.5t payload would be useful, 3 sections with 3.5t payload would be good. My landers are unusually light and small, though.

Cargo SSTOs are harder to build though,  you have worse centre of mass problems,  and the drag to overcome is much higher.      A  CG-04 with a mk1 fuel tank in it has over twice the drag of a mk1 fuel tank,  so it's easier to just send the whole damn airplane to a lot of destinations.    If your airplane can reach Minmus with a small drill and resource converter, happy days.    Even if it needs drop tanks and disposable booster panther/whiplash engines to get out of  Kerbin,  it's worth it for the sheer convenience.

Depends where you go of course.  I tend to go to Minmus a lot (a nuke spaceplane can drive from the flats to the polar biome for about 20 units of liquid fuel.). and of course Duna.    I've just got used to having wings and wheels and not having to worry about whether my lander will topple over or if the ladders are going to work this time and actually let my kerbal climb back in.   I also find the sheer size of the vessel comforting, even if that makes no practical difference to the amount of living space available.

For airless, moderate gravity worlds i can see the appeal of a capsule mission.      Also,   from a practical point of view,  your Kredits decreases by 50k when you launch this expensive, 3 nuke airplane, and they don't get refunded till you land and recover it.   If you're just deploying a capsule to low orbit, you get that money back in a few hours, but if you send the whole airplane to Dres,  that's 50k tied up for 10 years until the mission finishes.

Re: Cargo plane - my shift at work finishes tomorrow evening, if i don't fall asleep as soon as i get home.     3 CG-04 is enough you say?   Those are just the small mk2 bays ?

I think i'll also add 2 more landing legs, some rcs and some parachutes and make a Duna Landable version of the Kranker.

 

 

[AeroGav]

2 hours ago, Zosma Procyon said:

Aren't Nervs a little heavy for an STO spaceplan? I've never used them in that application.

They are heavy, 3T compared to 0.5T for a Terrier with the same thrust.    But when accelerating from 750 m/s to Orbit  the fuel used by the Terrier is so much more, it more than makes up the difference in engine weight.    Also lift/drag ratio can do a lot of good things for you.

If you want proof of whether 3 nervs can lift a plane this size to orbit,  here's a save file from just after the Panther engines flame out - copy this into your saves folder,  then go to space centre and ALT F9 and load the "Ready to stage" save

https://www.dropbox.com/s/iqlphh6wfr3qu23/ready to stage.sfs?dl=0

As soon as you're aboard,  put SAS into Prograde hold mode,  then right click on the fuel tank in the Panther nacelle.   When it shows empty, press SPACE BAR to drop them...   then enjoy the ride

[Zosma Procyon]

1 hour ago, AeroGav said:

They are heavy, 3T compared to 0.5T for a Terrier with the same thrust.    But when accelerating from 750 m/s to Orbit  the fuel used by the Terrier is so much more, it more than makes up the difference in engine weight.    Also lift/drag ratio can do a lot of good things for you.

If you want proof of whether 3 nervs can lift a plane this size to orbit,  here's a save file from just after the Panther engines flame out - copy this into your saves folder,  then go to space centre and ALT F9 and load the "Ready to stage" save

https://www.dropbox.com/s/iqlphh6wfr3qu23/ready to stage.sfs?dl=0

As soon as you're aboard,  put SAS into Prograde hold mode,  then right click on the fuel tank in the Panther nacelle.   When it shows empty, press SPACE BAR to drop them...   then enjoy the ride

I only use NERVs in deep space or on worlds with no atmosphere. I had a bad experience with a NERV powered Duna lander that ended up stranded until I burned a third of its fuel.

Edited October 23, 2018 by Zosma Procyon

[AeroGav]

On 10/22/2018 at 11:11 AM, TheFlyingKerman said:

Never mind, it just looks like the plane has enough dV for this mission.

In my experience cargo SSTO's are indeed more flexible. 2 CG-04 sections with 2.5t payload would be useful, 3 sections with 3.5t payload would be good. My landers are unusually light and small, though.

 

OK, sorry for the belated update.   I got home from work and decided to give this new game Rimworld a try for my base building fix,   and I really have no idea what happened to the next five days. 

I tried grafting mk2 cargo bay midsection onto this ship,  and the results indicate why you must never use mk2 parts on an SSTO.   They also show why i prefer just sending the whole airplane interplanetary rather than deal with the issues trying to overcome barn door drag like this in order for the miniscule cargo capacity mk2 bays offer.  It's a pity because the forward swept wings (necessary to have the exhaust plume from the wing engines clear the tail and still have the nukes far enough forward to put the empty CoM where i need it)  give it the appearance of some kind of Inca religious symbol.    I christen thee "Rainbird".    

Please compare  this pic from earlier in the thread -  

1220 m/s and 22km.  Drag is 44.7KN.   Flight time 11 minutes.

1200 m/s and 21.5km.  Drag is 104 KN.   Flight time is 18 minutes.     Look at the massive red drag line it is towing behind the fuselage.

Over twice the drsg.    The original airplane  has a mass of 46.6 Tons, of which 26.7T is fuel.

Rainbird actually weighs 5 and half tons less, fully laden, but drag is more than twice as much.   It had 14.9T of fuel and the payload was 6.5T,  I only flew it once and ran out of fuel before i could circularize the orbit (AP 80km  PE 20KM - close!). 

The original airplane,  with 180kn of thrust and 40kn drag, while it isn't like a chemical rocket, accelerates relentlessly and is a joy to fly.   The effect of the drag is not only difficulty accelerating and high fuel consumption,   it  is less directionally stable despite having increased fin area.     Heading corrections required more often on a longer flight to orbit. 

I guess a chemical plane with 2 swivels would have much more thrust and the higher drag from the mk2 fuselage makes less difference... but your delta v or payload fraction is inherently low in such a design anyway.

I did try my best to optimise Rainbird,   I discovered that one intake can run both jets,  I went down to a single engine nacelle but added two more mk1 tanks.   I decided to ditch the "fuel tanks either side of the main cargo bay" arrangement,  and put the tanks ahead and behind the cargo bay.  This saves the drag from four NCS cones total, which  had been on the front and rear of each tank.     This is a bit tipping your Gin and Tonic over the side rather in an effort to keep the Titanic floating longer... but I had to try.      It was a major redesign and I was sorry to lose the "Rainbird" appearance,   though the reworked plane wasnt entirely unappealing.

This got to orbit with a small margin.   Next,  I swapped out the basic nose cones on the back of the NERVs for some Tier 5/6 Advanced nose cones (this is like spitting over the side of the Titanic) and decided that since i'm paying the drag penalty of two mk2 to mk1 fuselage adapters,  i should fill the oxidizer tanks and find a way to use it.      I snuck a pair of Spark engines in, which are small and light enough not to force a total redesign.   If I've now got 220kn thrust instead of 180 kn and my drag is still 105kn,  then  my excess power goes up from 75kn to 115 kn - a 50% increase in acceleration.  By the time the oxidizer runs out,  we're at such high altitude drag is not so bad anymore.

 

This did actually get to orbit with the payload and 500-600 delta V.    

Earlier in the week however,  i saw a Youtube  where someone showed how to make a mid fuselage payload bay by mounting two 2.5m fairings facing each other.    By this point I was getting disillusioned with KSP and was itching to get back to my Rimworld colony, but i hurriedly threw this thing together - 

Drag is back down to the levels of my original post aircraft,  the 4700dv two stage airplane, and it flies great.   With payload , it comes in at 39.7tons, nearly ten less than the final "Rainbird" derivative (with the Spark engines +  oxidizer) yet it reaches orbit more quickly, with more fuel remaining.  

Craft files -

"Rainbird" - https://www.dropbox.com/s/ksck8ig0mt7h770/Rainbird.craft?dl=0

"Abort" action group toggles nukes,  all of the mk2 variants reqiore this to reach mach 1.      Frist you got to get to 7km at over 240 m/s and shallow dive too.

"SwanSpark"   https://www.dropbox.com/s/9auwd83yqb3c2b5/SWANSPARK.craft?dl=0

Abort action group for nukes on this too.  Also, RCS action group deploys trim flap that lowers nose by a couple degrees

"Fat Fairy"   https://www.dropbox.com/s/v0g8bz5wu1xkp68/Fat Fairy.craft?dl=0

the one with the two 2.5m fairings back to back as a cargo bay.   Abort action group toggles nukes too,  but you don't really need them.   It was put together rather shoddily and the whole tail assembly is attached via the nose cone on the back of the centreline nuke,  yet it works best of the three by a country mile.

 

 

[TheFlyingKerman]

Err... I did not expect such difficulty, is it because my flight profile is different?

For my 22t chemical ship:

I start the rocket engine at 16000m. Speed: 815m/s (on Panthers alone). Note that I am also climbing at over 300m/s. Drag: 26.1kN, a little higher than half of your MK1 design.

22000m Speed: 976m/s Drag: 10.7kN.

The spaceplane reaches 1200m/s at 28600m. Drag: 4.2kN

Edited November 1, 2018 by TheFlyingKerman

[AeroGav]

2 hours ago, TheFlyingKerman said:

Err... I did not expect such difficulty, is it because my flight profile is different?

For my 22t chemical ship:

I start the rocket engine at 16000m. Speed: 815m/s (on Panthers alone). Note that I am also climbing at over 300m/s. Drag: 26.1kN, a little higher than half of your MK1 design.

22000m Speed: 976m/s Drag: 10.7kN.

The spaceplane reaches 1200m/s at 28600m. Drag: 4.2kN

Nice design BTW,   I see you're using the prograde lock method as well :-

Something weird is going on here.   Are you on the current 1.5,1 version of the game? 

Flight profile shouldn't come into it.  Once you're past the transonic high drag region,  lift/drag ratio is pretty constant all the way to orbital velocity.   The only other factor is angle of attack, which we're both similar on as we're both flying prograde.      Your craft is getting a Lift / Drag ratio of 4.1  ,   my  mk2 cargo bay ship was getting 2.2 - the only difference can be the craft itself.

In supersonic flight, at optimal angle of attack, wing parts have a L/D of over 15 to 1,  but fuselage parts with negligible lift and higher drag pull the average for the whole craft down.

For your airplane to be doing better than mine on total L/D ratio it must either have  more wing relative to the fuselage or more of the fuselage must comprise lower drag mk1 parts vs mk2 parts.     Neither of these things appear ot be the case.

So,  something must be glitching out with my craft file...  i did build the interplanetary ship a few weeks ago, before the latest hotfix and the cargo derivatives were all made yesterday. Perhaps grafting this stuff on to an older ship caused a problem?  Or I've done something really dumb,   like attach one of the rear cargo bays to the payload instead of the cargo bay in front of it, etc.   

I checked the obvious bt enabling the "show aero data in action menu" option and clicking each new part in turn, and couldn't really account for the doubling of overall airplane drag.

Can you share the craft file of the pictured vessel, and i'll see if it gets 4.1 Lift/Drag on my KSP install,  and would you mind taking "Rainbird" for a spin and seeing if it only gets 2 to 1 max on yours?

 

[TheFlyingKerman]

I am trying to update KSP. It is taking ages. Please test my plane https://kerbalx.com/TheFlyingKerman/HKA-4BII-SSTO It is a small improvement over an older design. Flight profile is in the KerbalX page.

[AeroGav]

13 hours ago, TheFlyingKerman said:

I am trying to update KSP. It is taking ages. Please test my plane https://kerbalx.com/TheFlyingKerman/HKA-4BII-SSTO It is a small improvement over an older design. Flight profile is in the KerbalX page.

Your plane has a small decrease in L/D ratio but nothing major.   I was getting 3.8 to 1 instead of 4.1 to 1 in the supersonic regime

Sorry about the extreme cropping but i'm still having issues with image uploading , this was the only way to get the file size small enough to upload

And I have finally discovered what is wrong with Firefox, and its derivatives.

IT WAS THE TEST PAYLOAD.

I never flew that airplane empty or changed the cargo bay contents.    I right clicked on the payload, with "show aero data in action menus" enabled, and when it showed zero drag,  I believed it.    Yet my craft's total drag was higher than i could account for by adding up the drag of its individual parts.   The issue appears to be I'd used an FT 800 tank and an FT400 tank as a test payload for my three small cargo bays.        It appears that having the FT800 tank span two short cargo bays does not work,  the game thinks it is outside the bay and applies drag accordingly,  but it does not appear on the action menu.

With it gone,  we are now rocking 4.2 to one  L/D !   What a horrible glitch though.

 

[TheFlyingKerman]

Thanks for the test. So the Mk2 parts aren't THAT bad after all. But no long payload for short cargo bay sections is a silly bug...

[AeroGav]

Alright, my last image was from an empty flight.    This time i changed the cargo to a stack of 3 ft400 tanks.   This does not appear to trigger the bug, maybe it only appears if individual pieces are longer than the cargo bay.  Because the extra drag is not shown in the aero data gui for the cargo bay or payload,  you  have no way of knowing if this is happening or not, short of making full test flights which is very time consuming :-(

As you can see,   the lift to drag ratio is the same when flying empty.    There is more weight so we are lower in the atmosphere at the same velocity, so we have more lift and more drag -  but the ratio is the same.   Due to the extra drag, excess thrust is a bit less which combines with the extra mass to give us a slightly shallower  climb angle and slower acceleration.

So it turns out the craft is actually massively overbuilt,  after subtracting the LF in the payload we still had 1036 LF remaining  so  we could eliminate a pair of mk1 fuselage tanks for sure.

I may in fact be able to get rid of that engine nacelle in front of the cockpit , (makes the nose too long and spoils the look imho)  and replace one pair of the tanks either side of the cargo bay with a nacelle (or even go to a circular intake,  yours appeared to survive the flight to orbit without melting)  as well as eliminating one of the mk1 tanks

So the side tank stacks would now consist of   an engine nacelle and a mk1 tank with an ncs on the front and on the back

 

[AeroGav]

This is the truncated version of the 6.5 ton payload craft,  minus extra fuel tanks.   Cockpit gets hot, would be cooler with a lighter payload.   You could just turn this into a drone i suppose,   you only need the prograde hold feature when flying to space not when returning,   even then it just helps to maximise your delta v.   Of course, the reduction in dry mass up front means pushing the wing mounted nukes further forward.   Perhaps reduce the chord of the wing to a single wing part,  and push the whole front wing forward