Space Plane

[Slipstreamable]

Hi

I've watched countless youtube videos, read a whole bunch of tutorials, but I just can't get my space plane into orbit with enough fuel left. I've only got the whiplash engine at this stage...On launch I'm at 10-15 pitch until the jet engines starts losing thrust, then I engage the dart engines pitching up to about 45 and jettison the jet engines when they flame out. My goal is to land on the moon and return, short of refueling in orbit what am I doing wrong or what can I improve?

 

Edited March 25, 2017 by Slipstreamable

[AeroGav]

Landing on the Mun is a very tall order.   The delta V requirement is much more than for Minmus, in fact it's probably more than a round trip to Duna, given that an airplane can aerobrake and glide in to land.  

Improvements - 

The mk2 fuselage is a bit draggy and the pointy cockpit is a bit vulnerable to heating effects, but that just forces you to use more jet engines and you aren't carrying those past flameout anyway, so it's only a cost issue.   As regards the heating ,  Whiplash probably don't get fast enough to be an issue.    

How much velocity are you managing on air breathing?  900 m/s is max power on those engines, but you've got four so you should be hitting 1100-1200.

Assuming we're still set on the Mun,  I'd go with the "detach rear fuselage in orbit" trick.      

At the back of the fuselage, put a terrier engine, then an inline mk1 cockpit, then a fuel tank, then some docking ports to attach it to the rest of the airplane.   Make some tailbooms off the wing for vertical stabilizers (or strakes rotated vertical hanging off the trailing edge).   

In orbit, transfer the remaining fuel to this rear tank and undock that section , go to the moon, on the way back, dock with the airplane again and make your re-entry.

[Alshain]

I don't know if it will get you to the Mun and back, but you have Asymmetric thrust and mass issues that are just going to eat your fuel.  Having that much mass mounted mounted high is going to make it hard to balance the plane, on top of that the engines are thrusting high, which will push the nose of the plane forward.  While you may be getting it to space ok, you are forcing it to ascend using the ailerons.  Using the ailerons to hold your nose above the velocity vector will eat away at your fuel quickly.

If those engines were mounted a bit closer to the center of mass (vertically) then you could probably do with less fuel getting up to their flameout, reducing overall mass and allowing you the option of packing fuel in for the rockets.

[Slipstreamable]

21 minutes ago, AeroGav said:

Landing on the Mun is a very tall order.   The delta V requirement is much more than for Minmus, in fact it's probably more than a round trip to Duna, given that an airplane can aerobrake and glide in to land.  

Improvements - 

The mk2 fuselage is a bit draggy and the pointy cockpit is a bit vulnerable to heating effects, but that just forces you to use more jet engines and you aren't carrying those past flameout anyway, so it's only a cost issue.   As regards the heating ,  Whiplash probably don't get fast enough to be an issue.    

How much velocity are you managing on air breathing?  900 m/s is max power on those engines, but you've got four so you should be hitting 1100-1200.

Assuming we're still set on the Mun,  I'd go with the "detach rear fuselage in orbit" trick.      

At the back of the fuselage, put a terrier engine, then an inline mk1 cockpit, then a fuel tank, then some docking ports to attach it to the rest of the airplane.   Make some tailbooms off the wing for vertical stabilizers (or strakes rotated vertical hanging off the trailing edge).   

In orbit, transfer the remaining fuel to this rear tank and undock that section , go to the moon, on the way back, dock with the airplane again and make your re-entry.

Thanks for the reply, yes the mun is quite hard this is a tourist contract I'm trying to complete. Could do it with a rocket but my plane division is way behind so trying to make it up.

On air breathing I'm maxing out on 1010 m/s, engage rocket engines up to 1160 m/s until the jet engines flame out which takes me to 1820 m/s reaching 80,000m apoapsis.

I will try your suggestion with the "detach rear fuselage in orbit" trick, but that will add extra weight meaning more jet engines?

 

[Slipstreamable]

18 minutes ago, Alshain said:

I don't know if it will get you to the Mun and back, but you have Asymmetric thrust and mass issues that are just going to eat your fuel.  Having that much mass mounted mounted high is going to make it hard to balance the plane, on top of that the engines are thrusting high, which will push the nose of the plane forward.  While you may be getting it to space ok, you are forcing it to ascend using the ailerons.  Using the ailerons to hold your nose above the velocity vector will eat away at your fuel quickly.

If those engines were mounted a bit closer to the center of mass (vertically) then you could probably do with less fuel getting up to their flameout, reducing overall mass and allowing you the option of packing fuel in for the rockets.

I thought having those engines up high would cause trouble, I had to add wings to the top as well to raise the COL, although it handles quite well but fuel is an issue as you mentioned.I couldn't think of way to mount them on side with wings and eventually jettison them with losing my wings as well.

Edited March 25, 2017 by Slipstreamable

[bewing]

Your pitch angles and therefore climb rates are very high. You save a lot of fuel by being more gentle and taking more time -- and you would probably only need half as many jet engines.

Also, changing your pitch angle causes a dramatic loss of speed -- which you need to burn more fuel to recover. If you want to save fuel, don't pitch up -- just keep flying straight.

 

Edited March 25, 2017 by bewing

[Slipstreamable]

10 minutes ago, bewing said:

Your pitch angles and therefore climb rates are very high. You save a lot of fuel by being more gentle and taking more time -- and you would probably only need half as many jet engines.

 

I'll try 5-10 pitch angle? I just realized I can only take a max of two tourist on this contract, so I removed the mk2 crew cabin saving 2 tons and using fly-by-wire. But I still need to use my rocket engines to blast past mach 1 with my 4 jet engines at this moment. I'll also try removing 2 jet engines and see how it goes with the lower pitch angle.

Edited March 25, 2017 by Slipstreamable

[bewing]

When you are trying to get through mach 1, your pitch angle should be about 0. Using the "F" key to lower your nose helps you maintain your speed while pitching down.

Edited March 26, 2017 by bewing

[AeroGav]

42 minutes ago, Slipstreamable said:

I will try your suggestion with the "detach rear fuselage in orbit" trick, but that will add extra weight meaning more jet engines?

Two docking ports add a fair bit of drag, though probably not as much as all that mk2 fuselage you have atm.   You can get a fairing to cover this area if you want the ultimate in efficiency.  The main problem is time added to the mission , why i don't do this more often.  Redocking with the airplane again at the end when you just want to go home and cash in.   I suppose you could put a radial chute on this section and land it separately - if the airplane handles ok with its tail off.

[Slipstreamable]

I will try getting through mach 1 at 0 degrees, I will try and see what works better redocking/seperate landing strategy.

[Slipstreamable]

Thank you everyone, all the suggestions helped, I think it's smooth sailing for now. Gave me some great things to think about. Didn't realize how different space planes are to rockets till now, I love how KSP still challenges me after all this time

[Alshain]

1 hour ago, Slipstreamable said:

I thought having those engines up high would cause trouble, I had to add wings to the top as well to raise the COL, although it handles quite well but fuel is an issue as you mentioned.I couldn't think of way to mount them on side with wings and eventually jettison them with losing my wings as well.

Try mounting them under the wings.  The wings can be a little high, in fact, mounting the wings high makes the plane more stable (mounting them low makes it more maneuverable but this isn't a fighter jet, you are going in a pretty much straight line to orbit).  Plus if you are using a drop-tank design, under wing mounts carry less collision danger.  However, you may still need more wing, that little pair of wings may be a bit small for such a large craft.

 

If you haven't seen it already, read this.  It's old but still relevant.  Comments on the KSP atmosphere are outdated however.

 

Edited March 25, 2017 by Alshain

[Slipstreamable]

7 minutes ago, Alshain said:

Try mounting them under the wings.  The wings can be a little high, in fact, mounting the wings high makes the plane more stable.  Plus if you are using a drop-tank design, under wing mounts carry less collision danger.  However, you may still need more wing, that little pair of wings may be a bit small for such a large craft.

 

If you haven't seen it already, read this.  It's old but still relevant.  Comments on the KSP atmosphere are outdated however.

 

I'll try and mount them under the wings, currently mounting them high up makes me nervous when jettison them...angled up wings makes it more stable, interesting.

Haven't come across that post yet, skimmed through it and loads of information I'll need to study. This is why I like KSP, steep learning curve with exceptional satisfaction.

[Alshain]

Dihedral (angled up) high wing mount does make it more stable, but I'm just talking high wing mount on it's own.  You don't want it too stable, then you won't be able to make even small maneuvers.  But as an SSTO or TSTO in this case, you don't need to turn on a dime either.  If it still ends up over-stable, you can make the wings anhedral high mount and still mount the drop tanks under the wing. The big problem with TSTO is making sure it's CoM doesn't change so much that the plane is great for ascent and then flips out of control on descent.  Losing all the engine mass is a pretty big change.  So make sure you test the position of the CoM with the drop tanks removed and most the fuel gone too.

Edited March 26, 2017 by Alshain

[Slipstreamable]

4 minutes ago, Alshain said:

Dihedral (angled up) high wing mount does make it more stable, but I'm just talking high wing mount on it's own.  You don't want it too stable, then you won't be able to make even small maneuvers.  But as an SSTO or TSTO in this case, you don't need to turn on a dime either.  The big problem with TSTO is making sure it's CoM doesn't change so much that the plane is great for ascent and then flips out of control on descent.  Losing all the engine mass is a pretty big change.  So make sure you test the position of the CoM with the drop tanks removed and most the fuel gone too.

Thank you on the clarification on the high wings, will test it make sure and I can still land afterwards.