Heavy SSTO Efficiency Challenge

[Nefrums]

I try to keep a fairly constant climb rate  8-12 degrees depending on the twr of the ship.   Ideally you what to reach 1650 m/s in air breathing mode, but anything above 1600 is ok.

I use smart A.S.S. from  mech Jeb as this lets me type in the exact angle that the sas should try to hold.

 

I've been trying to build a ship that does not look like s-it and still is resonable efficient.  It is hard to get the balance right when using cargo bays.

 

 

Edited June 15, 2016 by Nefrums

[Nefrums]

Here you go!   First time i used the cargo ram for anything :-)

 

7374 LS and 2563 OX used -> 6361p

 

Flight profile is simple.

1. Accelerate to Mach 1.25 at sea level  
2. Then 9 degree climb to 23km and 1630 m/s, 
3. Lock prograde, light up the nervs and engage Closed cycle to get to 31km and 2060 m/s
4. Let the nervs burn until AP reaches 300km.

[mk1980]

wow that's really impressive.

one question: are 2 shock cones actually enough to run 10 rapiers? i always used something like 1 cone per 2 rapiers, but your craft looks like it only has 2 shock cones (and no precoolers or other intakes)? or are there hidden/clipped intakes somewhere?

[Nefrums]

2 shock cones is enough, as long as you wait until ~10m/s to throttle up to full power.

[icedown]

@Nefrums @herbal space program

I will hold to ruling that all parts of the craft except the 2 jumbo must return to Kerbin, with the exception of decouplers and docking ports used to make the cargo releasable.  This should make designs without a cargo bay like the Stingray doable with the addition of 2 parts.

[herbal space program]

6 hours ago, mk1980 said:

wow that's really impressive.

one question: are 2 shock cones actually enough to run 10 rapiers? i always used something like 1 cone per 2 rapiers, but your craft looks like it only has 2 shock cones (and no precoolers or other intakes)? or are there hidden/clipped intakes somewhere?

My impression, based on discussions here from 1.0.x,  was that this is moot because a shock cone is actually the best thing you can put on your stack, front or back, to reduce drag. Is that not true? It was certainly true with the small circular intakes when I was trying to make a 0.625m SSTO. I had them front and back on my rocket stack just to reduce drag.

[mk1980]

i think the shock cones used to be more light weight and their mass was increased quite a bit with some patch, so it may be a good idea to use something else that not only adds mass but also helps otherwise. like the 1.25m -> 0.625m adapter tanks with a small 0.625m nosecone on top. they look fairly aerodynamic and they hold some fuel.

[herbal space program]

4 hours ago, icedown said:

@Nefrums @herbal space program

I will hold to ruling that all parts of the craft except the 2 jumbo must return to Kerbin, with the exception of decouplers and docking ports used to make the cargo releasable.  This should make designs without a cargo bay like the Stingray doable with the addition of 2 parts.

It's actually possible to just stick a single docking port between two tanks and then release the one that's connected to the business end by using "decouple node" in the right-click menu., so this is not in fact the sticking point. The problem with this is that AFAICT it's not possible to create any circular configuration using docking ports in the SPH, so you can't actually place the tank between two that are both connected, and the drag model won't occlude the rearward part if it's not connected. From what you said however, I now surmise that the solution mk1980 came up with, that is to turn your tank nose cone into a separate probe that you release and then re-dock with the mother ship on orbit is allowable, since all parts will return to Kerbin. Is that correct?

[icedown]

1 minute ago, herbal space program said:

 I now surmise that the solution mk1980 came up with, that is to turn your tank nose cone into a separate probe that you release and then re-dock with the mother ship on orbit is allowable, since all parts will return to Kerbin. Is that correct?

This is acceptable as the only parts that are not reusable are the tanks.  I really wish I had access to the rapier in my current career game.

[herbal space program]

4 minutes ago, mk1980 said:

i think the shock cones used to be more light weight and their mass was increased quite a bit with some patch, so it may be a good idea to use something else that not only adds mass but also helps otherwise. like the 1.25m -> 0.625m adapter tanks with a small 0.625m nosecone on top. they look fairly aerodynamic and they hold some fuel.

I did notice that they ran to 0.1+t, which is a lot when you're sticking them on both ends of 6 separate stacks. I also noticed that the C7 slanted 2.5-.1.25 adapter performed very well drag-wise. Maybe I'll go with what you said on my side stacks and see if that improves drag.

[herbal space program]

10 minutes ago, icedown said:

This is acceptable as the only parts that are not reusable are the tanks.  I really wish I had access to the rapier in my current career game.

Excellent. I spent last might building one like this, but it still needs some optimization. Nefrums' score will not be in danger either way

[Nefrums]

I'm getting a lot of issues with drag from parts inside cargo bays. Very annoying.

Sometimes I get drag from one tank in the middle of a stack that is inside the cargo bay, but no drag from the parts before and after it in the stack. 

I think it somehow has something to do with stacking several cargo bay parts. The parts that generate drag are always overlapping the area where the cargo bay parts connect.

 

 

[herbal space program]

26 minutes ago, Nefrums said:

I'm getting a lot of issues with drag from parts inside cargo bays. Very annoying.

Sometimes I get drag from one tank in the middle of a stack that is inside the cargo bay, but no drag from the parts before and after it in the stack. 

I think it somehow has something to do with stacking several cargo bay parts. The parts that generate drag are always overlapping the area where the cargo bay parts connect.

 

 

Are you sure everything is actually connected? I've had situations where one tank was clipped into another rather than actually connected, and the only way I could tell was because there was no fuel crossfeed anymore and  the nose cone in the front was no longer occluding its face-on drag.

 

..or perhaps it's that the tank is only drag-occluded by the part of the cargo by it's actually connected to?

Edited June 15, 2016 by herbal space program

[icedown]

If you put the cargo in before you assemble all of the cargo bay, this can cause issues too, as instead of connecting to the cargo bay in front of it, it connects to the cargo who's attach point overlaps it.

[herbal space program]

18 minutes ago, icedown said:

 If you put the cargo in before you assemble all of the cargo bay, this can cause issues too, as instead of connecting to the cargo bay in front of it, it connects to the cargo who's attach point overlaps it.

Ahh. That might explain the terrible performance of my cargo bay-based design as well.

Edited June 15, 2016 by herbal space program

[g00bd0g]

16 hours ago, Nefrums said:

Here you go!   First time i used the cargo ram for anything :-)

7374 LS and 2563 OX used -> 6361p

Flight profile is simple.

1. Accelerate to Mach 1.25 at sea level  
2. Then 9 degree climb to 23km and 1630 m/s, 
3. Lock prograde, light up the nervs and engage Closed cycle to get to 31km and 2060 m/s
4. Let the nervs burn until AP reaches 300km.

That thing is amazing! I'm always impressed with your novel solutions. Orange Pooper, lols...

[Grenartia]

Any advice on how to deal with planes veering off to one side or the other because of the landing gear? I'm pretty sure I've got a workable design aside from my inability to take off because of that. I've got a bunch of reaction wheels, more than enough EC generation, plenty of working control surfaces, LG steering is on, etc.

[herbal space program]

7 minutes ago, Grenartia said:

Any advice on how to deal with planes veering off to one side or the other because of the landing gear? I'm pretty sure I've got a workable design aside from my inability to take off because of that. I've got a bunch of reaction wheels, more than enough EC generation, plenty of working control surfaces, LG steering is on, etc.

Try using two front gears instead of one. Try putting your front gear further back, towards your GOG. Try pulling up on the stick once you get above 50 m/s to take weight off the front wheels.

[Grenartia]

Just now, herbal space program said:

Try using two front gears instead of one. Try putting your front gear further back, towards your GOG. Try pulling up on the stick once you get above 50 m/s to take weight off the front wheels.

Thanks, I'll try it.

[KroShan]

@Nefrums wow thats great... i always thought that 1300-1400m/s is the maximum with rapiers in airbreathing mode. I think i have to reduce my numer of air intakes...
That cargobay drag issue is really not welcome for this challange.
Also i wonder how you can maintain such a low Angle of Attack to keep leveled at sealevel.

@Grenartia two tips from my side if the tips from above don't work: Use heavier Landing gear - the supension is stronger and therefor the deviation due to the load is lower. The second avice is to check if the Landing gear is really parallel to the takeoff direction.

• For this select the landing gear with the rotation gizmo.
• Press 'F' for absolute mode and 'C' for toggle angle snap on.
• Than rotate the gear around every axis so that it looks right.

The Problem there is that many Aero parts are curved in two directions and espacially Landing gear on the BigS wing parts will never be inline with the takoff direction

[mk1980]

i've had some success with using the Large or Extra Large landing gear (with the suspension slider set to something higher than the default "1") as main gear fairlyclose to the CoM and using one (or 2) medium gears on the front. medium gears a lot shorter, so it's a bit of a hassle to place all the gears so the plane is still somewhat level, but the medium gears in the front are steerable, so that's an advantage.

i've experienced some very annoying "swerving" on the runway when the main gear is not perfectly parallel. that can easily happen when you attach it to something curved like BigS wings. that's especially true if you angle the wings upwards to generate more lift in level flight.

it's often easier to attach it to one of the the mk3 parts of the main fuselage and use offset/rotate to move it a bit outwards.

regarding the cargo bays: i think i read somewhere that there may actually be a bug with the aero overlay/gui. ie. the parts in the cargo bay actually don't produce drag, but the aero overlay still shows the alarming super long drag vectors. not sure what's actually going on there. TBH i never found much use for cargo bays in career, so i rarely use them.

[Grenartia]

2 hours ago, KroShan said:

@Nefrums wow thats great... i always thought that 1300-1400m/s is the maximum with rapiers in airbreathing mode. I think i have to reduce my numer of air intakes...
That cargobay drag issue is really not welcome for this challange.
Also i wonder how you can maintain such a low Angle of Attack to keep leveled at sealevel.

@Grenartia two tips from my side if the tips from above don't work: Use heavier Landing gear - the supension is stronger and therefor the deviation due to the load is lower. The second avice is to check if the Landing gear is really parallel to the takeoff direction.

• For this select the landing gear with the rotation gizmo.
• Press 'F' for absolute mode and 'C' for toggle angle snap on.
• Than rotate the gear around every axis so that it looks right.

The Problem there is that many Aero parts are curved in two directions and espacially Landing gear on the BigS wing parts will never be inline with the takoff direction

 

1 hour ago, mk1980 said:

i've had some success with using the Large or Extra Large landing gear (with the suspension slider set to something higher than the default "1") as main gear fairlyclose to the CoM and using one (or 2) medium gears on the front. medium gears a lot shorter, so it's a bit of a hassle to place all the gears so the plane is still somewhat level, but the medium gears in the front are steerable, so that's an advantage.

i've experienced some very annoying "swerving" on the runway when the main gear is not perfectly parallel. that can easily happen when you attach it to something curved like BigS wings. that's especially true if you angle the wings upwards to generate more lift in level flight.

it's often easier to attach it to one of the the mk3 parts of the main fuselage and use offset/rotate to move it a bit outwards.

regarding the cargo bays: i think i read somewhere that there may actually be a bug with the aero overlay/gui. ie. the parts in the cargo bay actually don't produce drag, but the aero overlay still shows the alarming super long drag vectors. not sure what's actually going on there. TBH i never found much use for cargo bays in career, so i rarely use them.

 

I'm pretty sure that's the issue, is that I have my gear attached to the BigS wings. I knew that if they weren't parallel to the takeoff direction, things would be messed up, so I made sure to check for that first, and I was using the larger gears. But I didn't know about the wings. Thanks.

[Nefrums]

Attaching wheels to bigS wing parts is asking for trouble.   Better to attach them to the side of the fuselage. 

Another thing that sometimes helps is lowering the friction setting on the front wheel.

I often use similar wheel placement to real planes.  That is a pair of big wheels very close to CoM to take most of the wight, and then one smaller wheel far from CoM for balance and stearing.

[zolotiyeruki]

Nefrums, besides the two orange tanks, did you have any more fuel in those cargo bays that you used for your ascent?  It seems like you hardly have any fuel in that thing!

[Nefrums]

25 minutes ago, zolotiyeruki said:

Nefrums, besides the two orange tanks, did you have any more fuel in those cargo bays that you used for your ascent?  It seems like you hardly have any fuel in that thing!

About 3 rows of tiny tanks. There are plenty of room at the bottom if you offset the big tanks up a bit.