How efficient is my design?

[Shaun]

Hello fellow Kerbonauts!

So I'm creating a small/medium universal SSTO with interchangeable payloads. I've cracked a really good design, but just needs a little more testing. That being said, I'm wondering just how efficient my design is.

These are the details:

OEW: 17,500kg

Fuel weight: 26,000kg

Maximum payload: 12,000kg (tested so far, with 350dV left after 150km orbit reached, before payload released).

MTOW: 55,000kg (So far).

Lift: 13.14

My lift value is speculated. It includes the Mk.2 cockpit, but doesn't include vertical stabilisers or rotated Mk.2 adapters, as I'm assumed wings and Mk.2 parts rotated 90 degrees would have no lift, correct?

Edited August 15, 2016 by Shaun

[nosirrbro]

It's quite good. As with anything, there is always ways to improve, but as of now it is pretty solid.

[Shaun]

I'm looking for numbers haha! Like what's the best payload/fuel/aircraft ratios you can get?

[nosirrbro]

15 minutes ago, Shaun said:

I'm looking for numbers haha! Like what's the best payload/fuel/aircraft ratios you can get?

Do you mean I personally or the maxiumum possible?

[Shaun]

Both. I take no pride in super efficient ships that don't look any good

[nosirrbro]

2 minutes ago, Shaun said:

Both. I take no pride in super efficient ships that don't look any good

Well, I've not got any data about any SSTOs I've made, and I also don't have any save files on me. I also don't think that a maximum possible exists, really. You can however just go and look at a whole bunch of other people's SSTOs and see how well you do compared to everyone elses, if you want exact numbers.

[OrbitalBuzzsaw]

Pics plz?

[Shaun]

5 minutes ago, OrbitalBuzzsaw said:

Pics plz?

In time my friend

[cubinator]

In rocket science, there is no "best" or "worst" design. There is only "good enough" and "not good enough". If it's proven to be "good enough" (i.e. ship does what it's supposed to without any issues), you can make more changes if you want but you probably don't need to. If it's proven to be "not good enough" (i.e. it explodes/runs out of fuel/Mark Kerman has to grow potatoes in his own poo for a year), then you should probably make more changes to get it above the "good enough" threshold. I think your ship is probably "good enough" if you've done lots of testing and refining already.

[GoSlash27]

Shaun,

 I define "efficiency" in space planes as operational cost per tonne of payload to orbit. There's not enough info provided here to evaluate that, so the next criteria is payload fraction.  It looks looks decent. Not great, but decent. 22% is respectable for a Mk. 2 design. IIRC, I hit 28% in that range.

 Looking past pure efficiency, there's also the matter of utility and reliability. IMO that's even more important than efficiency. A good SSTO is easy to operate and completes the mission safely every time. You'd be in the best position to evaluate that.

Best,
-Slashy

 

Edited August 16, 2016 by GoSlash27

[StahnAileron]

4 hours ago, Shaun said:

My lift value is speculated. It includes the Mk.2 cockpit, but doesn't include vertical stabilisers or rotated Mk.2 adapters, as I'm assumed wings and Mk.2 parts rotated 90 degrees would have no lift, correct?

That's true of wings for the most part. The body parts I'm not sure of because KSP does simulate a little bit of body lift overall. It's not as pronounced as when a part is given lift numbers, but it's still there. If you want to be certain, just turn on the Aero view while in flight and watch during a typical launch sequence. If you don't see any lift arrows from those parts, it's either non-existent or too small to matter much.

[W. Kerman]

I can whip up a rocket to go to Bop in 10 minutes, where it takes me 30 minutes for a basic, non-cargo SSTO. My standard for efficiency is, can it do it better than something that takes less time.

[Shaun]

1 hour ago, W. Kerman said:

I can whip up a rocket to go to Bop in 10 minutes, where it takes me 30 minutes for a basic, non-cargo SSTO. My standard for efficiency is, can it do it better than something that takes less time.

True, but in career mode, SSTOs definitely come out on top.

[TheDestroyer111]

Shaun you have an extremely high payload ratio! why ask people if this is efficient

[GoSlash27]

4 hours ago, W. Kerman said:

I can whip up a rocket to go to Bop in 10 minutes, where it takes me 30 minutes for a basic, non-cargo SSTO. My standard for efficiency is, can it do it better than something that takes less time.

This is why I scratch my head when people make interplanetary space planes; sure you can do it... but why would you want to? Longer R&D time for something that's only going to get used once, more risk, and it's carrying a lot of stuff that's not needed for the trip.
 To each his own and all... but perhaps a ship destined for Bop is a bad comparison.
 Space planes do a good job at shuttling crew and supplies between KSC and LKO. When used in this role, the measure for efficiency is how cheaply it operates.
 

Best,
-Slashy

[Randazzo]

7 hours ago, Shaun said:

True, but in career mode, SSTOs definitely come out on top.

Meh, they're alright if you're into flying them constantly. Personally I find that once I've developed a reliable round-trip SSTO spaceplane, I'm just about done with career mode. Having to fly the dang thing into orbit and back for every supply run or crew transfer becomes a chore.

[foamyesque]

8 hours ago, GoSlash27 said:

This is why I scratch my head when people make interplanetary space planes; sure you can do it... but why would you want to? Longer R&D time for something that's only going to get used once, more risk, and it's carrying a lot of stuff that's not needed for the trip.

For the challenge, really. Besides, there's spaceplanes and spaceplanes, you know? On Eve and Laythe, wings give you a huge amount of control on reentry, and on Eve they work wonderfully for liftoff and for keeping your lander's CoG low.

[Guest]

21 hours ago, Shaun said:

My lift value is speculated. It includes the Mk.2 cockpit, but doesn't include vertical stabilisers or rotated Mk.2 adapters, as I'm assumed wings and Mk.2 parts rotated 90 degrees would have no lift, correct?

My attempts at sideways Mk2 design have always resulted in the craft pulling to one side, which may be due to poor design, but it seems the parts lift toward whatever way their tops are facing. And about alternating the facing of inline fuselages to even out the sideways lift: getting Mk2 fuselages to keep their rotation instead of getting it from their parent part as they seem to prefer doing every time the whole craft is rotated (to place landing gear, etc.) is a pain.

Edited August 16, 2016 by Guest

[Red Iron Crown]

20 hours ago, Shaun said:

I'm looking for numbers haha! Like what's the best payload/fuel/aircraft ratios you can get?

I ran a challenge for a long while on exactly this, the best entries for single stage airbreathers got over 50% payload by mass to orbit. Those are very tightly optimized designs and ascent profiles, though.

[Shaun]

Interesting... doing some more testing and I'm able to get 18 tonnes into a 150km orbit with a TOW of 61.5T, giving me a payload/mass ratio of 0.29. After which I still have 220m/s d/V before payload detachment and 400m/s d/V afterwards. When i burn for re-entry I still have 120m/s d/V left. 150km is a good 80km above 70km so hopefully with more testing I could get 20.5T into a lower orbit like 80km. If I achieve this, that's a MTOW of 64T and a payload/mass ratio of 0.32, and I'm pretty much right as rain with about 1/3 payload, given the ascent profile is pretty basic, fast and very easy to control. The only issue is packing all the payload at the front makes me nose heavy. It's bearable and controllable, but the control surfaces are creating more drag so on ascent I'm constantly pumping as much fuel as I can to the back. Other than that, with lower payloads, CoG and CoL are dead on, giving higher efficiency as control surfaces aren't creating as much drag.

Also thinking about adding optional drop-tanks. This thing can get smaller payloads to low munar orbit, so who's to say it couldn't land and return?

Overall, very happy so far. My far my best SSTO yet, and only 35 parts.

[KerikBalm]

22 hours ago, Shaun said:

Hello fellow Kerbonauts!

So I'm creating a small/medium universal SSTO with interchangeable payloads. I've cracked a really good design, but just needs a little more testing. That being said, I'm wondering just how efficient my design is.

These are the details:

OEW: 17,500kg

Fuel weight: 26,000kg

Maximum payload: 12,000kg (tested so far, with 350dV left after 150km orbit reached, before payload released).

MTOW: 55,000kg (So far).

Lift: 13.14

My lift value is speculated. It includes the Mk.2 cockpit, but doesn't include vertical stabilisers or rotated Mk.2 adapters, as I'm assumed wings and Mk.2 parts rotated 90 degrees would have no lift, correct?

So while you haven't tested it to its limits, your numbers so far ( maximum payload mass / maximum takeoff mass)* 100% : 12/55 *100% = 21.82%

Not bad. I don't really use Mk2 based planes for cargo... mostly just crew shuttles for training kerbals to lvl3 or early rescue from kerbin SOI contracts. When I was using mk2 planes, they were typically to launch small probes out of the mk2 bay, and my guess is they probably actually had terrible payload fractions considering only the small probe in the mk2 bay.

Mk3 based SSTOs should easily exceed 30% payload fraction... if you're really pushing and don't care so much about what the payload is (ie, inline ore tanks, vs a lander in a fairing/cargobay), you can get a touch over 50% payload fraction.

While I mostly didn't use mk2 craft for large payloads, I did make one mk2 SSTO that had a quite large payload capacity... I never did calculate its payload fraction though:

Spoiler

That was when I was still learning the new 1.0 aero as I progressed with my 1.0+ career save. I haven't looked at making a cargospaceplane without mk3/2.5m+ diameter parts and rapiers in a long time

- often they are actually mk1 based

Spoiler

10 hours ago, GoSlash27 said:

This is why I scratch my head when people make interplanetary space planes; sure you can do it... but why would you want to? Longer R&D time for something that's only going to get used once, more risk, and it's carrying a lot of stuff that's not needed for the trip.
 To each his own and all... but perhaps a ship destined for Bop is a bad comparison.
 Space planes do a good job at shuttling crew and supplies between KSC and LKO. When used in this role, the measure for efficiency is how cheaply it operates.
 

Best,
-Slashy

Indeed, mk spaceplanes aren't meant to go beyond kerbin SOI. Even single stago to Minmus and back is dubious to me, but avoiding another rendevous wins out for me. I do like using them for more than just "supplies"... ie payload transport to LKO... but taking SSTOs beyond low orbit seems questionable to me

-laythe SSTO planes excepted, as long as they are just serving as the lander (which happens to launch itself from kerbin), and not the whole ship... ie like this

Spoiler

Where it is simply docked to the main mission ship as a 6 kerbal lander. (and yes, the main mission ship is overdesigned, it was made big for fun and RP reasons)

^after the ejection booster detaches and retroburns to stay in kerbin SOI

 

7 hours ago, Randazzo said:

Meh, they're alright if you're into flying them constantly. Personally I find that once I've developed a reliable round-trip SSTO spaceplane, I'm just about done with career mode. Having to fly the dang thing into orbit and back for every supply run or crew transfer becomes a chore.

My supply runs late in career are pretty much always at Mun or Minmus, and for crew transfers, you have to haul the crew up and back anyway, the only difference is if you want to land at KSC, or not care where you come down.

I don't become "done" with career mode. Just because I've upgraded all the buildings and unlocked all the tech nodes doesn't mean its over. I'm still planning missions with a budget in mind, leveling up kerbals, occasionally taking a contract (right now my budget is primarily based on mobile labs and science -> fund conversion... so level 4 and 5 scientists really help make those mobile labs churn out funds, while engineers operating ISRUs mean that I don't need to spend so much on my craft with all the refeulable tugs and cargoplanes ot orbit that I've got now)

Edited August 16, 2016 by KerikBalm

[Randazzo]

1 hour ago, KerikBalm said:

My supply runs late in career are pretty much always at Mun or Minmus, and for crew transfers, you have to haul the crew up and back anyway, the only difference is if you want to land at KSC, or not care where you come down.

I don't become "done" with career mode. Just because I've upgraded all the buildings and unlocked all the tech nodes doesn't mean its over. I'm still planning missions with a budget in mind, leveling up kerbals, occasionally taking a contract (right now my budget is primarily based on mobile labs and science -> fund conversion... so level 4 and 5 scientists really help make those mobile labs churn out funds, while engineers operating ISRUs mean that I don't need to spend so much on my craft with all the refeulable tugs and cargoplanes ot orbit that I've got now)

I become done when I'm bored with it. When I'm spending 20-30 minutes just flying to orbit and back, boredom is soon to follow.

With a capsule and mechjeb I can "set it and forget it" both ways. With a plane I have to sit there and babysit it. As I said, if you're into that, it's alright.

[Shaun]

20-30 minutes??? Moor boosters