Nukes to Orbit

[sevenperforce]

This is very simple.

Place at least one Kerbal in orbit, using ONLY the LV-N engine for propulsion/impulse. 

Lowest launch mass wins.

Go.

[FleshJeb]

The atmo TWR won't even lift the engine until you hit 3.5km. Am I allowed to use a 4km-high launch clamp?

[Starman4308]

I tried.

It's not going to be easy, in large part due to the LV-N being heavily vacuum-optimized. I suspect that if somebody manages it, it's going to involve a lot of LV-Ns and some wing parts parachuting down to Kerbin's surface... possibly even before the plane leaves the runway.

[sevenperforce]

1 hour ago, FleshJeb said:

The atmo TWR won't even lift the engine until you hit 3.5km. Am I allowed to use a 4km-high launch clamp?

You hafta take off horizontally to have a chance.

1 hour ago, Starman4308 said:

I tried.

It's not going to be easy, in large part due to the LV-N being heavily vacuum-optimized. I suspect that if somebody manages it, it's going to involve a lot of LV-Ns and some wing parts parachuting down to Kerbin's surface... possibly even before the plane leaves the runway.

Parachuting? Just jettison. This is not about recoverability.

[FleshJeb]

1 hour ago, sevenperforce said:

You hafta take off horizontally to have a chance.

I can only accuse myself of being a short-sighted idiot for that one.

[Laie]

Not sure if I'm even going to try but.... I suggest you specify a command module. Otherwise there will be a "flimsiest crew module" sub-competition.

ETA: Success!

-> Craft File <-

The underwing tanks are almost spent at takeoff, then it becomes a game of eking out as much climb rate as possible. By the time you reach 4km, things fall into place nearly on their own -- but by then, most of the fuel has already been spent. Success or failure is determined by how much time you need to gain some altitude.

Next stage detaches the wings; by then you should be above 10km with at least 30sec to apoapsis. There's nothing wrong in delaying the last staging a bit and consuming some of the core tank's fuel first. If there's some 300u left after staging, that's still generous. I managed to make space with 500m/s left.

The control surfaces on this vessel are mere adornments. It's controlled by magic torque, of which there is plenty. There's also plenty of room for refinement; but I don't have much time right now, so please forgive me for just dropping this here.

Edited December 7, 2017 by Laie

[AeroGav]

4 hours ago, Laie said:

Not sure if I'm even going to try but.... I suggest you specify a command module. Otherwise there will be a "flimsiest crew module" sub-competition.

ETA: Success!

-> Craft File <-

The underwing tanks are almost spent at takeoff, then it becomes a game of eking out as much climb rate as possible. By the time you reach 4km, things fall into place nearly on their own -- but by then, most of the fuel has already been spent. Success or failure is determined by how much time you need to gain some altitude.

Next stage detaches the wings; by then you should be above 10km with at least 30sec to apoapsis. There's nothing wrong in delaying the last staging a bit and consuming some of the core tank's fuel first. If there's some 300u left after staging, that's still generous. I managed to make space with 500m/s left.

The control surfaces on this vessel are mere adornments. It's controlled by magic torque, of which there is plenty. There's also plenty of room for refinement; but I don't have much time right now, so please forgive me for just dropping this here.

Wings are your friends here, I'd personally not want to drop them unless i'm within 90% of orbital velocity.   Those airliner wings don't like heat though, not good for over mach 5.

I'd be more inclined to keep the wings to orbit and ditch the underslung nervs and their tanks when empty, past a certain point - over mach 5 or so,  orbital freefall is supporting most of your weight,  so you will be able to maintain  altitude over 30km even with a small angle of attack.  So drag will be very low.

 

   BTW , is there a rule against rover wheels?   If not i'd take a drive to the mountains behind KSC and launch myself off the top at 5km,   when the NERVs will already perform pretty good due to height.

[sevenperforce]

39 minutes ago, AeroGav said:

BTW , is there a rule against rover wheels?   If not i'd take a drive to the mountains behind KSC and launch myself off the top at 5km,   when the NERVs will already perform pretty good due to height.

Rover wheels are a form of propulsion -- otherwise you could build a ramp and launch yourself off at speed with clever use of staging.

[zolotiyeruki]

Here's successful attempt #1.  38.3 tons

https://imgur.com/a/tgnqo

What happened to imgur albums this time?

Edited December 8, 2017 by zolotiyeruki

[Mayer]

I tried yesterday but my plane could only fly around 100m with 24 LV-N despite asparagus-staging. Looking at that picture, less might have been more.

[zolotiyeruki]

Yeah, just like the Circumnavigation challenge, reducing dead weight is key.

[Laie]

17 hours ago, AeroGav said:

Wings are your friends here, I'd personally not want to drop them unless i'm within 90% of orbital velocity.

Not so sure. One needs a lot of wing to get of the ground, by 10km most of that is definitely no longer necessary. Maybe some winglets later on, but shedding most wings is certainly justified.

Behavior is quite different from jets. Performance doesn't improve with airspeed but altitude, for example. This is the kind of challenge where a deep knowledge regarding lift and drag would be most useful, but the problem is quite different from a jet-powered plane.

[Laie]

Single engine, rolls out at a little under 15t, works nicely. Gallery and craft file.

[AeroGav]

4 hours ago, Laie said:

Not so sure. One needs a lot of wing to get of the ground, by 10km most of that is definitely no longer necessary. Maybe some winglets later on, but shedding most wings is certainly justified.

Behavior is quite different from jets. Performance doesn't improve with airspeed but altitude, for example. This is the kind of challenge where a deep knowledge regarding lift and drag would be most useful, but the problem is quite different from a jet-powered plane.

Well, my 50% payload fraction lifter certainly had a lot of wings, and was NERV powered ! 

...and this thing..

Has a lot of wings, which add mass,  but they enable us to get a 4.2 to 1 lift/drag ratio.       This means it can continue to gain altitude and accelerate with only 0.3 to 1 power to weight ratio (it has  a lot fuel, enough to ssto to Mun surface and back).     Wings are lighter than nervs, so its generally better to add wings than extra nervs

[Laie]

23 minutes ago, AeroGav said:

Well, my 50% payload fraction lifter certainly had a lot of wings, and was NERV powered ! 

From the ground up?

23 minutes ago, AeroGav said:

Wings are lighter than nervs, so its generally better to add wings than extra nervs

Sorry if I sound rude, but.... while everything you say is true, I don't see how it relates to the challenge at hand. Have you as much as looked at other people's entries? The barebone vessel that eventually makes space has approx. 2500m/s@TWR=1. You cannot reduce the number of engines, so there can be no wing<->engine tradeoff. At best, the question is: will it perform better with extra wings attached?

However, even that question misses the point. The much more important problem is, how do you get said barebone vessel to 15km, using nothing but low-TWR gas-guzzlers? On takeoff, my latest submission can hardly keep up with the Wright Flyer...

[zolotiyeruki]

Dangit Laie, and here I was so excited about my 22 ton craft!

[Laie]

On 12/9/2017 at 6:28 AM, zolotiyeruki said:

Dangit Laie, and here I was so excited about my 22 ton craft!

Having been in the same position myself, in other challenges, I know how this feels... and am actually a little sorry about that.

[zolotiyeruki]

No worries--I kinda did the same with the Circumnavigation Challenge (14x around kerbin on air-breathing engines without refuelling!).

[AeroGav]

On 08/12/2017 at 9:10 PM, Laie said:

Sorry if I sound rude, but.... while everything you say is true, I don't see how it relates to the challenge at hand. Have you as much as looked at other people's entries? The barebone vessel that eventually makes space has approx. 2500m/s@TWR=1. You cannot reduce the number of engines, so there can be no wing<->engine tradeoff. At best, the question is: will it perform better with extra wings attached?

Yeah I see what you mean.    The hard bit is getting up to 10km ,  after that you've actually got pretty good TWR, but the question is , is there enough fuel left?   More wings means less drag (because you can fly lower aoa and get up to greater altitude sooner), but more mass needs to be accelerated to orbital velocity.

I got frustrated with the initial takeoff part, and eventually just installed Mechjeb to give me the precise control of AoA you need to make that marginal low altitude flight work.

My entry is 15.689 tons for a command chair to orbit,  though it does keep hold of its wings.   The only parts discarded are the wheels.   I suppose if 100% recycling is your thing, you could make a re-usable dolly to carry it on the ground.

https://www.dropbox.com/s/gj692nirssnd46v/zimtstern.craft?dl=0

 

 

Edited December 11, 2017 by AeroGav

[Laie]

1 hour ago, AeroGav said:

More wings means less drag (because you can fly lower aoa and get up to greater altitude sooner), but more mass needs to be accelerated to orbital velocity.

Oh, wings add drag, too. On my vessel, when I dropped the airliner wings @7km, it took a noticeable leap forward, nearly doubling it's airspeed.

Are all wings created equal? That is, do you always get the same lift:drag for the same mass of wing? Or is there a free lunch to be had somewhere?

[AeroGav]

1 minute ago, Laie said:

Oh, wings add drag, too. On my vessel, when I dropped the airliner wings @7km, it took a noticeable leap forward, nearly doubling it's airspeed.

Are all wings created equal? That is, do you always get the same lift:drag for the same mass of wing? Or is there a free lunch to be had somewhere?

Lift/Drag ratio is the same with all wings.    Lift / Mass ratio is the same for all wings except the basic swept wing.    The Swept Wing, and aerodynamic parts where 100% of the surface area is control surface, have half as much lift as they should for their mass.

Lift/Drag ratio is best about 2 degrees at low speed (below 150m/s),  is optimal at about 3 degrees at 200 m/s,  then at supersonic speed 5 degrees is best.

Jettisoning a wing can temporarily give you a speed boost but since lift is reduced,  drag performance may worsen in the medium term as you end up at a lower altitude which increases drag from non-lifting fuselage parts.    If course, if you are below optimal AoA then it could actually help to correct things by reducing lift.

Of course, you are also shedding dry mass by doing this as well.

I suspect the optimal amount of wing shedding is somewhere between our designs.  Carrying the whole wing to orbit , like mine is too much, because it's extra dry mass and there isn't much fuselage drag to be reduced by gaining altitude sooner due to lift (fuselage is already tiny, compared to wing).    However,  I think going from a FAT 455 to a single Big S wing strake is too drastic.     Don't think i'll build any more entries however, i don't like these edge-of-the-seat flights !

[zolotiyeruki]

IIRC, unless Squad have changed the aero model, wings don't generate parasitic drag, only induced drag.  You *do* get a significant boost when jettisoning the wings, but at least in my experience, that's due more to the loss of mass than the loss of drag.

Is there documentation somewhere of the 2/3/5 degree AoA rule for wings?

[AeroGav]

45 minutes ago, zolotiyeruki said:

IIRC, unless Squad have changed the aero model, wings don't generate parasitic drag, only induced drag.  You *do* get a significant boost when jettisoning the wings, but at least in my experience, that's due more to the loss of mass than the loss of drag.

Is there documentation somewhere of the 2/3/5 degree AoA rule for wings?

Ages ago,  I did an experiment - attached a number of different wing segments to an airplane, flew it with "display aero data in action menus" turned on, to verify that all wing parts have same lift/drag.

 

I then used mechjeb to fly an airplane at different angles of attack,  and found the best l/d values.     It's easy enough to get a "whole craft" l/d value by enabling aero data gui in the  alt f12 menu, and use that to tune Mechjeb.   In subsonic flight (less than 0.6 mach) you can get very high l/d ratios from the wing parts (over 40) at low AoA,  but the parasite drag from the fuselage limits the total craft value to less than half that.

[astrobond]

Hi All

Fun challenge !!! I had to test

Here is my try, KSP 1.3.1 stock + KER, weight of the "plane": 12.713 Ton. (with command module)

 

And Merry Christmas !