Duna SSTO Troubles

[Mk3 Maniac]

I hav a serious issues with my good for nothing tri-fueselage Mk3 SSTO. The craft in question is loosely based off Matt Lowne's Artemis SSTO and Mark Thrimm's Gallene SSTO. The craft has a ten ton Cargo Capacity. But the previous model can't take off from Duna. Maybe it is because the TWR is "abysmal" (https://www.youtube.com/watch?v=t1EbS9ZnI94) The Craft gets the apoapsis up to 20 Km until it reaches apoapsis and begins slowly descending into the evil ground killing the crew instantly. I would love to upload a picture and a craft file but I am locked out of my steam account, for reasons to convoluted to get into. But the Oxidizer is at 10,000 (rough estimate) and the Liquid fuel at 45,000(estimate), and weighs in at 427 tons (with cargo). Another thing I can think of is that I may not know the best way to fly a Duna SSTO. 

PS would someone please give me advice on how to upload Craft files?

Mark Thrimm's SSTO:https://www.youtube.com/watch?v=UuDOdFQP4pY

And here is the link to the pictures: 

 

Edited March 26, 2017 by Mk3 Maniac
No picture of actual space craft.

[Mk3 Maniac]

Here is the craft file

https://drive.google.com/file/d/0B3I_z4W2q1AGSVhGSTRSYjNBbDg/view?usp=sharing

 

[Razorforce7]

Pictures please. Your craft may be based on Matt Lowne's or Mark Thrimm's SSTO designs but it is not any of those so videos or links of their craft are useless to us.
Obviously this makes answering your question nearly impossible.

However, based on what you've said I wouldn't go straight to raising my Apoapsis to 20km.
Try a more gentle ascent profile.
Dunas Atmosphere is very thin. You want to go as fast as possible throughout all the parts of Dunas atmosphere. If you don't have alot of TWR and you just burn on a steep ascent to raise your Apoapsis you will be needing more thrust then necessary to circularize. Instead use the atmosphere of Duna itself untill you got sufficient speed.
If that doesn't work I suggest to install a one or two extra Nervas.

Above might be completely useless to you because...... you forgot to upload a picture. But I hope the suggestion was usefull either way.

[Snark]

1 hour ago, Mk3 Maniac said:

would love to upload a picture and a craft file but I am locked out of my steam account

...Looks like you solved the .craft problem, but would still be really helpful to have a screenshot, as has been suggested.

Note that any Steam troubles you may be having are irrelevant for posting screenshots.  Just pick some image-hosting site for the shots.  The most common and popular one here on the KSP forums is imgur.com, possibly because it's so easy to use, and you don't need any sort of account or anything to use it.  Just go to imgur.com, click a button, drag-drop your image, copy the image URL.  Paste the URL here, it gets automagically turned into an in-line image.  There, done. 

[AeroGav]

Many of my SSTOs are Duna-capable (have a look on my KerbalX link, a lot of these Duna vehicles have landing videos too),   they have a generous amount of wing area though, strong landing gear and some Vernor thrusters to lower landing speeds.    I take off and fly to orbit with LV-N only.  

Until I can get home and DL your craft file I won't know how it's built, but three mk3 fuselages sounds like an extremely heavy beast.  I'd be very surprised if it has enough wing area to actually fly like an airplane on Duna.

Remember - wings support you while building up to orbital velocity in horizontal acceleration.  Sounds like you're taking off vertically, running out of oxidizer,   and falling back to the ground before your nukes are able to circularise? 

 

Edited March 26, 2017 by AeroGav

[Foxster]

Fundamentally the problem with your craft is that you have  thrown moar boosters and fuel at it until you hope it works. 

The first mistake is the choice of cockpit/capsule. Everything balloons from there. 

Edited March 26, 2017 by Foxster

[Mk3 Maniac]

11 minutes ago, Foxster said:

Fundamentally the problem with your craft is that you have  thrown moar boosters and fuel at it until you hope it works. 

The first mistake is the choice of cockpit/capsule. Everything balloons from there. 

But, but, but, The mk3 cockpit  is very heat resistant. Also which engines/fuel tanks should I take out IF that is the case.

[Foxster]

I suggest asking yourself: What is the minimum number of Kerbals I want to take to Duna and back? Then, what is the lowest payload mass to achieve that?

Of course, that's only if you are looking at doing this efficiently or want to have a good chance to succeed. If you are doing this as a self-imposed challenge of getting a Mk3 SSTO to Duna and back then don't mind me and carry on. 

[fourfa]

Perhaps the OP isn't yet aware - Duna's surface is essentially a vacuum.  ~0.7% of Kerbin's surface pressure. Vacuum-optimized engines like 909s and LV-Ns are operating at over 99%.  Planes designed to land on Duna at survivable speeds in the wispy trace atmosphere look like spindly gliders with dead minimal mass.

The easiest way to land on Duna is forget that there's even an atmosphere, and land retropropulsively like on Mun or Moho.  A couple drogue chutes will slow you down to a couple hundred meters per second, making the final landing burn fairly simple.

But if you're determined to land an office tower on Duna, first step might be to start designing around some core vacuum-optimized engines (Rhino, Poodle, Terrier, Aerospike, LV-N) capable of Duna takeoff thrust, then add what you need to take off from Kerbin.  Insist on landing horizontally - add about a hundred times as much wing area, enough parts to melt your CPU, and build it to basically survive a crash landing.  Might be a bit easier to make it HOTOL on Kerbin, VTOL on Duna.  Easier yet to HOTOL on Kerbin and land on its tail on Duna.

PS - the two videos you linked are craft for Eeloo and Laythe, both quite different than Duna.  Matt Lowne has a video of a Duna plane which crashed and exploded over 120 times before managing to stick the landing just so - that doesn't seem like a winning strategy to me.  Mark Thrimm has a Duna SSTO video tutorial series, where he builds a much smaller SSTO that uses lots of VTOL thrust and parachutes to essentially crash land and mostly survive.

One last thing - there isn't enough re-entry heat on Duna to blow up even 1200K parts like solar panels.  So you must be talking about Kerbin ascent and re-entry.  If you feel forced into Mk3 parts for heat tolerance, it's likely that your design and trajectory is suffering from other problems, as many of us manage to work around heat problems even with Mk1 and Mk2 command pods at the nose.  And I think you'll find more and more SSTO noses made of fairings, which can be very light and low drag.  Just a few more ideas.

Edited March 26, 2017 by fourfa

[AeroGav]

1 hour ago, Mk3 Maniac said:

But, but, but, The mk3 cockpit  is very heat resistant. Also which engines/fuel tanks should I take out IF that is the case.

I don't have time to fully rebuild your ship but i might have a look for easy mods.

The mk3 cockpit is right at the front so gets the worst of the heat.  At mk2 or even mk1 inline cockpit , if placed some way back from the front , does much better heat wise.   I agree with @Foxster though, moar boosters doens't work on airplanes.

I have a couple of Duna mk3s, all the same -

 

 

[Mk3 Maniac]

4 minutes ago, fourfa said:

Perhaps the OP isn't yet aware - Duna's surface is essentially a vacuum.  ~0.7% of Kerbin's surface pressure. Vacuum-optimized engines like 909s and LV-Ns are operating at over 99%.  Planes designed to land on Duna at survivable speeds in the wispy trace atmosphere look like spindly gliders with dead minimal mass.

The easiest way to land on Duna is forget that there's even an atmosphere, and land retropropulsively like on Mun or Moho.  A couple drogue chutes will slow you down to a couple hundred meters per second, making the final landing burn fairly simple.

But if you're determined to land an office tower on Duna, first step might be to start designing around some core vacuum-optimized engines (Rhino, Poodle, Terrier, Aerospike, LV-N) capable of Duna takeoff thrust, then add what you need to take off from Kerbin.  Insist on landing horizontally - add about a hundred times as much wing area, enough parts to melt your CPU, and build it to basically survive a crash landing.  Might be a bit easier to make it HOTOL on Kerbin, VTOL on Duna.  Easier yet to HOTOL on Kerbin and land on its tail on Duna.

fourfa the Craft has 4 aero spike engines on it's belly.

[AeroGav]

Edit - finding 1

The engine mount method for your main engine cluster is incredibly draggy.

You have a 3.75m engine mount, which has one attach point for a 3.75m engine.  You are putting one 1.25m engine on it.   The game calculates the surface area of the 3.75m,   subtracts the surface area of your 1.25m engine and then assumes the rest (90%) plus has just been left as a flat plate, and applies drag accordingly.  

It doesn't see the extra engines neatly mounted around the outside of the central one, it treats them as separate 1.25m stacks, which you have 6 of,    and because they don't have pointy cones on the front, it gives them flat plate drag too.

Remember - a craft file is a root and branch structure.   Every branch needs to end in a pointy object.   No weeping stumps.   All transitions from one diameter stack to another need to be handled by a size adapter.

 

You've solved the high drag by adding more jet engines, then more oxidizer to lift those heavy jet engines to space.

Not enough wings or nukes to support the resulting heavy craft on Duna.

Radial mount vs using adapters.

 

[Mk3 Maniac]

Ok what I am getting from all of the feedback is that I need more wing area, or make everything lighter. But how do I do this without ruining the look of the craft, I did some changes though, here they are  

[Mk3 Maniac]

Ok I changed the craft so I am now using adapters instead of radially attaching stuff, which is different than what I usually do. Is there anything else I can do?

[Mk3 Maniac]

 

[Mk3 Maniac]

One last question, is it possible to reduce drag on the other engine array?

[bewing]

Did you straighten the whiplashes? They were crooked in my download.

I disagree with AeroGav about the heating in this plane. It's not an issue. Bad veering on the runway is definitely an issue, though. And drag is only a marginal issue. It gets to LKO OK.

[Mk3 Maniac]

4 minutes ago, bewing said:

Did you straighten the whiplashes? They were crooked in my download.

I disagree with AeroGav about the heating in this plane. It's not an issue. Bad veering on the runway is definitely an issue, though. And drag is only a marginal issue. It gets to LKO OK.

The  drag is not bad in getting to LKO but rather LDO as it ruins the ability to fly in the super thin atmosphere.

 

[bewing]

I don't think I agree with that. If you actually want to fly this thing at Duna, you're going to need some incredible wings. The atmosphere is very thin to support any significant weight, and "signifcant weight" is definitely what this thing has. You certainly need more controllability, though. Some vernors would do some good.

 

[Mk3 Maniac]

Thank you for the advice I will keep this in mind in the future, this SSTO will be repurposed for trips farther than Duna due to the extra fuel in orbit. I will show that SSTO in the future.

[AeroGav]

6 hours ago, Mk3 Maniac said:

The  drag is not bad in getting to LKO but rather LDO as it ruins the ability to fly in the super thin atmosphere.

 

The problem with drag is that you need lots of engines to get past mach 1,  each engine weighs 2 tons,  which then needs lots of oxidizer to lift into orbit.  It's the weight of all that oxidizer and all those jet engines that really make the craft so heavy.

The other problem your craft has is that when the fuel tanks are empty it is tail heavy and unstable.    I need to find a way to get more dry mass up front without spoiling the looks, and more fuel mass in the back.   Using wet wing parts for the tail surfaces might help with the latter.   Some ISRU equipment placed behind cockpit would help with the former.

The huge fuel tank in front of cargo bay would have to go or get swapped for a much shorter one.  That's a major job because everythign else attaches to it .

 

[Wanderfound]

On the ship in general:

It is much larger than you need, and that's where most of your troubles are based.

Too many engines, too much fuselage, too much mass, too much drag. You can cover the entire system (i.e. an ISRU equipped SSTO with enough range to reach Minmus unrefuelled; do that, and you can go anywhere except Moho) with a Mk3 this size:

(you can also heft 60+ ton to LKO with a ship about that big)

You can also Grand Tour in a Mk2 this size:

 

So, first up: if you're willing to do so, streamline and simplify. Chop it down to a single-fuselage build if you can.

You need enough jet thrust to get you up to takeoff speed (which should be 100m/s or less if you've got enough wing) before the end of the runway; any more than that is a luxury. Somewhere between three and eight RAPIERs should be enough for a Mk3 if you keep the mass within sensible limits.

For fuel, you want just enough oxidiser to lift the apoapsis out of the atmosphere on Kerbin (after a normal airbreathing ascent to 30,000m/1,500m/s). The rest of the tankage should be devoted to LF for the nukes.

 

Regarding Duna specifically: the atmosphere is crazy thin, and this makes landing difficult. Slow down much below supersonic in a normally-winged ship and you'll fall from the sky. So, you either need to take a huge-winged glider (not a good use of mass when you're spending 99% of the trip in vacuum), or find a method to quickly dump a lot of speed just as you land.

For any long-range spaceplane, I normally place Vernors on the belly for low-G VTOL. Not enough to work on Kerbin, but something that lets you soften the last few metres of a wheels-down descent on the Mun or Minmus (i.e. descend tailfirst on the engines, then flip it to horizontal and fire up the Vernors at the last moment). Like this:

Those also come in handy on Duna. They won't actually hold you up, but they help a lot to soften the landing impact and control your descent rate as you begin to stall. Pitch up enough and they work as retrothrusters, too.

Even after touchdown, Duna is tricky: it's bumpy, low-G and there's no runways. So you want a very wide and stable wheelbase, and a braking method that doesn't rely upon tyre friction. I usually go with drag chutes (just stick a pair of radial chutes around the tail), but small retrothrusters (e.g. a pair of Twitch engines at the wing roots, facing forwards) work as well.

For takeoff on Duna...similar issues to landing. Bumpy ground and thin atmosphere. You won't get much lift until you're doing speeds that are too fast to safely do on the ground...but, fortunately, there isn't much gravity.

I usually handle a Duna takeoff with a few seconds of RAPIER boost to give me a bit of altitude and airspeed, then switch over to the nukes for the rest of the ascent. Just keep an eye on your climb rate; keep it positive but stable and low. There's no need to climb steeply to avoid the negligible drag.

Edited March 27, 2017 by Wanderfound

[Mk3 Maniac]

Dear everyone who recommends ISRU, I already did this before with a SSTO. It feels unrealistic, plus if I could do it with ISRU then could I try without? In case you care about said craft here it is, though may I say it is quite sloppy. https://drive.google.com/a/iusd.org/file/d/0B3I_z4W2q1AGbjlTakdsMU1zVFk/view?usp=sharing

Also Aerograv I am very impressed with your Mk3 duna SSTOs, when I first looked at them (after they where downloaded) I asked myself, do you really need all of those NERV engines? Whats the trick behind it all?

[Wanderfound]

What I posted is pretty much the same whether or not ISRU is involved. Thanks to the tyranny of the rocket equation, increasing vessel size brings sharply diminishing returns, especially when dealing with the inefficiencies of wings etc. You'll get the longest range from the most efficient ship, not the biggest one [1].

Are you trying to get from KSC to Duna unrefuelled, or are you planning on refuelling it once it's in Kerbin orbit?

 

[1] But there's nothing wrong with building huge things if that's what you're into, even if it does cost you a bit of range. There is no One True Way; if you're having fun, you're doing it right.

Edited March 28, 2017 by Wanderfound