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MitchS

SSTOs to and from Laythe

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Hi, all!

After a lot of help and guidance from you wonderful people over the last month or two, I went from building Single-Stage-To-Nowheres to building compact and capable Mk1, 2, and 3 spaceplanes that happily deliver station modules into orbits all over the Kerbin system--and look good to boot. With active stations and surface bases on Kerbin, Mun, and Minmus, my 30+ Kerbonaut fleet is finally put to use, and the time between transfer windows is actually as fun as the interplanetary stuff. Life is good. Thank you!

...But now a Jool window is coming up, and I want to take my new Bachelor of Science degree in Spaceplane Engineering and apply for a Masters program.

If I have a spaceplane that can take a 10t payload to LMO and return with 5% fuel left, could I just put an ISRU in one half of the cargo bay and extra fuel in the other--enough Delta V for a Jool transfer, etc--and make the Laythe trip, simple as that? Or does a spaceplane need to be designed with Laythe in mind? How does a spaceplane behave differently there? Is the ascent profile the same, with slightly different altitudes in mind, or is it fundamentally different? How do engines behave?

What did YOU learn about spaceplane design when you started going interplanetary that you think might not be obvious to a Kerbin-system SSTO builder? What did you learn when you started going to Laythe?

Thanks!

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The main point about Laythe is that you are going to be landing on the water. If you are careful, you may always be able to take off from land -- but you will certainly always be ditching to get landed. So build your spaceplane with a < 70 m/s water landing in mind. Expect your glide speed to be about 20 m/s higher on Laythe.

The 500 m/s lower orbital speed makes reentry trivial.

 

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On 10 January 2017 at 2:32 AM, MitchS said:

Hi, all!

After a lot of help and guidance from you wonderful people over the last month or two, I went from building Single-Stage-To-Nowheres to building compact and capable Mk1, 2, and 3 spaceplanes that happily deliver station modules into orbits all over the Kerbin system--and look good to boot. With active stations and surface bases on Kerbin, Mun, and Minmus, my 30+ Kerbonaut fleet is finally put to use, and the time between transfer windows is actually as fun as the interplanetary stuff. Life is good. Thank you!

...But now a Jool window is coming up, and I want to take my new Bachelor of Science degree in Spaceplane Engineering and apply for a Masters program.

If I have a spaceplane that can take a 10t payload to LMO and return with 5% fuel left, could I just put an ISRU in one half of the cargo bay and extra fuel in the other--enough Delta V for a Jool transfer, etc--and make the Laythe trip, simple as that? Or does a spaceplane need to be designed with Laythe in mind? How does a spaceplane behave differently there? Is the ascent profile the same, with slightly different altitudes in mind, or is it fundamentally different? How do engines behave?

What did YOU learn about spaceplane design when you started going interplanetary that you think might not be obvious to a Kerbin-system SSTO builder? What did you learn when you started going to Laythe?

Thanks!

 

Okay; first up, a demonstrator:

Unlike Duna or a vacuum world, flying on Laythe is fairly similar to flying on Kerbin. A bit less atmosphere and gravity, but basically the same.

The main trouble you'll run into is in landing. The surface is mostly water, and there ain't no runway. However, this does not mean that you need to build an interplanetary seaplane. Just plan your entry to the planet with a bit of care, so that you slow down to reasonable speed while having enough fuel aboard to reach land.

Most of the islands have areas sufficiently flat for landing, but you do need to build for it. A wide, stable wheelbase is useful; so are drag chutes and retrothrusters.

As well as Laythe issues, you need to deal with Jool issues. Spaceplanes don't have the heat tolerance for an interplanetary aerobrake; you're going to have to burn fuel during your Jool capture. Aerobraking the Jool/Laythe transfer should be fine, though. Kerbin-Laythe direct isn't really practical without a heatshield.

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Flight handling is pretty similar on Laythe; it's pretty forgiving and Rapier work very well there.   You might want a little more wing for the thinner air,  but that's about it. 

I have not done the ISRU plane before but I'm sending one now.   No reason it shouldn't work,  as long as you find a site with adequate ore concentration.  (Small drill requires 3.5% I think).

One of the most important things is getting good at gravity assists.   They will allow you to inject at Jool/Laythe for next to nothing. 

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Posted (edited)

Not a spaceplane guy myself, but the key factors are gravity (~75% of kerbin),  atmospheric pressure (60%) and atmospheric height (50km). 

So I'd expect a jet engines to have the similar performance of higher heights in kerbin,  more wing area needed to produce the same lift, less drag and less weight. 

All in all looks to me more wings are the way to go in Laythe,  given the fact drag is less an issue and (jet)  engines will produce less thrust. Reaching orbit seems easier than kerbin because Laythe is smaller and less massive. 

 

Anyways,  this is just guessing. And you probably can imagine it yourself,  I for one will wait the spaceplane guys to give more embased advice. Edit:and,  since my connection suks right now,  such advice come while I was trying to post my answer and getting error messages

Edited by Spricigo
Small remark

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I would also say refuel at minmus and go from there,

Yes I know oberth blah blah blah, but you'll be full of (free) fuel launching from very high kerbin orbit so would negate any oberth benefits. 

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Posted (edited)

2 hours ago, MitchS said:

Hi, all!

After a lot of help and guidance from you wonderful people over the last month or two, I went from building Single-Stage-To-Nowheres to building compact and capable Mk1, 2, and 3 spaceplanes that happily deliver station modules into orbits all over the Kerbin system--and look good to boot. With active stations and surface bases on Kerbin, Mun, and Minmus, my 30+ Kerbonaut fleet is finally put to use, and the time between transfer windows is actually as fun as the interplanetary stuff. Life is good. Thank you!

...But now a Jool window is coming up, and I want to take my new Bachelor of Science degree in Spaceplane Engineering and apply for a Masters program.

If I have a spaceplane that can take a 10t payload to LMO and return with 5% fuel left, could I just put an ISRU in one half of the cargo bay and extra fuel in the other--enough Delta V for a Jool transfer, etc--and make the Laythe trip, simple as that? Or does a spaceplane need to be designed with Laythe in mind? How does a spaceplane behave differently there? Is the ascent profile the same, with slightly different altitudes in mind, or is it fundamentally different? How do engines behave?

What did YOU learn about spaceplane design when you started going interplanetary that you think might not be obvious to a Kerbin-system SSTO builder? What did you learn when you started going to Laythe?

Thanks!

I've flown around a bit on Laythe, but to get there I always stopped on Minmus or Duna to refuel.       Going direct to Laythe is hard - the transfer burn to Jool is a fair ways larger than for Minmus or Duna, but the delta V to get from a circular orbit of Jool to a Laythe intercept can be even larger than the Jool transfer burn itself. 

If you're clever with orbital mechanics you can use an Eve flyby to get to Jool  and a Tylo gravity assist to capture and set course for Laythe - but i am not ! 

Laythe itself is a peach.

It is mostly water, but it's still pretty easy to dead stick into one of the islands if you're coming in from orbit.   Your craft would have to fly like a brick to not make it.

The land on those islands is hilly, like the highlands of Kerbin, but if you can land there you can land here.   Gravity is 80% of Kerbin's and the air pressure at sea level is a bit less, so overall landing speeds are about the same they would be on Kerbin.   So, before the grand voyage, check your plane is landable in Kerbin's highlands when empty of fuel and that's a pretty good simulation.

In terms of taking off again, it's much easier.    The air starts a bit thinner but doesn't lose density with increasing altitude as fast as it does on Kerbin.   Rapier's don't flame out till about 42km - and at 50km you're in space !  What also helps is that the orbital velocity is lower than on Kerbin - it's only a couple hundred m/s faster than the air breathing top speed of rapier engines.

Overall the main challenge is getting to Laythe.   Stop at Minmus to fuel up, stop again on Ike to brim the tanks and don't underestimate the Laythe capture burn.   Once you're able to aerobrake on Laythe you're home and dry.

The fact that launching from Laythe is easier than from Kerbin does open up possibilities if you want to push things, eg. go direct from Kerbin with no refuels or gravity assists.

You won't need as many engines to get off Laythe and/or won't need to fill the oxidizer tanks.   You could, for example, have some booster engines for the launch from Kerbin that get decoupled, since they won't be needed on laythe.  This will reduce mass for the interplanetary voyage making that bit so much easier.

20161028201210_1_zpstzsv2qhi.jpg

Edited by AeroGav
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8 hours ago, bewing said:

The main point about Laythe is that you are going to be landing on the water. If you are careful, you may always be able to take off from land -- but you will certainly always be ditching to get landed. So build your spaceplane with a < 70 m/s water landing in mind. Expect your glide speed to be about 20 m/s higher on Laythe.

The 500 m/s lower orbital speed makes reentry trivial.

 

I dunno about that; with some liberal use of f5/f9 I've always been able to find a dry spot to land on.   But dry does not always mean flat,  though - most of the land is pretty bumpy.  In any event,  being able to water land is certainly helpful,  especially if you have a less maneuverable plane. 

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Ok listen here lad. Got a dang lot of experience in this area. DV wise,  5k m/s in orbit of Kerbin and you are good. That is without ISRU. A mk1 50 ton SSTO can get you to Laythe no problem and no ISRU... that is if you turn down the darn re-entry heating on the difficulty options. Ok seriously. A laythe and back shouldn't be too hard if you are willing to planet hop there... but when coming back, you are going to either need a very heat resistant craft or do a heck ton of gravity assists to get your speed down enough to re-enter safely. I have tried many times without ISRU and trust me on this... it is NOT fun. Hence the somewhat aggravated approach on this post. Sorry about that! :/ But if you decide not to heed my advice and dive straight into Kerbin's atmosphere at 5k m/s, good luck! You are going to need it. :P 

Oh and ascending from Laythe is a walk in the park. You can have a much more aggressive angle of attack due to the lower gravity. And you probably don't need oxidizer on ascent. It helps but if you want to save fuel or something, you most likely don't need it!

Fire

Edited by Firemetal

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11 hours ago, AeroGav said:

I've flown around a bit on Laythe, but to get there I always stopped on Minmus or Duna to refuel.       Going direct to Laythe is hard - the transfer burn to Jool is a fair ways larger than for Minmus or Duna, but the delta V to get from a circular orbit of Jool to a Laythe intercept can be even larger than the Jool transfer burn itself. 

Stop at Minmus to fuel up, stop again on Ike to brim the tanks

 

2 hours ago, Firemetal said:

A laythe and back shouldn't be too hard if you are willing to planet hop there...


Why does everyone think planet hopping is worth it? It takes much more fuel and a lot more effort. Look at the dv chart, from a trans-Jool orbit you can reach Laythe with about 400m/s dv. OP wants a "compact and capable Mk1, 2, and 3 spaceplanes", they can aerocapture much easier than interplanetary ships.

@Palaceviking is onto something here:

12 hours ago, Palaceviking said:

I would also say refuel at minmus and go from there,

Yes I know oberth blah blah blah, but you'll be full of (free) fuel launching from very high kerbin orbit so would negate any oberth benefits. 

I am a big fan of Oberth, but realize that in some situations it is less efficient because of being "further away"(going back to eliptical Kerbin orbit)
From Minmus low orbit it takes 1160m/s dv to reach a Jool intercept(the launch window depends on Kerbin-Jool positions, but also the Minmus relative position as to burn in a prograde direction). The advantage here is that using nukes(or even Ions) are certainly possible, since doing a 15minute burn won't be less efficient

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Do you plan on refueling on laythe's surface? On most of my games, I find the low flat terrain to be entirely devoid of ore, and finding a flat spot with any ore at all has been a challenge. You don't have to plan for a water landing, but it can't hurt:

Spoiler

12232672_10104009213191453_3293490752122

Even if its just a small surface explorer:

kerbin testing:

KuGRZmV.png

new version, on laythe:

4ZAW15O.png

You certainly can land a spaceplane on laythe though:

Spoiler

xsE3Kur.png

akhX6tm.png

ievBgHk.png

Laythe space planes used to perform the same as on kerbin, except better. It used to be 80% surface gravity, 80% atmospheric density - so the exact same landing speed resulted, TWR was higher because jets didn't lose thrust in the thinner atmosphere, and orbital velocity was 500 m/s lower.

The gravity is still 0.8 Gs, but the atmospheric density is 0.6 (it may be slightly higher if KSP models that colder air is denser, but the MW of the gas is the same as on kerbin, and the pressure is 0.6 atms). So landing speeds are roughly sqrt (0.8/0.6) x higher... so 15% higher - this applies to parachute descent too, FYI. Jet TWR is also lower because of the thinner atmosphere. The planes will fly pretty much the same, but not quite.

Note, as mentioned above, the air doesnt stay thinner:

IQrDY6X.png

from 10 km to nearly 50 km, the pressure on laythe is higher (it drops off steeply around 50km, to vacuum). At 40km though, its ~ 4x denser than kerbin's atmosphere at 40km (which still isn't very dense). 40km on laythe is equivalent to 30 km on kerbin. Contrary to a previous poster, I find my jets flame out at about 38-40 km on laythe (it depends upon which speed you are going when you reach those altitudes though). In contrast, 0km on laythe is equivalent to about 3km on Kerbin.

Reentry from low laythe orbit is less intense than on Kerbin due to the lower orbital speed, but not as much as you'd think because you get into the thick atmosphere faster (you may recall that 20-30km is around peak reentry heating for kerbin.. and you reach the same air density on laythe very fast before you can slow down much). Still, reentrering from 1850 m/s isn't hard.

Its the aerocapture that is hard - coming in from a hohman to jool gets you going pretty fast relative to laythe. Make sure you come in going in the smae direction as laythe's orbit, not in the opposite direction. Com in tangent to laythe's orbit.

Better still is to use gravity assists to capture around Jool, and get your velocity relative to laythe much lower... then try for the aerocapture.

If you use low heat tolerance parts thinking reentry from low laythe orbit is easy, you may find yourself getting burned to a crisp trying a direct aerocapture.

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Contrary to a previous poster, I find my jets flame out at about 38-40 km on laythe (it depends upon which speed you are going when you reach those altitudes though). In contrast, 0km on laythe is equivalent to about 3km on Kerbin.

I might have said 44km in my hazy recollection, but you get the idea much much closer to space than on Kerbin !

Thankyou for the graph btw!

32 minutes ago, KerikBalm said:

Do you plan on refueling on laythe's surface? On most of my games, I find the low flat terrain to be entirely devoid of ore, and finding a flat spot with any ore at all has been a challenge.

 

My space planes tend to land at 50 m/s or less empty, so landing on the top of the hilly islands (3 or 4km up) wasn't a problem.  However, first time,  i was completely out of fuel at this point  and came to a stop in a low ore concentration.  Released the brakes, ran downhill a bit, and fortunately snagged myself some ore.     Does having an engineer aboard help with the min ore concentration?

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9 hours ago, Blaarkies said:

 


Why does everyone think planet hopping is worth it? It takes much more fuel and a lot more effort. Look at the dv chart, from a trans-Jool orbit you can reach Laythe with about 400m/s dv. OP wants a "compact and capable Mk1, 2, and 3 spaceplanes", they can aerocapture much easier than interplanetary ships.

@Palaceviking is onto something here:

I am a big fan of Oberth, but realize that in some situations it is less efficient because of being "further away"(going back to eliptical Kerbin orbit)
From Minmus low orbit it takes 1160m/s dv to reach a Jool intercept(the launch window depends on Kerbin-Jool positions, but also the Minmus relative position as to burn in a prograde direction). The advantage here is that using nukes(or even Ions) are certainly possible, since doing a 15minute burn won't be less efficient

I mean if you have less than 3,000 m/s to start with in LKO. Also sometimes you can get low orbital insertions. (If your spaceplane overheats way too easily in which case, you ain't comin' back!)

Fire

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55 minutes ago, Firemetal said:

I mean if you have less than 3,000 m/s to start with in LKO. Also sometimes you can get low orbital insertions. (If your spaceplane overheats way too easily in which case, you ain't comin' back!)

Fire

From LKO you need 2000m/s to reach Jool(with a small margin for error). With a 800m/s at Jool you can definitely go straight to Laythe if you have confidence in the vehicle. My point is that you need about about 2000m/s to get to Ike/Gilly surface to refuel...but 2000m/s could just as well get you to Jool where maneuvers are really cheap:
-Unless you start LKO with 1270m/s...then jump to Minmus, then to Ike and so forth(Minmus to Jool costs 1160m/s, i don't want to take that risk either)

Sorry i don't mean to bash any playstyle, planet hoping is a valid reason for completionist exploration and all fun of the game...i just found it odd that it is so popular :blush:

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5 minutes ago, Blaarkies said:

From LKO you need 2000m/s to reach Jool(with a small margin for error). With a 800m/s at Jool you can definitely go straight to Laythe if you have confidence in the vehicle. My point is that you need about about 2000m/s to get to Ike/Gilly surface to refuel...but 2000m/s could just as well get you to Jool where maneuvers are really cheap:
-Unless you start LKO with 1270m/s...then jump to Minmus, then to Ike and so forth(Minmus to Jool costs 1160m/s, i don't want to take that risk either)

Sorry i don't mean to bash any playstyle, planet hoping is a valid reason for completionist exploration and all fun of the game...i just found it odd that it is so popular :blush:

Well. To be honest, I would find planet hopping boring. I usually build SSTOs that have enough DV to reach a destination in the first place rather than have to stop along the way to refuel. Also when I said 3k m/s, I added 1k extra for wiggle room. It seems I always have to wiggle.

In my post I was just saying that no matter how much DV you start with and whether you use ISRU or not, re-entry heat is ALWAYS your biggest problem.

Fire

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2 hours ago, AeroGav said:

Does having an engineer aboard help with the min ore concentration?

Not as far as I know, for puroses of the little drill's minimum requirement.   Also,  if you're playing on hard and the concentration is literally zero, I don't think engineer multipliers will help.

On sandbox test for my new Laythe ISRU base, the first beach I landed on had something like 14%.  Sure it won't be that good in my career game...

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15 hours ago, Blaarkies said:

 


Why does everyone think planet hopping is worth it? It takes much more fuel and a lot more effort. Look at the dv chart, from a trans-Jool orbit you can reach Laythe with about 400m/s dv. OP wants a "compact and capable Mk1, 2, and 3 spaceplanes", they can aerocapture much easier than interplanetary ships.

@Palaceviking is onto something here:

I am a big fan of Oberth, but realize that in some situations it is less efficient because of being "further away"(going back to eliptical Kerbin orbit)
From Minmus low orbit it takes 1160m/s dv to reach a Jool intercept(the launch window depends on Kerbin-Jool positions, but also the Minmus relative position as to burn in a prograde direction). The advantage here is that using nukes(or even Ions) are certainly possible, since doing a 15minute burn won't be less efficient

No, never ions please, still gives me twitches thinking about 35minute burns.

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Hi everyone! Thanks for being so prolific on this post while I've been gone.

I designed my SSTL, and it's giving me some serious problems that I can't put my finger on. It behaves fine to get to orbit, but on reentry and landing, it's inherently unstable despite a correct distribution of CoL and CoM, perfectly balanced wet mass and dry mass (for both my oxidizer tanks and my LF tanks), and adequate control surfaces. The plane has a strong nose-down tendency in unpowered flight, and at when I raise the AoA above about 15 degrees, it flips retrograde like my CoM is behind my CoL or something. So in pitch-up maneuvers, it acts like my CoM is too far back, but with less than 10 degrees AoA, it acts like my CoM is too far forward and I'm holding the stick back near full to keep the nose up. WHAT is going on? 

Here's a picture of final approach so you can see the CoM and CoL markers with the pitch inputs...
3wXfrcg.png

And here's an album with a few captioned pictures that highlight some of the problems. 
http://imgur.com/gallery/IDBLp

Oh, and here's the craft file. https://www.dropbox.com/s/wc6b20y56cvqvfc/SSTL Mk_ I.craft?dl=0

The section in between the short rocket fuel segments in the rear of the fuselage is a small ISRU setup, which opens downward. I think that's the only non-intuitive thing about the ship.

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You may want to try zooming your camera in on your plane, to see if the game agrees with your mod on where the CoM is. (If the red dot doesn't stay in the center of the picture, then they disagree.) You may want to manually transfer some fuel backward to balance out your pitch control, no matter what your other readouts are telling you.

Other than that, the flipping issue is probably going to be drag related. Turning on the aero display, looking at the plane from the side, and deliberately inducing a flip while spamming F1 may get you some pictures of which parts are contributing too much drag to the front of your plane.

If nobody else does it, I'll take a peek at your design in a few hours.

 

Edited by bewing

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Hey @bewing. I did what you asked! No dice.

The markers appear to be accurate, and reflect what I designed in the SPH

When I transfer weight back, it just becomes more flip-happy. I have the symptoms of a CoL too far forward AND too far backward at the same time.

I turned on the aero display, but I don't know what you mean by spamming F1... is that a screenshot hotkey for steam or something? Either way, I did some flipping (meant to do some of it, too) and viewed the overall picture with blue and red lines, and nothing seemed particularly out of the ordinary, and then viewed individual parts by their right-click menus for their drag values. Again, nothing strange except maybe one thing. The rearmost short rocket fuel fuselage (that I clipped two nukes into) had a very high drag value during takeoff and climbout, as well as while I was flying fast and low to test parts in thick atmo. Where other fuselage parts had a drag value of around 6, this one had a drag value around 20 or more. Maybe it's because it's the rearmost part, but I had already put a small nosecone on the unused node to avoid the excess drag that open nodes produce, so I don't think it should really be THAT draggy.

Anyway, I'm not sure what I'm looking for with the aero menu (I don't ever really use alt-f12 functions or debug menus) so I feel a little bit like where I started. Stumped.

Are my canards producing too much lift with pitch inputs? I tried turning down their deflection limits but didn't see much improvement--and it became hard to lift the nose below 90m/s on the runway, which I consider unacceptable for a spaceplane.

I would really love it if you could take a look at my design and see how it flies for you. I'm out of ideas.

Edited by MitchS

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6 hours ago, Palaceviking said:

No, never ions please, still gives me twitches thinking about 35minute burns.

Same here, I unlock them every career but only use them once on a useless probe, then never again. But now i learned they should be used like we do with nukes...not enough thrust? add more! :P

To be serious, they should be added as a ratio of the payload(like any other engine actually): 
(1 ion engine + xenon tank + electricity supply) per 1 ton of payload, expect to get 0.1 TWR. (thats about 14 minutes for a burn from LKO to trans-Mun)
...sadly, that is where they fail. Long burns are not fun, even though those can go into low Mun orbit and back to LKO 5 times before refueling

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1 hour ago, MitchS said:

I would really love it if you could take a look at my design and see how it flies for you. I'm out of ideas.

Can't load it -- it still has 3 non-stock parts attached: the OmniLights, the Scansat-Scanner32, and the Engineer7500 chip.

 

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I can't open the craft file because i don't have the mods installed - what do i need?  I'm off to work soon, so i might not get a chance to try it .

Are you sure mechjeb isn't messing with you here?  I've had trouble with it doing crazy stuff before.       When the aoa exceeds 15 degrees, do the control position displays on bottom left corner of the screen indicate that nose down correction being applied or is MJ trying to pitch up further?

Also i've started to fall out of love with reaction wheels.     Does it still do the same with them disabled?   I've found that in low dynamic pressure regimes,  (low and slow, or high and not v fast, near stall) they have enough torque to overcome the natural stability of the airplane and push you way past stall angle.  

 

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11 hours ago, MitchS said:

I would really love it if you could take a look at my design and see how it flies for you. I'm out of ideas.

Since I couldn't open it, I rebuilt it from the pix as best I could. I left the stuff out of the cargo bays. After rebuilding, even though mine was lighter than yours (because there was nothing in the cargo bays), I couldn't get the thing to mach over. So I don't quite know what you did to make yours get to orbit.

So then I started messing with it. I saw some of the instability you were talking about, and I had some ideas for things to try. I tried lots of things, and they all sort-of worked, but I can't tell you definitively which was the "right" answer -- if there even is such a thing in this case. Also, I didn't spend the time to balance the fuel perfectly, so my CoM shifts a little backwards as my fuel burns off. If you want to modify my modifications, you should fix this, of course.

So, general quibbles and stuff I did:

Each part has drag. And if you can move the draggy bits from ahead of the CoM to behind the CoM, that increases stability. And the farther the better. So, I moved the batteries and reaction wheels in the nacelles to the back. I moved the solar panels as far back as I could. I moved my wheels as far back as I thought I could get away with.

I stuck on a pair of stationary tailfins to add a little more drag at the back, and to give a little additional yaw stability for fun.

I don't like the Standard Canards. I don't think they give you enough bang for the buck. So I replaced your 4 with 2 tailfin canards. I moved them far forward to give maximum leverage. You really do want to give them maximum leverage -- your placement had them a lot closer to the CoM than they needed to be.

I thought that a lot of the drag that was preventing me from getting through mach 1 was from the way you had attached the nukes. So I replaced that whole scheme with a bicoupler and attached the nukes normally.

I saw that you had attached your wings with what looked like 5 degrees of incidience -- and that's a lot. So I was thinking maybe that had something to do with it. So I reduced the indicence to 3 degrees.

IMNSHO, a plane this big needs more wing than you had. So I doubled it.

Oxidizer is heavy and not good to carry. You want as little as possible. Just enough to hop from 24km at 1400 m/s to 31km at 1600 m/s. The nukes can do the rest, much more efficiently. So I replaced most of your rocket tanks with LF tanks. If you plan on landing on Tylo, maybe add some ox storage back, but leave it empty.

After flying mine, I decided I could do away with 1 reaction wheel, so I aced the one off the nose.

Yes, it has fewer control surfaces than yours. It's a quirk of mine. But it does get to orbit with quite a bit of fuel left, and it flies OK without all that instability.

H8YELDj.jpg

craft file:

http://pastebin.com/raw/5m3hxfyf

 

 

Edited by bewing
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@bewing THANK YOU for doing so much work for me. I really appreciate it! Sorry I couldn't get you the mods sooner. The only mods that should be affecting that craft file are MJ, KER, SCANsat, surface-attach lights, and... oh. Well, I have golf clubs and screwdrivers in the inventories of a couple of the seats, so maybe KIS/KAS...? Not sure how that gets noted in the craft files. Tonight when I get home from work, I'll make a stock version of the file that nixes all those parts.

A couple notes in response: (Sorry I can't nicely quote your post on my work computer)

"...After rebuilding, even though mine was lighter than yours, I couldn't get the thing to mach over. So I don't quite know what you did to make yours get to orbit."
Yeah, it has a pretty slow climbout compared to my other spaceplanes--around 160-220m/s up to 10km--and doesn't get supersonic until a speedrun at 10km. After that first speed run, the increased lift points the prograde vector at about 12-15 degrees and gets me to my real speedrun at 22km, where I can reach 1,550m/s on airbreathing cycle. When my RAPIERs drop to 30kN or so of thrust and my speed isn't climbing more than a m/s per second, I switch modes and use about 80% of the oxidizer I'm carrying to boost the Ap to 40km and 1m30s ahead of my ship. After that, it's all nukes--with about 7 seconds of oxidizer left in reserve so if I want it, I have it available. I logged the stats on three successful launches with this latest version of it (I spent so much time troubleshooting reentry and landing that I only had 3 ascents in all this time) and IIRC, powered flight took around 18 minutes and circularization happened at 23. So... not terrible but pretty tolerable considering I had 3200m/s delta v in LKO before reloading. Seems a pretty efficient setup to me.

"And if you can move the draggy bits from ahead of the CoM to behind the CoM, that increases stability."
I was wondering if the LF nosecones ahead of the in-line Mk1 fuel tanks (and their accompanying canards) were causing too much drag too far forward. I can't really tell where my CoP is, or where my CoL is when body lift is taken into account (which, why would it ever NOT be, Squad?!), so I'm not really sure how to check this, besides just assuming it's too far forward and trimming back. Which I don't like, because it's really, really well balanced right now barring the problem at hand which may not even be being caused by the things I'm considering removing.

"I stuck on a pair of stationary tailfins to add a little more drag at the back, and to give a little additional yaw stability for fun."
I might add more yaw stability too, but our aesthetic tastes are different so I'll play around with something I like better than those awful things. :wink:

"...I replaced your 4 with 2 tailfin canards. I moved them far forward to give maximum leverage... your placement had them a lot closer to the CoM than they needed to be."
I looked at the lift and deflection values, and it looked like my standard canards had the same lifting area and deflection as most of the other comparable control surfaces... So I picked them aesthetically. Why do you think they don't give enough bang for the buck? Also, isn't one of the symptoms of my craft that it's overmaneuverable as it is? I would normally place them farther forward too, but I was trying to limit the torque moment of their drag at high AoA so I brought them closer to CoM. Paired with tailfins, they provided ample pitch control, from what I could tell from the moments of nominal flight.

"I thought that a lot of the drag... was from the way you had attached the nukes. So I replaced that whole scheme with a bicoupler and attached the nukes normally."
I guess that was my most egregious deviation from design convention... and therefore probably a good place to target for troubleshooting when the design didn't perform as expected. I'll try that on my design (replacing the rearmost fuel tank with a bicoupler) and see where it gets me.

"I saw that you had attached your wings with what looked like 5 degrees of incidience -- and that's a lot."
Really? I use 5 degrees (one fine-control notch with the rotate tool) on all of my spaceplanes for consistency. I find that it gives me a nice balance between drag and lift during my upper atmosphere phase of ascent, and helps get off the runway at a nice, low speed. I rather like 5 degrees of incidence, and in my initial thread on SSTO advice, people advising me generally did too. What does the rest of the community think about it as far as you know? Are you alone in your opinions, or am I in the minority?

"IMNSHO, a plane this big needs more wing than you had. So I doubled it."
Did you notice that there are two Big-S wings, one above the other, with the bottom wingtip clipped gently into the top? I DO have double the wing already. :wink: ...I've noticed other SSTO guys stacking wings, and while I was a little opposed to it at first, I feel I can justify it because I'd be carefully designing the profile of the wing on a real spaceplane in a way that a single board-wing on KSP doesn't really allow or reflect. Does KSP aero dislike stacked, gently clipped wings?

"Oxidizer is heavy and not good to carry. You want as little as possible."
Okay. I'll remove some oxidizer and try to accommodate a shorter rocket burn in my already-nearly-underpowered-but-otherwise-efficient ascent profile. Probably should have done that to start with... :( 

"After flying mine, I decided I could do away with 1 reaction wheel, so I aced the one off the nose."
Okay. I guess 3 is a bit much. I'll accept the bonus part/drag reduction and drop it to 2.

--


Quick PS to @AeroGav's comment about reaction wheels, and falling out of favor with them--yes, it does behave the same with or without the RWs activated. I don't think they're a problem for this ship (especially considering I'm reducing their count from 3 to 2). I think something a little wonkier and less intuitive is causing problems, to be honest... I think some unassuming part of the design is resulting in a non-realistic and disagreeable effect with KSP's physics models. Maybe KML will reveal something odd in the craft file. I'll try that soon. KML only shows the helpful tree diagram from persistence files, I guess. Limited display for .craft files alone, which is all I have access to until I can get to my laptop. 

Edited by MitchS

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2 hours ago, MitchS said:


I was wondering if the LF nosecones ahead of the in-line Mk1 fuel tanks (and their accompanying canards) were causing too much drag too far forward.

No, those NCS adapters have a small fraction of the drag of your main fuselage. MK2 parts have triple the drag of MK1 parts, so if you want to find the drag, look there. But your fuselage is well-designed, so it's best to stick with it.

2 hours ago, MitchS said:

I can't really tell where my CoP is, or where my CoL is when body lift is taken into account (which, why would it ever NOT be, Squad?!)

Because it's non-linear with speed, so you can't place a dot without knowing the exact speed. So it would need graphs and printouts and analysis -- and can't be nicely displayed in the editor.

2 hours ago, MitchS said:

Also, isn't one of the symptoms of my craft that it's overmaneuverable as it is?

Not exactly. One thing you need to understand is that pretty much all planes will swap ends on you if you push them too far off prograde. All planes have a region around prograde where they will fly straight. So it's not that yours is overmaneuverable -- it's that your dynamic stability region is too small. All you need to do are some tricks to add a bit of stability, to make that zone bigger. (Yes, there are designs that are inherently stable, but I don't think that is a smart design goal, considering the tradeoffs.)

With your CoM and CoL right on top of each other, you are guaranteed to have a plane that is extremely sensitive to the controls. So that's good for SAS, which can use fine control deflections to steer your plane. So it doesn't need to do much work (and create a lot of drag) to keep you flying straight. But it's bad for manual control -- especially if you are using a keyboard like me, where all you have is either 0 or max deflection (turning on soft-control mode helps, of course).

2 hours ago, MitchS said:

Why do you think they don't give enough bang for the buck?

I usually find that they hit max deflection while I'm still within my stability region -- so I could have remained stable if the darn things would just respond more. Maybe I should play with my authority slider more. *shrug*

2 hours ago, MitchS said:

I would normally place them farther forward too, but I was trying to limit the torque moment of their drag at high AoA

Understood. Maybe turn the authority up to 150%, instead, though. During reentry, you may be wise to pump fuel forward to enhance high-AoA stability. Move the CoM, rather than the canards.

2 hours ago, MitchS said:

What does the rest of the community think about it as far as you know? Are you alone in your opinions, or am I in the minority?

I don't think there are enough hardcore spaceplane designers here to form a statistical base. So you're stuck with individual opinions that you have to try one by one. :P But basically, to get optimal performance out of your spaceplane, you launch it with 0 degrees of wing incidence. Then you see how far your nose is above prograde, on average, while you climb -- and especially during your speedrun, which is when it is the most vital. During my check, it looked like it was 2 degrees to 5 degrees, with an average of 3 -- and it was about 2 degrees during the speedrun. So 5 degrees of incidence would put you nosedown during the speedrun, which is bad.

But in any case, you were complaining about how the plane assumed a nosedown attitude with SAS off, so wing incidence is just one more thing you need to mess with to see if it's causing you trouble. Like I said in my above post, I'm not sure if each of my tweaks was necessary or not -- but it seemed like something to check out.

2 hours ago, MitchS said:

Did you notice that there are two Big-S wings, one above the other, with the bottom wingtip clipped gently into the top? I DO have double the wing already. :wink:

Nope. I failed to notice that from the pic. So that's OK.

2 hours ago, MitchS said:

 ...I've noticed other SSTO guys stacking wings, and while I was a little opposed to it at first, I feel I can justify it because I'd be carefully designing the profile of the wing on a real spaceplane in a way that a single board-wing on KSP doesn't really allow or reflect. Does KSP aero dislike stacked, gently clipped wings?

KSP is just fine about wing clipping. Just so long as it's only wings. The amount of wing area you get from unclipped wings is unreasonably small, most people agree. Doubling it up makes it come out about right, visually, I think.

2 hours ago, MitchS said:

Okay. I'll remove some oxidizer and try to accommodate a shorter rocket burn in my already-nearly-underpowered-but-otherwise-efficient ascent profile. Probably should have done that to start with... :( 

I think you'll find it bumps your orbital deltaV up quite a few notches. Yeah, it takes longer to get to orbit, but it's worth it. If you rush an SSTO spaceplane to orbit, you'll be sorry. :wink:

 

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