Kerbodyne SSTO Division: Omnibus Thread

[lordcirth]

Reentry: keep the nose 5 to 15° above Surface Prograde, and hold it there until you've levelled off. From then on, slowly descend further while keeping an eye on your heat; if it gets too hot, halt the descent (and maybe climb a little) until you've cooled off / slowed down a bit. You can get away with a higher AoA during the early stages of reentry, but pull it down as soon as you start to feel the wind.

A 20km periapsis is a good conservative height, but once you get the hang of it you can come in steeper. I often set my periapsis to intersect the ground on the western edge of the KSC continent.

Airbrakes, flaps, spoilers and S-turns will all help to ditch speed, but none of them are absolutely necessary.

Demonstrations:

http://imgur.com/a/044nt

http://imgur.com/a/hreAx

BTW: Astrotaxi would also work well with the forward section replaced by a Mk2 cockpit, docking port and short LFO tank. Adds slightly nicer aesthetics and refuellability, plus your tourists would no longer need to spacewalk to the orbiting resort.

Thanks for the tips! I have 2 spaceplanes, an Astrotaxi with 4 tourists and a Light Cargo v1.5 (Great name, I know) in LKO waiting to come down. I'm rather liking the Light Cargo, I'll post it after I tweak it once more after it's first full test flight. I'm still having trouble on reentry with the Astrotaxi though. You said 20km Ap, 5-15 deg pitch, right? Well, holding 10 deg, by the time I get to 40km I lose control. It doesn't twitch suddenly, it just starts getting slowly less stable. I think the craft still has the control authority to hold it, it's just too hard to manage all 3 axes at once. I tried SAS tuning stock/your settings, FAR assist, Pilot Assistant's pitch hold (which I am probably using wrong because I don't understand the interface very well). What system do you use to keep it steady? Just tuned SAS?

And I think I will mod the Astrotaxi with a docking port as you suggest - it looks like I will soon need a shuttle to de/orbit crew & experiments from lab stations.

[Wanderfound]

What system do you use to keep it steady? Just tuned SAS?

Yup; Dynamic Deflection and Kerbal Pilot Assistant's PID tuner. I don't use any of the autopilots or FAR stability aids; reentry is best piloted manually.

If you start to lose control, reduce the AoA; if you start to cook, increase the AoA. Aim to level off somewhere a bit above 20,000m. You'll need to tweak pitch on the way down as the Surface Prograde marker moves (clarifying just in case: that 5-15° is relative to Surface Prograde, not relative to the horizon).

Airbrakes make it easier; as well as enhancing deceleration, they'll also enhance stability if placed behind CoM (and keeping them activated as yaw controls is helpful, too).

Edited May 29, 2015 by Wanderfound

[lordcirth]

Nevermind, found the problem. I just had to pump the remaining fuel from the rear adapter to the nose adapter. You didn't have that problem? You still using Goodspeed?

[Wanderfound]

Nevermind, found the problem. I just had to pump the remaining fuel from the rear adapter to the nose adapter. You didn't have that problem? You still using Goodspeed?

No, but I was about to edit the previous post to mention the "pump fuel forwards for enhanced stability" trick.

As it is, the lateral tanks should drain first; I thought that they were rearset enough to counteract the weight shift when the front tank drains. With enough fuel line trickery you could make the tail tank the first to drain, but it probably isn't worth the trouble.

[lordcirth]

Well, I just overshot KSC at 28km going 1300m/s. Not sure how I keep managing to screw this up with such an easy plane. I tried to come down but my cockpit hit 99% heat at 25km. I slowed down to transonic, at which point I went from 1000m/s to 600 almost instantly (engines still off). I couldn't turn, rolling did nothing and pitching up just wobbled, I guess I was going to slow for once lol. Ended up ditching safely in a field on the next continent, thanks to the drag chutes.

It's probably just bad piloting, but I was always better at designing than controlling craft. Do you think adding Airbrakes would help a lot? Do they generate much heat if you use them during shock heating? Somehow I was on the edge of exploding the whole time after 28km, despite not generating much drag.

If I can get this working, it will be great - 72,000 Funds from the 4 Tourists aboard, and I have 2 Tourists and 2 Rescues waiting, which are very lucrative if I can do them all in one launch. I had >800m/s in orbit, so I don't see why not.

[Wanderfound]

Well, I just overshot KSC at 28km going 1300m/s. Not sure how I keep managing to screw this up with such an easy plane. I tried to come down but my cockpit hit 99% heat at 25km. I slowed down to transonic, at which point I went from 1000m/s to 600 almost instantly (engines still off). I couldn't turn, rolling did nothing and pitching up just wobbled, I guess I was going to slow for once lol. Ended up ditching safely in a field on the next continent, thanks to the drag chutes.

It's probably just bad piloting, but I was always better at designing than controlling craft. Do you think adding Airbrakes would help a lot? Do they generate much heat if you use them during shock heating? Somehow I was on the edge of exploding the whole time after 28km, despite not generating much drag.

If I can get this working, it will be great - 72,000 Funds from the 4 Tourists aboard, and I have 2 Tourists and 2 Rescues waiting, which are very lucrative if I can do them all in one launch. I had >800m/s in orbit, so I don't see why not.

Airbrakes do make it a lot easier, and shouldn't present any overheating troubles. If you overshoot, it's generally best to get down into the low supersonic and below 20,000m before trying the turn (which you do by rolling then pitching up). To avoid overshooting in the first place, aim to get down to normal, slow controlled flight while still to the west of the KSC continent, and crank the jets back up for the final flight home.

I'll take one up for a demo run and concentrate on getting clear screenshots showing the reentry process.

[Wanderfound]

Some reentry demonstration: the first bit shows how to do it easy, the second bit shows how to recover if you screw it up.

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BTW, that fuel-pumping trick works both ways; if you're having trouble keeping the nose up, shift some mass rearwards.

Edited May 29, 2015 by Wanderfound

[eddiew]

Do you think adding Airbrakes would help a lot?

Airbrakes are the most important thing you can do to avoid heating Pop them up before you hit the atmosphere, and you'll barely see flames even if you can't keep the nose up. 1 brake per 10-15 tons of plane works well for me.

Just make sure you turn OFF the pitch/yaw response on them, else they'll ruin your ascent. Really bad feature imho; they don't respond fast enough to be control surfaces and they kill your velocity (because they're brakes).

I'm tending to retroburn somewhere over the edge of the desert to the west, aiming to land just a fraction east of KSC. It varies by plane though, since some will glide better than others, and some will lose speed more efficiently. The nice thing with airbrakes is you get a lot more control about the length of the descent path; aim to overshoot then brake as required. Also nothing really has any control over 25km, I don't even worry about that anymore

Edited May 29, 2015 by eddiew

[Wanderfound]

Airbrakes are the most important thing you can do to avoid heating Pop them up before you hit the atmosphere, and you'll barely see flames even if you can't keep the nose up. 1 brake per 10-15 tons of plane works well for me.

Just make sure you turn OFF the pitch/yaw response on them, else they'll ruin your ascent. Really bad feature imho; they don't respond fast enough to be control surfaces and they kill your velocity (because they're brakes).

Actually, I'm finding yaw-enabled airbrakes really useful.

They're good for keeping big Mk3 jobbies on line in the thin air. They're not for countering or creating rapid motion, they're for fighting those sorts of slow nose wanders that sometimes gradually overcome your yaw authority in the upper atmosphere. The slow response mean that they don't do anything unless the yaw control is held on for some time (as it is when the SAS is trying to fight a slow yawing motion).

[lordcirth]

I landed the Light Cargo 1.5 after considerable quickloading. I added airbrakes set for yaw as you suggest, but there was also a roll instability. I'm not sure if it's a result of the yaw or not, we'll see. It also ran out of liquid fuel coming over the mountains, with quite a bit of oxidizer remaining. I landed it on the grasslands with the drag chutes.

Here's the .craft and screenshots if you're interested:

https://www.dropbox.com/s/paahbt1avprcc8y/Light%20Cargo%201_6.craft?dl=0

http://imgur.com/a/6fryC

Also, could you post the .craft for the Astrotaxi mk2?

Edited May 29, 2015 by lordcirth

[Wanderfound]

I landed the Light Cargo 1.5 after considerable quickloading. I added airbrakes set for yaw as you suggest, but there was also a roll instability. I'm not sure if it's a result of the yaw or not, we'll see. It also ran out of liquid fuel coming over the mountains, with quite a bit of oxidizer remaining. I landed it on the grasslands with the drag chutes.

Here's the .craft and screenshots if you're interested:

https://www.dropbox.com/s/paahbt1avprcc8y/Light%20Cargo%201_6.craft?dl=0

http://imgur.com/a/6fryC

Cool.

And, yeah, change those nacelles to Mk1 LF tanks. Intercoolers are for heat problems, nacelles are for radial/wing engine mounting. Don't use 'em otherwise. They're good in certain circumstances, but they're heavy for what they do relative to pure tank or intake parts.

BTW, to embed an Imgur album, put in [noparse]

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[/noparse]

Like this:

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They aren't excessive if you want easy takeoffs and landings with heavy loads, but that is a bit generously supplied with wing surface by my standards. What mass do you have them set at? There's a fair bit of weight to be saved by getting that right.

A bit of dihedral on the tailplane might sort out your roll issue. Plus getting your PID tuning set up:

Also, could you post the .craft for the Astrotaxi mk2?

Slightly modified version:

https://www.dropbox.com/s/v70je24mrs35q8w/Kerbodyne%20Astrotaxi%20III.craft?dl=0

The original placement of the SAS and battery was leading the LV-T45 to overheat a bit, so I shifted them to behind the jets. The mass is balanced.

You could also experiment with slightly increasing the control authority on the rear elevators, for a bit more pitch control at high altitude. At the moment it's deliberately built with maximum deflection wound down so as to be very hard to over-control, but the cost of that is reducing your ability to throw it around when you want to.

Edited May 30, 2015 by Wanderfound

[lordcirth]

Can't wait to try both planes out with the changes, but it'll have to wait till morning. I just docked a lander to Kerbin Station with 2 rescued scientists from Minmus, and I have a bus docked as well with 3 Kerbin rescues. With just a pilot, I can take all 5 down in the Astrotaxi III in a single, enormously profitable trip! And not a single piece of hardware consumed since they were launched up there! I love SSTOs & orbital refueling. Soon I will have a refinery on Minmus, and the Grand Armada will begin assembly for their trip to Duna.

You've shown several SSTO's with ISRU onboard, but do you use traditional lander refineries as well? I've been thinking of installing KAS just for the fuel hoses, which seem the easiest and most realistic way to refuel on the ground. I'd like to know what you think the best ways are to transfer fuel while landed.

[Wanderfound]

You've shown several SSTO's with ISRU onboard, but do you use traditional lander refineries as well? I've been thinking of installing KAS just for the fuel hoses, which seem the easiest and most realistic way to refuel on the ground. I'd like to know what you think the best ways are to transfer fuel while landed.

I'm not up to the ISRU bit in my career game yet; I tend to restart every release, so I'm constantly redoing the first 2/3 of the tech tree.

Easiest ground fuel transfer: rover with a moderately big fuel tank, a Klaw on the nose, and strategically placed aircraft landing gear so that the Klaw can be raised or lowered if necessary (e.g. have it running on normal rover wheels to start, but have a retracted aircraft gear or two under the nose somewhere). Stick some drills and ore tanks on and it can be a roving miner, as well.

Edited May 30, 2015 by Wanderfound

[Wanderfound]

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[Wanderfound]

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[Wanderfound]

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[lordcirth]

I landed the Astrotaxi III ! I ended up having to come down too sharply at the last minute, and rolled off the runway while deploying chutes. But the rest of reentry was actually really easy, it's a great plane. Thanks so much for your help. 568,068 Funds in one trip!

I just got the first equipment recovery contract, I didn't know these existed. Is that why you made the Salvager with the Klaw?

I'm trying to fly my Light Cargo 1.8, but as I reach 10km, ascending steeply, I get yaw instability. The SAS slows it, but if I try to keep it on target, the plane promptly disintegrates, since I'm at 80 kPa dynamic pressure. I have to climb over 50 degrees if I go full throttle. I tried throttling down to 2/3 as soon as I took off, but I still lost control at 13km or so. All the numbers in FAR seem good, so I'm not sure what the problem is. It gets really wobbly, kinda like you're going too slow, but at 40kPa?

Also, the wings are tuned to 0.7 mass and controls to 0.6. Since I'm not good at flying, I kept it conservative. Rocket TWR is pretty low at 0.57 (with a light payload I'm testing with), but I've never gotten this plane to rocket phase yet anyway. EDIT: I did actually, it actually had decent Dv left, it just took a dozen tries to land it, and it wasn't the runway either. That was before I added airbrakes, but I'm still having trouble on ascent.

https://www.dropbox.com/s/24i7wtpfoh12cbi/Light%20Cargo%201_8.craft?dl=0

Edited May 30, 2015 by lordcirth

[Wanderfound]

Yup, the Salvager is for salvage-ing.

I've been having a few nasty yaw surprises myself lately, not always caught by the stability derivatives. But the standard response to yaw problems should work: moar tailfin, and/or pull CoM forwards.

[Wanderfound]

lordcirth, try this one: https://www.dropbox.com/s/8q63vgie02oobkn/Light%20Cargo%201_8WF.craft?dl=0

[Wanderfound]

Krokoduck. Get your Minmus mining operation set up in one launch.

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Craft file at https://www.dropbox.com/s/fmis3ep4bu48uu8/Krokoduck.craft?dl=0

[Wanderfound]

Krokoduck SP.

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Craft file at https://www.dropbox.com/s/1m53ww9y81bh5qm/Krokoduck%20SP.craft?dl=0

Edited June 1, 2015 by Wanderfound

[lordcirth]

lordcirth, try this one: https://www.dropbox.com/s/8q63vgie02oobkn/Light%20Cargo%201_8WF.craft?dl=0

Thanks, that works much better. Got that payload to orbit with almost 1 km/s to spare!

[Wanderfound]

Kerbobee.

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Craft file at https://www.dropbox.com/s/5qzix822rswwlqo/Kerbobee.craft?dl=0

[nfpinto]

HEy man, how do you fly the kangaroo?

[Wanderfound]

HEy man, how do you fly the kangaroo?

As per usual. What's the problem?

The Kangaroo ​does require Kerbal Joint Reinforcement, though.