Kerbodyne SSTO Division: Omnibus Thread

[WhiteKnuckle]

Fine by me.

BTW, I use Open Broadcaster Software for screencaps, and VideoPad Video Editor to edit and add the voiceovers that I record on my iPhone. OBS is free, and Videopad has a free trial (and a reasonable pricetag).

Yeah I picked up OBS last night. Unfortunately running it at any of the higher resolutions makes my computer pack up instantly. And even running it at a lower setting doesn't solve all the issues, so I'm going to try to get it optimised before I worry about editing software.

[Wanderfound]

Wanderfound, Can you recommend me another Kerbodyne VTOL? What model is your favourite?

What do you want it to do? Long range, bulk cargo, sporty toy? Dragonfly X (http://forum.kerbalspaceprogram.com/threads/90747-Kerbodyne-SSTO-Division-Omnibus-Thread?p=1652100&viewfull=1#post1652100) is probably the best of the light atmospheric ones.

[CrisK]

What do you want it to do? Long range, bulk cargo, sporty toy? Dragonfly X (http://forum.kerbalspaceprogram.com/threads/90747-Kerbodyne-SSTO-Division-Omnibus-Thread?p=1652100&viewfull=1#post1652100) is probably the best of the light atmospheric ones.

Thank you, I will play around with the Dragonfly X. That being said, I prefer the Kerbodyne VTOL designs that have three VTOL engines for stability. I built this little Kerbodyne-style trainer to illustrate what I mean. I also took screenshots so that you can see how to VTOL land on a helicopter pad.

1. Align the craft with the H.

2. Cut horizontal speed.

3. Drop vertical speed to -2 to -3 m/s.

4. Toggle the brakes.

5. Apply for a job within the Kerbodyne sales division.

Notice that my vertical speed was -3.75m/s when I landed and my horizontal speed was 0.02m/s.

Javascript is disabled. View full album

[WhiteKnuckle]

Ok quick vid of me flying the Kerbodyne VTOL Trainer like a nut.

Note how I almost never touch the throttle, I use rolls to control my vertical speed. This is pretty mandatory for aerobatics, but I use it all the time when setting up for landings as well.

[CrisK]

WhiteKnuckle, that was amazing. I can pull of the acrobatics, but that landing at the ending made me sweat a bit. Jesus.

[Wanderfound]

Thank you, I will play around with the Dragonfly X. That being said, I prefer the Kerbodyne VTOL designs that have three VTOL engines for stability.

The most popular of the big ones was the Dropbear. That's getting a bit long in the tooth now, though; it could probably use a tuned-up 2015 edition.

[WhiteKnuckle]

WhiteKnuckle, that was amazing. I can pull of the acrobatics, but that landing at the ending made me sweat a bit. Jesus.

Ha, thanks dude. The landing was actually easy. I wanted to get in a minute or two of aerobatics and then do a landing, and, well... let's just say the first dozen or so videos I tried to make never made it to the landing stage.

[Wanderfound]

Another staged spaceplane design: Kerbodyne Sabotage.

Test flight at http://s1378.photobucket.com/user/craigmotbey/Kerbal/Beta/Kerbodyne%20Showroom/Sabotage/story

Alternate format at http://s1378.photobucket.com/user/craigmotbey/slideshow/Kerbal/Beta/Kerbodyne%20Showroom/Sabotage

Craft file at https://www.dropbox.com/s/4r9gc6zi5p57lrp/Kerbodyne%20Sabotage.craft?dl=0

Edited February 8, 2015 by Wanderfound

[eddiew]

Those staging planes look strangely awesome in the way they split apart Loving the escape-pod style return too.

Thanks again for the tutorials and explanations. Having finally earned my vernors (about time!) last night, I set about designing a little (medium) Munlander. B9 procedural wings and lights, pretty sure the rest is stock.

Turned out to be the most stable thing I've ever made. Took off at 90m/s after only half a runway, despite having the lowest TWR of all my planes to date (0.47 ASL)! Stable at 20km at anything over mach 2; stretched the jets to 24km and 3.9. CoL tight behind the CoM, which doesn't significantly move and made it fly like a fighter without ever getting out of control

96kN of thrust with less than 20kNm of torque from the 8 ventral vernors, wet and dry. Needed an LKO topup, which gives the nuke about 4200 delta-v. Enough room in the bomb bay for a small rover to get those survey contracts done. Easy to land - if a little reluctant to touch down due to the low lift-off speed. Could probably have reduced the wing area by a good 30%... and four of the six reaction wheels are likely overkill. ah well, will revise next flight, seeing as Minmus is up next. Not losing the safety 'chutes though; landed gracefully using just half the runway this time, but I don't trust myself to make a regular job of it

And who knew kerbal helmets were so pliable? The boys have some space cleavage going there...

Edited February 8, 2015 by eddiew
too hasty with the post button!

[CrisK]

Ha, thanks dude. The landing was actually easy. I wanted to get in a minute or two of aerobatics and then do a landing, and, well... let's just say the first dozen or so videos I tried to make never made it to the landing stage.

Are you using the latest version of FAR? I tried to replicate some of the stunts that you pulled and I was unable to generate enough thrust.

Wanderfound, please allow me to offer some slight constructive criticism. On planes that are meant to be acrobatic like the trainer and the Dragonfly X, the wings that you're using are too small for acrobatics and wild maneuvers. The designs are essentially lifting body planes; the wings offer little or no lift and function as mild roll stabilisers. For an acrobatic/highly maneuverable plane you need more lift to compensate for high speed turns, dives, etc.

If I add a relatively small trapezoidal wing with forward-facing and rear-facing control surfaces then the trainer can pull out of dives where the vertical speed is -65 or so. With the current wings, the limit is around 20. This is because the wings do not provide lift on their own due to their small size and limited horizontal speed; the lift of the craft is generated entirely by the vtol engine. With larger wings (delta, trapezoidal, whatever) the maneuverability increases tremendously.

This is meant to be a positive constructive criticism. I'm not trying to take anything away from your excellent designs.

On an unrelated topic, there was a Soviet spaceplane called the MiG-105 that used staging similarly to yours. It had three stages if my memory serves me right, and the top stage was the actual Spiral spaceplane.

[WhiteKnuckle]

Are you using the latest version of FAR? I tried to replicate some of the stunts that you pulled and I was unable to generate enough thrust.

As it turns out, I was behind on my FAR updates, I was using 14.5 rather than 14.6 so thanks for bringing that to my attention.

But I just took the Kerbodyne trainer and one of my VTOLs for a quick spin and they seem to act exactly the same, or so close that I can't tell the difference? Did the latest FAR update nerf things even more? (of please god noooooo....)

A few thoughts:

-It is quite possible that I have screwed something up. I don't computer all that well.

-The flight in the video was at the ragged edge of what I can do. Flying like that has a 95% mortality rate for me. So don't think that it should be easy to replicate.

-I have run into strange problems before that I think were caused by FAR, where engines (usually turbojets) went from regular FAR-nerfed to supper-nerfed for no apparent reason, then back again after loading a quicksave. I've also had regular jets sometimes act like they weren't limited by speed at all, then they go back to normal.

Not sure if any of those reasons could be giving you trouble. You say you're running out of thrust, vertical or horizontal? If vertical, are you using the rockomax engines to fine tune vertical speed? And one last bit of advice: When flying like this, horizontal velocity kills. If you get into a dive going 150m/s nothing is going to be able to save you. Constant turning to avoid picking up a lot of speed is key.

[CrisK]

As it turns out, I was behind on my FAR updates, I was using 14.5 rather than 14.6 so thanks for bringing that to my attention.

But I just took the Kerbodyne trainer and one of my VTOLs for a quick spin and they seem to act exactly the same, or so close that I can't tell the difference? Did the latest FAR update nerf things even more? (of please god noooooo....)

A few thoughts:

-It is quite possible that I have screwed something up. I don't computer all that well.

-The flight in the video was at the ragged edge of what I can do. Flying like that has a 95% mortality rate for me. So don't think that it should be easy to replicate.

-I have run into strange problems before that I think were caused by FAR, where engines (usually turbojets) went from regular FAR-nerfed to supper-nerfed for no apparent reason, then back again after loading a quicksave. I've also had regular jets sometimes act like they weren't limited by speed at all, then they go back to normal.

Not sure if any of those reasons could be giving you trouble. You say you're running out of thrust, vertical or horizontal? If vertical, are you using the rockomax engines to fine tune vertical speed? And one last bit of advice: When flying like this, horizontal velocity kills. If you get into a dive going 150m/s nothing is going to be able to save you. Constant turning to avoid picking up a lot of speed is key.

Hmm. Yes, FAR now sets a hard thrust limit of 50% on all engines that use intake air. It also individually weakens each jet engine and the Rapier. Confusingly, FAR uses a third set of values if AJE is installed.

The "supernerfed" state that you're describing is the turbojet's default thrust state at low altitude if FAR is installed.

I run out of vertical and horizontal thrust when trying to do maneuvers. Here's the thing: if I increase the size of the wings to a realistic size then I CAN dive at 100m/s or more (given an altitude above 1000) and be absolutely fine. I'm tempted to slap some wings on a Kerbodyn body and record an example.

[WhiteKnuckle]

Hmm. Yes, FAR now sets a hard thrust limit of 50% on all engines that use intake air. It also individually weakens each jet engine and the Rapier. Confusingly, FAR uses a third set of values if AJE is installed.

The "supernerfed" state that you're describing is the turbojet's default thrust state at low altitude if FAR is installed.

I run out of vertical and horizontal thrust when trying to do maneuvers. Here's the thing: if I increase the size of the wings to a realistic size then I CAN dive at 100m/s or more (given an altitude above 1000) and be absolutely fine. I'm tempted to slap some wings on a Kerbodyn body and record an example.

Yeah but the 50% limit has been around for a while, when I say super-nerfed I mean unable to break 200m/s or climb past 5km in something that should be able to do over 1km/s at 20k. It was definitely a bug, even if it was supposed to be that way it should do it all the time, not only on some quicksaves.

[Wanderfound]

Are you using the latest version of FAR? I tried to replicate some of the stunts that you pulled and I was unable to generate enough thrust.

Wanderfound, please allow me to offer some slight constructive criticism. On planes that are meant to be acrobatic like the trainer and the Dragonfly X, the wings that you're using are too small for acrobatics and wild maneuvers. The designs are essentially lifting body planes; the wings offer little or no lift and function as mild roll stabilisers. For an acrobatic/highly maneuverable plane you need more lift to compensate for high speed turns, dives, etc.

If I add a relatively small trapezoidal wing with forward-facing and rear-facing control surfaces then the trainer can pull out of dives where the vertical speed is -65 or so. With the current wings, the limit is around 20. This is because the wings do not provide lift on their own due to their small size and limited horizontal speed; the lift of the craft is generated entirely by the vtol engine. With larger wings (delta, trapezoidal, whatever) the maneuverability increases tremendously.

This is meant to be a positive constructive criticism. I'm not trying to take anything away from your excellent designs

It's a fair call on the trainer; the design is optimised for straight-line speed. As I mention at the start of the demo video, if you want it to turn sharply at low speed you need to take advantage of the VIFFing ability.

With the Dragonfly, though...given that it's able to generate G-forces sufficient to snap the fuselage in half, I think it already has enough wing...

(the 11G showing is post-snap, the meter was pegged a second earlier)

[Wanderfound]

An update to my standard fuel depot:

Flight test at http://s1378.photobucket.com/user/craigmotbey/Kerbal/Beta/Kerbodyne%20Showroom/Instant%20Infrastructure%202015/story

Alternate format at http://s1378.photobucket.com/user/craigmotbey/slideshow/Kerbal/Beta/Kerbodyne%20Showroom/Instant%20Infrastructure%202015

Craft file at https://www.dropbox.com/s/rff371i1h9lzar6/Kerbodyne%20Instant%20Infrastructure%202015.craft?dl=0

Edited February 9, 2015 by Wanderfound

[eddiew]

I... have got to try a jet powered fuel depot now... made a little 3 man capsule with rapiers, never went bigger.

[eddiew]

Hey Wanderfound (and other interested spaceplaners, since there seem to be a few in this thead ), mind if I shoot a couple of questions? Basically I took...

...added a passenger cabin behind the docking port, and now it fails horribly at life. This has led me to ponder:

a) Is there a rule of thumb about the minimum TWR to get a plane to orbit? FAR analysis says the revised bird is still completely steady in all sensible ranges, it takes off at ~110 m/s and the CoM and dCoM are aligned perfectly, but with 0.39 TWR ASL I just can't get the thing above 24km and mach 3.5. At this, it's got excess intake air, but the drag seems to equal the thrust, and it can't gain lift without a dangerous AoA. The successful plane above started with 0.47 TWR and has no such struggles.

Is it ever worth having more than one shock cone intake per engine? Was experimenting with MK2 nacelles for two shocks and a radial engine body per rapier, but once again got to that magic 24km mark and couldn't go any faster or gain any altitude, despite only using 45% of its intake air. Was rather hoping to get to 30km and mach 4.5 on air, but maybe that's expecting too much?

It's entirely possible that there's another design flaw holding me back - maybe suffering from too much wing surface? Anyhoo, thanks for any advice

[Wanderfound]

Fun little challenge: http://forum.kerbalspaceprogram.com/threads/110068-Itty-Bitty-Aeroplanes%21

- - - Updated - - -

Hey Wanderfound (and other interested spaceplaners, since there seem to be a few in this thead ), mind if I shoot a couple of questions? Basically I took...

http://foxwoodstudios.co.uk/kerbal/spaceplanes/shortbow-munlanding.jpg

...added a passenger cabin behind the docking port, and now it fails horribly at life. This has led me to ponder:

a) Is there a rule of thumb about the minimum TWR to get a plane to orbit? FAR analysis says the revised bird is still completely steady in all sensible ranges, it takes off at ~110 m/s and the CoM and dCoM are aligned perfectly, but with 0.39 TWR ASL I just can't get the thing above 24km and mach 3.5. At this, it's got excess intake air, but the drag seems to equal the thrust, and it can't gain lift without a dangerous AoA. The successful plane above started with 0.47 TWR and has no such struggles.

Is it ever worth having more than one shock cone intake per engine? Was experimenting with MK2 nacelles for two shocks and a radial engine body per rapier, but once again got to that magic 24km mark and couldn't go any faster or gain any altitude, despite only using 45% of its intake air. Was rather hoping to get to 30km and mach 4.5 on air, but maybe that's expecting too much?

It's entirely possible that there's another design flaw holding me back - maybe suffering from too much wing surface? Anyhoo, thanks for any advice

TWR required is itself dependent upon drag and lift, and intakes enhance flight ceiling rather than speed.

Intakes let you run jets at higher altitudes, but the AoA required for a given altitude is a function of both speed and lift. Extra intakes are no use if you don't have the combination of speed and lift required to reach those altitudes.

More lift = lower AoA. More speed = lower AoA. More AoA = more drag, too much AoA = can't fly there.

While more wing increases lift (reducing AoA), it also increases weight and drag (reducing speed, increasing AoA). It's a balancing game.

Ditching some wing would enhance speed by reducing weight and drag, but go too far and the increase in AoA required may outweigh the gains. It also depends upon piloting style; low-drag/low-lift ships need to build speed before climbing, high-drag/high-lift ships want to get up above the soup before accelerating.

A low-lift/low-drag build allows higher speeds before rocket ignition, saving fuel. But they require more finesse in ascent path and are harder to land.

Edited February 11, 2015 by Wanderfound

[UnusualAttitude]

a) Is there a rule of thumb about the minimum TWR to get a plane to orbit? FAR analysis says the revised bird is still completely steady in all sensible ranges, it takes off at ~110 m/s and the CoM and dCoM are aligned perfectly, but with 0.39 TWR ASL I just can't get the thing above 24km and mach 3.5. At this, it's got excess intake air, but the drag seems to equal the thrust, and it can't gain lift without a dangerous AoA. The successful plane above started with 0.47 TWR and has no such struggles.

I too have been trying to add a passenger cabin to a light cargo spaceplane with a similar configuration to yours and so far I've failed...

We're talking in FAR version 14.6, right?

For a twin RAPIER design, 31 tonnes on the runway is the absolute limit for me so far (at least if you wan't to go anywhere once you're in orbit), even with a pretty sleek airframe.

0.39 TWR sounds very low to me, unless there's some out-of-the-box solution I haven't thought of. I ended up adding a third engine ;-)

[Hodo]

I too have been trying to add a passenger cabin to a light cargo spaceplane with a similar configuration to yours and so far I've failed...

We're talking in FAR version 14.6, right?

For a twin RAPIER design, 31 tonnes on the runway is the absolute limit for me so far (at least if you wan't to go anywhere once you're in orbit), even with a pretty sleek airframe.

0.39 TWR sounds very low to me, unless there's some out-of-the-box solution I haven't thought of. I ended up adding a third engine ;-)

http://i.imgur.com/2wzKvzV.png

You have to take into account that the TWR changes on the RAPIERs as you go faster. There is a point where they will generate barely 60kn of thrust, and a point where they will be pushing 100kn. The other thing is you have to look at the drag of the craft vs the overall thrust generated by the craft and the pressure of the air the craft is traveling through. (I know math right?!)

The simplest way to figure this out is P*cd=loss through drag. (that is if my memory is right, which today has been one of those days so check with others on that.) This does not factor in the skin drag that FAR now adds. Which is another factor.

But a decent design can overcome this. Most of my SSTO space planes have a TWR of 0.8 sitting on the runway, and climb to over 1.2 at mach 3.5. So getting to space is a matter of building speed then climbing. But I have to be around 20-25km before I can go fast enough to get close to orbital velocities.

[Wanderfound]

Orbit with speed and precision: Kerbodyne Dolphin. Very fast, lovely flight handling.

Flight test at http://s1378.photobucket.com/user/craigmotbey/Kerbal/Beta/Kerbodyne%20Showroom/Dolphin/story

Alternate format at http://s1378.photobucket.com/user/craigmotbey/slideshow/Kerbal/Beta/Kerbodyne%20Showroom/Dolphin

Craft file at https://www.dropbox.com/s/s0rwq375mszd4nf/Kerbodyne%20Dolphin.craft?dl=0

[Wanderfound]

Update of an olde: Kerbodyne Dropbear 2015.

Flight test at http://s1378.photobucket.com/user/craigmotbey/Kerbal/Beta/Kerbodyne%20Showroom/Dropbear%202015/story

Alternate format at http://s1378.photobucket.com/user/craigmotbey/slideshow/Kerbal/Beta/Kerbodyne%20Showroom/Dropbear%202015

Craft file at https://www.dropbox.com/s/jgcm811uiwkxvhy/Kerbodyne%20Dropbear%202015.craft?dl=0

[eddiew]

Intakes let you run jets at higher altitudes, but the AoA required for a given altitude is a function of both speed and lift. Extra intakes are no use if you don't have the combination of speed and lift required to reach those altitudes.

...

Update of an olde: Kerbodyne Dropbear 2015.

Yeah, I learnt the hard way that there's no point in pushing your flight ceiling up if you can't actually get any higher on air anyway Unfortunately the balancing act proved to be

The revised Dropbear is oddly topical though, since that triple MK2 is exactly what I've been going for as a crew transport. I have no idea how you VTOL'd it and had enough fuel for orbit, however... you look to have about the same number of fuel tanks. I might see about revising my double-shock nacelles (pictured in spoiler below) to mimic Dropbear and see if the drag reduction helps any...

We're talking in FAR version 14.6, right? ... 0.39 TWR sounds very low to me, unless there's some out-of-the-box solution I haven't thought of. I ended up adding a third engine ;-)

http://i.imgur.com/2wzKvzV.png

FAR, yes - latest version, whatever that is. My hope was to have a sporty looking, not-too-big plane that would do those 5-kerbal base missions. Trouble is, as dawned on me after many hours - you do have to consider a passenger cabin to be a 3 ton cargo, and that's about what the average sporty plane will max out with. Unfortunately I needed to shift a 'docking buddy' (RCS probe with 2 sizes of docking port) and a Station Science experiment in the main cargo bay, which was just too much to ask.

I thought it was pretty sleek, but the game disagreed. A third rapier would almost certainly have been enough, but I really wanted to have a nuke on board so's to be able to top up and take the crew out for Minmus/Mun orbits - so naturally I took the hammer o' brute force to it

Dirty secret; there's a 5th shock cone in the short cargo bay. It shouldn't work, but it does

Not very happy with the small amount of delta-v that remains once in orbit, might have to push some extra tanks in there. 0.78 TWR gives plenty of room to scale up a bit. And yes, you can guess by the revision number that it took rather a few tries!

Most of my SSTO space planes have a TWR of 0.8 sitting on the runway, and climb to over 1.2 at mach 3.5.

0.8 is satisfying, but higher than 'required'. Admittedly I have a couple of 1.3-1.6 TWR 'aim away from ground' crewed missiles, which are great fun to fly, but my Munlander plane (inc rover) only has ~0.47, lifts off at just 90m/s and gets to orbit without a fuss. Clearly 0.39 was too low for the Boomerang however, and it's not a particularly draggy design. Maybe the golden-minimum for most spaceplanes is somewhere around 0.45? Definitely going to target 0.5+ in the SPH as my starting point from here on.

[CrisK]

Update of an olde: Kerbodyne Dropbear 2015.

Orbit with speed and precision: Kerbodyne Dolphin. Very fast, lovely flight handling.

I am a fan of both. Nice work, Wander!

eddiew, I suspect that your trouble getting to orbit is 70% flying and 30% design. I think that I could get all of the planes that you designed to orbit. However, they're not optimal. The reason that Wander uses minimal wings on SSTOs is that larger wings actually work against you for spaceplanes. They're dead weight from 30km on up. They'll also serve to pull your nose down and keep you in the atmosphere when you try to break out.

Just by looking at your crafts, here is how I would expect them to fly with inexperienced piloting: they should reach 400-500m/s at around 24km and then the nose will pull down. If you attempt to pull the nose up, the nose will probably drift to the side. The plane might even flip.

Here is how I would pilot your Boomerang plane: fly it up to 20km then level off. Maintain altitude until your combined speed is 1200m/s or higher. Angle upwards by 5-10%. As soon as the thrust of your Rapiers drops to 50%, switch their mode from airbreathing to rockets. Angle upwards to 20% or so. Leave them on for about 10-15 seconds. That should get your apoapsis to 45km-50km. Cut your engines. Keep your nose pointing at 5-10% and do not let it dip down. If you do, it's not a huge problem. You'll lose height and speed, but you can make up for it with a sort burn.

Once you're over the 40km mark, turn on the lv-n and angle upwards to 20%. Your momentum will mean that you will add very little vertical height, but you don't need to. At this point, as long as your time to apoapsis is staying the same or increasing you are fine. Actually, increasing your horizontal momentum is very important at this point because you're exploiting the Oberth effect and increasing your orbit. When your apoapsis is in the 80-90km range, tilt your nose down and burn horizontally. You should slip easily into orbit. If you have trouble at this point, toggle the rapiers back on to give yourself extra height and then try burning horizontally again with the lv-n.

[Wanderfound]

Basics to orbit:

* Get as high and as fast as you can before lighting the rockets. Ideally, you want to be over 30,000m and Mach 4 before you touch the oxidiser supplies.

* Keep your wing mass down. If you aren't doing low altitude aerobatics, you don't need full-strength wings. 0.5 on the mass tweakable is plenty unless it's a super-high wing loading design.

* Keep the wing area down. With totally inadequate wings, you'll start getting red numbers all over the Longitudinal Derivatives, but until you get to that point you can afford to shave off some wing surface.

* Power covers for a multitude of sins. Anything will fly if you get it fast enough.

* Less is more. Often the way to fix a design is to strip it back rather than bulk it up. See De Minimus, Karnifex and Alkahest (and Skylon...) for examples.

From a quick glance, the Boomerang could afford to lose some torque wheels (one is plenty) and probably has heavier wings than necessary: there's plenty of wing surface, so they aren't too heavily loaded, so they don't need to be super strong.