"simple" rule to build spaceplanes?

[Just Jim]

Now I have to figure the most efficient way of flying her into orbit....steep climb or shallow climb and all that. Is there a thread going on best SSTO flight strategy???

[panzer1b]

I instantly flip over on takeoff. CoL, CoM and CoT are in line. CoL slightly behind CoM.

There is one major thing that can cause this that ive come across:

angle of incedence altering your CoL. Ive found that you need to make sure the CoL is BEHIND the CoM when the wings are 100% level with the craft. Then you are free to angle them to add AoI afterwards, but do not move them around or you will flip oftentimes.

See the thing is, that AoI does not alter your plane's stability whatsoever except if you are flying prograde or very close to it. A craft that has its wings moved into teh correct positrion AFTER adjusting AoI is gonna be flippy.

Now I have to figure the most efficient way of flying her into orbit....steep climb or shallow climb and all that. Is there a thread going on best SSTO flight strategy???

It HEAVILY depends on TWR, drag, ect, but i can give you some verey generic tips for the 2 types of SSTLs im used to: highish TWR, and very bad TWR.

For high TWR, you have no benefits whatsoever from being down low, so my tactic involves gunning for ~10-15km as quickly as possible without dropping below 300m/s (at very low speeds you are inefficient too), and then gain speed around 15km until 1400m/s, then slowly angle up and try to be around 1600m/s and up at a 20 degree angle optimally before you switch to rockets, kraken-drives, warp-drives, witchcraft, hyperedit, or whatever propells you into space.

For low TWR (such as a single rapier pushing 35 tons), its much different. My best way is to go fairly flat until ~300m/s (this can take a while with excessively bad TWR), climb up to 3km without dropping below 300m/s, and once you reach ~3-4km, level out till you exceed 400m/s, and then slowly start to climb making sure you are gaining speed at all times and never lowering it. Then get to ~15km, you should be going in excess of 700m/s, level out and gain speed till around 1400m/s. Once there, slowly pitch up and try to maximize ejection angle while gaining a velocity of at least 1600m/s on rapiers. here is is better to get higher velocity then higher angle of ejection, but you dont want to eject perfectly flat, so try to have a climb rate of at least 100m/s before switching to rockets (and keep speed at least 1600m/s). If you use a nuke or other low TWR engine, i reccomend enabling it before the rapiers die out, nukes i engage at ~20km for most builds to help me get above 1600m/s before pure rockets, and more powerful LFo engines i engage at 25km or so (rapiers start to more or less die that high up).

Edited September 10, 2015 by panzer1b

[GoSlash27]

Now I have to figure the most efficient way of flying her into orbit....steep climb or shallow climb and all that. Is there a thread going on best SSTO flight strategy???

Just Jim,

There's a best launch profile for each individual spaceplane, but no single "best" profile for all spaceplanes.

You basically want to

1) exceed Mach 1.1 as efficiently as you can

2) Accelerate and climb to 17km as efficiently as you can

and then

3) get as much speed as you can while climbing shallowly.

For a spaceplane like yours you probably want to exceed Mach 1 around 8 km or so. The key is to maintain the prograde vector dead ahead for the entire atmospheric flight without losing speed. This yields the lowest drag.

You'll have to experiment.

Best,

-Slashy

[Gooru]

Ok, the problem with the flipover is solved. The rear landing gear was too much behind so i had to oversteer for takeoff and then it flipped.

I reach 10km & 1000m/s without problems.

Then it is very hard to accelerat to 1400m/s, even 1200m/s hard.

I reach 17km fast but without the described velocity.

Prograde often rises above the nose vector in this phase.

When the acceleration brakes i switch to rockets (usually around 22km & 1200m/s)

From this moment i can´t really move the prograd marker. It stay around 5° above the horizon no matter where i point my nose.

Even if i point my nose up 15° or more. So i aline the nose.

Wing lift brakes (nearly no blue lines in F12-view)

Anything more then 5° climbing is impossible. I just shoot at max speed close to the horizon.

Is this ok?

i can reach an AP of 150km and more but i fly a long time like a fireball through the atmosphere.

[Nothalogh]

You're climbing too fast in your acceleration phase

[Val]

...

i can reach an AP of 150km and more but i fly a long time like a fireball through the atmosphere.

That is the reality of Spaceplane SSTO ascents. Sounds like you're doing just fine.

I usually do my ascents slighly different. At first I level out and build speed to 1000-1100 m/s at 9-10 km, like you do. And then I ascend at 10 degrees from there (15 if high TWR), making sure I pull up slowly enough that the prograde marker stays above the pitch indicator on the navball, while I pull up. It'll start dropping below as I'm nearing the point to engage rockets. And then I just keep at 10 degrees until AP is above 60-70 km, then turn prograde.

[Gooru]

That is the reality of Spaceplane SSTO ascents. Sounds like you're doing just fine.

I usually do my ascents slighly different. At first I level out and build speed to 1000-1100 m/s at 9-10 km, like you do. And then I ascend at 10 degrees from there (15 if high TWR), making sure I pull up slowly enough that the prograde marker stays above the pitch indicator on the navball, while I pull up. It'll start dropping below as I'm nearing the point to engage rockets. And then I just keep at 10 degrees until AP is above 60-70 km, then turn prograde.

It seams my prograde marker "moves" more than yours. Between 1000m/s and 1400 m/s it climbs easily above the nose and this is why i´m climbing too fast.

When i have to switch to rockets, it drops a lot (as i´m usually to slow, i guess) and i can´t keep it at 10°. I can tilt my nose up, this doesn´t change the prograde, so i "eject" very flat.

[Val]

It seams my prograde marker "moves" more than yours. Between 1000m/s and 1400 m/s it climbs easily above the nose and this is why i´m climbing too fast.

When i have to switch to rockets, it drops a lot (as i´m usually to slow, i guess) and i can´t keep it at 10°. I can tilt my nose up, this doesn´t change the prograde, so i "eject" very flat.

Yeah. I didn't mention that. My prograde marker also drops below the nose once I get above 18-25 km. But I keep the nose pointed at 10 degrees, not the prograde marker. The prograde marker will drop to near the horizon for the rest of the ascent.

[Warzouz]

Now I have to figure the most efficient way of flying her into orbit....steep climb or shallow climb and all that. Is there a thread going on best SSTO flight strategy???

Nice work. Your plane si quite nice looking too.

Tweaking ascent profile can help a lot to save fuel. Try various approach. You can also try to simplify your plane. Usually it helps.

I'm starting to wirk on a SSTO for Laythe. It will start from a space station, fly and land (maybe several times) and return to the orbiting station. It's a science plane, it should be a simple one. I think I'll go for the wiplahsh + LV909 instead of one rapier.

My question is : how can I test it to Kerbin and translate to Laythe. Laythe is smaller so I'll need less rocket fuel to orbit. But Atmo is lighter, so I should get less lift and less drag. So I should get faster with less fuel ? Should I put more intakes ?

[Val]

...

My question is : how can I test it to Kerbin and translate to Laythe. Laythe is smaller so I'll need less rocket fuel to orbit. But Atmo is lighter, so I should get less lift and less drag. So I should get faster with less fuel ? Should I put more intakes ?

My experience is, that if it flies on Kerbin then it flies on Laythe as well.

I built this NanoJet with very small wings and a Weasley engine, that fit in a Mk3 Cargo Bay.

Tested it by circumnavigating Kerbin, then went on to explore Laythe with it.

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[Gooru]

I close to give up.

i really don´t know what is going wrong.

I followed every advice i could find.

I move the CoL 1mm back and the plane gets stable as so solid wall of bricks and unflyable.

I move the CoL 1mm forth again and the plane gets unstable like hell.

I increase the angle of incidence 1° and eveything stalls.

I decrase it 1° and the prograge drops like hell all the time.

It´s impossible to balance it.

[Warzouz]

Do you have screenshots ?

[Gooru]

Do you have screenshots ?

never mind - i deleted it and started over.

another try - another problem. But i like this on.

Now everything is fine till i reach the 1000m/s to 1400m/s phase (without any trouble).

But then, around 1300m/s, my cockpit explodes due to overheating. This is a very kerbal.

[GoSlash27]

never mind - i deleted it and started over.

another try - another problem. But i like this on.

Now everything is fine till i reach the 1000m/s to 1400m/s phase (without any trouble).

But then, around 1300m/s, my cockpit explodes due to overheating. This is a very kerbal.

Gooru,

Clearly it's going too fast too low.

Best,

-Slashy

[Starhawk]

Clearly it's going too fast too low.

Clearly it's just exploding too early!

Happy landings!

[Warzouz]

Yes basicly, successful SSTO space planes are vehicles that failed to explode in atmosphere

[kreutzkevic]

How do you build your planes?

I usually just...

(•_•) ( •_•)>âŒÂâ– -â– 

(âŒÂâ– _â– )

wing it.

[jlcarneiro]

Gooru,

The ratio of parts required varies with the parts you're using. An early career passenger shuttle with Mk2 parts is a different beast than a late career tanker with Mk 3 parts.

For a simple early career crew shuttle it goes like this:

for every 5t cargo (everything that isn't either engine, fuel, oxidizer, tank, or wing) you will need roughly:

1 Whiplash

2 LV-909s

10t lf&o to feed the rockets (450/550)

400 fuel to feed the Whiplash (about 1.76t)

Put that all together as aerodynamically cleanly as you can (don't forget the ram air!) and then total up your mass. You should be around 19t per 5t payload.

For wings, there's a surprisingly wide range of ratios that can work. The important thing isn't so much "lift to mass", but rather "zero nose incidence at Mach 1". You can do this with small wings at high incidence or large wings at low incidence.

A good starting point would be mass/3 with 2° incidence (3 clicks of fine rotation).

This is good for roughly 26% mass efficiency (payload/ total mass)

[... SNIP ...]

Best,

-Slashy

Hi! I'm having trouble with spaceplanes on 1.04 (I've succeeded on 0.90 and yes, I took a long time to get to spaceplanes on career, have little time to play) and tried this tip from Slashy but I'm still having problems. I did make to 50km but went out of fuel. My plane took ages to get to 10km and 300m/s. Can you help me?

Javascript is disabled. View full album

Another question: why I always get that cyan arrow on that right tank on Aerodynamic Overlay (F12)?

Edited September 25, 2015 by jlcarneiro

[Val]

Hi! I'm having trouble with spaceplanes on 1.04 (I've succeeded on 0.90 and yes, I took a long time to get to spaceplanes on career, have little time to play) and tried this tip from Slashy but I'm still having problems. I did make to 50km but went out of fuel. My plane took ages to get to 10km and 300m/s. Can you help me?

http://imgur.com/a/UqakG

Another question: why I always get that cyan arrow on that right tank on Aerodynamic Overlay (F12)?

I recreated your craft (Epsilon) as best I could from your pictures. I couldn't figure out what part(s) you have behind the cockpit, so I replaced that with a dummy weight to get as close to same weight as yours. I also didn't put any surface lights on it.

It is a very capable design. I got it to orbit with nearly 1400 m/s dV left. Very nice!

I don't know, why you couldn't, but I have 2 guesses.

1. You didn't include a fuel line and forgot to transfer leftover fuel from the center tank.
   
2. Your ascent profile needs improvement.
   

This is the ascent profile I used.

1. Take-off, then continue at 5^o pitch to gather speed.
   
2. When speed is 250 m/s, pitch up to 15^o.
   
3. At 8 km altitude start pitching down so your flying level between 9 and 10 km.
   
4. Let the speed build up to 1000 m/s.
   
5. Pitch up slowly (over 10-15 seconds) to 10^o above horizon without losing speed, but fast enough that you don't overheat.
   
6. At 18 km engage the LV-909s. Keep nose at 10^o.
   
7. Point the nose prograde when AP is above 60 km. (Around 35-40 km).
   
8. Throttle down, when AP is above 80 km. (A few seconds later)
   
9. Coast to space and circularize.
   

Javascript is disabled. View full album

Last 2 images from SPH

[jlcarneiro]

First, and above all, thank you, Val!

I recreated your craft (Epsilon) as best I could from your pictures. I couldn't figure out what part(s) you have behind the cockpit, so I replaced that with a dummy weight to get as close to same weight as yours. I also didn't put any surface lights on it.

Sorry, didn't think of it, should have uploaded the craft file. The parts you see are two units of Mk1 Cargo Bay to put the payload (a microsat, for example).

It is a very capable design. I got it to orbit with nearly 1400 m/s dV left. Very nice!

Thanks! A compliment from someone like you worths a lot!

I don't know, why you couldn't, but I have 2 guesses.

1. You didn't include a fuel line and forgot to transfer leftover fuel from the center tank.
   
2. Your ascent profile needs improvement.
   

LOL! So I'm basically a good designer and a lousy pilot!

This is the ascent profile I used.

I'll try this ascent profile and will let you know the results (this weekend, maybe tomorrow), thanks!

BTW, do you have any rule to help me plan such a profile, since they change from craft to craft?

EDIT: AH! Did your Epsilon also get that cyan arrow pointing up from the right rocket tank?

Edited September 25, 2015 by jlcarneiro

[SpaceplaneAddict]

I have a rule! Just pitch up/down according to acceleration. Pitch up as long as your engines are accelerating. Pitch down is they are slowing down. Make sure to stay level during the "speed run" part of the ascent.

[jlcarneiro]

I have a rule! Just pitch up/down according to acceleration. Pitch up as long as your engines are accelerating. Pitch down is they are slowing down. Make sure to stay level during the "speed run" part of the ascent.

Thanks! Seems simple enough to be used by me!

About this specific craft, thanks to you all (and with a little help from Pilot Assistant), I managed to achieve orbit!

Unfortunately, I ended with only 500m/s... (I must be a really lousy pilot! )

And the craft file... (I used Mk1 Cargo Bay, Aviation Lights and Surface Lights): Epsilon craft.

[SpaceplaneAddict]

Pfft, the first SSTO I made ran dry. At a 70x70 orbit.

[Val]

First, and above all, thank you, Val!

...

Thanks! A compliment from someone like you worths a lot!

You're very welcome. Glad to be of service.

EDIT: AH! Did your Epsilon also get that cyan arrow pointing up from the right rocket tank?

Yes, my recreation had the cyan spike on the right tank, too. (Added to my album)

...

Unfortunately, I ended with only 500m/s... (I must be a really lousy pilot! )

...

And the craft file... (I used Mk1 Cargo Bay, Aviation Lights and Surface Lights): Epsilon craft.

First of all. Gratz on making it to orbit. Well done!

Unfortunately, I wasn't able to load the craft, with those mods installed... (So I can't prove whether you are right )

But I am a lousy pilot. I like the designing part of KSP more, so I let MechJeb Smart A.S.S fly my crafts. The only part of the flying I do, is to tell MechJeb what pitch angle to hold. Makes it much easier to make consistent, reproducible ascents.

Once above 10 km and 1000 m/s, how much dV you end up with in orbit is highly dependent on drag (craft's base drag and control inputs), the speed you achieve while airbreathing and your pitch-to-ascent-angle ratio (I just made that term up. Is there an official term for it?)

Well, to get that ratio low I initiate the pitch up from 10 km, because down there, the air is thick enough, that prograde marker will follow craft pitch changes very swiftly. The wings produce more lift and the air-breathing engines are still close to maximum thrust. Doing the pitch up at higher altitudes causes more drag losses, because it takes longer to change the direction of the craft. It's going faster, has less lift from wings and less thrust from engines. At least in my experience.

The exact pitch angle I choose is dependant on TWR in the phase after air-breathing. I use 10^o on most my designs, 15^o on a few, and 20^o on a couple of high TWR designs. But the lower the angle, the better in my opinion.

Edited September 26, 2015 by Val
Too many and, and, and ands

[jlcarneiro]

You're very welcome. Glad to be of service.

Yes, my recreation had the cyan spike on the right tank, too. (Added to my album)

http://i.imgur.com/MK63Q7c.png

First of all. Gratz on making it to orbit. Well done!

Unfortunately, I wasn't able to load the craft, with those mods installed... (So I can't prove whether you are right )

But I am a lousy pilot. I like the designing part of KSP more, so I let MechJeb Smart A.S.S fly my crafts. The only part of the flying I do, is to tell MechJeb what pitch angle to hold. Makes it much easier to make consistent, reproducible ascents.

Once above 10 km and 1000 m/s, how much dV you end up with in orbit is highly dependent on drag (craft's base drag and control inputs), the speed you achieve while airbreathing and your pitch-to-ascent-angle ratio (I just made that term up. Is there an official term for it?)

Well, to get that ratio low I initiate the pitch up from 10 km, because down there, the air is thick enough, that prograde marker will follow craft pitch changes very swiftly. The wings produce more lift and the air-breathing engines are still close to maximum thrust. Doing the pitch up at higher altitudes causes more drag losses, because it takes longer to change the direction of the craft. It's going faster, has less lift from wings and less thrust from engines. At least in my experience.

The exact pitch angle I choose is dependant on TWR in the phase after air-breathing. I use 10^o on most my designs, 15^o on a few, and 20^o on a couple of high TWR designs. But the lower the angle, the better in my opinion.

Thanks for all these advices!

About the cyan arrow, why both crafts, created differently had this asimmetric body lift? Something about the design? Do you have any idea what it might be?

About the craft, here it is without lights and without mk1cargobay. I used an almost empty tank to simulate its weigth, though. I think the main difference is that the tank is a "bit" longer than the two cargo bays...

About mechjeb, thanks, I'll try it (until now I've only used the node executor and the precise landing assistant)...

EDIT: Hey, Val, I've tried MechJeb and got a worse result (210m/s), removed two of the intakes and it got even worse (no orbit). I think my (space)plane takes too long to get to 300m/s. If you have time, can you please fly its stock version (above)?

Edited September 26, 2015 by jlcarneiro
Test results