Need Help On Improving SSTOs

[NightshineRecorralis]

Here is the craft in question: https://kerbalx.com/NightshineRecorralis/Firestorm

 

It can get to orbit just fine, but I'm having trouble with the payload, especially beyond 10 tons. The thing is over powered as it is and has plenty of fuel, but I can never fit anything heavier without risking dropping back down into the atmosphere. Suggestions?

[SpaceFanatic10]

Make the design a little bit smaller,and dont put that many ore holders! Thos are really heavy!

[Starhawk]

This question about how to play the game has been moved from KSP Discussion to Gameplay Questions.

Happy landings!

[NightshineRecorralis]

4 hours ago, SpaceFanatic10 said:

Make the design a little bit smaller,and dont put that many ore holders! Thos are really heavy!

The point was to haul cargo into orbit, and any other cargo SSTO would. I am simply having trouble with the limitations of the MK2 form factor. It can bring the amount of cargo currently in the picture (10 tons), but it needs more lifting capability.

[SpaceFanatic10]

1 minute ago, NightshineRecorralis said:

The point was to haul cargo into orbit, and any other cargo SSTO would. I am simply having trouble with the limitations of the MK2 form factor. It can bring the amount of cargo currently in the picture (10 tons), but it needs more lifting capability.

then use the vector engine,its super good and really overpowered!

[NightshineRecorralis]

Just now, SpaceFanatic10 said:

then use the vector engine,its super good and really overpowered!

You know, if it was that easy, I wouldn't be asking this question. Vectors are really too heavy for a small SSTO like this one, and I rarely, if ever, use it on mk3 or larger SSTOs unless I have to. Using a vector would completely imbalance this craft, too, as it only has ~600ox and relies on Nukes. I provided a video on kerbalx, please go and watch that before giving advise that doesn't help.

[NightshineRecorralis]

Still looking for help and suggestions.

[fourfa]

First thing - if you want to carry 10T of useful, spaceship-shaped cargo, you're going to need a bigger cargo bay.  The ore tanks are much, much denser than any other rocket parts. I frequently use a 14T-to-orbit spaceplane and the payloads in its cargo bay double your size are usually less than 10T. 

You'll also probably notice that my 14T'er has a LOT more wing than your 10T'er.  It's hard to comment in depth further without seeing the CoM/CoL relationship on your craft.  You have a little more intake than you need - a pair of ramp or spike intakes on the side nacelles will suffice.  Or personally, I'd use only the nose spike intake, replace the ramp intakes with the tapered LF tanks and nose cones, and be careful to use only half throttle until you get to 50m/s, then punch full throttle and ride to orbit.

Otherwise it looks OK - overpowered a touch (I like this for gameplay personally), minimal extraneous cruft bolted on the outside.

Edited December 11, 2016 by fourfa

[Deddly]

Hi everyone! I removed a couple of posts because of the forum rules about bad words. Please be careful with the language, everyone.

[NightshineRecorralis]

1 hour ago, fourfa said:

First thing - if you want to carry 10T of useful, spaceship-shaped cargo, you're going to need a bigger cargo bay.  The ore tanks are much, much denser than any other rocket parts. I frequently use a 14T-to-orbit spaceplane and the payloads in its cargo bay double your size are usually less than 10T. 

You'll also probably notice that my 14T'er has a LOT more wing than your 10T'er.  It's hard to comment in depth further without seeing the CoM/CoL relationship on your craft.  You have a little more intake than you need - a pair of ramp or spike intakes on the side nacelles will suffice.  Or personally, I'd use only the nose spike intake, replace the ramp intakes with the tapered LF tanks and nose cones, and be careful to use only half throttle until you get to 50m/s, then punch full throttle and ride to orbit.

Otherwise it looks OK - overpowered a touch (I like this for gameplay personally), minimal extraneous cruft bolted on the outside.

Ah, thank you for that! You see, this was originally designed as an ore ferry to and from my LKO fueller. While your design does have its own merits, I would rather prefer nukes. Any suggestions as to lower TW ration orbital insertions?

[Signo]

Following are just my personal opinions based on my experience; I do not wish to start a classical kerbal debate on planes -

 

You need a few positive angle of attack for your wings and you could ditch a few "dead weight" like the whiplash pair.

Maybe find a place in the bay for the solars too.

You actually have more intakes than needed as @fourfa wrote above, but they are pretty light, tough and overall a good choice as nosecones.

You may try to reconfigure your craft to get rid of the canards, they are comfortable but draggy.

You might want to substitute the Mk2 decoupler with a random 1.25 adapter + tail connector - the decoupler is really draggy and moving the rapiers at the end of the Mk1 nacelles will move your CoM toward the centre of the craft, making way for an easier canard disposal.

In my experience a couple of rapiers are enough to push up more than 65t with ease.

 

I hope you can get through, the design is really cool.

Good luck.

Cheers.

[foamyesque]

What's your flight profile and cutoff on the airbreathers in terms of velocity, vertical speed, and altitude?

 

EDIT:

 

Better still, can you provide the craft file?

Edited December 11, 2016 by foamyesque

[g00bd0g]

Try using the large delta wings, they have the best lift/mass ratio with built in fuel capacity.

Shock cone intakes have less drag.

Turbojets don't provide as much thrust as rapiers at higher speeds and altitudes

Edited December 11, 2016 by g00bd0g

[Firemetal]

3 hours ago, SpaceFanatic10 said:

then use the vector engine,its super good and really overpowered!

Vector is a rocket engine. It runs on LF + OX.  This SSTO is powered by mostly jets, and also uses the rapier's alternative mode which is rocket. Therefore you need less OX. The Vector engine is for one very heavy and also uses too much fuel too quickly.  If you were carrying a shuttle on the back of it, then I would say add lots more fuel and add vectors but this plane is for small light payloads to LKO. So a vector would be quite impractical.

I'd say add more fuel and add two more rapiers. When it comes to SSTOs, you want more of the rapiers than a whiplashes since I think the problem you are having is once you get high enough to switch to rocket mode, your TWR isn't good enough. 1 rapier to 50 tons in rocket mode? Nope. I actually think the rapier has something like 250 KN thrust in rocket mode. Divide that by 9.81 and your TWR is way below 1 so it cannot do that. Once out of the atmosphere, you can usually manage being a bit under 1 and in this case, with no payload, that checks out but adding 10 more tons just pushes it under.

Fire 

Edit: Nevermind, watched your video and yes I see you do have two rapiers on board. Unfortunately if rapiers do indeed have 250 KN thrust on rocket mode, then that makes the TWR just over 1. More rapiers and more ox for those rapiers.

Edited December 11, 2016 by Firemetal

[NightshineRecorralis]

32 minutes ago, foamyesque said:

What's your flight profile and cutoff on the airbreathers in terms of velocity, vertical speed, and altitude?

 

EDIT:

 

Better still, can you provide the craft file?

Look at the Original post, the video and craft are on kerbal x here:

https://kerbalx.com/NightshineRecorralis/Firestorm

19 minutes ago, g00bd0g said:

Try using the large delta wings, they have the best lift/mass ratio with built in fuel capacity.

Shock cone intakes have less drag.

Turbojets don't provide as much thrust as rapiers at higher speeds and altitudes

The intakes are purely cosmetic, by the way, but thanks! Same with the delta wings, they look really bulky and I reserve them for mk3 SSTOs. The Whiplashes are there to push the craft through the first 10k of altitude and the sound barrier, and having an over powered space place feels nice when it takes less than half an hour to run through a whole mission ^^.

19 minutes ago, Firemetal said:

snip

Not exactly sure what you were trying to say in your post, sorry!

38 minutes ago, Signo said:

Following are just my personal opinions based on my experience; I do not wish to start a classical kerbal debate on planes -

 

You need a few positive angle of attack for your wings and you could ditch a few "dead weight" like the whiplash pair.

Maybe find a place in the bay for the solars too.

You actually have more intakes than needed as @fourfa wrote above, but they are pretty light, tough and overall a good choice as nosecones.

You may try to reconfigure your craft to get rid of the canards, they are comfortable but draggy.

You might want to substitute the Mk2 decoupler with a random 1.25 adapter + tail connector - the decoupler is really draggy and moving the rapiers at the end of the Mk1 nacelles will move your CoM toward the centre of the craft, making way for an easier canard disposal.

In my experience a couple of rapiers are enough to push up more than 65t with ease.

 

I hope you can get through, the design is really cool.

Good luck.

Cheers.

Indeed, I have some positive angle on the lifting surfaces, they work out just fine  

I'll see what I can do about no canards, but at lower speeds (landing troubles @40m/s) they are invaluable, however, a CoM change might also fix that, so who knows?

I've never really tried pure RAPIER builds, and I don't intend to anytime soon, but thanks for the info!

[foamyesque]

@NightshineRecorralis: That video shows the craft successfully hitting orbit; from your OP I gather you're trying to upsize the payload. Are you just adding more ore tanks to the thing without changing the other parts, or what?

EDIT:

Probable cause for fallback is that the nukes that do the bulk of your orbital insertion don't have the TWR as you amp up payload. I'll do some fiddling to check.

Edited December 11, 2016 by foamyesque

[NightshineRecorralis]

16 minutes ago, foamyesque said:

@NightshineRecorralis: That video shows the craft successfully hitting orbit; from your OP I gather you're trying to upsize the payload. Are you just adding more ore tanks to the thing without changing the other parts, or what?

EDIT:

Probably cause for fallback is that the nukes that do the bulk of your orbital insertion don't have the TWR as you amp up payload. I'll do some fiddling to check.

I'm probably going to add 4 to 6 radial tanks, which I think gives it close to 15t to orbit, as anything above that and it really struggles.

[AeroGav]

NightshineRecorralis

 

Unfortunately i'm working very long hours the next couple of days.  I do remember working on your Kendrel or was it the Wyvern mk3?

I think the whiplashes aren't doing anything for you.   You have an inline cockpit which can take 1650  m/s at 21.5km,  you should be able to get that fast air breathing.  Unfortunately the Whiplashes are  passengers at that speed, they peak at 900 m/s and by 1350 are down to half power.    They weigh 1.8 tons each so that's payload you're giving up.

How are you falling back into atmosphere?   Running out o f oxidizier?   Zooming above 29km in a steep climb but at low speed (should be over 1600!)?

You should be able to get a 50 ton ship to orbit with 2 rapiers alone if low drag, and it looks to be.    Wings can help too with not falling back down on an underpowered ship, but your ship is not remotely underpowered in rocket mode.

There's another help thread , JSI's ship currently is 90 tons, 4 rapiers, 6 nukes and no oxidizer.   6 nukes at 60 kn each = 360 kn thrust for 90 tons.   You got 2 rapier at 180 kn each = 360 kn total, same as him, in a 50 ton ship....

 

 

[NightshineRecorralis]

11 minutes ago, AeroGav said:

snip

The rapiers are there for a small boost around 40sec on rocket power. the ship circularizes on nuclear engines. 2 of them clipped into the whiplashes give me 120kn of thrust and 480kn peak vacuum with the rapiers, which don't last long enough for sustained burns.

[bewing]

1 hour ago, NightshineRecorralis said:

The Whiplashes are there to push the craft through the first 10k of altitude and the sound barrier

Eh?? The whiplashes are supposed to get you to 19km altitude (minimum) and at least 1150 m/s speed. So part of your problem may be that you are discarding them way too soon. Another part may be that you are climbing above 42km way too early. The nukes need a slow ascent -- you want the Ap to be maybe 2 minutes ahead of you and lock Prograde on your SAS while you thrust.

[NightshineRecorralis]

Just now, bewing said:

Eh?? The whiplashes are supposed to get you to 19km altitude (minimum) and at least 1150 m/s speed. So part of your problem may be that you are discarding them way too soon. Another part may be that you are climbing above 42km way too early. The nukes need a slow ascent -- you want the Ap to be maybe 2 minutes ahead of you and lock Prograde on your SAS while you thrust.

I've realized that rapiers have the same or more thrust at 10k, which is why I say that. The whiplashes don't cut out until ~1350 to ~1440m/s, depending on my flying skills, and the AP being 2 min ahead doesn't help if it's at 30k. I usually aim for a 45~50k AP and more than 40sec away when the rapiers cut out.

[Firemetal]

2 hours ago, NightshineRecorralis said:

Look at the Original post, the video and craft are on kerbal x here:

https://kerbalx.com/NightshineRecorralis/Firestorm

The intakes are purely cosmetic, by the way, but thanks! Same with the delta wings, they look really bulky and I reserve them for mk3 SSTOs. The Whiplashes are there to push the craft through the first 10k of altitude and the sound barrier, and having an over powered space place feels nice when it takes less than half an hour to run through a whole mission ^^.

Not exactly sure what you were trying to say in your post, sorry!

Indeed, I have some positive angle on the lifting surfaces, they work out just fine  

I'll see what I can do about no canards, but at lower speeds (landing troubles @40m/s) they are invaluable, however, a CoM change might also fix that, so who knows?

I've never really tried pure RAPIER builds, and I don't intend to anytime soon, but thanks for the info!

Basically saying, not enough thrust, add more rapiers. You don't have a high enough TWR in rocket mode. I think purely RAPIER is the right way to go but if you disagree, that's fine too.

Fire

[SpaceFanatic10]

12 hours ago, NightshineRecorralis said:

Still looking for help and suggestions.

but,you know what,JEB,MORE BOOSTERS!

For real,boosters are key,add as many as you can,not the terrier,not the vector,but add engines in the wings,and also supersonic intakes!

[GoSlash27]

Nightshine,

 I second what Signo said above. You don't need that much intake and you would benefit from some static wing incidence.

Here's where I go off the reservation from the rest of the suggestions....
You don't need "moar boosters", you need less. You've got basically twice the frontal area and tonnes of fuel/ engines in order to provide t/w that provides you no benefit. You don't need a t/w that high to make an SSTO, and those Whiplashes are dead weight during the orbital insertion.

 Focus more on clean aerodynamics and less on brute force.
Here's an example of what can be accomplished with just 4 engines when you make a clean design:

30t of payload to orbit on just 4 RAPIERs. Really 38t if I were to optimize the fuel loading.

Good luck,
-Slashy

Edited December 12, 2016 by GoSlash27

[Raideur Ng]

Slashy is correct in every regard here. Streamlining is extremely important to produce an efficient and effective SSTO spaceplane. You can make it into orbit with 0.5 TWR if your craft has very low drag. Keep in mind every part you add, unless it fits properly into a streamlined body, produces considerable drag. That includes your physics-less parts that give that drag to its parent part, like your solar panels.

Key observations:

Too much intakes, 1 shock cone can generally feed 4 engines.

Wings lack fixed Angle of Attack (or incidence). You will need to test this to see how much is required in order for your vehicle to fly straight.

Wings, and thus center of lift and drag is very far back, which means you need more control surfaces to fly.

Streamline everything. If you remove the Ramp intakes, replace them with tail cones, advanced cones, or NCS adapter with nosecone.

Hit F12 during flight and see what forces are in play, red is bad, minimize it.