So, how do you make MK3 SSTOs?

[juanml82]

I've been trying for a few days, and I can't get them to work. Basically, what I want at the least is an SSTO capable of putting a 16 kerbal cabin in LKO along which includes a docking port so I can dock it with a nuclear tug and take it from there. Yes, it's likely to be easier with vertically launched rockets, but I'd like to be able to do it with HOTOL SSTOs. At best, I'd like to add a long MK3 cargo bay with cargo (say, a jumbo tank).

So, after adding the stuff, I end with something in the 80-100 tons range, so I'm trying to go with 8 rapiers. I may need a bit more, though. The problems are:

The aircraft turns over at take off: just a few presses of the S key and the aircraft flips over

I make a design able to take off, and which begins to pierce the sound barrier at around 8-10 km altitude. But I loose horizontal control. Is asymmetrical flameout/thrust still a thing?

I make a design able to take off, but I loose control at about 10,000 meters, even before reaching the speed of sound.

I make sure the CoL is behind the CoM and the DCoM - I also usually stick the CoM and DCoM as close as possible. I've tried placing the rapiers at the back of the fuselage using the MRS 3.5 to 7 1.15 m adapter, I've tried placing them radially around the center tanks, I've tried in clusters of four behind wing mounted 2.5 m tanks, I've tried wing mounted stuck to Mk1 fuel tanks either hanging from the wings or along the wings. I've tried the largish wet wings, I've tried the shuttle like wet wings, I've tried Mk2 wings. I've tried canards, I've tried no canards.

Here are some pics of different designs I've tried

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So, what works to make it happen?

[Blu_C]

A lot of this is going to be TWR. I don't know the numbers exactly (I prefer making my space planes MKII).

Now, you've said you "lose control" at around 10k meters. That can mean a LOT of things and your images really don't help to show exactly what is happening (you go from 10k to 200m in the span of one image jump). What do you mean you lose control, exactly? Are you starting to flip? Unable to pull the nose up? Something else completely?

One thing I've heard is you should have 1 rapier per 13 or 14 tons of spacecraft minimum. It doesn't LOOK like that is your problem, however you may want to give that a check anyway. RAPIERS only really start to kick in their thrust after you break a speed threshold so if you have trouble getting yourself to break Mach 1 then you never have a chance to see their full power.

[KerikBalm]

In thrust we trust

That was in 1.0, and had 12 rapiers... I had to add an additional pair ot each of the rear wings inf 1.02... so 16 rapiers total now.

[cpt_nosh]

I had the same problems over and over. Loosing horizontal control either at start or thenagain at 8k feet. Even though the points were in good match. What's the deal with this?

[Jaeleth]

Check if the CoT is along the same line that the CoM and the CoL, since you are using that many engines, engine placement can be a problem and the place you put them can Induce unwanted torque. Replace them by a, say, single flipper engine just to see if the problem persists.

enable the forces overlay F12 to try to visualize what is happening

displace the CoM further ahead, or the CoL further back, and put some canards, not wings, on the front to compensate for that.

remember that the fuselage also yields lift. When speed increases, so does lift, i don't know if wing lift and fuselage lift increase proportionally with speed, if they don't, that could be the cause, the forces overlay will help you to find this.

try to use less wingspan and more like a shuttle wing, a sort of delta. This should reduce drag at high speeds, caused by the wing, which i am not sure the game considers, but happens in real aircraft, anyway so, just to be on the safe side... That's why fighters have swept back wings and, say, a C152 Cessna has, practically, a square wing

[cpt_nosh]

Check if the CoT is along the same line that the CoM and the CoL, since you are using that many engines, engine placement can be a problem and the place you put them can Induce unwanted torque. Replace them by a, say, single flipper engine just to see if the problem persists.

enable the forces overlay F12 to try to visualize what is happening

displace the CoM further ahead, or the CoL further back, and put some canards, not wings, on the front to compensate for that.

remember that the fuselage also yields lift. When speed increases, so does lift, i don't know if wing lift and fuselage lift increase proportionally with speed, if they don't, that could be the cause, the forces overlay will help you to find this.

try to use less wingspan and more like a shuttle wing, a sort of delta. This should reduce drag at high speeds, caused by the wing, which i am not sure the game considers, but happens in real aircraft, anyway so, just to be on the safe side... That's why fighters have swept back wings and, say, a C152 Cessna has, practically, a square wing

Forces overlay? Wow, are there more things like that which I'm not aware of!

[Claw]

Also, there's currently a bug with cargo bays. They do not properly occlude parts behind them. If you're not opposed to add-ons, there's a fix in my stock bug fixes: http://forum.kerbalspaceprogram.com/threads/97285

It's quite a significant amount of drag and certainly impacts Mk3 designs a lot. Extra thrust will definitely help overcome it. Hopefully it'll be sorted out in the next release.

Cheers,

~Claw

[panzer1b]

Also, there's currently a bug with cargo bays. They do not properly occlude parts behind them. If you're not opposed to add-ons, there's a fix in my stock bug fixes: http://forum.kerbalspaceprogram.com/threads/97285

It's quite a significant amount of drag and certainly impacts Mk3 designs a lot. Extra thrust will definitely help overcome it. Hopefully it'll be sorted out in the next release.

Cheers,

~Claw

Is this exclusive to MK3 parts, or are other cargo bay like things such as MK-2 also suffering from no occlusion? The MK-3 parts i dont quite use often enough to bother, but if this is an issue with MK-2 then thats VERY BAD!

Still, nothing stopping you from building your entire craft inside a MK-2 bay, i have a new micro starfighter that has EVERYTHING fromcockpit to engines inside a MK-2 bay, gotta love planes that are for all intents and purposes dragless (well the nose intake+mk1-2+cargo bay have weight, but everything else including landing gear is all internally placed, 0 drag FTW!

[Dr. Jet]

Just a small tip I came across when balancing my sample crafts - HAVE SOME MEANS TO PUNCH TROUGH TRANSSONIC!

Airbreathing RAPIERs are oftenly too weak to go supersonic by themselves and when it happens at around 10km height - it gives you that "lose control" feeling... but once reaching 400+ m/s with any external help - their thrust (in AB mode) increase enough to continue gaining speed and thrust on their own.

Short burn of any liquid engines or manually switching RAPIER's mode for a couple of seconds to CS then back to AB will do the trick.

[Claw]

Is this exclusive to MK3 parts, or are other cargo bay like things such as MK-2 also suffering from no occlusion?

As of right now, looks like it's only Mk3 cargo bays.

Cheers,

-Claw

[juanml82]

In thrust we trust

https://fbcdn-sphotos-a-a.akamaihd.net/hphotos-ak-xap1/v/t1.0-9/s720x720/11205152_10103548408288173_5405657931943816741_n.jpg?oh=671e5c9de0015e93937d253eb139b57c&oe=55E14F5D&__gda__=1440838886_34aea1d9d7230c416499035265a71b60

That was in 1.0, and had 12 rapiers... I had to add an additional pair ot each of the rear wings inf 1.02... so 16 rapiers total now.

https://fbcdn-sphotos-e-a.akamaihd.net/hphotos-ak-xpa1/v/t1.0-9/s720x720/11141311_10103548411940853_8862798995332673601_n.jpg?oh=fc832d2efe3abbaa1f7b11428137df40&oe=55C1172B&__gda__=1439955924_c8f81a343b7c57dd47beeeb4f31fa8de

https://scontent-fra.xx.fbcdn.net/hphotos-xfp1/v/t1.0-9/s720x720/11150580_10103548412275183_8857780883844404207_n.jpg?oh=98a5cc4c9d15461f9c9dbe4b6e04fe05&oe=55C63354

I'll be trying to copy that

Also, there's currently a bug with cargo bays. They do not properly occlude parts behind them. If you're not opposed to add-ons, there's a fix in my stock bug fixes: http://forum.kerbalspaceprogram.com/threads/97285

It's quite a significant amount of drag and certainly impacts Mk3 designs a lot. Extra thrust will definitely help overcome it. Hopefully it'll be sorted out in the next release.

Cheers,

~Claw

Yeah, I have your fixes already

Just a small tip I came across when balancing my sample crafts - HAVE SOME MEANS TO PUNCH TROUGH TRANSSONIC!

Airbreathing RAPIERs are oftenly too weak to go supersonic by themselves and when it happens at around 10km height - it gives you that "lose control" feeling... but once reaching 400+ m/s with any external help - their thrust (in AB mode) increase enough to continue gaining speed and thrust on their own.

Short burn of any liquid engines or manually switching RAPIER's mode for a couple of seconds to CS then back to AB will do the trick.

Good tip

Another thing, I was playing with Quiztech Aero and assymetric thrust/flameout is still a thing. It's not as serious as it used to be, but it happens. That may be causing the issues at 10,000 meters (too bad I deleted those ships)