Why this thing won't go to orbit?

[Horophim]

I have also seen the scot manley guide for spaceplanes. The problem with this is that it will explode if i try to fly horizontally at 10 Km to reach about 900 m/s and it will start to burn as rocket a little above 11km and won't have enough deltaV to reach orbit. I also tried to put 2 jet engine and 2 rocket engine but without success

How do i have to fly it to make it to orbit give a payload and deorbit?

Album

Edited July 10, 2015 by Horophim

[capi3101]

Get up to 10k, then level out so that your prograde vector is about 10 degrees above the horizon; you still want to be going up to get out of the soup, just not as fast. Plus moar intakes - one per engine at a minimum if you can manage it. Try adding four radial intakes (a pair for each of the center engines) and see what that does for you. Add the ability to toggle air-breathing mode as an action group if you can, and keep it in air-breathing mode until you're at least up to 20k if it auto-switches. Bear in mind that if it does auto-switch and you switch back, you're liable to start seeing flame-outs.

If you're not adverse to mods, you should consider adding Intake Build Aid; with it, you'll reduce the risk of asymmetric flame-out substantially, without having to go through the fuss of putting your intakes and engines on the plane in the right order (which, incidentally, could be another cause of the issues you're seeing - craft with RAPIERs install tend to switch over all at once as soon as the first one runs out of sufficient air to continue operating in air-breathing mode).

For 33 tonnes in the soup, you shouldn't need more than 3 RAPIERs. The fourth helps, I suppose (nothing wrong with excess thrust), but watch that you don't overheat.

Edited July 10, 2015 by capi3101

[micr0wave]

Not sure about the optimal/most efficient way, but i tend to keep my plane below 350m/s under 10km

and then acclerate up to 22-25 km with the rapiers still on airbreathing mode, should be above 1000m/s by then.

The rapiers are better put on manual switching and maybe the switch (from air to rocketmode) on an actiongroup.

There are 4 engines and i can only see 2 intakes, i'd either remove 2 engines (similar sized planes can reach orbit with 2 rapiers easy) or add 2 intakes.

If you have trouble to break sound barrier, you can give a small boost by switching to rocketmode shortly, or, maybe better, take a small dive to acclerate.

edit: capi3101 types faster than me

[Chaos_Klaus]

they switch, because they run out of intake air.

staying below 350m/s is not advisable, becausethe engines would produce more thrust if you go faster. Also, 350m/s is just above the sound barrier already so there is really no reason to not fly faster.

[capi3101]

Taking another look at your screenies. This is not related to the initial problem but just something I'm noticing - you've got two fuel lines running from the central fuselage to the portside outboard fuel tank. I'm not seeing corresponding fuel lines on the starboard side. If you've been seeing problems with your plane wanting to yaw uncontrollably in flight, that's almost certainly why.

Edited July 10, 2015 by capi3101

[Horophim]

i know about the sound barrier (not sure if going subsonic is better for the climb to 10km) i will try more intakes, the main problem is that i either explode due to overheating (going too fast around 10km) or i get to the rocket engine too fast

- - - Updated - - -

mmm i have 2 for connecting mid to side and side to mid (but i probably have missed the one on the starboard when i built it again a couple of times)

P.S. I'm not sure what's the use for the engine precooler and if here can be helpful

Edited July 10, 2015 by Horophim

[capi3101]

The pre-cooler acts as a combination air intake and fuel tank, but it's not going to provide you with the amount of air you'll need to keep your engines operating in air-breathing mode much more than what they're doing now. Apparently they do help with radiating away some of your engine heat.

Sub-sonic is generally better for the climb to 10k; don't try to go supersonic until you're out of the soup if at all possible. 45 degrees up to 10k is perfectly fine; back in my own soup days I would occasionally manage 60-70 degrees. Best you can manage for that part of the flight, then flatten out to 10 degrees once you're at 10k and stay there until your engines kick over. If you start to see heat bars, increase to 15-20 degrees.

Fix the intakes first - that's what's causing the bulk of your issues.

[Red Iron Crown]

Taking another look at your screenies. This is not related to the initial problem but just something I'm noticing - you've got two fuel lines running from the central fuselage to the portside outboard fuel tank. I'm not seeing corresponding fuel lines on the starboard side. If you've been seeing problems with your plane wanting to yaw uncontrollably in flight, that's almost certainly why.

Fuel lines aren't relevant to Rapiers, they ignore them entirely.

OP: I'd have to say the design is under-intaked for high altitude work, one ram intake or shock cone per Rapier works well. You should also use Intake Build Aid to balance intakes and engines (or interleave them manually). The bulk of your air-breathing acceleration should happen between 12km and 20km altitude, it's what happens there that determines how efficiently it will go to orbit.

[capi3101]

Fuel lines aren't relevant to Rapiers, they ignore them entirely.

Nice to know. OP did mention trying out a Whiplash/rocket combo - the fuel line setup would've been relevant to that configuration.

[Horophim]

Ok i put the thing in orbit with a few fuel left and 4 ugly intakes on the belly of the craft. I obviusly then burnt in the rientry but that's another problem I will try to cut out the fuel line and see what happens, also i will put a rcs system for space and see if i can still reach orbit with the added mass but i'm confident now. TY all

[Merandix]

What's your intended payload?

One, drop the hugemongous wings. You have huge lift, but even at a slight angle of attack, that also means hugemongous drag. Go for sleek and aerodynamic. Mk2 provides lift anyway. If it can get off the runway and fly with an Angle of Attack of 5 degrees or less, it's fine.

Two, drop a RAPIER, 3 should be enough. Each RAPIER can get 13 tonnes of total vehicle weight (including itself) into orbit quite reliably. By engine output, you should easily be able to push a nearly 50 tonne craft into space. A bit less if you want to get there quickly.

Three, I think you should be able to actually drop a fueltank.

Four, add two (for example) pre-coolers. They give you a little fuel, but more importantly, they also give you more air for your third engine. Two engine pre-coolers should be enough for a single engine. They can go on the side tankage. Build your engines / intakes like this: pre-cooler, pre-cooler, engine, ram intake, engine, ram intake, engine. Not really necessary anymore, but it might help a bit.

Those big wings and wing-strakes are for far bigger planes.

Climb to about 10 km... ideally, you shouldn't stay below 350 till 10 km... because then you need to build up too much speed above, which will slow your ascent and thus increase the fuel bill (and thereby decrease your chance of getting into orbit). A little overheating isn't a problem. I often break the sound barrier by like 5 km. Your rapiers should no longer be accelerating you on airbreathing at about 24-25 km. By then you should do at least 1300 m/s and if you really do it well, over 1450 is possible (though you will run a bit hot by then). Shallow out at about 10 km, but no sharp turns.

My personal gut feeling is that letting the engines run at low key and keeping apo at 45-50 seconds till you actually hit your target apo at near orbital speed saves some fuel compared to shutting the engines down after hitting the projected apo and then coasting up to there, then firing the heck out of them to circularise. My gut tells me you'd be reaching the same speed twice... and since I lose up to 200 m/s while coasting up, that sounds quite non-efficient to me. (note, the earlier method does take a bit more time). I don't know if this is correct, but it feels that way.

[Horophim]

Ty for the tips i will try it out

BTW how do i know how much lift do i need?

Edited July 11, 2015 by Horophim

[Merandix]

Generally crashing at the lip of the runway is a good indication you have too little

You don't need a lot. A full deltawing is probably already pushing it.

How did it work out?

[selfish_meme]

Two, drop a RAPIER, 3 should be enough. Each RAPIER can get 13 tonnes of total vehicle weight (including itself) into orbit quite reliably. By engine output, you should easily be able to push a nearly 50 tonne craft into space. A bit less if you want to get there quickly..

You should check the Single stage entries in the stock payload fraction challenge, Rapiers can do a lot better than 13 tons.

[Sharpy]

You estimate your lift by judging the difference between your AoA and prograde direction at cruise speed. If your prograde icon still touches the center of navball with the circle, (about 5 degrees) that's quite enough. If it hangs so low the tip of the "central fin" doesn't touch the -v- mark, some 15 degrees it's definitely not enough and you're losing speed to increased drag as the plane flies too "belly front" instead of attacking with the nose. Anything between is up to you, although that largely depends on application and flight profile. E.g. a deeper dip is allowable early into the flight when you're with full tanks - try to take the plane for a test flight with half the fuel and if the prograde marker still dips below the central dot, add more lifting surfaces.

OTOH if the marker sits firmly in the middle of the central mark or dips just a degree or two, you're probably wasting speed to drag caused by too many unnecessary lifting surfaces.

[mrclucks]

I had a similar design and weight reach over 100km by going at 45 degrees up from the start.

Get smaller wings for the back and maybe some control surfaces in from for pitch if you need them

[Merandix]

You should check the Single stage entries in the stock payload fraction challenge, Rapiers can do a lot better than 13 tons.

You missed the 'quite reliably'. As in, with 13 tonnes per RAPIER dependency on piloting is MUCH less than at, for example, 16 tonnes per RAPIER. But you're completely right to point out that when you get the hang of stuff, it RAPIERS can do far better. Just that my personal recommendation is to stick with 13 tonnes per RAPIER for learning the basics.

[capi3101]

Ty for the tips i will try it out

BTW how do i know how much lift do i need?

The old rule of thumb used to be a lift coefficient of one per tonne of plane (i.e. a pair of delta wings, with a lift coefficient of two each, would safely lift four tonnes). These days I couldn't tell you with the stock model; I fly FAR and use a series of formulas to determine the size and shape of my wings (based on desired wing loading and aspect ratio). A pair of standard-sized delta wings might cut it for your design, though I have never measured the area of the stock parts so I couldn't say one way or the other. Merandix's tip of "crashing at the lip of the runway is a good indication you have too little" is actually fairly sound advice...

EDIT: Hell. I'll take a stab at it anyway. So I usually shoot for a wing loading of 0.3 (about the same as a Eurofighter Typhoon) and an aspect ratio of 2:1 (roughly the same as the SR-71, Concorde and Shuttle).

The formula for wing loading is L = M/A, where L is the wing loading, M is the mass of the craft and A is the wing area. Solve for A: A = M/L. Plug in values: 33 t/ 0.3 t/m^2 = 110 m^2.

The formua for aspect ratio is R = B^2/A, where R is the aspect ratio, B is the span and A is the wing area. Solve for B: B = sqrt(RA). Plug in values: B = sqrt(2*110) = 14.83 m.

Semispan = span / 2, so your wing semispan should be 7.42 meters, give or take.

For your root length, I go with the definition of the area of a trapezoid: A = 0.5 * [r+t] * s, where A is the area, r is the root length, t is the tip length and s is the semispan. Now, we have the wing area, but that's the total wing area; for each individual wing, we want half that area, so you've got 0.5A = 0.5 * [r+t] * s. The 0.5s cancel each other out: A = [r+t]*s, and then you solve for r+t: [r+t] = A/s = 110 / 7.42 = 14.825 meters. You put the root length at half the total length of your plane, and whatever's left goes to the tip. If the tip length turns out to be longer than the root length, you need to lengthen your plane. If the tip length is zero or less, you're building a pure delta. In between those two cases your plane is a cropped delta.

But like I said, I don't have knowledge of the stock parts, so I couldn't tell you what combination of parts would give you these figures. The formulas work; I can tell you that much - anything that flies in FAR should fly in stock just fine.

Edited July 13, 2015 by capi3101

[SAI Peregrinus]

If you use FAR just look at the AoA value, if it's under 5 degrees you've got enough lift for easy level flight.

eg:

That also tells you wing area, and quite a lot of other info about how the plane will behave. It's great because it lets you design the whole plane and know it will work correctly before you even leave the SPH.

[Nich]

First off remove your vertical fins (2) and go with a single smaller fin those are VERY draggy for some reason and you dont need that much yaw control. Also get rid of your strakes in the front they may be blocking airflow for your intakes. Finaly switch to shock cone and precooler as I feel this gives more air when you going faster then 1100 m/s for less drag. Just like with everything else less here means less there. Less wing area means less weight and less drag. Thus you can have less engines. less engines means you need less fuel which means you can have less lift. My SSTO achieved 21.5t per engine and i think 12.9t per lift

Basically if it can barely takeoff you probably have a good chance of making it to space. I do want to try trading lift for thrust i.e. 18t per engine and 16t per lift and see if that works better. Aiming for something that can hit 200+ by the end of the runway and just barely fly until 350ish. This should be able to hit 1470ish at 22km on air saving you a ton of fuel.

Edited July 13, 2015 by Nich

[kurja]

With 4 or 3 rapiers, set air breathing /rocket modes to action groups so that when you start running out of intake air (flaming out), you can toggle only two of them to rocket mode (or maybe just one if using 3 rapiers). That way you can use that economic air breathing mode to as high altitude as possible, switch the rest to rocket mode only when they start flaming out again. I find doing this helps spare some fuel.