GoSlash27

Chrysoprace, Yes it is true, but no it is not helpful. Beyond a certain altitude and Mach number, air breathing engines will only create *negative* thrust if they're still running. Better to shut them down and switch to closed cycle. Well... that depends on what you're doing. If you're going interplanetary, than carrying the nukes is worth it. Otherwise, no; the RAPIER is King and the only reason to not use it is because you haven't unlocked it yet. The main reason isn't the additional mass, but the additional parallel nodes. They come with a big drag penalty. You need more air breathers to overcome the drag of the rockets and more rockets to overcome the mass of the air breathers. These combine to create a larger and less efficient spaceplane to accomplish the same job. Best, -Slashy

I actually *do* crunch the numbers myself using a spreadsheet and I'm a big advocate of that approach, I just do it backwards. It's how I zero in on cheap and efficient designs before I build. There's a lot to be said for doing the math yourself -Slashy

Up until 1.2 my cash cow was the simple satellite launcher. Now it's Tourist2. Good for completing tourist contracts and multiple rescues in 1 shot. Best, -Slashy

Spricigo, My main point would be that since there's nothing special about the Isp figure, there's no reason why the OP must use it in the rocket equation if he just doesn't want to. The rocket equation actually uses exhaust velocity, and he can pretty easily calculate that by his thrust and mass flow rate. It seems kinda silly to me to not just go ahead and use Isp since it's right there in the part description and .cfg file, but hey... to each his own *shrug* Best, -Slashy

8/10 You are Korbin Dallas. I often enjoy doing many human things. Like being relatable and laughing. HA. HA. HA. HA. And being not at all like a robot.

"Rescue contracts are like taking candy from a baby that hates candy" - Me

^ ditto. I never bother with strategies until the tech tree is unlocked. You need lots of cash early in the game and science is plentiful, so that's not a recommended strategy. Best, -Slashy

And 3 it pays well. I mean... just getting experienced kerbals for the cost of the mission is worth it, but then they *pay* you pretty handsomely for doing it! It's like taking candy from a baby who hates candy. Best, -Slashy

Echoing the others above... Space planes are good for putting kerbals and supplies (fuel/ o2/ monoprop) in LKO and returning kerbals from LKO for cheap. Those are the only jobs I use them for. Best, -Slashy

^ This, as I said earlier. The rocket equation itself is derived using calculus, but specific impulse is just straight algebra. It's simply exhaust velocity divided by standard gravity or thrust divided by mass flow rate. Best, -Slashy

Interestingly, these values can be directly added to give you an idea of how parts will behave when stacked because occlusion has already been factored in. For example, a Mk1 cockpit+precooler would be 1.88 while a shock cone + Mk1 inline would be 2.46. Mk.1 cockpit+2 radial structurals is 3.92, and so on. You can mix and match the values to give you an idea of how clean your arrangement would be.

Yeah... I wouldn't know where to begin on that one. I've built testbeds that fed 3 whiplashes from 1 shock cone and 4 whiplashes from 1 shock cone and 1 precooler (necessary only for takeoff). OTOH, the VRI, while fine for keeping the engine lit, is extremely draggy for a front node part. If you're relying on clean aerodynamics rather than raw thrust, you really don't want to use that part. Best, -Slashy @swjr-swis, Absolutely right. The longer a part is, the more susceptible it is to losing it's low Cd when not perfectly aligned. Sometimes it's worth using a physically shorter part to alleviate this tendency. I always preach "nose perfectly prograde at Mach1". The plane should be built with enough incidence to make this happen, else all those wonderful "high speed low drag" parts work against you. Best, -Slashy

Surprisingly, the small circular intake is actually capable of driving the Whiplash at full thrust and 20 km altitude without flaming out. But yeah, the thermal limit makes it impractical for SSTO use. Best, -Slashy

Okay, I build a simple Mk.1 testbed and recorded the actual drag for some parts at Mach 1.00 and 1km altitude. They pretty much line up like I'd expect from the drag cubes. Front stack parts: Drag Tail Connector A 0.94 NCS adapter + small circular intake 1.17 NCS adapter + small nose cone 1.25 Shock cone intake 1.26 Mk1 Cockpit 1.36 Tail Connector B 1.44 Advanced Cone A 1.95 Circular intake 3.13 Advanced Cone B 3.28 Adjustable ramp 4.22 Aerodynamic Nose Cone 8.83 Nuthin' (structural fuselage) 101 Inline parts: Precooler 0.68 Mk1 Inline Cockpit 1.20 Engine Nacelle 1.43 Mk1 Diverterless intake 2.61 Radial parts: Structural Intake Radial 1.28 <-- but really you need 2, so 2.56 XM-G50 4.46 <-- I haven't tested to see how many are needed, but it doesn't matter. It sucks. Best, -Slashy

tseitsei89, Empirical testing and "idiot" should never occur in the same thought. What would be *really* illuminating would be building a testbed aircraft and checking the drag of these parts at 340 m/sec. I'm home sick today, so I think I'll give it a shot... Best, -Slashy

Monstah, I'd suggest trying it with 4 so you can judge the difference. I'm occasionally forced to use 3 fins in early career due to part count, and I notice the weird behavior immediately. Best, -Slashy

I'd just like to point out that fins are worthless above 27km altitude. If you need more control authority up there I'd recommend reaction wheels or RCS. And yeah... I imagine you're going to have a very hard time getting that long spindly shape to behave during reentry. I think your original roll instability was from arranging your tailfins in a multiple of 3. If you put fins in planes that aren't aligned with pitch and yaw, they will induce cross- coupling every time they move. Good luck, -Slashy

...furiously restraining myself from pushing the big red button....

That it is. I'm just pointing out that it's not needed to derive Isp. Best, -Slashy

Isp is actually just a measure of the fuel efficiency of the engine; if it has a mass of fuel equal to it's thrust it will run for (Isp) seconds. Multiply the Isp by g0 and you have the velocity of the exhaust. It's not a value that's derived from calculus. Part of the problem is that this calculation doesn't take into account the diminishing mass of the rocket, but the bigger problem is that it doesn't reflect what a rocket does. In the simplest form it takes part of the mass of the rocket, expels it from the rear at high speed, and imparts an equal and opposite reaction in the rocket. m1v1=m2v2. If you have the thrust of the rocket and fuel mass flow rate, then you have the exhaust velocity. Vx=T/m*. Vx*ln(Mw/Md)=DV. tl/dr... If you don't want to use 9.81*Isp in your calculation, just use T/m* instead. They're the same thing. HTHs, -Slashy

I'd say we can call this one answered -Slashy

*embarrassed look*... I appreciate that, @tseitsei89, but there are quite a few folks on this forum that I'd consider spaceplane gurus including (but not limited to) @Starhawk, @Right, and @foamyesque. I'm sure I'm forgetting people, but you know... senility... We don't always agree on everything, so it's wise to pay heed to their advice as well. Best, -Slashy

Looking at the 1.2.2 drag cubes, here's what I see for the intakes: Type Area Cd XM-G50 .728 .425 Circ Intake 1.213 .450 Shock Cone 1.213 .300 Radial Long .121 .351 Mini Circ .303 .400 RamAir 1.218 .375 Precooler 1.213 .886 Nacelle 1.494 .812 Fus Intake 1.718 .617 By way of comparison, some other things you might put on the front of a stack: Nose Cone 1.213 .631 Adv cone A 1.213 .348 Adv cone B 1.213 .454 TailConnA 1.213 .132 TailConnB 1.213 .187 Mk1Cockpit 1.215 .232 Judging by this, I would expect the shock cone to still be the lowest drag intake for the front of a stack. Best, -Slashy

tseitsei89, The ramp intake worked fine, but I only tried it with 1 engine. Best, -Slashy

sevenperforce, Is it your intention to enter low munar orbit? If so, then you want your Hohmann transfer to put you at that altitude. If you're looking for the gate munar orbit, I'd have to calculate that. Best, -Slashy