GoSlash27

Nich, That spaceplane design has wandered off into the weeds like a drunk on a bicycle! Please don't take that as any kind of disrespect; you know that *I* know that you are a steely- eyed missile man. But I mean... look at it, amiright? It looks like it would be an unstable lawn dart. Okay. Best advice I've got from this pic is to completely scrap it and start with a fresh sheet of paper. Step #1 is to define the mission and thus payload capacity. Get a feel for the scale of it. Step #2 is to build a simple SSTO in accordance with the ratios that you (and of course the rest of us) have established in previous designs, but build it completely out of fuel tanks. Tweak and adjust as necessary until you are successfully orbiting enough mass to account for the mass of your orbital mission payload (the mining equipment, fuel to get to Minmus, etc). Step #3 is to take all this data in hand and build your spaceplane with the required parts, supplies/ etc. And build it like a proper spaceplane. Make it clean, efficient and well- balanced from the start. If it's deficient, don't succumb to the urge to crutch it by tacking stuff on. Look for things that you can eliminate or design to be more aerodynamically stable, clean and efficient. Take it from the top if necessary. What's wrong here isn't a technical deficiency in the design, but the philosophy behind how it was laid out, assembled, and adjusted. Specific suggestions: - a plane that light doesn't need that much wing with that much incidence. You just need enough to keep the nose firmly aligned with the prograde marker throughout the ascent. With all that t/w, you don't need that much wing *or* that much incidence. - the vertical stabilizer(s) should be as far aft as you can possibly get it. - don't stack bulky draggy equipment radially out in the slipstream. Find a way to shield it from the airflow. - Don't add additional parallel stacks if you can help it. Good luck! -Slashy

Starhawk, I don't know, but I bet you could test to find out. Try launching the rig with both intakes open and close one of them after they are full. If it flies straight, then you know the imbalance is due to mass. Best, -Slashy

Jiminator, Lookin' good The air breathing engines decrease thrust rapidly with airspeed and altitude. That's why I like to hang out in the 17-22km range to get all the speed I can from the jets before I switch to rockets. Also, you should set it up for manual switching. It auto-toggles way too early and that costs a lot of rocket DV, which translates to mass and drag. I don't bother closing the intakes in 1.04. I haven't seen a difference in the drag. Best, -Slashy

Ikare, Lots of good info here: http://forum.kerbalspaceprogram.com/threads/132178-how-to-make-space-shuttle Good luck! -Slashy

Capt. H@dock, You would think that's the case, but it doesn't quite work that way. The physics engine alters the lift and drag with velocity and incidence IAW spline curves in the physics.cfg and of course lift decreases with the lower air density. Upshot of all of this is the lift stays pretty constant through the flight. Best, -Slashy

Stoney3k, This is true, but we *do* know a lot about the aerodynamic properties of the parts we use and how the aerodynamics engine behaves. We have the drag box figures for all the parts, aero overlay curves for the wings and lifting bodies, and we know about how occlusion does and doesn't work. While this doesn't give us our exact drag figures at any given moment, it does allow us to design aerodynamically clean aircraft. Capt. H@dock, I usually don't need to use this much wing incidence. I wanted to use a low number of wing panels to keep them from being floppy and needing a lot of strutting. The idea is to incline them as much as necessary to keep the prograde vector forward throughout the flight so the fuselage is flying with zero incidence. Once you have that, you don't need any more incidence. While the nose is level, it is actually still climbing. When I switch to closed cycle, I'm pitching up about 15° to bring up my prograde vector. It is very slippery on reentry, even with the speedbrakes deployed. S-turning is mandatory to get it slowed down before overshooting KSC. As you can imagine, landing speed is very low. Roll response is weak on the tanker, so it's a good idea to have the lineup sorted out early. I'll see if I can get you a copy of the craft file this evening. Wikisend isn't cooperating with me right now. Best, -Slashy

jiminator, Apologies, wikisend is acting up. I'll send you a copy and walk you through it once I'm able. Best, -Slashy

sardia, That's really just for convenience around the runway. Having the nose angled that way gives me a place to mount the nose gear and having the tail mounted that way gives me a convenient spot to mount the tailplane and avoids breaking stuff when I rotate for takeoff and landing. It doesn't particularly help or hurt the aerodynamics. Best, -Slashy

This is the way I do it as well. For my heavy boosters I discard the main tank to burn up on reentry and recover the expensive bits. Best, -Slashy

xtoro, Actually, I think you're in the large majority and folks like myself are in the minority. I plan out the entire mission on paper before I design the hardware and then I design the hardware before I set foot in the VAB. There aren't very many people who do it that way. But you know... lots of ways to play this game. Best, -Slashy

Nich, As much fun as that would be (and I'm confident I could do it), I won't be participating in that. I only design and build SSTOs to shuttle between KSC and stations in LKO, and then only with kerbals and supplies that can be transferred through a docking port. Anything beyond that is (IMO) an egregious waste of resources. I view SSTO spaceplanes as glorified delivery vans that are very good at accomplishing that small part of the mission, but inefficient for the rest of it. I am interested in seeing what the rest of you folks come up with, tho' Best, -Slashy

ajburges, I'd be inclined to agree, but as a practical matter how much real time is it going to take to deliver 38 tonnes of fuel to a station with a faster spaceplane? And what's the part count? How much will that slow the experience down? I think it's worth it to take the slow boat to orbit in the long run, everything considered. You still have to match inclination, intercept, rendezvous, dock,transfer, undock, retroburn, deorbit, and land once for every flight and delivering fuel to orbit is a regular evolution. That takes a huge amount of time, especially when the payload is small for each flight. The amount of time spent in the ascent to closed cycle is miniscule in comparison with the time spent flying an entire mission and if you have to do just one more trip to transfer the same load you've just wasted way more time than you ever could have saved with a faster ship. In this case, it took 1 hour and 6 minutes game time to deliver 38 tonnes. Using faster means I could shave off maybe 6 minutes, but it either won't be the same payload mass (meaning I have to do another mission) or else it will reduce the frame rate to a still-life,cost a whole lot more, and not actually save any time. A few extra minutes to deliver a large payload without frame lag is worth it in the long run IMO. YMMV. Best, -Slashy

Update: Flight of the Brawndo: http://s52.photobucket.com/user/GoSlash27/KSP/Brawndo/story No way this behemoth is gonna get supersonic on just 4 engines, right? Except it does. And this is just before I switched to closed cycle. The trick is drag management. You see... it's not the thrust to weight that keeps you from going supersonic, it's the thrust to drag. So if you build it clean you can do more with less. And the wings are critical because they allow you to keep the fuselage aligned with the airflow without falling into denser air. Wings create very little drag even when they're angled up at a very high incidence. Fuselage parts, OTOH, create a lot of drag even when they're not misaligned very much. So it's worth it from a drag standpoint to use wings to create your lift instead of the fuselage. This can all be bypassed if you use a lot of thrust to weight because you jump out of the atmosphere so quickly that drag isn't really an issue. But you pay a price in efficiency from having so much of the mass you carry to orbit being engines. Best, -Slashy

A_Name, Most of my stuff is pretty uninteresting, actually. For me, SSTOs are just glorified short haul delivery vans. So in the case of this one, it merely exists to transport fuel to orbit and transfer it through a docking port. No reason to waste payload on an actual tank just to leave it floating up there. The only reason I mentioned it is because it's not difficult to fly at all despite being large and ridiculously underpowered. Best, -Slashy

tbarcello, Well... not necessarily. There's a lot of different ways to make SSTOs. I'm just saying that you won't make an SSTO that's worth a darn unless it either has high thrust, adequate wing loading, or some combination of the two. While it is true that you don't "need" wings for an SSTO spaceplane, you do need wings if it's a low t/w spaceplane. Best, -Slashy

Not really. I'm working on a design now that lifts 37t of LF&O to orbit on 4 RAPIERs at over 30% mass efficiency. The takeoff procedure is pretty much "maintain 5° pitch". Best, -Slashy

Renegrade, The discrepancy is from somewhere, but it's not a result of shortcutting the formula. Also keep in mind you're talking an error of 5mm/sec, which is effectively nothing. KSP only shows velocity to the nearest .1m. If you try the same exercise with a very eccentric transfer in a steep gravity well, you'll see it still works out the same. *edit* Actually, having worked this in some extreme examples, I actually did find a discrepancy. I think you're right and the Oberth effect plays a part. In most cases though, the error will be low enough to safely ignore. Best, -Slashy

A_Name, While it is true that you don't "need" wings to achieve orbit, they do help to make a spaceplane more efficient, particularly when you don't have your spaceplane spammed with engines. Wings produce a lot less drag than fuselage sections cocked up at high incidence angles to produce the same lift, so if you have sufficient wing area you can go hypersonic at very low thrust, which means higher efficiency. It's not possible to do this without wings, although if you cram on enough engines you will eventually achieve orbit. This is an example of what can be achieved with wings: Compare and contrast the fuel expenditure for the payload to orbit with the wingless designs above. Best, -Slashy

Renegrade, Just rounding errors, most likely. If you add together the DV on your kick and circularization burns, you should find that it equals the difference in orbital velocity between the first and second orbits. Using the vis-visa for my example initial orbit altitude 0, v= 570.5 tx orbit sma 207km with Vpe=580.1 and Vap=542.1 kick burn 580.1-570.5=9.6 m/sec circ burn 551.5-542.1=9.4 m/sec total= 19.0 final orbit altitude 14km, v=551.5 570.5-551.5 also equals 19.0. Best, -Slashy

yukon, It can be calculated precisely for airless bodies, but you'll need to make a very rough estimate if it has an atmosphere. For an airless body you will need it's radius and mass. First you find the velocity of an orbit at it's surface Vo= sqrt(6.67*10^-11*M/r) where M is in kg and r is in meters. You have to achieve this velocity before you can Hohmann transfer to your desired orbital altitude. This is straight DV plus or minus whatever sidereal rotation it gives you. Next you calculate the velocity at your desired orbital altitude using the same formula. The velocity is lower at the orbital altitude, so you take the difference between the two. This is the DV required to move your orbit from the surface to your desired altitude Add the 2 together and you have the theoretical minimum DV required to achieve orbit, but this assumes 2 instant impulses. Since your thrust isn't infinite you'll need to pad it a bit for safety. ex. the Mun. Mun has a mass of 9.76x10^20 kg and a surface radius of 2x10^5 m. orbital velocity at surface= sqrt(6.67x10^-11 x 9.76x10^20 / 2.00x10^5)= 571 m/sec. orbital velocity at 14 km altitude= sqrt(6.67x10^-11 x 9.76x10^20 / 2.14x10^5)= 552 m/sec. Hohmann transfer DV= 571-552= 19 m/sec Total DV = 571+19= 590 m/sec. Best, -Slashy

Claw, Okay, so if KSP uses the curves in the physics cfg to generate the lift and drag, then what value are the results applied to? The stock lift and drag coefficients in the part config files, or just the lift rating? If both values are used, then it would definitely matter which wing parts are being used. Thanks, -Slashy

I not only assign tasks to different control surfaces, I don't use an active rudder and I keep active control surfaces to the bare minimum. Many of my smaller designs have no active control surfaces whatsoever. Best, -Slashy

This is a known bug. I think we need a ruling on this. It's not really fair to penalize a pilot for a flight that was ruined by a bug. I'd recommend amending the rules to state that flights that encounter the "collision kraken" don't count. Best, -Slashy

Scoring question: For tankers or payload delivery, is the value of the payload deducted from the cost of the flight? Example: I deliver $1,000 of fuel to orbit and burn $1,000 of fuel in the process. I therefore land with $2,000 less value. Does this flight cost 1 point or 2 points? Thanks, -Slashy

Claw, I found it. It's in the physics.cfg file. Thanks about a million! This is gonna be handy! *edit* Wait... there's only a generic set of curves in there. Are these values all multiplied by the wing's lift rating to generate the final values? Best, -Slashy