Tips on building a reliable VTOL Science module.

[FREEFALL1984]

So, I want to learn how to build a reliable (and controllable) Vtol. It needs about 4000m/s of DV and enough T/w to be able to safely navigate on kerbin (more than 2 should be ok) Ideally it should also be able to function using wings alone in an emergency although since it will primarily be operating on the mun they need to be light and small. It also needs a central docking port on the top and bottom to enable me to both dock with a station and attach it to the top of a big lifter to get it into orbit.

Since this will be my first Vtol craft I dont know where to start, I know that balance will be important and lots of RCS is a must. but I have no clue where to begin, what can you guys advise

[Osprey]

It sounds to me like you might be expecting too much out of one vehicle. My advice would be design something different for vacuum use from atmospheric, particularly if it's only for use in the Kerbin atmosphere, as then you can use air-breathing engines instead of liquid + oxidiser. This means you save on fuel weight in the Kerbin version, and in non-functioning lift-generating parts on the vacuum version.

For the latter, I'd experiment with a nuclear-engine powered lander rather than something that flies horizontally but lands and takes-off vertically. 4km/s Delta-V is quite a lot for a single vessel though, but not impossible for nuclear engines. Alternatively, try experimenting using Ion-power if we're talking about a teeny probe with only a couple of sensors.

[Osprey]

Here, made one using stock parts, unmanned of course. (4092m/s Delta-V (Vac), T:W 0.99 (Not enough for Kerbin, but certainly enough for the Mun))

Vacuum Science Craft

Edited April 23, 2014 by Osprey

[thereaverofdarkness]

I prefer to leave the lab in orbit and take a much smaller lander to the surface because that saves a lot on fuel. But what you're asking for can totally be done. In fact, if you have Kethane installed, you might consider expanding your giant lander a bit further and make it pick up kethane at each landing site, as that can greatly reduce the logistics of refueling the thing every now and then.

I wouldn't worry about the wing mass, they'll be far lighter than the rest. Just worry about their size. If you aren't using FAR, then all you need for wings are a handful of canards or AV-R8 winglets. Just put your center of lift about midway between your center of mass and center of thrust, but have a frontal/upper set and a rear/lower set of control surfaces for better maneuverability in atmosphere.

Now that giant lightweight lab is going to be a major part of your structural design. If you want your craft to fly like a dart in atmosphere (and I assume you do), then you want to put the lab down low by the engines, and the dense fuel up near the nose. A perfect dart design has its own drawbacks though: it'll fly straight in atmosphere but is difficult to turn, and on the Mün it'll be easier to tip over. Alternatively, if you put the lab near the top and fuel at the base, it'll be difficult to put the wings far back enough to keep it stable and it won't turn as easily just because the front and back sets are so close to each other, but it'll stay upright on the Mün easily. So you just have to decide about how high you want your lab, and you might tweak it a bit as you go. Also consider the mass of the engines--most of them are pretty heavy too.

I'd put on a single 750-unit RCS tank and two sets of 4 RCS thruster blocks, one near the top and one near the base--but this might be big enough to warrant more. You'll want to adjust them a little to be almost equidistant from the center of mass. If you're smart or mathy enough to figure it out, the best position is to put them equidistant from where the average center of mass will be, after accounting for fuel use. But to save brain energy you can just center your fuel mass at the center of mass of the rest of the ship, or learn to use short RCS bursts and not overdo it when it is unbalanced. SAS is your friend when using unbalanced RCS.

You'll definitely want a good amount of SAS control. Given how big I see this thing in my head, I might go for two large SAS units. You should have enough SAS to turn it comfortably, but not so much that you can't make small course corrections. The large SAS are also lightweight and can affect your center of mass. If you'd prefer something denser, use the smaller SAS.

Now you want to consider your engine setup. You might want to use a variety of engines for different scenarios, and assign action groups to switch which engines are active. Or you might want to use one set of engines for all operations to keep it simple or reduce total engine mass. R.A.P.I.E.R. engines can help you conserve fuel in atmosphere, though they are pretty heavy and also lack thrust when you're close to Kerbin's surface or just going too slow in air breathing mode. Aerospike engines are also pretty efficient in atmosphere and are still powerful at any altitude. The LV-909 and Rockomax Poodle are pretty efficient in vacuum and make good lander engines, but are inefficient in air. The aerospike actually has superior attributes to the 909 and Poodle except that you can't attach anything under it. The LV-N nuclear engine is even more efficient in vacuum (but even less in air!) and is a great way to save delta-v. I think th LV-N is something you should definitely consider using for space maneuvers if you intend to be taking the ship very far. If it's just making short trips-like hopping to new biomes-it can go without them. And lastly, don't forget about the regular array of liquid fuel rockets. They are reasonably efficient in a wide variety of situations. They might end up being exactly what you need.

That should be enough tips to get you through building what you want. Also go through this checklist to make sure you don't forget anything important and waste a ton of time going without them!

1.) batteries

2.) photovoltaic panels - the little ones if you're forgetful like me because you won't have to remember to extend them or put them away

3.) either enough electricity storage or fast enough generation to power everything, like science or kethane drills

4.) data collection tools: goo, science jr., thermometer, barometer, accelerometer, gravioli detector, even the atmosphere sensor thingy. And since you have a lab right on your lander, no need for more than one of each tool! Just stick the goo canister on top or something. Or use two. Or balance it with something of similar mass on the other side. Radial parachute works, if you want one.

5.) antenna

6.) if you have Kethane mod: kethane surveyor (or set up a satellite to do that), kethane drill, kethane storage tank, kethane converter. KE-WAITNONOSTOP-01 entirely optional.

7.) ladders if you're operating anywhere with high enough gravity that kerbals can't fly with the EVA suit. They can fly on Duna and Moho but not on Tylo or Laythe.

8.) docking ports. I'd recommend a large 2.5m on the bottom just to make it more stable. If you have KW Rocketry, try out the 3.75m docking ring. It's big and heavy but has a 2.5m docking ring inside it.

9.) balance your thrust to weight ratios. You want enough to take off reasonably quickly but not so much that you can't land smoothly. You've got to be able to hover so you can line up your docking port with RCS. Alternatively, you might even succeed in making it able to take off all by itself and not need that lower docking port.

10.) lastly, re-check your center of lift/center of mass, and your action groups. Make sure they haven't shifted or been messed up. And before you launch, check your crew. It'll reset every time you go back to the VAB.

Edited April 23, 2014 by thereaverofdarkness