What is a VTOL, exactly, and how would I go about designing one?

[Sharkman Briton]

Okay, so I have a basic idea of what a VTOL is, it's pretty much a plane that takes off vertically, I'm quite interested in these things because you can land them vertically too, which is a good alternative to a normal plane landing because I'm rubbish at that, but I don't really know the FULL details of exactly what a VTOL is, and how I would design one, I see these replicas with a jet engine at the bottom, that looks cool but I dont know how I would make that, including intakes and making it so I can swap engines from vertical to horizontal, to clarify, when I say VTOL I mean planes, I don't count rockets as VTOL's because they always (hopefully) take off vertically, so if anyone can give me anything from a quick rundown to a detailed guide, I'd appreciate it, thank you for your help, 'cause I'm itching to try them!

[InterCity]

VTOL means exactly "Vertical Take-Off and Landing". Excluding rockets, there is just a handful of jet-powered VTOLs - for example, the Harrier jump jet. This design uses thrust vectoring to make the thrust go vertically and lift the plane off the ground. In ksp, however, there is no such vectoring. You need to put jet engines facing downward around the CoM with enough TWR to lift off, and then some horizontal engines (optional) to propel your plane forward. It's not as easy as it sounds, though, since it's really touchy for balance - you'll spend a lot of time tweaking the downward jets so that the plane doesn't flip. And even then, it's difficult to get it back to the ground in one piece. IMHO it's way easier to make a normal plane - doesn't mean you shouldn't try VTOLs

[Scarecrow88]

In previous versions of KSP the Weasley was usually the engine of choice for vertical lift. Unfortunately in 1.0.4 it no longer has the power to lift anything other than the smallest of designs, which means you now generally have to us the turbojet. This isn't a problem as such, but it is a bit longer than the Weasly, which makes it a bit more difficult to attach without having half of it hang out the bottom of your craft, and with the new graphics you now have a large flame effect below your craft when you use it.

For switching from vertical engines to horizontal engines when in flight, it's best to set them up on action group keys so that you can toggle them as necessary.

[selfish_meme]

There is a stock hinge you can make that has a probe core with two docking ports, so in VTOL mode it is docked on one port with the jet pointing down, when you change you undock that port and use the probe core torque to move to the other port and hopefully dock and the jet should then be facing horizontally for normal flight. I have not built one so I can't help you do it, I understand theoretically how it works. I also don't know how reliable/useful it actually is.

[steve_v]

While possible, they tend to be time consuming to build and both fiddly and temperamental in flight... I'd suggest building a few "normal" VTOLs with separate lift engines first.

If you don't have any reason to stay totally stock, both the Mk.2 Expansion and Quiztech Aero part packs have some nice VTOL lift engines that work and look a lot more like the real thing.

Edited August 3, 2015 by steve_v
Links

[eddiew]

In previous versions of KSP the Weasley was usually the engine of choice for vertical lift. Unfortunately in 1.0.4 it no longer has the power to lift anything other than the smallest of designs

Both of these use a pair of Wheeslys The Tortuga only gets 1.01 TWR with them when full of fuel though, so it's best to do a hybrid launch from the runway. It's always lighter after a few hundred km

General tips:

- mostly it's about symmetry; preserving the CoM preserves your life. If you have a fuel tank 1m ahead of the CoM, you need an identical tank 1m behind it, and both must drain together.

- it is not an option to offset fuel tanks relative to each other because then the weight balance shifts during flight. They must align with the CoM along one axis or another. (Tortuga demonstrates both.)

- place your vertical engines in alignment with the CoM, either equally distant forward/backward, or to either side (both options shown above).

- add cockpit, engines, and wings last, since these are most configurable.

- use small parts like reaction wheels and battery packs to keep the CoM stable. Be generous with reaction wheels, it will help a lot.

- packing the verticals into an MK2 bay will save you a lot of drag during normal flight.

- the hotkey tip is wise. With a T2 SPH, I have the lights (U) toggle both the vertical engines and cargo doors, and RCS ® control the turbojet. It's vital to have them independent.

- plan intakes to allow for all engines to be used at once.

- learning to control a VTOL isn't immediate. You'll spend a while practising before you can do gentle drifts and hovers.

- mountain landings are still hard. If you have to land on a slope, your down jets will push you away from it, so try for the flattest possible corner and be prepared to walk.

[Sharpy]

Here's a VTOL that handles really well. You can download the .craft to see how it was achieved.

Unfortunately, as with most VTOLs its other parameters aren't nearly so good - poor top speed, poor range, poor ceiling. As result, it's fun but useless.

Expecting a combination of good handling, good range and good power - and even SSTO capability - is asking quite a lot As result VTOL are mostly a quirk done for fun.

[Mic_n]

Make a plane. Put a mass of parachutes around the front, and some landing gear/struts hanging out the back. Make sure it has a TWR > 1. Build it, then in the hangar, select the whole thing and rotate it so it's pointing straight up.

Launch.. throttle up on the runway and take-off straight up, then nose-down as you build speed to cruise. When you're ready to land, slow down and nose-up to stall, then hit your chutes and drift gently down to land on its tail end. Take the engineer that's flying it on eva and repack the chutes and you're good to go again.

Ta-daaaa, VTOL. Also a lot more efficient than you're likely to get otherwise.

[Wanderfound]

Most importantly: your lift thrust needs to be in line with CoM. Mods such as Kerbal Engineer or RCS Build Aid are very useful for getting this right; tweak the engine position until you've got the engine torque as low as possible.

VTOLs were much simpler when you could stash a couple of basic jets in a cargo bay. Unfortunately, the nerfing of the basic jet means that you'll need turbos these days, which don't fit easily in a bay. But there are other mounting options...

Javascript is disabled. View full album

[Mic_n]

correct me if I'm wrong, but doesn't the 'basic jet' (turbojet) produce more thrust at low speed than the 'turbojet' (turboramjet)? Also, although I'm pretty confident you're doing it for the aesthetics, no need to mount the entire "engine pod" vertically like that, it'll be creating masses of drag in forward flight. Only thing that needs to be pointing down is the nozzle.

[ajburges]

Ya, the Weesley was really hit hard by the Nerf Bat. Even ASL it has the same TWR as a RAPIER and 2/3 that of a Whiplash. Still, its the only jet engine that can be occluded by a Mk2 bay. Drag is king in the jet realm. If you can't occlude the jet, there is not much point to using high thrust power plants. The drag will really kill any performance.

There are a few extra concerns for VTOL design:

> CoM, CoL, and CoM become a maddening dance.

- You need CoL set for traditional stability

- You want CoM to be within a hairs breadth of VTOL CoL at all flight stages.

- Jet's offset mass will throw your CoM way high! Mount the wings high for added stability and consider offset/rotated main engine mounting to reduce low fuel engine torque

> You will want some hefty reaction wheels for VTOL attitude control. A few centimeters of CoL to CoT misalignment can create tens of kNm of torque!

> You will want more pitch control than normal to fight engine torque in flight mode.

Even when you do those. Adding VTOL systems creates a huge mass penalty that is proportionate to craft mass. Getting global (or better) range is tough. Mk2 becomes unwieldy at the needed sizes.

I've resolved that a carrier jet is the more sane solution. I am waiting on scientist and engineer return to test a Mk3 mining jet with a reuseable rover. Should be able to land at a safe site and refuel as the rover fetches the survey sites. The rover has VTOL rockets to allow it to re-dock with the jet (as an added plus, it can sip up to half its fuel with a fuel cell to save battery weight). Heck, the on site refinement should remove the need to return to KSC after a survey.

If you want to stick to VTOL craft. I recommend a STOVL (Short Takeoff Vertical Landing) or a pure STOL. If you only have the power to hover (1.1-1.2 TWR) at half fuel, you drastically reduce the VTOL engine requirements. Wings still give a surprising amount of lift at post stall speeds, they just need some help to prevent gravity from progressing the stall.

You can also make your jet into a paraglider for much less mass. Being limited to 10-20 m/s at full throttle makes precision landing easier as well.

[Mic_n]

Speaking of paragliders... in the waaaaaaay back for a challenge in here I built me a "set and forget" plane (ie, throttle it up and then disconnect it from all controls) with one Round-8 toroidal tank worth of fuel that covered well over 1000km.. at an average a bit under 10m/sec...

It'd be interesting to see how the new aero handles a similar concept...

[Goddess Bhavani]

I just have one tip. Start small.

Do not, repeat, do not attempt to start off your STOVL or VTOL career with a single stage to orbit, do everything super plane with vertical takeoff and landing capability. There comes a point where insisting on VTOL for a fully loaded configuration is just absurd, when there's something like 2 miles of open runway or flat grass you can run on to takeoff. Also I spent 3 weeks making a STOVL spaceplane with variable geometry, forward swept wings, and realized in the end, it's utterly useless. I wasn't going to land something as large as a hundred ton spaceplane on a helipad anyway LOL!

It's a good reminder that one should start small, and only add capability to a proposed design when it's truly needed. For Career games, I typically require a VTOL for mountain recon and I like to keep them small. Or, I might use a helicopter. Or a rotary-winged rocket (this is called, tail-sitter VTOL and is truly not recommended to try and handle if you're new to VTOLs )

[Scarecrow88]

Both of these use a pair of Wheeslys The Tortuga only gets 1.01 TWR with them when full of fuel though, so it's best to do a hybrid launch from the runway. It's always lighter after a few hundred km.

My comment was aimed at using a single Weasly as the lift engine as that's not really viable any more. I still build VTOLs using 2 or more Weasleys so I know they can still be used if preferred but it can be more difficult to balance the lift of multiple engines or find the space to fit them in a compact design.