Transition from VTOL to horizontal flight

[gilflo]

Hello guys

I need some advices as i want to build a VTOL atmospheric jetplane Like a Harrier, not a plane taking on his tail like a rocket. I want it to be able to turn right and left while being on VTOL.

As it seems to me there is no real possibility to build it with jet engines being able to turn on an axis from vertical to horizontal i think i must build it with vertical jet engines for vertical flight and use horizontal jetengines for conventionnal flight.

My questions are: do i need a SAS for vertical flight and a SAS for horizontal flight?- SAS for horizontal flight will be needed for further VTOL Space plane. In this case how do you manage transition from vertical to horizontal flight?

About the best position for vertical engines, i suppose it shoudl be each side of the COM and how to deal with variation of COM du to fuel consumption with vertical flight: RCS, flight controls, both of them.?

If you have advices for design of such a plane, they are welcome.

Thank's

[Thahat]

stock only: you will need multiple engines, some pointing down, some pointing back, rotation will be done by SAS only in VTOL mode.

if you might concider mods, well im not the spindoctor for this guy and his mods but.. take a look at this other place on this forum i'd say.

http://forum.kerbalspaceprogram.com/threads/111691-WIP-90-QuizTech-Aero-Pack-v1-1-1-Updated-3-20-15

in both cases: make sure your center of mass is balanced around your center of thrust in both VTOL and normal flight modes, you can see this in stock by using the engines thrust limiters and setting them to 0 for the engines you are not using.

in the case of the mod, same thing + the rear engines toggle in-editor aswell. hope this helps!

[Wanderfound]

No, you don't need separate SAS (torque) units for vertical vs horizontal flight. As for transition...keep the VTOL engine on, fire up the HOTOL engines, wait until you've gained enough airspeed for conventional flight before shutting down the VTOL engine. And expect to lose a bit of altitude during the transition.

You can build so that fuel draws evenly from tanks around the plane, but you'd probably find it easier to use a fuel balancing mod such as TAC-FB (good) or Goodspeed (better). RCS Build Aid is extremely useful when it comes to placing your VTOL engines.

These videos are all for FAR, but the basic principles are the same in stock aero.

VTOL flying:

Very good (not me) VTOL flying:

VTOL building:

Edited March 23, 2015 by Wanderfound

[Tweety]

If you build small enough 1 ASAS should be enough as with 1 VTOL engine. My engines normally consist of 1 circular air intake, 2 or 3 cubic struts, ASAS and a basic jet all stacked together right over centre of mass at lift off. Normally 1 engine per 10 ton is enough, don't forget action groups are your best friend for VTOL jets. As for flight profile throttle up VTOL engine and achieve reasonable height, then toggle horizontal jet to gain forward speed until you know you won't ditch, then toggle off VTOL again. Best to find out slowest take off speed and use that as a benchmark to toggle off VTOL, e.g take off speed of 50m/s, aim for 70m/s horizontal velocity before turning off the vertical engine.

Hope this helps.

Tweety

[gilflo]

Hello everybody, thank's for your answers. I got TAC fuel balancer mod and also RCS Build aid. I have goodspeed to but it looks to me quite complicated, but i will look again.

About the ASAS do you place it vertical way or horizontal way?

[Wanderfound]

Either way, KSP torque wheels don't care about alignment.

[Mister Dilsby]

If you don't mind carrying oxidant, I find the Vernor engine an excellent choice for easily controllable stock VTOL. Just place enough thrusters pointing downward to lift the ship, enable RCS, and press 'K' to go up. If you balance right and have enough torque/monopropellant RCS, SAS will automatically tune the thrusters for you and the ship will stay quite level. You can then move around in a hover either by steering control surfaces/torque with WASD or via RCS thrusting with IJKL controls.

[Slam_Jones]

The single best technique I've personally found (which will only work if you use mods) is to take a hinge from Infernal Robotics, stick it on the bottom of the craft in line with the CoM, so that it can swing toward the nose or tail. Attach an engine of your choice to the hinge, and clip into the fuselage as needed.

Now, you can set the IR controls to something simple (I usually do '3' and '4') so that you can aim the VTOL. Aim it ahead of you slightly, you'll start losing horizontal speed (while holding vertical speed). Aim it behind you, and you'll start gaining horizontal speed (while holding vertical speed).

If you also have an engine on the back, then you can make smooth transitions from on to the other. Just keep in mind the spool-up time if using Jet engines.

First image show VTOL in "flat state". The VTOL is pointed straight down, and the craft moves straight up.

Second image, the VTOL is tilted back. This gives the vessel forward thrust in addition to VTOL'yness.

-- At this point, you can activate the main engine, then shut down the VTOL once you're moving quick enough.

Third image, the VTOL is tilted forward. This allows the pilot to burn horizontal speed without losing vertical speed.

-- Here, you would throttle down gently to set her down how you want it. Alternately, you can use this to stop mid-air, then get going again without landing.

And lastly, one of my VTOLs that uses this technique. You can see the VTOL in the "flat" position on the bottom of it there.

Edited March 23, 2015 by Slam_Jones
typo

[Tweety]

I have just knocked up a very basic training craft if you're interested, balanced COM (although you use TAC fuel balancer anyway). Conventional takeoff at about 45-50m/s, vertical takeoff at just over 2/3 throttle (engine is thrust limited) and VSTOL can be achieved with both engines at about 15m/s.

Action group 1 for VTOL, 2 for horizontal engine.

VTOL craft.

I have quickly tried it and after a vertical takeoff at 2/3 throttle activate horizontal engine and toggle of vertical engine at about 70-80m/s.

Tweety

Edit: Activate ASAS before VTOL

[gilflo]

Thank's again everybody.

Very interesting thread about all the technics about transition from VTOL to HTOL

I was thinking about puting an engine on a hinge from infernal robotic but i was also thinking it would never be strong enough to manoeuver an engine.

Thank's also TWEETY for the Vtol craft.

Very interesting to see how you build it

[Tweety]

I suspect the craft I gave you is more than enough to slap some 24-77's on and turn into an VTOL SSTO as well. I just didn't have time to play with it last night.

With the TAC fuel balancer you could just fill all the tanks and away you go.

Tweety

P.S. Also let me know how you get on with it. I wanna know if the crafts I build for people are actually user friendly.

[gilflo]

I suspect the craft I gave you is more than enough to slap some 24-77's on and turn into an VTOL SSTO as well. I just didn't have time to play with it last night.

With the TAC fuel balancer you could just fill all the tanks and away you go.

Tweety

P.S. Also let me know how you get on with it. I wanna know if the crafts I build for people are actually user friendly.

I download the craft file and put it in my SPH files with my other planes but I can't see it when I want to load it.

[Tweety]

That's the super secret invisibility cloak my kerbals have been working on at work hmmmm I will have another look tonight when I get home but I'm sure I'm not dumb enough to screw even this up. Don't want to sound condescending, just trying to troubleshoot, but is the craft file in your save SPH or? 0.90? Maybe some other screw up my end. I will get back to you as soon as I suss it out after work. Ps try re download again just incase of computer weirdness.

Tweety

[gilflo]

Never mind, I duplicate the file and save it both in my SPH save and in 0.90 SPH and I can see it now but I can't open because some parts are locked even in sandbox mod, so I think I am missing a mod, despite I got a lot of them

[Rematog]

Not a jet, but I've developed two Atomic (LV-N) powered landers with either 24-77's (small diameter one Kerbalnaught) or Mk 55 radial (large diameter 3 Kerbalnaught) side mounted engines for vertical landings. The smaller "Eagle" lander weights 9.21 or 11.8 tons (for "stretch version w/more fuel) and can fly on Kerbin with 4x 24-77's with partial fuel (8.1 tons thrust). The bigger "Kondor" at 31.2 tons with 2 Mk 55's (24.4 tons thrust) can also fly with partial fuel on Kerbin.

Using these landers so far on Mun, Minmus and Gilly (getting ready to go to Pol and Ike when I get a launch window), I've found the transistion painless. I've got one SAS, same size as vehicle, plus capsules SAS, and normally don't need the RCS on. I've a single bottom mounted Vernor front and rear and a pair of RV-105 thruster blocks at the front tip (longest moment arm) to use the "Free" monopropellent in capsule. Mainly use RCS for chute landings on Kerbin.

I've found the transition easy enought, I kill horizontal/vertical speed with main engine, then use Action groups to toggle main engine off, and thrusters on (not having fully unlocked, I use "abort" for main engine and "lights" for vertical thrust).

Do take care to keep thrusters at CG. I've designed ship so fuel full, fuel empty CG shifts very little. I'm really happy, especially when landing on slopes. Last nights Mun landing in crater I ended up on a steep one. None of my early game normal landers could have stayed upright!

P.S., Playing Beta, as a first time player and going straight thru Career mode, totally stock, "Look Ma, No Mods"

Edited March 24, 2015 by Rematog
typo... dang autocorrect

[ShadowZone]

I have used a hybrid approach for my F-35B9. One vertical engine right behind the cockpit and one on a hinge (Infernal Robotics mod) at the tail. From landed position: activate vertical engine and tilt aft engine down, fire them up, enjoy flying.

Transition: gain a little height, move the aft engine back to horizontal and as soon as the plane tries to pitch up (due to the disproportionate thrust from the now lone vertical engine) shut that front engine off.

All in all easy to fly and to control. Just keep in mind when construction a VTOL that the center of mass and center of vertical thrust have to be aligned for this to work. Also keep in mind how that CoM shifts due to the fuel draining. I sometimes add two fuel tanks, one in front of the vertical engine and one behind it so that they can drain evenly and the CoM stays more or less where it was.

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[FlipNascar]

As previously stated, get yourself RCS build aid. It's an invaluable tool! I build the normal parts of the plane first, and make sure Dry, Average, and Max Weight CoM, are aligned as possible. Then I slap on the VTOL engines. And I second the suggestion of Vernor engines for control. Didn't the Harrier itself have some sort of ducts to provide control authority at very low speeds? Because the ailerons and elevons aren't going to work with zero forward airspeed.

Moreover, with RCS build aid, you can't start playing around with aesthetically pleasing engine placements because you'll get the visual representation of the torque induced by them. Also, just keep building them and watching them explode!

[Tweety]

My bad, fire spitter may be the contributing reason for the craft file now working. I will rebuild again in fully stock or at least check it over again.

Tweety

Edit: I just checked it with a brand new stock install and it loads and works as intended. Maybe there is some part on it that one of your mods interferes with. I honestly wouldn't know where to start with the troubleshooting other than maybe going through each one of your mods and checking them off one by one to determine the problem. That could take quite some time if you have alot of mods so I will leave you with a pic or 2 to see if maybe you can replicate the same craft?

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Edited March 24, 2015 by Tweety

[gilflo]

Well guys here is trial, a Twin engines VTOL craft using RAPIER: 2 RAPIER for VTOL, they are in the wings because I did not succeed putting them in Cargo hold on a cubic strut, I don't know why I could not put them straight.

Anyway this configuration is very easy to fly from VTOL to HTOL and landing is even easy without SAS

Here at Take off with RCS and SAS. as RCS I use K21 RCS Jet Thruster that use diverted Air intake - from QuizTech Aerodynamics division. Total weight around 16T and 1550DV

Transition to HTOL with 4 engines on, RCS and SAS

Easy to fly with my COL just slightly above and ahead of my COM. I find that easier than COL behind COM.

Engines cut, slowing down for landing

Landing without SAS, quite easy

Now I must try it at lower weight with a little fuel.

Maybe you are wondering why so many Air intakes?

The first purpose being to build a VTOL space plane like this one with 4 RAPIER able of 3300DV in close cycle.

She got 400 liters of fuel for the jet aircycle that brings her to 30000m before switching on close cycle.

I play on stock and the only way I found to climb that Spaceship at 30000m on jet engine air cycle is to add a lot of air intakes, the more the air intakes, the higher it seems to climb on air cycle

If you have advices about that you are welcome, because I plan to put 2 of these RAPIER on hinge to use them on VTOL and then on HTOL

The moving Canards you see on my spaceship and the plane below are here to move the COL in flight to keep the plane manoeuvrability as easy as possible when COM moves du to fuel consumption.

My second hope is to build a Karbonite VTOL jet like the one I sent to Duna

I landed it with parachutes because DUNA is very hard to land while flying. She can refuel by mining Karbonite.

I think a VTOL would be easier to fly on Duna, for landing and also for turning which is very difficult....

[FlipNascar]

On your first design, have you considered switching all of those structural intakes for shock cone intakes? You get more intake air per intake compared to the structural ones. As for placing them, you have a that flat empty pancake-esque space on the front and rear of those fuel tanks. In theory adding shock intakes there would also make it more likely to be drag friendly with the impending aero updates. Not to mention, reducing the number of intakes will also reduce drag, and don't forget to close them once you switch to closed cycle on the Rapiers, and possible more aesthetically pleasing (in my opinion anyway).

[gilflo]

Are those shok cone intakes from stock?

Do you mean that wherever the Air intake is place it will work? No need to put them on the engine?

[FleshJeb]

I find turning off the gimbal on your VTOL engines to be invaluable. Your whole craft is your gimbal when in VTOL mode. It's very hard to do precision flying when you're competing with the engine.

[Tweety]

Yeah the shock cone intake is stock. Place them wherever you like (ideally behind COM I believe)

Tweety

[gilflo]

On your first design, have you considered switching all of those structural intakes for shock cone intakes? You get more intake air per intake compared to the structural ones. As for placing them, you have a that flat empty pancake-esque space on the front and rear of those fuel tanks. In theory adding shock intakes there would also make it more likely to be drag friendly with the impending aero updates. Not to mention, reducing the number of intakes will also reduce drag, and don't forget to close them once you switch to closed cycle on the Rapiers, and possible more aesthetically pleasing (in my opinion anyway).

If you consider the amount of air, it's 0.5 per radial and structural intake air and 0.4 per shock cones intake, so are you sure i'll get more air via shock cones intake?

[FlipNascar]

Given that the goal is space you need to be going hypersonic, so at that point why you want the shock cones is because they have the biggest intake area. I did a quick and dirty direct comparison (on the shock cone jet added a reaction wheel and batteries because the first was a bit too unstable, did a repeat with structural intake for control, findings no different to first flight in screenshot, it actually did worse...). Used a similar climb profile, take off, 45 degrees and let Mechjeb throttle back to prevent flameout avoided giving any control inputs. If you look at the difference in thrust levels and altitudes you should be able to maximize your airhogging with shock cones.

Structual

Shock cone

Second test with structural intake:

Edited March 25, 2015 by FlipNascar
Added control image