Stock: Medium and large space planes that DON'T look like a Dassault Rafale?!

[-Velocity-]

All my big space planes always evolve to the same basic design. Why?

1) There is only one stock landing gear, and it is ridiculously tiny and short. Everything stems from this...

2) Landing gear must be placed closed behind the center of gravity or you can't pitch up the nose during take-off.

3) The nose must pitch up during takeoff (duh), bringing the tail closer to the ground (double duh). The fulcrum for this movement is the aft landing gear (triple duh).

4) Therefore, because 1), the aft landing gear must be near the aft of the plane to provide enough freedom for angular motion for the nose to pitch up without the tail touching the ground and exploding.

5) Therefore, by 2), the center of gravity must be near the aft of the aircraft.

6) Therefore by 5) most of the wing area must be at the aft of the aircraft to keep the center of lift behind the center of gravity. A delta wing does this well.

7)Because the trailing edge of the delta wing is close to the center of gravity, ailerons placed there do not provide sufficient pitch authority during flight. Pitch authority is established by placing canards by the nose, far from the center of gravity, giving them sufficient authority to pitch up the nose.

8) horizontal stabilization is established by placing vertical stabilizers to the aft of the aircraft.

And therefore, all large space planes end up looking vaugely like this-

Have you guys thought of any ways to fight this "problem" with stock parts? I've got some ideas-

1) Place landing gear at the end of something the juts downwards from the fuselage. It looks ridiculous, is unrealistic, and unbalances the spacecraft when in space under rocket power

2) A variant of the above; place engines on the top and bottom of the fuselage, and attach the landing gear to the bottom engines. It will look pretty ridiculous, but I imagine it would work, and at least it would look different. Another problem though- the nosewheel must be extended downward too.

3) Make the space plane a TAIL-DRAGGER? It would be pretty ridiculous, but it might be kind of hilarious to fly a space plane into orbit that looks kinda like a Vought F4U or Sopwith Camel. Do you guys think a tail-dragger would actually be practical in KSP?

Not that I have a problem with the Rafale in particular, I'm just sick of ALL my big space planes looking exactly the damn same. For once, I'd like to put the engines on the WINGS, which are located where wings are USUALLY located on aircraft. Wouldn't that be nice?

ANYWAY, I'm curious what you guys might have thought up. Remember, stock only. I did my time on mods last year, right now, I'm just seeing what I can make wholly with stock.

Edited February 16, 2015 by |Velocity|

[breakthrough]

It turns out I like canards, so all the pictures I have on hand feature them. But the landing gears can be mounted on ventral fins.

As for mounting engines in the wings, most of the mass is in the engines anyway so the CoM should follow them forward substantially allowing you to have the wings more forward as well.

EDIT: After reading your post more carefully, I guess you don't want my solution for aesthetic reasons. Just in case you don't already know, the other stock solution for working around the landing gears is VTOL.

[-Velocity-]

It turns out I like canards, so all the pictures I have on hand feature them. But the landing gears can be mounted on ventral fins.

http://i.imgur.com/jQ93BzR.png

As for mounting engines in the wings, most of the mass is in the engines anyway so the CoM should follow them forward substantially allowing you to have the wings more forward as well.

The problem is that the landing gear are short and must be near the CoG. Moving the CoG to the middle of the plane does not solve anything; it becomes impossible to take off without scraping your tail against the ground due to the short stubby landing gear.

EDIT: After reading your post more carefully, I guess you don't want my solution for aesthetic reasons. Just in case you don't already know, the other stock solution for working around the landing gears is VTOL.

I've built vertically launched air breathing rockets that can land again vertically, but they're not really space planes.

I'm interesting in seeing all other solutions people have come up with. Even if I don't want to USE them, they still might give me ideas. It looks like your space plane is beginning to go down towards the tail-dragger category, though it's still obviously a tricycle.

I think tonight I might try building a space biplane.... the dumber looking, the better.

Edited February 16, 2015 by |Velocity|

[breakthrough]

The problem is that the landing gear are short and must be near the CoG. Moving the CoG to the middle of the plane does not solve anything; it becomes impossible to take off without scraping your tail against the ground due to the short stubby landing gear.

The CoG thing is a common misconception born out of a standard practice rather than a physical necessity that can't be engineered around. I'm a little too sleepy to KSP properly right now, but I'll whip something up next time I have a chance to play that will lift off before the end of the runway with absolute zero possibility of striking its tail and post a pic.

[capi3101]

One thing I've done is to "build" a re-scaled landing gear using the procedure outlined here. The "Large Gear Bay" has come in handy on quite a number of occasions, none of which have involved (so far) Mk3 spaceplane parts since I've yet to unlock them in the R&D.

Really, though, a lot of spaceplane design is just a matter of following formulas and figuring out what you want to do with a given plane. Your aero model has a lot to do with it too - you can get away with crap in the soup that you can't with FAR and NEAR. Take this ugly monstrosity for example...

Flies in stock, delivers a Mun lander to orbit and then brings it back down again. Pretty much as far from a Rafale as you can get...

- - - Updated - - -

I should mention that another thing I've done to help guard against tail strike is to put a "kickstop" wheel in the back and set it on its own action group. This wheel's sole purpose is to hold up the tail until the plane is going fast enough (about 20 m/s or so). You then retract that wheel, and you can take off on the back gears as you would with any other plane. In general that's not an optimal solution, but it does occasionally save a few headaches.

[-Velocity-]

The CoG thing is a common misconception born out of a standard practice rather than a physical necessity that can't be engineered around. I'm a little too sleepy to KSP properly right now, but I'll whip something up next time I have a chance to play that will lift off before the end of the runway with absolute zero possibility of striking its tail and post a pic.

Well, it's based on personal experience for me, I can't get a plane to be able to rotate unless the landing gear is near the CoG. I'd be interested to see what you have.

One thing that I HAVE wondered about doing is forcing rotation with nose-mounted rocket engines. Crude, but it should work and the nose engines would only be on for a very short period, so they shouldn't waste much fuel. But... it's so crude. Just give us bigger landing gear, Squad! It's pretty ridiculous we got such huge space plane parts, but not bigger gear to compensate. We're still stuck using RC plane wheels...

- - - Updated - - -

...

Thanks for the ideas... and that's definitely gotta be the ugliest space plane I've ever seen. I actually intend that as a complement It's a masterpiece demonstration of how bad the stock aerodynamics are. It's like you made an SSTO Wright Flyer.

[Reactordrone]

Landing gear height can be increased by mounting them on small hardpoints and by using inverted gull wings like a stuka or F4U corsair and an extra landing gear can be added at the rear of the plane to act as a tail bumper. With the offset tools they can be positioned to give enough rotation for takeoff while preventing your engine from being ripped off if you flare too aggressively on landing.

Failing that you could always try the B-52 method and just increase the angle of attack of the wing so you fly off with a perfectly level fuselage.

Edited February 16, 2015 by Reactordrone

[tsotha]

Take this ugly monstrosity for example...

That... flies?

[capi3101]

Thanks for the ideas... and that's definitely gotta be the ugliest space plane I've ever seen. I actually intend that as a complement It's a masterpiece demonstration of how bad the stock aerodynamics are. It's like you made an SSTO Wright Flyer.

That's what it reminds me of as well. And you're right - it's only works because of the stock aerodynamic model. I'm interested in seeing if it'd be possible to run the same mission with one of the more advanced aero models.

That... flies?

Flies and flies well. Takes off at 55 m/s. The undercarriage needs to be reinforced; that's its major design flaw.

Wanna give it a spin yourself?

Edited February 17, 2015 by capi3101

[panzer1b]

I never had the issue of my spaceplanes/sstos/whatnot looking like real life jet planes.

Always prefered a more sci-fi look, with most of my SSTOs looking liek stuff outta movies, games, or just impossibilities.

Then again, the reason most viable planes end up looking liek real life jets (at least in FAR/NEAR), is that that design works well, is aerodynamic, and well works (and is that way for a good reason, in modern military everyone builds the best craft perfromance wise they can).

[MarvinKitFox]

All my big space planes always evolve to the same basic design. Why?

Lack of imagination

3) The nose must pitch up during takeoff (duh), bringing the tail closer to the ground (double duh). The fulcrum for this movement is the aft landing gear (triple duh).

Basic fallacy. The nose does not need to pitch up during takeoff, your flight path must simply be more up than down. By *forcing your design to this criteria, you are forcing it into a very limited range of designs.

8) horizontal stabilization is established by placing vertical stabilizers to the aft of the aircraft.

This is the only true statement you make.

Try constructing your plane so that, while resting on its landing gear, the plane is at optimal angle for level flight/very slight climbing.

You do NOT need to rotate to takeoff. This is merely a tool used to shorten the runway length needed, and to reduce noise footprint after the runway.

You want a spaceplane's wing design to be optimal at high speed, high altitude. It should only barely be able to take off with a full load. If you are *capable* of stunt flying at low altitude, then by definition your vehicle is not optimised as a space plane!

[ajburges]

I just place a rear gear bay as a tail strike guard. With the new tweakables I can clip everything but the wheel in the body and remove it from the gear action.

VTOLs and STOLs want wide gear for stability. They compensate with active lift.

OT: is nearly unable to take off really the best route. I find my planes suffer while attempting to build speed with that little lift. Optimal AoA for accent is 25 degrees in stock. As such you want to cruise at 12-16 degrees so you maintain altitude control.

[capi3101]

I mentioned following formulas for the soup - here are the ones I go with:

*10 tonnes takeoff mass per Basic Jet (Basic Jets for airplanes/VTOLs only), 13 tonnes per RAPIER, 15 tonnes per Turbojet.

*.03+ Intake Area per engine (equates to 3 Ram Intakes) regardless of engine type. (If you look at the engine setup on the Bat, that's how I usually build "engine units" - start with the Nacelle).

*1.5 units of SAS per tonne of takeoff mass.

*1 unit of lift coefficient per tonne of takeoff mass (For example, if you have a four tonne craft, you only need a pair of Delta Wings - each has a lift coefficient of 2)

*40 units of Liquid Fuel per tonne of takeoff mass and 25 tonnes of Oxidizer.

*Plan for a payload fraction of 25%; a crappily-designed plane will still usually achieve at least that.

Now, lemme explain that in action. Payload is anything you're hauling up that doesn't help the plane fly itself up into space (like say you want to go interstellar with your craft so you give it a pair of nukes and dedicated fuel supplies; that would count as payload). For the Bat, that would be the 18 tonne lander it hauls up there. So I multiply that mass times 4 and get the estimated mass of my plane - 72 tonnes. I then pick an engine array that is capable of supporting that much mass. For 72 tonnes, that would either be 6 RAPIER engines (72/13 = 5.538) or 5 Turbojet/24-77 clusters (72/15 = 4.8). I went with Turbojets on the Bat because it's a career-built plane and I only have access to the Level 2 R&D, so RAPIERs are still locked. Plus truthfully I think I like the Turbojet/24-77 combos better, especially since I started using Intake Build Aid (that mod saves some serious headaches). With my engine setup selected, I assume the plane will have the maximum mass the engine units can support, and use that to determine how much fuel I'll need. For example, I have 5 turbojets, so I'll assume the plane will be 75 tonnes at takeoff. That means I need 75x40 = 3000 units of Liquid Fuel and 75x25 = 1875 units of Oxidizer (I think you can actually get away with a mere 10-15 units of oxidizer per takeoff mass with a Turbojet setup but I need to do more experimentation with that figure; your oxidizer needs will depend a lot on the speed at which you switch over to rocket mode, and the 25 per tonne figure originates from use of RAPIERs with a switchover Surface speed of roughly 1750 m/s). I then go about selecting a combination of fuel tanks that will give me at least that calculated amount. From there it's a matter of adding the wings, gear, ASAS (for 75 tonnes, you want 112.5 kN of SAS, so 4 Large ASAS Wheels, 8 Stabilizers or 24 Wheels or a combination thereof), command core, and power generation. I set things up so the plane's CoM doesn't shift, the CoT is aligned with the CoM and the CoL is slightly aft but aligned with the CoM. I do use canards; the soup likes canards. Last things I do before launch are to unlock the steering and disable the brakes on the nose gear and to make sure I've got any fuel lines I'm using correctly configured. I set up my action groups generally as 1 = toggle jets, 2 = toggle rockets, 3 = toggle intakes, though nothing says you can't set the jets and intakes onto the same action group.

Building an engine unit cluster is simple - you start with the Nacelle on your craft's centerline, put the Turbojet on the back, then turn on radial symmetry, add 2-4 24-77s (this one I'm fuzzy about; I think you could get away with 2 but I use 4 in case I botch the ascent; by the time of switchover a Turbojet is usually outputting about 60 kN anyway, so 3 is a good balance there), and then remove the Nacelle. Go back to mirror symmetry, put the nacelle along side your fuselage, add a tricoupler, and add a Ram Intake to each. When you need to copy it, hit ALT and click the Nacelle. Works well enough for initial placement purposes anyway; when time comes to re-order your intakes/jets, you can just pick them off one by one and then reset them as needed (to minimize the issue of assymetric thrust when the jets start flame out). Or you could just install Intake Build Aid and hit the magic button prior to takeoff, which will do the same thing for you automatically. Seriously useful.

Anyways, those are the formulas I follow and the process I use when I go about designing a plane. Bear in mind that the formulas work for the soup; I haven't explored FAR enough to know if they all still apply or not, and it's something that I needs to investigate given the changes to the stock aero model with the upcoming 1.0 release of KSP.

Edited February 17, 2015 by capi3101

[FlyingPete]

Just give us bigger landing gear, Squad! It's pretty ridiculous we got such huge space plane parts, but not bigger gear to compensate. We're still stuck using RC plane wheels...

This is why so far I've built absolutely nothing using the Mk3 parts. They're pretty pointless without larger wing parts and landing gear IMO.

[WhiteKnuckle]

-Use the Rotate tool to give your wings a positive AoA when the aircraft is sitting level

-Use higher front landing gear/lower rear landing gear to give the whole aircraft a positive AoA

-Use a tailstrike guard landing gear to prevent engine strikes when pitching up

-Design aircraft with a large tail, use full wings with control surfaces rather than canards. This moves your CoL back allowing you to place your wings farther forward without moving your CoL ahead of your CoM

-Use highly swept back wing designs, the farther back the wing sweeps, the farther back the CoL is while the wing root can be mounted midships

-Elevate the tail using some of the non-symmetrical parts, mount engines farther forward, this lets you pitch up without hitting anything in the back, also moves CoM forward.

That's all I can think of off the top of my head, I'll post a pic of some of my Mk3 spaceplanes when I get home tonight to give you an idea of what's possible.

[breakthrough]

Feels a little a redundant with all these good replies from people, but I did say I would post pics.

The engines are mounted in the wings and CoM and CoL stay aligned both with and without the 4.5t payload

This shot of the undercarriage shows how I normally mount the gears. They are angled so the light is in a better direction and they are clipped upward so as to keep the gear bays from sinking into the terrain if the gears are raised while on the ground. A gear bay that is partly clipped into the ground won't lift the vessel up off the ground when it lowers.

As I said, despite the Com being very far in front of the rear gears, it easily rotates by the middle of the runway.

This vessel has about 600 delta-v left on orbit, enough to circularize at 500km. Probably should have used RCS tanks as the test payload since my delta-v displays insisted on using the fuel in the payload so I don't have more exact numbers.

craft file on MediaFire

[thereaverofdarkness]

Lots of people manage to build planes with the center of mass further forward, but it usually involves putting a lot of empty structural stuff in the back. Hiking it up out of the way of the runway is the easy part. The hard part is that all of the engine weight is focused at the engine nozzles, where in a real plane, the nozzles are the only lightweight part of the engine, and the heavy part runs along the entire length of the plane. That's why real planes can mount wings forward of the back. Also real planes don't take off with red Radio Flyer wagon wheels, and they can spread their gear base apart without slanting the wheels at a strange angle, clipping them inside the fuselage, or mounting them to the wings.

[-Velocity-]

Thanks for the ideas, at least those of you (all except one) who did so in a respectful manner. I didn't manage to get any time to play in the SPH last night, maybe tonight though.

[WhiteKnuckle]

My biggest stock SSTO. Showing several of the design cues I talked about before.

[-Velocity-]

My biggest stock SSTO. Showing several of the design cues I talked about before.

I like it. What's the underside look like?

[eddiew]

This big beast uses stock landing gear, visible in the lower right panel. Only mods are procedural wings to keep the part count down, and flies with FAR. There's tailstrike-guard gear on the back end, so you can't pull up too sharply, but the asymmetric MK3 adapter automatically lifts the tail up so this isn't a major hazard anyway

Annoyingly, I find the stock gear to be less wobbly than B9's much larger 'heavy' gear and often use it in preference!

[Ion Man]

You can launch or land anything with the regular gear. It may not look good or is very aerodynamic, but it works.

Design wise: It's up to your imagination and until 1.0 and the new aerodynamics model is implemented, you can fly a lot of crazy stuff. Most of the time the slick, regular designs work very well.

[KerikBalm]

Its old stock, but:

Also

Nearly stock (SP+ in 0.24, used with NEAR)

Stock, but not stock aero:

I think they all qualify as... not looking like a rafale

[theend3r]

Most of my designs have canards but there are few exceptions such as:

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which surprisingly handles very well and can get to orbit with over 3 km/s dv (if I remember correctly, haven't flown it in a while) without payload, altough an orange tank doesn't make much difference since it's rather heavy (triple B9 wheels bend and dance under it like crazy if you're not careful).

Edited February 19, 2015 by theend3r