tetryds

Official FAR Craft Repository

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Lifting bodies are fine until you want to land them, KSP parts are a bit too dense to make that work...

Re-entry needs a couple of things:

* rear-biased areas of pressure - this is one reason to use airbrakes at the rear, but not necessary

* Lots of pitch control. Yaw control is also important but I find I'll usually tumble rather than sideslip

* gentle piloting! allow a good 1/4-1/3d of an orbit to re-enter, leave the craft pitched up a couple of degrees and just let it slow down. Especially don't do anything violent when you're in the worst area of heat, because that's also high dynamic pressure.

The first two are somewhat interlinked - it gets worse as your craft gets longer because body lift tends to be a positive feedback loop, start pitching down and you'll get negative body lift in front of CoM, which leads to more pitch down if it's not corrected. You can design that out by having CoM fairly forwards - so you get more body lift behind it - and a rear mounted tail but those are not always compatible with spaceplane designs. Generally you want both full & empty CoM in the middle of your payload bay, and having canards means every surface is contributing positive lift.

Mach angle for Mach 6 - you go faster than that but pressure is so low it doesn't matter - is a bit under 10 degrees, try and keep all parts of the craft inside a 20 degree cone off the nose. Not sure what FAR does with aero stress with things that stick out of the shock cone but it's not good for drag either way. You get more drag at the wingtips than the root, so delta wings are also a good shape.

Does anyone know the mach 1 wave-drag area of some real jets? I want something to compare my designs to.

Can't seem to find numbers on that anywhere - you could probably get an estimate from running the numbers on some blueprints! easy stuff *cough*

I was going to say "KSP craft are pretty small" but this thing appears to have the same span as an EE Lightning. Looks a bit shorter than one though.

21452641784_d4c4cb6981_z.jpg

Edit: wait, maths fail. About 2/3ds of a Lightning, so I suspect the cross section is probably similar.

Edited by Van Disaster

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Can't seem to find numbers on that anywhere - you could probably get an estimate from running the numbers on some blueprints! easy stuff *cough*

I was going to say "KSP craft are pretty small" but this thing appears to have the same span as an EE Lightning. Looks a bit shorter than one though.

https://farm6.staticflickr.com/5724/21452641784_d4c4cb6981_z.jpg

Edit: wait, maths fail. About 2/3ds of a Lightning, so I suspect the cross section is probably similar.

The shape is a massive factor, look at this large fighter's wave drag.

GW1R7B4.jpg

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Yep, long, slim, wide bits are a long way from the nose. Try it with double or triple the voxel resolution though.

Also less cross section than my little thing, somehow...

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Yep, long, slim, wide bits are a long way from the nose. Try it with double or triple the voxel resolution though.

Also less cross section than my little thing, somehow...

Tripled the voxel resolution, adjusted some parts for the new setting. If I had some time I could probably get it down even lower. The setting's fully strict, 3x the regular resolution. Wave drag IS mostly dependent on the shape, not the size of a plane, at least with relatively small ones. I'm using tons of mods with which I can fine-tune my jets.

c17SEwe.jpg

Edited by Shazbot

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I meant the max cross-section is slimmer than my rather smaller craft - although that one is using fat stock wings ( stock everything, given what it was built for ) & has missiles sticking out which won't help too much. Still, a little odd.

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I meant the max cross-section is slimmer than my rather smaller craft - although that one is using fat stock wings ( stock everything, given what it was built for ) & has missiles sticking out which won't help too much. Still, a little odd.

I think the intakes and fuselage shape are a big deal here - much of the Cassowary's wide fuselage is covered by those two massive intakes, whereas the Midge F4B's fuselage flares out at the tail, which probably contributes a lot. Combined with the missiles, the gear bays on the wings and the general nature of stock parts, I think that amounts to a lot of cross-section area.

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So I was just playing around in the SPH, basically attaching parts pretty much randomly, but then the FAR analysis told me the thing was actually pretty stable, so I thought I'd turn it into a proper craft. Only trouble is, I can't get it off the runway because it always veers off horribly to the right.

The centre of mass, dry centre of mass, centre of lift and centre of thrust are all perfectly lined up. Iirc every single part is attached via symmetry, except for the front landing gear and the fuselage along the central axis. The landing gear are medium adjustable landing gear from the adjustable landing gear, and according to the alignment guides should be perfectly aligned with the ground.

And it's not the engines being misaligned, because it happens even when it's just using the motors for the wheels...I'm completely at a loss as to what's causing it to keep veering.

http://imgur.com/gallery/LsrS6/new

- - - Updated - - -

And before anyone asks, it's already strutted to hell and back, but with the B9 invisible struts.

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So I was just playing around in the SPH, basically attaching parts pretty much randomly, but then the FAR analysis told me the thing was actually pretty stable, so I thought I'd turn it into a proper craft. Only trouble is, I can't get it off the runway because it always veers off horribly to the right.

The centre of mass, dry centre of mass, centre of lift and centre of thrust are all perfectly lined up. Iirc every single part is attached via symmetry, except for the front landing gear and the fuselage along the central axis. The landing gear are medium adjustable landing gear from the adjustable landing gear, and according to the alignment guides should be perfectly aligned with the ground.

And it's not the engines being misaligned, because it happens even when it's just using the motors for the wheels...I'm completely at a loss as to what's causing it to keep veering.

http://imgur.com/gallery/LsrS6/new

- - - Updated - - -

And before anyone asks, it's already strutted to hell and back, but with the B9 invisible struts.

This could be a problem with the collision boxes of some mod part you are using.

You will not have a very good time if you add AoA to your wings and then tilt them backwards, there will be an inwards resultant force that can mess things up when wing flexing is taken into account.

Also, why does your center of lift has the arrow things on it? it should not (but this may be the editor mod you are using).

But if I had to bet, I would say the landing gears.

Try increasing their stiffness, and pitch up as soon as possible.

If nothing solves your problem, please provide a list of the mods you are using, and make sure to remove KIS.

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Anyone interested in a F-22 like fighter?

Well here is one: http://kerbalx.com/RevanCorana/FAR---F-22-raptor-Joystick

Not 100% accurate (~30% smaller and lighter) but without tweakscale it's pretty much impossible.

Still very fun to fly with a joystick/controller, it can get over 2100 kN of lift (maybe more)

1iulRxf.jpg

Edited by RevanCorana

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Also, how to reenter with a plane meant for subsonic surveying flights on laythe?

Get a booster and slow it down propulsively?

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Get a booster and slow it down propulsively?

Is it not possible just to re-enter still? pitch the thing up & keep dynamic pressure low until it's slow enough that it just sinks down. I'd be a bit worried about retroboosting, either you do it in orbit & fall into the atmosphere like a rock, or you do it in the atmosphere which sounds like a bit of a wild ride :P

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Sooo... does anyone have any suggestions for how to build for reentry? It seems I can make perfectly functional SSTOs but I can't bring them down. General pointers would be helpful.

Also, how to reenter with a plane meant for subsonic surveying flights on laythe?

Also, I'm playing with lifting body aeroshells out of Mk3 hulls but that's not panning out. In that they're violently unstable and don't actually produce any lift. Help here would be appreciated too.

The best option, in my opinion, is to prepare a re-entry package, with the plane as a payload.

Lots of AIRBRAKES, a drogue chute in the back, a detachable heatshield in front if you want a very high speed re-entry.

Deploy the airbrakes while in space, and deploy the chutes as early as possible. Once you slow down to manageable speeds, cut the chute, decouple the heatshield and nose up from the dive.

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Is it not possible just to re-enter still? pitch the thing up & keep dynamic pressure low until it's slow enough that it just sinks down. I'd be a bit worried about retroboosting, either you do it in orbit & fall into the atmosphere like a rock, or you do it in the atmosphere which sounds like a bit of a wild ride :P

Sounds like a plan! I may have to go back to Eve with that retroboosting idea. Place a solid rocket booster on the craft so it can counter burn and fall from orbit.

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Interesting. I also have Maritime Pack installed, and, unfortunately, the Buoyancy Blisters are not very low drag (even though they are designed to be). Thoughts on why that could be?

As for floating high in the water - there's not too many parts that are highly buoyant but low in drag, it seems. I've tried numerous different parts, and, for buoyancy, it seems that intakes are some of the best ones. What parts are you using?

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Hmm I am still not managing to get my "return glider" to be stable. Each time around an alt. of 20km it has a very slight yaw, which then can't be corrected and the craft start spinning until the speed has reduced, ending in a nose-down stall which I can't recover from in the last 5km or something.

The craft is "stable" if I don't do a re-entry. It's just the sudden yawing moment that is created at the lower atmosphere.

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Area of high drag at the nose? it'd help to have a picture. You might be able to just fly around the problem by taking a gentler trajectory on re-entry & keeping dynamic pressure down. The other answer to out of control yaw is "more yaw authority" obviously.

@Wolfman29: I don't suppose you've tried procedural parts & made floats out of structural tubes & nosecones? might be a bit dense, I don't know. Procedural floats sounds like a suitable cfg mod ( just make them less dense & consequently structurally weaker ).

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20 km is fairly high, some aircraft might feel "floaty" on the controls there. During re-entry I find I want plenty of RCS or reaction wheel control authority, because the aerodynamic forces are strong enough to be noticeable but not strong enough for control surfaces to work well.

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20km on re-entry is usually pretty violent though, especially if you take a fairly steep trajectory; one reason I like taking 1/3d an orbit to come down is I can bleed a lot of speed off before Q builds up and the craft gets a bit wild. On the other hand I usually use heavy craft which take forever to slow down...

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Well this is how it looks:

hmVc3Xu.png

The center of gravity is slightly in front of the neutral point. (At the last stage). The goal is to do rescue missions up to an altitude of 120ish km

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If you have yaw instability you might just need a larger vertical stabilizer. At high mach / low Q you tend to need a lot of yaw stabilization.

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For that one you might try a fixed ventral fin as well as your moving rudder piece. I would think that span & that height rudder is going to give a nice amount of roll couple...

What engines do you have available? you can make a functional HOTOL spaceplane with the bigger jet & a pair of 48-7s.

Edited by Van Disaster

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