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In my continuing quests to actually build functional aircraft, I've designed this as a lightweight (comparatively) hobby craft:

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It has two main problems:

  • Very hard to control at takeoff - weaves all over the place and 70% of the time a wing crashes into the runway
  • When trying landing approach, it becomes very difficult to keep it running reasonable straight - lots of waving back and forth

How can I reduce these problems? Anything else obviously wrong with the craft?

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It has two main problems:

  • Very hard to control at takeoff - weaves all over the place and 70% of the time a wing crashes into the runway
  • When trying landing approach, it becomes very difficult to keep it running reasonable straight - lots of waving back and forth

How can I reduce these problems? Anything else obviously wrong with the craft?

Your plane is awfully short. That'll make your plane prone to spazzing out, as you've seen. Imagine stretching it in length, and it'll point into the wind like a weather vane, with the stability you're looking for. Moving your front wheels back a bit toward the center of mass will help with the ground handling, but as narrowly-spaced as they are, and with the way KSP deals with wheel colliders not at 90° angles to the ground, it'll always be a bit tricky to handle. My favorite plane right now is a tail-dragger, and even with rudder pedals, it'll still get away from me from time to time.

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@Xgkkp: check out my sig on how to setup your control surfaces after you fix the issues mentioned by Voculus.

It will help preventing waving, but first you need more pitch stability which is what making it longer will fix.

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In my continuing quests to actually build functional aircraft, I've designed this as a lightweight (comparatively) hobby craft:

http://imgur.com/a/Tox3G

It has two main problems:

  • Very hard to control at takeoff - weaves all over the place and 70% of the time a wing crashes into the runway
  • When trying landing approach, it becomes very difficult to keep it running reasonable straight - lots of waving back and forth

How can I reduce these problems? Anything else obviously wrong with the craft?

It'll be much easier for us to help if you give us a craft file. :)

However, just looking at it I would say that the wallowing could be a result of your ailerons being so far above your centre of mass that rolling induces some sideslip. The lack of control is likely to be due to the placement of the control surfaces and the mass. The further your control surfaces are from your centre of mass the more authority they have - yours seem fairly close. Lengthen the plane with a fuselage section and see if it helps. Also, consider where the mass of your aircraft is - the centre of mass does not actually give much indication of where the mass is in the plane, but you can guess by looking at the part weight. The closer to the centre of mass the mass of your aircraft is, the easier it is for your aircraft to turn.

As for take-off, I guarantee it'll either be that the wheels are not properly aligned, or that the craft is too heavy, from the look of your plane I'd guess it was the first.

Edit: Also, is there any particular reason why your ailerons and, I presume, flaps are such a strange shape? I can't imagine they help aerodynamically.

Edited by Littlerift

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It has two main problems:

  • Very hard to control at takeoff - weaves all over the place and 70% of the time a wing crashes into the runway
  • When trying landing approach, it becomes very difficult to keep it running reasonable straight - lots of waving back and forth

I haven't got anything to add that other folks haven't said already. Check the alignment of your gear and lengthen the fuselage (a piece of structural fuselage or two will do just fine there). I might also suggest a bigger tail-fin; the one you've got looks fairly anemic; some additional yaw stability might help alleviate some of your waving control issues. What kind of part is the tail, anyway? Is it an all-moving part? If it isn't, then you should add a rudder; an Elevon 1 cobbled onto the end would probably do the job. If it is, on what setting do you have it set?

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Is that a procedural wing? I had all sorts of weirdness with procedural wings and FAR... regularly told me the CoL was somewhere to the left of centre, and acted like it while in flight.

I think Capi3101 has a good point about tail fin - it's hard to have too much vertical stabilizer, especially at low speeds. Also, may sound silly, but considered a 1.25m reaction wheel? Torque can compensate for quite a lot of control surface problems.

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It'll be much easier for us to help if you give us a craft file. :)

However, just looking at it I would say that the wallowing could be a result of your ailerons being so far above your centre of mass that rolling induces some sideslip. The lack of control is likely to be due to the placement of the control surfaces and the mass. The further your control surfaces are from your centre of mass the more authority they have - yours seem fairly close. Lengthen the plane with a fuselage section and see if it helps. Also, consider where the mass of your aircraft is - the centre of mass does not actually give much indication of where the mass is in the plane, but you can guess by looking at the part weight. The closer to the centre of mass the mass of your aircraft is, the easier it is for your aircraft to turn.

As for take-off, I guarantee it'll either be that the wheels are not properly aligned, or that the craft is too heavy, from the look of your plane I'd guess it was the first.

Edit: Also, is there any particular reason why your ailerons and, I presume, flaps are such a strange shape? I can't imagine they help aerodynamically.

  • Craft file (lengthened slightly) here: https://www.dropbox.com/s/sbtghyco46453ca/HobbyFly%20I.craft. Uses B9 Procedural Parts, Procedural Parts, KAX
  • If having the ailerons up is a problem, how do planes in that configuration manage? e.g. Cessnas seem to have about the same offset (or is it all mass distribution?)
  • I don't know about not aligned, but the wheels were slightly off of directly vertical - but were aligned with the runway. It's tilted wheels it doesn't like?
  • Correct: The inner surfaces on the wing are flaps.
  • Strage shape: No reason, just that's how they were when I finished, I think I had the wing more angled at some point. I should try changing them, but I can't imagine the effect is that big?

I haven't got anything to add that other folks haven't said already. Check the alignment of your gear and lengthen the fuselage (a piece of structural fuselage or two will do just fine there). I might also suggest a bigger tail-fin; the one you've got looks fairly anemic; some additional yaw stability might help alleviate some of your waving control issues. What kind of part is the tail, anyway? Is it an all-moving part? If it isn't, then you should add a rudder; an Elevon 1 cobbled onto the end would probably do the job. If it is, on what setting do you have it set?

The tail is an AV-R8 winglet. I suppose I could make it a tail piece, but it doesn't seem that far off in area. It's a full moving surface, at least. It's set on Deflection 15, 100% pitch yaw roll, so, I think the default settings.

Is that a procedural wing? I had all sorts of weirdness with procedural wings and FAR... regularly told me the CoL was somewhere to the left of centre, and acted like it while in flight.

I think Capi3101 has a good point about tail fin - it's hard to have too much vertical stabilizer, especially at low speeds. Also, may sound silly, but considered a 1.25m reaction wheel? Torque can compensate for quite a lot of control surface problems.

It is a procedural wing - I haven't noticed anything really odd, and it both looks much better and seems a lot stronger than the flimsy cobbling together of smaller parts and struts :). As for the reaction wheel, I could, but It kinda feels like cheating for aircraft - like a magic "Stabilize this!" button. I don't know if I'm the only one turning off cabin torque....

As a minor aside, I just my most Kerbal landing ever whilst trying out designs of this aircraft:

fu0S3cn.png?1

(hit the beach in front of the KSC landing pad, this is how I came to a rolling halt).

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Is that a procedural wing? I had all sorts of weirdness with procedural wings and FAR... regularly told me the CoL was somewhere to the left of centre, and acted like it while in flight.

I think Capi3101 has a good point about tail fin - it's hard to have too much vertical stabilizer, especially at low speeds. Also, may sound silly, but considered a 1.25m reaction wheel? Torque can compensate for quite a lot of control surface problems.

Last time I had an issue with that was when I tried to build an asymmetric plane (BV 141) (without procedural wings). Bug got fixed though.

You sure you have the latest B9PW and FAR versions?

EDIT:

If having the ailerons up is a problem, how do planes in that configuration manage? e.g. Cessnas seem to have about the same offset (or is it all mass distribution?)

Using ailerons adds some yawing movement anyway (in opposite roll direction). Not sure if ailerons above CoM will make that worse, or counter it, but you usually add some rudder in the direction you want to roll anyway.

If you want to avoid that, you either need to set the rudder to negative roll deflection (or mount below CoM and positive roll direction), or put the ailerons on some dihedral part of the wing.

EDIT2:

Uploaded another replica. The Heluan HA-300, designed by Messerschmitt. Managed to participate in the 5th Generation Fighter Challenge with it.

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Craft file on KerbalX

Edited by FourGreenFields

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My first planes with FAR, AJE and Realism Overhaul (no reaction wheels in cockpits, kerosene instead of liquid fuel):

No names yet:

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Powerplant: General Electric J79 (75kN thrust with afterburner)

Dry mass: 5100kg

Wet mass: 12000kg

Max Takeoff weight: 17000kg (with droptanks)

Takeoff speed: 360km/h - 100m/s

Service Ceiling: 20000m

Range: ~ 6000-7000km without afterburner, ~8000km with drop tanks

Max speed: >Mach 2.5 - 2700km/h - 750m/s Engine will explode at Mach 2.8 (image 16)

Max speed at sea level: Mach 1.21 - 1520km/h - 422m/s (image 15)

***

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Powerplant: 2x General Electric J85 without afterburner (13kN thrust each)

Dry mass: 2300kg

Wet mass: 4500kg

Max Takeoff weight: ?

Takeoff speed : 280km/h - 78m/s

Service Ceiling: 11000m

Range: ?

Max speed: 800km/h - 222m/s

Max speed at sea level: ?

***

Mods:

AJE

RO

Cockpits: Fantom Works, SXT

Procedural Parts

Procedural Wings

Adjustable Landing Gear

Ven Stock Revamp

Graphics: RVE for RSS

Thanks,

The pitch does indeed come exclusively from the tailplanes. The high-alpha assistance is done with the leading edge slat-thingies. The setting on them is maximum control deflection and -100 AoA. I since modified the plane to be both more aerodynamic and maneuverable, the result can be seen here:

http://imgur.com/a/1QnJS

The new canards have the exact same setting as the slat things, with the addition of some roll control.

I also made a dedicated thread for my jets here so that if I make more of them I don't flood this thread: http://forum.kerbalspaceprogram.com/threads/130659-The-Flightless-Birds-a-series-of-FAR-fighter-jets

Awesome! I really love designs with procedural tanks instead of stock ones.

Edited by winged

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Yt5VySd.png

Why is wave drag graph tilted like this when I attach BD Armoury missile and rails to things?

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Is there any way to make a flying wing more stable without adding additional vertical surfaces to stabilize it? Seems like flying wings like to slip left and right some. I know about making it more dihedral, but maybe some other way to do that as it seems not enough?

Are there any documents regarding the stability issues on flying wings like Horten? It seems like the engine housings on XB-35 were enough to stabilize it and there were vertical surfaces on YB-49 dedicated to do exactly that, but I could not find anything about Horten 229's system of stabilization. Perhaps the side slip (+asymmetrical thrust from the failed engine) killed the test pilot of 229, or were the flaps designed in such way to prevent it at low speeds?

I'm asking about Horten specifically as it seems to have no apparent stabilizers at all. Will experiment with dihedral some more, but would also like to know what you guys think.

EDIT: I also know about B-2's, which uses the engine thrust and nozzles (read somewhere on the forums, not sure where) to direct and cancel out the slip, but I'm using propellers, so that's not possible.

Edited by Veeltch

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Most flying wing designs use differential airbrakes on the wings for yaw stabilization. That's supported with FAR control surfaces now.

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Most flying wing designs use differential airbrakes on the wings for yaw stabilization. That's supported with FAR control surfaces now.

You mean the brake rudders? I use those, but it's really hard to use them during the landing with keyboard. Eh, maybe I should try flying it with joystick. Is it the trick to flying wings, though? Just applying the rudders when slipping should be enough?

The engine placement and angle, along with the wing twist and tail probably helped.

http://greyfalcon.us/pictures/go_229_01.jpg

Ooooh, the wing twist! Didin't think of that!

Edit: Also about the engine angle: I do that too, but might think about increasing it a few more degrees.

Edited by Veeltch

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Loosely based on Rune's Longsword orange tank lifter: as soon as I can figure how to keep the large landing gear from falling off the bottom on the runway, this thing will even be able to land, at which point I'll attach the craft file.

It works well with FAR, and is decently stable, save for a bit of Dutch roll and sideslipping as it gets higher in the atmosphere, which is tolerable as long as you use the flight aids. I haven't tried it out in stock, but expect it'll handle similarly (although stock doesn't include FAR's intake ducting). Because it has a low-ish TWR (~.5 on take-off), it won't break the sound barrier in level flight. I could probably tweak the elevons to give it more control authority, but since it makes orbit decently well...

It has 750 monoprop and eight block thrusters for rendezvous and keeping the nose up on re-entry, as well as an RGU tucked in front of the monoprop tank.

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Edited by Little Green Mensch
getting image titles and descriptions to show up

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You mean the brake rudders? I use those, but it's really hard to use them during the landing with keyboard. Eh, maybe I should try flying it with joystick. Is it the trick to flying wings, though? Just applying the rudders when slipping should be enough?

Ooooh, the wing twist! Didin't think of that!

Edit: Also about the engine angle: I do that too, but might think about increasing it a few more degrees.

Brake rudders work just like a normal rudder in practice. I messed around with a little craft for a bit, you *need* a little dihedral - my test craft went from terminal sideslipping to fully usable with just a couple of degrees.

21633906472_865491df75_c.jpg

Pressure-forward on that and still directionally fairly stable, haven't tried it supersonic yet though.

Edit: seems ok at lower levels supersonic - I'm not sure yaw spoilers are a good idea for a large spaceplane though, you really don't want to be using spoilers for anything on the way up.

Edit2: here's a bigger one. Need fairly large yaw spoilers and also some sort of PID yaw controller.

21458584218_d38fdbf467_c.jpg

Disabled the cockpit reaction wheel and the engine gimballing, it's pretty stable at low levels - higher levels I need to do some pid tuning to manage.

Edited by Van Disaster

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EDIT2:

Uploaded another replica. The Heluan HA-300, designed by Messerschmitt. Managed to participate in the 5th Generation Fighter Challenge with it.

http://imgur.com/a/bOqZN

Craft file on KerbalX

Area rule is strong in this one.... I was wondering how to reduce wave drag without rescaling parts/using procedural parts

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Area rule is strong in this one.... I was wondering how to reduce wave drag without rescaling parts/using procedural parts

Judicious use of clipping is usually enough.

21085274203_0be787d6be_z.jpg

21680207686_edabbecc79_z.jpg

Landing gear are quite handy to smooth transitions.

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Judicious use of clipping is usually enough.

Landing gear are quite handy to smooth transitions.

You'll want to make sure there aren't too many bumps though, or you'll ruin hypersonic aerodynamics. Main reason the P 12 Flying Pencil "only" reaches Mach 2.08 on two basic jets, while the P 18 Firecrown reaches Mach 2.14 on one basic jet.

If possible, try to have a smooth shape that is area ruled. Using landing gears may not be allways be the best thing to do here. It's easier said then done ofcourse, especially without rescaling parts and procedural parts.

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