tetryds

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@cantab, you may also consider to move main wing area closer to CM, that way with only small force on tail elevators you can have more than enough pitching authority.

Here is some small info that I just added in post where you can find more info about FAR graphs. Might help someone.
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Common question is how to reduce "sawfish effect" of plane, to wobble as less as possible with SAS turned on. There is several mods that attempts to improve this behaviour.
But first step in wobble reduction is in creation of stable craft. When craft start to loose pitching, SAS increase pitching trough control surfaces and engine gimbals. When you set neutral pitching moment in high AoA area (most often mistake), craft will loose lift by large amount. When graph blue line start to drop rapidly, that is AoA when stall starts. Small thin lines tells how craft will behave when fall back to lower AoA until craft is controllable again. Thanks to Tetryds on clarification about stall effect and how it is represented trough FAR graphs.

Craft on picture can have 23 degree of AoA before stall starts, however it is not wise to set neutral pitching moment at AoA just little lower than 23 AoA.
For several reasons. FAR graph shows only pitching momentum from craft hull wings and control surfaces, you need to consider also momentum from engine gimbals and also momentum of inertia from previous craft movement. Those forces could push craft in AoA that is larger than it is shown in graph and that little extra can push craft in stall AoA area.

Also if you choose large AoA where drag is significant, despite high L/D ratio, craft will start to loose speed. With speed loss, craft will also loose lift, this is more important at high speeds and high altitudes where small changes in lift can cause significant height loss where drag is even higher and cause even more drag forces. Or even worse scenario, craft can be disintegrated due to overheating.
This is more important in creating of spaceplanes than it is if you try to build fighter. For fighter planes, rapid loss of speed and high AoA is desirable to achieve high maneuverability, but is not SAS friendly and something you want from spaceplane.

2YvCKN5.jpg

Picture shows only graph for low speed. This craft have similar L/D line for 2/3/4 mach, so those graphs were not shown, but don't foreget to check those too when you build spaceplane.

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Excessive dihedral effect seems plausible. I did have the wingtips angled up a touch, removing that and slightly enlarging the tail significantly helped, but the plane still wanted to bank over once I hit about Mach 1.2 at 13 km, and I'm also getting red L-beta again at say M1.7. It seems troublesome to fix the derivatives and the dynamic simulation, sorting one breaks the other is what I seem to get,

Saying to reduce the wing sweep seems odd, I thought delta wings were good for supersonic aircraft??? Reducing the sweep is something I can try though, though it's one of the fiddlier things to do with stock parts.

As far as the nose goes, sure, I can change it, but is it really likely to help stability much? I just tried a 2.5m adapter and a nosecone A and that made things *worse* in the analysis.

kcs123 pitch authority isn't directly a problem any more. At subsonic speeds the main wing's Col is already near-level with the CoM, both being around the middle of the payload bay. Of course the tail pulls that back, but in flight it will be making less lift than the wings. It *does* seem like pitching up affects the roll stability, and that's something I don't really understand and if it's a real effect doesn't seem to be covered by FAR's roll analysis tools.

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Trough various craft design, I have found that small vertical wingtips on the edge of main wings helps a lot with rolling stability. Add those if you have reached limit with dihedral angle of main wings. Something similar I have done on craft shown in few posts back. That craft, despite it size have really low drag. That was accomplished by respecting smooth cross area change from nose to tail.

In previous iteration of similar craft for KSP 1.0.2. I have found also trough design process that even small change in swept angle, like 2-5 degree can make significant difference with stability. That is more noticable if you try to create craft for 360t of payload only, like I did in past. Unfortunately, it is not so easy to accompish with stock parts. Swept angle on stock wing parts does not often offer swept angle for craft you want to create. That is reason why I love procedural wings so much, makes whole design process much easier - meaning less time is needed to place parts in proper order to create larger surface area.

Anyway, trough test flights, check out visual aerodynamic overlay. I have found that if you form lifting surfaces in a way that overlay arrows crosses in one point in large distantce from craft hull, it helps with roll issues. Not exactly best picture that describe what I want to explain, not even best scientific explanation, but it was practical for game purpose. Worked for me, at least.

57mr3hp.jpg

 

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59 minutes ago, cantab said:

I'm also getting red L-beta again at say M1.7

What? How come you are losing roll stability as your speed increases with highly swept wings, that's weird.
I suggested you to reduce dihedral because sometimes too much stability can cause your system to become unstable, having the derivatives red however means that you don't have enough.
I suspect it's your tail, it looks like you have a built in AoA on them to keep your nose up, that will behave badly when supersonic.

Sincerely, I am not sure if it's worth to fix that design, even if you fix it there is a chance that it will behave badly when carrying heavy payloads.
I recommend you to throw away those wings and try a different approach.
Also, start with decent vertical stabilizers, on the top of the craft, and make it fly well before you add the constraints, it's easier to modify something that works than to fix something that does not.
Edit: specially because you will know what you changed that caused it to fail, and try a different approach.

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Hey guys, what do you think of this design?
Been messing around with it for some time now, and I must say it looks really cool to me. Has some problems with maneuverability but all in all it flies straight, and at supersonic speed it's just mother-stability - no wobbles or oscillations at all. Hard to land though, especially with airbrakes deployed.
mWkCRFt.png

wGdhdSp.png

J0rCXme.png

LGZEDXp.png

Edited by Paul_Sawyer

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@Paul_Sawyer Looks neat, maybe if you angled the inner wings up and the outer wings down you can eliminate that vertical stabilizer and use horizontal yawing.
What do the cross section curves look like?

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Dear Kraken I hate this new editor.

1 hour ago, tetryds said:

I suspect it's your tail, it looks like you have a built in AoA on them to keep your nose up, that will behave badly when supersonic.

It does. This is motivated by the elevator having trouble holding the nose up at supersonic speeds, I thought the built-in AoA would emulate an all-moving tailplane as used on some supersonic aircraft and reduce induced drag. I'm not sure what good alternatives there are? The overall CoL can only go so far forward before there's trouble at subsonic speeds, and pumping fuel seems like it'll be a lot of hassle. Do some wing planforms keep the lift more consistently placed fore-aft than the delta I've currently got?

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@cantab If you want to angle something, angle the main wings or the chines when you have any, but not the horizontal stabilizer.
It's often better than built in AoA on the horizontal stabilizers.
In fact, you may not even need them, because at hypersonic speeds they get shielded and you would need to have massive stabilizers to compensate for that, or put them on a weird position, and these are very silly.

Just move your main wings back a bit and add some chines.
Now is the time to experiment around and see what fits that design better.

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Something that I just uploaded. Having some fun with KAX parts.

And here it is successful Electrical SeaPlane. Created with KAX, B9PW, Tweakscale(for solar panels) and tested with FAR beta release available on GitHub. Created for incoming GAP (Giving Aircraft Purpose) mod. Performed even better than I expected.

 

 

 

 

Edited by kcs123
Added album for another plane.

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Another day, another SR-71-alike plane

(and I finally gave up on Photobucket :rolleyes:)

 

Edited by blowfish

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9 hours ago, blowfish said:

Another day, another SR-71-alike plane

(and I finally gave up on Photobucket :rolleyes:)

 

Looks nice. Is that cockpit from WIP B9 Mk2 parts ?

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5 hours ago, kcs123 said:

Looks nice. Is that cockpit from WIP B9 Mk2 parts ?

Definitely the spaceplane one. wow don't know why I thought that said baha blowfish is right below me :confused: 

Edited by Svm420

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Thanks for the help earlier everyone. I carried on working on my craft and at last got the Space Shuttle Gallifrey into LKO.

23303830964_c6b0b7a167_h.jpgAnother angle by cantab314, on Flickr

The design is still recognisable but I took on the advice. Since the last pics it has larger tailfins inspired by the X-15, a more rearwards tailplane with the angle removed, and the main wings brought forward. It could handle better but it's flyable enough.

On KerbalX if anyone cares, but I do consider this a test article without much useful purpose. That said if you put extra fuel in the payload bay as well as a cargo it might work.

http://kerbalx.com/cantab/Space-Shuttle-Gallifrey

Now to set myself to actually making this into a shuttle. Which will mess up my carefully-placed CoM on the orbiter, fun fun.

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7 hours ago, Wanderfound said:

Just beat me to it... :D

 

Kerbodyne Shuttle

Craft file at https://www.dropbox.com/s/ho9fv7xmqi9g99g/Kerbodyne%20Shuttle.craft?dl=0

I see you compensated for the increased length with canards so that you could get a bigger cargo bay,

 

One thing though which I have always found interesting, I wonder if it's possible to make a space shuttle with a returnable, flyable first stage. It would look like this and launch from an upright position, the lower aircraft would accelerate both craft and detach close to orbit, it would then land somewhere downrange while the shuttle burned to orbit

 

19gh10hkjkc4mjpg.jpg

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It is possible to create, but somehow hard achieve in KSP due to game engine limitations.
Problem is that you need to maintain stable flight with craft used for first stage while you control upper craft trough second stage to orbit.

In other words, you need to put desired craft in orbit before KSP game engine despawn other craft and you are able to switch to it and land safely. It is real pain to do that due to game engine limitation, more than design challenge.

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11 minutes ago, Halsfury said:

One thing though which I have always found interesting, I wonder if it's possible to make a space shuttle with a returnable, flyable first stage. It would look like this and launch from an upright position, the lower aircraft would accelerate both craft and detach close to orbit, it would then land somewhere downrange while the shuttle burned to orbit

 

*picture*

Definitly doable. Only real problem I see is controlling the first stage after seperation, while still ensuring the second stage reaches orbit. Possibly either make both reach orbit, and then return the first stage, or use SRBs for the final burn. Or use stage recovery and loads of chutes...

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I was thinking of having enough fuel on the first stage to enable a skip reentry, basically the first stage would reach a 75 by 27 km orbit, and then separation would occur, the shuttle would circularize, and the booster would fall down into a skip reentry.

I managed to do a Falcon IX style booster landing before, I had to launch at an angle so that I could drop the booster onto the southern continent but that was before we had shuttle SSME's stock, consequently it was pretty easy to get it wrong and slam into the ground too fast.

Maybe VTOL would do the trick, Even with a forward flying craft some rocket assist might increase booster survivability

Edited by Halsfury

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20 hours ago, Halsfury said:

I see you compensated for the increased length with canards so that you could get a bigger cargo bay,

 

One thing though which I have always found interesting, I wonder if it's possible to make a space shuttle with a returnable, flyable first stage. It would look like this and launch from an upright position, the lower aircraft would accelerate both craft and detach close to orbit, it would then land somewhere downrange while the shuttle burned to orbit

 

19gh10hkjkc4mjpg.jpg

 

This design may work better in RO, because of the scale differences.  On stock Kerbin scale it is to easy to achieve orbit.  Something like this while would be a cool project to do but not quite to the scale of the one in the artwork.

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On 12/28/2015 at 5:38 AM, Halsfury said:

I see you compensated for the increased length with canards so that you could get a bigger cargo bay,

A similar size design will work without the canards, but it makes it about as much fun to fly as the real thing (i.e. it flies like a brick, but you can glide it to a high-speed landing if you judge your reentry just right and don't try anything fancy). Adding the canards makes it much more user friendly.

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