New SAS can be wobbly...

[El wonso]

New SAS shakes the hell out of my plane just like old ASAS.

Download link (stock): https://dl.dropboxusercontent.com/u/7213764/KSP/G-killer.craft

[Torham234]

The new sas is MUCH, MUCH improved, but if the craft is just too unstable, it will still start shaking. Try removing the flaps at the ends of your main wing. Also strutting down the wings greatly reduces the wobble and improves stability. Further more, most craft are unstable out of their designed cruise altitude/speed. If those two radial intakes are the only intakes onboard, you will flame out long before your wing surface will loose most of its effectiveness. You can safely reduce the wing area without loosing ceiling altitude.

[bogpad]

The plane might be shaking, but it seems Jeb is more than pleased with it, so why change anything!?

[El wonso]

I designed that plane for sharp turns and high Gs.

[Torham234]

I designed that plane for sharp turns and high Gs.

In that case your wing surface is totally over the top. If you want something that pulls a lot of G's than you need something very nimble with lots of power. Here, I made this one as an example in the past 15 min.

It dances like the Bride from Hell, and is amazingly unstable, but it can turn on a dime, and the twin jet engines give it a nice punch.

[El wonso]

In that case your wing surface is totally over the top. If you want something that pulls a lot of G's than you need something very nimble with lots of power.

Well, my creation is very stable, turns as hell, uses 2 engines and you can reach almost 20G with it.

E: I don't know how well it flies at ~10km, I fly at 3km max.

[Torham234]

I fly at 3km max.

Even more of a reason to cut down the wings. At 3 km the air is so thick that you need only minimal wing surface. By looking only at your wings, I would have guessed it was designed to fly at 20 - 25 km height (apart from insufficient air intakes for that height).

[marach]

Even more of a reason to cut down the wings. At 3 km the air is so thick that you need only minimal wing surface. By looking only at your wings, I would have guessed it was designed to fly at 20 - 25 km height (apart from insufficient air intakes for that height).

if not for the intakes I would have gone even higher you can do decent stability with just the standard deltas upto about 20km with 2 engines pumping it forward

[Xeldrak]

Also, for sharp turns and high Gs, this plane looks just...massive. In these tanks is probably enough fuel to fly around half kerbin. If I were you I would simply go much smaler, less wing surface. The canards are fine...

My try one a (fancy) plane like this:

Note much smaler wing surface, very lightwight, lost of power (2 engines) a many control surfaces. You could add canards, but that would look stupid

Edited July 27, 2013 by Xeldrak

[Torham234]

Nice one Xeldark. It looks more like a flying car than a plane. and I like you sig too

I downloaded your Iguana, if you don't mind.

[CptNuts]

New SAS shakes the hell out of my plane just like old ASAS.

Download link (stock): https://dl.dropboxusercontent.com/u/7213764/KSP/G-killer.craft

*snip*

Reminds me of my last unstable plane, let me reach about 16km before flame out (i will have to add more air intakes somehow^^) and turned on the smallest turnradius i have ever achieved. It was shaking like a mad man^^

[Xeldrak]

Reminds me of my last unstable plane, let me reach about 16km before flame out (i will have to add more air intakes somehow^^) and turned on the smallest turnradius i have ever achieved. It was shaking like a mad man^^

Yeah, it's the same in real life - if you want a very agile plane, its best to go with a unstable design. Look at the X-29, that thing has not only forward swept wings, but also has its center of gravity well aft of the center of lift. VERY agile - but not flyable without a computer to make corrections.

@Torham Well, thanks I'm happy if you download it - that's why I uploaded it

[Xeldrak]

Well, this threat go me thinking....and after looking up the X-29, I found a design that is more agile and more capricious.

[El wonso]

Also, for sharp turns and high Gs, this plane looks just...massive. In these tanks is probably enough fuel to fly around half kerbin. If I were you I would simply go much smaler, less wing surface. The canards are fine...

My try one a (fancy) plane like this:

Note much smaler wing surface, very lightwight, lost of power (2 engines) a many control surfaces. You could add canards, but that would look stupid

Hmm, I tried Iguana and it does not turn as good at low altitudes, download my plane and see what I wanted to build.

E: My plane is only .5t heavier, you have used very heavy structural components.

Edited July 27, 2013 by El wonso

[Xeldrak]

Well, yes, the Iguana was tuned to be more stable and lacks cannards because it had to look good. The plane I posted a picture of 40 minutes ago is more tuned for agility and is more unstable (and harder to fly).

Anyways, I downloaded your G-Killer and contrary to all my expectations, it realy does turn like a madman

This probably has to do with the fact, that you placed the center of wight and center of lift exactly ontop of each other. Well, it seems to me, that if want a plane THAT maneuvrable the SAS will be wobbly because the plane is unstable and the SAS is working hard to keep it straight.

I experimented a bit and if I move the main wing a bit to the back, the plane stops to wobble. But it also becomes more stable and less agile...

[purpletarget]

krl.krl, I've been fiddling with your craft file for a few minutes...I don't know if it'll meet your objectives as designed.

Basically your problem the wobble is because it has way too much control authority with all the control surfaces, so no matter how little SAS touches an adjustment, it overshoots and has to correct the other direction. You can see in the jitter just how little roll the SAS is actually using (1 tickmark).

Now, if you rip out the canards, and all ailerons, and replace the elevators with small control surfaces instead of standard, your plane should calm down when running under SAS. (Though you might need to shift your wings back as well to keep the CoL behind the CoM so it doesn't try stalling out) The trade-off is that it won't be an unstable acroabat doing mid-air gymnastics.

Edited July 27, 2013 by purpletarget

[El wonso]

To be honest I did not started this thread to fix that hmm... 'problem', I just discovered that new sas can be wobbly and wanted to share

[zarakon]

In that case your wing surface is totally over the top. If you want something that pulls a lot of G's than you need something very nimble with lots of power. Here, I made this one as an example in the past 15 min.

It dances like the Bride from Hell, and is amazingly unstable, but it can turn on a dime, and the twin jet engines give it a nice punch.

http://i1289.photobucket.com/albums/b514/yes753cac/screenshot16_zps88af9808.jpg~original

http://i1289.photobucket.com/albums/b514/yes753cac/screenshot17_zps519496f9.jpg~original

http://i1289.photobucket.com/albums/b514/yes753cac/screenshot18_zpsdfca3f65.jpg~original

That's the kind of plane that could fly beautifully with the old avionics package

Flying small planes kind of sucks now, in comparison

[purpletarget]

To be honest I did not started this thread to fix that hmm... 'problem', I just discovered that new sas can be wobbly and wanted to share

Fair enough, but it's also important for people (lurkers reading) to know what design issues can cause things like this wobble, and how they can fix it if they so desire.

[dlmarti]

Just curious, but why do you guys add reaction wheels to planes???

Your in the atmo, you need flaps not reaction wheels.

[Xeldrak]

Well, in my case is a before .21 design, so I had to add a ASAS to keep the plane stable.

It's also for the ladies looks.

Nowadays it wouldn't be necessary....

Edited July 27, 2013 by Xeldrak

[marach]

Just curious, but why do you guys add reaction wheels to planes???

Your in the atmo, you need flaps not reaction wheels.

It's suprisingly possible with just jets to get the your speed and altitude so high that a hiccup puts you up and out of the atmosphere you kinda need them then for reentry