How make my rocket more stable ?

[Pawelk198604]

I used the same design i used for my manned mission, but now i i need to send probe to equatorial orbit, but the basic probe is crap and i did not have anything better, i just spend my 45 science on adv rocketry to unlock better engines.

[video=youtube;TeTAamGLdk0]https://www.youtube.com/watch?v=TeTAamGLdk0[/video] Edited November 24, 2015 by Pawelk198604

[HoloYolo]

Try using wings in between the radial rockets, and replace the first stage engine on the bottom with its gimbiling cousin.

[Guest]

Well, you have a Stayputnik probe core on the top of that thing, that can´t use SAS. So you should upgrade your probecore so it is able to stabilize your flight. Next you could use some fins to have more control authority in the lower atmosphere, and if it doesn´t help - MOAR SAS!

[AeroGav]

Doesn't look like you initiated that tumble, seems the rocket is unstable. The C7 Aerospace Tail Fin is something i aim for even in a rocket centric game, four of those suckers at the base gives you a whole lot of stability and control up to about 60km.

As for tumbling, you have 2 problems

1. rocket engines drain from the highest up tank first. This means your center of gravity moves aft , and aft CG = instability. You either need a mod like Tac Fuel balancer or limit yourself to no more than 1200 fuel in a vertical column, eg. 3 x 400 fuel tanks on a size 1 rocket.

If that's not enough fuel (it probably won't be) put two more columns either side as boosters, punch them off with radial decouplers when you get up a bit.

2. draggy nose. Fairing maybe? Or use that hexagonal probe core thing and put it in a service bay, with nose cone on the front.

Edit - A lot of people have trouble with spaceplanes, but i've been flying flight sims on home computers since the 1980s and my aircraft have always flown safely and often reach orbit.

My rockets however, made yours look like Cupid's arrow. I'm on my third career game and am finally forcing myself to build rockets. The other two were done solely with aircraft. Edited November 22, 2015 by AeroGav

[GoSlash27]

Pawelk,
You have too much thrust and no tailfins.
You'd be better- off to remove the Thuds and replace them with fins.
If you do it right, you won't need to touch the controls at all through the launch phase.
For the upper stage, the solution is actually in the lower stage: Moar DV. If you are over 30 km when the first stage burns out, there's not enough air pressure left to flip the upper stage on decoupling.
*edit*
Try this one: I made it with all parts I see you using or assume you already have.
[img]http://i52.photobucket.com/albums/g13/GoSlash27/Pawelk1_zpsexr9yze6.jpg[/img]
[URL]http://wikisend.com/download/374320/Pawelk1.craft[/URL]
Best,
-Slashy Edited November 22, 2015 by GoSlash27

[Sanic]

The new 1.0 aero model makes fins a must have.

[Harry Rhodan]

[quote name='Pawelk198604']i just spend my 45 science on adv rocketry to unlock better engines.[/QUOTE]

New parts aren't automatically better that old parts. You replaced the things that keep you stable with things that just push more. How should that work? You have to realy think about what those parts are doing before you remove or add them.

The part you should actually be looking at is the Terrier engine that you should put on your upper stage, because that one is much more efficient in the upper atmosphere and in space. Just don't put it on your first stage because it will produce next to no thrust at sea level.

[GDJ]

I would build your first initial rockets just like a model rocket, with fins (3 is the bare minimum for stability, 4 is better but more drag, 5 is my personal limit based on real life experience with model rockets)

Fins are a cheap effective way to gain stability on a booster stage at lower altitudes.

[Pawelk198604]

[quote name='Kaboom!']Try using wings in between the radial rockets, and replace the first stage engine on the bottom with its gimbiling cousin.[/QUOTE]

Still had a problem :(
[video=youtube;I4j-9ueYfi0]https://www.youtube.com/watch?v=I4j-9ueYfi0[/video]

[GoSlash27]

[quote name='Pawelk198604']Still had a problem :(
[URL]https://www.youtube.com/watch?v=I4j-9ueYfi0[/URL][/QUOTE]

Pawelk,
That still has too much thrust, not enough fuel, and you're over-controlling it.
Keep your t/w on launch at 1.5 or less. Fly it with fine control (caps lock) and you're definitely going to need more DV in the first stage (about 1800 m/sec) so the second stage won't flip. As it sits, it wouldn't make orbit even if it did fly straight.

Best,
-Slashy

[Pawelk198604]

i need reach this orbit
[video=youtube;-bs40gS6zME]https://www.youtube.com/watch?v=-bs40gS6zME[/video]
I wonder how much DeltaV i need to go there. Edited November 22, 2015 by Pawelk198604

[AeroGav]

Your rocket flies much better in the second video, the first stage is now perfectly controllable.

Unfortunately the second stage is aerodynamically unstable. It has centre of gravity towards rear, a lot of drag at the front, and is without fins.
The trouble is , if you add fins, you will just mess up the centre of lift on the first stage.

So , you need to be at higher altitude when going to second stage, where the air is so thin aerodynamic problems won't matter, and the thrust vectoring from your engine can overcome bad aerodynamics.

This might be tough to do with a single stack of mark 1 engines and fuel tanks, either your first stage will become too tall, and suffer from centre of gravity shifting to the rear as the fuel burns, or the whole rocket will become too tall and wobbly.

That is why i suggest putting another column of engines and fuel tanks on the left and right side of the main stack, to give the first stage more power without making everything too tall.

ALSO - If you want to keep your Thuds, put them on radial decouplers like I did.

They are good for getting you up to 240 m/sec as fast as possible, to minimise gravity losses.

After that, you will throttle back anyway, to keep below mach 1 below 10km (wastes fuel fighting drag).

So the Thuds are just extra weight and aero drag you are carrying upwards at this point. Punch them off as soon as you hit 240.

Once the cool factor wore off, I stopped using Thuds. Now I use a cluster of 9 Flea engines to boost me to 240 m/sec super fast. You can punch them all off with one stack separator :-)

The Thuds have better ISP than Fleas and make for a lighter rocket, but fleas are much cheaper. Edited November 22, 2015 by AeroGav

[Pawelk198604]

i redesigned my rocket shortened 2nd stage and switched to tearier engine, and enlarged the 1st stage, but now rocket flip, here is my video i tuned on the aerodynamic force overview, maybe you tell me what i made wrong this time.
[video=youtube;MC8ADHJKPcE]https://www.youtube.com/watch?v=MC8ADHJKPcE[/video]
I think i try other contract to make the science and money i need

[*Aqua*]

[quote name='Pawelk198604']I wonder how much DeltaV i need to go there.[/QUOTE]
You'll need about 3500 m/s for reaching a low orbit.
From there to the geostationary orbit (AP and PE at 2.8 Mm) you'll additionally need about 1200 m/s.
But you need some more to raise the AP to 4.8 Mm... I guess about 600 m/s.

3500 + 1200 + 600 = 5300 m/s

This is just a guess. The exact amount depends on your skills.


Your rocket flipped because you pointed to far away from your prograde marker. In lower atmosphere this is deadly. Edited November 22, 2015 by *Aqua*

[Pawelk198604]

[quote name='*Aqua*']You'll need about 3500 m/s for reaching a low orbit.
From there to the geostationary orbit (AP and PE at 2.8 Mm) you'll additionally need about 1200 m/s.
But you need some more to raise the AP to 4.8 Mm... I guess about 600 m/s.

3500 + 1200 + 600 = 5300 m/s

This is just a guess. The exact amount depends on your skills.


Your rocket flipped because you pointed to far away from your prograde marker. In lower atmosphere this is deadly.[/QUOTE]

But it was very small deviation, beside i need to make gravity turn.
Does my rocket have any chance reach desired orbit?

In old KSP (alpha and beta version) it was so easy :(

[GoSlash27]

[quote name='Pawelk198604']But it was very small deviation, beside i need to make gravity turn.
Does my rocket have any chance reach desired orbit?

In old KSP (alpha and beta version) it was so easy :([/QUOTE]

Pawelk,
No, I don't think that rocket has the DV to reach geostationary orbit.
It should be able to make low Kerbin orbit if you fly it gently, though. I still think you should ditch the Thuds.

If I were to build a low tech 2 stager to geosynchronous orbit, it would look like this:

First stage:
LV-T45 with 7 FL-T200 tanks
Second stage:
Terrier with 3 FL-T200 tanks

*edit* After looking at your contract spec, the DV for a GSO launch should be close enough, but 1 small thing: [U][B]The inclination is 180°! [/B][/U]That means you have to launch West, not East. That will cost you another 350 m/sec because you're fighting Kerbin's rotation instead of using it.
Best,
-Slashy Edited November 22, 2015 by GoSlash27

[Harry Rhodan]

[quote name='GoSlash27']I still think you should ditch the Thuds.[/QUOTE]

Really Pawel, ask yourself why you want to use them.

If the answer is "because they are new" - ditch 'em.
If the answer is "because they look cool" - they really do, but ditch 'em.
If the answer is "my TWR is 1 or lower" - ditch 'em and use a pair of tweaked down solids to help your first stage.

Look back at the lessons you learned when you tried to launch Bob and Bill. Those were valuable lessons and they aren't devaluated by any new parts you are unlocking. New parts are mostly just bigger or more efficient or specialized like the Thuds. You can do this.


Edit: And you need some solar panels to fulfill the contract and to be able to move your satellite longer than a few minutes. Edited November 22, 2015 by Harry Rhodan

[Pawelk198604]

[quote name='GoSlash27']Pawelk,
No, I don't think that rocket has the DV to reach geostationary orbit.
It should be able to make low Kerbin orbit if you fly it gently, though. I still think you should ditch the Thuds.

If I were to build a low tech 2 stager to geosynchronous orbit, it would look like this:

First stage:
LV-T45 with 7 FL-T200 tanks
Second stage:
Terrier with 3 FL-T200 tanks

*edit* After looking at your contract spec, the DV for a GSO launch should be close enough, but 1 small thing: [U][B]The inclination is 180°! [/B][/U]That means you have to launch West, not East. That will cost you another 350 m/sec because you're fighting Kerbin's rotation instead of using it.
Best,
-Slashy[/QUOTE]

I tried to do as you told, but the 2 nd stage is unstable now see...
[video=youtube;y2b9lI7XhBQ]https://www.youtube.com/watch?v=y2b9lI7XhBQ[/video]

[quote name='Harry Rhodan']Really Pawel, ask yourself why you want to use them.

If the answer is "because they are new" - ditch 'em.
If the answer is "because they look cool" - they really do, but ditch 'em.
If the answer is "my TWR is 1 or lower" - ditch 'em and use a pair of tweaked down solids to help your first stage.

Look back at the lessons you learned when you tried to launch Bob and Bill. Those were valuable lessons and they aren't devaluated by any new parts you are unlocking. New parts are mostly just bigger or more efficient or specialized like the Thuds. You can do this.


Edit: And you need some solar panels to fulfill the contract and to be able to move your satellite longer than a few minutes.[/QUOTE]

Thanks for both of you, i think i let slide on satellite contract until unlock other parts, and try to gain science other way.

[GoSlash27]

[quote name='Pawelk198604']I tried to do as you told, but the 2 nd stage is unstable now see...
[URL]https://www.youtube.com/watch?v=y2b9lI7XhBQ[/URL]



Thanks for both of you, i think i let slide on satellite contract until unlock other parts, and try to gain science other way.[/QUOTE]

Pawelk,
You should have better luck with the second stage if you fly the first stage more steeply. If you're above 30km it won't spin on you. You tried to stage at 20 km and that's too low.
Good luck!
-Slashy

[Pawelk198604]

I managed to put satellite with decent amount of fuel, but i have almost no control over it it seems that i can control only when i using engine,

[Ulfstein]

Put fins on the second stage as well will help with the fliping

[Razgriz1]

Do you have fairings unlocked? Because a fairing around that probe core would help you out tremendously.

[GoSlash27]

[quote name='Pawelk198604']I managed to put satellite with decent amount of fuel, but i have almost no control over it it seems that i can control only when i using engine,[/QUOTE]

Pawelk,
Yeah, I'm not surprised. You don't have any reaction wheels or RCS to play with, so engine gimbaling is your only means of control. You need to unlock a reaction wheel to control your ship in orbit. You will also need batteries to keep it powered.
On the bright side, you've made a lot of progress today! You're not flipping during launch anymore.

Best,
-Slashy Edited November 23, 2015 by GoSlash27

[Pawelk198604]

[quote name='GoSlash27']Pawelk,
Yeah, I'm not surprised. You don't have any reaction wheels or RCS to play with, so engine gimbaling is your only means of control. You need to unlock a reaction wheel to control your ship in orbit. You will also need batteries to keep it powered.
On the bright side, you've made a lot of progress today! You're not flipping during launch anymore.

Best,
-Slashy[/QUOTE]

Thanks!
I think i made wrong in spending my tech, i should spend it on flight control instead adv rocketery

[*Aqua*]

A summary of already given tips and new ones:

[B]Beating the lower atmosphere[/B]
- Below 30 km the atmosphere is thick enough that it can flip your rocket if you deviate too far from your prograde marker. Be gentle when maneuvering! This includes thrust control. If you throttle down too much your engines might not be able to keep your rocket on course.
- Build an aerodynamic rocket! That means: Center of lift* should be far down, center of mass should be above the CoL sphere during all times (empty tanks in the VAB to see how the CoL will change). This is not mandatory but it helps a lot! The further away the CoL is behind the CoM the more stable the rocket will be and the less likely it flips. But that also means than it will react less on your steering inputs. An easy way to archieve this is to attach wings or winglets at the bottom.
- You want to get out of the lower atmosphere as smooth and efficient as possible. That means the first stage should be large enough to push you at least 30 km high. To be more efficient you should have a TWR of 1.2 to 1.5 during that time.** Also don't fly too fast or you'll burn up, disintegrate from aerodynamic forces or needlessly burn your fuel fighting drag. It's okay if your rocket only flies <300 m/s below 10 km. At 30 km altitude should have a speed of about ~750-1500 m/s (depends on what you can handle) and point to about 30-45° above the horizon.
- SAS and RCS usually aren't strong enough to fight atmospheric forces, use gimballed engines and wings/winglets for steering instead.
- If it's too difficult, don't make a gravity turn and simply go straight up. Of course this is inefficient but at least you'll get high enough to start orbital insertion without too much interference from the atmosphere.

* Center of lift (CoL, blue sphere) and center of mass (CoM, yellow sphere) can be toogled in the VAB in the lower left.
** TWR or thrust to weight ratio is an indicator how fast your rocket can accelerate. At TWR = 1 you hover because you compensate for 1 g of gravitational force. At TWR > 1 you'll accelerate, at TWR < 1 Kerbin will pull you back to ground. In flight your have an accelerometer at the right of the navball. The acceleration range of 0 to 2 g is marked green. Keep the acceleration at about 1.2 to 1.5 g. As you fly your tanks empty and your rocket becomes lighter. That means your TWR will rise, so keep an eye on that and lower throttle as needed. Don't forget to increase throttle again when staging.


[B]Beating the upper atmosphere[/B]
- Activate your second stage here if you don't have a SSTO (single stage to orbit).
- Your rocket doesn't need to be as aerodynamic as before. You usually can decouple your fairings at an altitue of ~50 km.
- At the end of the atmosphere (70 km is the border between space and atmosphere on Kerbin) you should point exactly to the horizon. Your speed should be around 2000 m/s.
- Note that wings and winglets are become more and more ineffective. Above 40-45 km they become almost useless, rely on SAS, RCS and gimballed engines from that point on.
- Switch to the map (key [M]) from time to time to make sure your AP isn't getting too high. Aim for about 90-100 km altitude until you'll get the hang of this. Throttle the engines or turn them off to do it. Then wait until you're in space (music will start playing).


[B]Achieving orbit[/B]
- For a low orbit you'll need your AP and PE to be within 70-120 km.
- Usually your PE is underground when you just reached space because you are not fast enough. Quickly make a maneuver node at the AP in the map view and change it so that the PE is raised > 70 km. The orbit doesn't need to be perfectly circular, just make sure you don't end up in the atmosphere again. At the right of your navball there'll be two times displayed. One is the time to the maneuver point the other one is the time you need to perform that maneuver. Take the later, divide it by 2 and you'll have the start time to perform that maneuver. Example: Your maneuver point is 10 minutes away. That maneuver takes 3 minutes to complete. 3 minutes dived by 2 is 1.5 minutes. => You start your maneuver when the maneuver point is only 1.5 minutes away and you'll end it 1.5 minutes after passing the maneuver point.
- Don't forget to extend your solar and radiator panel(s) and antenna(s).
- Also be aware that when you enter the shadow of Kerbin your solar panels won't generate electricity but your probe will [U]keep draining[/U] it continuously. You'll have to rely on batteries, engines with an alternator (generates electricity when the engine is firing) or an RTG during that period. [U]If your batteries are empty you'll lose control of your craft so make sure you archieved a stable orbit before.[/U] When you get back into the sun your solar panels will generate electricity and your probe will power up again. Seriously, that's an important point! I lost an uncountable number of rockets to this.


[B]Maneuvering in space[/B]
- When raising your PE be near your AP to do it more efficiently.
- When lowering your AP be near the PE to do it more efficiently.
- When changing your inclination be near the ascending node (the point where your orbital plane intersects the equatorial plane going 'north') or descending node (the points where your orbital plane intersects the equatorial plane going 'south').


Note: Most of the numbers are estimates. I usually follow the approach "If it goes up without going boom it's fine".

In tech I usually go the lower route where the science experiements and the solar panels are. Once I got solar panels I'll invest more in new engines and tanks. Edited November 23, 2015 by *Aqua*