Can't get the gravity turn right

[Strupo]

Can't figure out the best way to get to orbit with this ship.

Tried the new '10 degrees at 1000 m and STS off, 45 degrees by 15000 m etc... but the ship ends up at 45 degrees by 5000 m if I'm lucky.

Please help!

https://drive.google.com/file/d/0B3ppHHQCtIL5VHpObnl3cXhXXzQ/view?usp=sharing

Edited May 3, 2015 by Strupo

[MisterFister]

Can't figure out the best way to get to orbit with this ship.

Tried the new '10 degrees at 1000 m and STS off, 45 degrees by 15000 m etc... but the ship ends up at 45 degrees by 5000 m if I'm lucky.

Please help!

https://drive.google.com/file/d/0B3ppHHQCtIL5VHpObnl3cXhXXzQ/view?usp=sharing

http://i62.tinypic.com/35a6ikm.jpg

You're not crazy, I found this thing quite wobbly as well in nuStock aero. I also ran into overturn problems, though on my first shot I managed to get it into orbit with lots of fuel to spare in the core launch stage (the engines were rather toasty, however.) All I did to compensate was to periodically turn on piloted SAS to hold the vector until after my altitude increased, then released it to allow the nose to fall, then reactivated, etc. I think I did that three or four times, and yes, the first was way before I got to 2400m up.

http://imgur.com/YOZCKzb

I get the impression that you built this in career mode, given the tech. The main issue that I see is that it's a needlenose pair of capsules providing only so much heading authority against such a thick trunk of a launch stage fuselage. With your stationary fins shedding away with the LRBs as well, it means that the much heavier ass end is winning.

Make no mistake, however, this is flyable as is.

[impyre]

Well, I've played with old stock aero, NEAR, and FAR... and it seems the new stock aero is inclined to prefer a slightly steeper/later turn than FAR/NEAR, but much sooner than old stock. I've found (and this is just loosely based of some limited experience) that the best results are obtained by starting gravity turn around 2-4km, gently edging over with an angle of attack that's no greater than about 5 degrees at most (maybe 10 occasionally). Try to minimize mach effects, and shoot for around 65-70 degrees at 10km. After 10km you can slightly increase your angle of attack with less fear of flipping. Try to aim for about 40 degrees at 30km, and continue bringing the prograde down until about 45-50km. Whenever the navball switches to "orbit" mode, you can essentially take any angle of attack, just try to get out of atmosphere somewhere around 45s to 1 minute to apoapse. You can do further, but it's harder to keep it low without burning radial-in... of course if you're aiming for a higher initial orbit, then by all means raise that apoapse.

A couple tips that help me out.

a) Always have *at most* one gimballed engine (or at least decrease gimbal limit on the others), this decreases SAS-wobble significantly.

Consider using control surfaces *only* for attitude control below 35km, will eliminate wobble... take advantage of the new aero.

c) Strut *through* fairings. I know, it looks derpy... but it works. And since the fairings don't auto-strut, it's quite necessary. This can easily be done so long as the payload is smaller in diameter than the launch stage (which it should be). Run struts from the size adapter to the payload in whatever way is convenient. I've launched payloads attached by docking port with struts and had no wobble.

d) Always use control surfaces/wings on the lower end of your rocket. If in doubt, test it out. You may need larger wings for bulkier payloads that induce more drag.

EDIT: e) *Never* use follow prograde SAS setting during launch... it's derpy *especially* if it's given more attitude control than it needs. If you find that when you click the "hold *** mode" button, where *** means radial-in, maneuver node, prograde, etc.... with sas on and your ship gets twitchy and can't seem to point exactly where it's supposed to (slightly off to the side), chances are high that you have too much attitude control... try decreasing by turning of some reaction wheels.

EDIT: The "10 degrees at 1km" is highly dependent on your TWR. For people used to playing old stock souposphere which rewarded much higher TWR... this is a valid strategy. If you're using a lower launch TWR of closer to 1.8-2, the method I described is much better. Also, the only time turning SAS off for a "natural" gravity turn will work is if you have sufficient lift. Since your rocket is built in 4x symmetry, it will produce less body lift. It also has nary a wing to speak of, which is why your nose is dropping like a rock (probably combined with a lack of attitude control authority and/or low TWR). If you want a more "natural" gravity turn, build in 2x symmetry and launch with flat side facing the direction you plan to turn in. Wings are good too.

Edited May 3, 2015 by impyre

[maccollo]

Your TWR is very low, 1.16 at lift off, and then you stage right as it's starting to build up. As a result this rocket has to very slowly claw it's way out of the lower atmosphere. The gravity turn only begins after about 2 km. Don't ditch the engines so fast, you need the thrust!

Also while you don't have enough thrust early on, way more than you need on the final stage. As a result you are carrying more engines further than you have to, your staging is less efficient than it could be, so your rocket is heavier than it needs to be.

I redesigned your rocket, and now it's almost 30 tonnes lighter, carries two less engines, carries cheaper engines for the boosters and gets to the Mun with more delta V to spare.

Instead of 4 boosters there are now 6 equipped with reliant engines, and the core only has one swivel engine, and instead of ditching them in pairs the rocket holds onto all of them until high thrust is no longer needed.

[MisterFister]

I redesigned your rocket, and now it's almost 30 tonnes lighter, carries two less engines, carries cheaper engines for the boosters and gets to the Mun with more delta V to spare.

Instead of 4 boosters there are now 6 equipped with reliant engines, and the core only has one swivel engine, and instead of ditching them in pairs the rocket holds onto all of them until high thrust is no longer needed.

https://dl.dropboxusercontent.com/u/22015656/newROcket.png

You don't post the .craft for the OP (or me or anyone else) to examine and learn from. Also, did you consider the possibility that maybe the inefficiencies of which you speak were necessary due to the tech tree? The OP doesn't specify which nodes are unlocked, so pulling this over to a sandbox for testing, as I did, might not provide the greatest insight in terms of redesigns.

[maccollo]

You don't post the .craft for the OP (or me or anyone else) to examine and learn from. Also, did you consider the possibility that maybe the inefficiencies of which you speak were necessary due to the tech tree? The OP doesn't specify which nodes are unlocked, so pulling this over to a sandbox for testing, as I did, might not provide the greatest insight in terms of redesigns.

It did occur to me that OP might not have those wings with control authority, and they were needed to maintain control during transonic flight, so I had to keep tweaking it a bit. only 1 swivel engine didn't give enough control authority with the static fins, and so I changed it to have 4 reliant engines, and 3 swivels.

https://dl.dropboxusercontent.com/u/22015656/MunLanderOne_ASP4.craft

[Superfluous J]

That corrected ship looks surprisingly like my Mun lander. I'm not going to post it because It works in 1.0 which means it's horribly underpowered for 1.0.2. I will be remaking it for 1.0.2 because (with a bit more dV) it's hopefully going to be my first Minmus hopper.

I used no gimbaling engines in the first stage (the 6 outer engines were Reliants) and the center stack, which was stage 2, had a single Swivel. Everything else were 909s (whose new name escapes me at the moment). I did not have control surface fins so I used the basic ones. In 1.0.2 I plan on trying the dinky ones as they're lighter and much cheaper.

[maccollo]

That corrected ship looks surprisingly like my Mun lander. I'm not going to post it because It works in 1.0 which means it's horribly underpowered for 1.0.2. I will be remaking it for 1.0.2 because (with a bit more dV) it's hopefully going to be my first Minmus hopper.

I didn't actually land on Mun with this thing, but the remaining delta V on the two stages check out, and thrust obviously wont be a problem. Also OP could use a single stage for the entire Mun part with a single 909 cram out another 700 m/s out of this thing.

Anyway, I've posted 2 gravity turn videos already, but here we go.

A slightly steeper than necessary gravity turn with this rocket.

[MisterFister]

Everything else were 909s (whose new name escapes me at the moment).

Terriers.

[Eric S]

It looks like this is getting resolved, but I'll chip in with ten degrees pitch below 1000m being way to much in my experience unless you've got a high TWR. The rockets I'm launching right now, I do a one degree pitch maneuver when they hit 35m/s, let it go long enough that the prograde moves off of vertical, then just follow the prograde up. Usually hits ten degrees pitch at about 3500m and 35 degrees at 10km altitude. These rockets maintain a TWR between 1.4 and 1.8 until about 30km altitude.

[Eleven]

Here is a boring 15 minute video of me getting this to a 100k orbit. I put a few little notes in while recording and even had a bad failure with the boosters hitting the craft and throwing me off a little

Dunno if you can read the notes clearly, but I said 'At 50k apo I turn to 180degrees', I meant to say 90degrees

So in short, this has worked for almost every craft I launch, sometimes I have to wait longer to start turning, but all in all, its:

Start turning at 50m/s, little by little to get prograde to start moving. Stay inside prograde, pointing too far east of prograde tend to tip the craft.

As long as I'm around 45degrees by 12km, I'm happy. I stay there until 50km APO.

At 50km APO I turn close to 90degrees until 100km APO, then circularize.

Edited May 3, 2015 by Eleven

[Strupo]

Thanks all. Haven't had time to try it again. I did manage to get this to the Mun and back but it was very touch and go during takeoff. I'll incorporate the advice redirected here and I'm sure this will get me to Minmus tomorrow.