• 0
Sign in to follow this  
SlabGizor117

How's my gravity turn? What's the best?

Question

For my gravity turns, I watch my apoapsis(KER FTW!) and point my nose down the navball accordingly.  At 5,000m, I turn to 70 degrees, then 10,000, to 60.  Then about 15,000 to 45, 20,000 to 40.  25,000 to 35, 30,000 to 30, 35,000 to 25, 40,000 to 20, etc.  Then by 60,000 I'm level and the distance of my aposapsis causes my thrust vector to push it slowly upwards still.  What do you think? Too shallow, maybe?  How do you do it?  How should I modify mine?

Share this post


Link to post
Share on other sites

10 answers to this question

Recommended Posts

  • 2

I can't judge the efficiency of your gravity turn because I run mine so differently that I don't track the same info.

 I launch vertically until I establish a specific velocity. It might be 40 m/sec for a high t/w or 100 m/sec for a low t/w lifter.

 At this point, I pitch prograde to establish an 85° prograde vector, turn off the SAS, and go get a beer.

I expect to see a 30° prograde vector at 27 km altitude (when I stage). Beyond that, I simply pitch as necessary to keep my apoapsis 45 seconds ahead until I clear 40 km altitude, then throttle prograde until apoapsis is established.

I don't have many benchmarks or really track the turn all that closely.

Best,
-Slashy

 

 

Share this post


Link to post
Share on other sites
  • 1

If you're manually setting the angle then technically it's not a gravity turn, as you should only have to put in the initial angle and then let gravity do the rest as Slashy describes.  I'm no so confident in my crafts stability though so I tend to start the turn, and then set the SAS to prograde (plus the beer's a lot stronger over here so if I had one every launch I'd forget what the mission was supposed to do :D).  If it feels like it's turning a bit too fast/low I switch the SAS to hold current vector for a bit, and then turn it back to prograde.  If it's turning too slowly backing off the throttle a bit will tighten the turn but I don't usually bother and accept that it'll need a longer circularisation burn.

 

Share this post


Link to post
Share on other sites
  • 0

My gravity turns would use those numbers as an altitude guide rather than an apoapsis guide.  i.e. at about 5000 m altitude I'd be turned over to 70 degrees, at 15000 - 45 degrees, etc.

I still keep an eye on the apoapsis (yay KER) and am ready for MECO when the apo hits about 77-79 km.

I tend to think my gravity turns are a bit shallow, and they're not as shallow as yours.

Happy landings!

Edited by Starhawk

Share this post


Link to post
Share on other sites
  • 0

One thing you can try is to install the Gravity Turn mod, in order to watch how it's done on your KSP, with ships you have build, etc...

It helped me more than video or tutorial for learning the trick... And now i can do it by myself :P

 

______

Keep in mind that it'll show the most efficient launch, and not the quickest or the most enjoyable one. I mean the mod is helpful in order to visualize the best theoretical launch, in practise i tend to do my launch in more steeper ascent profile to gain some time :P

Edited by kaptain_kavern
added precisions

Share this post


Link to post
Share on other sites
  • 0

Whenever I DO fly rockets, I go so shallow that even with a high TWR, my apoapsis is at 70km, but I already have a periapsis of whatever altitude I finish burning.

Share this post


Link to post
Share on other sites
  • 0

There was a video about evolutionary testing ascent profiles. Best profile was keeping apoapsis 2000m above actual height. But it was a little ICBM Style Rocket so lots of TWR i guess. And no Rockets share the same "best" ascent profile and its actually a near impossible thing to calculate.

Greetings

Ben

Edited by Navy2k

Share this post


Link to post
Share on other sites
  • 0
20 hours ago, SlabGizor117 said:

For my gravity turns, I watch my apoapsis(KER FTW!) and point my nose down the navball accordingly.  At 5,000m, I turn to 70 degrees, then 10,000, to 60.  Then about 15,000 to 45, 20,000 to 40.  25,000 to 35, 30,000 to 30, 35,000 to 25, 40,000 to 20, etc.  Then by 60,000 I'm level and the distance of my aposapsis causes my thrust vector to push it slowly upwards still.  What do you think? Too shallow, maybe?  How do you do it?  How should I modify mine?

Too shallow? No way! TOO STEEP!
I usually let MechJeb handle most launches but when going manually I use the following rule of thumb:
The atmosphere gauge at the top centre of your screen has four colours: black, dark blue, blue and light blue. When the needle passes from light blue to blue you should be at roughly 60 degrees. From blue to dark blue at 30 degrees. And from dark blue to black at 0 degrees. Coast to Ap and circularize.

Share this post


Link to post
Share on other sites
  • 0

I go with speed limits and try to go full throttle the whole time

500 m/s < 5km

900 m/s <10km

1100 m/s < 15km

1300 m/s < 20 km

1500 m/s < 25km

1900 m/s < 35km

Holman transfer from 40-50km

 

Share this post


Link to post
Share on other sites
  • 0

There was a Scott Manley video where he compares a couple different gravity turns, and finds that there isn't a very great difference between the results. As long as you're not at the extremes of shallow or steep, you won't gain or lose much efficiency by perfecting your gravity turn.

Share this post


Link to post
Share on other sites
This thread is quite old. Please consider starting a new thread rather than reviving this one.

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Answer this question...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this