RCgothic

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Posts posted by RCgothic


  1. First entry of 1.0.5!

    I've gatecrashed previously using FAR, but I thought I'd use the opportunity of a clean install with the new patch to do things properly.

    On the runway:

    2015-11-12_00011_zpsjfrqingg.jpg

    Orbit achieved:

    2015-11-12_00002_zpse6iykexf.jpg

    Preparing for re-entry:

    2015-11-12_00007_zpst2pomtd1.jpg

    Getting hot:

    2015-11-12_00008_zpsxyb51451.jpg

    Safe return!:

    2015-11-12_00010_zpsjywjsv7d.jpg

    For certain definitions of safe. Unfortunately didn't quite stick the landing and hit quicksave instead of screenshot, but that's just a case of re-doing the mission later. I assure you nothing had blown up by the time wheels hit tarmac. :blush: My landings still leave a little to be desired.


  2. Remember, it's thrust to weight ratio, not thrust to mass ratio. Your weight changes as you get further from the center of gravity so that means the higher you go, the more your TWR increases.

    Uh, what? I think you have some misconceptions.

    It's technically true that you get lighter as you ascend, but not as much as you think. The acceleration due to gravity at LEO is 7.8m/s2, 80% of that at sea level. TWR increases during a flight primarily because you burn fuel and get lighter, not because you're getting higher!

    Secondly, TWR is useful as a measure of how much acceleration your ship can pull normalised to multiples of kerbin's (or other reference body's) gravity (at sea level). It doesn't change with altitude. On Kerbin it's basically synonomous with TMR. It's specified as weight rather than mass because weight is easy to measure (IRL) and gives you an instant indication of whether you'll be able to take off from whatever body you're on.

    Weight becomes totally irrelevant once you stop burning with a radial component. It's all about mass.


  3. By rotating your ship to keep up with normal/antinormal, you're actually wasting fuel because you're canceling out half of the cosine part of the angle you turn through of dV of the burn, because you added it in the first half of the burn but removing it again in the second. By adding retro as you set up the node to keep your eccentricity, you can go in the direction you're supposed to be going without wasting that dV. Also, you don't have to do that later (which is also a waste).

    Simplified explanation to aid understanding. I offered three different solutions in ascending order of difficulty and reduced fuel consumption. As always, use of manoeuvre nodes does help a lot.


  4. Burning normal/anti-normal doesn't change apoapsis. However, it DOES change which direction normal/anti-normal is in. If you don't rotate your vessel as you burn you will no longer be burning in a purely normal/anti-normal direction and so will be burning a little bit pro/retrograde, which will change your orbital velocity and therefore altitude of periapsis/apoapsis.

    Choose one of three solutions:

    -Accept the change in orbital velocity and compensate with a later burn to adjust apoapsis/periapsis. (Easy)

    -Rotate your vessel as you burn to stay pointing normal/antinormal. You can dynamically compensate for any small error by deliberately burning off-normal yourself. (Moderate)

    -Guess which angle will be normal at the midpoint of the burn and burn in that direction. Any pro/retrograde vector added in the first part of the burn will be compensated by the second half. (Hard)

    Hope that helps.


  5. Correct RCgothic, I am afraid it changes the flight conditions which means we are not comparing like for like, though there are several gatecrashers who did likewise so if you wanted to make a mission report then it would get a link among the infamous ;) gatecrashers!

    Alright, time to bust these gates wide open! Any consensus over whether using FAR is easier or harder than stock these days?

    Take off: 9vyVda9.jpg

    Orbit: That's about 400dv remaining.

    MQ01Yng.jpg

    Re-entry:

    ji17vxY.jpg

    Overshot a bit:

    lr3pdHA.jpg

    Sightseeing:

    BQKdBSo.jpg

    Coming in for landing:

    65CvWGW.jpg

    Touch down!

    2lY8hm2.jpg

    Not so useful payload: One bored scientist. Several hundred unused units of fuel.

    Now to upgrade to something actually useful.


  6. Sure? It seemed to respond pretty well.

    I'm only going on my recent experience in building my first SSTO spaceplane. At 20km and 1200m/s I started to lose control, with the craft wanting to go into a flat spin and then backflip. It was solved by the addition of forward canards (pitch) and a much larger tailfin positioned further back (Yaw).

    If that's not your issue, then where are you struggling? Not enough dv?

    - - - Updated - - -

    Sure? It seemed to respond pretty well.

    I'm only going on my recent experience in building my first SSTO spaceplane. At 20km and 1200m/s I started to lose control, with the craft wanting to go into a flat spin and then backflip. It was solved by the addition of forward canards (pitch) and a much larger tailfin positioned further back (Yaw).

    Note: small active fins can work well until the air gets thin. but larger fixed fins will still work.

    If that's not your issue, then where are you struggling? Not enough dv?


  7. Thanks guys, all very useful! I'll make sure to double check where all the fuel is and shift it forward before my next re-entry attempt. I suspect the fuselage tasks will be basically empty with the nacelles half-full and I'll need to pump those forward.

    I may try adding some airbrakes too. It sounds like flaps/spoilers won't be terribly useful for a canard/delta design though as the trailing edges are too far from the COM.


  8. Thanks for the tips. Is there anything to add regarding the use of flaps, spoilers and airbrakes? I.e. how to.

    What I meant by keeping my periapsis up is generating enough lift such that even though I'm slowing down, periapsis doesn't fall too deep into the atmosphere before I'm properly slowed.

    I guess I also don't understand why speed and altitude have such a negative effect on stability parameters. Why does Yaw Stability fail? It's not like the nose is getting larger and the tail smaller.


  9. Hi guys, a little help here? I've managed to get it into a 75x75km orbit with enough L/Ox to deorbit again to about 35km periapsis. Payload is currently only one passenger and about 400 units of Liquid Fuel. Powerplant is two Whiplashes and a Swivel (career limitations).

    I'm struggling to de-orbit it successfully. At the moment I can't keep the periapsis up and everything ends in a lack of control and a fireball at about 22km. Any hints? I'm not clear on how airbrakes, flaps and spoilers work, so that could be a start.

    http://imgur.com/a/VGB3w


  10. I built my first SSTO spaceplane (career) powered by 2 whiplash and a swivel and successfully put it in orbit. Payload was only 1 passenger and around 450 units of liquid fuel to 75km x 75km. Unfortunately I couldn't keep it under control on reentry and it exploded at about 22km.