Jump to content

Surefoot

Members
  • Posts

    371
  • Joined

  • Last visited

Posts posted by Surefoot

  1. Screenshots will help a lot. Loss of control authority at transonic speeds is called Mach Tuck, you can do a quick research about it as it's well known, and simulated properly by FAR. Ways to counter it depend on your design, usually all-moving control surfaces (or elevons on a tailless delta) that are shielded from the compression wave will keep some level of control. Then there are cases where your design is TOO stable and will not move away from prograde, thats where you introduce dihedral /anhedral and other unstable elements of design..

  2. fatcargo, that's *really* weird. I'll check it out.

    I have the same issue with radial symmetry, when changing the length. I think all of this is related to my still-existing issue of radial stretchies inducing torque.. I still have it whatever i do, of course 8x symmetry with heavy tanks will show it very clearly.

    Also when changing sizes, the fuel distribution goes off (always to the side of "too much oxy") (i use stock fuel). Even when i go to the actions menu, click on "45/55" again, go back, launch the ship, when the fuel is almost used up i have plenty leftover oxydizer. I can provide you with test ships upon demand.

  3. I haven't tried S-turns yet, but that's something on my "to-try" list.

    If you know about piloting, it's a bit like this:

    http://www.combataircraft.com/en/Tactics/Air-To-Air/Forward-Velocity-Vector/

    or a kind of high-speed yoyo could do it (but watch that AoA !). Basically any move that costs energy / velocity.. And yeah i wonder about those B9 airbrakes too, they seem to get through a few mods including DRE (where they just burn off even when closed..).

  4. Yeah i know, right. This was just for one of the upper stages of my Eve lander-lifter. 126t is actually 2 other stages above that one. With your tool i tackle multi-stage by considering the stages above as payload - that's why i dont need to have 15% payload fraction (also i use FAR, i can get around 21% payload fraction on Kerbin and get to orbit.. and for Eve it's more like 3%).

    That's why the middle stage not respecting the min. TWR is a problem here, and i suspect for other lower stage calculations. With 15% fraction my stage would be too heavy (i am trying to balance the whole thing, it has to be able to land.. also FAR punishes unwieldy designs)

  5. Thanks. Played with it a bit, found a problem with one design:

    payload 126t

    payload fraction 30%

    twr 1.8 to 3.0 (that's for an Eve upper stage)

    center stack size 3.75m

    boosters 2 - 6

    max center outer engines 4

    center radials 0 0

    max booster outer engines 4

    booster radial engines 0 4

    only "true radial engines" checked

    i calculate for best ISP, with stock, KW and Novapunch

    Result ends with center stack having a Bearcat with 3x 48-7S, which is quite not enough to propel its own weight along the top payload - TWR is maybe 0.8 at best and of course way under the 1.8 that i need for Eve. Once i drop the side boosters the craft drops like a stone.

    Shouldnt the center stack respect the min. TWR ? (i went around that by replacing that cluster with a KW Titan, but that's maybe not optimal)

  6. .craft file for my blackbird-like speed demon:

    https://www.dropbox.com/s/pt6b6ds3ekiaiql/HyperJet%20Z.craft

    mods needed: B9, P-wings. And of course FAR and KJR (that's a given if you're reading this :) )

    It's capable of mach 6+. Beware, it's not very easy to fly (got a spiral unstability, use a joystick..), get a good ascent going for transonic then over 16km you'll be able to reduce AoA and start moving reallly fast. See how it wants to put itself into orbit by just flying straight. Have fun improving my design i'll be very pleased if you do so (by improving the yaw /roll coupling issues and eliminating the spiral mode, for example). Reducing the mach tuck at transonic is secondary. Reducing the pitch/roll coupling that seems to happen for no good reason (?? is there one ?) could be nice too.

    (edit) i put the leading edge slats on an action group, dont forget to retract them when over mach 0.8...

  7. Made it :) Blackbird-like delta winged beauty with scramjets. Can put itself into orbit by just going forwards at full burn. Low speeds are taken care of by leading edge flaps. Transonic is terrible (mach tuck is huge ! i'll have to investigate why, delta wings are supposed to counter that effect somehow) but once over mach 2 things look good again, when i switch the engines to ramjet mode.

    Ascent:

    rUAkMJU.jpg

    g5Mts9Q.jpg

    Scramjet mode:

    I9agWsn.jpg

    Notice the chimes:

    LXumCkP.jpg

    I didnt make use of the full set of tricks the SR-71 did, p-wings can do so much only :) Also notice the raised tail with small chimes around it, that's needed to balance out mach tuck.

    It's got too much dutch roll for my taste, but i spent too many hours on it already :P

×
×
  • Create New...