Project Here goes nothing: The Delta-StarLiner G42

[Moach]

awesome plane, Nutty! :thumbup: - kudos on your aero-modeling skills!

and you win one free internet for pointing out the rudder dynamics - i had not thought of that!


the reason why the G42's "rudderbrakes" have very little effect on direction, is that they are currently implemented as actual "rudders" as far as orbiter is concerned :hmm:... and without a meaningful vertical surface area, although rotation is applied, very little lateral acceleration takes place... this is because Orbiter is mostly unaware of the drag being caused by the rudderbrakes

now, by seeing how your plane flies, i'll have to try something different - i shall REMOVE the code for rudders, and replace it by independent "variable-drag" elements (aka: Airbrakes), to be controlled by the rudder axis

doing it this way should "force" Orbiter to simulate the true effects of this type of rudder - i hope


i'm not sure how it's gonna behave, but it should indeed have a little more effect on direction, i guess...

remember, an empty G42 weighs 38 tons, and flies at about 500km/h... i don't know how much effect the rudderbraks should have, in comparison to your awesome little plane... i guess we shall soon find out :hmm:

---------- Post added 09-21-10 at 10:52 AM ---------- Previous post was 09-20-10 at 11:18 AM ----------

i was thinking today....

the G42 needs to haul 30 tonnes of LOX about half-way up to orbit so it can have something to burn on the main engines in the last stage....

but - what if - instead of a full LOX tank, the G42 could takeoff with an EMPTY one and a ram-stream compressor?

it hit me that we could save 30 tons of takeoff mass by developing some form of collecting the needed oxidizer "on the fly" - when the LOX tanks become full, over half the propellant would have already been used :hmm:


but there are a few hindrances one must overcome to make this viable....

namely, the heat --
at mach 14, at which point the collector scoop/probe/thingy would open, the incoming air is insanely hot... now, i reckon most gasses take up an awful lot of volume when in high temperature.... this could be a problem, being that we're trying to compress such gas

it would need cooling - and LOTS of it...

now, the G42 burns dense fuels, which are stored at mostly mundane temperatures (unlike LH2, which is tanked at cryogenic levels)... with that, we can't really use our own fuel to cool off the incoming air, as the SABRE engines would do....

30 tonnes is still a nice mass relief, but i wonder what amounts of coolant would be needed by this system


so, once again, i beckon all the OF sim-scientists to pitch in with ideas on how this could work


30 tons of takeoff mass - that's almost as much as the empty mass of the whole ship...

 

[Mindblast]

Ideally your airbreathing engines will burn all the O2 in the incoming air so theres nothing left to store. That means you have to use an extra inlet for collecting air on the way which increases your drag significantly. Also compressing and cooling the incoming air as well as separating the O2 from it will use enormous amounts of energy.. and then theres the problem of where to dump the heat into. At M14 you'll have enough problems with keeping your ship cool already.

 

[Moach]

yes... i do believe extra drag is the last thing you'd want when running a scramjet....

this could be perhaps avoided, to an extent, if instead of a scoop, we used a long probe (like an oversized pitot tube), which could extend in front of the larger shockwaves formed in front of the hull, then slowly draw in the air during the course of the ascent...
mostly during the early phases where cooling isn't such a huge problem...

the G42 should burn about that same 30 tonnes of propellant in the first and second stages (must check, but probably) - in that case, there would be no need to collect oxidizer above mach 6~7, thus alleviating part of the problem

but although lessened, there will still be oodles of heat to dump... onboard coolant would be needed


as for separating the O2 from the air.... it could perhaps be unecessary (?) - being that the G42's main engines are designed to breath external air....

where's that thinking hat when i need it?

 

[Mindblast]

Storing air is probably the last thing you want to do as you'd have to store about 120 tons of air to get 30 tons of LOX.

Oh and then collecting 120 tons of air will take quite a while actually even assuming zero loss on the inlet. Even at sealevel flying with 300 m/s you'll need about 5 minutes with a 1m^2 inlet.

Actually it just occured to me there is a simple reason why this can not really be much more efficient than taking the O2 along right from the start.
Every single kg of O2 you are collecting during the ascent will have to be accelerated to orbital speed just at it would have to be when you take it along from the start. So the only energy you can actually save here is the potential energy of the collected air at higher altitudes, because you don't have to do the work of lifting it from the ground to this altitude.. but that is not much compared to the kinetic energy it gains when it is accelerated to orbital speed.

 

[Moach]

aha! i knew there had to be a simple reason why this wouldn't be viable :thumbup: - thanks for putting it so clearly!

i was having trouble putting my finger on it - but you nailed it just right! - mathematically, the only gain achieved from this would be the in potential energy contained in the high-altitude gas... but it would still need to undergo the same amount of tangential acceleration as if it was carried from the ground up - providing very little benefit in the end :hmm: and most likely even penalizing performance, with the technical toll involved in the actual "scooping" process

THAT's why i can't be done... now it makes sense

 

[Moach]

ok, i realized it had been a while since the last screenies...

so here's one:

look! textures!
i got my old pen tablet rigged up again... makes a ton of difference, indeed! :thumbup:


i finally did the full unwrap for the external mesh... now i have the underside painted (with scorch marks and all) :hmm: - but i'm not done there...

but now it's getting late and i must sleep... i have yet i figure out a way to remove that stupid habit... such a waste of able time :lol:


cheerz

 

[Sky Captain]

Now that's an awesome looking ship, can't wait to take it for a spin. Keep up the good work:thumbup:

 

[Zachstar]

Such a future craft ought to not be too bothered by O2 mass. Tho it was a nice idea too bad physics got in the way. Darn Physics!

There is a simple way to stop sleeping.. Become Borg and just Regenerate... Now if we can only find some Borg...

 

[Moach]

there, just did some editing on the first page...
now new readers may get to see the most recent screenies as they enter: rolleyes:

i'll try and keep it up to speed from now on

cheers!

 

[NuttyPro67]

Looks awsome, Moach! Gosh, its looking like its time for another WIP release. :shifty: Riiiighhht?

 

[Moach]

i'll have one up as soon as i get the texturing done on the aft cabin :thumbup:
shouldn't be too far off now

 

[Moach]

just a quick update to let you all know this is still alive :thumbup:

i'm currently in the process of moving out of my mom's place to go and live with my girl, so you can immagine how my not-at-work time has become a little cluttered...

but in the little able time i managed to scrounge up this weekend, i solved the bay mash visualization problem from the aft cabin... turns out, there's a special rendering flag to cause external parts of the ship that should be visible from inside the cockpit to render properly around other objects.... very convenient!

but i'm still getting a little clipping on the bay doors where they are closest to the cabin... (extpass meshes clip at 2.5 meters from cam) perhaps i'll simply adapt the model a bit so it doesn't show... dunno, i'll think of something :hmm:


other than that, i've exported the new textures - looking good - and have redone the "physical" thruster points for RCS control... the ship has a flight computer, it should be able to accomodate thrusters in a less-than-perfect configuration - so as far as Orbiter is concerned, they are aligned perfectly to remove any collateral translation/rotation during maneuvers


the URMS looks pretty cool from the bay-cabin view... i wonder if there's a way to bring up it's control dialog without having to change vessel focus, so it can be controlled from there
which reminds me... i have it mounted on the wrong side of the bay... i modelled the cabin so that the docking controls are on the starboard side, and the arm operator's station on the port side... so the RMS should be on the port side as well, so it's more visible from the operator's position... no biggie, tho, i'll make a mental note to change that later


cheerz!

---------- Post added 10-05-10 at 11:03 AM ---------- Previous post was 10-04-10 at 11:40 AM ----------

another update, for any whom may care


last night i've reworked the rudder system - as pointed out, it didn't feel very realistic, so i made the rudder area null, and "rewired" the controls so the rudder axis now activates the airbrakes on either side....

although that was apparent before, it was only a visual thing... but not anymore - now, the "rudder" control surface has zero area, and the actual "ruddering" is done by using VariableDragElements (aka: airbrakes). :thumbup:


thus, just as it was beautifully demontrated by the model plane in the recent video, the G42 now has a lot more turning with the rudders alone (particularly at lower speeds)


another thing i did, was to add ground-effect lift to the flight model...
i imagine an object with the shape and size of the G42 would cause a considerable air-cushion when close to the ground....

particularly during "rotate", where before it was pretty easy to cause a show-stopping tailstrike, now the G42 elegantly floats aloft with relatively little AoA and speed.... once clear of the runway, it's safe to pitch up higher as to start a climb

the effect has an exponential decay up to about 30 meters AGL - which i have yet to tune up properly and find the most realistic setting

so now, as you pitch up for takeoff, you can expect to leave the ground a lot sooner... on landings too, you can expect some "padding" as you near the runway at otherwise dangerously high vertical speeds

the ailerons felt a bit "heavy" during the last test... i'd have them boosted a bit, but i had to leave for work... guess i'll do that tonight, then :hmm:

 

[Zilesio]

Moach, You're a crazy genious and we all love everything you come up with! (^^)d

keep it up!

 

[Moach]

genious i don't know... crazy, on the other hand, i'm pretty certain.... :lol:

thanks, anyways!
i'm pretty stoked about this ship - it's looking like quite a fun ride right now.... too bad i don't have more time to spare on it :hmm:

i might have a new WIP release coming up soon :thumbup:

 

[Coolhand]

Hey Moach, haven't looked in here in a while, looks like you've really been working on the textures, they're looking great.

I also like the wing reduction its got at some point, looks a lot faster than before.

 

[T.Neo]

I also like the wing reduction its got at some point, looks a lot faster than before.

Wing reduction is not always a good thing, since wings are what makes an aircraft fly.

 

[Moach]

Hey Moach, haven't looked in here in a while, looks like you've really been working on the textures, they're looking great.

I also like the wing reduction its got at some point, looks a lot faster than before.

thanks! :tiphat: i guess i got inspired by seeing your progress on the MK2 :blink: -- getting my tablet drivers up to speed also helped a bunch :lol:

Wing reduction is not always a good thing, since wings are what makes an aircraft fly.

they do, but turns out at mach 14, they kinda do too much, so i figured it needed to get a little sleeker in order to look as capable as it really should be

i remember at one point i had to cut down on the (somewhat excessive) lift factor which i initially "borrowed" from the stock DG... it didn't suit the ascent profile very well and tended to force the nose up a lot...
but then i noticed that takeoff and landing were quite cumbersome - so yesterday i added ground-effect lift to the equation, which i figured in a ship like this, would not be anything negligible - made a world of difference :thumbup:

some time ago, i've seen a video of a 747 landing and noticed it hardly adds any pitch to flare before touchdown, that's how powerful the ground effect is when you have a large wing area -
so last night i spent a few hours just tuning it to get it to act in a coherent way....


if anyone cares (and perhaps has any better ideas) i just might post the modified lift function code - i don't have it with me right now...
work-pc != home-pc... you know how it is ...


i'll keep you all posted :thumbup:

 

[Coolhand]

Moach i'd have suggested it a long time ago, but its your project and everyone else seemed happy with it... Surely a massive challenge for spaceplane designers, particularly SSTO's is what shape to give the wing, and how much wing to give it... the delta glider has really far too much wing, as do all its descendent designs such as the DGIV and XR1.

Arguably more recent designs for orbiter such as your starliner, or my own design still have too much wing - compare to proposals like HOTOL or Skylon... but we all get around that with advanced materials and fuels, and enjoy the lower landing & takeoff speeds and spacecraft designs that visually sorta meet peoples expectations based on their experience with winged aircraft and the shuttle.. Where do you draw the line between it looking like an aircraft, or looking more like a sled.. or resorting to variable geometry wings. Perhaps its no surprise that we end up having a similar plan view to the space shuttle orbiter... But, as proved in the 60's lifting body programmes, perhaps based on work done earlier in germany in ww2, you dont really necessarily need what we would consider 'wings' at all as there are other ways of providing lift. But i think visually you've got a nice balance going on there.

 

[T.Neo]

There's a whole science behind aerodynamics that aircraft need at hypersonic speed, and aerodynamics that aircraft need at low speed, and where compromises need to be made. And that also fits into other aspects of the system, like center of gravity and design features.

I'm sure there are some pretty good resources out there on the 'net, but I know very little about the subject.

 

[Moach]

i chose to go with a high-lift design based on the concept of performing most of the orbital ascent inside the atmosphere... this allows airbreathing engine operations up to very high velocities...

the G42 is equipped with two RAMCASTER engines, which are capable of altering their internal geometry to function as both ramjet and scramjet, depending on the stage of flight

so the starliner's concept is to simply bite the drag bullet and go for the tradeoff of not having to thrust it's own weight up...
using a VERY shallow ascent profile (in comparison to the shuttle or even the stock DG) - we can exploit the airbreathing engines to a maximum...

thus, the G42 avoids the need to generate more than it's own weight's worth of thrust at early flight



it's a tradeoff - we lose on air drag on the way up, but we gain valuable wing lift at early flight and air for the engines to burn

IMHO, i think it's worth it :thumbup: