[Is this a good simple plane design?]

 

 

What I do to post screenshots is open the image in a new tab and then copy that URL onto my post.  

I flew a near copy of your plane.  It looks like I set my landing gear further apart than yours...  Mine sat level on the runway.  

Good is partly a question of style.  I found it easy to do yank and bank maneuvers around the KSP buildings.  Easy to do Immelman maneuvers.  Easy to land.  

The biggest downside for me was high takeoff speed.  This would be easy to fix by ensuring the wings are not level on the runway, but angled up slightly (that could make it trickier to land however).  Once I was off the runway the pitch controls were fine, but due to massive wing area the G forces and drag braking caused by sharp pitching were the highest I've ever encountered (at least at low speed).  Yaw control and sideslip were a bit excessive compared to what I'm used to, but it worked and I didn't tailspin, besides that's easy to calibrate.  Roll was about perfect.  

This plane doesn't really need medium landing gear in the back, smalls are fine.  The wing surface was much larger than what I normally build, which is mostly a question of style.  

Overall I say this is a good plane and fun to fly.  

 

 

 

 

[A study regarding the feasibility of airships using real-world physics within the scope of KSP.]

14 hours ago, Fengist said:

Steam has been used for a long time to attempt to make lighter than air ships.  And while it's density is 0.6 which means it can produce lift, it's a far cry from hydrogen at 0.08.  The difficulty with steam isn't just the condensation (and the resulting weight and corrosion), in order to generate steam you not only need to lift water but you need to lift the fuel to boil it as well.  And neither of those are light.  You could probably rig up a recapture system similar to what I described was designed to capture water from engine exhaust but the problem still remains that you have about 1/8 the lift of hydrogen with the same weight.  I'm sure it could be done but you'd need some serious... serious volume and then, you'd be dealing with Newton's law of cooling which would be a nightmare to figure out.  As aviators have discovered, hot air works well but even it needs massive volume to lift even small mass.  Case in point is the Skyacht which has 205,000 cu/ft of envelope just to lift a small payload.  Most hot air ballons (from what I understand) keep the air at a temperature of around 200 C.  At 204 degrees, air's density is 0.7, which is close to that of steam at the same temperature without having to lift all that water.  Now, if you could superheat that steam and keep it that way, you may be onto something but that's gonna take a lot of energy from something.

GL with it.

 

 

I think those numbers are incorrect.  Bouyancy is the mass of air displaced minus mass of balloon.  

So if outside air is 1.225 kg/m3

Steam at 100C is about 0.587 kg/m3, then it lifts 0.638 kg/m3

Steam at 200C is about 0.462 kg/m3, then it lifts 0.762 kg/m3

Hydrogen being about 0.08 kg/m3, lifts 1.145 kg/m3

Air at 100C is about 0.921 kg/m3, at 200C about 0.726 kg/m3, with lift of 0.3 kg/m3 and 0.5 kg/m3 respectively 

Roughly steam has 2x more lift than hot air (at 100C).  Hydrogen has 2x more lift than steam.  Hydrogen has 4x more lift than hot air. 

 

Hot air gets relatively better the more its super heated, so the solar greenhouse balloon is potentially a big improvement for the hot air.  Steam has really great performance as long as we prevent condensation on the inner surfaces of the balloon.  Catching condensation and reboiling it works to some degree, but it's better to prevent condensation altogether as far as possible.  I propose to do this by not letting steam contact the outer surface of the outer balloon, instead keeping it in a balloonet.  If I had a 3 layer balloon, I would vent exhaust gasses into the middle layer.

Hydrogen and Helium lift twice as much as steam.  Hydrogen is dangerous, helium is expensive, and they both escape through surface.  

 

[KSC2 Mountain Buggy Challenge]

With a change of wheels my rover was able to make it to the summit.  (it also lacks the docking port and parachute this time)  I could only handle about a 35 degree climb, but was able to switchback across the steepest part of the mountain.  No significant accidents on the way up.  

At the highest point I discovered I was stuck, with the MK2 crew cabin in contact with the ground and electric charge almost fully depleted.  That was a save point.  Not gonna lie.  I spend about two hours and many quickloads figuring out how to get back down after that.  Fortunatelly a kerbal was able to push the rover loose, only pointed backward on the wrong side of the mountain.  That was easily recoverable.  Next step glider mode.  The concept of using all 4 kerbal parachutes led to a few disasters and was abandoned.  Still the rover is a good glider all on its own.  I went for the steepest section I could find and straight over a 2000 m drop !!!  The good news is the glider can go quite far, the bad news is I need to land on a downslope to survive without any parachutes.  And the bottom of that cliff has somewhat of a bowl shape, so it had to be a steep descent.  After satisfaction with that another save point. 

Coasting the rest of the way down took several tries.  Given the high drag of my rover I had trouble making it uphill the last km or so to KSC2.  Sliding around the east side of the base while preserving as much altitude as possible until the last proved the solution.  

 

 

[[KSP 1.5.*] Outer Planets Mod[2.2.1] [25 April 2018]]

This mod failed to load for me.  I'm running KSP 1.4.3.2152.

I downloaded CustomBarnKit 1.1.17.0

Kopernicus 1.5.1-1

Outer _Planets_Mod-2.1

 

I got error messages saying do not open my savegames because they would not play well with Kopernicus.  So I started a new game, but no outer planets were visible.  

[KSC2 Mountain Buggy Challenge]

 

I'm getting somewhere on this challenge, but having difficulties.  I can't quite make the grade (as in gradient) just yet.  Tips on how to improve this craft would be appreciated.  I really want to know purpleivan's secrets.  I've tested rovers similar to his and I flip those over really easily.

 

My rover evolved roughly as follows.

Wheel design:  Front steering unpowered, rear drive wheels non-steerable.  I'm not sure if I can fully defend the idea of using unpowered front wheels, but it's simple and it works.  The training wheels are valuable for some of my other rovers to prevent flipping, this design might not need them because the aero-surfaces are so good.  

Aero-surfaces: testing at KSC it seems to me that vertical stabilizers and spoilers are invaluable for making a nearly unflippable rover.  This craft uses elevon 3 for spoilers.  All degrees of freedom are disabled in rover mode, but pitch and roll can be turned on to glide.  An early idea was to use the kerbal parachutes for wings.  That worked in preliminary testing, but for some reason would not work while descending from orbit.  The MK2 cab was originally intended just to load 4 kerbals.  But then I figured they would want some snacks on this mission, and it turned out to help the glider performance anyway.  I was once able to land this craft undamaged from orbit with zero parachutes but that was hard to repeat.  I added a docking port to have an extra control node and one little parachute makes landing easy every time.  

Aero-dynamic spoilers generate a small amount of lift in the reverse direction, which limits top speed a lot.  I wonder if this reduces my hill climbing performance, but I don't think it would when the speed is close to zero.

 

I tested this craft by running over the crawlerway at KSC in every concievable way.  It is virtually unflippable with traction control and friction control on auto.  When I stalled climbing the mountain at KSC2 I fiddled with the friction controls.  I think setting friction control to 5 and drive limiter to 100 is supposed to give best hill climbing performance ?  Is that correct.  The craft becomes flippable with friction control turned up.  

The two most obvious redesigns I can think of are 1. reduce weight 2. increase torque.  The crew cabin could be removed, but I've started to like it... I guess adding a lot more rover wheels would increase torque...

BTW: I eventually figured out how to get to KSC2 by cheating into orbit and using a detatchable swivel engine to start the descent.

 

[Moho blues]

[Moho blues]

22 hours ago, DerekL1963 said:

The functions that only work for the SOI you're in aren't the one's you're looking for...      Try the Advanced Transfer function in the Maneuver Planner window.

I'm not sure what you mean by "eyeballing the brown line".

Well that't part of my problem.  I guess I cut my teeth on MJ in career mode and was only using the basic options.   

The difficulty I'm having now is returning to Kerbin using Advanced Transfer and requiring a >4000 DV capture burn. 

My return stage uses a command seat and ion engine.  With lower velocity I can aerobrake this type of vessel, keeping the kerbal in the shadow of the other parts.  This time he blows up at 69000m.  Also my periapsis is in Kerbin's shadow.  

I can probably do better with transfer, and try heat shields.

[A study regarding the feasibility of airships using real-world physics within the scope of KSP.]

Very cool.  I really would love to play with realistic airships.  

If you click on my avatar, it is a simple representation of a lifting balloon(s) I would like to build in real life. 

 

Steam is an excellent lifting gas.  Steam has an advantage over helium in that a steam balloon can be operated at ambient pressure and small leaks will not ruin the lifting performance.  The difficult thing with steam is to keep the temperature high enough to prevent condensation.  I propose to do this using the greenhouse effect.  The surfaces of the balloons are variously transparent, reflective, or highly absorbant to focus solar energy on the inner balloonet.  The inner steam balloonet is insulated by surrounding hot air.  

 

 

[Moho blues]

8 hours ago, DerekL1963 said:

MechJeb will do that, and calculate a burn that will place you on a direct trajectory from where you are to where you want to go.  (That is, it combines the ejection burn and the plane change burn into a single burn.)  It's much cheaper than doing plane change burns out in solar orbit.  Then you can either manually fly the node, or let MJ do it for you.

"Cheaper" is of course a relative term, it's expensive to transfer Moho <-> Kerbin no matter how you cut it.

I am using MechJeb maneuver planner tool.  Many of the functions only work for the SOI I'm in.  There is some information about the next SOI (brown line), but I'm sorta eyeballing the brown line.  

[Moho blues]

I'm trying to land on Moho and return a sample to Kerbin.  The landing part is easy, getting back is the hard part.  I find myself using ridiculous amounts of dV.  It takes me almost 2000 dV just to match inclination.  I'm OK at gravity assists if they're fairly easy to eyeball, but I can;t seem to set up anything especially complex.  Perhaps I need some mods to help find exact transfer windows...The inclination changes are the real killer.  I have learned to launch from Kerbin when I'm near the ascending node of Moho (roughly eyeballing it) but didn't manage to get much of the inclination change I needed while in Kerbin's SOI.

 

Tips of navigation mods?

Tips of better inclination changes?

  

[Are nuclear engines really low thrust at sea level? Why?]

The reactor design of the NERVA is different in several important respects from a conventional power plant.  It uses a different control rod mechanism and higher enrichment fuel.  Still, lets consider the decay heat problem is roughly similar to what the people on quora are describing.  This implies that a nuclear engine requires a cooling system that can dissipate secondary decay heat about 5%-7%  of critical heat.  If we have that type of cooling system, then we can shut off the hydrogen flow within about one second, before the reactor temperature has dropped significantly.

[Are nuclear engines really low thrust at sea level? Why?]

8 hours ago, wumpus said:

 

If you want the engine to start and stop repeatedly (which of course you will for any mission that can justify nuclear propulsion), then lowering the thrust makes the whole start/stop cycle wildly easier.  Nuclear engines have a relatively long cool down between adding control rods and the (secondary) nuclear reactions stopping.  Presumably some of this would be included in the delta-v of the burn, but you will still need to feed cooling hydrogen through the reactor while it cools down, leaving the end of the burn rather inefficient.

Hmmm thats interesting.  I wonder if would need a long cool down, or if the shutdown would last on the order of 1 second?  

So the reactor is turned sub-critical with hydrogen flowing and the core temperature begins to drop.  This lowers the ISP.  The question is how much temperature change is needed for safe operation, and how much time this takes.  I'm guessing it only takes on the order of a 1% temp drop which happens in less than 1 second, but I could be wrong.  

[de laval nozzle in the center of a toroidal aerospike]

I should have included more background reasoning for the question.  I'm curious what happens when we expand the diameter of a toroidal aerospike considerably, and also expand the diameter of the blunt tip.  

One of the problems with long thin spikes in practice is cooling.  This is why they are all blunt tipped in practice.  But an air jet out the tip is like extending the spike.   I suspect the reason why the linear aerospike was developed to a larger scale than the toroidal aerospike also has to do with cooling.  The linear aerospike also theoretically benefits from an infinitely long nozzle, however the one for the X33 has a large blunt end at the tip.  Plenty of space for coolant circulation.  Why else would they make it that wide?  

So my thought experiment is to make a large nozzle shaped like the letter W, with a conventional nozzle at the center and also exhaust gasses around the outer rim using the W as an aerospike nozzle.

In the limit where the conventional center engine is powerful and the outer engines are minimally powered, the only downside I see is the mass.  This is offset by three advantages that can be gained.  

1. vectored thrust without gimballing
2. superior aerodynamics from having a streamlined tail

3. the possibility of an air augmented rocket

 

 

Edit: 4.  altitude compensation for the central nozzle.  

Edit: 5.  One large combustion chamber flowing directly into a de laval nozzle can probably handle higher combustion temperatures, than the types of combustion chambers that would work for an aerospike.
 

[Are nuclear engines really low thrust at sea level? Why?]

At least in KSP, onion staging always beats bamboo staging.  If someone can explain the advantage of lifting an engine that is not firing, that would explain why nuclear sea level engines are not desirable.  

I'm also skeptical how radioactive the normal exhaust would be.  There are a few radical neutrons in the exhaust, but these are mostly thermal neutrons (having been moderated by graphite).According to wikipedia: neutrons from U235 fission have energy 2 MeV.  Moderators bring them to the thermal range of 1 eV.   By comparison a neutron bomb released neutrons at 14 MeV.  I suppose all the thermal neutrons released on Earth would be absorbed by something... making normal matter slightly more radioactive than normal.  I'm not suggesting this is environmentally benign, but probably way to low to be considered a weapon.  

 

[Are nuclear engines really low thrust at sea level? Why?]

 

Here is an old school video about the NERVA engines.  There is a graphite moderator, and a rotating control rod design.   Presumably this means the nuclear reaction can be controlled at various levels of hydrogen throttle.  They say the engine operates at 4000 degrees Fahrenheit.  It can start and stop repeatedly.  I would assume the operating temperature is chosen based on the other materials (besides uranium and hydrogen) that make up the structure of the rocket engine.    

 

 

[de laval nozzle in the center of a toroidal aerospike]

According to what I've read the toroidal aerospike typically exhausts a small amount of gas out the spike to simulate an infinitely long "air spike".

What if we expand the diameter of a toroidal aerospike considerably and put a de laval nozzle in the center.  Suppose the center nozzle is vacuum optimized.  Would it operate well at sea level while the outer combustion chambers are firing?  The high velocity of surrounding gasses would lower pressure, offering better performance for the center nozzle.  The exhaust gasses from the outer combustion chambers would be pushed radially outward somewhat below the base of the spike, but I'm not sure how much of a problem that would be.

 

Also the literature about the linear aerospike engine makes a big deal about how they use many seperate combustion chambers, and therefore differential throttling allows vectored thrust.  Would many small combustion chambers with different throttle also work well on a toroidal aerospike?  I am not certain, but I suspect varying the throttle on the sides of a toroidal spike would give more lateral thrust than would be the case with the linear aerospike.    I'm also not sure how the toroidal aerospike works with half the combustion chambers firing and half of them off.

 

[Are nuclear engines really low thrust at sea level? Why?]

The subject of the thread is the question.  In KSP the NERV engines have terrible thrust at sea level.  Is this necessarily the case?  Why?

[How To Land an Orbital Rocket Booster]

Here is my version.  It carries a 4.5 ton payload to orbit and lands in the grasslands near KSP.  The concept of this vehicle is low moment of inertia, and high reaction wheel torque.  This allows the vessel to control the direction of lift and drag on re-entry.  It flips tail first, but still retains some aero-control.  Enough lift/drag to easily avoid crashing into the mountains or the sea.

 

The autopilot can land on the engines.  I have a hard time hitting the surface with zero tangential velocity, so I tipped over and sustained no damage.  Aerobrakes would probably help with that part.  I used the RCS a bit on final decent, but this design probably doesn't need them.  

 

 

 

[The Ultimate Jool 5 Challenge Continued]

This is an extremely awesome mission.  I've failed several serious attempts so far.  It has really taught me to be careful about gravity assists.  I once made the mistake of trying to capture Jool by entering opposite the direction which its moons orbit... which adds about 2000 dV to try to capture the big moons.  Several times I've taken the incorrect gravity assist off the major moons and added over 1000 dV to the mission requirements to get my landers back to the mothership.  My best missions so far can accomplish everything except returning all my Kerbonauts safely to Kerbin, simply because I ran out of dV.  I am pretty happy with my landers.  To succeed now I think what I need to do is divide my mothership into two seperate pieces.  One that can just wait for the return journey to Kerbin, and another that can swing around all of Jool's moons and rendevous with the landers after their job is complete.  I haven't earned the badge yet, just getting close.  

 

A small craft I call "superbike" can land on Val and the other two small moons, and take off again.  The core stage is a single RCS tank and ant engine.  Below that are crossfeed enabled couplers with toroidal tanks and spider engine, currently 4 stages of those.  It's more spider engines than I need, but such a tiny fraction of overall mission payload that I didn't fuss too much about trimming in down for Pol...  The superbike has way more solar panels than it needs for one tiny reaction wheel, but using the fixed solar panels I once got stuck with my engines facing the sun and ruined the mission.  

 

The Tylo lander is a "superbike" with 3 radial extensions.  It also had another stage for decent, that was discarded shortly before landing.  

The Laythe lander is unique.  It lands on water with about 1/8 throttle on the Junos.  I rolled it onto shore for this shot.  

I have a comfy margin of extra dV on the Laythe lander.  The nose separates giving me plenty of dV to circularize the orbit, even if I spent extra fuel in the atmosphere.  However I do not typically have enough fuel to escape Laythe's gravity well.  Therefore another ship must spend ~1000-2000 dV to rescue this guy.

[Totally gamey discoveries]

[Totally gamey discoveries]

I've made at least two totally gamey discoveries recently.  

1) Kerbals can splashdown safely using only their jetpacks.  So I was deorbiting a vessel of some kind in career mode, when I realized my vessel had no parachutes or other provision for landing, it did manage to aerobrake to a reasonable speed. OK no problem, I'll go EVA and the kerbonaut will land on his personal parachute.   Oh crap, he doesn't have one, must be a rookie.  Using the jetpack he managed to hit the water at just under 50m/s and survived.   

 

2) Aerospike engines can fire safely through large numbers of toroidal fuel tanks and tiny decouplers.  Many players have probably tried putting toroidal fuel tanks and decouplers below their spark engines, nothing gamey about that.  Well I decided to try it with the Aerospike and it worked.  It worked too well.  I've added dozens of extra stages of fuel tanks that pop off the bottom when depleted. I've never caused an explosion through overheating.  Aerodynamic instability... and even wobblieness in vacuum eventually becomes a problem, but autostrut goes a long way toward fixing it.  The exhaust flames are definitely bigger than the hole through which they go, but it seems 100% efficient, not like what normally happens when some part of the craft is below an engine.  

[Progress in Theoretical Rocket Cost Optimization]

Outstanding post!  I'm slowly figuring out the answers to my first few questions.  I'll have to reread the entire thing again sometime.  Thanks.  

[magnetic alignment and orbital maneuver]

The advantage seems to be that electromagnets are among the longest lived components.  Presumably the power generation system, batteries, or computers would fail first.  If using primarily chemical thrusters, the fuel could be made to last longer.

Compared to a gravity gradient tether, the electromagnets are probably lighter, and offer deorbit capability.  

[magnetic alignment and orbital maneuver]

I'd like to know why this very simple idea is not used on satellites.  Three solenoid electromagnets powered by solar panels could give any satellite its own directionally controllable magnetic field.  The magnets on the satellite would interact with the Earth's magnetic field.  This would give useful orientation control, the entire satellite could slowly orient like a compass needle.  If the satellite starts to spin along an axis parallel to the Earth's magnetic field, this would be difficult to control, but I think through careful wobbling it would be possible to eventually cancel the spin.  The satellite could also gain some component of prograde or retrograde thrust, while usually changing its inclination at the same time, because it can accelerate with respect to the Earth's poles.  

I can see two drawbacks.  1) the effect may be very weak.  2) controlability is poor or non-existent in some directions from some positions.  

Despite these limitations, a triple electromagnet seems like a very useful thing to have.  Reaction wheels or thruster fuel are often the first things to fail on man-made earth satellites.  The electromagnets are much more long lived.  Electromagnets would allow many satellites to remain pointing in the proper direction much longer.  It would also give them a capability to deorbit themselves when their mission is over, without depending on moving parts or finite propellants.  

[Photo-ablative pellets to clean space junk]

And I meant to say the maximum amount of aluminum vaporized is 5*10^-5 m3 not 5*10^5 m3.