Using the nuclear turbojet from Atomic Age

[AlphaMensae]

Ok, I have this idea for taking a nuclear turbojet (from Porkjet's Atomic Age mod)-powered plane to Eve, but I'm out of practice at making planes since I built a simple little science jet in the early days of Science Mode (v1.04), as I've only built rockets since then.

This is my current version:

It takes off and climbs just fine, even does slow turns ok, but get a little agressive with the maneuvering and it goes out of control...or I'm just terrible at flying planes.  

I've locked the gimbal on later test flights, and that seems to help, but only so much.

[Streetwind]

I'm not the biggest expert on planes, but I would say:

- Lengthen the plane by adding a structural fuselage after the cockpit
- Move the center of lift a little closer to the center of mass
- Use a larger tailfin

Basically, your plane is short and wide and has no tail. It'll struggle to fly straight. By lengthening the plane, moving the main wings a little bit forward and making the tailfin more pronounced, you should by able to stabilize it... theoretically.

 

Edited January 22, 2016 by Streetwind

[ineon]

This is fairly common advise on the forum, but I'll say it anyway in case you have not seen it: what happens to the CoM marker if you start to empty out the fuel? Does it move nearer to the CoL? If it shifts about too much depending on fuel level then you could have a plane that flies fine one moment and then flips out the next when you burn some more fuel. 

Also be aware that the centre of lift and the centre of drag are not the same thing. CoD is what causes you to flip. Unfortunately CoD changes even more in flight, and there isn't a nice simple marker that you can apply in the SPH. 

Edited January 22, 2016 by ineon
CoM vs CoD

[Val]

Nuclear Jets don't use fuel, @ineon. They function purely by heating up intake air. They are usually game balanced so that they can't run for very long without overheating. At least at full throttle.

For a real life equivalent concept see Project Pluto.

[Snark]

Yeah, the nuke turbojet's deliberately designed to be a bit of a bear to use, since it runs for "free" without fuel.  So Porkjet deliberately made it awkward, most notably that it's insanely heavy (9.5 tons) and limited to fairly low speeds.

Bear in mind that simply having CoL behind the CoM doesn't ensure stability.  What matters is where your center of drag (not lift) is, which isn't shown in the SPH, so it's a bit misleading to see "oh, CoL is behind CoM so I'm good."  You have that lightweight section sticking way out in front, which is going to make it want to spin out.

Unfortunately, there's not a whole lot you can do to move your CoM forward, since so much of the craft's mass is concentrated in that monster engine.  However, things are not hopeless, I've successfully flown craft that are pretty similar to what you've just drawn.

One thing you can do that should help somewhat:  make sure you've disabled pitch and roll authority (especially roll!) on your tailfin.  Reason:  that tailfin is going to induce roll every time it controls for yaw, and if it has roll authority turned on, it's going to try to fight itself and will become much less useful for yaw authority.

Can you slide your tailfin any further aft?  That will increase its yaw authority (which you want) without increasing its (unwanted but unavoidable) roll authority.

You may want to consider replacing the inline cockpit with a regular Mk1 cockpit.  The nuke turbojet has its own built-in intake, and you don't actually need that shock cone intake at the front of the plane.  You certainly don't need those structural intakes on the sides.

The nuke turbojet will eventually overheat under sustained use.  What I did on my own plane that looked like that was to add a couple of the "edge" radiators, with mirror symmetry, on the back end of the plane, sticking up like tail fins (I put 'em on either side of the "real" tail fin).  Not only does that provide needed cooling, but they also act a bit like extra tail fins to help give yaw stability.

You may want to consider adding an RTG or two (side-mounted on the engine, with the axis parallel to the flight axis) for electrical supply.  You'll need radiators, and the radiators will draw electricity, and the nuke turbojet unfortunately does not have an alternator for providing electricity while in use.

 

 

[AlphaMensae]

Thanks, Snark, that was what I'm looking for.  Yeah, that engine is a beast, it must be throwing me off.

Didn't know the nuke has its own intake, thought that little turbine in front was just for looks, guess I misread the info.  While in-flight I noticed it was getting .1 less than required Intake ATM, so that's why I added the structural intakes.

Yup, I did disable pitch and roll on the tailfin (I remember THAT from Scott Manley  ).  I also only enabled pitch on the canard and roll on the elevevons, is that going too far.

I started with the regular delta wings, then switched to the Big-S Delta, thinking this plane needs much more lift.  Also switched from two to one tailfins, should I go back to two?.

While I don't plan on doing extended flights with this plane on Eve (just far enough to get to as many biomes as possible from the 60-100 degree longitude region), I'll put radiators and RTGs on it to be safe.  Don't want it unintentionally turning into a nuclear lightbulb.

 

[Snark]

18 minutes ago, Laguna said:

I also only enabled pitch on the canard and roll on the elevevons, is that going too far.

I'd suggest leaving pitch enabled on the canards and on the elevons.  It'll help your pitch stability a lot.

19 minutes ago, Laguna said:

I started with the regular delta wings, then switched to the Big-S Delta, thinking this plane needs much more lift.

Regular deltas are probably fine-- bear in mind that Eve has an extremely thick atmosphere.  That said, it's not like the Big-S are really hurting anything.  It's essentially a matter of how slow you want to be able to go on takeoff / landing.

20 minutes ago, Laguna said:

Also switched from two to one tailfins, should I go back to two?

Shouldn't be needed, I flew just fine with a single tailfin.  (I used the AV-R8 Winglet for mine.)

[AlphaMensae]

11 minutes ago, Snark said:

I'd suggest leaving pitch enabled on the canards and on the elevons.  It'll help your pitch stability a lot.

 

<slaps head> Stupid me, elevons=elevator+ailerons...that would explain the difficulty in trying to pull out of a five when the plane ended up going ground-ward.

[RocketSquid]

I think atomic age includes an example craft, see if you can reverse engineer it. Honestly, they have been really annoying for me, and I've never used them in a successful plane.

[Snark]

37 minutes ago, RocketSquid said:

I think atomic age includes an example craft, see if you can reverse engineer it. Honestly, they have been really annoying for me, and I've never used them in a successful plane.

In practice they're hard to use, because on Kerbin you don't really need 'em, and anywhere else, they're stupidly hard to get there.  There's no attachment node on the bottom of the thing, so any spacecraft that wants to loft one of these things to orbit and beyond ends up being some sort of hideous Rube Goldberg contraption.

Where I've found that they really come into their own is when paired with Extraplanetary Launchpads, which lets you mine metal and build your own ships off-planet.  Then it's great for exploring places with thick, non-oxygenated atmosphere.  I like sending a mission that lands on a planet with fairly minimal equipment (just enough to mine & refine fuel & metal, and the ability to build ships), and then builds its own base, exploration equipment, return vehicle, etc.  It's loads of fun.

In the stock game, Eve is about the only place where the nuke turbojet would be of any real use.  But with other planetary mods come other opportunities.  It's great for exploring Arkas, or for Sarnus' moon Tekto in Outer Planets, or Titanus in New Horizons.

Here's a design that I've flown successfully on several planets.

The example shown is on Tekto from Outer Planets, but I've flown essentially the same identical plane on other thick-atmosphere planets as well.  Rock-solid stable, flies like a charm, lands and takes off very easily.

Notable features:

• The tail fin is stuck as far to the rear as it can possibly go.  This gives it good yaw authority and helps reduce roll interference.  (That's probably the biggest single thing contributing to its aero stability.  I note that the OP's plane has the tail fin set quite a bit forward.  Move it farther back, and turn off its roll authority, and I expect it'll do a lot better.)
• The biplane design leaves the left and right sides of the nuke jet unobstructed.  That gives me a convenient place to stick on a pair of airbrakes (barely visible in this picture) and other paraphernalia such as RTGs, radial batteries, etc.
• Note the radiator fins, which keep the engine from overheating and help give some yaw stability.
• The lightweight Science Jr. is out in front of the heavy cockpit.  Normally, that would be a bad thing for aero stability (you want the heavy bits in front).  However, I found that I was having severe rigidity problems.  Putting the heavy cockpit up front meant that I had to put the canards up front, too, which generated too much bending torque at high AoA.  When this thing is slamming along at better than Mach 1 through 3 atmospheres or more of pressure, and I've got physics warp cranked up so that I can get where I'm going in a hurry... the aircraft was prone to suddenly (and without warning) stubbing its toe on the air, and bending almost 90 degrees in the middle!  Really annoying.  Doing it this way, I've got a nice solid joint between cockpit and engine, and the canards don't have to be so far forward, and I don't have any bending problems at all, even at very high-gee maneuvers.

("But Snark, that has an intake on the front, and you said that the nuke jet doesn't need a--"  Yes, I know what I said.  But putting the Science Jr. in front meant I couldn't use the pointy cockpit, and I had to put something on the front, and I thought this looked cooler than a nosecone.)

Edited January 30, 2016 by Snark

[AlphaMensae]

18 hours ago, RocketSquid said:

I think atomic age includes an example craft, see if you can reverse engineer it. Honestly, they have been really annoying for me, and I've never used them in a successful plane.

Yeah, there is an aircraft included (forgot the mod had sample craft), but it's a large 2-engined Mk2 cockpit beast...way too much for my Eve runabout.  It also has air intakes..and no radiators.

That's a real nice plane, Snark...might just, um, borrow some things from it.  But I did move the tailfin back, and now it flies pretty good.  I'll get it to Eve by puting a docking port on the bottom, carrying 2 into space radially-attached to a lifter, and then attaching them to my Eve ship, which will have matching ports on the sides.

[Snark]

16 minutes ago, Laguna said:

That's a real nice plane, Snark...might just, um, borrow some things from it.  But I did move the tailfin back, and now it flies pretty good.  I'll get it to Eve by puting a docking port on the bottom, carrying 2 into space radially-attached to a lifter, and then attaching them to my Eve ship, which will have matching ports on the sides.

Having two of 'em radially attached to a craft ought to work.  The main challenge will be atmospheric reentry from Eve orbit-- it's hard to come down on Eve without a heatshield.  I tried landing a plane like this on Eve from orbit without a heatshield, and really had a hard time.  That big ol' turbojet gives it so much mass that it generates a lot of heat while slowing down.  Even a super-gentle approach with a really high Pe and an AoA to try to make maximum use of lift, the dang thing kept exploding from overheat long before it shed most of its velocity.

So you may need some sort of heat-shielded contraption to get the plane through the worst of reentry-- be warned.

Edited January 30, 2016 by Snark

[AlphaMensae]

10 minutes ago, Snark said:

Having two of 'em radially attached to a craft ought to work.  The main challenge will be atmospheric reentry from Eve orbit-- it's hard to come down on Eve without a heatshield.  I tried landing a plane like this on Eve from orbit without a heatshield, and really had a hard time.  That big ol' turbojet gives it so much mass that it generates a lot of heat while slowing down.  Even a super-gentle approach with a really high Pe and an AoA to try to make maximum use of lift, the dang thing kept exploding from overheat long before it shed most of its velocity.

So you may need some sort of heat-shielded contraption to get the plane through the worst of reentry-- be warned.

Yup, I'll be adding an atmo-entry package to the plane, will have the heatshield, retro-engine, chutes, and possibly a fairing.

I've already done the radial-attach launch method with a now-abandoned super-rover design that was built around an orange tank; launched two of them at once into orbit just fine.  I do have KJR installed, that probably helps.

[Snark]

26 minutes ago, Laguna said:

Yup, I'll be adding an atmo-entry package to the plane, will have the heatshield, retro-engine, chutes, and possibly a fairing.

Heatshield & retro-engine, sure.  Parachutes, though, definitely don't need-- it's a plane, it can fly itself just fine once you get past the hot part of reentry.

Fairing would be ... bulky.

[AlphaMensae]

2 hours ago, Snark said:

Heatshield & retro-engine, sure.  Parachutes, though, definitely don't need-- it's a plane, it can fly itself just fine once you get past the hot part of reentry.

Fairing would be ... bulky.

Well, I do have the Space Y 5m fairings  (and the 7.5m ones in the Extended for 1.0.5).

Yeah, I was thinking of dropping the plane to the surface with chutes, as I wasn't sure if one could "launch" a plane while in the air and falling, but I guess you can.

[Snark]

1 hour ago, Laguna said:

Well, I do have the Space Y 5m fairings  (and the 7.5m ones in the Extended for 1.0.5).

Ah, that'd do it.

Have never used SpaceY, do they have big heatshields, too?  If there's a heatshield big enough for the whole plane to hide behind, then you don't need a fairing.

1 hour ago, Laguna said:

Yeah, I was thinking of dropping the plane to the surface with chutes, as I wasn't sure if one could "launch" a plane while in the air and falling, but I guess you can.

Yup.  A plane's a plane, doesn't matter which side of the sky it came from.  As long as the craft is aerodynamically stable, you can throw it at the air in pretty much any orientation and it will sort itself out pretty quickly.

[Geschosskopf]

On 1/30/2016 at 7:54 PM, Snark said:

In practice they're hard to use, because on Kerbin you don't really need 'em, and anywhere else, they're stupidly hard to get there.  There's no attachment node on the bottom of the thing, so any spacecraft that wants to loft one of these things to orbit and beyond ends up being some sort of hideous Rube Goldberg contraption.

I prefer the nuke turbojets in the Mk2 Expansion pack.  Not nearly as heavy but not as powerful, either.  And no attachment node on the rear.  Still, they have built-in radial intakes so you can just slap a Mk2 cockpit on the front and you're good.

Quote

• The tail fin is stuck as far to the rear as it can possibly go.  This gives it good yaw authority and helps reduce roll interference.  (That's probably the biggest single thing contributing to its aero stability.  I note that the OP's plane has the tail fin set quite a bit forward.  Move it farther back, and turn off its roll authority, and I expect it'll do a lot better.)

I prefer not to have rudders on the tailfin.  Instead, I have a fixed tail fin (or 2 if the docking port is on top of the fuselage).  For yaw control, I then use the small, square control surfaces out on the wingtips.  That way, the rudders are on the fuselage centerline so produce no unwanted roll.  Here is my Tekto SSTO showing this philosophy (actually using 4 rudders):

This has the Mk2 Extensions nuke turbojet in the middle and 2x Atomic Age LANTERN engines for space.  Due to the low gravity,  you don't need much wing at all on Tekto.

Now, getting this to Tekto was a poodle.  The only way I could figure was to send a pair of them mounted low as the tailfeathers of a bass-ackwards SSTO rocket lifter...

Edited January 31, 2016 by Geschosskopf

[Snark]

6 minutes ago, Geschosskopf said:

I prefer the nuke turbojets in the Mk2 Expansion pack.  Not nearly as heavy but not as powerful, either.

Ooo, interesting.  Hadn't heard of those, should go check 'em out.

8 minutes ago, Geschosskopf said:

and 2x Atomic Age LANTERN engines for space

Love those things.

8 minutes ago, Geschosskopf said:

Due to the low gravity,  you don't need much wing at all on Tekto.

Yeah, Tekto's a lot of fun.  Really pretty, too, and interesting terrain, and a nice sky with Sarnus hanging up there.  I just love Tekto, it's one of my favorite places to visit.  (That plane I pictured earlier can actually take off at about 8 m/s there!)

[Geschosskopf]

16 minutes ago, Snark said:

Ooo, interesting.  Hadn't heard of those, should go check 'em out.

They're powerful enough to fly a small plane at fairly low speed on Kerbin, but of course you have unlimited range.  Good for recovery-rescue missions if you don't mind only moving about 150m/s.  However, my Tekto SSTO doesn't fly at all on Kerbin (single stage to ocean not far off the beach).

16 minutes ago, Snark said:

Yeah, Tekto's a lot of fun.  Really pretty, too, and interesting terrain, and a nice sky with Sarnus hanging up there.  I just love Tekto, it's one of my favorite places to visit.  (That plane I pictured earlier can actually take off at about 8 m/s there!)

Agreed.  I really, really like the whole Sarnus system, especially Tekto.  I will never get the cloud mod that reduces visibility to near-zero there, it's just too pretty and fantastical.  But you know what else is cool?  Land on the leading surface near the equator on tide-locked Orvok or Hale, and just warp to watch the rings go by.  Both these moons oscillate above and below the plane of the rings so the light show is amazing

 

[Snark]

6 minutes ago, Geschosskopf said:

Agreed.  I really, really like the whole Sarnus system, especially Tekto.

+1 for Sarnus.  Just lovely, all of it.

8 minutes ago, Geschosskopf said:

But you know what else is cool?  Land on the leading surface near the equator on tide-locked Orvok or Hale, and just warp to watch the rings go by.  Both these moons oscillate above and below the plane of the rings so the light show is amazing

Yeah, I love doing that, too.

I realize that at this point we've totally hijacked the original topic of the post, but I gotta take a moment to put in a plug for Outer Planets.

There are very few mods that I say "this should be stock" about.  There are plenty of mods that I love, but "I like this" does not equal "this should be stock" (a point that most this-should-be-stock folks seem to miss).  However, this is one of the very, very few mods I would say "this should be stock" about.  It's incredibly well done, very professional, matches the style of the stock game (right down to the chatty science descriptions), adds cool new types of challenges without being gimmicky, and is just frickin' gorgeous.

And gives us somewhere new to go, which is something we haven't had in years.

If you're reading this, and you haven't tried this mod-- it's worth your while!

[AlphaMensae]

3 hours ago, Snark said:

Ah, that'd do it.

Have never used SpaceY, do they have big heatshields, too?  If there's a heatshield big enough for the whole plane to hide behind, then you don't need a fairing.

 

Yup, Space Y has a 5m heatshield, which I Tweakscaled up to use for my Eve lander tests (and worked better than a bunch of smaller ones, less parts too, so that's what I'll use).  I'll just stick one on, add the retro engine, and drop the thing after the lander into Eve.

[Edax]

On 1/30/2016 at 5:54 PM, Snark said:

In practice they're hard to use, because on Kerbin you don't really need 'em, and anywhere else, they're stupidly hard to get there.  There's no attachment node on the bottom of the thing, so any spacecraft that wants to loft one of these things to orbit and beyond ends up being some sort of hideous Rube Goldberg contraption.

 

In the stock game, Eve is about the only place where the nuke turbojet would be of any real use.  But with other planetary mods come other opportunities.  It's great for exploring Arkas, or for Sarnus' moon Tekto in Outer Planets, or Titanus in New Horizons.

 

So why isn't a nuclear turbojet effective on Duna, Jool, or Laythe?  

[fourfa]

Duna is a vacuum planet, as far as engines are concerned.  Rockets operate within a percent or so of their vacuum performance there - the nuke turbojet surely has trailed off to near uselessness already.  No need to look at anything except rockets.

Laythe has oxygen and works great with the huge and convenient (some would say OP) selection of air-breathing jets.  But flying around Kerbin and Laythe without fuel for years, no heavy/bulky ISRU gear - definitely space for interesting design.  

I can't comment on whether flying on Jool is possible.  Mainly there's nothing to do - no biomes, little science, nowhere to land, can just dip in and go back to space.  Nevertheless that's worth investigating for its own sake

Eve though - it's such a colossal P.I.T.A. to move around there, this opens up whole new worlds of gameplay

[Geschosskopf]

7 hours ago, Edax said:

So why isn't a nuclear turbojet effective on Duna, Jool, or Laythe?  

It's possible to actually fly a plane (as opposed to ballistically jumping around with rocket thrust) on Duna but the best powerplant is an electric prop running on fuel cells or some other form of lightweight resource-eating generator.  This is because Duna has such thin air that even a very light plane needs beaucoup wing so the sheer weight of the Atomic Age nuke jet make it pretty much a non-starter.  Also, the nuke jet needs air to run at all and there's not much of that on Duna.

Laythe is pretty much the same as Kerbin.  The thinner air is balanced by the lower gravity so a plane that flies on Kerbin will fly pretty much the same on Laythe, except it will have a lower operational ceiling due to Laythe's atmosphere not being as tall, and might not be able to land safely on ground several km about sea level  So, nuke jets on Kerbin are pretty much limited to low, slow flight.  Same on Laythe, but they're limited to even lower altitudes.  You can get around a lot easier with a regular jet so the only reason to use a nuke jet on Laythe is if you just don't want to bother with refueling.

As @fourfa said, there's not much reason to fly on Jool, mostly because there's nowhere to land.  And the nuke jet is too low-powered to regain orbit, and too heavy to be worth carrying by a Jool plane with rockets.  If you want to dip into Jool's atmosphere, use aerospikes or something that has high thrust in dense air.

Basically,nuke jets are only useful for exploring planets with thick, non-oxygen atmospheres and more and/or harsher terrain than you want to drive a rover on.  They need thick air to run very well and so that you can lift their heavy weight with a reasonable amount of wing.  So Eve in stock, Tekto if using OPM.  On Eve, a nuke jet is not a viable component of an SSTO due to the high gravity and too little thrust-to-weight.  They'll work as the jet part of an SSTO on Tekto, however, where the gravity is minute.

[Snark]

11 hours ago, Edax said:

So why isn't a nuclear turbojet effective on Duna, Jool, or Laythe?

Agree with what @fourfa and @Geschosskopf have said.  It's not a question of not being effective (it could be made to work in all of those places), just that it's some combination of being less necessary, more difficult to use, or less attractive than an alternative.

Duna has really thin air, so airplanes need to be super light and have lots of wing area.  The nuke jet is monstrously heavy, and on Duna would provide very little thrust (haven't tried it, but I'd guess you'd get no more than 20-25 kN out of it at best).  So it's very poorly suited for use there.  Also, there's less need for it:  Duna has a much lower gravity (and thinner atmosphere) than a place like Eve, and is relatively small, and doesn't have many biomes, so doing rocket-powered suborbital hops is fairly straightforward and you don't need a fuelless jet engine as much.

Jool, there's simply no need for the thing.  You're sure as heck not going to want to lift the turbojet back up to Jool orbit.  And there's nowhere to land.  And in any case, there's no point in "exploring" Jool, because there aren't any biomes and once you've seen one spot on Jool, you've seen them all.  And Jool's so far from Kerbin that it takes a lot of dV to ship stuff there.  If you're going down into the atmosphere to sample it for science, you'd be better off with something small and light that has rocket power (if you want to recover it), or unpowered with parachutes (if you don't).

Laythe has oxygen in the atmosphere, so you get a lot more bang for your buck if you just use a simple, lightweight Juno-powered plane for local exploration, or something with Whiplashes or Rapiers to get back to orbit.  Also, there's not a lot of long-range exploration to do on Laythe.  Come down on one big island, and you can get all of Laythe's biomes right there; there's never any reason to fly halfway around Laythe in atmosphere.  So the nuke jet would work just fine there, but it's not needed.

Edited January 31, 2016 by Snark