Drunkard's Walk Forums

In part inspired by the Jet/Rocket combination prototypes such as the NF-104 or the Saunders Roe SR.177. What happens if you stick a speed drive and an acceleration drive on the one spacecraft?

The way I figure it

1: The acceleration is additive on top of the speed drive. You rattle around, shudder a bit, and then bang, you're accelerating at some g north of .2 for as long as you have fuel in your boosters. It's not easy to control, and requires The Right Stuff to stop from going spinning through space out of control. When the drives cuts out, you rapidly drop back down to .2 (or thereabouts).

2: The acceleration drive merely reduces the power draw on the speed-drive, which finds it has an easier time of maintaining an absolute velocity for a bit.

3: Something else.

Storywise, why would you want to do this? Well.... because it makes for an interesting space craft. One that has a massive turn of speed.... but for a very short period of time. Who'se only really advantage is it's boosted speed. It's probably a pig to fly fast because of it.

And I always liked The Right Stuff....

Basically, my thoughts are something like:

Quote:JF-21
Basic airframe: Handwaved Mig-21bis
Engine: 1 speed drive(rating .18c). 2x acceleration drive boosters. Limited .19C
Armament: 1 20mm coilgun 2x underwing hardpoints.
Purpose: Point Defence Interceptor
Crew: 1 pilot.
Life Support: n/a
Primary User: 12 Colonies of Kobol. Various Belter Colonies.
Introduced : Prototype 2021

The name gives the original intent behind the JF-21 project. Jet Fighter, model 2021, recalling Automat Kalashnikov, model 1947. The aim was to creat a flying AK-47... a simple, fast space-fighter that could be built by anyone, and maintained by anyone. A fighter that would bring power to anyone cheaply. Rather than being produced for sale solely by the {{designer}}, the plans would be licensed cheaply, with the proviso that any constructed JF-21 should be able to swap parts with any other JF-21, regardless as to whether they were built by Rockhounds, Hepheastus, Scorpian yards, or on Backarsabeyond mining colony out in the main belt. In that regard, the project was a success.

Unlike it's assault-rifle inspiration, the 21 has never achieved widespread popularity. The spacecraft is difficult to handle at speed, and developed an ill reputation early in it's lifetime that it never quite succeeded in losing. The main users of the type are the 12 Colonies of Kobol, who appreciate the 21's lack of onboard computers beyond that bare minimum, lack of AI integration, and lack of any comm's beyond basic lightspeed radio. The raw speed is a secondary bonus to hotshot BattleStar Pilot's. Colonial manufactured 21's generally carry the nameplate Viper MkII, and differ from the prototype by mounting the refuelling probe on top of the nose, rather than underneath, and an added arrester hook for landings on a Battlestar.

------ more info.

Based on on airframe of a Mig-21bis purchased surplus from the Indian airforce, the JF-21 is astonishingly crude and simple for a Fen combat aircraft. It''s design emphasises absolute speed at the expense of maneuverability, or hard hitting armament. The aim was to create a cheap, lightweight and most of all simple point-defence interceptor that could chase down almost any other spacecraft short of the Magnificent Midnight. Anything unnecessary for going fast or fighting has been stripped from the craft... and two acceleration boosters have been fitted, mounted on the tip each wing.

The 21 has no onboard AI, or computer assistance to the controls. It has no interwave receiver and only a basic lightspeed radio as standard. It doesn't even have a life-support system, the pilot is either required to wear a pressure suit in the cockpit, or be an android not needing oxygen. The navigational computer and radar system are shared with the older F-EZig, with which the 21 also shares the same basic basic armament of a coilgun and 2 underwing hardpoints capable of mounting most standard missiles.

Most of the cockpit instruments are just modified versions of the originals, with the machmeter recalibrated so that it now reads in fractions of C, redlining at .19. The original radar screen was replaced with a simple TFT display that can switch between the spacecraft's navigational computer, or combat radar. Most everything else in the 21 is done through a combination of analogue gauges, chunky switches that thunk satisfyingly and indicator lights lit by incandescent bulbs.

Handwavium use was restricted to the airframe and the main engines. Everything else is either carried over from the original aircraft design to the point where a good few parts remain compatible, or has been newly built out of hardtech.

The 21's big trick is it's hybrid propulsion system, based on high-speed research craft. Already fast with it's speed drive, the acceleration drive boosters bring it up into the real high-speed class. The 21 is one of the fastest regular production spacecraft in Fenspace, although with only a few minute's endurance at top speed. However, rather than using complicated drive field control to adjust exhaust gas velocity, the 21 uses the simple expedient of mounting a pair of acceleration drives on the tips of each wing, and adjusting the speed-drive field so that both thrusters are just outside the field's effect.

This speed comes at the price of maneuverability and control. The 21 is slow to change direction at high speed and prone to snapping into a hard to recover tailspin if the Pilot applies too much control authority. Also, having the boosters outside the drive field stresses the wings a great deal, causing the tips to flex as the 21 increases speed. With the boosters burning, this flexing changes the angle of thrust of the engines slightly, upsetting the aircraft's controls and generating a strong vibration. There is a danger that if this continues unchecked, an engine could snap off, throwing the 21 into a high-g flat spin due to the differential drag and thrust. The second prototype was lost in just such an accident, however the Pilot was able to eject safely.

Because of this, a safety system is fitted to all production models cutting booster and engine power at .19c or if wing-flex exceeds certain limits. There have been no engine-loss accidents reported on 21's fitted with this system. Rumours fly of unrestricted 21's being tracked at much higher speeds....however, these rumours remain just that.

The 21 can be flown on just it's acceleration drive alone, with the speed drive off-line. They are usually ferried out to their customers this way.... firing the acceleration drive only, and coasting the rest of the distance to the destination. The speed drive is then only used for braking at the end. This allows the 21 to travel a great distance economically, even if it's far from the most luxurious way to get around. Ferry pilots often wear nappies in their pressure suits for a reason.

Tactically, the spacecraft is unsuited for a dogfight, having poor high speed maneuverability. Slower, more maneuverable spacecraft such as the TIE or even an old F-Ezig can easily defeat a 21 caught at low speed, the 21 looses speed too fast in low speed turns. The 21's big advantage is it's raw velocity and acceleration advantage, and pilots are encouraged to make high speed hit and run passes on targets, firing their missiles on one enemy and then escaping. As a point-defence aircraft defending against attackers, it excels... however for longer patrols or interceptions, the 21 risks running out of legs fast, unless it is refuelled inflight, or tied to a mothership.

The 21 has yet to appear in in common use, with only the 12 Colonies being a major user of the type, most factions prefer either almost-as-fast Ga-15's and TIE's or Thunderhawks if they need speed, and an F-EZig if they need something simple and reliable.

Attributes:
Missile with a Man in it: The JF-21 is best described as a big engine, a big booster, small wings, a pilot and not much else. It's fast as hell, but isn't even fitted with a life support system, never mind an onboard AI or even a flight control computer. The pilot is required to wear a pressure suit. Instrumentation is basic, simply a modified version of the original aircraft's analogue gauges. The radar system and navigational computer are taken directly from an F-Ezig, and aren't hooked into the craft's controls.

Analog girl in a digital world: The 21 lacks any sort of computer control system for an AI to interface with, the craft's controls are mechanical... stick inputs directly activating thrusters, or hydraulics actuating the Jet's aerodynamic controls. If an AI wants to pilot a 21, they must have a humanoid body.

Tough as Nails: Bigger than an F-Ezig, with a simple but robust construction, the 21 has an astonishing ability to absorb punishment and still limp home. There's very little to actually damage. Maintenance is simple enough, and many parts in the cockpit can be swapped straight with it's terrestrial cousin. New parts can be manufactured easily by any reasonably competent gadgeteer with access to basic machine tools. Or duct tape.

Short legged: The 21 only has a range of about 2AU on speed-drive power... though ferry range is unlimited through use of the acceleration drive.

Blazing arrow: The two boosters give an acceleration drive boost for about ten minutes, adding on top of the 21's current speed. While the boosters are burning the 21's maneuverability is severely restricted. A skilled pilot can adjust the vector slightly, but doing so risks throwing the spacecraft into a difficult to recover spin.

Quirks
Fishbeds Fishbeds, roly poly Fishbeds: The 21's maneuverability improves notably if the Pilot is listening to Fish Heads by Barnes and Barnes. However, though you can ask a fishbed anything you want to, they won't answer because they can't talk... the 21's radio system is disabled for the duration of the music. The pilot should also test SAN the longer it is playing.

The Right Stuff: Lacking any sort of AI assistance, the 21 is not an easy spacecraft to fly. The 21 will refuse to start it's engines for a pilot it feels is incapable of handling it's performance. It seems to prefer pilots who have previous flight or combat experience, though this is by no means a guarantee or requirement. Needless to say, some Fen who consider themselves hotshot pilots have gotten nasty surprises. The 21 is a very different animal when compared with an F-EZig or TIE.

Shake, rattle and roll: When approaching it's top speed, the 21 starts to shake like it's been driven over a rough road at high speed, threatening to get out of control. Instruments vibrate and blur becoming difficult to read. Panels clatter loudly in the cockpit and non-critical nuts and bolts will come lose and drop to the floor. Not normally dangerous... provided the pilot doesn't exacerbate the effects, but can be extremely distracting.

Screaming Demon: Sound may not travel in a vacuum... but somehow, people are still able to hear these things approaching on an attack run, passing with a sound often described as like a crack of a whip, mixed with a banshee's howl and a thunderous boom. They're even louder in an atmosphere.

You must Think in Russian: Most of the instrumentation is untranslated from the original Cryllic, except for a few notes here and there where it's absolutely important. What onboard computers there are default to Russian on startup, and must be changed each time. The setting never sticks. A cheat-sheet is usually provided, though it isn't always comprehensive. Pilot's seem to learn quickly what everything means anyway.

Actually, come to think of it... the speed boost can be negated if need be. The infinite cruise range coasting to your destination is handy enough on it's own for what is otherwise a lightweight, short legged, missile carrier. Even if it's not exactly comfy for the pilot in their flightsuit. Or hardsuit.

What do ye all think? Or would a hybrid drive do something else? Another possibility is the A-drive allowing the 21 to sneak up on a target emitting minimal power before lighting it's mains and surprising it.

EDIT: Made a few changes based on Cobalt's suggestions. Added a hard figure for the speed-drive. Still not sure who actually designed the thing originally.
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The effect of attaching a rocket to a car or boat or propeller plane with a 'waved-in-place propulsion system should be approximately equivalent to attaching a rocket to an unwaved car or boat or propeller plane, which I think would be a massive boost in acceleration for as long as the rocket burns, then a rapid deceleration to normal maximum speed as soon as the rocket cuts out (and probably severe damage to the normal drive train), which negates the inertial travel benefit of pure reaction drives.

The problem with combining Speed and Acceleration Drives is that the drive field affects everything inside it. Which means that the thrust from the Acc-Drive down-ramps upon leaving the field to the speed it was travelling relative to the ship it was mounted on. Even drives waved specifically for acceleration don't add much.

Thus, you have to push from outside the drive field. There's the simple way, and the mind-bogglingly complex way.

The simple way is best shown by how the Fenspace Speed Record is usually done. Take a Virgil Samms type ship, tweak the drive field to make it as tight to the skin as possible, then bolt on outriggers with acceleration drives such that the acc-drives are outside the ship's drive field. The main problem with this is the spars of the outriggers have to be really strong to take the stresses involved.

Still, the current Fenspace speed record is held by Hades Station's Research Team, after Eddie discovered that it was possible. They managed to get to a respectable 0.223c in empty space. Their next attempt used a gravitational slingshot around Jupiter and made a whopping 0.24c, but this method was disallowed.

The mid-bogglingly complex way is how the Woodsman UCAVs and Talons get their tremendous speed. By careful manipulation of the Speed Drive field (which requires far too much computer time for many people (sane or insane), and some frighteningly complex drive construction), it was possible to have the drive field end INSIDE the exhaust. Thus transferring the momentum of the thrust inside the field to the thrust outside it.

Yes, it was an effort for Eddie to do the calculations.

The extremely tight control of the drive field also grants higher manoeuvrability and better efficiencies in gravity wells. However, it led to engines as complex (if more reliable and actually able to be learnt by others) as Ben Rhodes' Waved Ion Engines (used by the Midnight and others).

Cobalt Greywalker Wrote:The problem with combining Speed and Acceleration Drives is that the drive field affects everything inside it. Which means that the thrust from the Acc-Drive down-ramps upon leaving the field to the speed it was travelling relative to the ship it was mounted on. Even drives waved specifically for acceleration don't add much.

Thus, you have to push from outside the drive field. There's the simple way, and the mind-bogglingly complex way.

The simple way is best shown by how the Fenspace Speed Record is usually done. Take a Virgil Samms type ship, tweak the drive field to make it as tight to the skin as possible, then bolt on outriggers with acceleration drives such that the acc-drives are outside the ship's drive field. The main problem with this is the spars of the outriggers have to be really strong to take the stresses involved.
Still, the current Fenspace speed record is held by Hades Station's Research Team, after Eddie discovered that it was possible. They managed to get to a respectable 0.223c in empty space. Their next attempt used a gravitational slingshot around Jupiter and made a whopping 0.24c, but this method was disallowed.

Actually.... that just gave me an idea. Take the same theory, then scale it up a bit. Most fencraft based on aircraft still have wings. Well, what are wings to a spacecraft but somewhere to mount something?

They're already going to be pretty strong after waving... they have to take the entire weight of the original aircraft as built along with combat maneuvering. So, instead of mounting the drives on the fuselage, mount them on the wingtips, with the drive field cutting off somewhere close to the engines. There is a precedent for this arrangement in aviation. However, it's not exactly condusive to being an easy to control spacecraft. A fault with one of the engines, or if one of them slips inside the drive field for whatever reason.... she's going to spin out in a big way.

Something like: http://i101.photobucket.com/albums/m57/ ... 13view.gif
Prototype, painted in blue and raw metal: http://i101.photobucket.com/albums/m57/ ... r-blue.jpg

So you got a big main engine... probably a fuel-hungry version of an ion drive, and then these two boosters outside the drive field. At high speeds, the interactions between the spacecraft and the edge of the drive field cause the juddering and shimmying and all round crappy handling. The wingtips are flexing, changing the thrust vectors ever so slightly.... A problem if you accidentally exacerbate the effect. And if you let it do it too long, you snap a wing off.

It's not intended to be nice to fly... or even safe.

EDIT: It wasn't my original intention... but putting those nacelles on the wings actually looks pretty cool.
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