Tailkinker's RPG Site

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====== Air Propulsion ======

There are three ways of selecting your aerial propulsion system:  By desired top speed, by engine power, or by mass.

To determine your aircraft's required thrust, you will first need to determine its Drag.  This is easier than you might think:  Take the aircraft's total Area, and divide by an amount based on the Streamlining, as found in the table below.

^Streamlining  ^^
|None  |  1  |
|Mild  |  2  |
|Moderate  |  3  |
|Good  |  5  |
|Excellent  |  10  |

To find the thrust you need to meet your desired top speed, multiply the speed (in kph) by itself, then by your Drag.  Divide this by 7,000.  This gives you the thrust you need, in Newtons.

===== Airfoils =====

These are things that move, and push air behind them as a result.  Typically, propellors, ducted fans and helicopter rotors are built as small wings, relying on the Bernoulli effect to move air.  Ornithopters, on the other hand, flap the entire wing, producing thrust by doing so.

^  TR  ^Type         ^  Mass (kg)              ^  Power (kW)        ^  Cost (\[ce])  ^  Volume (m\[s3])  ^
|  -1  |Propellor    |  Thrust \[di] 16.5 + 8  |  1.5 \[mu] Thrust  |  Mass \[mu] 10  |  --               |
|   0  |Ducted Fan   |  Thrust \[di] 16.5 + 8  |  2 \[mu] Thrust    |  Mass \[mu] 10  |  Mass \[di] 150   |
|   0  |Helicopter   |  Thrust \[di] 6.5 + 8   |  5 \[mu] Thrust    |  Mass \[mu] 20  |  Mass \[di] 75    |
|   0  |Tilt Rotor   |  Thrust \[di] 4 + 12    |  5 \[mu] Thrust    |  Mass \[mu] 20  |  Mass \[di] 75    |
|  +1  |Ornithopter  |  Thrust \[di] 4 + 3.5   |  4 \[mu] Thrust    |  Mass \[mu] 45  |  Mass \[di] 75    |

Mass and Power are per Newton of thrust.  Helicopter blades and Tilt Rotors also produce 1kg of static lift per Newton.  However, a Tilt Rotor can switch to forward flight, trading off its static lift for a 50% increase in top speed.  Ornithopter wings generate 0.25kg of static lift per Newton.

===== Jet Engines =====

Hot air expands, so heating air to very high temperatures makes it expand a lot.  This is the core principal of the jet engine.

^  TR  ^Type               ^  Mass (kg)              ^  Fuel (l)          ^  Cost (\[ce])   ^  Afterburner  ^
|  -1  |Pulse Jet          |  Thrust \[di] 2 + 45    |  Thrust \[di] 150  |  Mass \[mu] 2   |       |
|  -1  |WWII Turbojet      |  Thrust \[di] 15 + 225  |  Thrust \[di] 120  |  Mass \[mu] 20  |       |
|  -1  |Cold War Turbojet  |  Thrust \[di] 30 + 70   |  Thrust \[di] 250  |  Mass \[mu] 20  |  Yes  |
|  -1  |Cold War Turbofan  |  Thrust \[di] 20 + 90   |  Thrust \[di] 400  |  Mass \[mu] 20  |  Yes  |
|  -1  |Ramjet             |  Thrust \[di] 45        |  Thrust \[di] 90   |  Mass \[mu] 40  |       |
|   0  |Turbo-Ramjet       |  Thrust \[di] 35 + 120  |  Thrust \[di] 250  |  Mass \[mu] 50  |  Yes  | 
|   0  |Modern Turbofan    |  Thrust \[di] 45 + 45   |  Thrust \[di] 750  |  Mass \[mu] 20  |  Yes  |
|  +1  |Hydrogen Turbofan  |  Thrust \[di] 45 + 25   |  Thrust \[di] 60   |  Mass \[mu] 20  |  Yes  |
|  +2  |Fusion Turbofan    |  Thrust \[di] 90 + 25   |  \[dg]             |  Mass \[mu] 40  |       |
\[dg]Fuel is not needed for the fusion turbofan, but burning reaction mass allows it to exceed its service ceiling

Fuel is in liters per hour.  Volume for all engines listed above, in cubic meters, is equal to their mass divided by 75.

==== Afterburner ====

Some jet engines can be fitted with an afterburner.  If you choose to fit a compatible engine with an afterburner, increase the mass by 10% and the cost by 50%.  While the afterburner is running, your vehicle's top speed is increased by 25%, but your engine drinks fuel //five times faster!//

==== Service Ceiling ====

Some of the jet engines in the table above might look sub-optimal.  In the case of the pulse jet, this is correct:  This is just an awful system, with its only benefit being its cost.  But in other cases, the tradeoff is service ceiling.  Beyond a certain altitude, there isn't enough air pressure or oxygen content to keep the engine running.

Of course, technology helps with this, and better engines allow for higher service ceilings.

^  TR  ^Type               ^  Service Ceiling  ^
|  -1  |Pulse Jet          |  1,000m           |
|  -1  |WWII Turbojet      |  15,000m          |
|  -1  |Cold War Turbojet  |  20,000m          |
|  -1  |Cold War Turbofan  |  18,000m          |
|  -1  |Ramjet             |  23,000m          |
|   0  |Turbo-Ramjet       |  26,000m          |
|   0  |Modern Turbofan    |  20,000m          |
|  +1  |Hydrogen Turbofan  |  25,000m          |
|  +2  |Fusion Turbofan    |  28,000m          |

=== Fusion Turbofans and Fuel ===

A fusion turbofan burns no fuel when below 28,000 meters, where there's sufficient air to use as reaction mass.  However, you can carry reaction mass for it, and just toss it into the heating chamber.  This will allow your fusion turbofan to exceed its service ceiling and travel into space, effectively becoming a fusion //rocket//.  When used in this mode, a fusion turbofan will burn water as though it were fuel, at a rate equal to its Thrust divided by 600.

===== Space Drives =====

If your vehicle is a spacecraft that is capable of operating in atmosphere, you may want to use your space drive as though it were an aircraft engine.  This is allowed, for certain types:  chemical fuel rockets, metal oxide rockets, fission and fusion rockets, and antimatter thermal rockets.

In such cases, you'll need to find your vehicle's maximum speed in atmosphere.  To find this, divide your Thrust by your Drag, and multiply by 7,000.  Then take the square root of the result.  Drop fractions, just to make your life easier.