Even though we know that BattleMechs aren't really 'alive', a number of the terms used to describe them do help to foster this impression. Mechs have 'skeletons', 'bones', and 'muscles'. They have a torso, arms, legs, and a head; many even have fists. (Okay, so chairs have arms and legs too ... but they can't punch or kick!) It seems that most anything man works (and regularly dies) with, man identifies with and BattleMechs are no exception. As a result, mechwarriors almost invariably name their vehicles, much as frontier colonists name their beasts of burden, and other men-at-arms name their tanks, planes, or ships.
Once we accept the notion that a Mech is alive, at least alive enough to identify with, then the analogy can be carried one step further. The fusion power plant, the engine, must certainly be the Mech's' heart', the vital source of energy that keeps the entire vehicle (and its mechwarrior-occu pant) ,alive and well'. Are all engines equally efficient?
Table #1 Maximum BattleMech Movement
10-ton 11 MP
15-ton 13 MP
20-ton 13 MP
25-ton 11 MP
30-ton 10MP
35-ton 8 MP
40-ton 8 MP
45-ton 8 MP
50-ton 7 MP
55-ton 6 MP
60-ton 6 MP
65-ton 6 MP
70-ton 5 MP
75-ton 5 MP
80-ton 5 MP
85-ton 4 MP
90-ton 4 MP
95-ton 4 MP
100-ton 4 MP
Do some engines perform their job better than others? Is there a way to evaluate the efficiency of a Mech engine? If so, what might it be? This technical essay examines these questions and the relative efficiency of all 79 of the standard BattleMech power plants.
How Big, How Fast?
According to the BattleMech Design section on page 37 of BattleTech Rules of Warfare, a particular BattleMech engine is selected based solely on the tonnage of that Mech multiplied by the desired 'walking' movement rate - generally described in increments of about ten kilometers per standard hour (or one hex per turn, in simulator terms). Thus, if someone designs a 70- ton Mech to travel at four hexes per turn, a VOX 280 engine will be needed.
When attempting to figure out engine efficiency, problems do arise. Are some models of Mech fusion engines Thirty First Century 'gas guzzlers'? The simulator rules don't say, seeming to imply that there is no significant difference. Apparently, kilometers per microgram of fusion-generated plasma is not used an an indication of the engine's ability to function efficiently. What about size? All engines seem to occupy the same six locations on the critical hits table, regardless of model. And as far as the mechwarrior is concerned, that's all that matters.
Engine reliability? Again, nothing much is said. Published accounts appearing in various BattleTech Technical Readout manuals and in BattleTechnology's own 'Technical Readout' feature often give off-the-cuff reports on the suitability of a specific engine in a particular Mech or vehicle. However, two descriptions of the same engine used in two different vehicles will often appear contradictory, as these reports probably only apply to their respective vehicles. In short, there is insufficient data. That only leaves us with one other unique identifying factor for determining efficiency: engine tonnage.
Most BattleMech engines weigh different amounts; the greater the rating, the heavier the engine. Some, like the Omni 10, are very light (0.5 tons), while the mammoth LTV 400 weighs more than many Mechs (52.5 tons). Although a Pitban 20 does weigh exactly the same as an Omni 10, it is worth noting that a VOX 280 doesn't weigh exactly the same, or even twice, what a Hermes 140 weighs; it actually weighs almost three times as much! The scale is clearly not a simple rating-to-engine tonnage proportion. If it were, then by this standard all engines would be identically efficient, and there would be no question.
But the weight of the engine isn't the only thing to take into consideration. Engines also require a gyro, and the gyro's tonnage is based, in turn, on the rating of the engine. This must be figured in, remembering that every ton of capacity taken up by the engine and its accompanying gyro is one fewer tons available for other things, such as weapons and heat sinks and armor. In fact, the engine is the single largest removable system carried aboard a Mech. That's why, when trying to enhance the firepower of a Mech design, the easiest single system to downrate is the engine (and gyro, if appropriate). For example, decreasing the movement by one from 40 kph to 30 kph (more or less) - will give a 100-ton BattleMech an 'extra' 34.5 tons of room for other hardware.
It is true that since Mechs of a certain size designed to travel at a certain speed absolutely require the use of a certain engine, it doesn't matter what that engine's efficiency is, if the Mech designer has no choice. Still, in the never-ending pursuit for THE ultimate BattleMech, it may be nice to know if one particular combination is unusually wasteful of overall tonnage.
BattleMech Top Speeds
To find out exactly how many BattleMech-engine combinations were possible, it was necessary to find out the maximum speeds for each weight of Mech. This was done by calculating the largest engine-and-gyro system that would fit into each size of Mech. Certain components, such as internal structure and cockpit, are mandatory on all Mechs, regardless of speed, and so their weight was subtracted first. A minimum of 0.5 tons of armor was assumed for each Mech, though no weapon systems were figured in.
After making all necessary calculations, the following maximum movement limits were determined (see Table # 1). Few lightly-armored, unarmed BattleMechs will ever be designed for the sole purpose of travelling at their speed limits, though it is theoretically possible that a very rare unarmored Mech design or two may actually exceed the limit stated here for its tonnage.
Rating the Engines
After calculating the size of every engine that could fit into every tonnage of Mech, ranging from minimum to maximum movement, it was time to create an 'Engine Efficiency Rating'. Only the tonnage-efficiency of the engine is being judged. A lightweight engine that produces as much power as its heavier counterpart will thus receive a higher rating. The rating itself was calculated by adding the sum of the tonnage of each engine and necessary gyro, dividing the engine's rating by that sum, then multiplying the result by 4, rounding down to the nearest tenth. By coincidence, this gave the most efficient engines a rating of 100, with all other engines receiving proportionately lower values.
I do not mean to imply that any engine with a rating of 100 has 100% efficiency. (It seems doubtful that engineers will ever develop the 100% efficient engine; this quest for the ultimate machine still exists, even in the 31st century.) Instead, the engine rating is a yardstick by which engines of different sizes can be objectively compared. An engine with an 80 rating is twice as tonnage-efficient as an engine with a 40 rating, even though the engines may not be interchangeable between their respective Mech models.
Table # 2 contains a list of every BattleMech fusion engine, its weight, the weight of its gyro, the size of Mech that it can be fitted into, the movement that it will give such a Mech, and the engine's efficiency rating. This efficiency rating remains the same no matter what Mech the engine is installed in.
In some cases, there will be a notation in the table "no Mech uses". It means exactly that - there is no combination of Mech tonnage and movement allowance that would permit such an engine to be used, ever. (If anyone can find a genuinely good use for these misfit engine sizes, they ought to consider writing an article about it, and sending it to a technical journal such as this.)
Table # 3: 15 Most Efficient Engines in Use
Placement : Model : Rating
1 GM 75 100.00
1.(tie) Hermes 100 100.00
3. DAV 85 87.1
4. Leenex 60 96.0
5. Nissan 95 96.0
6. Omni 70 93.3
7. VOX 80 91.4
8. GM 45 90.0
8.(tie) DAV 90 90.0
10. VOX 55 88.0
11. Nissan 85 88.6
12. DAV 170 85.0
13. Mason 125 83.3
14. Magna 135 83.0
15. VOX 165 82.5
The Best of the Bunch
For the sake of convenience, the fifteen most efficient engines (by rating) appear in Table # 3. Only engines that actually can be used by some model of Mech are included in this table. (Who cares about efficiency if the engine doesn't fit anything?)
Even so, BattleMech designers should not let these findings drastically alter their own design philosophies. Individual models of BattleMech will require certain rates of movement based on their primary missions, and no 'efficiency rating' can alter that fundamental reality. Nevertheless, the numbers may be a helpful guideline; and if nothing else, it is now clear that the larger the engine, the less efficient it becomes. If the idea of a 400-rating engine seems on the awesome side, just think for a moment (but not too seriously) about a 450-rating engine - and the 150-ton BattleMech required to carry it! My best estimate is that such an engine would weigh between 95 and 100 tons, hardly worth having from an efficiency standpoint.
There is one other possible factor to keep in mind: the actual cost of the engine. But then, that too may be a suitable topic for a future article!
The Heart of a Mech: Tables (very slow: 328K)
Back to BattleTechnology 12 Table of Contents
Back to BattleTechnology List of Issues
Back to MagWeb Magazine List
© Copyright 1990 by Pacific Rim Publishing.
This article appears in MagWeb.com (Magazine Web) on the Internet World Wide Web.
Other military history articles and gaming articles are available at http://www.magweb.com