Automation Aero Challenge
Engines aren’t just for cars, you know - ever since the Wright brothers first flight in 1903, reciprocating engines have driven hundreds of thousands of aircraft around the world, big and small alike. From tiny powered parachutes to ocean-spanning airliners, reciprocating engines have efficiently and safely powered them all…and now, we can take the engines we have created in Automation and power a fictional aircraft with them!
I have created an Excel-based model that can (relatively) faithfully simulate the entire flight profile of an aircraft, from takeoff,climb, cruise, descent and landing, while giving consideration to both technical and legal requirements to complete a full flight. Working within the limitations of both my model and of Automation, it should be possible to simulate aircraft ranging from self-launching gliders to aircraft up to the equivalent of an 80-100 seat airliner!
##How the Challenge Works
Each round of the challenge will have a pre-set airframe. In each round, the aircraft’s basic specifications, construction year and desired mission will be provided, along with some information on aircraft of a similar size and mission. Your goal will be to build a powerplant combination, consisting of engine, reduction gearbox and propller, that is best suited to the aircraft and the mission desired. After an inspection by the aviation regulator (me!), your powerplant(s) will be attached to the aircraft and evaluated on the following categories:
- Time Between Overhaul (TBO)
- Takeoff Run
- Rate of Climb
- Range (NBAA IFR range or legal VFR range, depending on the aircraft)
- Cruise Speed
- Fuel Burn at Cruise Speed
- Service Ceiling (if applicable)
- Aircraft Payload at Maximum Fuel (a measure of the powerplant weight)
- Aircraft Unit Cost (powerplants and airframes combined)
Points will be awarded in each category, with the leading powerplant in each category being awarded 100 points, then each subsequent powerplant being awarded a number of points based on how close it scored to the leader. For example, if powerplant A has a TBO of 2000 hours to win the category, powerplant B has a TBO of 1800 hours and powerplant C has a TBO of 1000 hours, the points will be as follows:
- Powerplant A: 100 points;
- Powerplant B: 90 points;
- Powerplant C: 50 points.
The winner of the challenge will be the entrant who scores the most points over all the categories.
To enter the challenge, first read and understand the challenge at hand (!), then design an engine that you feel is appropriate. Second, use this Google Sheets spreadsheet:
Fill in the green boxes completely (with the exception of the unit calculator), like so:
Then send a copy of the completed sheet (either as a screenshot or as a PDF in a ZIP file) to submit with your engine family and variant files to me.
So, considering this is well outside the realm of what we’re used to seeing in most Automation challenges, there are some things we need to discuss in terms of the nuts and bolts of aircraft propulsion. First of all, let’s talk propellers.
The big spinny thing on the front of the aircraft, or engine nacelle in the case of a multi-engine aircraft, is what converts the rotation of the engine into the thrust needed to make the aircraft fly. Broadly speaking, there are two types of propellers used in aircraft:
Fixed-pitch propellers, where the blades are one piece with the propeller hub and are at a fixed angle (“pitch”), and
Constant-speed, in which the blades change their pitch using a system of governors, flyweights and either engine oil pressure or electric actuation to continuously vary the blade pitch at all times. With a fixed pitch propeller, the propeller will (almost) always turn at a speed selected by the pilot (or by the computer).
Think of it this way; a fixed-pitch propeller is like a bicycle with a single gear, while a constant-speed propeller is like an automobile CVT transmission (except that constant-speed propellers are excellent and extremely reliable). So why don’t all aircraft use constant-speed propellers? Because they are heavy, expensive (both in terms of initial cost but also ongoing maintenance as well) and are often overkill for certain applications. The trade-off, is that they are efficient at a wide range of speeds, unlike a fixed-pitch propeller:
Another thing to discuss is the difference between fine pitch and coarse pitch. With a fine pitch propeller, you have a propeller that takes a relatively small bite out of the air each time it goes through a rotation, just like a car in first gear…it’s great for takeoff and climb performance, but a fine-pitch propeller becomes a liability at cruise speed, as it runs into efficiency limitations beyond a certain speed.
On the other hand, a coarse-pitch propeller takes a rather large bite out of the air with each rotation. This makes it just like high gear in your car; great for going down the highway in, but not so great at setting off from a traffic light. A coarse-pitch propeller is very efficient at cruise speed, but it might leave an aircraft with poor takeoff performance and very low climb rate.
Turbocharging was invented for aircraft - quite literally. As an aircraft climbs higher into the air, the air becomes less dense, which starts robbing the engine of its power. At 10,000 feet (3048 metres) above sea level, a naturally-aspirated engine is only producing about 70% of its sea-level rated power, and it only gets worse from there. A turbocharged engine can produce its sea-level rated all the way up to altitude, and loses power at a less dramatic rate in comparison. Here’s an example, using a 250-horsepower naturally-aspirated engine and a 200-horsepower turbocharged engine, fed into my model:
While the turbocharged engine starts off making less power than the NA engine, by about 8000’ altitude (2350 metres) they pull even, and beyond that the smaller engine actually makes more power, out of a smaller, somewhat lighter package.
So, why aren’t turbocharged engines the norm in aircraft? Well, the same reason why they aren’t in cars; they are much more expensive, less reliable and require much more cooling, which in an aircraft becomes pure drag.
So if you’ve read this far, you’ve probably looked at the sample Powerplant Calculator form and wondered, "gee MrChips, what’s this “flat-rating” thing you mention? Well, flat-rating means you take an engine that can produce more power than you need, and artificially limit it by some means - in an aircraft, it could be an RPM limitation, a manifold pressure limitation (manifold pressure is a measure of the pressure in the intake manifold, and is often the primary means of setting engine power in an aircraft reciprocating engine) or whatnot. This also allows you to run a lighter, cheaper propeller and (in the case of this challenge) reduction gearbox. It also allows you to negate some of the advantage that a turbocharged engine has over a naturally aspirated engine, as your engine can now produce your power needs over a wider range of altitudes.
##Challenge General Rules, Formulae/Evaluation Criteria and Other Pertinent Info
For this challenge, there are relatively few general rules; the aircraft themselves combined with the laws of physics and aerodynamics make for what should be a fairly level playing field. Slight variations in power will be negated by the simple fact that it takes eight times the power to go twice as fast in an aircraft, and that’s even before you get into the weight penalties from their larger propeller and reduction gearbox, as well as the drag penalty from their increased cooling needs…to say nothing of the enormous cost penalty they will pay!
Therefore, the general rules are as following:
- No LUA or Powerplant Calculator editing whatsoever - these will be checked against my results;
- Engines are to run on 93 AKI (98 RON) leaded or unleaded fuel only, unless otherwise noted;
- No negative Quality Points sliders;
- Since aircraft have no emissions regulations, no catalytic converters; and
- All engines must use race intakes - air filtration is generally only necessary below a couple of thousand feet of altitude anyway and therefore does not really apply in the real world.
The formula for cost and weight calculation of engines, propellers and gearboxes are in the Powerplant Calculator, so I will not be going into those, and the equations used to build the flight model are widely available on the internet - and are heinously complicated to get working with one another…but trust me, they do work as advertised!
Flight profiles that the model uses are as such:
Note that in the IFR flight profile, the aircraft does in fact land at its destination airport; the alternate requirement is not flown, but calculated for in the aircraft’s range.
##Engine Cooling and Nacelle Design
In multi-engine aircraft, each engine is installed into a nacelle of the following design parameters:
Total engine nacelle drag in a multi-engine aircraft is calculated from these formulas. In a single-engine aircraft, there is no nacelle drag, as the nacelle is part of the fuselage; the only drag penalty that must be paid is that of the cooling system, which is calculated identically to a multi-engine aircraft.
Engines with fixed pitch propellers will have their cruise fuel burn determined by examination of the “curves” data in the engine variant LUA file to find the RPM level that is closest to 75% power. Constant-speed propeller equipped aircraft will have their rated power multiplied by 0.75, then multiplied by their overall specific fuel consumption.
Turbocharged engines will have their turbocharger stats imported to a reference engine to determine their maximum possible boost, which will allow the critical altitude (the altitude beyond which a turbocharged engine can no longer produce maximum power) to be determined.
- Airframe Basic Weight - The total weight of the airframe without any powerplants installed. Includes the weight of any nacelles (if required).
- Airframe Basic Cost - The total cost to manufacture the complete airframe, minus the cost of powerplants.
- Calibrated Airspeed - Airspeed uncorrected for air density changes; the airspeed that the aircraft “feels”, for lack of a better way of putting it. As air density drops with altitude, an aircraft travelling at a uniform calibrated will move faster over the ground the higher it flies (known as True Airspeed). At sea level and low speeds, Calibrated Airspeed and True Airspeed are equal. The “Planned Airspeed” section of the Powerplant Calculator uses Calibrated Airspeed.
- Crew Weight - Crew weight is the estimated weight of the aircrew required to operate a given aircraft. For the purposes of this challenge, each pilot will weigh 200 pounds (90.72 kilograms), and any required flight attendants will weigh 165 pounds (74.83 kilograms).
- Critical Altitude - In an aircraft engine, the critical altitude is the highest altitude at which the engine is capable of producing its sea-level rated power. In a naturally-aspirated engine, the critical altitude is zero, while in a forced-induction engine, it is well above sea level.
- Maximum Takeoff Weight - The maximum weight an aircraft is allowed for takeoff.
- Optimal Altitude - The cruising altitude at which an aircraft can travel the greatest distance; this includes the time, fuel and distance covered when climbing and descending, and as such may not be the altitude at which the aircraft flies fastest.
- Passengers - Self-loading, semi-sentient cargo that weighs an average of 195 pounds (88.44 kilograms) per unit. Rude, smells foul and complains about drink and inflight entertainment choices.
- Payload - The difference between an aircraft’s maximum takeoff weight and the combined total of the airframe basic weight, total powerplant weight, crew weight and fuel requirement for a given flight. In larger aircraft, payload at maximum fuel may be severely constrained.
- Service Ceiling - The altitude up to which an aircraft is capable of maintaining a sustained climb rate of 100 feet per minute, or the maximum altitude permitted due to structural reasons (such as pressurisation limitations).
- True Airspeed - Calibrated Airspeed corrected for air density, or, how fast the aircraft is travelling over the ground in zero-wind conditions. For a given Calibrated Airspeed, True Airspeed increases as an aircraft climbs in altitude.
With that, I feel as though I have established a baseline from which we can begin the challenge; if anyone has any questions, comments or concerns before the first challenge begins, please post them so I can do my best to answer them, or fix a potential problem!
[Aero Challenge, Round Two - Four-Place Utility Single,] (Automation Aero Challenge - Round Four Results Are Up!) won jointly by @MrChips and @nialloftara