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Automation Aero Challenge - Round Four Results Are Up!


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:

This is the Powerplant Calculator for Round Four (Google Sheets Version) or (Excel Version)

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.

##Technical Knowledge

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.

##Forced Induction
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.

##Flat-Rating Engines

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

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.

##Important Definitions

  • 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!

###Previous Rounds

Aero Challenge, Round One - Light Sport Aircraft, won by @koolkei

[Aero Challenge, Round Two - Four-Place Utility Single,] (Automation Aero Challenge - Round Four Results Are Up!) won jointly by @MrChips and @nialloftara

Aero Challenge, Round Three - Two-Place Basic Trainer, won by @Dragawn


#Current Challenge - 8-12 Place Executive Twin

This challenge, as selected by @Dragawn, will expand the boundaries of the Aero Challenge considerably, as this will be not only our first multi-engine aircraft, but also the first that turbocharging will be allowed as well:

Automation Aero Challenge - Round Four Design Brief PDF

##Submission Guidelines

  1. Please completely fill out a copy of the Aero Challenge Powerplant Calculator - FOUND HERE (Google Sheets Version) or FOUND HERE (Excel Version) - and download a PDF or save a screenshot of it…I need this information in order for my flight model to work!

  2. Once you are satisfied with your engine, use the Export function in Automation to export your engine family and variant files, then send the ZIP file along with the PDF or screenshot of your Powerplant Calculator results to me via PM. The submission deadline for this contest is 2359 GMT on Monday, May 15th (7:59 PM Eastern Time, 0059 CET on Tuesday, May 16th).

Please submit your entries named as follows:

Engine Family Name: “AAC R4 (Your Username)”
Engine Variant Name: Your Choice
Good luck to everyone!


Very interesting challenge. I can’t see any glaring issues, and it’s something a little bit different.


Looks very interesting indeed, need to start getting some practice in on engines then.


VERY interesting…

i need to try this. after the csr reviews


#Round 1 - Light Sport Aircraft

Since this is the first round of the Aero Challenge, let’s start off nice and simple, with a, err, nice and simple aircraft. The design brief is as follows:

Automation Aero Challenge - Round One Design Brief PDF

##Submission Guidelines

  1. Please completely fill out a copy of the Aero Challenge Powerplant Calculator - FOUND HERE - and download a PDF or save a screenshot of it…I need this information in order for my flight model to work!

  2. Once you are satisfied with your engine, use the Export function in Automation to export your engine family and variant files, then send the ZIP file along with the PDF or screenshot of your Powerplant Calculator results to me via PM. The submission deadline for this contest is 2359 GMT on Monday, September 5th (7:59 PM Eastern Time, 0059 CET on Tuesday, September 6th).

Please submit your entries named as follows:

  • Engine Family Name: “AAC R1 (Your Username)”
  • Engine Variant Name: Your Choice

Good luck to everyone!


is the desired propeller length a dead set rule? can’t be slightly longer or shorter?


I should have probably been more clear; the maximum length is 66 inches. If you want shorter, that’s fine.


oh. i think you made a slight mistake in the pound to kg conversion calculation.
the one on the right i think should be =F10*2.205 not /2.205

and the desired engine power is the pure engine power or the flat rated power?

and the VisualFlightRange Range is the max fuel load divided by our engine economy then divided again by 2? or how is that calculated?


The error in the calculator is fixed, chalk it up to throwing in the unit converter as an afterthought :stuck_out_tongue:

Now to answer your more serious questions - first, the “desired engine power range” in the design brief is the suggested power range at the propeller; it is the power after any flat-rating at the gearbox. So for example, if your engine produces 105 horsepower according to Automation, and you specify a 100-horsepower reduction gearbox, the power at the propeller will be 100 horsepower, which happens to fall into the desired engine power range.

For the second question, VFR range is calculated in three steps. First step is to figure out how much fuel remains for cruise after takeoff, climb to optimal altitude, descent and landing, plus an additional 45 minutes of flight at the optimal altitude at 75% power. This number, is divided by the fuel burn of the aircraft at cruise, which is at that 75% power mentioned before (it could be lower than 75% power depending on the altitude, but never more). Finally, this is divided by the cruise speed to get the distance traveled at cruise, which is then added to the distance spent climb and descending to cruise altitude to get the aircraft’s total range. Here’s a visual representation that I hope is a little clearer:

Hope this helps a bit!


What is “Static Thrust” and “Required Power” and how does it affect us?

I’ve been tuning the reduction ratio so that the required power matches my flat rate as closely as possible.


Required power is the amount of power needed to turn that particular propeller at the RPM the results from the engine redline and the gearbox. It is strongly advised you tune your gearboxes/props to match your power, otherwise you will will waste a good portion of your total output.

Static thrust is there more for my purposes. :slight_smile:


What is the deadline for entries?


2359 GMT on Monday, September 5th (or, 7:59 pm Eastern Time, 0059 CET Tuesday, September 6th). :slight_smile:


I just went through rules and I must say I love a concept of a competition where I learn something new. I will need some time and maybe couple of rounds to fully understand what should I actually do :slight_smile: but it looks impressive and I’m in!


Tad confused here. Forgive me for possibly not reading the rules corrently :wink:

1): “Engine RPM” - Do you just want us to put the max rpm/redline?
2): “Reduction Ratio” - What does this mean?
3): “Planned Speed” - I assume this is just the speed we except our aircraft to achieve?


Reduction Ratio is just gearing (Engine RPM : Propeller RPM)

But also, what do I do with “Required Power”? Should I match it with the Flat-Rated power? What happens if it’s higher/lower?


Max RPM is your call, whether it’s the engine redline, or where you produce maximum power; my advice is that I recommend tuning the engine to make maximum power at the redline, as unlike in an auto engine, there is no benefit to going past peak power in the rev range.

@FrankNSTein is correct; Reduction Ratio is just the ratio between engine RPM and Propeller RPM. Large reduction ratios increase the weight and cost of the reduction gearbox - dramatically, as you’ve no doubt noticed - and also lower the calculated Time Between Overhaul (TBO) of the powerplant.

Planned speed is just the speed you expect the aircraft to operate at; for this challenge, there is a maximum speed (120 knots) that this aircraft is allowed to fly for certification purposes. In later challenges, I will give a range of speeds that would make the challenge aircraft competitive with its real-world counterparts.

I should also say this; adjusting the Planned Speed, as you’ve no doubt noticed, has a direct effect on the propeller pitch value. By lowering your Planned Speed, the propeller pitch value will decrease (for a propeller of a given size), which will increase takeoff and climb performance, but at the expense of cruise speed. The opposite is also true; if you increase planned speed, you will gain cruise speed, but you will do so at the expense of takeoff and climb performance.

Required Power tells you approximately how much power your aircraft will need to reach your Planned Speed. If the Required Power is greater than your engine’s output, it means your propeller is oversized for your application, which means your powerplant will lose some efficiency over the entire operational range. Try reducing the diameter or the Planned Speed values, or increasing your Reduction Ratio.

Conversely, if your Required Power is less than your engine’s output, it means your propeller is undersized for your application, and means you are making more power than you can use - also not ideal. Try increasing propeller diameter or Planned Speed, or reducing the Reduction Ratio (unless you’re already butting against the tip speed limitations).

A small overage or underage from the Required Power isn’t a big deal; as long as you’re within a few percent either way it should be fine, but ideally you want to match Required Power with engine power as closely as possible.


How do we go about choosing the best propeller material?


for this round. i think you can rule out metal. it’s expensive and heavy, and too overpowered for the needs. it’s either the cheaper wood, or the lighter composite. i have to suspect this will come into play in later rounds where we need to make an engine for a super fast plane.

now, i’m confused what’s the difference between propeller pitch, the diameter, and what is advance ratio?

i googled it. too much for my brain to handle, but i get the feeling that you want it to be as close to 1 as possible for maximum efficiency?