Introduction
I have been lurking in the element14 space for many months now. I am always amazed at the interesting projects and wealth of information being shared. I am humbled to have been chosen to give back to the community that has given so much. For the sake of the "Smarter Spaces Design Challenge", I am a private pilot and member of a flying club whereby a group of roughly 50 individuals share ownership of a fleet of 4 airplanes. What follows is the submission for my "Smarter Spaces: Hangar Control System".
Overview
A system is needed to control pre-heating of a fleet airplanes operated by a large number of pilots. Airplanes are kept in unheated hangars which means that the engines quickly cool to the ambient temperature. Prior to use, pilots are required to preheat the aircraft engine. The preheating cycle can take up to 2-hours. Pilots do not live close enough to the airport to conveniently turn on the heater at the appropriate time, nor are there operations staff to initiate the preheat cycle. Thus, a method to remotely operate the heaters is needed.
Necessity of the System
(This portion represents a summary from The Whys and Hows of Preheating, Mike Busch. http://www.avweb.com/news/maint/182846-1.html)
Airplane engines are, by their very nature, strong and durable machines. At the same time, they are very sensitive devices that must be operated carefully to avoid catastrophic results. Of major concern to the aircraft engine are the startup conditions. After shutdown, the oil settles to the bottom of the engine seeping away from critical parts and, more importantly, the various components that make up the engine begin to contract. Aircraft engines are made of dissimilar metals: The crankcase, pistons and cylinder heads are aluminum; the crankshaft, camshaft, connecting rods and cylinder barrels are made from steel. When heated, aluminum expands about twice as much as steel. Likewise, when cooled, aluminum contracts about twice as much as steel.
Consider a steel crankshaft, which is suspended by thin bearing shells supported by a cast aluminum crankcase. As the engine gets colder, all of its parts shrink in size, but the aluminum case shrinks twice as much as the steel crankshaft running through it. The result is that the colder the temperature, the smaller the clearance between the bearing shells and the crankshaft. That clearance is where the oil goes to lubricate the bearings and prevent metal-to-metal contact.
How significant is this problem? Take the Teledyne Continental Motors (TCM) IO-520-series engines used in many general aviation singles and twins, for example. The IO-520 overhaul manual lists the minimum crankshaft bearing clearance as 0.0018 inch (that's 1.8 thousandths) at normal room temperature. What happens to that clearance when you start cooling the engine down? TCM doesn't say, but tests performed by Tanis Aircraft Services in Glenwood, Minn. indicated that an IO-520 loses 0.002 inch (2.0 thousandths) of crankshaft bearing clearance at -20°F. An engine built to TCM's minimum specified bearing fit at room temperature would actually have negative bearing clearance at -20°F. In other words, the crankshaft would be seized tight!
Why not leave the heater on all of the time? There has been considerable controversy about whether or not it's a good idea to leave an electric preheating system plugged in continuously when the airplane isn't flying. Our first concern is one of utility costs. Second, both TCM and Shell have published warnings against leaving engine-mounted electric preheaters on for more than 24 hours prior to flight. I am not here to solve a debate that has been raging for as many years as there have been planes operating in below freezing environments. Let’s just accept that continuous heating is not desirable.
Current System in Use
Through a clever use of cell phones and relay switches, each hangar has its own phone number. Two hours before flight, the pilot places a call to the “hangar’s cell phone” to activate the engine heater. This system is elegant in its simplicity. Unfortunately, it has been plagued by unforeseen issues: Most seriously being that “non-contract” phones are purchased each winter which results in new phone numbers being assigned. With the new phone numbers come all of the former callers of that phone number who are still dialing it. Each wrong call results in a 2-hour preheat cycle. During a recent month, the heater operated 24-hours per day for 30 days!
Proposed System
Create an intelligent control that provides a convenient and cost effective means for pilots to preheat the aircraft engines. Some key considerations are:
- Universally accessible interfaces: web, SMS, and phone
- The hangars do not have internet access.
- The individual hangars do not have access to adjacent hangars which eliminates running cables to each hangar.
- Initial and recurring costs are a primary concern.
- Client side will use jQuery Mobile to implement a single web-client application across the desired devices.
- The SMS and IVR components will use Twilio as the front end.
- Turn on/off engine heater. Due to energy requirements, GPIO connected to a 20/30-amp SSR will perform the actual load switching.
- Turn on/off cabin heater. Use GPIO pin connected to suitable relay.
- Provide temperature conditions of engine compartment. This feedback would provide the pilot with knowledge that the engine has come to a safe starting temperature. In addition, it would allow for the regulation of preheating by cycling the heater to maintain the desired preheat temperature.
- Provide temperature conditions of cabin. In addition, provide for the regulation of cabin temperature by cycling heater.
User Interfaces
To satisfy the desires and technical prowess of all the pilots, the proposed system shall be available using a variety of media: web browser supporting all of desktops, tablets, and smart phones; SMS or text messaging; and, IVR or telephone “interactive voice response”.
- The web server will be written in Python with Flask as the framework.
- Client side will use jQuery Mobile to implement a single web-client application across the desired devices.
- The SMS and IVR components will use Twilio as the front end.
- Turn on/off engine heater. Due to energy requirements, GPIO connected to a 20/30-amp SSR will perform the actual load switching.
- Turn on/off cabin heater. Use GPIO pin connected to suitable relay.
- Provide temperature conditions of engine compartment. This feedback would provide the pilot with knowledge that the engine has come to a safe starting temperature. In addition, it would allow for the regulation of preheating by cycling the heater to maintain the desired preheat temperature.
- Provide temperature conditions of cabin. In addition, provide for the regulation of cabin temperature by cycling heater.
Backend
A single Raspberry Pi 3 running Raspian implements a local area communication hub, Hangar Central. Communication is performed using WiFi or, should this project receive the “Challenger’s Kit”, an EnOcean Transceiver. The “Hangar Central” component maintains the current state of the available hangars and communicates with the other hangars in the network. Hangar Central also provides the single point of contact for the pilot interfaces and all security and authentication. While it is intended to be a “headless” device, the Raspberry Pi LCD Touchscreen included in the Challenger’s Kit would provide a compelling reason to include an “in-hangar” local status and control interface.
Each “Hangar Device” provides the current state of an individual hangar as well as an endpoint for controlling the available devices in that hangar.
Each hangar will have a hangar control device:
- Raspberry Pi used to communicate with Hangar Central.
- Turn on/off engine heater. Due to energy requirements, GPIO connected to a 20/30-amp SSR will perform the actual load switching.
- Turn on/off cabin heater. Use GPIO pin connected to suitable relay.
- Provide temperature conditions of engine compartment. This feedback would provide the pilot with knowledge that the engine has come to a safe starting temperature. In addition, it would allow for the regulation of preheating by cycling the heater to maintain the desired preheat temperature.
- Provide temperature conditions of cabin. In addition, provide for the regulation of cabin temperature by cycling heater.
Conclusion
I understand that this project may appear similar to products which are presently available. The differences lie in the target audience: existing products present a solution for individuals or small groups as evidenced in the “user management” and authentication components; also, existing products attempt to provide a “general use” power control with appeal across a wide variety of use cases.
In contrast, Hangar Control targets a large group of users with very similar usage needs. User management and authentication is based around the needs of a frequently changing population, while “hangar control” is tailored to the specific needs of environmental control and status for airplanes and their users.
“Hangar Control System” is arguably a “Smarter Spaces” project worthy of both inclusion in the 2016 element14 Design Challenge and sponsorship as represented by the Challenger's Kit.
Thank you for your consideration.
Sincerely,
Rick Havourd
Pilot
