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This is one of the areas where we are still considering our options. After flying VFR-only in the Grumman for several years, we decided an instrument rating (both for me and the Grumman) would increase the utility of our aircraft. The decision process involved in equipping our Grumman is as valid then as now. I flew for 20 years as a Boom Operator on the venerable USAF K(E)C-135(A,C,E,G, Q & R) Stratotanker. Although I wasn't a pilot, I sat right behind two for nearly 5000 hours and watched how they did (or didn't do) things. One thing I learned very early: even with two pilots (and Navigator, and Boom Operator) things get forgotten. How can four people all focused on flying an aircraft forget to accomplish a required task even if they each have a checklist? A very good question, Grasshopper, that's been asked for as long as people have been flying. On one memorable KC-135A mission early in my USAF career I came up front, after accomplishing my Descent Checklist in the back of the jet, to see the rest of the crew preparing for a crash landing, uh oh! For some unexplained reason the pilot couldn't arrest the descent even with the throttles at full-power. The pilot had a handful of aircraft nearing initial buffet (the plane vibrates and bounces as the airflow over parts of the wing goes turbulent just prior to a stall). He was trying to stop the descent, the copilot was busy declaring an emergency with ATC and the Nav was trying to find a soft spot to hit. Imagine everyone's surprise (and embarrassment) when I reached up and pushed the speed brake handle to 0º. I had single-handedly (literally) averted a fiery crash! Apparently the pilot had placed the speed brakes at 60° to meet a crossing restriction, and then simply forgot about them during the busy descent; and so did everyone else! (NOTE: Under certain operating conditions, the old KC-135 "A-model" didn't have enough thrust to maintain level flight with the speed brakes deployed.) Unfortunately, I traded my bragging rights (and surely a medal) for my Pilot's agreement to purchase dinner at a fine restaurant of my choice and a case of my favorite adult beverage. I know, stupid decision, but you gotta cut me some slack; I was living in the barracks, eating in a USAF chow hall and wasn't actually old enough to drink at the time! You gotta keep an eye on those crafty pilots...
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Accepting my personal failings (the only one of which I'm willing to admit to here is that I sometimes forget things) helped us make some equipment choices. Retractable landing gear for example. Some of you may be wondering why we've chosen the fixed gear version (Legacy FG, get it?) of this aircraft. Simply put, we're willing to give up the 20 - 25 knots we'll lose to reduce insurance costs, simplify building & maintenance and guarantee we'll never land with the gear up. BTW, 25 knots more airspeed shortens our 1000 nm by slightly more than 40 minutes. My peace of mind is worth an extra piddle pack! Remember K.I.S.S? This same philosophy carries over to all equipment selections. We will not be using a vacuum system; we'll be building an all-electric airplane. There have been so many accidents attributed to "vacuum system failure" (real or imagined) that the idea of installing a vacuum system in a "new" airplane seems almost ludicrous. For more information about all-electric systems visit the AeroElectric Connection and read this article. One system to power all accessory equipment in the plane, simple.
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Our avionics choices will also reflect the K.I.S.S principle. Whatever systems we choose should require the fewest number of steps for me to get the information I need when I need it. For example: a horizontal situation indicator (HSI) is a great situational awareness (SA) tool, but it requires so many steps to set up (set the right frequency in the nav radio, check the ident, select the correct nav source, check the nav flag, set the correct course, interpret the CDI and TO/FROM flag indications, did I forget anything?) it's almost overwhelming when you're in the soup. Contrast that set up with, say, a Garmin GNS-430. Tune the frequency, ident, then... look at the moving map, that's it! As an SA tool, the moving map is unbeatable. You never have to check the TO/FROM flag, never have to interpret a CDI, just look at the map. You'll instantly know where you are in relation to the airport or nav aid. The least amount of work to provide flight-critical, necessary info; that's what we want! Here's the latest list of equipment I believe we'll need:
* The interblower is the chamber between the turbocharger and the intercooler. Measuring the temperature of the the air charge in the interblower is an indirect measure of the turbine speed which should not exceed 135,000 RPM. * * Monitoring fuel temp is suggested by DeltaHawk. The fuel is warmed as it's pumped through the engine compartment. Fuel temperature shouldn't exceed 150º F (for obvious reasons). This may only be required during flight test as once a method of cooling the fuel is developed (if needed) it should operate full time and not require pilot intervention.
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There've been many exciting developments in the Electronic Flight Instrument Systems (EFIS) market for experimental aircraft. An EFIS utilizes a variety of sensor systems to consolidate data necessary to aircraft control and systems management on one or two dedicated displays. Multi-Function Displays (MFD), sometimes called Primary Flight Displays (PFD) if they are used as the sole attitude reference for instrument flight, contain all the data a pilot needs to fly the aircraft, navigate, and manage power, electrical and fuel systems. An EFIS can replace many instruments with one or two MFDs. Typical info displayed includes:
Most of this equipment isn't legal for use in certified aircraft (Chelton's is, but it costs 50 grand, yikes!) because manufacturers wish to: a) keep costs down (read about R & D and the FAA in the powerplant section if you missed it), b) limit liability, c) keep costs down, d) avoid having to deal with the FAA and e) keep costs down. Examples of PFD/MFD-based EFIS systems for experimental aircraft are the Blue Mountain Avionics EFIS and the Grand Rapids Technology (GRT) Horizon Series 1. Another EFIS-like system is Dynon Avionics EFIS-D10A. Although Dynon bills this instrument as an EFIS, it's really just a supercharged attitude/heading reference instrument (AHRS). The D10A doesn't incorporate any of the moving map/navigation capabilities normally associated with a true EFIS, although it does include an Angle of Attack indicator; a very nice feature that we definitely intend to install in the Legacy. Dynon's reduced price compared to the other offerings reflects the reduced capability. Dynon is working on upgrades to this system that'll include navigation and engine monitoring functions. Here are some pie-in-the-sky "artist's renderings" of an EFIS panel in a Legacy. These images were generated courtesy of Experimental Panel Builder online; a very cool site if you've never visited!
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Click to see a larger picture
GRT EFIS & Legacy Panel Dynon EFIS & Legacy Panel |
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My biggest concern for all these electronic systems is what happens when something breaks. Because all of your instrumentation is presented on one panel display with no (mechanical) moving parts, you've greatly increased reliability and mean time between failure (MTBF), but you've also placed all your eggs in one basket. When your display craps out you will have lost the only means of displaying flight-critical information to the pilot, unless you've installed backup mechanical instruments--so what's the point? Additionally, if your EFIS breaks will the company still be around? Will they still be making parts to support equipment that may be generations old by now (try to find parts for your 80386-based computer)? The thought of redesigning (and rewiring, reinstalling, etc.) a completely new flight, navigation and engine instrument system sometime down the road gives me sweats; I only want to do this once. Because of these concerns, I'm leaning towards sticking with equipment that's been around a while. Dynon's D10A might be a good AHRS around which to build the rest of the system, but I'd still include some backup flight instruments such as turn & bank, airspeed and altitude indicators. GRT makes a very capable engine monitoring system that has been in service for many years and (I predict) will continue to grow in popularity due to it's simplicity and durability. Another good feature of the GRT is the capability to display altitude and airspeed data; great backups. Add a good moving map approach-certified GPS integrated with an autopilot, and you'll have covered most of your navigation needs. Additionally, the autopilot will have it's own electronic attitude reference system adding yet another layer of redundancy for IFR operations.
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To replace the other capabilities of the EFIS, I'm seriously considering a PDA or Tablet PC-based Electronic Flight Bag (EFB). These devices can display charts, approach plates, flight planning information and performance data. Add a GPS receiver and your EFB becomes a moving map display. Linked to a satellite receiver such as XM WX Satellite Weather service and you have a legal aviation chart (IFR or VFR) showing your current position in relation to your flight plan and current weather; situation awareness galore!. Should the EFB decide to go TANGO UNIFORM you can still navigate with your GPS. If you've tracked the nearest VMC (you always do don't you) that's where you head if you can't continue the flight (thunderstorms, icing, etc.) without the weather info provided by the EFB. And the best thing about an EFB is when it breaks (or becomes obsolete) you don't have to redesign your instrument panel for a new piece of equipment. Additionally, you can use the EFB for all your flight planning before you go out to the plane. Some of the devices I've looked at are NAVAir and Anywhere Map products. I'm leaning more towards the tablet PC equipment as opposed to the PDA-based devices due mainly to screen size. The Casio MPC-701 is about the right tradeoff in overall size vs. display area for a small cockpit. There are many other companies just beginning to develop tablet PC equipment. As this technology matures we're sure to see some great products.
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A panel full of goodies and gadgets looks really cool, and it may even be functional once you learn which buttons to push when. But I think for our purposes, we'll stick with the basics for flight instrumentation. A modest electronic replacement for the attitude indicator such as the Dynon unit might be an option since it doesn't cost much more than an electric attitude indicator anyway. Fortunately, we're not starting on the panel until further into the project. We'll have more time to research and the manufacturers will have more time to mature. In the mean time, I think we'll use an EFB for the fancy stuff.
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