Comparing and Contrasting: GRT and Dynon

[Ironflight]

As some people know, I have been flying with the dual-screen GRT Horizon 1 EFIS for a little more than two years (and 670 hours) in my RV-8. I was a fairly early adopter, and use it in IFR conditions whenever the need arises. When I started designing my panel, electronic flight displays were just beginning to become available, and my first iterations actually had a Dynon D10 as an ADI, along with an HSI and something like a VM1000 as an engine monitor. My first trip to Oshkosh gave me a chance to examine the four or five different EFIS systems available at the time, and I came away with the decision to go with GRT when I saw the sunlight readable displays and talked with the company founder and engineers. I have a good working knowledge of aerospace guidance and navigation systems, and liked what I saw in terms of design philosophy and robustness. This was clearly something that I could fly with! Coupled with the engine monitoring system that GRT had been building and selling for many years, I felt this was a great integrated solution that fit my requirements.

I have written a lot about flying the Valkyrie with the GRT systems, and have hopefully given people insights into just how flexible and informative it can be. This allows me to make maximum use of the airplane as a travel platform, as well as a local aerobatic machine with systems that I don?t have to worry about hurting despite g-loads and unusual attitudes. What I have resisted doing is commenting on how GRT compares to other available systems, because, quite frankly, I have not had enough experience (to this point) with any of the other systems to make a valid comparison. I could say that the GRT was GREAT ? but that didn?t mean that other systems weren?t as well. The recent project to upgrade Louise?s RV-6 that included a Dynon D10A and D180 has finally given me a chance to use these other systems enough to allow a valid comparison, so I thought that I would make a few comments that might help folks make their own decisions when choosing a glass cockpit option for their projects.

This is in no way intended to be a complete and final review with a firm recommendation as to which one I think anyone should buy! I would never be so presumptuous as to make that kind of recommendation to anyone ? there are too many variables in mission and means (what you intend to do with your panel, and how much you can afford to spend) for that to be useful. I have told people that comparing two different EFIS?s can be like comparing apples to oranges ? especially when you consider that some folks like apples, and some folks like oranges! There is no single right answer. But I can make some comparisons in a few areas that are important to me. I?ll say up front that I would choose the GRT again for my purposes. I also understand and stand by Louise?s (and my) decision to use Dynon in the -6. Having two planes that can be used as required allows us to optimize each one differently.

Once people have chosen to go with glass for their panel, the decision on which system to buy can and will be made on many different factors, some of which are inter-related. Sometimes, a particular factor (such as cost) will drive a person?s decision. In other cases, they can be equally weighted in terms of mission requirements. It is important to be honest about both your resources and your mission requirements before getting into the game. In general, we all have to compromise on requirements to fit things into a budget. Among the many ways to compare EFIS?s, are:

Features (what can it do?)
Reliability (How likely is it to continue doing it?)
Cost (What?s your budget?)
Company Stability (How long have they been around ? will they stay around?)
Maturity (How many units are in the field, and for how long?)
Robustness (both hardware and software)
Upgradability (can the system grow? What will new software features cost?)
Will it fit? (Does it work in your panel?)
Compatibility (Will it work with other systems/radios/GPS?s?)

[Ironflight]

Comparing cost can be tricky, because the systems have to be truly comparable. It?s easy to price a D180 with full engine sensors and compare that to a GRT Sport, with engine sensors ? you?ll find the Dynon to be cheaper ? but it doesn?t have the moving map capability that the GRT offers. Add in a GPS (to the Dynon panel) that will give you a moving map, and the prices come much closer. I?m not really going to say much more about cost because frankly, everyone can go out and crunch their own numbers. But to be fair, you have to start with a list of features, and then make sure that you include equipment to cover all those features if you want the results to be valid. Another thing to remember is that if you are building an airplane with a glass cockpit, the difference between systems might be a couple thousand dollars ? and that is a pretty small fraction of the overall finished aircraft cost. If you save $500 - $1000 and settle for less features than you want, you will probably be disappointed once you?re flying.

[Ironflight]

OK, this is going to be subjective because quite frankly, reliability is better measured statistically rather than anecdotally, and a few units does not qualify as a statistical sample, but I can relate my experiences. My GRT units have very low serial numbers, yet they all powered up from the very start and ?burned in? during the build process for hundreds of hours in the workshop. After a month or two of occasional power-on testing, I experienced a slow ?roll-off? of the attitude, and called GRT. Within minutes, I was talking to Greg, the designer, and he asked me to ship the unit right back at his expense. The next day, I heard back that I had a unit with gyros from their original supplier which he was no longer using. The unit was repaired and sent back within a couple days, my building was never slowed down, and I have not had a single problem with the hardware ever since. I have had one time that I had to reload software due to my own mistake ? I let the unit go down ?dirty? by leaving the battery on, and had to load software from a thumb drive (I did this while taxiing to the runway). All software upgrades have installed as advertised and I have not experienced any bugs.

The Dynons had a few growing pains, all of which have been dealt with quickly by Dynon. Louise had to send the original D-10A back twice in the two years that she had it, once for a heading problem and the second time for a failed (dark) display. After building up the new panel with the new D180 and old D10A, we had a display board failure of the original D180 during a software upgrade. Dynon sent us a new one overnight, and let us return the dead one at our convenience. During troubleshooting to figure out why the DSAB (Dynon Systems Avionics Bus) wasn?t working, the D10A locked up hard, and they sent us a refurbished unit under the same arrangement. Then they sent us a new PAIR of units to further troubleshoot the DSAB problem, which turned out to be a floating socket in a connector in the harness. So we?ve had more trouble with the Dynons, but Dynon had been quick to address them.

Overall, based on this very limited experience, I have a lot more faith in my GRT?s than I do in the Dynons. However, the pair of Dynons give us two attitude platforms, so it is unlikely that they would both fail at the same time, unless there was a common software issue. Nevertheless, based on my experience so far, I have to say that I feel better with the GRT?s.

[Ironflight]

To me, the heart of any EFIS is the Attitude Heading Reference System and Air Data Computer. Different companies have different acronyms for their systems, and GRT uses AHRS for theirs, but the bottom line is that what I see on the display (in terms of fancy graphics and cool features) is inconsequential if I can?t trust the navigation base to be stable, accurate, and reliable. The have been many threads on the VAF forums discussing how the various systems use airspeed for aiding the Nav solution ? Dynon uses airspeed, GRT doesn?t (as best I can tell). The GRT has never given me a bad in-flight solution. I had a chance to look at the Dynon in flight without the airspeed (I screwed up the connections on the first flight, and it had no pitot) and was able to see it have significant lag in both pitch and roll. But when hooked up properly, It appears to be stable and tumble-free, based on some limited aerobatics. I have talked at length with Greg of GRT about their AHRS software and hardware design, and am comfortable that it uses proven, state-of-the-art concepts and is reliable and robust. I can?t comment on the Dynon?s design, as I am not familiar with it, but then again, we have two of them. I actually have found it a little disturbing to have two different Air Data computers in the two Dynons ? while the attitude displays always seem to agree, it it hard to get the two altimeters to match ? and harder still to keep them matched. My GRT and standby altimeter match perfectly to 20,000? when I have the IFR cert performed ? I am not sure how well the Dynons will do yet. Remember the old saying about redundancy ? the man with two watches never knows for sure what time it is. The GRt does a great deal of internal checking on itself, and the software design is fairly sophisticated to make this happen

[Ironflight]

There is no doubt that one of the advantages that the GRT Horizon 1 has over the Dynon is that it?s moving map gives it the capability to truly integrate piloting/cockpit tasks. Whereas the Dynon gives you traditional cockpit information in an electronic format, the GRT takes that information, combines it in a way that multiplies its usefulness, and adds the capability to use the multiplied data for control. That?s a lot of stuff in one sentence, so let me explain. The Dynon has a good PFD layout, giving the traditional horizon, compass, airspeed, altitude, etc. It also has a nice HSI layout which can be driven by GPS or VHF Nav data. And of course, it has engine and fuel monitoring information. Coupled to a GPS it can give you more useful information on fuel state, such as miles per gallon, and fuel at the next waypoint. This is vastly superior to flying with traditional instruments and having to rely on off-line computations to tell you how the fuel will hold out. Now jump ahead to the GRT, which includes a moving map and database. With a flight plan in the system, or supplied from a GPS, it can tell you the expected fuel at all the waypoints on the route ? at a glance. When you bring up the HSI, it not only gives the familiar needles and pointers, but overlays this information on the IFR map, so that you see the locations of waypoints, intersections, and runways. Navigation is a no-brainer when flying an approach ? it is clear where you are at all times. The GRT also allows you to run multiple GPS sources, and to have simultaneous (and different) internal and external flight plans, so that you can be running one and ?what-iffing? with the other.

In addition to integrating the navigation picture into the equation, the GRT also integrates the autopilot into the system. You can control the autopilot from the EFIS Screen, either coupling it to the internal or external flight plan, or to the heading pointer on the moving map. This means that you can ALWAYS use the EFIS to control the autopilot, and don?t have to look elsewhere for information, then translate it to the A/P The Dynon (at least at this point) don?t have anything to do with the autopilot, but since they don?t really have any significant navigation data, this really isn?t to be expected. The GRT also gives you a full terrain database which allows for terrain warnings right where you are looking ? on your PFD or moving map. Granted, the moving map does not look like a sectional ? it is more of an IFR tool, showing waypoints, airports, an Nav aids ? but this is fine if you are IFR. For an additional cost, the GRT also allows you to display XM weather on the moving map, along with waypoints, along with terrain, etc?.in other words, it puts all of the information in one place for the pilot to absorb. You can twist the knobs to move the course line clear of weather and the autopilot will take you there ? simply amazing!

[Ironflight]

This is probably one of the toughest and yet most important areas of comparison between any EFIS devices. There are so many different features that you can have, and in many cases, they are difficult to compare on a one to one basis. I will say up front that I believe the feature set of the GRT system to be much more complete and richer than those of the Dynon. But then, the Dynon is not as expensive of a system as the GRT Horizon. This is where the ?Apples and Oranges? factor comes in. However, many (but not all) of these features require nothing more than new software to make them appear ? I predict a software arms race is in the making!


The Dynon?s that we installed basically provide the functions of traditional gyros, airspeed and altimeter, engine monitoring, and fuel flow monitoring. The GRT does all of those things, but adds navigation functions, including a moving (IFR) map, flight planning capability, autopilot control, synthetic approaches, and flight recording. The GRT HSI functions as a full-featured RMI, displaying bearing pointers from two different Nav sources at once, as well as overlaying map and course information. The Dynon?s HSI can use either GPS or VHF Nav data, but I haven?t found a way to do both at the same time.

The GRT can display Nav CDI information on either (or both) the moving map/HSI or the PFD. The Dynon can display this on the HSI, but I haven?t found it on the PFD. This, of course, is again only a question of programming ? once the data is in the box, a clever programmer can do just about anything with it. One of the most remarkable features of the GRT (that it shares with even higher-end systems) is the ?Highway in the Sky? guidance boxes that are used with synthetic approaches and can be coupled to the glide slope. I have found no more intuitive method of flying an approach than keeping the velocity vector inside the boxes ? it is extremely easy to do. In fact, I think it makes the need for an approach-coupled autopilot more difficult to justify.

Clearly, the GRT has more features because it has more hardware options ? such as weather and terrain (and even traffic!). The Dynon does not yet support these function, and I don?t know if they are in the works or not. I am impressed with what the Dynon does, and it does those things fairly well, make no mistake about that ? but in the feature department, it is hard to beat the GRT (even with a more expensive unit).

[Ironflight]

I am fairly well convinced that the recent ?explosion? in the number of companies marketing electronic flight systems is not going to last ? there are only so many airplanes being built, and it is far more difficult to build a successful business than it is to design a flight instrument (which isn?t easy in itself!). ?Hobby? businesses (and neither GRT nor Dynon fall into that category, in my opinion) are going to fall by the wayside. In this respect, I think we?ll end up with a reasonable number of survivors that will give a choice all along the price curve. The survivors will be the ones that not only have a good product at the appropriate price, but have a reputation for honesty, integrity, and going the extra mile for their customers. I have had incredibly good results with GRT over the more than three years that I have dealt with them. They have always responded to questions, and been quick to provide service the one time I needed it. In addition, they have a remarkable policy on payment and delivery. Order when you want ? they will not charge you until they have a unit to ship. They are also very conservative about not over promising ? they will not talk much about what will be coming ? they prefer to deliver first, and then talk about stuff.

My relationship with Dynon is much shorter, but so far has been pretty good. Once we got into troubleshooting mode with Eric at Dynon, he went the extra mile sending us replacement units to try until we found the fault in the system. I felt like we were able to communicate on a technical level, and exchange ideas on the problem as we worked toward a solution. I can?t say whether or not everyone gets the same treatment as Louise and I did ? I certainly hope so. As EFIS manufacturers see interesting features in other company?s software, I suspect that the functionality of the surviving systems is going to converge, making it harder to tell them apart, At that point, attention to customer?s needs is going to become much more important in how builder?s select the systems they will buy.

[Ironflight]

In summary, I am not sure that I have really done a comparison between the GRT and Dynon systems so much as I have pointed out the features and the differences of both systems. I have tried very hard not to tell anyone which one they should pick, as that is none of my business ? I just hope that I have honestly laid out some of the similarities and differences, as well as what I found to be useful and/or lacking in each system. Given the two different systems in their current state of development, the GRT is the more complete and feature-rich choice. It is my choice for serious IFR work. The Dynon is a good lower-priced option, excellent for VFR cross-countries, and OK for lite IFR (A term that many people do not like, but one that I believe is realistic if you are willing to ruthlessly enforce personal weather limits). The truth of the matter is that very few RV pilots are going to use their airplanes for extensive IFR work. For that matter, I would bet that the percentage who routinely set out on long (half-continent or more) cross-countries is probably less than those of us who do. My fully-IFR airplane has made 10 very long cross-countries in the past year, and many, many shorter ones, and I?ve only shot a couple of approaches for real in that time. I thoroughly enjoy having all of the features of the GRT system even for VFR cross-countries, because it gives me so much insight into the big picture The Dynon?s give less, but that is probably enough for many people.

I love analogies (if you haven?t guessed by now) and this is sort of like comparing a Mazda Miata to a Ferrari. Both are sports cars, and both are a blast to use. The Ferrari can beat the Miata hands-down in a full-out performance situation ? but unless you go to a race track, where can you legally use anything more than the Miata can provide? Yet some folks want to own the Ferrari because they appreciate what it is, and what it can do (and might even occasionally use it slightly above the posted limit?.). The GRT provides a capability unheard of in light aircraft until only recently ? it can do just about everything useful that you will find in a big airplane EFIS (when coupled with a sophisticated IFR GPS). The Dynon serves as an outstanding replacement for traditional instruments in a cost-effective manner. I am sure that the features and functions for both will continue to grow, as will both company?s customer base. It?s good to have choices, because everyone has different needs. And that said?.rather than blather on pedantically, I will open the floor for specific questions!

(Please note ? I cannot address questions or comments about any systems other than the GRT or Dynon, because I haven?t flow them?well, with the exception of some experimental stuff that NONE of us can afford!)

[lucky333]

Great writeup, Paul, and much appreciated. I'm finally getting around to the buy- the-avionics part (I'm on the 'interminable build plan') and got the same impression of GRT from talking to them, researching the stuff and following user posts. They made a lasting impression when they indicated that they designed it like it should be then priced it accordingly. Works for me.

That was a few years ago. Lately, I have to admit being tempted by some of the new dazzling displays, etc. but just don't get the same warm, fuzzy feelings like I do with GRT. A flying RV7A buddy and I were discussing my panel just this PM.. very timely.

Again, thanks for taking the time to share your experience and insight.

John

[Radomir]

Good stuff.. at first I saw post after post... didn't know if you were just talking to your self.. or if we should read it..