Is a 7'' screen so much better than a 4.2'' or a 3.8'' ?
At what size does a handheld start to become too bulky?
Generally bigger is better, but as you suggest, there is a limit to how big you want to go. I use a 4.8" device that sticks to the windscreen for for me that is about perfect size. I think if you want to go for anything much bigger, then you need a different mounting solution. Beyond 7" and you definately need to put it on your lap, for me would not be the ideal solution, and it's in your line of sight, nor in a convenient place to look.
So I'd say no bigger than 5-6" for windscreen mount, no bigger than 7-8" for mountain on your portable panel somewhere (hard to find a bigger gap without covering something else important). After this you need to put it on your lap.
Ability to fix safely in cockpit?
As above. For the smaller ones, they usually come with a suction mount that attaches to the windscreen, and they work fine.
How important are the different screen resolutions and refresh rates?
Refresh rates refer to how often the screen is updated rather than the processing power of the machine. Basic GPS systems only update once per second. So if you're in a steep turn, the little airplane might not turn smoothly. Most modern GPS's run much faster than this, but really it's hardly all that important to it's basic function of navigation. Do you really care if your position/speed/heading is only updated once per second?
Resolutions are a different thing altogether. For example, if device A has a resolution of 320*240, and a screen size of 3", and device B has a resolution of 320*240 and a screen size of 7" then you see nothing extra on device B; everything is simply stretched to make it bigger. So whether you want a bigger resolution or not might depend on your eyesight.....if you by a device with a small screen size, and a high resolution, then you better have good eyesight as everything will be small
If you buy a bigger device to make things bigger to see, but the resolution is also bigger then you end up zooming in to make stuff bigger so lose a lot of the benefit. It will still look crisper and sharper with a higher resolution screen, but personally I don't find it that much of an advantage.
Having said that, if you decide to use a gps system with a paper designed map onscreen, then the higher resolution will probably mean that the map is readable on more zoom levels.
What do you view as crucial connections?
Power and some for of data. Power is really necessary if you don't want to spend a fortune on batteries and run the risk of eventually running out of battery during a flight.
Data is necessary, because it's much quicker to plan your route on a PC with a large keyboard and mouse, than it is to program it on to a handled device. Pretty much every gps will allow a data connection to a pc, and come with some form of flight planning software. Garmin and Memory Map are at the most basic levels here, where others such as PocketFMS and SkyDemon see the PC and mobile device as been essential partners and are very closely connected and have powerful flight planning systems.
However for Garmin, this is generally got around by purchasing NavBox which will allow you to do detailed flight planning on your pc and upload to your GPS.
What do you view as crucial battery life?
I suppose that depends on if you have aircraft power available. My device (a car nav device) only last for approximately an hour on the battery. For me this is fine, as it's always powered from the aircraft. The battery is simply a backup. If I loose electrial power in the aircraft, I still have GPS available for 1 hour which should be plenty to sort myself out and find somewhere to land
Types of GPS receivers?
Not sure really what you mean by this question. Dedicated GPS systems will come with a built in receiver, so you don't have much choice.
GPS software that you load onto a mobile device (eg PocketFMS, SkyDemon, Memory Map) leave you more choice for a receiver:
A Car nav device which also has a receiver built in, or
A PDA where you can choose:
a wired GPS receiver-Plugs into your PDA but is connected to an antenna with a wire with allows you to place it where you like
A bluetooth GPS receiver, which connects wirelessly to your PDA so you can choose it whereever you like.
As you haven't mentioned PDA anywhere, I assume that you haven't got one. In that case, I wouldn't go down that route. Get either an aviation GPS (which will have a gps built in) or a Car SatNav (which will have a receiver built in) and load aviation software onto it. These are neater solutions, and the screens then to be brighter and more sunlight readable.
If you can't connect to the internal electrics do you need supplementary batteries and what are the best sort?
I suppose it all depends on how long the unit runs on batteries! Some run on AA batteries, some run on internal rechargable batteries, and some can be charged from a USB port. For example my car nav device can be charged from a USB port, so I simply bring a USB battery which can be plugged into the device to keep it charged, if no aircraft power is available.
Are all touch screens the same?
Yes and no. In terms of touching then yes...pretty much. There are two types one which just requires a light touch (like the iphone) and one that needs a somewhat firmer touch. Virtually all GPS systems use the second sort, so in this sense, they are all pretty much the same.
What IS different and varies a lot, is the brightness of the screens. Some are excellent and easy to read in the sunlight, and others are too dim, and full of reflections. They only way to be sure is to turn it on and bring it outside and have a look! You can't tell very easily when indoors, as they nearly all look good indoors!
Advantages / disadvantages CAA map loaded compared vector map?
CAA map:
Advantages
1. The map is familiary, so there is no new learning
2. It is easy to relate to your paper chart.
3. It has a lot of detail for dead reckoning type navigation, but you're not likely to use the device in this way (unless you have a pretty large screen, and even then probably not lightly....you bought a GPS after all, and will probably have a paper chart with you which will be easier to work with than any screen
)
Disadvantages
1. If you fly track up, then all text labels are the wrong way around (even upside down) if you're flying any direction other than north.
2. Only clear on a small number of zoom levels. Generally when you're zoomed in a long way. Try zooming out, and they are impossible to read. When you're zoomed in, you may not be able to see that much around you (depending on your device resolution and speed).
3. You can not declutter them. On many (all?) vector based systems you can declutter items so that they don't over lap. Some systems the system takes away detail of it's own choosing, and on some it's left to the user to decide what they want shown on what zoom level. Eg. You might device you want VRP's shown when zoomed in, but they aren't relevenat when you zoom out.
This is a MAJOR disadvantage in my opinion.
4. VRP's not shown on the paper maps.
5. If you fly to another country then you need more maps. Some companies have different maps available for other countries (at a price) which by necessity are a different format because the CAA only does maps for the UK, and some companies don't have maps outside the UK at all.....so when you really want to use your GPS the most...on a long unfamiliar trip, you can't!
6. CAA Chart maps are only updated once per year. If airspace changes, your GPS does not get updated charts until the CAA issue a new chart. With a Vector chart system, the charts are updated as soon as airspace changes.
7. Pretty much all (if not all) vector based systems will warn you if you are about to enter controlled airspace or restricted/danger/prohibited airspace etc.
Ones based on the CAA charts are different. Some don't know anything of the airspace, and simply show you a picture of the map and leave it up to you to avoid airspace busts, and others do have some knowledge of the airspace and can give warnings.
8. Airspace labels showing vertical limits may not be shown on the screen of the device with a CAA chart, and you have to drag it around to find the label. Vector charts don't show the airspace vertical boundaries, but generally have a way of displaying it such as clicking the boundary.
I hope you find this of some help...forgive the typos.....I'm going to sleep now, so not going to proof read it
dp