ARF (Almost Ready to Fly), and (RTF) Ready to Fly airplanes have become very commonplace in recent years. Building an airplane from a kit has its own rewards, but many people find they just do not have the time. An ARF or RTF airplane is a pleasant solution for these people.
The question is, how does one define "almost"? Sometimes manufacturers might say something like 90% ready to fly, but what does that really mean anyway?
Some of these pre-manufactured airplanes still require considerable assembly to get to the flight-ready stage.
A few hours to as much as 20 hours is not unheard of.
Now if you build your own kit you will be intimately familiar with every glue joint. The almost-ready-to-fly airplane is made in a factory assembly line, in a location where labor is cheap.
Some of these demonstrate amazing craftsmanship, some not so good. Since you will be the one flying the aircraft and responsible for it, check the workmanship.
Look over the glue joints; twist and bend the parts a little to make sure that the joints are solid. Inspect the covering: it should be well sealed around the edges of the airframe (nothing coming loose) and should not have cuts in it.
Pull on all the control surfaces, making sure that the hinges are really glued in.
If these come loose in flight, you could a mess on your hands. The wing is another are to pay attention to. Most kits will instruct that the wing halves be joined together then the covering applied.
However, an ARF airplane needs to fit in a box to be shipped to the happy modeler, and so the wing halves are left unjoined and the covering applied. Make sure that you glue the halves together securely per the instructions.
You can make the wing joint stronger by adding fiberglass or nylon to it. Using a single edge razor, carefully strip away the covering at the wing center (being careful to not cut into the wood).
Then apply 1-2 inch wide fiberglass or nylon tape over the top and bottom section of the wing, right onto the bare wood. Use epoxy to saturate the tip. When dry this will create a nice strong center reinforcement.
Install the engine and the radio per the instructions. Check that there are no areas of wood exposed to contact with the glow fuel.
This can saturate the wood and create weakened, oily mess. If there are exposed areas, get some fuel-proof wood sealer / paint form the hobby shop and apply with a small brush.
If you'd like more tips on assembling ARFs, there is a good reference book written by Harry Higley. Here are some popular ARF and RTF airplanes.