Read the rules.  "Scale" isn't divided up that way, and "semi scale" isn't a classification.

In scale, you're mostly trying to duplicate the full-size prototype as exactly as possible, and you get a higher static score the better you do.

In Designer Scale (which is the closest to your "scale" that one can come) the judges can get right up to your plane for static judging.

In Sport Scale the judges can't get closer than 15 feet.  Sport scale is intended to be a more relaxed event, obviously.

A semi-scale stunter isn't any official class -- it's just a design approach to stunt competition where a competitor, either because he thinks he'll garner more points, or because of personal preference, chooses to make a model that more or less resembles some full-size prototype.  There's no rule to keep someone from building a Nobler and claiming that it's a semi-scale Cessna 120 -- there's just no advantage, either.

You could, in theory, build a semi-scale stunter and enter it into both stunt and scale competition.  But the two classes have mutually exclusive requirements (the aerodynamic requirements of stunt don't match the outlines of many full size prototypes), not to mention the fact that scale ships tend to be heavier to get more static points.  So you probably wouldn't do well at either, assuming that you could get into the scale competition at all.

The semi-scale stunt plane designer, in order to avoid building a semi-stunt scale plane, must basically build a "stunter in full scale clothing" -- i.e., you've got to choose a prototype plane that sorta-kinda has a general arrangement that is close, then you have to modify the outline into this massive compromise that flies well, but still has people looking at it and seeing the bird that you intend for them to see.  It's nothing like building a scale airplane, where ideally the outline of the full scale airplane dictates the outline of the model.

Tim and JIm have some great comments

One thing to remember is that In CL sport scale 1/2 of your points are the static points (100 static, 100 flying). And a majority of the static points are based on the outlines of the model as compared to the full size 3-view. If you were to enter a CL semi-scale stunter you might get low outline points if the outline of the model did not match the outlines of the 3-view that you present the judge. There are many semi-scale stunt models that look like the full size aircraft but some critical outlines such as top view of the wing have been modified for CL stunt. Another deviation is changing the size of the elevator, same overall shape but it might be enlarged compared to the wing, that is another problem that would cost you points for CL scale static judging.

Another tip - pick the 3-view you show the judge carefully....some are incorrect and some show way too much detail for some events. Choose a detailed 3-view for FAI and a less detailed 3-view for sport and fun scale.

A semi-scale stunt model does fantasticl in Fun scale because you only have 10 static points and 100 flying points, and you can do a stunt option in fun scale but in sport scale they may not let you do inverted laps if the full size version could not do inverted flight.

Tim and Jim are right about the throttle control, to earn maximum flight points you need to have throttle control and use the throttle like the full size pilot would to earn full points for CL sport scale. Pick either 3-line or electronic controls your choice they both work.

Read the rules on the AMA web site regarding fun scale, that would be a great place to start scale with a semi-scale stunter. You also need to create documentation for your aircraft even for fun scale and this should not be taken lightly.

Sport scale requires documentation that matches one particular aircraft and then you have to fly it correctly. Trying to get a model that does well in sport scale and CL stunt would be a tall order.

Good luck,
Fred Cronenwett

If low on experience you may want to consider an electric powered aircraft.  Throttle on electric is easy to setup with an electronic control (Clancy sell a really good setup).  I agree Fun Scale is a good starting point.  The rules even waves the builder of the model rule. So any aircraft including ARF qualifies.  Converted RC are common.
Event 526 is fun scale.

Another suggestion is profile scale - Event 521.  Scale judging is at 15 ft and has 100 points scale 100 points flying.  You can also put a profile scale ship in Fun Scale.

By the way the rules are at:
http://www.modelaircraft.org/files/2011-2012RC-CLScale2.pdf


 

There should be a stand "way way off" scale. There would be more modelers involved. My guess.

CB