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Old Aug 14, 2015, 08:28 PM
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Is 1/2A limited to .049 Size Engines?

I like small models but like them a little bigger than the .049 class of engines. One of my favorites was a scratch built model with a 48" wingspan powered by an FP-15 engine. I like the bigger size because regular servos and their weight is not so much of a penalty like it is when they are installed on a smaller model.

I would like to scale up a QT to about a 48" wingspan and use a .10-.15 size engine on it. Would that still be considered in the 1/2A category?
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Old Aug 14, 2015, 09:26 PM
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.05 is the max for competition. A is considered .05 to .15 for control line speed and free flight. You can use any size that you desire. I like the .15 size myself. You can use up the standard servos as you said, they cut through the wind ok, and still it is a cheap date. There are some pretty hot .15s too. The .049 can be more critical to throttle, and start, and many don't have a muffler which some clubs regulate. On this forum, .15 is the max, but that is just so the guys with the .10's and .15's don't feel left out.
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Old Aug 14, 2015, 09:55 PM
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If you are not competing at a competition where engine displacement is important, then it is no biggie. Go for it. But in the 1/2a class .05 is the largest displacement allowed. A class is the next up in displacement which is how they derived the 1/2a class. Cox made the Tee Dee .051 so a person could use a Cox Tee Dee .049 for 1/2a competition. Then swap out the engine with the .051 engine and run the same plane in the A class competition.

Originally the engine classifications were:
CLASS A: .000-.200 cu. in. piston displacement of engine
CLASS B: .201-.300 cu. in. piston displacement of engine
CLASS C: .301-.500 cu. in. piston displacement of engine
CLASS D: .501-.650 cu. in. piston displacement of engine

But later they broke out the 1/2a class below the A class engine sizes.
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Old Aug 14, 2015, 09:59 PM
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OK whatever pleases... is All that matters.
However one can buy Hobby king hxt 900 servos @ $2.50 Which Work Very well in a 1/2a QT.
Don't let servos be the excuse :-)
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Old Aug 14, 2015, 10:42 PM
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Thanks guys. I tried to google that information a while back but didn't come up with the excellent information you provided.

And Bare its not just the servos but I also want an engine with a reliable throttle and a quiet muffler. I have a park just around the corner from me that I think I could fly at with a quiet engine.

And I know I could go electric but I really don't like them or that whiny sound they make. Plus I just don't want anymore batteries in my life.

I have owned two QT planes and really enjoyed flying them. A model just a little bigger might just be a little more fun.
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Old Aug 14, 2015, 11:12 PM
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Interestingly enough the little HP VT-21 and VT-25 engines tend to be excellent four stroke engines that put out power similar to a regular sport .15 engine. The engines are amazingly quiet in the air and sound good too. Now the engines aren't super fast powerhouses though. But they can run good. They do turn larger diameter propellers which helps with efficiency and performance though.
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Old Aug 14, 2015, 11:48 PM
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I have ran the OS Surpass engine .20 and .26 the .26 can put out some rpm. The car guys run them up to 19k
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