Cox QZ .049 Decibel Test in the May 1966 Model Airplane News

Kim Thu Jan 06, 2022 3:45 pm

I've been ordering assorted model airplane magazines from Ebay lately, and one has Dale Kirn, doing noise tests on the then-new QZ .049 engine.

Probably not all that interesting, but I have a fondness for these particular engines, as one powered my first successful control line plane, the Cox QZ PT-19 Trainer.

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Ken Cook Thu Jan 06, 2022 5:48 pm

Kim, I have about a dozen of these. My dad bought them and what I've discovered is that I had a lot of Babe Bee engines with dual ported cylinders. I thought that this was odd and then I found many of the mufflers. It then made sense to me. I believe the newly designed cylinder mentioned in this article is the cylinders I have. These are dual ported cylinders with no SPI. Now some of the earlier versions did have SPI in which you used the spacer under the cylinder to jack it up. I also am fond of these engines and I started putting many of them back together.

**Cribbs74** Thu Jan 06, 2022 10:13 pm

They are pretty neat and quite functional. The only QZ I have ever seen was on Kim’s PT. It really does quiet the engine down significantly and still keeps power. Well done Cox!

Great pictures Kim. You guys had it good. No video games, no internet, no social media. Just plain old fun and ingenuity. Your parents must have loved you a lot to buy you those nice gifts.

balogh Fri Jan 07, 2022 12:16 am

Very interesting historical relics..the article and Kim's photos.....so good to see all those big names ( Cox, Atwood, Selzer, Kirn..) frowning their foreheads over the newly developed engine, simultaneously dodging the engine sound emission and performance loss by the muffler....and fun seeing Kim (another big name here Very Happy

) and his buddies equally concentrated on starting the engine up in a COX PT-19 on that '69 photo..I wish I had grown up then and there with you guys in the US...

Such small details like why the 0.04" high flange was added to the top muffler ring and the function of hexagonal muffler base are just so genius, simple but inspiring ideas to me when trying to solve multiple issues of e.g. installing my engines with accessories in a plane, and inventing 2in1 tricks and measures for a solution...amazing how much I have learnt already from the various aspects of this little gem called COX engine....

I was trying to find the test location Prentice Park in Santa Ana by Google Maps but to no avail.

I wonder if the flats machined into the top fin for the cylinder wrench date back to when the muffler was introduced in the 1960-s? Without the flats, once the muffler was installed, it would have been near impossible to remove the cylinder (unless with pliers), because the old school method of using the fork end of the wrench over the exhaust ports would not have worked with the muffler on...yet, even my cylinders from the early 70-s have no flats on their top fin.

Thank you Kim for sharing just another documentary of COX heydays..