Thursday, June 20, 2013

My Version of a Pneumatic Launcher - QE21

My antenna launcher is based on the QE19 design in  The author limited his barrel length to what will fit into a Rubbermaid tote which is 19 inches in overall length.  I found a tote at Lowes which allowed a 21 inch overall length which improves performance a little bit.

The nomenclature stands for Quick Exhaust valve launcher 21 inches in overall length.

Here is the QE21 made from a 3/4" Quick Exhaust Valve and a few parts making a quick, effective and easy to build a launcher for heights up to about 150 feet.

The chamber volume for the pressurized air reservoir in the QE21 is about 75 cubic inches. It could be up to about 24" long. Longer than that doesn't buy much, and performance may suffer from friction and inadequate airflow for the barrel volume in the longer barrel. Optimal performance is expected to be near 24 inches in overall length based on the studies made by the author at . The 3/4" valve just is not big enough for high > 150 ft performance with Tennis Balls. Shorter than 18-19" the performance will also begin to drop off. Consider your transport and storage plans and size accordingly.

QE21 Performance

The performance of a QE21 should just be slightly better than the QE19 in  
With a 4 ounce tennis ball (a standard 2 ounce ball with about 22 pennies added to the interior), and towing a 30 pound kite line, this launcher has approximately the following performance:
QE19 Performance

QE21 Description

Starting at the top left is the barrel. 2.5 inch diameter schedule 40 is a tight fit for tennis balls, but does the job well.

A note here about the barrel. Schedule 40 PVC is fairly available, and Tennis balls fit quite tightly into schedule 40 barrels. It turns out that there is another PVC pipe material with a slightly thinner wall that fits Tennis balls almost perfectly. It is much easier to push the Tennis balls into SDR21 and the performance of the launcher is improved especially at low pressures. It is called SDR21 PVC and the outside diameter is the same, so it fits the PVC fittings. SDR21 is hard to find in 2.5" size, but I have also located a source at /div>

At the right end of the barrel is a 2.5" coupler, 2.5 to 2" bushing, 2" to 3/4 inch bushing, a short length of 3/4 nipple pipe and a cast elbow, a short 3/4" threaded pipe nipple, and the big aluminum object is the Deltrol 3/4" quick exhaust valve from McMaster-Carr.

Starting at the valve going left is a short threaded pipe 3/4", a bushing 3/4" threaded to 2", a 2" tee, 2" schedule 40 pipe, and on the left is a slightly special assembly. This is the end of the pressure chamber and there are two choices to go there. The easiest is a regular 2" cap.

My version in the photo uses a 2" cap. Then this assembly is glued together simply with PVC cement.

For detailed instructions please

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