Rocket fliers have been using black powder (gunpowder) for ejection charges for many years. Because of increased restrictions on the sale and storage of black powder, we've had inquiries about whether or not "smokeless" powders could be used. Smokeless powders are not usually subject to the same restrictions as black powder. However, many people reported that they didn't seem powerful enough to reliably eject a parachute. We decided to find out.
We prepared a test article that consisted of a fairly typical "main chute" compartment on a large rocket. The tubing is 4 inch diameter PML Quantum Tube, and the nose cone is a standard LOC Precision plastic cone. Inside there is a 50 inch Propulsion Polymers parachute, a large HeatShield Parachute Protector, and 10 feet of large Tubular Kevlar holding it all together. The TK extends out through the tube coupler and through the plywood bulkhead, and is epoxied in place. The tube coupler also has a 1 inch diameter PVC pipe fitting and cap, to make it easy to load various ejection charges into it.
We bought containers of Pyrodex RS, Pyrodex P, and Red Dot smokeless powders. All of them will fit into our two styles of Ejection Canister: the WEC with the snap lid, and the VCEC with the stopper.
We prepared the following ejection charges to test:
We wanted to answer these questions:
Is it possible to substitute a smokeless powder for black powder in an Ejection Canister?
Is there a difference between the various brands and grades of smokeless powder?
Will the filament igniter in Ejection Canisters work with smokeless powders?
The results: (click the picture to display the MPG video)
|Reference shot: a standard WEC Ejection Canister filled with 1.5 grams of black powder.|
|Pyrodex P in a standard WEC with no containment.|
|Pyrodex P in a standard WEC, similar to the one above but wrapped with three layers of electrical tape.|
|Pyrodex RS in a Variable Capacity Ejection Canister, three grams, with tape. Too much.|
We actually fired seven different combinations before we blew the back off the test article with three grams of Pyrodex RS in a taped VCEC canister. These video clips are the ones that best illustrate the results.
We learned that the filament igniters in Ejection Canisters will light smokeless powders with no problem. Simply substituting a smokeless powder for BP is inadequate. The smokeless powder will not burn completely if it is not contained in some way; we frequently saw unburned smokeless powder inside the tube after firing an uncontained canister. Red Dot was the worst at this.
All you have to do to provide adequate containment is to wrap the Ejection Canister with two or three layers of electrical tape. We used a continuous piece of tape. We wrapped it twice across the opening of the Canister, then around the outside, completely covering the Canister down to the igniter.
This method works beautifully with standard WEC snap-top Ejection Canisters. More testing needs to be done on the VCEC Variable Capacity canisters. An un-taped VCEC with 3 grams of Pyrodex P managed to push the chute out of our test article, but we observed a lot of flame from late combustion and there was a lot of residue inside the tube. Taping the first inch of the VCEC definitely produces adequate containment for complete combustion. We found that out when a taped VCEC with 3 grams of Pyrodex RS blew the back off the test article.
In conclusion, we are confident that Pyrodex P can be used in our WEC snap-top Ejection Canisters, as long as they are taped as described above. We'll add more information to this page when we get it. We want to publicly thank John Wickman and others who made suggestions that helped us perform these tests. Thanks, people!