Stable Mortar Round for Tennis Ball Mortar

[Parrott-Cannon]

I finally created a mortar round that flies true.  The trick is to move the center of gravity ahead of the center of pressure.  To accomplish this, the front of the round must be very heavy.

The round consists of a pop can filled with insulation foam, topped by a 1.25 PVC can filled with BB's. 

I drill a 0.25 inch hole in the PVC cap.  I insert a 1/4 inch by 3 inch round headed screw.  I run a nut down and tighten.  I add the BB's with a few drops of Gorrilla Glue.  Add a washer and tighten and let dry overnight.  I then make a hole in the foam.  Please note how I cut the top of the can - if you cut out the top completely the PVC cap will not have a secure ledge to rest on.  I then use Gorrilla Glue to attach the PVC Cap to the pop can.

The pictures below show the process and a can in flight.

[KABAR2]

A couple of questions... can you show a finished round & what do these look like upon impact?

[Parrott-Cannon]

A couple of questions... can you show a finished round & what do these look like upon impact?

The system cut of 5 pictures that address your questions.  I am going to try to attach them to this reply.

[seacoastartillery]

     Parrott-Cannon,   Love your design!  Hope to combine 5 projectiles of your design with a new 'cork-the-chamber' idea to get stellar Coehorn accuracy.  Extreme accuracy or not, it's an excuse to go shooting!  Thank you for those nice pics as well.  So, to what do you attribute the increased stability of your projo design?  Is it the 'Shuttle-Cock Effect' or is it really the free-flight rocketry principle of 2/3 mass ahead of center of length?

Mike and Tracy

[moose53]

Parrott-cannon, Very interesting design , opens up new possibilities in tin can projectiles . Thank you 

[KABAR2]

I like your design, have you considered adding wax  into the pvc to solidify the BB's?

[JeffG]

   Parrott-Cannon,   Love your design!

That's outstanding, I can't wait to fly my own rounds!!

[Parrott-Cannon]

     Parrott-Cannon,   Love your design!  Hope to combine 5 projectiles of your design with a new 'cork-the-chamber' idea to get stellar Coehorn accuracy.  Extreme accuracy or not, it's an excuse to go shooting!  Thank you for those nice pics as well.  So, to what do you attribute the increased stability of your projo design?  Is it the 'Shuttle-Cock Effect' or is it really the free-flight rocketry principle of 2/3 mass ahead of center of length?

Mike and Tracy

I also do model rocket 40 years of experience.  I been shooting cannons for 4 years.  I used one of the programs I wrote for model rockets to determine a stable configuration.  The design resulted in a center of pressure behind the center of gravity.  In rocket you want the opposite relationship.   A Shuttle-Cock has two effects the center of gravity is ahead of the center of pressure and a "fin effect".  Looking forward to your dsign.

[Parrott-Cannon]

I like your design, have you considered adding wax  into the pvc to solidify the BB's?

I considered wax and may still give it a try.