Our club has an annual pumpkin chucking contest. It is a duration efficiency contest, where you divide the time the pumpkin is aloft by the engine impulse. The pumpkin weighs between 6 and 10 oz and has a nominal diameter of 4 inches. I think this is a harder challenge than egglofting, because of the variable size and weight.
This year I decided to build it mostly out of leftover parts--I think the fin assembly came from a superroc. Last year I made pumpkin to BT adapters out of balsa--one flew away, leaving this one for 2.04" tubing. We launch these on pistons--no need for launch lugs or rails.
A 1/2 lb payload is a bit heavy for BT-50 to support, so I added some wooden strips to give it some strength. I also added some balsa gussets, so the load at the top of the motor mount tube would be distributed. These were later covered with a paper shroud to reduce drag and increase strength.
The fins are plenty strong for flight, but, they need to be strong for pre-flight preparations. Again, the 1/2 lb payload makes it a lot easier for damage to occur.
I had two good flights. The first was 36s on a D12-3. The 2nd was 68s on an E9-4.
A mistake I once made was angling the rocket away from the crowd. Unlike little NAR contest rockets, these aren't going fast enough to ignore the effect of gravity on the orientation of the rocket as it leaves the piston. The piston needs to be straight up/down.
This year I decided to build it mostly out of leftover parts--I think the fin assembly came from a superroc. Last year I made pumpkin to BT adapters out of balsa--one flew away, leaving this one for 2.04" tubing. We launch these on pistons--no need for launch lugs or rails.
A 1/2 lb payload is a bit heavy for BT-50 to support, so I added some wooden strips to give it some strength. I also added some balsa gussets, so the load at the top of the motor mount tube would be distributed. These were later covered with a paper shroud to reduce drag and increase strength.
The fins are plenty strong for flight, but, they need to be strong for pre-flight preparations. Again, the 1/2 lb payload makes it a lot easier for damage to occur.
I had two good flights. The first was 36s on a D12-3. The 2nd was 68s on an E9-4.
A mistake I once made was angling the rocket away from the crowd. Unlike little NAR contest rockets, these aren't going fast enough to ignore the effect of gravity on the orientation of the rocket as it leaves the piston. The piston needs to be straight up/down.
