The Longspear

[Neutron95]

My latest project is something I am calling the Longspear. First a little bit of backstory on the design. One of my first rocket kits was an estes Mean Machine, that has preformed very well over the years. Several years ago I got a Flis Kits Richetr Recker, and I loved it. Then due to a 1/3 ignition and subsequent destruction, I designed the spEEEEar a 9 foot tall 4E motor cluster. Due to using thin walled BT-80, the tubes started to buckle and it was eventually retired.

I am building the Longspear in preperation for Plaster Blaster. It will be more than 12 feet tall and fly on a 7 x 29mm cluster. The fins are a sandwich of 1/4" balsa and 1/32" plywood. Electronics will be a Raven and anything else that will fit. It will also be used to gain experience with electronics and to hopefully be able to do a 20,000 foot attempt in May or next Plaster Blaster. When I have a chance I will upload pix of the motor mount and the fins along with the SpEEEEar.

[gdiscenza]

Is there any combination of 7x29mm that is under the L2 certification limit?

G.D.

[COrocket]

Is there any combination of 7x29mm that is under the L2 certification limit?

G.D.

Good point, each motor would have to have (640/7) or 91.42 Ns or less. Aerotech makes F motors in 29MM, so it is possible.

[Neutron95]

Due to ecenomic constraints most flights won't be a full cluster, and my dad (Level2) and I will also be using some 24mm motors in the outboards, along with a larger central pro29 for the main thrust.

[bobkrech]

Is there any combination of 7x29mm that is under the L2 certification limit?

G.D.

Lots of them. 7 full F motors have a total impulse of 560 Ns or a 75% I, and well below the 0% J limit of 640 Ns.

There's nothing cheap about clusters. and multiple clustered motors typically about twice as much as one motor with the same total impulse. A load of 7 single use Roadrunner F60s are equal to an 539I420 or a 68% I. Retail cost about $133.

Bob

[Neutron95]

Well I have been hard at work building the Longspear. Here are a few pictures that I took today. I haven't been taking any during the construction so here they are:

First is a dry fit with all of the parts
Second is a detail of the fin construction 1/4" balsa laminated with 1/32" plywood
Third is avionics/parachute bay
Fourth is the seven motor mounts- Due to an inconsistancy in the Od's of the central mmt and the outboards there is a spacer between two of them.
And finally we have it all taken apart for storage.

[Neutron95]

Well I got some more work done last night and today. I did 3 of the 8 fillets, using the wildman method- with colloidal silica and a form. They have come out great. I also cut out the altimeter bay sled and glued it together.


The electronics will be a Raven and a Perfectflite Minialt. The rocket will come down in two sections. Everything above the transition will come down on one parachute, while the booster comes down on another. For Dual deployment I will use the remaining output on the Raven (Assuming 3 airstarts) for apogee, backed up by the motor, to deploy the booster 'chute the upper part will be attached with shear pins, and at a lower altitude the minialt will seperate the two sections.