Single Compartment Dual Deploy 2538

[MTEXX]

Utilizes altimeter based dual deployment but only one compartment and a reefed parachute.

My design considerations were to make a fairly sporty rocket without the typical overkill. Altimeter deployment eliminates a lot of problems. Drougeless DD eliminates a parachute. A reefed main eliminates the need for a second compartment and harness. The nose cone is a perfect candidate for an ebay and I elected to use the Intellicone which I am very pleased with. This reduced the need for a payload bay. It also helps with CG, so I don't need a coupler and extra airframe to make a longer rocket.

MMT=38mm
Dia=2.5"
Len=49"
Mass=2.5 lbs + motor

MMT is chambered in 38mm x 16" phenolic. I use 3 3/16" ply centering rings. The fins are PML's prism G10 1/16" A-09 planform (6.5" root, 3 span) and go to the MMT. The airframe is PML Quantum Tube 2.5" x 36". The nose cone and altimeter bay are PML's Intellicone- a good fit for this project. The altimeter is the Stratologger CF. I mounted a 110-220 switch on the sled which is accessible via the front static port. The e-matches are routed through a hole in the bottom of the Intellicone bulkplate and secured with a #8 well nut. Shock cord mount is Lariat Loop style. Motor retention is home bent z-clips using #8-32 screw and epoxied nylock nut inside. The rail buttons are small 10 size and will be mounted with well nuts when I can ever find a couple... I added a shear pin mainly to keep the static port holes on the airframe and NC aligned. The fin can was constructed externally so the fin slots extend to the aft end of the airframe. PML did the slots to within 3/8" of aft and I extended them with a sawzall. Recovery is 1/8" tubular kevlar leader tied onto 20' of 550 paracord for actual shock absorption. Figure-8 knots throughout due to high strength. A 1/8" stainless quick link (450lbs) connects the paracord to a 9x9 nomex, an 36" chute with swivel, the Intellicone tether and the Archetype cable cutter tether.

At apogee, the Stratologger will fire an ematch which is in a balloon with 1g of BP. The nose will pop off and the rocket will fall drogueless. The main parachute burrito is cinched up to the nose cone and bound with a zip tie. At 600 feet, the second ematch will go off inside the cable cutter hopefully freeing the parachute to the onlookers chagrin. I fully expect to hear a few people say "the parachute's tangled" ; )

I used OpenRocket 15 for modelling. Due to mach constraints, I'll be flying on H and I motors between 3000 and 5000 ft. This size rocket at 5000 feet merits some sort of locator beacon...

I made my own tube and CR templates via a C# application that generates SVG.
I used CA and West System 105 and 206 with Micro Balloons.



-Open Rocket model


-CR template and fin alignment jig if needed


-Tube marking template


-PML Intellicone!


-Parts arrived!


-Fin can
Idea borrowed from Vernk - https://www.vernk.com/Construction/AngelfireBooster.htm


-Motor retention detail with hardware-less shock cord mount


-Well nut holds e-matches in place


-Dry fit


-Recovery detail

 

[MTEXX]

The sled is 1/8" birch ply cut on a scroll saw. It is offset from the centerline so that the components will fit better. It also puts the switch face closer to the tube wall which is good because it will be activated from outside the rocket. Battery terminals are aft as per best practices.

I measured and cut and tacked pieces into place with CA. Then applied epoxy. The altimeter is secured with a single zip tie. Battery snap is the beefy hard plastic kind from Apogee. Again, the e-matches wire directly into the altimeter. The ebay is sealed with a well nut. Pretty elegant design IMHO


-Sled front


-Sled rear


-Well nut securing e-matches and also sealing ebay.

 

[kenstarr]

That looks pretty sweet! I like your av-bay design.
-Ken

 

[MTEXX]

@kenstarr - thanks. Got the idea from the Missile Works 3D printed sled.

 

[MTEXX]

I verified the technique of fishing the shock cord up through the holes and it worked just fine. 1/8" dowel and some masking tape. So today I epoxied the fin can guts to the airframe. I roughed up the inside of the quantum tube with 60 grit on a stick at all 3 centering ring marks as well as the inside of the fin slots. I slid the parts together and dribbled extra epoxy onto the forward CR. Then I took 2 sections of 3/16" dowel and lubed them with Vaseline to jam the aft CR's shock cord vias. Likewise lubed a couple of #8-32 screws and put them into the motor retainer holes- not threaded, just touching metal. I rotated the parts every 30 minutes or so to make sure they didn't seize. The vaseline trick worked just fine.


-60 grit on PVC pipe with depth markers sharpied on


-Inside of QT the CR areas were scuffed. Tough to photo because it's shiny inside.


-Aft CR showing Vaseline coated plugs

 

[MTEXX]

2 pair of external fin fillets went on yesterday. West System 105 with 206 hardener plus about 1/3 to 1/2 micro balloons. It's hard to just set it and forget it. I'm using a popsicle stick for shaping. Once they set in, it looked so puny that I wondered why I was spending this much time. Oh well. There is no internal fin to airframe bond so this really needs to be done. I suppose I can always go back over it with another layer.


-External fin fillets shaped with popsicle stick