Estes Doorknob, a two-stage version.

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Aug 19, 2019
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Howdy TRF readers! Wasn't sure where to post this - MPR, Staging, or Scale Forum, as it 'could' qualify for any of them, but decided to put it here.

Anyway, I thought others might appreciate a little project I've been working on for a few weeks, but thinking about/planning much longer. My bad for not doing a true build thread, but will share some of the in progress photos I did take.

The plan was to create the 2 stage variant of the Doorknob sounding rocket, as documented in Peter Alway's "Rockets of the World - 2002 Supplement". I purchased two of the Estes Doorknob kits for that purpose as soon as they were available through AC Supply. I knew this model would require electronic staging/ignition, which is a new skill/achievement for me. I also knew that the sustainer would require separate electronic deployment since the staging could not occur in some cases, yet another new skill/achievement for me.

Between the "thought" of doing this, and the "actually" doing this, I picked up some other bits and pieces to make the project a reality. These bits and pieces included plywood CR and fin upgrades from Bad Boy Rocketry (J Bassham), 3D printed details for the fin supports and launch shoes from Galactic Manufacturing (Mike Nowak), a Simple Timer staging timer and 400mAh LiPo from Apogee Components, an Apogee deployment altimeter kit from Eggtimer, a screw switch from Missleworks, and 3" coupler stock from Balsa Machining Services. I think I covered a broad spectrum of suppliers!

The actual build of the project started over a year ago when I assembled the Eggtimer Apogee. It was my first Eggtimer kit, and went together pretty easily. I enjoyed the assembly process, and have put together several Eggtimer products since then. I started playing around with a sim file in Open Rocket last fall to plan out the basic construction and layout. The real building started in mid-February after I received the 3” coupler stock from BMS as part of an order for several other projects, AND after registering for Michiana Rocketry Mayhem (proper motivation for building some new projects to fly!).

Some basic details of the build. It’s pretty typical MPR construction. The main body tubes from the Estes kits were cut down to appropriate lengths based on 1:5.29 scale factor (3” o.d. : 15.86” o.d.) - 17.2” for sustainer, 1.4” for interstage/spin motor section, and 14.7” for booster. Spirals were filled with thinned CWF. Spin motors were created from 1.6” lengths of BT5 with balsa supports and label paper straps. Centering rings and fins are plywood upgrade parts from Bad Boy Rocketry. The sustainer fin root tabs were shortened by 1.25” to allow for rear CR to be moved forward and the interstage coupler to be inserted 1.5”. Fin leading edges were sanded to scale-like profile and fin grain filled with thinned CWF. The nose cone was modified to have a bulkplate that the Apogee deployment altimeter is mounted to, with screw switch access in the nose cone shoulder. An interstage was created using 6” length of coupler stock, BMS plywood bulkheads, and a small plywood sled for the timer/battery/switch. Rail buttons are mounted on booster, interstage, and sustainer. 750lb Kevlar is used for recovery harnesses with the Estes PS nylon parachutes for recovery (24” in both booster and sustainer). Model was painted using Rustoleum 2x Primer, Rustoleum White and Black, Testors Competition Orange, Model Master Euro Gray (spin motors), Model Master Aluminum (fin brackets and launch shoes), the Estes decals for the fin can openings (black marks between booster fins), and some black trim Monokote and mylar tape trim.

Planned flight profile. The model is built with 29mm mounts in both stages. Initial flight is planned with F50-6 in the booster (with motor ejection for booster recovery), Simple Timer set for 2.5 sec (approximately 1 sec after booster burnout) igniting a D12-7 in sustainer with e-match. Sustainer apogee deployment by the Eggtimer Apogee altimeter (with D12-7 motor ejection backup) and JLCR set to 400’ after a predicted 1153’ flight. Follow-up flights are planned with G53-7/E16-8 and G72-8/F15-8 combos with predicted 1613’ and 2313’ altitude, respectively.

Thanks for reading, I’ll post flight details later.


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Yes, it does look great with all the details.

I also just did a 2-stage with electronic sustainer ignition. I used two BMS 3" school rocket kits plus extra couplers and bulk head. First flight went well using an F67-4 to D15.

Hope your flight goes to plan. Looking forward to the report.
Had a great weekend of flying at Michiana Rocketry Mayhem. Got in 18 flights, one of which was the first flight for the 2-stage Doorknob.

It was prepped with a F50-6 in the booster and a D12-7 in the sustainer. The Simple Timer was set to 2.5 seconds, which is approximately booster burnout +1 second. A MJG FireWire initiator was used to ignite the D12-7. The sustainer has an Eggtimer Apogee deployment altimeter in the nose cone for primary deployment, the sustainer motor ejection is backup. Sustainer also utilizes a Jolly Logic Chute Release (set to 400') to limit drifting on the 24" nylon chute.

Flight went according to plan. Got a poor cellphone video of the flight, that you can make out the boost, coast, then sustainer ignition. Hit 1674' with this motor combo.

Checked a lot of new boxes for me, so pretty happy with it. First electronic staging, first altimeter deployment, first Eggtimer build used in flight. On the next project(s). 🚀😎


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