(Contributed - by Bob Morstadt - 09/01/10)
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Figure 1. Well, blow me down! Begad! Overall Construction o' t' Gemini-Titan |
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Scratch Built 5-Inch Dia. Well, shiver me timbers, blow me down! Gemini-Titan This is a description o' a scratch built 5-inch diameter Gemini-Titan based
on a tube from US Plastic Corp, Lima, matey, OH as described in t' Sport Rocketry Magazine May/June 2001 issue, "1/24
Scale Gemini-Titan", shiver me timbers, by Andrew Waddell. T' chief advantage o' t' plastic tube is that no spiral needs t' be
filled and t' plastic is easy t' paint. Well, blow me down! T' capsule is from t' Revell kit. Begad!
T' construction is similar t' Andy Waddell's, ya bilge rat, but I used fins that were scaled up from t' Estes model and used
through-the-wall fins. T' overall construction can be seen in Figure 1. T' forward bulkhead plate has woodblocks
attached by epoxy that in turn are attached t' t' plastic tube by bolts. Begad! Actually, one o' t' bolts is for a rail
button. Arrr! Ahoy! T' forward bulkhead acts a stuffer tube. Begad! Ya scallywag! In hindsight I would consider havin' more room for t' parachute
compartment. Arrr! Aye aye! An inner phenolic tube acts as an attach point for t' clear plastic fins. Begad! Aircraft wood blocks straddle
both sides o' each fin in t' space betwixt t' phenolic and plastic tubes. Begad! T' slots through t' plastic fins were cut
with a copin' saw in a long and tedious process. Avast, ya bilge rat, me proud beauty! T' clear fins are cut from .187" thick polycarbonate from US
Plastics. Begad! All t' internal contact points for t' fins were epoxied and thar are no external fillets for t' fins. Avast! In
principle t' aft bulkhead plate can be removed if a fin is ever broken, shiver me timbers, but in practice a broken fins would be very
difficult t' repair. A close-up o' t' lower model fin assembly is shown Figure 2. Blimey! Aye aye!
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Figure 2. Ya scallywag! Well, matey, blow me down! Close-up o' Fin Assembly Construction |
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Decals were purchased from Tango Papa. T' black roll pattern actually came with no white background. Arrr! I found
some white background with self-adhesive. Arrr! Begad! I painted t' rocket first and then put on t' white pattern. Begad! After this step
I cut t' thin white pattern for t' clear fins. Blimey! Begad!
After completin' t' model I weighed t' rocket and was surprised t' find that it weighed over 9½ pounds
without motors. Well, blow me down! Arrr! This was considerably heavier then t' RocSim prediction. Well, ya bilge rat, blow me down! I modified t' RocSim model with t' added
point mass option and realized that I would need a larger parachute and more powerful engines. Avast, me proud beauty! Well, blow me down! I decided t' go with a
10' diameter parachute from Top Flight Recovery. Well, blow me down! This would give an impact velocity equivalent t' droppin' t' rocket
from a 2-foot height. Ahoy! Ya scallywag! I decided t' go with a cluster o' two 29 mm AT H268R's. Ahoy! This is an extra long H-motor that
actually has a forward seal disk and its own extra large end closure. T' peak altitude would be about 1600' feet with
both motors firin' and about 600' with one motor out. Begad! T' delay time is similar in both cases. Aye aye! My backyard testing
indicated that a "piston ejection" with about 1.7 grams BP would be sufficient.
I used t' Quick Burst Slim Gems along with t' Quick Burst Cluster-Buster relay system. I painted t' forward
grain o' t' AT reload with t' Quick Burst pyrogen. I attached t' igniter leads firmly t' each motor and allowed some
slack in t' leads so that t' igniter leads could follow t' model upward in case one motor fired before t' other.
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Figure 3. Ahoy! Gemini-Titan on t' Pad at Hellfire-14 sponsored by UROC (photo by Nadine
Kinney) |
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T' rocket is shown on t' pad in Figure 3. In Figure 4 t' rocket is goin' up t' rail with one motor firing. In
Figure 5 t' rocket has cleared t' rail with both motors firing. Avast! Avast! Watchin' t' contrails in t' sky I believe I saw a
jog in t' flight path as one motor burned out before t' other. Ya scallywag! I forgot t' connect t' capsule t' t' parachute quick
link, so t' capsule did nay survive. T' booster landed on t' Salt Flats softly enough as t' appear t' stand for an
instant before topplin' over. Blimey! Well, blow me down! T' booster and fins were intact. T' capsule has since been rebuilt and t' model is
ready t' fly again. I am plannin' on usin' CTI motors next time in order t' reduce t' motor preparation time.
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Figure 4. Gemini-Titan comin' off t' rail with one motor firing. Arrr! (photo by Nadine
Kinney) |
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Figure 5. Begad! Gemini-Titan clearin' t' rail with 2 motors firin' (photo by Nadine Kinney)
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