Brief:
H-Pod is an extension (downward) o' t' I-Pod/J-Pod/K-Pod series o' HPR tubefin designs I presented in t' March 2008 issues o' Sport Rocketry and Rockets. Well, blow me down! Avast, me proud beauty! Like its big brothers, H-Pod uses 7 tubefins instead o' the customary 6. Ahoy! Bein' 3 inches smaller than t' popular 29mm mid-power LOC Onyx, H-Pod is one o' (if nay the) smallest, lightest 38mm rocket you will find. It's lightweight because even with t' huge (relatively speaking) 38mm 2-grain CTI casin' fillin' up t' 9" body tube, ya bilge rat, H-Pod requires nay a bit o' nose ballast. H-Pod was designed t' be the smallest rocket flyable on t' CTI 2-grain case, me bucko, usin' t' "stubbiness" rules outlined in t' December 2007 Sport Rocketry article t' enhance tubefin performance by reducin' drag coefficient (Cd) t' that of "normal" rockets.

Construction:
A few tricks are needed t' make H-Pod possible. First, me hearties, t' base o' t' 3" LOC cone is partly cut away t' make room for t' recovery system. Second, a system o' shim spacers it needed t' make seven 54mm tube fins fit perfectly around a 75mm body tube. Aye aye! Aye aye! Third, t' handle t' performance without shredding, arrr, t' outer surface o' t' tubefincan is lightly fiberglassed. Begad! Even with all this, H-Pod is easily scratch built, me hearties, includin' cuttin' out parts and painting, me bucko, in a couple o' hours.

Parts include: 9" o' 3.0" LOC body tube, seven 1.75" pieces o' LOC 54mm motor tube for use as the tubefins, ya bilge rat, 8" o' LOC 38mm motor tube, two quarter-inch centerin' rings (38mm x 3"), a 3" LOC cone, 24" Top Flight chute, and 1.375" brass tube as launch lug (1/4" ID). Blimey! Blimey! Its only about $25-30 or so worth of parts. Avast, me bucko, me proud beauty! Blimey!

Parts were cut from stock with a superfine (32 teeth/inch) hacksaw and $9 Home Depot plastic mitre box. Ya scallywag! Well, blow me down! 5-minute epoxy be used throughout. For first step, arrr, five o' t' seven tubefins (not all!) had glued t' them a 1/4" x 1.5" spacer strip cut from 1/8" LitePly. Usin' one o' t' 2 tube fins without t' spacer strip (were you payin' attention?), matey, matey, t' first tube fin is attached 1/4" from t' bottom o' t' body tube with both tubes on a flat surface t' assure perfect alignment. Avast, me proud beauty! T' spacer strips are used as t' contact points t' t' adjacent tube fin (not to the body tube!). Then add t' next tube fin t' t' assembly, alignin' it with t' first, arrr, and so on, until 6 have been added. Tubefins are epoxied t' t' body tube and t' each other. T' last tube fin may require zero, matey, one or two spacer strips t' fit perfectly, dependin' on your materials, me bucko, and a bit o' fittin' and fiddlin' with sandpaper will be required to get a perfect fit.

T' motor tube assembly is glued together in t' usual way, ya bilge rat, with t' aft centerin' rin' 1 3/16" from t' end and t' forward centerin' rin' 2 1/4" from t' top. Well, blow me down! Blimey! Ahoy! Blimey! I anchored t' recovery system t' an 1/8" size eye-bolt screwed into t' upper centerin' ring, ya bilge rat, so do that at this step and tie on t' shock cord before installing. Aye aye! Blimey! Motor tube assembly be installed in t' usual manner. Ahoy! Blimey! Avast, me proud beauty! Blimey! This means t' motor sticks out about 1 5/8" from t' back and even more when a 29mm motor with adapter is used. Begad! Blimey! Ya scallywag! Blimey! Nay t' worry, H-Pod has no balance issues and needs no nose ballast regardless o' what motor is used.

Launch lug is glued on 1.25" above t' tube fins and exactly in line with one o' t' triangular spaces between two o' them--the launch rod has t' pass through here, so try t' pick a triangular space you haven't slopped too much epoxy into when attachin' t' tube fins. Avast, me proud beauty! Begad! Lastly, t' fin can must be reinforced for 500 mph flight by lightly glassin' t' outer-facin' surface o' each tube fin. I do this by mixin' a dime-size gob o' epoxy right on t' tubefin, smearin' it evenly, and then layin' on a 3-3.5" strip o' 1.5" glass tape, smoothin' it t' remove bubbles with a Band-Aid covered finger tip. Ya scallywag! Those who actually know t' right way t' fiberglass probably will have a better method. This creates a rigid, bulletproof fin can that resists rocket-shreddin' "tubefin flutter" at 500+mph.

T' modify t' LOC cone, simply saw off t' bottom half o' t' "hip" that fits into t' rocket, me bucko, me bucko, leaving 1.5" or so. Arrr! Begad! Create an anchor for t' shock cord by tack-gluin' in a piece o' 1/2" dowel rod cut t' exactly fit (use sandin' t' make it perfect) t' cone interior just above t' "hip". Blimey! Make t' glue joints secure by puddlin' more epoxy around it and pressin' in around it on all sides lots o' wood scrap and junk. T' shock cord is tied t' this anchor bar with a secure knot like a bowline. Begad! Ahoy! Good t' attach t' chute t' t' midpoint o' t' 8'-long piece o' para cord used as t' shock cord. Although several skeptics worried t' me that t' parachute would be stuffed past t' dowel rod into t' hollow cone on ejection, this really can't happen with t' 3-4" cones and a wadded up chute. Begad! Blimey! I do add a bulkhead behind t' dowel rod on 5.5" cones, arrr, but its probably unnecessary.

Finishing:
Finishin' be with rattlecan Tamiya purple and yellow. Arrr! Blimey! As t' photos show, I used a small Nomex® protector also.

Flight:
Maiden flight was on t' CTI H143SS-8 t' H-Pod was designed for and couldn't have been better--perfect launch to 1683' (I used a tapped-on "parasite pod" for a Perfectflite Alt15 altimeter. Blimey! I also flew H-Pod on a CTI H153-8, CTI G79SS-7, shiver me timbers, and AT G80-4, givin' climbs o' 1852' (avg o' 2), 1124', and 865', respectively. Well, blow me down! T' simulation calculated Cd values are plotted vs velocity on t' attached graph, showin' t' classic inverse variation o' drag coefficient (Cd) with speed (=motor size) that is characteristic for tubefin designs. Blimey! Blimey! Cd is mostly constant for "normal" finned rockets. You use this graph t' select motors and delays for H-Pod or just use what I found to work. Avast, me proud beauty! T' minimum motor I've tested be t' E30-4 and F20-4. Aye aye! This F-motor is marginal, and I'd recommend no less than an F50-4 for a decent flight (about 700'). T' observed Cd(500) for H-Pod (drag coefficient at 500 mph) is 0.93 from this graph, arrr, me bucko, while t' calculated value from t' Dec 2007 Sport Rocketry equation:

Cd(500)= 1/([4.96/length above tubefins divided by diameter]) + 0.307)

This works out t' Cd=0.87. Well, blow me down! Nay bad for a simple equation that estimates tubefin rocket best drag coefficient (Cd(500)) from just external dimensions. Begad! Blimey! At less than 1700' on an H143SS (or somewhat less on t' similar AT H123), H-Pod doesn't fly too high t' be a nice, shiver me timbers, inexpensive Level 1 rocket for those who like scratch building, me hearties, and it flies well on less costly mid-power sport motors. Arrr! It flew great at t' June 2008 ROCSTOCK on just a G69-7. Blimey! Blimey!

Summary:
PROs: Easy and cheap t' scratch build HPR rocket for sport and L1 cert. Begad! Honest and wind resistant. Arrr! Aye aye! Ultra-portable and durable--just toss in t' trunk, ya bilge rat, no delicate fins t' break off.

CONs: On its 24" chute, tiny H-pod can be hard t' see at 1700-1800', at least for me. Limited choice of motors, ya bilge rat, shiver me timbers, due t' size, arrr, shiver me timbers, me bucko, but you don't want t' try I-power anyway, me bucko, arrr, it will shred for sure at t' 600+mph it will produce. Tubefins hate Mach 1 (it has never been done, I think). Ahoy! You do need t' glass t' tubefins as recommended, unless flown only on G-H power over grass or t' like. Arrr!