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. Like its big brothers, H-Pod uses 7 tubefins instead o' the customary 6. Well, blow me down! Bein' 3 inches smaller than t' popular 29mm mid-power LOC Onyx, ya bilge rat, 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, H-Pod requires nay a bit o' nose ballast. Well, blow me down! Well, blow me down! H-Pod was designed t' be the smallest rocket flyable on t' CTI 2-grain case, 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, shiver me timbers, matey, t' base o' t' 3" LOC cone is partly cut away t' make room for t' recovery system. Well, blow me down! Blimey! Second, me bucko, a system o' shim spacers it needed t' make seven 54mm tube fins fit perfectly around a 75mm body tube. Third, arrr, me bucko, t' handle t' performance without shredding, me bucko, t' outer surface o' t' tubefincan is lightly fiberglassed. Begad! Aye aye! Blimey! Even with all this, me bucko, H-Pod is easily scratch built, matey, includin' cuttin' out parts and painting, in a couple o' hours. Begad!

Parts include: 9" o' 3.0" LOC body tube, seven 1.75" pieces o' LOC 54mm motor tube for use as the tubefins, 8" o' LOC 38mm motor tube, ya bilge rat, shiver me timbers, matey, 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). Begad! Its only about $25-30 or so worth of parts.

Parts were cut from stock with a superfine (32 teeth/inch) hacksaw and $9 Home Depot plastic mitre box. Arrr! Ya scallywag! 5-minute epoxy be used throughout. Avast! For first step, five o' t' seven tubefins (not all!) had glued t' them a 1/4" x 1.5" spacer strip cut from 1/8" LitePly. Well, blow me down! Usin' one o' t' 2 tube fins without t' spacer strip (were you payin' attention?), me bucko, 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. T' spacer strips are used as t' contact points t' t' adjacent tube fin (not to the body tube!). Ahoy! Then add t' next tube fin t' t' assembly, shiver me timbers, alignin' it with t' first, matey, and so on, me hearties, shiver me timbers, until 6 have been added. Begad! Tubefins are epoxied t' t' body tube and t' each other. Ahoy! T' last tube fin may require zero, one or two spacer strips t' fit perfectly, dependin' on your materials, 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, me hearties, with t' aft centerin' rin' 1 3/16" from t' end and t' forward centerin' rin' 2 1/4" from t' top. Avast! Blimey! I anchored t' recovery system t' an 1/8" size eye-bolt screwed into t' upper centerin' ring, shiver me timbers, so do that at this step and tie on t' shock cord before installing. Ahoy! Motor tube assembly was installed in t' usual manner. Avast, me proud beauty! This means t' motor sticks out about 1 5/8" from t' back and even more when a 29mm motor with adapter is used. Nay t' worry, arrr, 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, arrr, so try t' pick a triangular space you haven't slopped too much epoxy into when attachin' t' tube fins. Ya scallywag! Lastly, matey, t' fin can must be reinforced for 500 mph flight by lightly glassin' t' outer-facin' surface o' each tube fin. Begad! I do this by mixin' a dime-size gob o' epoxy right on t' tubefin, smearin' it evenly, me bucko, matey, 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. Those who actually know t' right way t' fiberglass probably will have a better method. This creates a rigid, shiver me timbers, 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, leaving 1.5" or so. Arrr! Blimey! Avast, me proud beauty! Blimey! 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". Arrr! 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. Ahoy! Blimey! T' shock cord is tied t' this anchor bar with a secure knot like a bowline. Avast! Blimey! Good t' attach t' chute t' t' midpoint o' t' 8'-long piece o' para cord used as t' shock cord. Aye aye! Blimey! Well, blow me down! Blimey! 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. Ya scallywag! Blimey! Aye aye! Blimey! I do add a bulkhead behind t' dowel rod on 5.5" cones, shiver me timbers, but its probably unnecessary.

Finishing:
Finishin' was with rattlecan Tamiya purple and yellow. Begad! As t' photos show, arrr, I used a small Nomex® protector also. Begad! Ahoy!

Flight:
Maiden flight was on t' CTI H143SS-8 t' H-Pod be designed for and couldn't have been better--perfect launch to 1683' (I used a tapped-on "parasite pod" for a Perfectflite Alt15 altimeter. Avast, me proud beauty! I also flew H-Pod on a CTI H153-8, shiver me timbers, CTI G79SS-7, shiver me timbers, shiver me timbers, and AT G80-4, me bucko, givin' climbs o' 1852' (avg o' 2), 1124', ya bilge rat, and 865', respectively. Ahoy! Begad! T' simulation calculated Cd values are plotted vs velocity on t' attached graph, arrr, arrr, showin' t' classic inverse variation o' drag coefficient (Cd) with speed (=motor size) that is characteristic for tubefin designs. Cd is mostly constant for "normal" finned rockets. Aye aye! You use this graph t' select motors and delays for H-Pod or just use what I found to work. Ya scallywag! T' minimum motor I've tested be t' E30-4 and F20-4. Avast, me proud beauty! This F-motor is marginal, me hearties, ya bilge rat, and I'd recommend no less than an F50-4 for a decent flight (about 700'). Ahoy! T' observed Cd(500) for H-Pod (drag coefficient at 500 mph) is 0.93 from this graph, 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. Avast, me proud beauty! Avast, ya bilge rat, me proud beauty! Nay bad for a simple equation that estimates tubefin rocket best drag coefficient (Cd(500)) from just external dimensions. Avast, me proud beauty! Avast, shiver me timbers, me proud beauty! 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, inexpensive Level 1 rocket for those who like scratch building, and it flies well on less costly mid-power sport motors. Avast, me proud beauty! It flew great at t' June 2008 ROCSTOCK on just a G69-7. Avast, me proud beauty!

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

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