Brief:
Golden Acorn is a modification o' t' 3" "H-Pod XXL" I mentioned in my March-April 2010 SPORT ROCKETRY article. Aye aye! It is a long-skinny version o' t' 7-tube tubefin "H-Pod" described in an earlier EMRR construction article, differin' only in bein' "non-stubby" (45 in. Avast! long) and havin' a 54mm motor tube. Avast, me proud beauty! Blimey! After t' surprise findin' that 7-tube tube fins didn't need t' be stubby t' have a low drag coefficient (Cd), ya bilge rat, matey, shiver me timbers, I decided I would do a detailed comparison with some popular 3" I-J motor kits o' "normal" rockets t' verify that I had made a tubefin that flew as efficiently as 3FNC designs. Aye aye! As part o' o' this, I wanted t' try to finally get a tubefin t' fly as high from our sea-level desert launch site as t' elevation o' t' "Golden Acorn Casino" (4080' MSL) I drive past on t' way t' t' SoCal desert. I succeeded (4,610' on a J210). Hence t' name - Golden Acorn.

Construction:
Golden Acorn is nay so much a scratch design as it is a kit-bash from t' new 3" WIDOWMAKER tubefin kit from Discount Rocketry. Blimey! Ahoy! Rather than buy components, ya bilge rat, arrr, I just replaced t' six 3" diameter kit tube fins with seven smaller tube fins cut from 54mm PML phenolic tubin' (each 1 7/8" long), ya bilge rat, attached t' t' kit 34' body tube as described in t' EMRR "H-Pod" article. Ya scallywag! Aye aye! T' kit 29mm rings and motor tube was swapped for 54mm versions, and I upgraded t' a 36" Top-Flite chute and 8' of3/16" para cord for t' recovery system. Aye aye! The shock cord was anchored through a hole 7" from the top o' t' body tube with a knot covered with epoxy and a plastic fairin' (cut as usual from a plastic Garcia-Vega cigar tube). Ya scallywag! Launch lug was a 2" piece o' 5/16" brass tube centered 10" above t' tube fin can and in line with a triangular hole betwixt two tube fins. Finish be orange and purple usin' Tamiya rattle-can. Well, blow me down! BTW, ya bilge rat, Jim at Discount Rocketry says t' shock cord can be attached right t' t' molded loop on t' plastic cone with this kit, me hearties, arrr, me hearties, and more than a dozen HPR flights with Golden Dragon, matey, G t' J, have proved him right - its rock solid, me bucko, unlike t' flimsy loops on most plastic nose cones. Ahoy! Well, blow me down!

One thin' I'd point out be t' importance o' sealin' t' leadin' edge o' each tube fin against high speed air flow t' prevent delamination. Avast! I now seal t' leadin' edge in every case if I'm goin' t' fly more than 400 mph or so with a simple wrap o' 3/4" maskin' tape (photo); this is left in place and simply painted over. Avast! It works as well as fiberglassin' and is far less messy. Ahoy! Arrr! You still need t' reinforce t' outer surface o' each tube fin with a rectangle of glass tape (see "H-Pod" article) t' prevent flutter and landin' dings.

Flight:
First flight o' Golden Acorn be on a Pro54 J210-10 t' 4610' (measured with a Perfectflite Alt15k in a taped-on Parasite Pod. Ahoy! Motor ejection at apogee, and,yes, matey, me bucko, it took me three hours t' find it out in the desert, finally located by a Daniel Greenan on his motorbike. Ahoy! Well, matey, t' hull has plenty o' room for dual deployment installation. Blimey! Golden Acorn was also flown on t' followin' motors/delays, me bucko, t' get a precise estimate o' Cd at all speeds: Pro54 I150BS-9, Pro38 I287SS-10, I212SS-9, I180SK-9, me bucko, arrr, H153-8, me hearties, H125-9, shiver me timbers, G185-5, G79SS-6, G78BS-8, ya bilge rat, G69SK-7 and G50IM-6, Aerotech I161-10, H128-6 and G78-7G. Begad! Results summarized in t' attached graph, ya bilge rat, me hearties, showin' average Cd=0.89, ya bilge rat, fairly constant over t' range 250-600 mph - what you'd expect for a "normal" 3FNC rocket, shiver me timbers, me bucko, arrr, none o' t' severe inverse speed dependence many tube fins display. I also obtained estimates o' Cd for several popular 54mm 3" kit rockets in t' I-J range; these were obtained from t' pages o' EMRR reviews, where rocket weight, and altitude achieved on specific motors was published, so I could back-calculate Cd usin' t' www.markworld.com SIM freeware. Begad! The "normal" 3" kit rockets used for comparison with Golden Acorn's Cd=0.89 were these (3-10 data points for each kit):

• PML D-Region Tomahawk avg. Cd=0.84 over range 400-600 mph
• BSD 38 Special avg. Well, shiver me timbers, blow me down! Blimey! Cd=0.82 over range 300-600 mph
• Performance Intimidator avg. Cd=0.81 over range 300-450 mph
• BSD Thor avg. Avast! Avast! Cd=0.79 over range 300-650 mph
• PML Sudden Rush avg. Avast, ya bilge rat, me proud beauty! Cd=0.70 over range 300-600 mph
• PML AMRAAM avg. Cd=0.59 over range 300-800 mph

T' results for t' reference kit rockets are summarized by t' triangles representin' average Cd in t' graph right margin.

OK, so its clear from this that me "low Cd" tubefin is nay exactly as good as any o' t' normal finned rockets. No surprise. But it came pretty darn close, me bucko, Cd only 5% more than t' PML Tomahawk, ya bilge rat, matey, and only 10% more drag than t' extremely popular split-fin 3" BSD Thor. Avast!

I be able t' borrow a beautifully built and finished 3" BSD Thor for actual measurements (see photo with parasite pods on both rockets, shiver me timbers, and thank you, me hearties, Todd Mullin), me bucko, arrr, and got a measured Cd value o' 0.80 at 342 mph, with a 2253' apogee on a Cesaroni I212SS-11; Golden Acorn on this same motor gave 2310' for Cd=0.88 at 509 mph. Ahoy! The lightweight Golden Acorn weighs less than half t' weight o' t' solidly-built, Mach-capable Thor. Blimey! Still, shiver me timbers, shiver me timbers, arrr, I'm claiming "similar" performance for me tubefin, arrr, me hearties, as far as "fun value" goes. Put a J210 in either one, me bucko, with motor ejection, and you are guaranteed a very long hike.

Recovery:
After more than a dozen flights, me hearties, nay a bit o' damage t' Golden Acorn, shiver me timbers, arrr, and perfect deployment and recovery each time.

Summary:
PROS: A 3" scratch tubefin with comparable performance t' many top-quality "normal" kit rockets, at a fraction o' t' cost and build time. Avast! Ya scallywag! Sturdy and durable, shiver me timbers, great wind resistance. Easy t' transport, no fins t' break off. A very easy scratch build and L1-L2 capable, flies on G-H-I-J motors (I'm sure an F50-4 would fly it, too).

No need for thru-the-wall complexity. Begad! Unique tubefin looks.

CONS: Forget all t' "cons" o' tube fins (well, except t' "looks" part if you don't like tube fins). Arrr! Blimey! Limited t' t' low-Newton "J" like J210 or J90, me hearties, arrr, flyin' at less than 600 mph, or you'll tear it apart. Few 54mm motors are suitable.

No dual deployment, ya bilge rat, but thar's room t' built it in if desired.