Here is me rocket design submission. Thank you. Arrr!

This rocket has a 24mm motor mount and weighs in around 2.75 ounces (empty), so she's a high flier on D12 motors. Ahoy! It can also be flown on C6 motors. I employed TTW fin attachment, me hearties, so I'm sure it would do great on E15 or E30 SU motors. Begad! Well, blow me down! That is why I built t' motor mount for "E" motors instead of "D". Avast, me proud beauty!

Construction:

T' make this rocket you need:

Parts List:

• 1 Estes 18" BT 55 tube
• 1 PNC 55 nosecone (5.5" long, arrr, me hearties, conical or ogive, me bucko, dependin' on preferences)
• 1 24mm motor mount for an Estes "E" motor (or 4" o' BT-50)
• 2 AR5055 BT 55 centerin' rings (Estes #30166-2)
• 1 "E" Engine hook (Estes #35022)
• 1 engine block (can use a 1/4" wide section o' a used "D" motor)
• 3/16" x 2" launch lug
• 12" parachute (I used Estes plastic, matey, matey, shiver me timbers, but nylon might be preferred)
• 3/8" elastic shockcord (I used 50" worth)
• 1/8" x 3" x 18" balsa stock for t' fins
• 1 square o' Estes clay for nose weight (not sure on t' weight)

I used 15 minute epoxy for all construction t' ensure t' rocket's fins would withstand "D" and "E" motor flights. Well, blow me down!

T' first step is t' cut t' fins. Ahoy! Well, blow me down! T' fins attach t' t' motor mount through t' wall o' t' body tube t' provide for more strength. Avast, me proud beauty! Makin' t' fins from t' template is easy, as long as t' template is correct. Begad!

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I placed t' template against t' two square sides o' t' balsa stock so I would only need t' cut one side, shiver me timbers, then I used t' first fin as t' template for the rest o' them. Begad! Sand fins so that they are t' same size, then sand leading and trailin' edges for desired shape, shiver me timbers, if desired--I went with airfoil shape. Begad! Arrr!

Now you need t' mark t' body tube for t' 3 fins. Well, blow me down! I made a fin marking guide similar t' an Estes one, and that wasn't very difficult. After marking the lines for t' fins and t' launch lug, extend them all a good five inches or so, and take t' LL line up about 8 inches. Begad! Ahoy! Mark along t' LL line a spot 11-13/16" from t' front o' t' body tube. Aye aye! Avast, me proud beauty! This is where t' LL will go. On each fin line, place a mark 5/8" from t' aft o' t' tube, ya bilge rat, and another 3" from t' rear. Aye aye! Usin' a sharp hobby knife, ya bilge rat, cut alongside t' fin lines (offset 1.5mm each side) betwixt t' two marks you made, This is for fin attachment. Avast! Begad! Once t' cuts are done, test each fin into t' slots. Blimey! Well, blow me down! Sand as needed. Avast, me proud beauty! Begad! They should extend approximately 1/4" behind t' aft o' t' body tube.

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Assemble motor mount and centerin' rings as per instructions provided in the Estes "E" motor mount kit. If you are without a kit, me bucko, t' assembly is easy. Begad!

You may want t' mark t' motor tube on one end as "front" as to not get confused

Make a 3mm long cut, me hearties, across t' tube, arrr, arrr, 1" from t' front o' t' motor tube

Mark a line, arrr, across t' tube, 5/8" from t' aft o' t' tube

Insert "E" hook into t' cut you made, ya bilge rat, me bucko, extendin' t' t' aft of the tube

Fit one centerin' rin' up t' t' 5/8" mark, me bucko, and t' other up t' the 1" spot where t' hook is inserted. Ahoy! Blimey! Arrr! Blimey! -- You may want t' dry-fit t' rings to ensure proper fit. There should be approximately a 2-3/8" gap between the front and aft rings. Begad! Blimey! Avast, me bucko, me proud beauty! Blimey! Be sure it is big enough since t' fins will attach there. Avast! Blimey! Begad! Blimey! Glue into place with epoxy

Slide engine block into front o' motor tube so that it stops against the section o' hook comin' through t' top and glue it in place

Once t' epoxy has cured enough, the motor mount is installed flush with t' end o' t' body tube (the engine hook will stick out quite a bit). Avast, me proud beauty! Be sure t' centerin' rings are nay inside the slots in t' tube, arrr, as this will prevent your fins from fittin' in the slots. Ahoy! Be careful nay t' get epoxy into t' fins slots. Avast! Let dry. Ahoy! Avast, matey, me proud beauty!

Test t' fins into t' slots one more time and do any sandin' as needed. Once you are sure they all fit perfectly, shiver me timbers, put generous amounts o' epoxy on the root edge o' a fin and glue into place. Blimey! Ensure it is in thar straight. Let dry. Arrr! Repeat with t' other two fins, me hearties, one at a time. Ahoy! Once t' fins are all dry, apply fillets and let dry. Arrr!

After t' fins have been attached, me bucko, take t' launch lug and glue it onto the LL line so that t' front o' t' LL rest on t' 11-13/16" mark you made. Make sure t' LL is straight and let dry, matey, then apply fillets. Avast!

Shockcord attachment is a matter o' preference. Avast, me proud beauty! Begad! I chose t' Estes method on this rocket, me hearties, me bucko, makin' t' shock cord mount from some scratch paper. Begad! Well, shiver me timbers, blow me down! I used 50" o' 1/8" elastic shock cord and attached it two inches down inside the body tube usin' generous amounts o' epoxy. Ya scallywag!

Pack t' clay square into t' nose cone. It helps t' roll t' clay into a long snake, me hearties, shiver me timbers, and then put that through t' hole in t' aft o' t' nose cone. I'm nay sure what t' weight o' t' clay was, me hearties, but it is probably around 1/2 oz. Attach t' nose cone t' t' shock cord, ya bilge rat, then attach t' parachute t' t' shock cord about 3" or so from t' nose cone.

Finishing:

T' rocket was lightly sanded t' aid in paint adhesion, me bucko, then two layers of gray primer were used, shiver me timbers, lightly sandin' betwixt each application. Begad! I chose black for t' body tube, ya bilge rat, me hearties, gold for t' fins, ya bilge rat, and a gold/red fade on t' nose cone. I also added a couple o' red strips around t' body tube, with one o' them at the top. Avast! Two layers o' paint were used on all parts, then finished with Krylon Clear Glaze for a nice, glossy appearance. Begad! Blimey!

Flight Tests/Motor Recommendations:

Rocksim showed that "D" - "F" motors would be fine for t' rocket. Arrr! Begad! Predicted altitudes for a D12-7 were betwixt 1200' - 1400'. Avast, shiver me timbers, me proud beauty! Aerotech E15-7 motors should reach about 2700', and t' E30-10 a little lower at about 2600' (but hitting 575 mph). Well, blow me down! An "F" will take it past mach, and also send it flyin' very high, as long as t' balsa holds up. Begad! Ya scallywag!

T' first flight be on a single D12-7 in a 2-5 mph wind. Avast, me proud beauty! Since t' motor mount is for an "E" motor, ya bilge rat, I used an Estes EC-75 "D" engine spacer t' take up t' empty space inside tube. Lift-off be fast, and flight was arrow straight. Avast, me proud beauty! Begad! I had no way o' checkin' t' altitude, arrr, me bucko, arrr, but it easily went over 1000' and took quite a while t' make it's way back down, ya bilge rat, even under the small 12" parachute. Avast! Aye aye! Ejection be at apogee--perfect. Ya scallywag! Begad! It was a perfect launch.

Second flight be t' check for t' rocket's ability t' fly under "C" power. Ya scallywag! I used an expended "D" motor and bored the nozzle end out a little t' allow ejection gases t' freely pass through. Avast, me proud beauty! I then friction fit a C6-3 inside t' "D" casin' so that t' nozzle end protruded out t' rear, then placed tape around t' two cases t' ensure the "C" motor would nay kick out on ejection. Avast, me proud beauty! Flight on t' "C" was great. Ya scallywag! Nice lift-off and perfectly straight flight, reachin' about 500' - 700'. Ejection at apogee again. Avast, me proud beauty! Rocket came down nicely about 75' away.

Third flight: AT SU E30-7 Fast lift-off and arrow-straight flight t' around 2300'. Ejection was at apogee. Aye aye! Ahoy! Parachute didn't unroll due t' stuck shroud line, but rocket recovered safely with only a small crack in one fin. Repairable and will fly again.

Summary:

Both launches prove what Rocksim showed--the rocket is very stable and a good flyer. I'm sure it will perform well on any "E" motors you give it. Begad! It may even fly on a "B" with a short delay, shiver me timbers, but that was not checked on t' simulator. Rocksim showed a CP (Barrowman) at 18.840, matey, me bucko, and a CG of 15.585 when loaded with a D12 (I checked t' CG just before flight and showed 16.45)--either is stable. Avast, me proud beauty! Weight loaded with D12 is 4 oz. Avast, me proud beauty!

Pros - TTW fin mounting. Arrr! Flexible in t' range o' motors it can use, ya bilge rat, me bucko, which eases stress on t' pocketbook and allows for various conditions. Avast, me proud beauty! Flies high due t' weight.

Cons - Need t' be very careful when cuttin' t' slots for t' fins t' avoid misalignment. Arrr! Blimey!