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

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

Construction:

T' make this rocket you need:

Parts List:

• 1 Estes 18" BT 55 tube
• 1 PNC 55 nosecone (5.5" long, ya bilge rat, conical or ogive, matey, 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, ya bilge rat, 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. Blimey!

T' first step is t' cut t' fins. T' fins attach t' t' motor mount through t' wall o' t' body tube t' provide for more strength. Blimey! Makin' t' fins from t' template is easy, shiver me timbers, as long as t' template is correct. Ya scallywag! Aye aye!

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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, ya bilge rat, me bucko, then I used t' first fin as t' template for the rest o' them. Sand fins so that they are t' same size, me hearties, then sand leading and trailin' edges for desired shape, matey, ya bilge rat, if desired--I went with airfoil shape. Ya scallywag!

Now you need t' mark t' body tube for t' 3 fins. Ya scallywag! 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. Avast, me proud beauty! Begad! Mark along t' LL line a spot 11-13/16" from t' front o' t' body tube. Ya scallywag! Aye aye! This is where t' LL will go. On each fin line, me bucko, me hearties, place a mark 5/8" from t' aft o' t' tube, and another 3" from t' rear. Ya scallywag! Usin' a sharp hobby knife, shiver me timbers, cut alongside t' fin lines (offset 1.5mm each side) betwixt t' two marks you made, arrr, This is for fin attachment. Begad! Once t' cuts are done, test each fin into t' slots. Sand as needed. Well, blow me down! They should extend approximately 1/4" behind t' aft o' t' body tube. Ya scallywag!

(Click t' Enlarge)

Assemble motor mount and centerin' rings as per instructions provided in the Estes "E" motor mount kit. Begad! If you are without a kit, matey, me hearties, 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, ya bilge rat, arrr, me bucko, across t' tube, 1" from t' front o' t' motor tube

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

Insert "E" hook into t' cut you made, me hearties, extendin' t' t' aft of the tube

Fit one centerin' rin' up t' t' 5/8" mark, and t' other up t' the 1" spot where t' hook is inserted. -- You may want t' dry-fit t' rings to ensure proper fit. Aye aye! There should be approximately a 2-3/8" gap between the front and aft rings. Begad! Be sure it is big enough since t' fins will attach there. Well, blow me down! 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). Begad! Be sure t' centerin' rings are nay inside the slots in t' tube, as this will prevent your fins from fittin' in the slots. Avast, me proud beauty! Blimey! Be careful nay t' get epoxy into t' fins slots. Let dry. Aye aye!

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

After t' fins have been attached, 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, me hearties, matey, then apply fillets.

Shockcord attachment is a matter o' preference. I chose t' Estes method on this rocket, makin' t' shock cord mount from some scratch paper. Aye aye! Arrr! I used 50" o' 1/8" elastic shock cord and attached it two inches down inside the body tube usin' generous amounts o' epoxy. Aye aye!

Pack t' clay square into t' nose cone. Begad! Ahoy! Blimey! It helps t' roll t' clay into a long snake, matey, matey, matey, 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, shiver me timbers, me bucko, me bucko, but it is probably around 1/2 oz. Attach t' nose cone t' t' shock cord, shiver me timbers, me hearties, then attach t' parachute t' t' shock cord about 3" or so from t' nose cone. Ya scallywag! Blimey!

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. Aye aye! Blimey! I chose black for t' body tube, me bucko, gold for t' fins, arrr, and a gold/red fade on t' nose cone. Avast, me proud beauty! Blimey! I also added a couple o' red strips around t' body tube, me bucko, with one o' them at the top. Two layers o' paint were used on all parts, then finished with Krylon Clear Glaze for a nice, shiver me timbers, glossy appearance.

Flight Tests/Motor Recommendations:

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

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

Second flight was t' check for t' rocket's ability t' fly under "C" power. I used an expended "D" motor and bored the nozzle end out a little t' allow ejection gases t' freely pass through. 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. Blimey! Flight on t' "C" was great. Ahoy! Nice lift-off and perfectly straight flight, reachin' about 500' - 700'. Ejection at apogee again. Rocket came down nicely about 75' away.

Third flight: AT SU E30-7 Fast lift-off and arrow-straight flight t' around 2300'. Avast, me proud beauty! Ejection be at apogee. 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. Begad! Begad!

Summary:

Both launches prove what Rocksim showed--the rocket is very stable and a good flyer. Avast, me proud beauty! Blimey! Avast, me proud beauty! Blimey! I'm sure it will perform well on any "E" motors you give it. It may even fly on a "B" with a short delay, matey, me bucko, but that be not checked on t' simulator. Begad! Blimey! Rocksim showed a CP (Barrowman) at 18.840, 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! Blimey! Weight loaded with D12 is 4 oz. Arrr! Blimey! Ya scallywag! Blimey!

Pros - TTW fin mounting. Ahoy! Flexible in t' range o' motors it can use, which eases stress on t' pocketbook and allows for various conditions. Begad! Flies high due t' weight. Arrr!

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