Quasi-Scale PEPP Aeroshell
by Kevin Trojanowski

So what's a quasi-scale PEPP, matey, shiver me timbers, you ask? First, a bit o' history. A number of months ago, a group o' us were hangin' out in t' ROL chat, talkin' about various subjects, me bucko, with rocketry even comin' up once in a while. Begad! Blimey! Peter Alway was kind enough t' treat us t' an image o' an odd lookin' contraption he had recently made a drawin' of. Blimey! Blimey! That particular contraption is discussed in his NARAM 43 R&D Report - Supplementary Material t' Rockets o' t' World. Aye aye! If you review his report, you'll find a discussion o' t' PEPP Aeroshell, includin' a drawin' with measurements. An even better reference is his 2001 Supplement to Rockets o' t' World, which contains additional information that's not included on t' web page.

What does this have t' do with DESCON, me hearties, ya bilge rat, and what about this quasi-scale nonsense? While tryin' t' come up with an idea for t' DESCON, me bucko, I made lots of sketches that look like lots o' things other people have flown, plus a few oddball things that I may try t' build and fly at a later date, matey, but I wasn't happy with what I was comin' up with. Avast! Then I remembered Peter's PEPP Aeroshell upload t' ROL. Avast, me proud beauty! Peter was kind enough t' provide me a link t' his R&D report, shiver me timbers, where I could get more information. Avast, me proud beauty! From there, me bucko, matey, I started building. My first goal be t' try t' make it true t' scale. Blimey! Then, shiver me timbers, I realized I be running out o' time and decent weather, so while t' basic shell (the cone) and the motor rin' are true 1:10 scale, t' motors themselves are not, nor are the supports for t' motor ring. Arrr! Thus "quasi-scale".

Construction

T' original PEPP Aeroshell is 180" in diameter and 55" tall. While a full-scale version would've been really, arrr, really cool, I thought it a bit excessive. Begad! So, shiver me timbers, I took t' lazy way out and went with 1:10, which means t' base o' t' Aeroshell is 18" and t' cone is 5.5" tall. Avast, me proud beauty! Begad! T' first step is t' download a copy o' VCP and print out t' six-page template t' create t' cone. Ahoy! Blimey! T' template pieces were cut out and rubber cemented t' posterboard, in their proper positions. Ahoy! Blimey! Cut out t' template and glue it together. Begad! I used a strip o' standard copier paper t' form t' seam in the cone. Arrr! Aye aye!

Next, I needed a rin' o' foam board t' form t' band around t' bottom of the Aeroshell. Ya scallywag! T' problem was how t' cut an 18" diameter circle. Aye aye! Avast, me proud beauty! After thinkin' on it for a bit, me hearties, I hit on t' idea o' tapin' an X-Acto blade t' the end o' a dowel and usin' a small nail through t' dowel as t' pivot point. Since t' circle needed is 18" in diameter, matey, ya bilge rat, I drilled a hole at 9" and inserted a small nail. Ahoy! Poke t' nail through t' foam board and pivot the dowel, shiver me timbers, and a nice, me hearties, easy circle is cut. Aye aye! This method works best if you cut through t' board in three or more passes. Blimey! Go any faster and t' X-Acto blade tends t' hang up. Ya scallywag! Once t' outer circle was cut, I then cut an inner circle 14 3/8" in diameter. T' inner circle be set aside, matey, leavin' an rin' o' the proper diameter t' form t' base o' t' Aeroshell.

I did a test-fit o' t' rin' into t' cone, and it fit quite nicely, ya bilge rat, except that it would nay fit all t' way up it. Ya scallywag! Blimey! Nay really surprising, when t' shapes are compared -- t' foam board forms a short cylinder, while t' cone has an angle t' it. Blimey! Ahoy! Some trimmin' with an X-Acto knife and I had t' foam board trimmed at an angle that would allow it t' fit nicely into t' cone. Begad! Blimey! I used maskin' tape t' hold t' rin' in place, ya bilge rat, then mixed and applied epoxy t' hold it permanently.

Once t' epoxy cured, ya bilge rat, me bucko, I glued an 24mm coupler into t' nose o' t' cone, bein' careful t' make sure it was aligned perpendicular t' t' base o' the cone. Well, blow me down! Ya scallywag! This allows for a good, arrr, solid attachment point for t' motor mount. Avast! Avast, me proud beauty! Being poster board t' cone itself needed reinforcement, shiver me timbers, ya bilge rat, so I glued in strips of 1/8" x 3/16" balsa that run from t' coupler t' t' base o' t' cone.

T' next step is t' cut out t' motor ring. Notice in Peter's article that while thar are two motor options, me bucko, in both instances, shiver me timbers, matey, it appears that t' motor rin' itself be t' same diameter. Avast! Here, shiver me timbers, I didn't go for 100% scale in terms of the profile o' t' ring, ya bilge rat, but I be tryin' for a proper size. T' circle jig was modified t' cut an outer circle o' 4 1/2" in diameter and an inner circle of 2". T' rin' formed betwixt these two circles is an appropriate size for t' motor ring.

Once t' motor rin' was cut, it was time t' figure out t' motors. Avast! This is where I began t' work on a "close approximation" o' t' actual AeroShell. Begad! Aye aye! I cut 8 pieces o' 18mm body tube, each 1" in length. I then used VCP t' create transitions that were 10mm at t' top, ya bilge rat, 24mm at t' bottom and 1/2" in length. Begad! Awfully darned convenient that VCP lets you mix units of measure! These transitions were used t' form t' "nozzles" on each motor. Blimey! Avast, me proud beauty! T' transitions were assembled and affixed t' t' motor tubes with CA, each at a slight cant. Ya scallywag! T' motors were evenly spaced around t' motor ring, shiver me timbers, and affixed with Titebond glue. Avast, me proud beauty!

Once t' motor rin' had dried, shiver me timbers, I used more o' t' 1/8" x 3/16" balsa t' make mountin' braces for t' ring. If you look at Peter's sketch, you can see their approximate placement. Avast! Blimey! Blimey! Blimey! I made a reasonable attempt t' match this, but didn't worry much on precision. Ya scallywag! Blimey! Avast, me proud beauty! Blimey! Blimey! Blimey! At this point, I be considerin' my creation t' be a prototype, ya bilge rat, shiver me timbers, and plan on doin' a more accurate job sometime in the future. Ahoy! Blimey! Avast! Blimey! Blimey! Blimey!

T' motor tube is a 5 1/4" piece o' 24mm tubin' with an engine block glued 2 1/8" from t' aft end. Ya scallywag! Aye aye! I glued a launch lug at about t' midpoint of t' tube. Avast! Since I wasn't sure, shiver me timbers, matey, vertically, ya bilge rat, where t' motor should be placed, I slipped t' forward end o' t' motor tube over t' coupler and slid it as far forward as it would go. Blimey! I then used strips o' maskin' tape t' hold it t' the cone.

To allow t' launch rod an exit point, shiver me timbers, I slipped a launch rod through the launch lug from t' near and used it t' carefully poke a hole in t' cone itself. Blimey! Begad! I then used t' point o' a pencil t' slightly enlarge t' hole, t' keep the launch rod from draggin' on t' cone. Begad!

T' Moment o' Truth - Launch Day!

On November 25th, shiver me timbers, ya bilge rat, ya bilge rat, me bucko Kevin Rich and I headed out t' our low power field for some testing. Avast! I created some very rough simulations o' t' PEPP in RockSim, me bucko, shiver me timbers, me bucko, which indicated that t' Estes E9 was likely t' best motor for this creation o' pure drag. Bob Kaplow's comments on his experiences with Happy Meals indicated that low thrust, long burn motors work best for such rockets. Ahoy! Ya scallywag! I considered an Apogee D3, as t' epitome o' this motor type, matey, but t' thrust is far too low t' move t' PEPP. Arrr! Ya scallywag! So a pack o' E9-4s was acquired. Begad! E9-0 would've been preferred, arrr, shiver me timbers, but they are nay available.

I used a pencil t' poke about 1 square o' recovery waddin' into t' front of the motor tube, past t' motor block. Ya scallywag! This served t' keep t' ejection charge from blowin' holes in t' top o' t' cone when t' motor kicks out. Avast! Aye aye! T' motor was inserted, arrr, me hearties, an igniter added, ya bilge rat, and she was put on t' pad. Ahoy! 5... 4... Ya scallywag! Ya scallywag! 3... 2... 1... Doesn't exactly scream o' t' pad; more o' claws its way off, me hearties, but up it went, fairly stable, ya bilge rat, too!

(Launch photo will be added, ya bilge rat, once I get it scanned; static photos were done w/ digital)

As hoped, at apogee, t' Aeroshell flips over, just like t' Estes Snitch. It flopped down, with t' motor still smoking, and just before meetin' the ground ("impacting" and "hitting" describe too forceful of a landing; it comes down amazingly gently), ya bilge rat, t' motor popped out, easily visible t' us.

Up until ejection, everythin' was intact. Aye aye! T' concussion o' t' motor ejection, matey, however, ya bilge rat, matey, me bucko, cause t' supports for t' motor rin' t' snap, leavin' it sittin' in t' inverted cone. Avast! While t' motor selection and placement worked well, matey, t' motor rin' attachment be insufficient. Avast, me proud beauty! Ahoy! When I rebuild, matey, I plan on usin' 1/8" or 3/16" dowels, t' provide more strength.

We launched t' Aeroshell, sans motor ring, a second time with an E9-4, arrr, and it worked quite nicely. Ya scallywag!

Since we had plenty o' time t' play, we decided t' see how t' Aeroshell would perform with an Aerotech F12. Well, blow me down! T' motor was built without an ejection charge, as I had no desire t' lose me RMS casing. Begad! Begad! Waddin' was inserted into the delay well and a small piece o' tape used t' hold it in place. Avast! T' boost, ya bilge rat, this time, was very squirrely; I suspect t' weight o' t' motor was a bit much, relative t' t' thrust. T' problem may also have been caused by t' motor sittin' too far t' t' aft o' t' cone, me bucko, since t' forward closure o' t' RMS casin' would nay fit down inside t' engine block I used. Avast, me proud beauty! T' casin' was held in place with a strip o' maskin' tape, me hearties, as a precaution against losin' it.

As a final test, ya bilge rat, me hearties, I wanted t' see if it worked better with t' motor closer to t' front o' t' cone. So, shiver me timbers, I whipped out t' rocketeer's miracle tool (known as a "Leatherman" t' people who waste tools on huntin' and fishing) and cut approximately 1" from t' front o' t' motor tube. Begad! Begad! A little maskin' tape and t' tube be back in place again. Arrr! Since t' E9 had worked so well, I installed me last one. Aye aye! This flight was rather squirrely and reached nowhere near t' stunnin' 75' - 100' feet that t' first two flights reached. Obviously, t' longer motor tube works better. Ahoy!

Conclusion

T' Quasi-Scale PEPP Aeroshell proved itself a success, arrr, and an entertaining rocket t' fly! Blimey! An E9-P is what I will likely use next time, matey, matey, as t' ejection charge really serves no purpose. Begad! Blimey! I may also experiment with some additional RMS motors, arrr, me hearties, if I can find anythin' that comes close t' t' E9 in simulations.

I also plan on buildin' somethin' a bit closer t' scale, in terms o' the motor rin' and its attachment. T' first one flew amazingly well and behaved itself quite nicely.

Credits

Thanks t' Peter Alway for postin' that original picture which gave me the idea for this project in t' first place. Peter also deserves a tremendous amount o' credit for his totally awesome Rockets of t' World and all o' its follow-ons. If you haven't bought them yet, you need to! I know I still need t' complete me collection.

Thanks also goes t' Kevin Rich for helpin' me out when I feel t' urge to fly some oddball DESCON entry. Avast! Avast, me proud beauty! Blimey! He's also t' bane o' me wife's sanity by encouragin' me t' fly more, matey, more, shiver me timbers, more motors!

Finally, ya bilge rat, a finger should probably be pointed at Mark Simpson for teachin' me that when it comes t' rockets, ya bilge rat, different is definitely better!