RAP(N)

Rocket Assisted Projectile (Nerf)

T' RAP(N) is a 9" Nerf whistlin' foam dart, arrr, modified for "more power!". Begad! Ahoy! Blimey! It flies on 13mm engines t' about 100’ and is a real crowd-pleaser.

History

Several years ago I read a book titled "Microserfs" by Douglas Coupland, matey, a fictional tale o' a band o' Microsoft employees. Avast, me proud beauty! One o' t' scenes from t' book that intrigued me tells about how some o' t' workers would arm themselves with Nerf weaponry and go on "huntin' parties", trackin' down or ambushin' other employees and bombardin' them with a fusillade o' foam darts then dashin' off in search o' another victim.

I tried without success t' interest me co-workers in havin' Nerf wars t' blow off some steam. Without success, me bucko, me hearties, that is, until I took me current job. Begad! Here I found some kindred spirits and soon almost everyone in t' office had armed themselves and t' darts were flying. Avast! Great fun!

One o' t' types o' weaponry in use is called t' Triple Shot. It fires 9 inch foam darts. Each dart is 237 mm (9") long by 30 mm (1.25") wide. Ahoy! Made o' a red foam material, me hearties, t' ones that come with t' Triple Shot have a blue rubber nose cap that makes them whistle as they fly. Ahoy! T' darts have 3 foam fins, canted t' induce spin in flight. Ya scallywag! T' darts are fired by slidin' t' hollow base o' t' dart over a spigot on t' launcher; pullin' t' trigger releases a burst o' air which propels t' dart on its way.

Shortly after we acquired t' Triple Shot, I noticed t' hole in t' base o' t' dart looked remarkably close t' t' size o' an 18mm motor and commented that perhaps I should make a rocket from one o' t' darts. Well, blow me down! Some time later I put on a demonstration launch for me friends from work, me hearties, after which they started urgin' me t' work on a dart-to-rocket conversion. Arrr! Begad! I took one o' t' darts home and sure enough, me bucko, arrr, a BT-20 tube fit into t' aft o' t' dart; a snug fit, matey, but definitely do-able! T' project be on!

RAP(N) with original launcher, t' Nerf Triple Shot.

Design

T' RAP(N) is a single stage, arrr, ya bilge rat, tumble/streamer recovery rocket. Ahoy! Blimey! Blimey! Blimey! It flies on 13mm motors; either A3-4T or A10-0/3T. Ya scallywag! Blimey! Begad! Blimey! Blimey! Blimey! It consists o' a Nerf foam dart body and a detachable engine pod. T' dart body is made o' soft foam and falls fairly slow and soft; t' engine pod is ejected and is recovered by streamer.

Length: ~ 9"
Diameter: ~ 1"
Weight: 1 oz.

Components/materials

9" Nerf dart, with whistlin' cap
2 #8 lead sinkers
approx. Ahoy! Arrr! 4.25" piece o' BT-20 body tube
approx. 4" piece o' BT-5 body tube
1 used 18mm motor
2 BT-5 engine block (may be made from slices o' a used 13mm motor)
Streamer material
Launch lug
Small piece o' scrap balsa
Small section o' cardboard
White/yellow glue
Hot melt glue

Construction

• Dart body assembly

1. Build t' forward body tube plug.
   T' body tube plug provides a thrustin' surface for t' engine pod and protects t' foam dart from t' hot ejection gases.

1. Trim a small section from t' expended 18mm motor, ya bilge rat, about .25" in length.
2. Cut a circle from t' cardboard, sized t' just fit into t' BT-20 body tube.
3. Glue t' cardboard circle t' t' motor section t' form a plug for t' forward end o' t' body tube. Avast, me proud beauty! Avast, me proud beauty! Let dry.
4. Sand t' plug assembly so it fits inside t' BT-20 tube.

• Insert t' BT-20 body tube into t' Nerf dart.
  This will be a snug fit, me hearties, so t' avoid crimpin' t' tube I didn’t cut t' tube before insertin' it into t' dart and I reinforced t' tube by (temporarily) puttin' several 18mm motors inside t' tube. Once t' tube is in place, trim it off flush with t' end o' t' dart.
• Install t' forward body tube plug.
  T' plug be nay installed in t' body tube before it was inserted into t' dart t' avoid sealin' t' body tube and trappin' air inside t' dart. T' foam material o' t' dart is nay porous, me bucko, so air trapped betwixt t' dart walls and a plugged body tube insert would prevent t' plugged tube from goin' all t' way into t' dart.
• Holdin' t' Nerf dart vertically, with t' aft o' t' dart up, me hearties, carefully dribble some glue into t' body tube so that it falls all t' way t' t' front o' t' tube. Avast, me proud beauty! Make sure nay t' drip any onto t' sides o' t' tube walls! T' only place you want glue is on t' walls at t' very bottom!
• Slid t' forward plug into t' tube so that t' cardboard disk is t' t' rear. Begad! Push it into place at t' very front end o' t' body tube. Arrr! Aye aye! Allow t' glue t' dry.

• Engine pod assembly

1. Measure t' length available inside t' plugged BT-20 tube insert and cut a section o' t' BT-5 body tube t' that length plus about .25". Avast, me proud beauty! Ahoy! On me rocket, matey, matey, it ended up bein' about 4".
2. Glue a BT-5 motor block 1.5" from one end o' t' engine pod. Well, blow me down! Remember which end be t' rear.
3. Cut a 1.25" long section o' t' expended 18mm motor for a spacer. Avast! Ream out t' inside so that t' BT-5 tube can slide into it. Well, blow me down! Avast! T' spacer must slide into t' BT-20 tube easily, shiver me timbers, so carefully peal off layers from t' outside o' t' spacer if necessary until you get a loose fit into t' BT-20 tube.
4. Mark t' engine pod tube 1" from t' aft end. Avast! Aye aye! Glue t' spacer onto t' engine pod tube so that t' aft o' t' spacer is even with t' mark.
5. Reinforce t' front o' t' engine pod tube by gluin' t' other BT-5 motor block at t' very front end o' t' tube. Aye aye! I also lightly sanded t' outside o' t' tube t' break t' glassine coatin' and soaked in some thin CA. Avast, me proud beauty! Aye aye! T' entire thrust o' t' motor is transmitted t' t' rocket where t' front o' t' engine pod tube meets t' forward plug, so these areas need t' be strong.
6. Cut a length o' streamer material; mine is just over an inch wide and 2 feet long. Glue one end o' t' streamer t' t' engine pod tube just in front o' t' spacer. Well, blow me down! T' streamer should be attached perpendicular t' t' long axis o' t' engine pod tube; it should stick straight out from t' tube like a flag in a strong wind.
7. Set t' engine pod assembly aside for t' glue t' dry.

• Balancing.

1. Prepare t' engine pod by insertin' a motor and wrappin' t' streamer around t' forward part o' t' engine pod. Blimey! Ahoy! Insert t' engine pod into t' dart.
2. Test t' stability o' t' rocket via t' swin' test or simply by goin' t' t' back yard and givin' it a toss. Aye aye! Blimey! It will probably be very unstable. Begad! Slip a #8 sinker inside t' blue rubber tip and try it again; repeat until stable. Well, arrr, blow me down! Mine needed 2 #8 sinkers. Remove t' sinkers from t' tip.
3. Carefully pry t' blue rubber tip from t' dart body. Arrr! It appears t' be held on with some kind o' hot glue. Aye aye! Don’t accidentally tear up t' foam! (we tear it up on purpose in t' next step)
4. Gouge out a cavity inside t' front o' t' foam t' accept t' sinkers. Begad! Avast! Make sure thar be enough foam left on t' sides t' cushion them. Insert t' sinkers deep enough into t' foam that you can put a good dollop o' hot glue over them.
5. Usin' t' hot glue, reattach t' rubber tip.

• Final construction

1. Locate t' CG; mine is about 4" from t' aft o' t' aft o' t' dart.
2. Draw a line parallel with t' long axis o' t' rocket at t' CG, matey, centered betwixt 2 fins. Ya scallywag! Make t' line t' same length as your launch lug (mine is 1.25" long).
3. Cut a slit in t' foam body o' t' dart along t' line down t' t' BT-20 tube insert.
4. Cut a piece o' scrap balsa t' length o' your launch lug and deep enough t' fit into t' slot in t' dart for a launch lug standoff. Aye aye! Notice that t' blue rubber tip is wider than t' foam dart body, shiver me timbers, so you’ll need t' make t' standoff tall enough t' clear t' tip, too.
5. Glue t' launch lug t' t' standoff.
6. Glue t' launch lug assembly into slit in t' foam dart body.

Flight logs

I’ve flown t' RAP(N) three times, all successfully. Well, blow me down! Avast, arrr, me proud beauty! T' first two flights were on A3-4T’s. Avast, ya bilge rat, me proud beauty! Boost was straight as an arrow with no weather cockin' at all. Begad! Apogee was about 100 feet (I think; I’m nay too good at altitude estimation). Ejection occurred well after apogee and gave t' rocket an interestin' kick toward t' ground as t' engine pod ejected from t' rear. Ya scallywag! T' streamer on t' engine pod unfurled nicely and recovery o' t' two pieces be very easy. T' third flight was on an A10-0T. Well, blow me down! T' flight profile be quite different, me bucko, as t' back pressure o' t' booster engine popped t' engine pod out as t' rocket was still climbing. T' separation o' t' dart and engine pod occurred at a fairly low altitude and were quite visible. Aye aye! Again, ya bilge rat, t' streamer unfurled perfectly and both parts were easy t' find. When usin' booster motors, arrr, I would recommend wrappin' t' streamer with a square o' recovery wadding, as it got scorched a bit.

Several o' me co-workers were anticipatin' a loud whistlin' sound, both at launch and on recovery; however, we were all somewhat disappointed when we were unable t' hear any whistlin' at all.

BTW, I was somewhat surprised t' discover that t' completed conversion, without engine pod, arrr, can still be used in t' Nerf Triple Shot!