RAP(N)

Rocket Assisted Projectile (Nerf)

T' RAP(N) is a 9" Nerf whistlin' foam dart, modified for "more power!". Arrr! 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, me hearties, a fictional tale o' a band o' Microsoft employees. Begad! Begad! 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", arrr, 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. Begad! Without success, that is, until I took me current job. Here I found some kindred spirits and soon almost everyone in t' office had armed themselves and t' darts were flying. 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. Begad! Made o' a red foam material, t' ones that come with t' Triple Shot have a blue rubber nose cap that makes them whistle as they fly. Well, blow me down! T' darts have 3 foam fins, me hearties, me hearties, canted t' induce spin in flight. 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. Blimey! Some time later I put on a demonstration launch for me friends from work, arrr, arrr, after which they started urgin' me t' work on a dart-to-rocket conversion. Begad! I took one o' t' darts home and sure enough, arrr, a BT-20 tube fit into t' aft o' t' dart; a snug fit, ya bilge rat, but definitely do-able! T' project was on!

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

Design

T' RAP(N) is a single stage, ya bilge rat, tumble/streamer recovery rocket. Begad! It flies on 13mm motors; either A3-4T or A10-0/3T. Avast, me proud beauty! Well, me hearties, blow me down! It consists o' a Nerf foam dart body and a detachable engine pod. Ahoy! 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, shiver me timbers, with whistlin' cap
2 #8 lead sinkers
approx. Ya scallywag! 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, shiver me timbers, about .25" in length.
2. Cut a circle from t' cardboard, shiver me timbers, 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. 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, shiver me timbers, 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. Ya scallywag! Once t' tube is in place, trim it off flush with t' end o' t' dart.
• Install t' forward body tube plug.
  T' plug was nay installed in t' body tube before it be inserted into t' dart t' avoid sealin' t' body tube and trappin' air inside t' dart. Begad! T' foam material o' t' dart is nay porous, me bucko, matey, 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. Well, blow me down! Make sure nay t' drip any onto t' sides o' t' tube walls! Blimey! 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. Push it into place at t' very front end o' t' body tube. Ya scallywag! Begad! 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". On me rocket, matey, arrr, me bucko, it ended up bein' about 4".
2. Glue a BT-5 motor block 1.5" from one end o' t' engine pod. Remember which end be t' rear.
3. Cut a 1.25" long section o' t' expended 18mm motor for a spacer. Avast, matey, me proud beauty! Ream out t' inside so that t' BT-5 tube can slide into it. Aye aye! Avast! T' spacer must slide into t' BT-20 tube easily, 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. 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. I also lightly sanded t' outside o' t' tube t' break t' glassine coatin' and soaked in some thin CA. 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. Avast, me bucko, me proud beauty! Glue one end o' t' streamer t' t' engine pod tube just in front o' t' spacer. Aye aye! Arrr! 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. 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. Blimey! Blimey! It will probably be very unstable. Slip a #8 sinker inside t' blue rubber tip and try it again; repeat until stable. Mine needed 2 #8 sinkers. Arrr! Blimey! Remove t' sinkers from t' tip.
3. Carefully pry t' blue rubber tip from t' dart body. Blimey! Blimey! Begad! Blimey! It appears t' be held on with some kind o' hot glue. Ahoy! Blimey! Don’t accidentally tear up t' foam! Blimey! (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. Make sure thar be enough foam left on t' sides t' cushion them. Well, blow me down! 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, ya bilge rat, matey, centered betwixt 2 fins. Begad! Begad! 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. Notice that t' blue rubber tip is wider than t' foam dart body, ya bilge rat, 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. Ya scallywag! Ahoy! T' first two flights were on A3-4T’s. Ahoy! Boost be straight as an arrow with no weather cockin' at all. Well, blow me down! Apogee be about 100 feet (I think; I’m nay too good at altitude estimation). Ya scallywag! Ejection occurred well after apogee and gave t' rocket an interestin' kick toward t' ground as t' engine pod ejected from t' rear. Aye aye! Blimey! T' streamer on t' engine pod unfurled nicely and recovery o' t' two pieces was very easy. T' third flight was on an A10-0T. T' flight profile was quite different, as t' back pressure o' t' booster engine popped t' engine pod out as t' rocket was still climbing. Begad! T' separation o' t' dart and engine pod occurred at a fairly low altitude and were quite visible. Arrr! Blimey! Again, shiver me timbers, t' streamer unfurled perfectly and both parts were easy t' find. Ya scallywag! When usin' booster motors, me hearties, 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, arrr, me hearties, I was somewhat surprised t' discover that t' completed conversion, matey, without engine pod, me hearties, ya bilge rat, can still be used in t' Nerf Triple Shot!