Sprint

The fins are of the classic high performance shape and are one of the reasons I chose this kit for the duration requirements. They are made from very thick ¹/10th of an inch balsa that took a sanded ¼ inch leading and trailing edge taper well. I'm sure the fins are this thick to resist damage on landing, the bird descends at ~30 feet per second under its streamer. Oddly, the instructions do not say to shape the fins in any way, though they do direct that a pre-coat of glue be applied to the root edge and allowed to dry, presumably to improve strength. The maker's image at right shows them attaching to the very end of the body tube, but the pic is missing the motor mount that sticks out a ¼ inch from the end. Or at least it's supposed to; I left mine hang out ³/8th of an inch, the same amount of motor overhang. This will allow me to tape the motor in with ¾ inch masking tape for additional retention. The bird is over stable on even the C6 motor, so I felt I could get away with this.

The two foot streamer is affixed using one of those horrendous plastic tabs that Quest uses on their parachutes. It does work better in this application, but only marginally, one just does fit in this small rocket. Ten inches of Quest's T20 tube makes up the main body, and the motor mount is a slip fit inside this, making for a very easy installation; no centering rings. The thick motor block provides an excellent attachment point for the ~300# Kevlar that forms half the shock cord. I've always avoided Quest's round elastic that makes up the other half in the past, but I used it this time. It is a lot stiffer than flat elastic, but I figured it couldn't do much harm here. I attached the streamer to the elastic with a small snap swivel so I could switch to a Rogue nine inch nylon 'chute for the parachute duration requirement.

It seems that the intention of the NARTREK allowance of using the same kit for both requirements is that the rocketeer switch a streamer into a parachute model, but it certainly seems more prudent to do it this way. A rocket that's designed to recover under a canopy might not survive the faster descent rate of a streamer. I may have trouble anyway; many folks have complained of busted fins on the Sprint. I think I'll attempt the parachute duration requirement first, and early in the morning when thermals are not too strong.

First, as always, I sealed the fins with light-weight spackle, sanded that with 400 grit sandpaper, then applied a coat of Krylon All-purpose Grey Primer just to the lower section. That was sanded with 400 grit as well, and then I added a coat of store brand white gloss for the upper section. In the same vein as the streamer/parachute issue, I figured I could finish the model in whatever manner I wished and still claim it was a kit. I'd considered painting the lower section black as shown in the bag art, but went with a store brand Apple Red instead.

The included decals are opaque, heavy, not pre-cut and only semi-gloss, which prompted me to scan and reprint them on real decal stock to reduce drag and weight. The bird was way over the manufacturer's claimed weight already, and I didn't want to add to the problem. I also took the opportunity to convert the color to a true red, the manufacturer's deep pink not appealing to me. The decals take up a lot more room than shown in the pic at right, too.

With the exception of the A6, my fin airfoiling eliminated all of Quest's recommended motors. Predicted performance is indeed impressive, and I'd only recommend the C motors if you never want to see the bird again. While the A8-5 is a bit late, the other motors are very well timed, and should eject near apogee. The 13 mm A3-4 with a well-built adapter still takes the bird higher than the 18 mm A motors. The ½A3-2 and ½A6-2 will work, but they only get Sprint to about 130 feet before ejection, which is a bit early. The parachute only adds about 10% to her weight, letting her reach over 800 feet on the planned B6-6.

Her first flight was on a B6-6 in streamer configuration. I had angled her into the wind way too much, and ejection was very late. The nose cone came back and hit a fin, but other than some paint transfer, no damage was done. Duration was around 27 seconds and given the poor flight path, I thought that was remarkable. Her next flight was on the same motor, same recovery device, but was pointed straight up this time, thank you. Deployment was at apogee and duration was 41 seconds, enough for the NARTREK Bronze streamer requirement.

Her next flight was on the same motor but with the parachute. Ejection was again at apogee, and wasn't noticeably lower than the last shot. Duration was a Buck fifty-one, almost double the full minute needed for the NARTREK Bronze parachute requirement. Her fourth flight was for a Predicted Duration event in competition, and I switched her back to the streamer and wrote "41" on the flight card. Time was 39 seconds, giving me less than 5% error, the best I've ever done in the event. This is significant, for the 41 seconds was achieved in near calm conditions, while the 39 was done in moderate winds.

I replaced the stock streamer with the one I'd built for my abortive D Streamer II bird, which is 3"x30" LDPE, and flew her on a B6-6. The flight went fine, with deployment occuring just past apogee. The flight was in high winds, so I didn't bother to time it. It didn't seem to improve her duration much, though; I'll refly this again when conditions are better and try to get actual numbers.

I flew her with the 3"x30" streamer on an A6-4 just to get a baseline for comparison, and she only spent 14 seconds and change in the air. Not good, but with work I can improve that.

Specifications

Statistic	Claimed	Actual
Length	14½ in.	1215/16
Diameter	0.787 in.	0.787 in.
Weight	2/3 oz.	0.8 oz.

Estimated Performance

Engine(s)	AGL (ft.)	Speed (ft./sec.)	Accel (Gs)
A3-4	410	170	15.5
A6-4	375	180	32.5
A8-5	395	170	24.6
B6-6	835	310	28.7
C4-7	1,690	415	26.8
C6-7	1,580	480	30.2