Way cool, John! I want to see this one fly.

A boosted dart has been on my list for a while. The problem is that I have too many other projects that are ahead on the priority list.

Just curious about you comment about the mass of a large booster affecting the seperation. Wouldn't it be more of a question of drag? Isn't point of separation is when the force of drag on the booster is greater than the mass times acceleration of the dart?

I'm sure there is some really cool math here and you could figure it out with fancy computers and calculus - but wouldn't it be more fun to just build and fly a few rockets. You know, like trial and error. Or, just like in college calc, multiple choice.

BTW, A boosted dart contest would be way cool, too.

Bill Heath and I are also in the design stage for a boosted dart. In our case we're looking at a 38mm dart and a 3" booster. In fact, we're building a 100% scale Loki Dart. (As a matter of fact, the original flew with 9000 nSec of total impulse in a 1.8 second burn and regularly reached altitudes in excess of 230,000') In that case the dart weighed approximately 15# (weight varied due to different instrumentation - the earliest flew with just a radar chaff dispenser)

I have a number of websites and resources you may be interested in John.

Warren

Just curious about you comment about the mass of a large booster affecting the seperation. Wouldn't it be more of a question of drag? Isn't point of separation is when the force of drag on the booster is greater than the mass times acceleration of the dart?

Drag is surely a big chunk of the equation, but you also need mass to play its part. The perfect scenario is a light booster with big draggy fins and a slender, heavy dart.

Just as a piece of paper that is crumpled up and tossed will not go far, the same sized piece of paper with a golf ball inside (for added mass) will go much farther. Same principle with the dart -- you want the lighter, draggier booster to get pulled away from the more massive, yet more slippery dart.

This will be very cool... I HOPE 😮

This will fly this summer. My thought is that I will use my SSSS bird for the dart. I'll have to add ~6# of lead, though. YIKES!

Bill Heath and I are also in the design stage for a boosted dart.

Warren, when will you guys be ready? I don't think we will be in the air much b4 July or August. Elvis Jr. is building the booster, and he is in school for a while....

I don't see our bird flying until '08 as we still have some issues to deal with such as what will we fly it on. The loki dart also requires a special helical launcher that spins the bird up to 60rpm or so during the launch as the fins aren't quite big enough for stability without spin stabilization. Also, I want to fly it on a 3" L or M motor, but we have to figure out how to keep the altitude down.

Warren

By the way, I'm thinking of turning my dart out of stainless steel pipe. with a solid stainless nosecone.

John,

I understand the analogy of the optimum weight of the combined golf ball and crumpled paper. Even in this case the ball will go further if it sheds it's paper shroud.

But it seems like your talking about "gravity separation" instead of "drag separation". Just like dropping a hammer and a feather on the surface of the moon, wouldn't drag be the deciding factor?

Could you RockSim it by putting a 1/4A in the dart and then runing the optimal mass function?

Bill Heath and I are also in the design stage for a boosted dart. In our case we're looking at a 38mm dart and a 3" booster. In fact, we're building a 100% scale Loki Dart. (As a matter of fact, the original flew with 9000 nSec of total impulse in a 1.8 second burn and regularly reached altitudes in excess of 230,000') In that case the dart weighed approximately 15# (weight varied due to different instrumentation - the earliest flew with just a radar chaff dispenser)

I have a number of websites and resources you may be interested in John.

Warren

I believe it actually was a bit more impulse than that. Looking at the specs here, it made 9.0 kN of thrust for 1.9 seconds, which is 17100 Ns of impulse. So, it used almost a full N motor. Considering that its ceiling was 180 thousand feet and it reached around mach 5.1, that's quite a bit more speed and altitude per Ns than any current hobby N record though, and if you make a decent replica, you should be able to push the BALLS waiver on a big M or small N.

Note that for a rocket to be classified as an "amateur rocket", it must have a ballistic coefficient that is lower than 12 lbs/ square inch, limiting a 38mm dart to 21 lbs and a 29mm dart to 12.27 pounds. You can still do a lot within this limitation though.

I was actually thinking about machining the dart body out of thin-wall stainless and using a solid nose. I have enough blueprints to actually duplicate the coupling transition if I can get the machinist where I work to turn his hand to it. Between the airframe, transition piece and nose, the dart will weigh in about 7#. Optimal weight is around 18-20# from the stuff I've read about the Loki.

I want to build a very lightweight booster of 3" carbon aerosleeve with maybe a 3oz sanding veil. No phenolic inside. I have a deployment mechanism that involves logically ANDing the apogee outputs of an altimeter with a timer output and a microswitch that closes when the dart separates. With a machined aluminum transition section at the front and CF plate fins with say 3 layers of tip-2-tip carbon I can probably keep the weight below 5# not including the motor casing. The most important thing in drag separation is that the booster not only have a greater frontal area than the dart, it must have much less relative mass in order for the air drag on the booster to reliably separate them.

Are you sure about those figures? I'm using Morrow & Pines "Small Sounding Rockets" book and they say a total of 9,000 nSec of impulse. What you say makes more sense to me though.

Warren

I'm just going off that site I linked to (the "here" is a link if you click it). It claims 9000 newtons thrust for 1.9 seconds, with a peak velocity just a hair over mach 5 (3900mph), and then a LONG coast to 180000 feet or so.

I'll note that it actually claims a much lighter dart than you are quoting. Here are the figures that I found:

Length (incl. booster): 2.63 m (8 ft 7.5 in); dart: 1.02 m (40 in)
Diameter: Booster: 7.62 cm (3 in); dart: 3.49 cm (1.375 in)
Finspan: Booster: 12.7 cm (5 in); dart: 8.6 cm (3.4 in)
Weight (incl. booster): 13 kg (29 lb); dart: 3.2 kg (7 lb)
Speed: 6275 km/h (3900 mph)
Ceiling: 55 km (34 miles; 180000 ft)
Propulsion: JPL 132A solid-fuel rocket; 9.0 kN (2030 lb) for 1.9 s

I also found specs for a super loki capable of 260000 feet, but that has over 50000 Ns (so it is up into the P range)

Length (incl. booster) 3.24 m (10 ft 7.5 in); dart: 1.16 m (45.7 in)
Diameter Booster: 10.2 cm (4 in); dart: 3.7 cm (1.44 in)
Finspan Booster: 20.3 cm (8 in); dart: 11.7 cm (4.62 in)
Weight (incl. booster) 29 kg (64 lb); dart: 6 kg (13.2 lb)
Speed ?
Ceiling 80 km (50 miles; 260000 ft)
Propulsion Aero Dyne SR110-AD-1 Super Loki solid-fuel rocket; 25 kN (5520 lb) for 2.1 s

Another one, the Loki-Wasp with the Loki booster (as opposed to the Loki-II) appears to reach just over 100k at mach 4 with around 11kNs:
http://www.designation-systems.net/dusrm/app4/hasp.html

John,

But it seems like your talking about "gravity separation" instead of "drag separation". Just like dropping a hammer and a feather on the surface of the moon, wouldn't drag be the deciding factor?

Could you RockSim it by putting a 1/4A in the dart and then runing the optimal mass function?

With regard to the sim, that exactly what I've been doing.

Regarding mass and drag... what got me going on all of this was an article at http://www.rocketryplanet.com/content/view/236/38/ That author had this to say:

"Basic Boosted Dart Theory: A narrow un-powered dart rides on top of a larger diameter booster. At burnout, the difference in drag separates the dart from the booster. By keeping the booster light, most of the remaining mass, and therefore energy, is retained in the dart and it coasts to a much greater altitude than the booster."

That said, this guy did a lot of thing that were far from optimal. For example, he used an Acme fin can on the booster, which weighs about a pound by itself. Definitely didn't keep the mass down in this booster. We are going to try to do just that. Also along those lines - you'd want a very fast burn motor, like Warp 9 or Blue Thunder. Negative gees will help separate the two.

BTW, darts are NOT allowed by TRA for altitude attempts. Don't know why, but they are specifically precluded from the record books.

BTW, darts are NOT allowed by TRA for altitude attempts. Don't know why, but they are specifically precluded from the record books.

Makes sense to me. Its a rocket altitude record not a dart altitude record.

BTW, darts are NOT allowed by TRA for altitude attempts. Don't know why, but they are specifically precluded from the record books.

Makes sense to me. Its a rocket altitude record not a dart altitude record.

On the other hand, if you put a 1/4A in the "dart" which weighs 10#, you'd be eligible for the staged/complex record. Gotta draw the line somewhere...

Our old website had all the club's rules for setting club altitude records, and IIRC darts were allowed for NCR records. Having said that, I don't believe I could build a dart that would exceed any one of the club's records. It is a cool concept, but I don't think it is the most efficient way to get there (not for me, anyway). L-O-N-G burn motors would be my first choice, all other things being equal.

This is a kind of project were there are so many different words that create the whole picture. There alot of ways to do some fial some work. I think with going to a perfect scale of the loki( which i did research ) isnt a good idea. Becasue there booster is very small with small fins and there booster was a solid rocket the whole way up.... and we want to get the booster back without going 20,000 feet. My hopes i dont know about John is to fly it at MHM give or take a month.