Let's talk about boosted darts!

[Off Grid Gecko]

So, yeah, it's a long way off and I'll probably never have the extra cash to get there, but I have been working on some "secret plans" for an L3 project I'd like to someday realize. It involves a separation of the nose cone and payload section after burnout to coast as high as possible while the booster drops away and deploys its own recovery system independently.
Been digging around the forums here and not really finding what I need. The coast stage of the rocket will have gyro stabilization as part of its pack, but this is mostly for killing rotation near apogee and I'm not sure it will do so well with a heavy booster attached, or for replacing stability of the coast stage, so that aside. I keep going over the numbers and it looks like the top part of the rocket will need fins. I'm sure even with rotation that unstable is still unstable (i.e. the CP is ahead of the CG), but I'm trying to figure out a way to rip the fins off the dart part to minimize drag.
Curious about how stability changes when one is solidly supersonic, and so far the answers point to the CP moving forward due to lower air pressure.
My drawing at the moment is a 60" dart with 3" tall fins (5.5" diameter blue tube body), and while it passes the checks on the Cambridge simulator, it looks ugly as sin as I envision this giant atop a 50-60" booster stage.
Since they are the same diameter pipe, I'm wondering if a separation (either by drag or by pyro) is even worth the trouble. It does make the rocket horribly complex, and at some point I'll be adding another booster stage below for the sounding rocket attempt.
Anyway, would love to hear thoughts on detaching a NC payload from the main rocket. Rules of thumb, past experience, etc. Anything you want to say. I had one idea of strapping 3-4 rods to the outside of the upper section that might stabilize it bottle-rocket style, but I'm not sure that's a good idea for tons of reasons.

 

[caveduck]

You should go have a look at the general design of the NASA Super Loki Dart. Best performance is when you put as much of the mass as possible into a very small diameter dart, and then crank it up to Mach 4-5 as fast as possible with a high thrust booster. The Super Loki used a 4" x 78" motor with 39,600 Nt-sec (basically a full O motor), and would put the dart to around 300,000 ft. The dart was 1.625" in diameter, largely steel, and weighed 13 lb. Liftoff weight was ~62 lb. It was launched from a helix launcher that spun the rocket up to around 1000 rpm since the fins become ineffective at altitude. The NASA final report on the meteorological version is a good read: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680026183.pdf. The key general parameters are on p. 7.

A full scale one would need to be flown at White Sands...at the standard 80 degree launch angle the ballistic trajectory goes 84km downrange. (!!!)

I'm surprised that no one in sport rocketry has done this very much (I've heard of one or two tries), a successful full scale one gets you close to the magic 100km mark without even staging once, and using a motor that Aerotech can build. It might be really interesting to build one with about 1/4 the performance (using a high thrust M motor perhaps) to see if it would get you to 75,000 ft.

 

[MClark]

Your description of the dart being the same large diameter as the booster separating would be no good. You have already accelerated the heavy mass of the motor case and have little drag reduction after separating.
I made a couple boosted darts in the '90's with fair results. I got it to separate and recover but never used the big motor for max altitude.
I have a couple real Loki darts. where I worked I was involved with making several hundred of the booster motors.

M

 

[Off Grid Gecko]

A full scale one would need to be flown at White Sands...at the standard 80 degree launch angle the ballistic trajectory goes 84km downrange. (!!!)

Thanks for the link, should make an interesting bedtime story for tonight. White Sands and Black Rock are my target launch zones for the final build, but I'll be launching 90deg or close to it, assuming I ever get that far.
I thought about making the whole thing thinner, but it just doesn't work out and I don't want to invest in making a rotary launcher. My gyro subsystem looks like I can stuff something worthwhile into a 5" space. I'm hoping by orienting the disks at 45deg from the rocket longitude they can be used together to either spool the rocket up or down, as each can contribute something to the spin axis. 1000rpm will be a tall order though, so I guess that's out. I'd like it to be zero roll at apogee for stellar pointing or still shots of earth. Another idea was to use a single gyro (much larger) along the rocket's axis, but I worry about precession effects.
For power with two stages I was looking at a maxed out N or low O on the booster and an N on the upper stage. Then deploy the nosecone to reduce drag. Guess I could always cant the fins as I'll be testing the upper stage for an L3 project and see what kind of RPMs I get.
A 5.5" rocket may end up being too large. Then again, I'm wondering if NC separation will actually help or not, as the sectional density will be higher with the spent motor still attached.

 

[Off Grid Gecko]

Your description of the dart being the same large diameter as the booster separating would be no good. You have already accelerated the heavy mass of the motor case and have little drag reduction after separating.
I made a couple boosted darts in the '90's with fair results. I got it to separate and recover but never used the big motor for max altitude.
I have a couple real Loki darts. where I worked I was involved with making several hundred of the booster motors.

M

Missed this while I was replying. Yess with a full diameter top section it makes little sense to stage it before apogee, or so it seems. To work effectively, the dart would need a higher sec.density than the booster it's attached to. That seems impossible with the dart being anywhere close to the same diameter now that I'm thinking about it.

 

[MClark]

For a dart to work better than a well designed conventional rocket the booster has to be high mass fraction, inert parts light. With the commercial motors we have available it is already too heavy before adding fins and recovery. Typically case weighs same as propellant. IIRC the Super Loki booster was about 40 pounds prop and all the rest was 12 pounds. Real numbers would be in above link.

M

 

[Off Grid Gecko]

For a dart to work better than a well designed conventional rocket the booster has to be high mass fraction, inert parts light. With the commercial motors we have available it is already too heavy before adding fins and recovery. Typically case weighs same as propellant. IIRC the Super Loki booster was about 40 pounds prop and all the rest was 12 pounds. Real numbers would be in above link.

M

Because rocket equation I sort of gave up on my hope of going orbital with hobby rockets where the mass fraction needs to be like 90% fuel.
According to these docs, I have a Super Loki showing 62.3 at takeoff, 25.1 after burnout, with 13.5 of that being the dart.
Really wish that the CSI case weights were posted somewhere so that I could factor it in (or does the CSI spec sheet factor in the motor casing??? hmmm), but their larger motors can be 2:1 propellant to spent casing. Not great but not terrible for a sounding rocket.

After looking at all this, however, I might try a dart one day for the funs. Just gotta boost that little sucker to Mach 5... no prob! hehe.

 

[Tim51]

Also check out the Phobos EAV, a project by Midland Advanced Rocketry Society here in the UK, a boosted dart project from 20 years ago:
https://www.mars.org.uk/phoboseav.html

 

[Nytrunner]

Really wish that the CSI case weights were posted somewhere so that I could factor it in (or does the CSI spec sheet factor in the motor casing??? hmmm),

Do you nean Cesaroni? (Cesaroni Tech Corp, CTI)

Go to thrustcurve.org, look up a motor, and youll find the Total weight vs Propellant weight. Subtract those and you'll get the case and nozzle weight

 

[rocketguy101]

In the early 70s I attended the Southwest Model Rocket Conferences in New Mexico. In 72 a guy named Gary Schwede introduced a boosted dart powered by an EnerJet "F" motor. This was before commercial timers, altimeters, etc were available. Gary designed/built his own timer system to deploy the recovery system on the dart. He modified an Estes Transroc to measure temperature from a nose-mounted thermistor. Pretty cool setup, really impressed this 15 year old (at the time ) It worked great!

The guys from Centuri/EnerJet were impressed, wrote an article about it in their newsletter https://www.oldrocketplans.com/pubs/Enerjet/9-72/Sep_1972.pdf

 

[Off Grid Gecko]

Do you nean Cesaroni? (Cesaroni Tech Corp, CTI)

Go to thrustcurve.org, look up a motor, and youll find the Total weight vs Propellant weight. Subtract those and you'll get the case and nozzle weight

that's what I meant by the spec sheet. Cool. I suspected that might be the case but I wasn't 100% sure and didn't want to assume. I'm guessing it also assumes you are using the "proper" case and not spacers, which would explain why everyone talks about the "added weight" of spacers rather than their actual weight.
And yes, CTI. I get acronyms screwy sometimes.

@rocketguy101, cool story thanks for sharing.

 

[Andrej]

Here are two boosted darts that I made. They were both powered by sugar rocket motors and flew to +35.000 feet and +57.000 feet.

 

[Off Grid Gecko]

Here are two boosted darts that I made. They were both powered by sugar rocket motors and flew to +35.000 feet and +57.000 feet.

Very nice. Is the dart a simple slip-fit on the booster? How are you attaching the fin can to the rocket body?

 

[Andrej]

Dart has a boat tail that fits snugly into the transition cone (see the drawing). It has two mating surfaces that are machined to tight tolerances. When the dart moves forward 15mm it detaches from the booster. Entire lower portion of the dart was turned from a stainless steel rod. Fins were made from stainless steel plate and were laser welded to the body. To make alignment of the fins easier, grooves were machined into the fin portion before laser welding.

 

[Off Grid Gecko]

Dart has a boat tail that fits snugly into the transition cone (see the drawing). It has two mating surfaces that are machined to tight tolerances. When the dart moves forward 15mm it detaches from the booster. Entire lower portion of the dart was turned from a stainless steel rod. Fins were made from stainless steel plate and were laser welded to the body. To make alignment of the fins easier, grooves were machined into the fin portion before laser welding.

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Making me drool just a tad. This modern obsession with "metal parts" being "dangerous" sometimes makes me want to puke, as it's somewhat limiting. I've been thinking about it though, and it seems that a strong epoxy bond between fiberglass pieces and a fillet of JBWeld should make attachment pretty solid with non-metal components.
Actually I was more curious about the can fit to the body of the dart. In the vid it looked like you slipped it on there, and I don't see any screws or other retaining pieces. Are there threads on the inside where the can screws into the dart? Or perhaps a plug in the rear end that holds it in place? I'm always curious about modular fin cans. They just seem so useful but difficult to implement well.

 

[Andrej]

To really get the most out of a boosted-dart you want to have a dart with a high ballistic coefficient, meaning that dart has to be as narrow as possible while being heavy (optimum weight). That basically means you have to use materials with high density. Nosecone on my dart was basically a steel shell with a lead core.
I'm not entirely sure what do you mean about the can fit to the body of the dart. The boat-tail and a straight portion of the body tube where the fins are attached are one single piece. The fins are then welded on it. There is a shoulder machined on the top side, where a fiberglass body tube is slid on and secured with four screws.

 

[benjarvis]

Also check out the Phobos EAV, a project by Midland Advanced Rocketry Society here in the UK, a boosted dart project from 20 years ago:
https://www.mars.org.uk/phoboseav.html

Just to confirm, it's the 'Mars Advanced Rocketry Society', formerly the 'Middlesex Advanced Rocketry Society' ;-)

When we designed Phobos EAV the target was a 65,000ft+ flight out of the Kosdon O10,000 with a 2" diameter 3ft long dart. The dart weighed about 6kg (12.5lb?) but even that wasn't heavy enough.

The dart only actually reached 34,579ft because we made the tail-cone joint too shallow (can anyone say 'Morse taper'?) and it took 7 seconds to vibrate loose and separate.

We actually purchased a CTI O25,000 as the booster for a planned follow-up in about 2008 or so as I recall, but never got to fly it. That with a 2" dart should have hit 120,000ft+

I've subsequently simulated an N5800 based boosted dart design with a smaller diameter dart that should, theoretically, also be capable of topping 100,000ft, but we'll see if I get time to actually build it

Ben

 

[benjarvis]

Actually, here's a couple of pics of Phobos EAV....

 

[MClark]

The Tetanus Tower!

 

[Tim51]

Just to confirm, it's the 'Mars Advanced Rocketry Society', formerly the 'Middlesex Advanced Rocketry Society' ;-)

When we designed Phobos EAV the target was a 65,000ft+ flight out of the Kosdon O10,000 with a 2" diameter 3ft long dart. The dart weighed about 6kg (12.5lb?) but even that wasn't heavy enough.

The dart only actually reached 34,579ft because we made the tail-cone joint too shallow (can anyone say 'Morse taper'?) and it took 7 seconds to vibrate loose and separate.

We actually purchased a CTI O25,000 as the booster for a planned follow-up in about 2008 or so as I recall, but never got to fly it. That with a 2" dart should have hit 120,000ft+

I've subsequently simulated an N5800 based boosted dart design with a smaller diameter dart that should, theoretically, also be capable of topping 100,000ft, but we'll see if I get time to actually build it

Ben

I'd be happy to make the journey and help out at the pad whenever you get round to it.

 

[ghostfather]

Actually, here's a couple of pics of Phobos EAV....

Wow, Ben, you were young once...

 

[ghostfather]

Just a question as far as categories: Is a boosted dart considered a single-stage or multi-stage?

 

[MClark]

Just a question as far as categories: Is a boosted dart considered a single-stage or multi-stage?

Single
But at this time TRA records do not allow darts.

 

[OverTheTop]

I seem to recall a discussion relating to the mass of the darts being a safety issue. I can't remember the details but there might have been mass limits discussed in case of non-nominal flight, and ever nominal recovery, due to the high density of the dart compared to regular HPR rockets. Maybe somebody from Tripoli can chime in if they recall the discussion outcome.

 

[MClark]

At LDRS the record committee gave the BoD a proposal for a boosted dart altitude class.
The FAA has a density limit for HPR and even the "real" Loki dart isn’t even close.
A boosted dart rocket must follow the same safety code as all other rockets. Darts have not been banned, but they are pretty rare.

Mark

 

[dhbarr]

Just a question as far as categories: Is a boosted dart considered a single-stage or multi-stage?

Single
But at this time TRA records do not allow darts.

d2.3 for a little base-bleed down in the soup, zoom it's a 2-stager.