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FSI Mach-1 Dart clone

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MarkII

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As I promised yesterday, here is my abbreviated build thread for my FSI Mach-1 Dart clone and faux RX-1 Thruster. First, a pic of the completed model. It's a little washed out; I'll try to get a shot with better lighting tomorrow.

I built this almost entirely with components from Semroc, and I used the plans available at YORP. It is the 17th build in my project to clone all 30 of the rockets produced by Flight Systems, Inc. (I have completed an 18th and I am working on the 19th.) A couple of things to point out: first, it is not painted (I haven't had a chance yet). I do have a complete decal set for it, courtesy of Excelsior Rocketry. The Dart sustainer will be painted white and the Thruster will be painted black, with fluorescent fins. Second, neither stage has a launch lug. More on that later.

The Dart was kit # MRK XVII (later changed to 1017 when FSI updated its inventory system) and it was the 16th kit released by the company (there was no kit #13). I have not been cloning their kits in release order, but by coincidence this is the 17th rocket that I have built in the project. The combined length of the two stages is 24.75" (628.7mm). The Dart is 19.25" (489mm) long and 0.921" (23.7mm) in diameter and the Thruster is 5.875" (149.23mm) long by 1.04" (26.4mm) in diameter. The combined weight of the two stages, without paint, motors or the streamer, is 2 oz. (60g).

A complete parts list will be provided in an upcoming post.

Mark K.

DSCF1216-2.jpg
 

ScrapDaddy

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As I promised yesterday, here is my abbreviated build thread for my FSI Mach-1 Dart clone and faux RX-1 Thruster. First, a pic of the completed model. It's a little washed out; I'll try to get a shot with better lighting tomorrow.

I built this almost entirely with components from Semroc, and I used the plans available at YORP. It is the 17th build in my project to clone all 30 of the rockets produced by Flight Systems, Inc. (I have completed an 18th and I am working on the 19th.) A couple of things to point out: first, it is not painted (I haven't had a chance yet). I do have a complete decal set for it, courtesy of Excelsior Rocketry. The Dart sustainer will be painted white and the Thruster will be painted black, with fluorescent fins. Second, neither stage has a launch lug. More on that later.

The Dart was kit # MRK XVII (later changed to 1017 when FSI updated its inventory system) and it was the 16th kit released by the company (there was no kit #13). I have not been cloning their kits in release order, but by coincidence this is the 17th rocket that I have built in the project. The combined length of the two stages is 24.75" (628.7mm). The Dart is 19.25" (489mm) long and 0.921" (23.7mm) in diameter and the Thruster is 5.875" (149.23mm) long by 1.04" (26.4mm) in diameter. The combined weight of the two stages, without paint, motors or the streamer, is 2 oz. (60g).

A complete parts list will be provided in an upcoming post.

Mark K.
Wasn't this the design that you pointed out on an earlier thread about optimal ***** for supersonic rockets? And will thi acctually hve supersonic capibilitys?
 

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MaxQ

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As I promised yesterday, here is my abbreviated build thread for my FSI Mach-1 Dart clone and faux RX-1 Thruster. First, a pic of the completed model. It's a little washed out; I'll try to get a shot with better lighting tomorrow.


A complete parts list will be provided in an upcoming post.

Mark K.
Mark:
thanks...looking forward to a parts list...and by all means - if you fly it - tell us what motors you might choose and how a flight goes...
 

Initiator001

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The F100 boosted my Mach-1 Dart system to 460 mph. This was during a night launch, supersonic trials, held outside of Las Vegas twenty years ago.

Sadly, the upper stage did not ignite so I don't know if it would have gone past Mach 1. :(
 

MarkII

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FSI was careful not to say that the Dart would exceed the sonic limit with the RX-1 Thruster, only that it had the potential to do so. The back of the kit instructions gave some detailed instructions about where to station observers so that they can detect the sound of the shock wave, and gave some indication of what to realistically expect from it.

Since it was an expendable unit that could only be used once, I suspect that the Thruster wasn't recovered very often. I also don't know exactly what the coupling between the thruster and the Dart actually consisted of, but the instructions say to recess the Dart's thrust block so that the motor projected 1" out of the aft end of the rocket if it was being built for supersonic flight attempts; for subsonic flying, the thrust block was pushed in until only 1/4" of it extended out of the aft end. Presumably, the extended motor "hang-out" was so that the aft end of the sustainer motor could act as a stage coupler. One question that occurred to me, though: how well did direct staging with either joined motors or with gap staging work when the rocket was undergoing very high acceleration? Could the high Gs affect it in any way?

Mark K.
 

MarkII

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Although I had already planned to build one anyway when I started my FSI cloning project, I still owe a great deal to Steve Naquin, who detailed the build process for his Dart clone on YORF right at the same time that I was getting started in 2007. He has given me helpful information and lots of encouragement.

OK, now for the parts list:

Dart:

  • Semroc BC-8F28 balsa nose cone
  • Small screw eye
  • Semroc ST-8F180
  • 1/16" thick aircraft plywood from BalsaUSA for fins
  • Semroc EM-78; can substitute Semroc CR-78F for the centering rings
  • 100 lb. microbraid tubular Kevlar from Pratt Hobbies
  • Mach-1 Dart decal set from Excelsior Rocketry
  • Streamer material - either crepe paper or trail marking tape (I haven't decided yet)
Faux RX-1 Thruster:

  • Semroc ST-1060
  • Semroc ST-980
  • Semroc LT-08580
  • A short section of BT-40
  • A short piece of Semroc ST-7, roughly 4"-6" of it
  • Some 110 lb. cardstock
  • Semroc HTC-8F coupler
  • Some more of the plywood for fins
  • One hardwood Doll Pin Stand - from a pack of 20, purchased at Michael's Crafts
Mark K.
 
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MarkII

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Here's another, somewhat better picture of the completed rocket, sans paint, decals and initial guidance device.

For instructions, I downloaded the set from Ye Olde Rocket Plans. I printed out page 5 with the fin template onto a separate sheet of 110 lb. cardstock. YORP does not have the plans for the RX-1 Thruster, but with a bit of information from Steve Naquin and Don Fent on YORF and the scans of the FSI catalogs at Ninfinger, I was able to figure out a way to clone it. The fins for the Thruster are identical in pattern to the fins used in the FSI Nova, MRK-III/#1003, so I downloaded those plans as well and printed out the fin page from it onto cardstock.

For fin marking, I generated fin marking wrappers using the tool in Gary Crowell's free VCP rocket design program. I have known for a long time that with that tool, you cannot simply plug in the OD of the tube that you will be using, because that number will always be a bit too small, since it does not include the thickness of the paper that you will be printing out the wrapper on. As I have used the tool, I have also been building up a table of values derived from trial and error for the various tubes that I have used. The Dart's airframe, made from ST-8F, has an OD of 0.921"; I plugged 0.936 into the tube diameter box in the Fin Wrapper Tool. The Thruster will be made from ST-10, which has an OD of 1.04"; I entered 1.061 into the tube diameter box. I print with an HP 970cxi inkjet printer onto 24 lb. printer paper. If another printer or another weight of paper is used, or even if you are working in a more humid environment than the breezy Adirondack Mountains, those figures might need to be tweaked a smidgen. To know if you have used the right value, cut out the printed template exactly on its outline and wrap it snugly around the tube. If the tips of the two pairs of arrows just touch with no overlap or separation, you have it nailed.

Mark K.

DSCF1201-1.jpg
 

ScrapDaddy

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Very cool mark! Just a quick question, does it still have supersonic capibilitys on present day motors?
 

MarkII

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Building the Dart is quite straightforward. The original Dart was designed to use FSI's 21mm diameter motors. These motors have been out of production for over 16 years, so I elected to modify the design to use standard 18mm motors. In the short time since I built it, Quest has released its 20mm diameter D5 motors. The Quest D5 is the same length as the old FSI D18 motor, which the Dart used in supersonic mode, and it is very close to it in diameter. One could easily omit the motor mount, and, using a centering ring (see next paragraph) as a thrust block, build a clone in the same manner as the original kit. The D5 has nowhere near the thrust of the D18, so it will never get the Dart up to supersonic speeds, but otherwise constructing it that way is an option that would enhance the verisimilitude (or truthiness) of the clone. The D5 would need to be given a few wraps of masking tape and then friction-fitted, just like the FSI motors were in the original.

First, I assembled the EM-78 kit for use as the motor mount. At the time, Semroc had not yet produced centering rings that were specifically sized for the ST-8F tube. ST-8F has an inside diameter of 0.885", which is very slightly larger than the ID of ST-8 (0.865"). The difference is small enough that the rings from the EM-78 can be used, but the fit is very slightly loose. If I were building it now, I would substitute the new CR-78F rings, but I would double them up. I neglected to include this in the parts list, but I attached a 24" length of 90 lb. test nylon coated stainless steel leader to the upper end of the mount, just behind the upper centering ring. The leader will be used as the shock cord anchor. I did nothing with the other end of the leader at that time. When I assembled the mount, I made sure that the rear face of the lower centering ring was 1/2" away from the aft end of the motor tube. I set the mount aside while I completed the next step.

Mark K.
 

MarkII

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Next I took the 18" long ST-8F tube and marked it all around 2" from one end. I used good tube cutting technique to neatly trim the tube to a length of 16". Next I test fit the motor mount into it, and made a mark with a Sharpie on the steel leader where I wanted it to terminate just a short distance below the end of the tube when the mount was installed. Using a double barrel crimp tube, I created a small loop in the free end of the leader, with the mark I made at the upper end. Then I tied about 4.5 feet of the microbraid tubular Kevlar to the loop with my usual anchor knot. I fed the Kevlar and leader back down through the motor tube and out the aft end.

I spread a bit of BSI Slow Cure 30 minute epoxy into one end of the tube at the approximate places where the centering rings would be, while making sure that I didn't get any glue on the first 1/2" inside the tube. Then I slide the motor mount forward into the tube until the aft end was even with the end of the tube. During the next 20 minutes or so, I held the tube in a horizontal orientation and slowly rolled it back and forth to insure that the epoxy was evenly distributed around the inside of the tube. Then I set it aside to cure.

I turned the screw eye into the base of the balsa nose cone, unscrewed it back out, and with a toothpick I placed enough 30 minute epoxy to fill the hole. I screwed the eye back in and spread the overflowing epoxy evenly around the bottom of the eye. I placed the nose cone forward end down into a scrap piece of ST-8F and stood it upright on my table with the eye pointing up while the epoxy cured.

Mark K.
 

MarkII

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I gave the tube a quick light coat of white primer by stepping just outside my back door with it, spraying it down quickly and then dashing back inside with the wet tube and setting it up to dry in my work room. This rigamarole was necessary because it was mid-winter and the outside temp was in the teens. After the primer had dried, I lightly sanded down the tube to remove all of the primer visible on the surface. Then with a nitrile-gloved hand I applied Bondo Spot Putty to the spirals. The next day, I sanded the tube down again with 220 grit until it was smooth.

I cut out the fin marking wrapper for the ST-8F and after the epoxy had cured, I used it to mark the tube for the three fins. I used my aluminum angle to extend the lines for the entire length of the tube. Although I will be aligning the fins to just a short section of the lines at the aft end, having the lines along the entire length helps me to visually check that they are all straight and they help me when I sight down the tube to verify that the fins are on straight.

I measured the length of the root edge on the fin template and then marked each alignment line that distance up from the end of the tube. Then I took a sturdy straight pin and poked 4 or 5 small holes spaced out along along the line and just to the left of it up to the mark. I am left-handed; if you are right-handed you would place the holes just to the right of the line instead. I didn't poke too many holes or make them too large, because it would have weakened the tube in that area.

Next I cut out the template for the Dart's fins and used it to trace out the three fin patterns on the plywood. With plywood fins, the orientation of the visible grain is irrelevant, but I traced out the patterns so that the leading edge was parallel to the visible grain (on that side) just out of habit. With a standard utility knife and a fresh blade, and with the aid of a heavy steel straightedge, I cut out the three tiny fins. After I verified that all three were perfectly flat with no hint of warping, I lightly sanded each side to make them smoother. Then I stacked them all together and evened up their edges with my sanding block until they were absolutely identical. Finally I used the sanding block to take the sharpness out of the edges on the leading and trailing sides of each fin. I left the root edges flat and square.

Finally I bonded the fins onto the tube using more 30 minute epoxy. I placed the root edges so that the covered the holes and so the the right side of the root edge lay exactly along and to the side of the alignment line, and the with the aft end of the root edge even with the end of the tube. I worked on one fin at a time, placing it and then obsessively checking to insure that it remained aligned and projecting straight away from the tube, making any necessary adjustments until the epoxy had firmed up well. I kept this up until the fin felt firm, then set it in my holder until the epoxy was well set. Only then did I move onto attaching the next fin.

This completed the construction of the Dart. I did not tie the nose cone onto the shock cord yet because I want to keep it separate until after I finished and painted everything.

Mark K.
 
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MarkII

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Now you know why I don't write many build threads. And I haven't even gotten to the Thruster yet! :eek:

Mark K.
 

MaxQ

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Now you know why I don't write many build threads. And I haven't even gotten to the Thruster yet! :eek:

Mark K.
Yeah....but we sure appreciate it.

Imagine illustrating the thread with your own pictures while doing the write up...real fun.
 

MarkII

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Yeah....but we sure appreciate it.

Imagine illustrating the thread with your own pictures while doing the write up...real fun.
I really need an editor. I may trim these last posts down a bit so that they focus more on the essentials.

If I had taken many pictures of the Dart build, I would have posted them. I do have a couple of "in progress" pics of the Thruster build, which is coming up next.

Mark K.
 

MarkII

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BTW, I never had any illusions that my FSI Dart clone would be able to flirt with the sound barrier. No combination of black powder motors available today is capable of giving it that kind of a ride. I built it because I was interested in the design and I wanted it for my FSI clone collection. This won't get near Mach, but no doubt it will still get upstairs in a jiffy. I would classify it as a performance-oriented two stager, one that will probably get some decent altitude for a sport rocket that is launched on BP motors. Tracking it on the return leg may be a problem.

Mark K.
 

green dragon

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I would classify it as a performance-oriented two stager, one that will probably get some decent altitude for a sport rocket that is launched on BP motors. Tracking it on the return leg may be a problem.

Mark K.
forget supersonic - I wanna see this fly on ( when available ) Quest F12 staged to D5, then we'll see about recovery :D

~ AL
 

ScrapDaddy

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BTW, I never had any illusions that my FSI Dart clone would be able to flirt with the sound barrier. No combination of black powder motors available today is capable of giving it that kind of a ride. I built it because I was interested in the design and I wanted it for my FSI clone collection. This won't get near Mach, but no doubt it will still get upstairs in a jiffy. I would classify it as a performance-oriented two stager, one that will probably get some decent altitude for a sport rocket that is launched on BP motors. Tracking it on the return leg may be a problem.

Mark K.

You know, with staging electronics you could stage a D21 upon D21 and I think that might get you[close to] there, you could stage 2X D3 RMS when they come out......then you can enjoy the thrill of a 12second burn time.....


Ps if you ever carry out with either of those, let me know, I wanna be there!
PPS. Do you have the Rocksim file for the Dart in it's 2 stage configuration?
 
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MarkII

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Now on to the RX-1 Thruster. This was the booster stage for the Dart when it was being flown for supersonic attempts. It is the bottom, larger diameter section in this photo.



The RX-1 Thruster kit was an add-on for the Dart, and consisted of an F100-0 motor that had been modified to enable it to mate with the aft end of the Dart, and a set of plywood fins that were to be attached to the outside of the motor casing with epoxy. FSI F100 motors were 27mm (1.063") in diameter by 150mm (5.91") long. These have been out of production for 16 years and are now very rare. There are no black powder motors being produced now that are even close to it in size, so I decided to make a faux (imitation) RX-1 Thruster that could hold Estes D12-0 motors.

I started by making a stage coupling. In the original, the Dart's motor, which was set up to extend 1" out of the aft end of the rocket, acted as the coupler, and fit into the top of the Thruster. As noted previously, I constructed my Dart clone to be flown in either single-stage or two-stage mode, so I located the motor mount so that the Dart's motor extended 0.25" out of the aft end.

I marked the inside of the HTC-8F coupler 0.5" from one end. I cut a 2.75" long section of BT-40 (left off of the parts list by error; I have since corrected this) and a 2.75" length of ST-7. ST-7 is a slip fit into BT-40. I glued it into the larger tube with Aleen's Quick-Dry Tacky Glue. Then I sanded down 0.5" of one end of the BT-40 until it would fit into the coupler.

Mark K.
 

MaxQ

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This won't get near Mach, but no doubt it will still get upstairs in a jiffy. I would classify it as a performance-oriented two stager, one that will probably get some decent altitude for a sport rocket that is launched on BP motors.

Mark K.
I'm there....I always wanted one and now I will make one.
Just to experience it.

I flew a Rocket Vision Machbuster, the Aspire, I've toyed with some lightweight high performance stuff....I may even eventually build a real carbon fiber "dragster" in the true sense of the word...but for now these smaller projects look fun ....
 

MarkII

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I glued the sanded end of the BT-40 into the coupler.

Next I cut a 2.5" length of LT-085 (Semroc Series 085). BT-40 is a loose fit in LT-085, so I glued a couple of wraps of 110 lb. cardstock around the free end of the BT-40 (see first photo) until it was a slip fit into the piece of LT-085. (See second photo.)

Mark K.

Dart coupler 1.JPG


Dart coupler 2.JPG
 

MaxQ

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You know, with staging electronics you could stage a D21 upon D21 and I think that might get you[close to] there, you could stage 2X D3 RMS when they come out......then you can enjoy the thrill of a 12second burn time
While a long burn is fun, I think if he wants to "get there" as you put it (and the " there " is supersonic flight) I think you need to trade long thrust time for short thrust time/high thrust level.

In other words, you want a sledge hammer blow, rather than a lengthy burn.

Getting through the transonic region gets increasingly difficult as you approach Mach ...as the drag increases dramatically.
The long burn motor would be good if the "there" he wants is "altitude"....not "speed".
For best "altitude" ...you would keep the rocket out of the high drag region and just keep plugging away...not trading off motor thrust just to fight the increasing drag....

It is a bit like comparing a sprinter to a long distance runner...one is high speed/short duration... the other distance (altitude)/long duration.

But then....I'm not a "Rocket Scientist".
Let's ask our "engineering student".....
 
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MarkII

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The FSI Mach-1 Dart was designed to be flown on black powder only. Staging of the Thruster to the sustainer was accomplished through direct coupling of the two motors. The Thruster consisted of an F100 motor with no delay or ejection charge (F100-0). The F100 was a high-thrust cored black powder motor that burned for 0.5 sec. and had a claimed maximum thrust of 35 lbs. (156 N).

Due to its size and the fact that it could only be used once, the RX-1 Thruster was often not recovered after the flight.

No currently made black powder motor produces a comparable thrust profile. The only motor that comes close is the CTI Pro29 56F120. It is slightly larger in diameter than the FSI motor and is substantially shorter in length. Since this is a reloadable motor, using it in the same way as the Thruster would require sacrificing a motor case with every flight, or else housing it inside a stage that would make it even larger in diameter. To ignite the sustainer, one would also need to use staging electronics. Given the very small size of the rocket, it would be very difficult to find the space to install an electronics bay. In addition, the extra weight of the electronics and bay would reduce the performance of the Dart, making it unable to reach Mach. These issues would defeat the very purpose that all of this complicated rigamarole was employed in the first place. On top of this, the challenge of recovering either stage means that one would have to be prepared to lose the electronics and the reload motor casing with every flight. This is, of course, ridiculous and no one but a complete fool with much more money than brains would even consider undertaking such a project.

Mark K.
 

MarkII

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The forward end of the F100/Thruster motor was chamfered down to match the diameter of the Dart.

I had picked up a bag of "Doll Pin Stands" at Michael's Crafts some time before, thinking that they might be useful for something. These are 1.125" diameter x 0.5625" long round hardwood plugs that are chamfered at one end and drilled with a 0.5" diameter hole lengthwise through the center. I wanted to use one of these to recreate the chamfered end of the Thruster. To do that, I would need to enlarge the center hole so that the piece would fit over the coupler.

I used a hole template to trace a 0.875" diameter circle on the flat bottom end of the piece, positioned so that it was centered on the piece. Then I used the large sanding drum of my Dremel to enlarge the hole out to the drawn circle, and then used a piece of coarse sandpaper and my finger to do the final sanding to enable it to fit over the coupler. This process removes a good deal of material, making the ring more fragile. I broke the first one that I tried to make and had to fashion a second one. Also, because one end is conical, widening the hole also reduces the height of the piece. My piece was reduced by 0.1875", down to 0.375" from its beginning height of 0.5625".

I slid the ring over the coupler and moved it down until 0.5" of the coupler projected above it. I glued it in place with Gorilla Wood Glue. Then I applied some wood glue to the inside of the short piece of LT-085 and slid that onto the other end and moved it up until it reached the bottom of the wooden ring.

Mark K.

DSCF1148.jpg


DSCF1149.jpg
 

MarkII

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Semroc Series 085 tubing, which is what the aft end of the coupler assembly was now covered with, has the happy coincidence of being a perfect slip fit inside Semroc ST-9 tubing. And Semroc ST-9 in turn is a perfect slip fit inside ST-10. I would use ST-10 for the body of my Faux Thruster because it had an outside diameter of 1.04", which was very close in size to the original Thruster's OD of 1.063".

I cut 5.5" long sections of ST-9 and ST-10 tubing. I spread some wood glue into the first 1.5" of the ST-9 piece, and slid the coupler assembly into it. After that had set up, I spread more wood glue inside the ST-10 piece, and slid the ST-9 section into it until the top of the ST-10 was up against the bottom of the wooden ring.

Mark K.

DSCF1152.jpg


DSCF1153.jpg


DSCF1124.jpg
 

MarkII

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At 1.125", the diameter of the wooden ring was slightly larger than that of the rest of the Faux Thruster's body. My next step then was to sand the outside of the ring down until the difference was eliminated.

Although I have never seen one "in the wild," I am pretty darned sure that the outside of the F100 didn't have tube spirals. Semroc ST-10 has very shallow, very faint spirals. I applied Bondo Spot Putty to them, and after it cured, I sanded the tube down. The thin red stripes of the putty-filled spirals are still quite visible on my as-yet unpainted Faux Thruster.

Mark K.
 

MarkII

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The fins included with the Thruster were the same set that the MRK-III Nova used. These were made from 1/16" thick aircraft plywood. Here is where I ran into a slight problem. After three years, I had finally used up all of the warp-free sections of the 1/16" plywood from my BalsaUSA order. The warp in the remainder wasn't extreme, but it was obvious, even in the small Nova fins that I cut from it. My local Michael's Crafts sells craft plywood, in every thickness from 1/64" to 1/2"; every thickness except, curiously, 1/16". I have been checking the store for several years, and have never found 1/16" there. Which is too bad, because the plywood at Michael's is nice quality and warp-free.

Fortunately I had bought a few very nice sheets of 1/32" thick plywood. I took the Nova fin template and lightly traced out 4 fins onto a sheet (I only needed 3, but I left enough to make an extra) in a rectangular arrangement. Then I cut that rectangle out, along with a second one of identical size. I placed the two pieces together so that their flexible dimensions were at right angles to each other, and laminated them together using BSI 20 Minute Finish Cure epoxy. Then I placed the sheet between two sheets of wax paper and piled several heavy books onto it.

After 24 hours, I removed the sheet from my improvised press. It was completely flat and hard as a rock! I retraced out the 4 Nova fin patterns and cut them out with a sharp utility knife and a heavy steel straightedge. I selected the 3 best fins and stack-sanded them together to make them absolutely identical. Then I sanded each side smooth and rounded the leading and trailing edges, but left the tip and root edges square.

Mark K.
 

MarkII

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I used the Fin Marking Wrapper that I had previously made for the ST-10 in VCP to mark three fin lines on the Thruster body. As I did with the Dart, I extended the lines for the full length of the tube. Since I lacked a copy of the RX-1 Thruster's instruction sheet, I didn't know exactly how high up on the body to attach the fins. I eventually decided to placed them so that the midpoint of the root edges were at the midpoint of the tube.

As with the Dart fins, I bonded the Thruster's fins with BSI 30 Minute epoxy. Again I worked on one fin at a time, clamping the root edge firmly against the body with my fingers and adjusting the position incidence and angle to the body as needed to keep it perfectly straight until the epoxy had firmed up well. (This took about an hour or so for each fin.) Then, after letting the epoxy cure for another hour or two, I would come back and bond the next fin. The entire fin bonding process took an afternoon and evening of one day.

It is perhaps a testament to the precision of the fin wrapper guides that VCP makes that, despite being built completely independently of one another, with two different sized tubes and two different fin planforms, the Dart's and Thruster's fins match up perfectly in line when the two stages are put together. :D I don't use any fin alignment tool or jig and I do all of my fin placements and alignments by eye.

Mark K.
 
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MarkII

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A few days later I used some 3M blue painter's tape to mask off fin fillet zones on the Thruster. Again, working on one side of one fin at a time, I created fillets with more 30 minute epoxy. After laying in the bead of epoxy, I swiped it with my nitrile-gloved finger and then immediately removed the tape from around that particular fillet. Then I held the tube horizontal for a few minutes to insure that the epoxy leveled out before placing it in my rocket holder and a few inches below the 100 watt incandescent bulb of a desk lamp. After an hour it was on to the next fillet. I repeated the process to fillet the Dart's fins.

I must have done something right because these turned out to be the absolute smoothest fillets that I have ever created. They are perfectly even glass-like and perfectly smooth. The heat curing from the light bulb not only sped up the curing process, it made the epoxy even harder and denser than than it normally gets with room-temperature curing. :w:

Mark K.

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MarkII

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A few final thoughts on my FSI Mach-1 Dart clone:

I hardened the balsa nose cone with water-thin CA. This was the last time that I used that technique before switching to using Finish Cure epoxy on nose cones. The CA method is quite valid and very effective. Compared to using epoxy, though, CA is a bit more of a pain to apply, definitely harder to reapply for a second coat, and it requires more elbow grease to sand smooth after it cures.

You will notice in some of the photos that my Dart has a motor hook. I know that using it is kind of passé now in some circles, but I still like to use hooks in low-power rockets when I can. The hook does not in any way interfere with the stage coupler. In fact, with a motor installed in the sustainer, the mating of the booster and sustainer stages is firmer and more stable. In the original rocket, the Thruster was never meant to be used when the motor in the Dart was mounted that far forward. I wanted my clone to be able to be launched in both single-stage and two-stage mode, though, so I set up the Dart's motor mount so that the motor was in the single-stage position, and I used a coupler to stabilize the connection. With such small fins, I was also concerned about the Dart's stability in single-stage mode. If I had placed the thrust block so that the motor hung 1" out the back like the instructions said (to enable it to be used in two-stage mode), I was afraid that the CG would be located too far rearward.

I have not placed any launch lugs on either stage yet. If the Dart was built for two-stage mode (supersonic flight), FSI instructed the builder to omit launch lugs from the sustainer (it would have need to be placed on a stand-off anyway) and only place a lug on the booster. I am still debating whether to do that or to leave it lugless and launch it from a tower. I don't have a launch tower, so I'll have to build one. Another possibility is to launch it from a piston. It is quite lightweight, but I'm not sure if it is low enough in mass for piston-launching.

I do want to fly this like it was meant to fly, but until I can get to a large field and have the help of several spotters, I won't be ready to try putting it into orbit.

Mark K.

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