Harpoon

This is a description of the building of the Harpoon, and eventually flying.

The Quest Harpoon is a sport scale model of the U.S. anti-ship weapon, which can be air-launched, ship-launched or submarine launched. I say sport scale because it generally appears like the real thing, but it is not exact. Changes have to be made to let this rocket fly well without a sophisticated guidance system like the real one employs. Usually this means larger rear fins and smaller forward fins and/or a slightly longer body.  This model has enlarged rear fins. Another important distinction is that this model is made up to look like the two-stage variant that is used for ship and sub launch, but this model only has one stage which does not seperate.  The air-to-surface variant doesn't have a booster rocket stage. The real missile uses a turbojet engine for the upper stage, so it is actually more like a cruise missile.

Here is a picture of the two stage being launched from a ship. The fins/wings are on hinges and pop out after launch.

This second picture shows the upper stage turbojet being used during cruise to the target, the booster not being used since this was launched from aircraft.

Whatever you want to call it, it looks cool, so I am building one. All those fins sticking out of it and the blue/white paint job is what I like, and I like military missiles in general. I was thinking of converting it to a real two-stage rocket, but Quest makes another kit called the Navaho which is a two stage, so I'll leave this one stock.

I begin building this kit by deciding how I want to install an altimeter compartment.  Normally, I just add a length of payload to the top, but that makes the rocket longer and heavier. Also, it is difficult to get parts sized to Quest standards, which use millimeters, while almost every other brand and the parts suppliers use the standard sizes of Estes. I had a lot of trouble finding couplers for Quest, in many cases even Quest doesn't supply them!

So instead I hatched a plan to use the space in the hollow nosecone. Normally that wouldn't be so difficult, but I found out the hard way that most glues, including epoxy and CA glue does not stick to this plastic! I went ahead and made one only to find the CA glue just cracked and seperated right away. So while taking that failure apart, I happened to notice that the hot glue that I used to glue the padding in did stick to the plastic, and stick very well.  So now I use hot glue to glue the critical door hinge piece to the plastic nosecone. I say critical because if that joint fails, it is likely the altimeter will fall to its death and be lost in a giant field of tall grass.

So here is the problem, inserting the altimeter into the nosecone on the left and keeping it secure in there during the high Gs of flight, but have it easily inserted and removed.

I start by cutting the base of the shoulder open, leaving the loop to attach the parachute and shock cord.

I create a hinge part out of scrap plastic (in this case, from a panel of an old busted VCR). The bottom is rounded to the inside curve of the nose cone shoulder, and roughed up a bit to give a good surface for the glue. It's hard to see in this photo, but the inside shoulder of the nose cone is also scuffed up quite a bit.

The plastic hinge is hot-glued in to the side of the nose cone, protruding just a hair beyond the edge. I apply a liberal amount of glue and then some, as a failure here could mean the loss of the payload.  The glue hardens in only a few minutes.

Next, plastic foam padding which was cut to fit is inserted into the empty space, leaving just enough space for the altimeter to be inserted.  Since the attachment loop is in the way, it has to be done in smaller pieces assembled like a puzzle.  Fortunately you don't need to be very precise with the foam, as it is soft enough to squeeze and bend to your wishes.

You could stop there, but I like to form a small box out of cardboard to fit inside the space. It allows the altimeter to slip more easily in and out of the compartment.

With the foam padding inserted, verify that it is a good, snug fit, then dab a few drops of hot glue to the foam to hold it in place.  The cardboard box is now inserted into the space.

A few more dabs of glue holds everything in place.  OK, it doesn't often look very pretty, but at least it is not seen in the finished model.  At least make sure the tiny threads from the hot glue are cleaned up and cut off.

The last step is to rivet a door to the compartment. Before riveting the door in place, make sure that when it is open it completely clears the opening for the altimeter.  When closed, make sure that it covers enough so the altimeter can't be lost with violent shaking.  This may produce an odd-shaped door.  Make sure you have a tight rivet, the door should be difficult to move.  If it is loose, the altimeter may slide out.

Try to file, cut or sand smooth any hard edges on this compartment, or the shock cord or parachute lines may get caught and tangle on any protruding pieces.

Another thing to be aware of when making the door, do not try to make a tight seal. Remember that air must freely flow into and out of the compartment, or the pressure inside may be too high at apogee, resulting in the altimeter will reading too low. Small gaps around the outside are a good thing. If necessary, drill a few small holes in the door.  Remember also to add three or four evenly-spaced vent holes on the body tube, spaced just below the shoulder of the nose cone.

Here is an example of the design change for a Tomahawk Cruise Missile. Notice the size (and weight) difference between the original nose cone, and a payload compartment previously added to the rocket.  The balsa bulkhead and body tube is all extra weight and length that is not needed if you can use the empty space in the nose cone.










With the payload task complete, I proceed to build the rest of the rocket according to the instructions. When building the fins, I break from "tradition".  Notice that the fins are laminated with a thin cardboard covering. This adds strength to the fins, and provides a naturally smooth surface for painting. No time-consuming layers of balsa fillercoat are needed, just a thin bit on the exposed edges.

After laminating, I shaped all of the fins for least wind resistance.  To do this, round the leading edge (top edge) and taper the trailing (bottom) edge.  This elongaged tear-drop shape is the most aerodynamic shape for the fins.  Be sure not to taper the trailing edge too thin, or it will be too flexible, easy to break and will not have an even edge.

Another technique I picked up on fins is to poke small holes in the root edge and the body tube before gluing. Although I haven't yet had an issue with fins popping off even after hundreds of flights in dozens of rockets, the fin to body tube joint can't be too strong.  These small holes allow glue to seep into the wood and cardboard, and provide more gluing surface. More gluing surface = more strength.  When dried, imagine the glue mass with many tiny fingers on it that acts like small rivets.  I say try it, it can't hurt!

With all the fins cut, laminated, shaped and poked, it is time for attaching them to the rocket body. This is the fun part, now that I have built a jig to hold the fins in perfect alignment while gluing them on.  I simply insert the body tube and hold it with bungees, pop the fin in and align the two pieces.  When satisfied, I pull the body tube down a bit and squirt in a line of glue. Then I release the body tube and it presses against the root edge, held fast until the glue dries.  Make sure you excersize patience here, Many rocket builders and kit directions tell you to glue all the fins at once, but it is better to do one fin at a time and let it harden without being disturbed at all.

Work has been slowly progressing on the Harpoon. It naturally slows down with the finishing, partly while waiting for good weather to spray outside, partly to give the many layers of primer and paint to dry, and mostly because all that sanding - necessary for a good finish - is also tedious and hand-numbing.  But slowly the rocket is getting finished...in fact almost done. All I need is one last sanding and a final coat.  After that the painting is done and the decals and final assembly will go quickly.  Here it is so far, I decided against pure white and went with a light gray, but the gray finish turned out much darker than I imagined.  I regret not using white, but at least it will photograph better in flight.


Well I just couldn't handle the gray, so I sanded and repainted gloss white. Much better!  It happened that the gray underneath was well covered by the white, and if it wasn't, I wouldn't mind.

The package shows the nosecone in a different shade of white, sort of off-white. I could have done that, but instead I chose again to make this one stand out a bit with a bright silver finish.

The first coat of silver (Rust-o-leum) was horrible, so I had to sand it off and try again. This time I used an old can of silver that always worked much better and the results were good enough (I believe the problem was the Rust-o-nauseum from underneath).


So here it is in the decal shop.  Starting to look like a real rocket now!

And finally...she's done!

Here are the "formal" portraits:

Of course we can't forget the imposing "big view":

Here's the tail end and motor mount tube, painted silver:

A look at the modified launch lug, set on a standoff. I no longer want the dirty launch lug to rub up along side of the rocket, especially this white one.

Here is a close view showing the static vent ports near the top of the body tube.  The shock cord and parachute will normally be behind these ports.


This is there to allow for the internal air pressure to match the outside air pressure at any altitude. Inside this area (housed in the nose cone just above) is the altimeter, which needs the ambient air pressure to make an altitude reading.



One last look, I wanted you to see the decal gap from the Quest supplied decals. Looks pretty stupid, huh?


OK, so I have it done after about 1-1/2 years since I started (life got in the way). Now it's time for its first test flights (which may take a while depending on the weather's cooperation)!

SPECIFICATIONS

Number of Stages: 1
Overall Length: 20.5" 520.7mm
Body Diameter: T40, 1.575", 40mm
Overall Fin Circular Span: 5.7", 144.76mm
Motor Mount: 18mm x 70mm
Motor Retention: Spring Clip
Recommended Motors: B6-4, C6-5
Stock Weight: 103.6 grams, 3.65 oz.
Altimeter Mod Weight: 3.5g, 0.123 oz.
Nomex Weight: 6g
Overall Weight (Less parachute, altimeter, motor): 114 grams, 3.8 oz.
Recovery Method: Parachute, 14" diameter
Recovery Protection Method: Nomex sheet, 6"x6"
Shock Cord Mount: Kevlar
Altimeter Capable: Yes
Altimeter Payload Volume: apx. 0.45 cubic inches
Date Completed: June 21, 2014

FLIGHT LOG

Has not been flown yet.

USS Prometheus

The USS Prometheus is a low-power kit from Red River Rocketry.  This was my first kit from Red River, and I must say the quality of the parts was excellent all around.  This is a light model, that is recommended to be flown with A, B and C motors.

Most unique for me in this kit was the bright gold Mylar parachute. It was almost unbelievably light - we'll see how it holds up to repeated flights and the occasional 'not enough wadding'.  It should be very visible from the air.  The balsa nosecone, fins, decals, body tube, shock cord, decals and all the other components were first-rate.  My only concern was the string to be used for the parachute, which although it might be strong, was very thin. Thin is more likely to cut through the parachute material, so I substituted it with my normal multi-colored string and made the lengths 1-1/2 the diameter and added a fishing swivel clip.

The "story" behind this is that this is a futuristic cargo transport ship.  They make another model that is a fighter/defender of this ship because of it being attacked by aliens.  My concern: I dont have that model yet, so my Prometheus may be vulnerable to alien attacks.



Construction went well, and this was my first introduction to using Titebond's filler glue for the fillets. It works well, but I should have used a little more to get really smooth results.  Fortunately, the priming and painting went well, with no crazing from the Rustoleum paint this time. It would have been a nightmare to sand out all the hard-to-reach nooks on this model.

As usual, I did add a payload compartment for an altimeter to this model, but instead of retro-fitting a payload, I incorporated it into the initial design, by cutting a three-inch length of the body tube instead of adding to the length of the rocket.  Basically, the only penalty is the weight of the altimeter and padding, and the bulkhead (which was balsa in this particular case).

In addition to the payload section, and parachute risers, other modifications include laminating cardboard to all the fin surfaces before sanding and priming, adding standoffs for the launch lug and hollowing out a portion of the nose cone (for payload space).  A few minor extra decals were added to the design.

There was one other construction technique I tried for the first time on this rocket. This involves punching/poking small holes in the fins and body tube before gluing.  The theory is that more glue will get into these internal spaces and act as small "rivets" of glue to help hold the parts together.  At least this provides more surface area for the glue to make a stronger bond. I find it also helps to "suck up" more of the glue and gives the excess a place to go instead of squeezing out and running.  This will hopefully provide more strength in the fin area, which considering this particular design, it might need it. Here is a look at this technique (as done to a different rocket).

SPECIFICATIONS

Series Number: 31
Number of Stages: 1
Length: 22"
Payload Volume: 2.64 cubic inches
Diameter: 1.325" (BT-55)
Wingspan: unmeasured
Vertical Rudder Height: unmeasured
Engine Pod/Tube Fins: 3
Basic Stock Weight: 76.7 grams
Payload Section Addition Weight (Bulkhead,padding): 5.6 grams
Total Weight with Altimeter: 89.2 grams
Liftoff Weight Range: 108-113.4 grams
Motor Diameter: 18mm
Motor Length: 70mm
Motor Mounting Method: Clip
Recovery Method: Parachute
Parachute: 12" Mylar
Recovery Protection Method: Wadding
Shock Cord Material: Kevlar & Elastic
Nose cone material: Balsa
Fin Material: Balsa, Cardboard Laminated
Completion Date: May 27, 2013

Launcher and Launch Area Technical Support Truck

Here is my LATS Truck, or Launch Area Technical Support Truck.  When the launch area is far away from the parking area, I spend a lot of time walking back-and-forth from the launch area to the car, so to save time and my legs I came up with this contraption.  This allows me to bring all my 'stuff' to the launch area in one trip, and allows me to work on the rockets without having to sit down on the grass and loose small items in the turf.

It is made from a steel utility cart, and has two wooden shelves to hold two toolboxes.  The lower toolbox has tools and various supplies for launching, such as masking tape, binoculars, spare fishing clips, streamers, wadding etc.  The upper toolbox holds plastic storage boxes with the various one-use motors, ignitors and more wadding.

The seperate toolboxes allows me to load them in the car seperately, so loading in the cart is not too heavy. The cart also has hooks to help carry the launch tripod, launch controller, cameras, clipboards and other assorted stuff.  The back of the cart has a fold-out table surface. This surface is framed to prevent small pens, motors, etc from rolling off the edges. It also has a nice, soft cork surface.

In the picture, I have my Alpha and X-Ray out for launching, with a box of wadding, Altimeter Two, masking tape, scotch tape, pliers, sandpaper. This makes it easier to prep rockets while standing, and I don't have to kneel down in the grass and work on often damp or muddy conditions.  It is a real time-saver and knee-saver!

Here are a few closer views of the truck.  This lower tool box has a lot of tools in three drawers and a few spare supplies for rocket launching. It is heavy and should remain in the truck to provide a heavy base for the table when it is extended. I also pack my altimeters, GPS and binoculars in there.

This is the upper toolbox. I use it mostly to store my motors. There are 18 little plastic boxes in seperate compartments in the bottom that hold an assortment of 13, 18 and 24 mm motors.  Above them are four more boxes that hold my most often used motors,  B6-4, C6-5, and D12s.  Of course all boxes are clearly labeled. When not actively flying, this box goes inside and remains in a cool, dry place.  I don't want any of these motors going bad in storage.

You may also notice in this picture that there are hooks on the one side to carry and/or hold camera bags, binoculars, jackets etc.  The large aluminum tube attached to this side holds 4-foot lengths of my three launch rods.  This keeps them safe from being bent and keeps them from taking out an eye or two.

Next I would like to show you my field-deployable rocket rack.  It is designed to hook on to the front of the cart shown above so I can carry all my rockets out to the launch zone with the cart.

I included two features in this design. First, notice that it is "flow-thru", in that reasonable non-hurricane winds will not tip it over and destroy the rockets.  It is also light weight.  All the arms that hold the rockets are padded with cheap pipe insulation.  I used four long bungees (normally used for higher-power shock cords) to hold the rockets tightly but gently to the rack.  While this worked great, I didn't design it to protect the rockets in the rain.  Sure enough, on day one of trying it out, it started sprinkling, so I had to throw a tarp over the whole thing, making it vulnerable to wind.  Oh well, I didn't intend to leave these out in the rain anyways!

Here is the view from behind the rack.  You can see the two posts on hinges that let it lean far back at an angle.  I didn't take any chances with that angle, I made sure it leaned FAR back so it won't tip over from heavy rockets.  You may also see the pipe insulation attached to the rack with staples on the sides of the wood.  You may also see one of the four white bungee cords swung over the back out of the way and not being used at this time.  What is harder to see here is that I used four steel wire sets going from corner-to-corner to keep the front and back frames square. I used stranded steel wire for hanging picture frames.  As it turned out, it was fairly rigid without the wires, but I had them so I put them on anyways.  There are also two strings holding the front and rear sections so they can't be spread too far apart and colapse backwards.

Closeup view showing how the bungees are attached. Simple really. Notice the insulation/padding continues up the wood backing to provide protection to the rocket from the rear also.

 

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This is what my launch system looks like from the inside. It is a fire-resistant box (meant for papers, cash etc.) that houses two 7.2-volt NiCd batteries, so there is a very short path between the power source and the ignitors. This is to minimize the voltage drop across long wires and allow for maximum power being delivered to the igniter.
This box also has a mechanisim to adjust the angle of the launch rod by turning a set of knobs, instead of having to loosen a screw and re-tighten it to tweak the launch angle.
For safety, it has three seperate relays which must all be activated to ignite a motor. This makes it very fail-safe because even if one relay welds itself on and is stuck, the other two will still prevent a ignition.  A long, 25-foot CAT-5 cable connects this box to the control box as shown below.

This controller is mounted on a 3-foot aluminum rod on the left side.  The rod is stuck into the ground and holds this at a comfortable working level.  The large meter on the unit monitors the battery voltage.  To launch, all three red buttons must be pressed and held, and they are spaced apart to require two hands to press all three. Each button enables one of the three relays in the launcher.  Also, the safety key must be inserted, and the arming switch must be on/up.  The small OK LED is used to verify ignitor continuity.






Here we see the launcher deployed in the field.  The entire system is inside the box and remote control.  Both of these parts are held up on a lightweight aluminum structure.  This saves both the back and knees, and in the case of the launch rod, may save an eye as well by being well above eye level for all but the freakishly tall, somebody on stilts or possibly a giraffe.

This closer view of the business end of the launcher shows the mechanisim to hold the rocket up above the blast deflector.  No more burned clothespins or balancing motor casings. It can be adjusted in height and also front-to-back to accomodate nearly any rocket.

The blast deflector is angled to direct the blast to the rear, which somewhat reduces the cloud of smoke obscuring the launch for closeup photography.  Notice too that the ignition wire clips are made using 14 guage solid copper.  This allows them to be bent into position to grasp the igniter wires without pulling them down under the weight of the wires.  These wires are not insulated, so there is no worry about melting insulation.

The only concern here is making sure not to let the two wires short each other or short onto the blast deflector, but that is fairly easy to do.  These clips have held up for dozens and dozens of launches and have not needed replacement yet.  If they do prove to degrade beyond use, I made several sets of spares that can be plugged into the banana jacks in about a second or two.

This launcher is able to use 1/8", 3/16", and 1/4" launch rods. Shown here is the 3/16".

Seen here (above), I added clear white labels to pretty-up the controller a bit, as the previous painted legend was getting a bit ugly.

OK - this is the normal continuity indicator.  It is an LED, so it draws very little current and will absolutely not be enough to heat a igniter.

ARM / SAFE - This basic switch will prevent the igniter from getting current.

CHECK - This button is pressed and held to see if continuity is good. If not pressed, zero current will flow through the igniter, not even a little bit of LED continuity current.  Also, this button must be held down by the left hand to allow ingition, since it completes the ARM current and allows the first of three redundant relays to be energized.

SIREN - This is a second arming circuit that is wired in with the safety key.  When this is pressed (normally at about T-2 seconds), it will energize the second of three redundant relays if the key is inserted.  It is named siren because my intention was to add a mechanical motor/siren to the launcher that will also sound when this second circuit is energized. (I didn't add it yet though, I had it on my workbench but I seemed to have lost it!)

KEY - This key needs to be inserted to allow the second arming circuit to be energized.  When it is removed, the circuit is open and launching can not be done.

LAUNCH BUTTON - This has a silver legend.  Assuming the ARM/CHECK circuit is energized, and the SIREN/KEY circuit is also energized, this button will energize the third of the three relays, completing a circuit from the battery to the igniter.  This is pressed at launch time T-0.  This button is placed on the right side, and is intended to be pressed with the right hand.  The other two buttons are purposefully placed on the left, away from this button, and need to be pressed by the left hand.  This is to prevent a inadvertent bump of  one of these buttons from likely hitting all three buttons.

BAT CHECK - This switch is flipped on to make sure there are no flying bats in the area before launch.  At other times, it switches battery voltage to the center volt meter to indicate the health of the two 7.2 volt batteries in series.  With normally fully charged batteries, this will deflect fully and read 15 volts (ok, 14.4 volts to be exact).  The switch is there to avoid having the meter, which does draw some current, from draining the batteries if left connected for extended periods.

In addition to having the ARM switch on and the KEY inserted and all three red buttons pressed & held, the main launch box which contains the batteries also has its own power on/off switch.  This is to make sure under any circumstance the batteries will not be drained, and is a handy backup swtich when one is at the launcher and about to connect the igniter.  A few times I am unsure and ask myself, "Did I leave the key in and the arm switch on again?"  Instead of having to check, I can just flip this switch to off and be sure I will not ignite the motor as soon as the second clip is attached.

The End.