I think the AGM-78 Standard Missile is, in my opinion, the most beautiful of all US military missiles. The fins  and strakes would be a challenge to fit on a dual deploy Level 3.

My goal is to certify at the Thanksgiving AHPRA launch on November 27, 2010 at Rainbow Valley, AZ

-Brad
May 15, 2010



   RIM-66 

Background

General Dynamics AGM-78 Standard ARM

The AGM-78 Standard ARM (Anti-Radiation Missile) was a development of the RIM-66 Standard shipborne air-defense missile. It supplemented the AGM-45 Shrike but like the latter has been replaced by the  AGM-88 HARM

In 1966, it had become clear that the AGM-45 Shrike was far from the ideal anti-radiation missile, its main problems being the limited range, small warhead, and unflexible seeker. The Naval Air Systems Command issued a contract to General Dynamics to develop an air-launched ARM variant of the successful RIM-66 Standard missile. Because no completely new components had to be developed, progress was quick, and after trials in 1967, the AGM-78 production version became operational with the USAF and U.S. Navy in early 1968.

The original AGM-78A-1, which was also known to the U.S. Navy as STARM (Standard ARM) Mod 0, was nothing more than an air-launched variant of the RIM-66A, fitted with the anti-radar seeker of the AGM-45A-3A. It was powered by an Aerojet MK 27 MOD 4 dual-thrust solid rocket, and had a blast-fragmentation warhead. The AGM-78A-2 added a BDA (Bomb Damage Assessment) capability, and an SDU-6/B red phosphorus target marker to mark the target for further strikes. In addition to the longer range and bigger warhead, another advantage over the Shrike was the gimbaled seeker of the AGM-78, which permitted a wider range of maneuvers for the launching aircraft. However, the AGM-78 was also much more expensive than the AGM-45, and could therefore not completely replace the latter. The carrier aircraft for the AGM-78A were the USAF's F-105F/G (using LAU-78/A launchers) and the USN's A-6B/E (using the LAU-77/A). An inert training version of the AGM-78A was built as ATM-78A.

In 1969, production switched to the improved AGM-78B (a.k.a. STARM Mod 1), which was to become the most important variant. It featured a new broadband seeker by Maxson, enabling the usage of the Standard ARM against many different types of targets without the need to pre-select a seeker. The AGM-78B also had a simple memory circuit, so that it could home on a previously locked target even after emitter shut-down. Some early AGM-78A-1s, which were upgraded with the Maxson seeker and memory circuit, were known as AGM-78A-4. The AGM-78B was one of the main weapons of the Air Force's F-4G aircraft. There was also an ATM-78B training variant of the AGM-78B.

The AGM-78C, built between 1970 and 1972, was mainly a USAF program. It was a variant of the AGM-78B with lower production costs and higher reliability, and it also had a new SDU-29/B white phosphorus target marker. Some AGM-78A/B missiles were upgraded to AGM-78C standard. The final version of the Standard ARM was the AGM-78D, built between 1973 and 1976. It had a new MK 69 MOD 0 motor. The ultimate AGM-78D-2 also featured greater digital reliability, an active optical fuse, and a new 100 kg (223 lb) blast-fragmentation warhead. The ATM-78C and ATM-78D were the inert training versions of the AGM-78C and D, respectively.

The shipborne anti-radiation missile RGM-66D combined features of the RIM-66 and AGM-78 missiles, and the AIM-97 Seekbat high-altitude air-to-air missile was based on the AGM-78 airframe.

More than 3000 AGM-78 missiles of all versions were built. The Standard ARM was removed from the U.S. inventory in the late 1980s, having been completely replaced by the AGM-88 HARM

Source: The Directory of U.S. Rockets and Missiles

Specifications

Note: Data given by several sources show slight variations. Figures given below may therefore be inaccurate!

Data for AGM-78B:

Length	4.57 m (15 ft)
Finspan	108 cm (42.5 in)
Diameter	34.3 cm (13.5 in)
Weight	620 kg (1370 lb)
Speed	Mach 2.5
Range	90 km (56 miles)
Propulsion	Aerojet MK 27 MOD 4 dual-thrust solid-fueled rocket
Warhead	97 kg (215 lb) blast-fragmentation

Building the AGM-78


I began by putting a Rocksim file together for a full scale AGM-78 based on available 2 dimensional plans. I could then scale it down to a convenient diameter for readily available materials.








This is a 3/5 scale Rocksim plan for the AGM-78 with an M1297 loaded. (I chose 8 inches because I could use nominal 8 inch Sonotube.) The plan calls for the upper airframe coupler to sit inside of the lower airframe. The strakes on both upper and lower airframes have to be perfectly aligned for launch. Since the airframe's wall thickness is about 1/8 inch, I planned to add an airframe doubler for both the upper and lower airframes, then the coupler and then multiple doublers in the altimeter bay. This may seem like overkill, but a groove has to be cut in both airframes for the strakes. The doublers will provide 1/4 to 1/2 inch depth. With epoxy, the strakes should hold nicely. Most of the strake and the entire fin are attached through-the-wall. I built a 4" diameter, 54mm prototype (1/3 scale) to test the basic design and fin/strake strength with an Aerotech K motor. The design with a weight estimate pad ready of 47-49 pounds would give an apogee of ~4000' on an Aerotech M1297 L3 special.

The aft fin and cone dimensions are determined by blowing up the image from the original plans and measure angles. I also had to make a decision about the organization of the altimeter bay and how it would be best coupled. With that completed, I could go ahead with a full scale RockSim plan. I would use this for all my down scaling.


                  








3-Dimensional View

Flight Characteristics





    

Parachute Characteristics

Main Parachute

Spherachute 168" with 12.9 inch spill hole gives a 13 ft/sec descent.




Drogue Parachute

A Rocketman 48 inch drogue chute gives a 32 ft/sec descent.

Airframes, Couplers and Doublers
June 2, 2010
June 3, 2010

                   


Today, I'm just starting to work with the Sonotubes. The lower airframe is 48 inches. The upper is 44 inches.  On the left I taped together a few sheets of copy paper and wrapped them around the tube aligned with marks at 44 inches. I can run a hobby knife along the paper edge. With pass after pass I can get a perfect, straight cut. I'll cut another 44 inch tube for the upper airframe "liner" or doubler. The doubler provides additional strength but will also be used to create a base for the slot that the forward portion of the strakes will slide into. Not shown is the doubler I cut for the lower airframe. It will create a base for the slot that the aft portion of the strakes will slide into. More on that later. I decided to cut the 32 inch phenolic motor tube, the 12.5 inch altimeter bay and the 22.5 inch coupler. More on those later. It might be difficult to see, but the edges of the airframes and other Sonotube pieces are all treated with ultra-thin CA for protection against nicks, dings and separation of the cardboard layers.

Hatch
June 6, 2010

                   

I just cut out the hatch in the upper airframe. This is for the altimeter bay. It's a pretty good fit. Finally, I practiced cutting bulkheads from 1/2 birch ply using a Dremel circle cutter. The one below is not finished. After the upper airframe liner is epoxied in place, the bulkhead will be further trimmed to fit inside and become the aft bulkhead for the altimeter bay.


       



Upper Airframe Liner (doubler)
June 24, 2010


It's Arizona in June. My garage is about 145 degrees. So I began doing some work in my kitchen. Below left, I've marked and began cutting 1/2 inch wide slots in the upper airframe.
The middle pic below shows one completed slot. To the right, I have the upper airframe doubler next to the airframe showing the lengthwise cut. Enough material has been removed to allow it to
 fit snuggly in the airframe. I also decided not to peel away the outer thin paper layer of the tube before epoxying. Instead, I used an orbital sander and 80 grit paper to thoroughly scuff the tube.
The remaining three strake slots have been cut in the upper airframe. You can see the position of the hatch.

                                                                                                               
          

June 25, 2010
June 26, 2010

Here is the end view of the upper airframe and strake slots. I have thoroughly scuffed the inside with 80 grit for a good epoxy bond later. Get the alcohol and paper towels. It's for wiping up the excess epoxy off the airframe after I load the doubler. I also need to get rid of any epoxy that might drip inside. I don't want to try to sand those drops later when I try to insert other tubes like the airframe and nose cone couplers. I also want a smooth airframe exterior when I glass it.


         

I'm just showing my lab coat and nitrile gloves below. I use West System  epoxy all the time. I want no  epoxy to get on my skin. I'm allergic to it, and where there is contact, my skin becomes inflamed and peels. I'm combining 10 pumps each of the 105 resin and 205 hardener. I'll use nearly all of it for this step. I'm using West for these tubes because it is very thin compared to two-part hobby epoxy, and it gives me some time before it starts to harden.

         

The adhesive is so thin, it can be "painted" onto the surface. It's absorbed into the surface of the Sonotube and will create a great bond.

        


Middle above, I'm painting some epoxy inside the airframe to make sure I get some on each side of those strake slots and around the hatch. Finally, I can lower the airframe over the doubler. I'm careful to line it up so that the slit in the liner is opposite the hatch, well away from any slot. The launch rail will be back there between the fins and strakes. I just flipped things around below so I can get to the hatch area and slots more easily. I'm going to wipe away excess epoxy from them.


         


     

I want to make sure that the entire length of the slots are attached to the doubler. So, I've wrapped the airframe with wax paper and applied several very tight elastic bands. Additional epoxy will inevitable be squeezed out especially after clamping below. If it hardens, I will use a Dremel burr to clean out the edges of the slots and hatch area. The clamps that I'm applying to the airframe are to ensure that the doubler is firmly bonded at both ends.I want no de-lamination to occur under stress.

            

June 27, 2010


    

I have cut out the doubler of the upper airframe to produce a hatch with a 1/2 inch frame for the hatch cover. The holes have been cut through the hatch and into the frame. I sanded the hatch frame to scruff the surface. Above right, I simply treated the frame with ultra thin CA. I do this to harden and strengthen it. It sands easily so the hatch cover will still end up flush. I have a couple more layers to go. The coupler will be epoxied in the upper airframe with 12.5 inches in and 9 inches out for the coupler portion (after glassing the upper airframe). The 12.5 inches will begin to define the altimeter bay. The third and final layer is a 12.5 inch piece of Sonotube epoxied in place starting at the forward end of the coupler. The forward bay bulkhead will slide into the airframe from the top and stop at the bay. I'll machine the bulkhead to create a 1/4 inch lip. The whole bulkhead should fit snuggly in place. More on that construction later.  All of this does add weight. But I'll need only a small amount of lead shot in the nose for the proper CG. I might not need any given how I plan to build the nose cone. This is in contrast to the prototype that needs ~2 pounds in the nose.

But I need to turn to the lower airframe.

       

Above, I have lined up the upper and lower airframes and extended the center lines for each of the four lower airframe strake slots. I'll go ahead and start to cut out the 1/2 inch slots as I did for the upper airframe. Above is the first. As for the upper airframe, I'll have a 1/8 inch deep slot for the most forward section of the lower airframe strakes. I will only cut enough of the slot to handle the doubler. When I epoxy the doubler in place, I will have have support for that portion of the airframe. If I didn't, and went ahead and cut the frame nearly the full length of the strakes, it would be like peeling a banana making the frame difficult to work with. After the epoxy dries, I'll go ahead and cut the remaining length of the lower airframe strake slots. There is an airframe "bridge" between the aft end of the slots and the cut for the fins.

 
 
Below is a completely cut fin and strake slot. Not that the lower airframe coupler lining now supports the forward part of the frame and provides that groove for part of the strake.  Below center is a test fit of the forward centering ring 20mm from the end of motor tube.  When the motor mount is fully pushed into the airframe, the forward ring butts against the airframe liner further locking the entire mount in the airframe. It produces the exact fit for the aft centering ring flush with the motor tube with a 1/2 inch of offset. There's plenty of room for the motor retainer and a good fillet. When the mount is eventually epoxied and foamed, it will be a rock solid single unit.

          

Back to the jig. Below, all the fin and strake slots have been cut and the lower airframe is mounted for glassing. The surface has been fully scuffed with 80 grit paper. It's also easy to see the final location of the fins and lower airframe strakes.

Here is an important idea that I missed.  It was really a big omission. I should of placed blue masking tape in the slots over the areas where there was airframe doubler. Then, after glassing, I could pull the tape out leaving the groove free of epoxy. I'll show you later what happens if you don't.


                       
 

July 24, 2010

Below right, I have "socked" the frame. I'll use one layer of Giant Leap's polyester sock with West Systems epoxy (105/206). It's very watery and it doesn't take much to flow into the sock material. I've already doubled up on the airframe so the whole rocket is very strong. The sock layer is really over-kill, but we tend to overbuild our rockets. This is not difficult to do. The sock is like a woman's stocking. It roles on the same way. I didn't roll it on when the frame was still on the rotisserie. I placed the airframe vertically and roll the sock from the end down. With it back on the rotisserie, I could stretch it more until it was a very taut fit. The ends of the sock (about 8" ) have to be held inside the frame so that a good "lip" develops at each end. I twisted the sock and used masking tape in the direction of the twist. I made sure it was also taped to the rotisserie pipe.


        

At the opposite end, I pushed on a loose fitting additional centering ring from my motor tube that pulled the sock in nicely. I'll use this method next time. I mixed up West Systems 105/106 as usual. I used plastic spackle blades to spread the epoxy while the rotisserie turned. Enough was added until the sock material was saturated, meaning any addition would only drip on the drop cloth. I then used a small paint roller to remove just a little of the excess epoxy and let the frame cure. In about an hour of so in the Arizona heat, I could touch the frame without much tackiness. Her's what you get.


        


   I then quickly trimmed the excess sock at each end with a hobby blade.

        

Then I began to remove the glass from the strake slots and grooves. The slots cleaned out very nicely. You can see below why I made 1/2" slots for the 3/8" fins and strakes. The additional epoxy on the edges of the cuts fills the 1/16" on each side and provides the snug fit I wanted. 0n the lower  right, I did my best to peel some of the epoxy out of the grooves, but then the curing made it impossible. I'll have to wait a day and go back with a Dremel burr and clean out all the grooves completely to accept the strakes. I could have prevented this additional work by simply masking the grooves.


          

   I continued to run the rotisserie the rest of the afternoon, total about 8 hours. It really wasn't necessary. The garage temperature was ~105 degrees.


July 25, 2010

This is the result of burring out the epoxy choked strake grooves of the lower airframe (all four of them!). I first used a cylindrical 1/4" burr to cut the edges of the excess epoxy and redefine the groove. A ball burr removed the rest. A ceramic cylindrical grinder took it all down to bare cardboard.

A wire brush roughed up the cardboard for a better epoxy grip when I mount the strakes. Brutal!!

On the right is the entire lower airframe sanded with 150 grit with a 5" orbital sander. I left a thin area unsanded to easily see my lug line. I need to identify my lug locations. After the lug holes are drilled, I'll go back and sand this area.


         

 Glassing the Upper Airframe
 July 24, 2010
 July 25, 2010

 Preparation is everything.

After preparing the upper airframe with GL polyester sock, I glassed with West Systems as I did with the lower airframe.  Below, I have cut away the excess fabric/epoxy after about 2 hours of curing. The blue tape masked the hatch frame and strake grooves and was easy to pull out. The usual areas required some work, but nothing like what I needed to do with the lower frame.  Soon, I'll get that coupler epoxied in.


         


     

Returning to the motor tube while waiting for time to pass;

In order to properly line up the 98mm Aero Pack motor retainer flange on the aft centering ring, Aero Pack requires that you test fit a 98mm casing in the tube. You have to use masking tape around the end of the casing. The tape centers the casing in the tube for the positioning of the flange. Huh?
Moe Bertrand had some simple advice. Place a 4" coupler into the motor tube and  leave a few inches sticking out. (I used a leftover piece of LOC.) You have just duplicated the placement of a 98mm casing into a 4" Blue Tube. When you slide the flange over the coupler up to the aft centering ring with its flush mounted motor tube, it's a very good, snug fit. And of course, the flange is now perfectly centered. Am I missing something important here?


      


 

 Launch Lugs
July 27, 2010

Just experimenting with launch lugs, altimeter bay ports and static vents.

First the lugs:
The issue here is to choose the number of 1515 rail lugs (2 or 3) and decide how far apart. For this rocket, I've place one in the mast aft centering ring and one within a caliper of the CG (with motor)  below the airframe coupler.


                                                                  

 I could forget about the middle lug that's screwed into the centering ring forward of the fins. It's more overkill, but they're in perfect alignment so drag or binding on the rail should not be an issue. I'm waiting on the census opinion on this one.



Then there's the issue of altimeter bay ports and static vents:

Here's the formula often cited for port sizing. There's even a spread sheet to plug in numbers.

Calculating Static Pressure Port Size

A good rule of thumb for the static pressure port is to use a 1/4" diameter hole for every 100 cubic inches in the altimeter bay compartment that is being vented.  This can be described by the following equation:

A₁ = V*(A_ref/V_ref)

where A₁ is the area in square inches of a single static pressure port hole and V is the volume in cubic inches of the compartment.   A_ref is the area of our reference 1/4" diameter hole and V_ref is our reference volume of 100 cubic inches.   For example, using this equation, if V = 100 cubic inches then it cancels with V_ref and leaves A = A_ref, which means we need a hole with the same cross sectional area as a 1/4" diameter hole.  If  V = 200 cubic inches, then A₁ will turn out to be twice the area of a 1/4" diameter hole.   Therefore, the equation yields one 1/4" diameter hole per 100 cubic inches of volume.

The volume of the compartment can be calculated from the following equation:

V = (pi/4)*D_T²*L

where D_T is the inside diameter in inches of the body tube compartment and L is the length in inches of the inside of that compartment.   At this point we could combine these two equations to get one equation that calculates the hole size needed for a given D_T and L.  However, it is not really a good idea to use just one hole.  Multiple holes are better because they can help null out undesirable pressure effects caused by cross winds or unstable flight profiles.  It is recommended that a minimum of three holes be used that are equally spaced around the body tube. (i.e. 120 degrees apart.)  Four is also a good choice and is sometimes more convenient for physical layout. 

Multiple holes can also be smaller than one hole so long as the total cross sectional area is the same.  We can calculate the area of one hole from the following equation:

A₁ = (pi/4)*D₁²

where A₁ is the area of one hole and D₁ is the diameter of the one hole.  We can also calculate the area A_N of any number of N holes of diameter D_N from the following equation:

A_N = N*(pi/4)*D_N²

Now by combining these two equations for area, we can calculate the diameter required for the N small holes that will give the same area as one big hole. The result is:

                                                                                                                                                                                                                                        D_N = D₁/sqrt(N)

where sqrt(N) is the square root of N.

We now have everything we need to combine all these equations into one final equation:

D_N = D_T*sqrt((A_ref/V_ref)*(L/N))

This equation is very useful because it directly calculates the diameter D_N of the small static port holes for a compartment with body tube inside diameter D_T, length L, and number of holes N.   This equation can be used to directly calculate the proper hole sizes, especially in situations that do not lend themselves to the charts above.

We can also take this one step further since we know A_ref and V_ref.  V_ref = 100 cubic inches and A_ref = pi*(0.25/2)² = 0.04909 square inches.

D_N = 0.02216*D_T*sqrt(L/N)

Where D_N is the diameter of the small static port holes for a compartment with body tube inside diameter D_T, length L, and number of holes N.  (All dimensions must be in inches for this equation.)

The diameter of the altimeter bay is ~8 inches and the length is 12.5 inches or 628 cubic inches. According to the formula, 3 ports would each be about 1/3 of an inch (.36 actually).

Here's the equation provided by Missile Works for the RRC2-mini for volumes greater than 100 cubic inches:

Bay Volume = radius X  radius X length X 3.14
Single Vent Diameter = 2 X  SQRT ( volume/6397.71))
Single Vent Radius = Single Vent Diameter / 2
Single Vent Area = ( Single Vent Diameter/2 ) X  ( Single Vent Diameter/2 ) X 3.14
Multi Vent Diameter = 2 * SQRT ( ( Single Vent Area / # of holes ) / 3.14)

It  comes out to .31 inches for each of three ports. So 1/3" it is.

Now static vents have all kinds of possibilities.

I have two airframes and I've generally put two vents in each frame just because. It might be a problem, but I have generally put them opposite each other.
The lower airframe volume is `8" x 17" or 854 cubic inches
The upper airframe volume is `8" x 22" or 1130 cubic inches.

Using the static port sizing equation above.
       For the lower framer that would be ~1/3 of an inch for each of 2 holes.
       For the upper airframe, that would be a little more than 1/3 of an inch for each of 2 holes.

My plan will be 1/3" for each of the static ports. Actually, 5/32" would probably be fine too.

Airframe Coupler
August 8, 2010


Today, I finally epoxied the coupler into the upper airframe using the same process as I did with the airframe doublers using West Systems 105/206. I prepared the coupler back on July 16. The bungy cord holds the airframe and coupler tightly together for good adhesion around the hatch. After a few hours in the Arizona heated garage, the epoxy was cured sufficiently to cut out the hatch again.

   

Below is the upper and lower airframes coupled. You can see on the right  the extension of the strake slots across the airframes. I made a Sharpee mark below the hatch. This is just to keep the slots lined up.  I'll make the same mark inside the airframes for future strake alignment. It's important after the rocket is painted. The slots, just like the fins of a two stage rocket, are not quite identically 90 degrees apart. Once the airframes are coupled, it's difficult to rotated them. It's nice to know the alignment for minimal adjustment at the launch site.

       

                                                                  
Motor Tube
August 8, 2010

I had an opportunity to start the epoxying of centering rings on the motor tube while waiting for the coupler epoxy to cure. Below is the forward centering ring. It had been epoxied using slow cure 2-part hobby epoxy. The u-bolts are 5/16" stainless steel. I placed the 5?16" fender washers on the top of the ring. The plate is below. People do this the other way around. I'm not sure it matters. I placed enough epoxy to not only produce a good bead around the motor tube but also to "paint" the ring. I just do this to protect the wood from future black powder exploding inside the lower airframe at apogee. After I tighten the nuts, I'll place some slow cure on the threads. Then, I'll flip the tube and create another bead of epoxy behind this centering ring. 

        

Altimeter Bay
August 9 and 10, 2010

I've used a Dremel cut-off to cut out a 12" portion of the strake groove overlying the altimeter bay. With the altimeter bay "stiffy" in place, a 3/8" slot is created for a portion of the forward strake. On the right below, the slot is clearer. I've left 1/2" uncut on the left of the slot.


      

Altimeter bay "stiffer" tube. On the right  the bay is test fit. There is now ~1/2" going from the airframe, through the airframe, airframe doubler, coupler and stiffer for the strake tab. The rest of  the strake will continue forward in a 1/8' groove.

      

View looking into the airframe through the coupler. The altimeter bay "stiffy" is very clear  See the 1/8" shelf created for the bay aft bulkhead.  Right, the vew looking down from the top of  the upper airframe. The flash caught the now 1/4" shelf created by the coupler and the bay stiffy.

           

After I cut out the remaining 3 strake slots, I can epoxy the bay permanently in place. After curing, I'll make the final hatch cut for the finished hatch.

Completion of the Basic Upper Airframe
August 12 and 13, 2010

Last night, the altimeter stiffer was epoxied in place using West Systems 105/206 as before. Here are multiple views: The lower left is the view from below through the upper airframe. The hatch opening is in the upper right. The most aft portion of the coupler has been slightly sanded for contrast, and the 1/8" bay aft bulkhead shelf is clear. On the right is the same pic offset slightly and close up. The 1/2" thick bay aft bulkhead fits snuggly on this shelf and into the bay by machining it 1/4" x 1/8".


        

Hatch (and strake slot thickness 1/2". Here are the four layers.



Here is the view down the upper airframe. The bay forward shelf is in contrast. The close up is on the right. That shelf is 1/4" and takes the brunt of the acceleration forces on the altimeter bay/bulkhead. The 1/2" thick bay forward bulkhead fits snuggly on this. The upper airframe as is weighs ~6 pounds.


August 25-28



          


Bay forward bulkhead (left) and bay aft bulkhead (smaller). To keep the bay all thread perfectly in line, the airframe coupler is now doubled (above). This also reinforces the coupler seam, strengthens the coupler for impact on landing and may help to prevent a zipper on drogue deployment. The bulkheads are snug and ready to receive the terminal strips and charge cups. The upper airframe is complete. Fins and strakes to follow.


    

Ready to get wired. I'll have to decide how I'll create a sled for the electronics.

August 27- September 2


I have been wiring up my altimeter bay. Just started the nose cone with the planned wood/foam/wood design.  I also epoxied the surfaces of the bay bulkheads and motor mount forward centering ring to protect the wood from flame and 10 gram charges! Also got disgusted finally with the drab look of the airframe, so I primed the upper with white (except for where the strakes will go). See the hatch cover. Really fit well.

The motor mount is finally epoxied in. Below I paired the centering rings that space the fins and strakes. I needed room for the 3/8" birch caps I plan to use to cover the honeycomb fins. I usually mark the spot on the centering rings before I epoxy the mount. The U-bolts (stainless steel) need to be in a place where they don't interfere with the point of contact of the fin and strake tabs. (Learned the hard way.) I taped  the length of the strake and fin compartment slots. This way, I can pour 30 minute cure epoxy into each compartment. I can role the tube on a 45 degree up angle creating nice forward ring beads, go vertical and after an hour or so, remove the tape. I'll do the same with the aft beads. It's just some eccentric thing I do to control some of the epoxy mess. May not matter really since when the fins and  strakes are in place, a layer of West Systems will go into each compartment to reach all the internal contact points.


         


          

September 3, 2010

Finally looking like what it’s supposed to. Bay inside completed and charge terminals wired. Starting fins and cone. The cone coupler is show. It will fit in the upper airframe up to the first layer of 1" Styrofoam. The first birch spacer is in place. It's machined to have a lip that fits tightly into the coupler. It's doubled inside with another ring. The machined ring has a diameter that allows the cone to sit on the coupler. The coupler has been doubled for durability and provide a good shelf for the first ring. Not shown is what will be alternating 1/2" birch ply spacers that are cut to shape the true contour of the cone taken off the original 1977 plans. The center tube not only makes it easy to line the fin up vertically, but will also add a compartment to add lead shot for CG/CP balance. I think I might not need much or any when this is completed. The upper airframe doubler and this cone with fairly heavy birch should balance pretty closely. This could have been made with all foam. But the birch "centering rings" provide a rasping then sanding guide for the proper shape. It's all held together with a 3/8" all thread. That will be used also to provide the solid connection to a 3/8" eye bolt for the recovery harness. The whole thing will be covered with a 7.5" Giant Leap glassing sock pulled tightly over the tip of the cone in the same way that the airframes were glassed. West Systems 106/205 will be used to laminate. The first coat will be sanded lightly and coated with another layer of West.

As with the prototype, I'll start with the fins so that they are perfectly lined up. Then I'll line the strakes to them.


          

September 4, 2010

Aft Strakes


I cut the aft strakes from 3/8" Giant Leap honeycomb. I number each slot and corresponding strake and custom fit the strakes in each.  I want a reasonably tight fit for epoxying.


         

The strakes are just test fitted. I'll do the fins and epoxy them in place. The fins and strakes have been cut back 3/8" to fit the 3/8" birch caps and stay in scale.


September 05 and 20, 2010


The aft fins (dimensions off the RockSim plan) have been sized and fit snuggly. Whenever there's some free time, I cap a strake. It's not difficult, just a lot of epoxy, carpentry and clamps. By the 20th, I need to set up my fin guide and start to epoxy the fins in place. The first is critical. The others are set 180 degrees apart. Each fin is cut from the GL 3/8" honeycomb "composite" according to the RockSim plan. Then each is caped with 3/8" birch. The caps are roughly rounded with a belt sander, then hand sanded to a sharp proportionate edge.


                                                                               



Here, you can make out the sanded caps on each fin, and each fin has been epoxied into their respective slots. I've mixed West System 105/206 fast hardener with a small amount of High Adhesion Filler (404). This produces a milky consistency that adheres well.. It ends up curing much harder than plain West and prevents any cracking of the fillets with curing.Good alignment. Fins are first because I'm going to line up each strake to its fin with a simple jig.

         


  




More Strake Work
September 22-23, 2010

Much more difficult and time consuming than I thought. For weeks with every opportunity when my real job wasn't top priority, I would go out and "cap" another strake. Each cap was also roughly rounded with the band sander then hand sanded. Below are a few shots of how they look. Below, I've done a quick mock-up of fin/strake #1. The end caps on fore and aft strakes are lined up.


               


Before I epoxy the strakes, I align each slot and mark the alignment on the airframe. Like a two-stage rocket, the two parts of the strake has to be carefully lined up for proper flight.

          

Each of the slots in the airframes are filled with the epoxy first. I want to move very quickly to weld the aft portion of the strake to the motor mount and lower airframe slot and the forward strake into its slot in the upper airframe. There is a small piece of wax paper between the two halves of the strakes so they don't get glued together. Any excess glue is wiped off the walls of the strakes with 91% isopropyl alcohol or my wood jig will be glued to them. Below, I'm using a couple of Home Depot yardsticks on each side of the strake. The clamps keep everything lined up. After all of this is cured (along with the other three strakes), I'll go back and apply epoxy fillets externally. This is for strength more than cosmetics. I always have other strakes in place without epoxy because I'm constantly working for a custom fit on each even while waiting for strake #1 to cure.


More Strake Work
September 26, 2010

   


Three more...  


More Strake Work
October 11, 2010


The shots below shows a typical fin/strake alignment after the epoxy has hardened and the jigs removed.The view is from the top down. Then the look with all four strakes attached and aligned compared to the prototype..          


                 

Fin Filleting
October 12 and 13, 2010

With the strakes "welded" in place for now, I went ahead and filleted the fins. These shots aren't great, but is possible to see the thin fillets. They appear slightly white because I've mixed West System 105/206 slow hardener with a small amount of High Adhesion Filler (404). This produces a thick milky consistency that adheres well and tends to run less. It ends up curing much harder than plain West and prevents any cracking of the fillets when curing.


         


Compartment Filleting
October 13, 2010


Before I start filleting each compartment, I have to confirm that there are no gaps in the strake to airframe welds. Otherwise, epoxy will just leak out when it is shot into each compartment. I tape each strake in the lower airframe as if I were going to do a standard fillet. But, I  do only a very thin fill with hobby epoxy  (slow cure mixed with a very small amount of adhesive filler). This is just to fill gaps. I'll do a full fillet later.

This may seem only slightly odd. With the holes in each centering ring already aligned, I can start the process of filleting each of the strake compartments. While there is some glue in the compartments from the first  placement of the strakes, there are no real fillets. There are 3 compartments between each strake for a total of 12 compartments. Each receives approximately 3-4 oz of epoxy (West 105/206 slow hardener with two teaspoons of high density 404 filler to produce the right sticky thin consistency). That's a 1/2" polyethylene flexible tube in one of the centering ring holes. I've marked the tube with a Sharpee to identify where each compartment will be. An all thread is placed inside the tubing to keep the tube straight until it hits the most forward bulkhead. I mix up approximate 12 oz of West and pour each shot into the funnel. The West has to be thin enough with the adhesive filler to still easily run out of the funnel into the tubing and into a compartment. It it slows, a basting bulb can be attached to the tube and compressed.  I pull the tubing to the next compartment and add another shot of epoxy. When I finish the most aft compartment, I can pull out the tubing and get rid of it (like a catheter). The airframe is rotated a quarter turn every 10-15 minutes for about two hours. Then,  I can let it cure for about 6 hours. The cup is cleaned with some acetone, air dried and used again for the next set of compartments. I only do two sets in a day.

Two part Giant Leap foam will be filled in each compart from forward to aft just like the epoxy. However, only one compartment is done at a time to see how much the foam expands.


 

Giant Leap Foaming
October 15-17, 2010

The same method for fin internal filleting was used for foaming. That is, foam was mixed 1:1 and poured into the rocket with it set up vertically. Mixed foam is poured into each cavity from forward to aft. It takes a couple of pours in each compartment. Eventially I over-foamed and had to hack saw the excess.


    


A Dremel burr gets all the excess foam out down to the fin tabs

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Here, I've fitted the aft centering ring into the airframe with the Aero Pack Adapter. It hasn't been epoxied in yet. I need to determine that the ring is in as planned so that I can drill a hole centered in the ring for the insert for the rail button.


 

Next I am just making sure that the 75mm motor fits in adapted from 98mm.


    


    

Nose Cone
October 2010


Method


I am building the cone from the coupler up. I cut bulkheads and some centering rings. The plan is still to use a cardboard tube to center the birch and foam rings. I decided to alternate the 1/2" birch with 2" of styrofoam. I will run a 3/8" all thread up the center of the tube to the nose cone tip and through the most aft bulkhead to a 3/8" eyebolt. The inner tube can be filled as needed with lead shot. The shot is held in place with the aft bulkhead. That bulkead is bolted into the most aft centering ring (below on the left) which is recessed 1/2". Note the most aft end of the centering tube flush with this centering ring.  It's epoxied to the coupler and internally filleted. The aft bulkhead is removable to add or remove lead.

The shape of the cone is dictated by the dimensions of the 1977 plans:





     


                 

       



        

  

 
   





At 1514 hrs today, November 12, 2010, the L3 AGM 78 build was finished.

Preparation for Painting

Automotive Filler/Primer
Bondo and Squadron touch-ups
Final painting

     

   

       

   

On-board video
BoosterVision Gear Cam

   

Level 3 Certification
November 27, 2010
The AGM-78 Raytheon "Standard Missile"

Rainbow Valley, AZ
L3CC: Terry O'Brien
Witness: Gerald "Skippy" Meux, Jr

Motor:
Aerotech M1297 W

Flight Data:
                                                                 Predicted:                                                                  Actual:
Apogee                                                        3726'                                                                        3180'
Peak velocity                                            543 ft/s                                                                   551 ft/sec
Time to apogee                                         15 sec                                                                    15.5 sec

Video

For Maurice "Moe" Bertrand's Flight Sequence Photos
Photos Maurice Betrand

For James Donald's Flight Sequence Photos
Photos James Donald

    
Photo Maurice "Moe" Bertrand                                                      Photo James Donald


Several photos of the launch sequence to main chute deployment and main backup charge
Maurice "Moe" Bertrand
      
Photos Maurice "Moe" Bertrand

            

     

         

         Gerald "Skippy" Meux, Jr


 
Several photos of the drogue and main deployments
James Donald

       

           


Photo Maurice "Moe" Bertrand

Successful Level 3 Certification