Estes Strikefighter, Kit #2015, Build, Part 5, Engine Mount

The instructions have you glue the upper ring 1/16" down from the top of the tube.

I set the upper ring lower, just over the top bend of the engine hook. This reinforces the mount and could prevent tearing of the tube if the ejection charge knocks the hook down.

Here's the Kevlar line against the underside of the ring.

The Kevlar loop goes under the engine hook.

On the other side, the knot butts up against the very small punched hole in the ring.

The finished mount - 

An engine block was glued in the tube top, slid down against the top bend of the engine hook.

The Kevlar line got a 1/16" diameter heat shrink tube slid down against the top of the upper ring. The tube is 1/16" diameter before heat shrinks it tight around the line.

I used a heat gun on the low setting to shrink the tube.

Estes Strikefighter, Kit #2015, Build, Part 4, Engine Mount

The 20/55 rings were loose on the BT-20.

TIP: The inside diameter of the ring can be made smaller and a tighter fit by applying a thin ring of glue on the inside edge. Let dry before sliding back on the BT-20.

Use a rotary punch to make slight relief notches for the engine hook and Kevlar line.

On top is the upper ring,

The bottom pic is the lower ring.

The Kevlar line is tied tightly around the BT-20 tube using a square knot. 

Note it goes under the top of the engine hook.

After tying the knot, rotate it around the tube opposite the engine hook.

Estes Mini Scale Combo Pak, #0874, Tomahawk & Exocet, Build, Part 6, Installing The Engine Blocks

In the instructions, both of the two models have a slit cut in the upper body tube. The shock cord is fed through the slit. The exposed shock cord gets a paper cover glued over the top.

One model will get the slit tube method, the other will get a Kevlar line tied to the engine block.  

A notch is cut into the outside of the engine block. The Kevlar line is tied and tightened over the notch.

Feed the Kevlar line through the middle and out the bottom.

The original yellow engine spacing tube was missing. I cut a BT-5 coupler to 1 3/4" long.

The fit in the tube was tight so I peeled off the outside layer for a slip fit.

The spacing coupler is pencil marked 1/4" from the bottom.

Slip the Kevlar line through and out the bottom of the spacer coupler. The engine block rest on top of the spacer coupler.

Apply a bead of glue 1 1/4" inside the low end of the BT-5 tube.

Push the engine block in and into the glue up to the pencil line on the spacing  coupler.

For now, leave the Kevlar line out the back of the model.

The second model got an engine block without the Kevlar tie.

Estes Aries SST, #1927, Build, Part 2, Engine Mount

The engine hook and Kevlar line relief notches are initially cut with a knife. 

Instead of picking out peeling out the wrap layer between the cut lines, I use diamond files to remove the recess. This makes a cleaner notch, especially on the Kevlar side. 

I don't apply a ring of glue then slide the centering ring onto it. Instead, I slide the rings on dry, apply spot glue at the joint and then smooth them. After the spot glue dries, it allows me to tighten the Kevlar wraps without the rings sliding around. Then apply full glue fillets

Note the upper ring is centered over and on top the upper bend of the engine hook. This makes a stronger mount - instead of the upper ring positioned above the upper bend of the hook.

Tighten the Kevlar wrap, then apply the glue fillet over the the Kevlar wrapped line.

An engine block wasn't included in the original kit, I added one, even with the tube top when slid against the top bend of the engine hook.

A 1/16" diameter heat shrink tube was slid down the Kevlar line and hit using the low setting from a heat gun.

Hold the heat shrink end down against the top of the upper centering ring. The after pics shows the tubing hugging tight over the Kevlar line.

Note the shrink wrap starts below the top of the engine mount tube. This protects the the low end of the Kevlar line.

Estes Sandpiper, Kit #1389, Part 2, Engine Mount

The instructions have you set a line of glue 2" up inside the 3 1/2" long BT-20 tube. Then push the engine block up from the bottom.

The engine mount tube is only 3 1/2" long, I can add a glue fillet from the top.

Tape and engine casing with 1/4" extending out the bottom. Slide the engine block in from the top dry, no glue yet. 

Slide the block down until it stops against the top of the engine casing.

Add glue using a Q-tip making a fillet around the joint.

After it is dry, remove the engine casing.

The upper 2050 centering ring gets a notch for the Kevlar shock cord.

There is very little room between the tubes for a knot, I did a wrap.

Tighten the Kevlar, set it into the glue fillet.

New Way Lunar Jumper Build, Part 3, Engine Mount & Shock Cords

The engine mount assembly is standard. A slip over coupler holds down the middle of the engine hook.

Here, the Kevlar line is tied beneath the upper plywood centering ring.

There isn't much space between the outer BT-50 and BT-20 engine mount tube. A larger square knot could bulge out the BT-50 tube wall.

I used an overhand knot, but rolled the Kevlar over and under the wrap 4 times. This still allows the wrap to be pulled tight and keeps the line close to the engine tube.

The wrap is set into the wet glue centering ring fillet. The loose tail is cut off and also set into the glue fillet.

The picture to the right shows the heat shrink tube slip down to the top of the ring, protecting the Kevlar line. 

The short shrink wrap is slid over the tied knot joining the elastic and Kevlar line.

Near the elastic, be careful with your heat gun - 

TIP: Using the low setting on my heat gun, the elastic started to melt!

I had to cut off the old knot and re-tie the elastic and Kevlar. I might tie an additional piece of elastic to the shorter line joined to the Kevlar.

The second time, I kept more distance between the heat gun and the heat shrink tube.

Second try was good! (Maybe that's why two pieces of tubing were included.)

Estes Shark #1111, Build, Part 8, Engine Mount & Fin Gluing

Set the engine mount and Kevlar line alongside the lower, longer tube.

The BT-20 engine tube is even with the bottom of the BT-50 main body.

This gives you an idea how long the Kevlar line should be, a little shorter than the top of the BT-50.

Tie a overhand loop knot (shown on the right) for the elastic shock cord attachment.

I used epoxy to glue the mount in, allowing me some positioning time.

Here's the BT-50 tube with the filler/primer scraped off where the fins will be glued. The scraping is a little shorter than the length of the leading edge.

The low fins are glued even with the end of the body tube.

On the forward fins and thrusters, I used a wrap of masking tape as an low alignment line at the corner of the trailing edges.

Estes Monarch Build, #7214, Part 3, Engine Mount

The finger tab was cut off and the engine hook flipped over.

A subtle curve was bent down the length of the hook for better motor retention.

The upper centering ring got a small punch for the added Kevlar line.

The upper ring was slid on just over the upper bend of the hook for strength. 

The rest of the mount was assembled as shown in the instructions.

A 1/16" diameter heat shrink tube was slid down the Kevlar line and against the top of the upper centering ring.

Thanks go to Rick Randoll of NewWay Space Models for this Kevlar heat protection idea. 

A heat gun on low setting shrinks the tube around the Kevlar line.

The inset picture shows the Kevlar line below the base of the lower ring, set into the glue fillet.

New Way Blade Runner, Part 7, Gluing In The Engine Mount

The Kevlar and shrink wrap are run down thru the mount so they won't get in the way.

The instructions have you apply glue 1 3/4" from the bottom of the main airframe tube.

I use a dowel to roll a line of glue inside the tube. Setting the dowel beside the engine mount shows me the glue line would be better at 1 7/8" to apply the glue just below the upper centering ring.

Notice the two depth pencil lines on the dowel. The lower pencil line is the 1 7/8" mark.

A ring of glue is set around the top edge of the dowel.

Set the dowel in the tube up to the 1 7/8" pencil mark and roll the glue into a ring line inside the tube. You will have to apply more glue on the dowel to get a ring all the way around inside the tube.

Slide the engine mount in, turning the mount when in contact with the glue to even out and make a smooth interior fillet.

With the mount glue dried, 

TIP: Note the straightened coat hanger hook in the right side picture. The hook will help get the shock cord back through the top of the tube.

 

There isn't much room to get a fillet at the lower centering ring/body tube joint. 

I applied a small glue drop to one side of my long tweezers. Set the drop in on the joint to smooth as best your can. Keep some Q-tips handy to pick up any glue boogers.

New Way Blade Runner, Part 6, Tying Elastic Shock Cord To The Kevlar

As I normally do, some steps are out of order from the instructions.

I like to mark the body tube seams with a fine point pencil for visibility when filling.

The tip of my knife blade is dipped in thinned CWF. Wipe off the back of the blade leaving the filler on the top side of the knife. Set the knife in the recess seam and with a back and forth motion of the knife, leave filler in the seam.

You should be able to leave filler for a length of about 1 1/2". If not, your filler needs more thinning with water.

The instructions spell out how to tie the elastic shock cord to the Kevlar before gluing the engine mount in. You don't want the Kevlar line to extend beyond the top end of the body tube. This can lead to a "zipper" at an early or too late ejection, the Kevlar tearing through the body tube. 

Set the mount along the side of the body tube with the 1/4" pencil mark on the mount even with the end of the tube.

Straighten the Kevlar line out down the tube to the top. Mark the Kevlar 2" down from the top of the tube.

At the 2" mark, tie the Kevlar to the elastic shock cord using a simple, overhand knot.

The short, larger diameter heat shrink tube is slid over the knot. 

Hit with a heat gun or hair dryer at the low setting. On the left is the before, on the right is after using heat.

You can cut off the excess.

New Way Blade Runner, Part 3, Engine Mount

The rings are glued in place on their 1/2" marks made earlier.

Tie the Kevlar with a small square knot. Cut the loose tail off at about 1/2" long.

Press the Kevlar loop, knot and tail into the glue fillet.

Slide the heat shrink tube down the Kevlar line until the end rests on the upper centering ring. 

While holding the heat shrink tube against the upper ring - 

Apply heat using a hair dryer or heat gun on the low setting. It should shrink around and tighten over the Kevlar.

When tying the Kevlar knot, make it small and tight against the motor mount tube. There isn't much space between the BT-20 and BT-50 tubing.

Notice the Kevlar relief notch is to the outside edge of the upper ring. This keeps the Kevlar to the outside of the hot ejection charge.

Estes Mini Bomarc Clone, Kit #TK-5, Part 3, Engine Mount

The original kit instructions don't mention it - 

I did have to cut a relief notch for the engine hook. Here I've marked it with pencil.

The burrs inside the rings needed some light layer peeling to fit over the BT-5 engine mount tube.

I don't like using a tri-fold mount in smaller diameter tubes so I laced some Kevlar below the upper ring. After pulling tight, a glue fillet will lock it in place.

The lower ring slides up to 1" from the bottom of the BT-5 tube.

The upper ring is even with the top of the tube.

There wasn't an engine block in the original kit. I added one.

Slide in place against the upper bend of the engine hook, then add a glue fillet and smooth with a Q-tip.

Also added was the new heat shrink tubing slid over the first four inches of the Kevlar line.

This is butted up against the top of the centering ring and hit with a heat gun.

After heating, the shrink tube ends up tight around the Kevlar line.

Estes AMRAAM AIM-120 Downscale, Build, Part 6, Engine Mount Assembly & TIPS

Many kits have you glue 20/50 centering rings at 1/2" from each end of the engine mount tube. That doesn't really give enough flex for a spring steel engine hook.

The mount shown here is flipped over with the hook pointing up.

TIP: I've found the best position for the low, bottom ring to be 7/8" from the bottom of the engine tube. This allows enough flex to slide in a motor.

TIP: This is a brilliant way to lock in the Kevlar line comes from the older Semroc kits.

The Kevlar line gets a small overhand knot.

This is slipped under the upper bend of the engine hook.

In the picture, the upper centering ring has not been glued in place yet.

The upper centering ring is slid up and glued on slightly over the Kevlar loop.

The centering ring also locks the upper bend of the engine hook in place.

TIP: In all my new builds, I am incorporating heat shrink tubing over the Kevlar line for extra protection. The heat shrink tubing idea comes from Rick Randoll of New Way Rockets.

BMS School Rocket, Build, Part 9, Tying It All Together

The nose cone shoulder was masked using a rolled sheet of copy paper and masking tape. 

Normally I don't tie on the shock cord until after it is painted. 

The kit is supplied with a Kevlar shock cord. I added a length of elastic.

The elastic and Kevlar was tied together using interlocking loops.

The elastic was tied to the screw eye using a Duncan Uni-Knot. 

From the instructions - 

Tape, fold and staple the streamer to the shock cord.

The shock cord is chrome Mylar. 

It is thick Mylar, 2" wide x 24" long.

BMS School Rocket, Build, Part 4, A New Kevlar Cord Protection?

I can't take credit for this idea - 

Props go to Rick Randall at New Way Model Rockets. He has incorporated this Kevlar protection cover in many of his LPR kits.

Kevlar lines start to break down and can fail at 10 to 15 launches.

Near the low end of the Kevlar, near the engine mount - Rick adds some heat shrink tubing over the Kevlar line. When you consider how hot a heat gun gets (to shrink the tube around a wire) it makes sense!

An black powder ejection charge is momentary, the heat gun take a few seconds to shrink around the Kevlar line.

Heat shrink tubing is not included in the School Rocket Kit. I found some on Ebay and am starting to use it in my builds.

For reference, here's a 1/16" diameter heat shrink tube slid over a 135 lb. LPR Kevlar line.

To fit it over the Kevlar knot under the engine hook,

I flared the open end a bit using a sharpened dowel. The flared end makes it easy to slide over the knot.

On the left,

The heat shrink is slipped down and over the knotted Kevlar line.

On the right,

A heat gun was used to shrink the cover tight over the Kevlar and knot. The hear gun was used on the LOW setting.

There is that square hole left on the other side. Some ejection gasses could escape out of the hole.

A small piece of scrap BT-20 was cut and glued over the hole.