Estes LTV Scout, Build, Part 4, Engine Mount Gussets

These are probably the thinnest centering rings I've ever run across - The thickness of two layers of 110 lb. cardstock. I've used gussets in the past to beef up an engine mount.

   

I wanted the gussets at a 120 degree spacing or close to it.

A copy paper strip was rolled around the BT-20 tube. Two even folds were made giving three gusset positions.

Wrap around the tube and mark at the folds and where the strip meets.

This is why I save excess balsa left over from other kits.

3/32" thick balsa strips were cut to fit between the two centering rings. These were made a little wide to be sanded even with the outside ring edge after the glue dries.

Here's the final, finished engine mount. 

It's always surprising how much stronger gussets make the mount feel.

This shouldn't be considered "bulletproofing" a LPR model. Just some lightweight strengthening.

Estes Antar #7310 Build, Part 2, Gussetts

This is the rear centering ring. The slots are cut out for the gluing tabs on the nine gussets.

The slots will have to be cut with a sharp knife.

Keep your gussets in a small bag. If you lose one you'll be out of luck!

There are quite a few in the bag, I was building four kits at the same time!

On the right I'm lightly sanding the laser burnt edges.

The gusset on the far left shows the burnt, rough edge. Next to it is another gusset cleaned up after a few passes with 400 grit sandpaper.

I like to seal the edges for a smoother look after the model is sprayed. A rough laser burned edge doesn't accept spray paint very well.

Run a bead of white or yellow glue and smooth off the sides with a fingertip. Try to get glue coverage from side to side of the edge. 

Don't rub the glue in, let the glue bed dry a bit rounded. 

After the glue bead is dry, smooth over with some 400 grit sandpaper.

Estes Green Eggs, #7301 Build, Part 3, Engine Mount Reinforcement

Occasionally I see a forum post where a builder will upgrade the centering rings to plywood. These kit supplied card stock rings are certainly strong enough for 24mm engines.
For those interested, I'll show how to make a much stronger engine mount using what was included in the kit.

I wrapped a copy paper strip around the engine mount tube. The overlap was marked.
The strip was folded into even thirds, the folds were marked with pencil.

The strip is re-wrapped around the tube. You must be sure the marked lines won't be in the way of the TTW fin tabs.
I set the first line just to the right side of the engine hook. This will place all the gusset lines to the sides of the fin tabs.

There is plenty of extra balsa on the fin sheet to make the three gussets.
Cut a wide piece with the grain running vertically. Sand to a tight slip fit between the rings. (shown above right)

Mark the gusset width a bit wide. (Bottom left) You'll sand off the excess afterwards.
A shallow notch is cut to fit over the black retainer band.

Glue the gussets into place. Sand off the excess gusset width little by little. Check the fit in the body tube as you are sanding.

Before adding and fitting the gussets, my centering rings were a loose fit in the body tube. After sanding them to size, the fit is much better and the mount will feel much stronger.

Quest Future Launch Vehicle #3013 Build, Part 3, Engine Mount

I'm not a big fan of the thin walled yellow engine mount tubes. This one was cut about 3/16" short of the normal 2 3/4" length.
If assembled by the instructions, using the engine hook slot - the engine block ring would extend beyond the top of the short tube!
I'll replace this tube with a Odd'l Rockets Heavy Wall BT-20H.

The fit of the centering rings is too loose in the main air frame tube. While it could be used, it would take too much glue to fill the gap.

The rings also needed a small relief notch for clearance over the engine hook. I used a rotary punch to make a partial crescent cut.

To make up for the loose centering rings, I made some balsa gussets. Cut them wide and sand to fit. These make the entire mount much stronger without adding any real weight.

To better seal the upper loose ring, a bead a glue was set around the edge and allowed to dry before gluing the mount in the body tube.

Centuri Argus #KB-9, Build, Part 4, Engine Mount Gussets

The outside diameter of the rings was a little small. I decided to add some balsa gussets for a better fit and a stronger mount.

Scrap balsa was cut to the width between the centering rings.
The glue fillets already in place didn't allow the balsa gusset to slide all the way to the engine mount tube. I sanded the corners off to fit over the fillets.

 A strip of copy paper was wrapped around the tube. After being cut to size, it was folded in thirds and marked. The mark locations were transferred to the engine mount tube.

The gusset pieces were cut wider than needed and glued to the 120 degree marks, with two centered around the engine hook.




The gusset sides were sanded to allow a slip fit into the ST-13 (BT-56) lower tube.
While the fit of the mount is much better, I still have build up the outside diameter of the centering rings with a bead of glue before gluing it into the tube. The gussets add a lot of strength to the mount.

Semroc Snake Jumper Build, Part 6, Fin Gluing and Gussets

The side rudders sere glued onto the wing halves using my 2" machine square. This insures a perfect right angle. Notice the wing is set into the top of the gusset.

Here's the model up to this point. It's an interesting sport "profile" fin design.

On the left is the Semroc instructions. The suggested gusset position didn't seem like it gave the best support for the wings.

On the right is the old Centuri instructions. The flat side of the gussets are glued onto the wing with the narrow root edge against the body tube.

Here's how I glued on the wing gussets, Centuri style. To me it seemed like a stronger joint.

A dowel and engine casing has been slipped into the engine mount. A paper towel is rolled and pushed into the engine mount to keep the spray paint out.

Semroc Snake Jumper Build, Part 5, Fin Gluing

Card stock fins are thinner than balsa and have a thinner root edge for gluing.
Just like the old Centuri kit, "gusset" reinforcements are used. The gluing position is lightly burnt into the side fins.
You can go ahead and fillet the gussets on the bottom, rounded side.

The long top fin and cockpit piece is easy to glue on crooked. Be sure it is straight before gluing. I used my aluminum angle to double check it down it's length.

The launch lug is sandwiched and hidden between the "wheels". The wheel halves glue on either side.


Before applying glue, do a dry fit and mark where the glue contact points are. Use less glue and there will be less to clean up.

Looking down from the front, double check to be sure the wheel halves are straight and parallel.

Estes Hi-Flier XL, #3226 Build, Part 3, Engine Mount Gussets

Here's the finished mount with the upper ring down and over the top bend of the engine hook.

As it is it's plenty strong for C11, D12 and E9 engines.
I like my mounts a bit more robust.
Gussets will be added.

I used some strips left over from the balsa fin sheets.
The leftover edge scraps are long and tapered.



The strips were cut to the length between the two rings. The gusset had to be notched to fit over the black retaining ring.

After three strips were glued and got fillets, the sides were sanded even with the outside diameter of the rings.

With the gussets in place, a dry fit feels much stronger than just the centering rings alone.

Estes Patriot Build #2056, Part 4, 24mm Engine Mount

This 24mm mount will have a replaceable Kevlar line.
The small holes are punched for the Kevlar tube. On the right the larger circle is for the engine hook movement.

In addition there are lines drawn for some reinforcement gussets.
This will be a D engine mount, I wanted it stronger than just the two centering rings.

Reinforcement gussets were cut from the excess 3/32" thick wood stock. Cut them longer than needed and sand to a good fit between the rings.
They are cut higher than the height of the centering rings for trimming later.

At the bottom you can see the Kevlar guide tube in place.

Before gluing on the gussets, wrap some electrical tape around and over the engine hook and Kevlar tube.
After the glue dried on the four gussets, they tops were sanded flush with the outside edges of the centering rings.

It's pretty surprising how much stronger the entire engine mount is with the gussets added.
Check the fit in the BT-60 tube before gluing. The gussets will require you to sand the rings a bit for a sliding fit.

Build time:
Assemble Engine Mount = 15 minutes
Add gussetts and sand = 15 minutes
Total build time so far = 1 hour