18mm Engine Size Comparison

I'd noticed some engine mount movement in the Quest Chinese made A6-4s.

Look at the difference in the length of these three 18mm engines.

The blue labeled Quest engine is German made. It is just under 2 3/4" long.

The Quest in the middle is a newer Chinese made engine. It is 1/8" shorter than the Estes engine at the right.

The Estes engine is a full 2 3/4" long.

Here's the upper side of the engines in the same order from left to right:

When checking the fit in a BT-20 tube:

The German made Quest (from Weco) is quite loose in the Bt-20. This one would require a few wraps of tape for a friction fit and to prevent some "blow-by" of the ejection charge out the back.

The Chinese made Quest engine is a slip fit, one wrap of tape and it 's tight in the mount. The paper wrap increases the outside diameter. This engine is 1/8" shorter than the others. At ejection it could recoil back against the rear of an engine hook.

The Estes engine is the best fit in the BT-20. Just over two wraps of tape gave a good friction fit in the BT-20.

FlisKits Interloper Part 9 Masking the Nose Cone

I had planned for the lower taper of the nose cone to be white. This would require a small mask.

Normally the darker color would be second but the shape of the nose cone made me do the white after the orange.

I cut a thin strip of clear Scotch tape and wrapped it around the widest part of the nose cone. A wide strip of tape would be hard to set down in a straight line.

More tape and a paper mask was laid over that first thin strip of tape.

Here's the nose cone after the white had dried and the mask removed.

For a small mask on a curved surface, I was happy with the results.

FlisKits Interloper Build Part 8 Black Trim Paint

The scalloped BT-20 piece had the interior colored black with a Sharpie pen.

This would be a hard mask at this size. The Sharpie was just an easier way to go.

I wanted the long main tube to be black at the rear. This black would give the white vanes a greater contrast on the lower engine end.

TIP: You should be very careful when handling any silver or metallic paint. Fingerprints and scratches show up easily long after you think the paint has dried.

I didn't want to use masking tape over the silver. The sticky "gum" of the tape will mar a metallic paint. I simply wrapped white paper around the tube for the mask.

I set the BT-20 piece alongside the body tube trying to visualize where it would sit when assembled. The paper mask went at the halfway point.

The exposed low end of the tube was spray painted black.

New CHEAP Cutting Board

I'm always looking for great buys on building tools and supplies . If I find something, you'll hear about it on this blog.

This is nothing new to most builders. I've just never owned one.
I cut squares from the sides of old shipping boxes to build on.

I've seen these "self healing" mats for sale before. Usually a mat this size would sell for well over $20.00.

This mat was picked up for $6.00 using a 40% off coupon at the new Hobby Lobby in Orlando, Florida. It's the Hobby Lobby brand called Tech Tools.
You can check it out HERE

The package advertises the mat as being 12" X 18". It's almost that size, it's a quarter inch shy. The actual measurement is 11 3/4" X 17 3/4".
But for $6.00, I'm not complaining.

Supposedly - this is how they work:
It's all in the chemistry!
Self healing cutting mats are made of a special plastic with a particular property: the molecules of plastics "stick to each other" in such a way that after they are cut apart, the broken bonds will re-form when put back together. Unlike paper, where broken molecular bonds can't repair themselves, a self-healing mat will reform as new after being cut.

Over time, however, the plastic can age and wither, or the molecules don't reform quite as they did before, and the bonds don't restore quite as quickly - so some mats won't stay perfect and new forever.
This information was copied online.

FlisKits Interloper Build Part 7 Toothpick Details

The toothpicks were sealed with two coats of sanding sealer, sanding between coats.

I sealed six toothpicks to have extras, just in case. The six were cut in half and punched into cardboard for spraying. These will be cut to size after the black spray dries.

These are the front guns to be glued below the nose cone / body tube joint.

I did my best to match the angle of the trailing edge of the balsa standoff.

FlisKits Interloper Build Part 6 Vanes and Fins Prep

The instructions give you three different suggestions for the fin shaping-

a double taper, rounded or square leading and trailing edges.

The fins feel thick for a model this size. I felt the double taper would look best but would be hard to sand a sharp bevel on such small fins.

I chose a wedge shape. The leading edge would taper to a "knife edge". The trailing edge would be full thickness.

To avoid a hard mask, the fins will be filled, primed and spray painted before gluing on the lower BT-20.

The laser cut interior vanes are thin. After a coat of gray primer they were sanded smooth. Two coats of gloss white followed, sanding between coats.

Any paint will be sanded off the root and outside edges for better adhesion to the body tube surfaces.

FlisKits Interloper Build Part 5 Fins

Both the long main tube and the shorter Bt-20 got thinned Carpenter's Wood Filler to eliminate the seams. This was sanded down with 400 grit sandpaper.

If you look at the original drawing, I wanted the interior ram jet fins to extend out the back instead of being flush with the rear of the tubes. With the outside edge of the interior fins cut trimmed, the BT-20 will end up being a little shorter than the supplied length of tube.

The end was cut at about a 45 degree angle. This first cut fin was used as a master template for marking the other five.

These are the four tiny fins. The face card says "Laser Cut Fins" but that refers to the smaller card stock internal vanes. You still have to cut these from the 1/16" balsa.

The outside edge was cut at the angle as shown in my first drawing.