Friday, February 27, 2015
The shoulder edge on the replacement nose cone wasn't very sharp.
I painted filler just over the edge. The clear payload tube was slid on and the tube edge pushed the CWF up into a bead.
This bead of filler raised the outside diameter of the shoulder edge.
After it dries the bead of filler will be sanded down.
Slide the clear tube back on to check how much should be sanded off and try to match the diameters.
Don't sand down the CWF shoulder with the clear tube in place!
Sand, slide on the clear tube, check, remove the tube and sand again if needed.
The lower half of the block got a wrap of masking tape.
The upper half got a brushed coat of CWF.
After that dried a little sanding got the diameter to a good tighter fit.
This rough look of the block under the clear tube will be covered later with a coat of paint.
The block fit in the lower BT-50 heavy wall tube was very good.
I use Teflon tubing for more control when applying thin CA glue.
I'm fortunate to have a hobby store close by that sells the tubing in the right diameter for use in the CA nozzles. Don't ask me what the diameter or suppliers are, I did a quick check online and can't figure out what the right Teflon tube is. Check with your local hobby store.
On the right is a new nozzle. The tip is closed and must be cut off with a sharp blade for the glue to flow.
To fit the Teflon tube applicator you have to shave off very thin slices of the tip until you reach the right hole diameter.
Like I said, shave off very thin pieces while checking the fit of the Teflon tube. When you have it right, the tube will be a friction fit in the nozzle hole.
Notice the Teflon tube is cut at an angle to allow easier insertion.
I leave the tube long and cut the end off after it is 1/4" inside the glue bottle tip.
Cut the exposed end off at about 3/8" to 1/2" at an angle.
TIP: After using the glue, squeeze the bottle sides to blow any excess glue out of the Teflon tube. Hold a paper towel over the top of the tube tip when blowing out the excess.
Thursday, February 26, 2015
With a sanding block I'm sanding in a 45 degree "corner" into the larger main fin.
Don't sand any more off the dorsal fin. Going down the rounded edge, use your block to "knock" into the main fin balsa cutting the small 45 degree notch.
The leading edge of the main fins are rounded. Be careful when you get close to the 45 degree notch already at the fin joint, that is your "stop point".
After applying filler the angled notch probably won't be as sharply defined. That's okay, the transition between the two pieces will probably be smoother than you would get otherwise.
Looking ahead -
The engine hook overhangs the back end of the tube.
If you've ever built a Estes Goblin, the rocket didn't stand up on its fins. It wobbled on the engine hook.
I'll recess the engine mount tube (not even with the main air frame BT-50 tube) so the model will stand on the fin trailing edges.
In some kits, the main air frame body tube is in two sections joined by a coupler.
The tube joint might be at a color separation point like on the Estes Cosmic Explorer. TIP: If the separation joint falls on a color separation, don't glue the tubes together during initial construction. Glue them together after spraying. and you'll have an easy color separation.
But on models like the Monarch, it seems the tubes are in two pieces only for shipping purposes. Estes could fit the tubes into a smaller bag and more kits into a shipping box. This is just a guess on my part.
This leaves the builder with the job of filling the tube end joints.
Some minimum diameter Centuri kits came with two part body tubes. This illustration is from the Centuri Scram Jet. In those kits the shorter tube was to the rear, the coupler served as the engine block. This saved first time builders from problems setting an engine block 2 1/2" from the end of the shorter tube.
Wednesday, February 25, 2015
The newer Estes kits have nose blocks that are 2" long.
The old 50 tube nose blocks were 1" long. Even back then it felt a bit short with only 1/2" on either side.
I'll compromise and cut this block to 1 1/2" for 3/4" exposed to join up the tubes.
1/2" inch was cut off the 2" long nose block with a razor saw leaving a short 1/2" block.
I'm building two kits so I have two short pieces. These will be glued together and thrown into the spare parts box.
The green adapter ring will need some inside peeling to fit the wider ST-7 tube.
A channel strip was also cut from the inside to clear the engine hook.
This is a dry fit to check the fit of the long adapter channel fit over the engine hook.
Cutting the channel takes away friction and compressing of the adapter and engine tube.
Here's the finished engine mount.
The Kevlar line was tied under the top bend of the engine hook, Semroc style.
Note the tied loop is long enough so the knot ends up over the top of the tube.
There is very little room between the tube diameters and the knot might get into the way when the mount is glued in.
The tail end was pushed back through the loop to hold it down against the engine mount tube.
The Centuri Rocketry Exploration set was introduced in the 1977 catalog.
Two "base" models were included, a one or two stage ST-7 based model and a ST-16 based rocket.
The manual guided you through different launch scenarios using both models.
Centuri had sent me this set for review. I didn't remember that a ping pong ball was included in the box.
This page showed the suggested X-16 model flights.
The ping pong ball used to get the approximate altitude.
"When the parachute ejects at the peak of flight, a ping-pong ball is also released. As it fall to the ground it accelerates (for less than a second) to a speed of 30 ft/sec. The ball is very light and offers so much air friction that at 30 ft/sec. it reaches "terminal velocity" and descends at this constant rate.
To measure this atltitude it is necessary to observe how long it takes from the parachute ejection to when the ball hits the ground.
Multiply the number of seconds by 30 and that product is the altitude in feet, even in a breeze."
Tuesday, February 24, 2015
On the left is the kit supplied BT-50. The clear payload tube is wider and overhangs the BT-50.
The inset picture shows the thick wall BT-50. It's a much better match to the payload tube diameter.
The thick wall tube has an outside diameter of .990, not quite (but closer) to the Centuri ST-10 at 1.04" diameter.
I'm also replacing the BNC-50K style Alpha nose cone with a parabolic custom cone from BMS.
It's about 1/4" longer and closer to the original Centuri kit shape. On the left is the kit nose cone, the inset shows the replacement. Cutting 1/4" from both sides gives an additional 1/2" of payload area.
Besides that, it just looks better. Why bother with a clear tube if half of it is filled with balsa?