Friday, September 19, 2014

Weak Shroud Lines

While building an Estes Patriot I tested the shroud lines on the pre-made 12" parachute. This newer chute was made in China, dated 6/20/2013.
I pulled on the line and it broke - very easily.

I've ran across this before. I wouldn't risk this parachute on a flight so the weak lines will be replaced.
I'll use Coats and Clark Button and Carpet thread for the new lines.
For a 12" chute, three 25" lines were cut.
On the pre-made chutes, check the tied knots at the parachute corners. I've ran across square knots and granny knots.
If the knot slips, it's probably a granny and can come loose on a hard ejection.
If a knot slips, tie an additional overhand knot over the top. That will stop it from coming loose.

Many kit instructions and a few online videos say to simply tie two overhand knots when tying on a shroud line.
Two identical overhand knots will result in a slipping granny knot.
To make a square knot, tie an overhand knot, but reverse the second overhand knot on top. Better yet, check out the Animated Knots website: CLICK HERE

When the lines were removed, I cleaned up the torn holes in the reinforcement rings.
Card stock was set underneath the chute material for a clean punch.

Estes Black Brant III, Part 8, Reinforcement Coupler

Lately, BT-50s in every build have buckled after recovery. Even with a soft landing the BT-50 crimps down the inside spiral above the engine mount.

I made an interior coupler from Crossfire BT-50 tube.
1 1/2" was cut and slit straight down its length.
The tube was overlapped and slid into the Black Brant tube.
Push it to the inside diameter and mark the edge with a sharp pencil.

Enlarge the picture to see the cut line.

With sharp scissors cut just to the side of the pencil line.
This should give you a tight slip fit in the body tube.
The edges of the split coupler will butt tightly together.

The coupler will be pushed in place with the engine mount. It will sit right above the upper green centering ring.
Apply glue far enough inside the tube for the coupler first, slide it in place with the engine mount. Remove the mount.

At the bottom of the engine mount tube is a pencil line. Apply glue in the main tube, the mount is pushed in up to the line.

Thursday, September 18, 2014

Estes Black Brant III, Part 7, Tube Fill, Fin Primer

This replacement BMS BT-50 had the tightest seams I'd seen in a while.
Normally I'll run a mechanical pencil down the seam rut so it's easier to see when applying CWF.
The pencil kept slipping out of the seam.
Still, if you can feel it with a fingernail it gets CWF and primer.

The front and back ends of the tube got a wipe of CA glue.
You can use your fingers as a depth gauge as you go around the edge.

The fins were shot with primer/filler and sanded.

On the left you can still see the sanded fin taper.
I sand the tapers first trying to keep the sandpaper away from the high ridges.

After sanding the primer still shows on the high points of the tapers.

As thin as the sprayed primer coat is, what's left after sanding helps define the sharpness of the taper edge.

Big Bertha / Ranger Fins

On YORF, Rich Holmes has done his homework.
Going back through old plans and kit balsa, he has put together an overlay that shows the subtle differences between the Big Bertha, Baby Bertha and Ranger designs.

Regarding fin thickness, it seems the single engine Big Bertha had 1/8" thick fins, the three engine cluster Ranger fins were 3/32" thick.
Go figure!
The Baby Bertha fins are 3/32" thick.

There have been changes to other designs over the years.
TRIVIA: There was some questions about differences in the Alpha nose cones. It seems the profile would change when the grinder stones would wear down.

Wednesday, September 17, 2014

Ebay Sales

More Rocketry items for sale on EBAY!
I just have extras of some things.
Good Prices on all . . .

A NEW BMS MIGHTY D Launch Controller


This item is SOLD!

Four NEW Packages of

Hoo Boy!
I'll throw in TWO New Odd'l Rocket Parachutes with each item sold!

Estes Black Brant III, Part 6, Fin Taper Sanding

Use your thumb as a "stop" against the high point lines.
(For clarity I left the pencil shading off the surface of this fin.)

Sand a few stokes and take a look at the black ink left on the leading edge. Turn over the fin and sand some on the other side.
Always check back to the ink on the leading edge. Make sure the remaining ink thickness is consistent on both sides.
When the taper is done, a quick hit with 400 grit will take off any of the remaining black line on the leading and trailing edges.

Here's a finished fin.
The pencil shading help you see how straight the sanded edge is even if you take off some of the original pencil line.

On the left is a view from the root edge.
The inset picture shows the outside edge closest to you.

Tuesday, September 16, 2014

What's Wrong With This Picture? Part 2 Answer

A few days back I posted this picture from the 1973 Estes catalog - What's wrong with it?

Lonnie responded:
If the inside and outside diameters are correct, the tube thickness should be .04" instead of 0.021.
From RichsRockets :
No, because inside and outside diameters differ by TWICE the tube thickness... think about it.
Anonymous wrote:
I remember seeing this ad as a kid and wondering what parallel winding meant and why was a line drawn around the center of the tube. Still doesn't make sense to me.

Here's how the drawing should have looked:

The illustration in the 1973 catalog looked like two smaller length tubes joined by an internal coupler. Parallel wound BT-30 tubes had a wrap joint that ran down the length of the tube.

The inside and outside tube dimensions don't add up!
Outside Diameter           .765" 
Inside Diameter              .725
                                         .40 ?

BT-30 tubes were thicker walled, more like a BT-55 or BT-60, but not that thick!

The listed wall thickness is listed as .021". That's probably close to the truth.
I would guess the printed inside diameter was incorrect.

TRIVIA: I read somewhere the original BT-30 sized tubes were made from file folder manila material. Gleda Estes hand rolled them on the kitchen floor.