Farside-XX

Farside-XX : A little variation on a classic stager

From a 1960's Estes catalog.

A few years ago, I was inspired to build a clone of the classic Estes Farside-X. I made several modifications to address a variety of issues.

While the rocket plans call for a BNC-60L, the same nosecone as originally used on the Big Bertha, in the early catalog artwork (left), the nosecone looks pointy, so I modified mine to include a point. As it turned out, it may be a bit too pointy. But I still like it
I made the payload section a little longer to ensure it would hold all that was needed. This is made clearer in the next point.
Payload rockets, while appearing to be spacious, often in fact leave little room for the recovery system (pink space at left). Since it resides in the main airframe and not in the payload section, it has to fit in between the sustainer motor tube and the base of the transition (orange regions). So, rather than having to squeeze the chute, wadding and shock cord into such a small space, I used the payload section to hold the recovery system. That is, it's now a fake payload section.
Item 3 addresses another issue as well. The base of a typical transition section is notoriously short and thus presents a failure point on the rocket, where it tends to want to fold in two. Also, the body tube opening tends to get stretched out of shape by the flexing of the short base. By making the payload section permanent, it allows the sections to be joined together thus eliminating the failure point and ensuring the two sections stay perfectly aligned (co-axial).
A fully loaded 3-stager is a lot to lift for a black powder rocket motor. Since B14 booster motors are no longer available, a 24mm motor mount was implemented in the first stage. This allows D12 and C11 booster motors to be used which ensures the rocket leaves the pad with sufficient velocity for stable flight.

Payload section and recovery system
In place of the original design's balsa transition, the lower BT-50 body tube was extended upward by about 4-½". And the BT-60 payload section above that was also extended.

A conical wrap - not yet installed in the pic at right - replaces the transition making it appear much the same as the original. Two inches of the added BT-50 are under the wrap, and the rest extends into the fake payload section. That is, the 4-½" extension equals the exposed length of the transition plus the length inserted into the payload section.

The recovery system is now deployed out of the payload section (nose-blow) so that section has been extended to accomodate it. With the stretch, it's now 6-3/8" long versus 5" stock. But, since the BT-50 below extends up into the bottom 2" (and the nosecone base consumes another 0.8") there's only about 3-½" left to hold the chute, wadding and shock cord. That is, even with all the added length, there is very limited space.

Nosecone tip
The nosecone point was built up using Elmer's Wood Filler. A few applications, taking great care to keep the point centered, made the rounded cone above look more like an ogive.

First Stage Booster - Motor Hook
Probably the most significant modification is upgrading the first stage to 24mm power. With the old B14-0 long out of production, getting a heavy 3-stager moving fast enough for safe flight requires the thrust only available in 24mm C11-0 and D12-0 boosters; a B6-0 or C6-0 just won't cut it.

A common problem with stagers is that a booster motor will sometimes eject aft at staging while the booster stage itself stays attached to the rocket with the next stage motor above exhausting through it. The result is a fried booster.

There are a couple solutions to this, but the common idea is to make sure the separating motor pulls the stage with it when the next stage lights. In the pic above, an external motor hook keeps the motor securely in the booster thus ensuring positive separation at staging. A wrap of tape keeps the motor and hook in contact, while the bit of fiberglass holds the hook securely to the rocket.

The hook is made with piano wire. The fiberglass is 6 oz cloth. A little wood flour was mixed in with the epoxy to thicken it a bit.

Brown fins
The balsa was salvaged from a non-rocketry application where it was stained brown, hence the discoloration.

First Stage Booster - Vent Hole

This is a close-up of the first stage vent hole. The second stage is ignited using gap staging which requires vents to relieve the pressure that occurs when the first stage motor burns through. These two vent holes are 1/8" diameter and drilled opposite each other about 1/4" below the forward end of the airframe. The aft end of the coupler extends 1/2" into the airframe (dashed line) and doubles as the motor block. The result is that the vent holes are about 1/4" forward of the motor.

After gluing in place, the coupler is coated inside and out with thin CA. Its outside is then buffed with 320 grit sandpaper. The CA provides protection against the hot staging gases inside and externally protects the coupler from getting the "fuzzies" due to repeated insertions and removals from the next stage.

Second Stage Booster

The motor tube for the second stage is shown above. Notice that the aft ring is well forward. This is to clear the coupler from the first stage.

Second Stage Booster - Positive Stage Separation

With a motor installed, the second stage looks like this (above). The sustainer motor is also shown along with the tape joining the two motors. (The 2nd to 3rd stage event uses "tape-together" staging.) In many stagers, the motor tube encases the joint between the motors, but in this rocket, I recessed the second stage motor tube. This allows a ring of tape to be placed on the forward end (of the second stage motor).

When the pressure builds up to force the 2nd stage motor to separate, the tape ring (3 layers) takes the entire second stage with it ensuring the booster separates and doesn't get fried by the sustainer motor.

Upper Stage (Sustainer) Motor Mount

The sustainer motor tube was made from standard motor tube stock, and lacks any glassine coating. So some CA was applied on the outside and also inside to makesthe tube a little more durable.

The three stages, all connected, are shown below with the staging couplers holding them together.

The aft ends of all three stages are shown below. On the second and third stages, the anular spaces around the motor tubes are very clear. This is because the centering rings for both stages have been moved forward about 1". This allows room for the staging coupler from below to slide all the way in.

This drawing is a cutaway showing the relative positions of the motors, centering rings, tape rings, etc, along with some dimensions.

All Dressed Up!

Here's a good view of the finished rocket from multiple angles. Trim monokote was used for the black stripes on the payload section. Black, white, chrome and checked trim monokote dresses out the fins.

More decorations
A while back, I entered the rocket in the DARS Fall Classic contest. It took 3rd place in the 1960's category. I was pleased it got the recognition

Recently, I got some decals made up, and added one to the Farside-XX. It really enhances it, I think.

8-27-2010