PROJECT DRAKE II
KG-25B • Ken Good

BACKGROUND

The original concept of the Drake project has been well-documented in an extensive discussion, found HERE. To recap, Drake is a two-stage proof of concept project intended to be the precursor for a much larger version – the Terra Nova. The staging method for both projects is a novel “motor feed staging” process. This is considered a modified version of the classic rack-rocket staging scheme, and entails the booster stage firing, and then ejecting from the airframe in a recoverable sabot, followed by the second stage sabot moving downward into the lowermost position in the airframe, locking into place, and firing for the sustainer phase of the flight. The force for downward movement of both stages is provided by a Rouse CO² unit which is triggered by a flight computer, and which pressurizes the motor/sabot compartment of the airframe.

This general staging process was the basis of the original KG-25 Drake, which was fully ground tested during the summer of 2006 and flown at BALLS 15, Black Rock NV, on October 1, 2006. However, due to a flight preparation error on the part of the designer, the Rouse unit failed to function as designed, and the second stage sabot never fully locked into position, which also meant it did not fire during the boost phase of the flight. The stage did inadvertently fire while in the recovery phase, but not being locked in place, much of the motor burn occurred inside the airframe, and severely damaged the internal structure, which included the sliding/locking components for the motor sabots. In effect, the motor-feed staging structure was a write-off, and further work on the project was suspended pending a full analysis of the test flight, and the identification of any needed design revisions. The latter were discussed in 2007-2008 but not finalized.

DRAKE II – Take Two
The irony of the unsuccessful flight test of the original Drake is that no intrinsic significant design faults were revealed, the flight problem being the direct result of a preparation error. However, it was recognized that the original design was relatively complex in the number of components used, as well as the special machining required to create these components. Chief among these was a three-rail internal rack, comprised of round rods on which the sabots slid, and which also had machined recesses for three spring-loaded ball bearings to seat as a locking device when stage 2 slid into firing position.

For the revised Drake, it was deemed desirable to simplify the design, curtailing the number of components and eliminate where possible special machining requirements. Accordingly, the internal rack structure is dispensed with altogether, and instead two 54 mm motor sabots are fitted with centering rings to slide along the inside diameter of the 75 mm airframe. In many respects, these sabots are little more than 54mm/75mm motor adapter tubes. In order to keep each sabot in a fixed rotational orientation, both are notched to match an anti-rotational guide which is screwed to the inside of the airframe, and which also serves as an anchor for the rail buttons.

In the original design, the motor casings themselves were effectively the “sabots” and special machining was required to closures of the motor hardware to accomplish this. An advantage to the revised design is that each sabot can contain a variety of commercial motors, using normal hardware and conventional motor retention methods, eliminating any machining operations to the motor casings.

STAGING MECHANICS
As in the original specification, the stage 1 sabot is intended to eject from the airframe upon pressurization of the motor-sabot section of the airframe, overcoming the light retention of a plastic sheer pin at the nozzle end of the sabot, which is required to hold the two-stage stack in place before ignition. Upon ejection, the sabot will free fall for a short distance and a small recovery parachute will eject from the upper end, activated by a simple motor ejection charge.

Unlike the original design, the stage 2 sabot, when forced downward, will rely on a special spring-pin assembly to lock it into the firing position. This assembly will have two pins oriented at 180º of each other, and will extend into two corresponding locator holes drilled in the airframe when the sabot reaches the lowermost position. These holes will be slightly oversized to ensure the pins positively engage, and also to provide venting for the internal CO² pressurization once the sabot is in place. The sabot will also contain a plunger switch mounted to an upper centering ring, which will be connected to a small 12v battery (type N) and the igniter for the stage 2 motor. The switch will be depressed (and the igniter fired) by contact with a threaded screw extending through the airframe into the chamber, this contact being made when the sabot is in firing position. It is anticipated that this screw will be added on the pad as a safety arming feature. Additionally, an arming switch will be mounted in the sabot in parallel with the battery/switch/igniter circuit, which will be accessible through an airframe hole when the rocket is being pad prepped (the hole then plugged to retain pressurization).

ANTICIPATED MOTORS
To keep the overall airframe length from becoming excessive, it was deemed desirable not to exceed 24” to 30” in length for each sabot. Accordingly, this points to 54/1706 AeroTech motors and reloads as being the most feasible to achieve the goals of providing sufficient impulse, availability of motor ejection for stage 1, and being proven & readily available.

The designer’s multi-staging experience over the years has reinforced the desirability of using a short-burn, high average impulse motor for stage one, and a longer burning, lower average impulse motor for stage two. This of course provides a favorable power to weight ratio for take-off, to ensure a safe and vertical trajectory, coupled with a more extended and visible sustainer boost. With this in mind, for the initial test flight, the AT K-1100T motor was selected for stage 1, and the K550W for stage 2.

FLIGHT PROFILE
The first test flight of the Drake II is scheduled for the BALLS 19 event at Black Rock, NV, in September 2010. Simulations of this flight reveal and expected apogee of approximately 10,000 ft, using conditions likely at Black Rock. A flight simulation summary is appended below.

EXPECTED RESULTS
Presuming the test flight is successful, a full analysis of the recorded flight data will be performed. It is expected that the Drake’s flight performance should exceed that of a single stage vehicle with the same weight, cross section, total Newton-seconds of impulse, and general airframe characteristics. Actual data will be plotted against simulated data from the theoretical single stage vehicle to calculate the performance differences.

Any anomalies or deficiencies detected in the flight test will be analyzed and any needed revisions to the design that may be needed will be considered. The desired outcome is that Drake II will represent the final proof of concept of the motor-feed staging concept, and detail design work may commence for the KG-24 Terra Nova, a much larger motor-feed staging rocket, anticipated to fly with two stages of greater than O-impulse per stage.

KG 25 DRAKE - Simulation detail report
Engine selection: [K1100T-0 ] [K550W-0 -2 ]
Launch conditions

• • • • • • • • •

Altitude: 3838.000 Ft. Relative humidity: 35.000 % Temperature: 70.000 Deg. F Pressure: 29.921 In. Hg. Wind speed model: Slightly breezy (8-14 MPH) Wind turbulence: Fairly constant speed (0.01) Wind starts at altitude: 0.000 Ft. Launch guide angle: 0.000 Degrees from vertical Latitude: 40.651 Degrees

Launch guide data:

Max data values:

Recovery system data:

Landing data:

RETURN