Apothree and Better-gee


Morphs of the Astron Apogee II

The Astron Apogee was Estes' first two-stage rocket and soon gave way to the improved Apogee II. 

Download pdf comparing
Apogee and ApogeeII:
Apogee1vs2-v4.pdf

Both were minimum diameter birds powered by 18mm motors.  A C6 to C6 combo would not only put one out of sight, but send it to rocket heaven.

Inspired by this classic kit, but wanting to do something a little different, I came up with the concept of the Apothree - a three stage version disguised to look just like the Apogee II.

Having overpowered a Quark on an A motor soon after becoming a BAR, I understand the unpleasantness of overpowering and losing a model rocket, especially a classic clone that stirs strong emotions for today's middle aged children of the space race.  Nobody wants to lose a rocket. 

Thus, the Apothree/Better-gee was built with the notion of not overpowering it  The sustainer is  limited by a 13mm motor tube.  If I had it to do over again, I might do it differently.  But I can still put a full A motor (eg, A3-4T) in the sustainer, so it's not terribly restricting.  Considering when the rocket was originally designed at Estes, B motors were the maximum impulse available.
 
The Apothree was engineered to use a stack of three 13mm motors, thus limiting the maximum total impulse to A-A-A, versus a maximum of C-C in a stock implementation.  This should help in getting all the pieces back.

The original Apogee II's booster is long enough to accommodate two of the shorter 13mm T motors so the booster could be split in two without adversely affecting the rocket's appearance.

Once the Apothree project was well under way, I got the idea for the optional 2-stage Better-gee configuration.  It improves on the original's booster by adding gap staging and an external motor hook.  Besides 18mm boosters, it is set up to use adapters for 13mm T motors and for the old 10.5mm motors from Apogee Rocketry.

The gap staging vent is visible in the pic above, near the top of the booster.

When construction began on this bird, the A10-0T booster motors were still certified by the NAR.  Like so many others, this rocket has endured long spells of inattention during construction.  During that time, the motors were removed from the certified list   Nevertheless, with a large stash of them, I can still fly the Apothree and Better-gee at non-sanctioned launches.

The original design includes a payload bay which I eliminated.  While they give the appearance of lots of room, they in fact reduce the available space for the parachute.  Starting with 6.5" of airframe, once the motor tube and payload coupler are considered, there is only about 3" of space left for the shock cord, wadding and parachute/streamer. 

So, the 2.75" payload section was converted to additional airframe length thereby increasing the space for the recovery system.

The paint scheme fakes the payload section.  It's painted white, and striped like the catalog art of the late 1960's. 




Apothree
The original concept was to have an invisible line between the two boosters thus making them appear as one.  And it started out pretty good.  You can see in the pic at right that the fore and aft fins touch for a very nearly perfect fit.

The stock Apogee II's booster is 3.5" in length, the same as two 13mm T motors stacked together.  The Apothree stretches this to 3-7/8" which allows for an aft engine block for the first stage motor plus the 1/4" overhang of the 3rd stage sustainer motor.

The result is that stage one is 2-1/8" long and stage two is 1-3/4".

Since the sustainer motor is 13mm, there is space around it for a mating staging coupler to slide into the sustainer.  This can be seen at right atop stage 2
Click for close-up




Boosters sometimes get fried because the staging event can result in the booster motor ejecting aft while the booster section sticks to the next stage, with the upper motor blasting through the booster making it a toasty mess.  I have seen several examples of this.


The solution is to add a thrust ring to the aft end of the booster, as shown at left on the Apothree's first stage.  When the upper lights and its exhaust blasts down on the booster, the booster motor pushes against the aft block and forces positive separation of the stage, avoiding toasted booster.
Three stage rockets present an added challenge. The first stage booster can include the aft ring, but it's not possible with the middle stage.  Instead, a tape ring can be used.  This works on non-minimum diameter rockets, and requires recessing the middle stage motor tube.  

In the motor stack at right, the top tape ring is the thrust ring for the sustainer.  The tape ring below that pulls the middle stage away at staging.  The middle stage's motor tube is recessed at its forward end to allow for the extra tape ring.  With this, there is no way the middle stage motor can be ejected without the middle stage going with it..


Here's a close-up of the staging couplers, S2 left, S1 right.  The tape is there to add some extra friction while carrying it around the house.  I don't want a booster falling and breaking a fin because I picked it up with one hand. 

Both couplers were soaked with CA then sanded smooth.  This toughens them up and prevents them from delaminating when the tape is removed.  More importantly, it guards against them getting the fuzzies from repeated insertions/extractions.



Here are the aft ends of the sustainer (left) and middle stage (right).  The aft centering rings are recessed forward to allow room for the couplers.




Click for close-up Left:  The Apothree boosters are shown with the sustainer positioned atop.  By carefully sanding the fins, the seam between the 1st and 2nd stages is almost imperceptible thus disguising them to appear as a single stage.  At least that's the way it started.  By the time is was finished, despite careful sanding, gaps had formed between them   I attribute some of that to shrinkage caused by the primer.




Getting the fins aligned fore and aft on the booster sections required some special tools.

Craft sticks were glued into the jaws of clothespins to make clamps.  Additional clothespins were added at the far end of the lower clamp.

Even with all the effort, by the time it was done, some misalignment had occurred.  I suspect that as the yellow glue cured, it tended to pull some of the fins unevenly resulting in a couple of them being slightly out of alignment.  That is, they were straight when I removed the clamps



tools2.jpg Click for close-up The long clamp was made by sanding a gap in the jaws of the clothespin, then gluing craft sticks in place.  The wide clamp was made similarly using popsicle sticks.


Even with the imperfections, Apothree turned out nice.  I still need to blood it.  Maybe, if the wind would die down here, I can soon fly it in the 3-stage configuration.




Better-gee
As taught by my mother, I need to finish what I start, so at some point, I pulled the long ignored Apothree sustainer out of the cabinet and began filling, sanding and priming.  While working on, I got to thinking about what else I could do with it besides the Apothree.  A conventional booster was obvious, then I came up with this (right). 

Externally, it's about the same as the stock booster, but there are several key differences. It's a bit longer than stock.  And it includes a motor block forward and gap staging vents.  It also includes a staging coupler and an external motor hook.

The tape is operational.  It allows me to adjust the amount of force required at staging separation.  The idea is to keep the booster joined just a tad longer to ensure the sustainer lights.  

With it this booster, a standard 18mm motor can be used, or adapters can be inserted for 13mm or 10.5mm booster motors.  I just happen to have a couple B2-0's, so they should make for some exciting flights.

The coupler functions as the forward block for the 18mm motor and for the adapters. 

One of the gap staging vents is visible in the pic.



There's a reason for the strange looking bend in the motor hook.  Besides clearing the ignitor plug on 18mm motors, it curves around the protruding motors when using adapters.


18mm motors insert all the way into the booster with their aft ends flush. 



Here's a close-up of the two adapters - 10.5mm top, 13mm bottom.  They are both 70mm long and thus fit flush into the booster.  The motor hooks are fabricated from piano wire approximately 0.03" in diameter.  S curves were bent into them, then they were contoured to the curvature of the tubes.  Masking tape fore and aft was used to hold them in place.  Wood glue and nylon mesh was then applied to fasten them securely. 


Here's a close-up of the nylon mesh anchoring the hook on the 13mm tube.



With the 10.5mm adapter installed, the need for the bend in the hook becomes obvious.


Here's a great shot showing the hook on the Better-gee booster.  A C-bend was put in the piano wire, then curved to contour to the tube.  Nylon mesh was glued over it to hold it in place.  A couple rounds of filling with wood filler are needed to get a cosmetically pleasing appearance over the mesh.



So far, I have only one flight on the bird.  It was an A10-0T staged to a 1/2A3-4T. There are lots of other combos I want to try.  My stash of Estes A10-0T's, A3-0T's and 1/2A3-0T's will give the Apothree boosters some work.  And my Apogee B2-0's and MPC A3-0's can be flown using the Better-gee adapters.

And with a B6-0 staged to a T motor, it can be flown at club launches, too.

Doug
 

Doug's Rockets Homepage

Dec-27-2008