(Contributed - by Frank Ross)
Augie - Sport
2-Stage, single-piece, ducted sport flier based on Estes MRN designs Nos. 10 28
Shortly after becoming a BAR a couple of years ago, I accidentally discovered
JimZ Rocket Plans site on the web and was overcome by nostalgia. I
quickly downloaded a bunch of old plans, especially the ones from old issues of Estes' Model Rocket News. One that I
particularly liked was Estes MRN plan No. 10, Lil' Augie, a two-stage, single-piece, ducted rocket. There's no hidden
secret to a ducted design, the idea is to create a two-staged rocket that doesn't carry the extra weight and drag of a
booster with large fins. The down-side is that you probably add enough drag with the sustainer motor air ducts to
offset the gains of eliminating the booster. Regardless of the , the rocket is fun to fly because of the
surprised looks you get from the onlookers when the booster motor snaps clear and the sustainer motor fires. No one
ever expects the little rocket to have a second stage, and it really flies quite high, especially when staged C6 to C6.
After Lil' Augie I built a second ducted design, the Augie-II, Estes plan No. 28. Same deal, just a modified design --
probably redesigned to avoid the eventual demise of the Lil' Augie, from the sustainer motor singeing the lower
airframe. I went on to create my own Augie-III, which was basically an up-scale of Augie-II, staging D12 to D12.
Finally, I decided I wanted to update the Augie with a smoother, more aerodynamic design, and I built the Augie-Sport.
In the original Augie designs a smaller-diameter, upper tube and a larger-diameter, lower tube are connected
together to form the airframe (i.e. for the Augie-II a BT-20 upper is connected with 4 balsa "fins" to a
lower BT-60 airframe). Two 18mm motors are taped (scotch, or transparent tape, not masking tape!) together end-to-end
and inserted into the upper BT-20 up to the tape joint. The booster motor is left free-floating, surrounded by the
lower, larger airframe tube but held in place by the tape connecting the motors together -- a method now often referred
to as C.H.A.D. (CHeap And Dirty) staging. Ducts to supply air for the upper, sustainer motor were created by the gap
between the smaller-diameter, upper airframe and the larger-diameter, lower airframe. The air ducts prevent the
over-expansion of exhaust gases (the "") from robbing the sustainer motor's thrust and burning
up the lower airframe. This design had the advantage of increased stability as the lower airframe tube acts somewhat as
a and keeps the center of pressure aft-ward. However it has the disadvantage of adding drag because of the
abrupt airframe transition, and also by nature of the fact that drag is directly proportional to area, and in the case
of Augie-II the area of the lower airframe is more than 4X that of the smaller upper.
For the new Augie-Sport design I wanted to try to minimize the added drag of the abrupt airframe transition. To
accomplish this I used only one airframe diameter for both the lower and upper stage, and built the ducts to draw air
into the lower airframe tube to supply the sustainer motor. I wanted to keep some resemblance of the earlier Augie
designs, but I was going to significantly change the design of the sustainer's ducting, and given that there isn't much
to a rocket that can be carried through from generation to generation, I decided to keep the same fin design as the
Augie-II. Finally, I ended up with a roughly 10" long, 6-finned, BT-60 design with 6 open air ducts 4" from
the tail of the rocket. The rocket flies beautifully straight using both B6 to B6 and C6 to C6 18mm motors.
1. (1) BT-60, 5-1/4"
2. (1) BT-60, 4"
3. (1) BT-20, 3-5/8"
4. (1) PNC-60A
5. (2) BT-20 to BT-60 cardboard centering ring
6. (1) EB-20 engine block
7. (2) LL-3/16", 5-1/8"L
8. (6) Balsa fin (see pattern)
9. (6) Balsa support fin (see pattern)
10. (6) Paper BT-60 to BT-20 transition form (see pattern)
11. (1) 12" chute
12. (1) 24" shock cord
Start by constructing the engine mount assembly. Insert engine block into fore end of BT-20 engine tube at a
position where the sustainer engine will protrude from the aft-end of the engine tube by 1/2". Glue centering
rings 1/8" from the fore end of engine tube and 1-5/8" from aft-end of engine tube.
Next attach the 6 balsa support fins to the engine tube, equally spaced around the engine tube, as shown in the
first diagram. Fillet fins for strength.
Glue the 6 BT-60 to BT-20 paper transition sections between each of the 6 support fins. as shown in the second
diagram. Coat each transition with 30-minute epoxy to add strength to the paper transition and to fillet each of the
Attach shock cord to engine mount assembly. I do this by cutting a small slit in the fore centering ring, passing
the shock cord through the slit, and tying a knot to hold the shock cord firmly. A small drop of glue on the knot will
help to keep the knot from untying and passing back through the slit.
Insert the engine mount assembly into the longer BT-60 airframe section and glue into place.
Slide the shorter BT-60 airframe over the 6 support fins until the two airframe sections are separated by a
3/4" gap, this forms the sustainers air ducts. At this point make sure the airframes line up straight. Glue aft
airframe section to support fins and fillet each support inside the aft airframe section.
Attach the 6 balsa fins to the aft airframe. Fins can either be lined up with support fins or offset, whichever
look you prefer. One can use the Estes fin alignment guide by taping two spent engine casings together and inserting
them into the forward engine tube. Fillet fins (That's a lot of filleting, by-the-way!).
Attach launch lugs at aft end of each airframe section. Fillet lugs.
Attach chute and shock cord to PNC-60 nose cone.