The BGM Rocket [Archive]

skranish

Feb 01, 1997, 01:00 AM

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<title>Bill Griggs Models RocketThe E Zone</title>
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<img src="http://static.rcgroups.com/articles/ezonemag/1997/../images/kran4.jpg" ALT="Rocket sitting on field box" ALIGN="CENTER" WIDTH="390" HEIGHT="245"> 

Preface 

<blockquote>
This review was originally written in early 1997, based on a kit produced for sale at
the September 1996 KRC Electric Fly-In. The kit was largely hand-cut, and as described
below, I had problems with both the fit of parts and the structure. 
A lot has changed since then. At the 1998 WRAM Show, Bill Griggs introduced his new
series of laser cut kits, including a completely re-done BGM Rocket. The totally
re-engineered kit uses tab-and-slot construction, and fixes all the things that I had
problems with in the original kit. The fuselage is now a box all the way to the rear
(rather than flattening in front of the fin), so it is much stronger. It looks like a
beautiful kit that will just fall together in a few evenings. 
 <a href="/articles/ezonemag/1997/billg.jpg"><img src="http://static.rcgroups.com/articles/ezonemag/1997/billg_small.jpg" alt="billg.jpg (34973 bytes)" border="2" WIDTH="66" HEIGHT="100"></a>
The above photo shows Bill displaying some of his new laser cut parts. The elevator and
stabilizer on the right have pre-cut lightening holes. On the left is a bulkhead and a
control horn that interlocks into the elevator. The new kit parts show really nice
attention to details. 
The new kit is so drastically different from the original kit described below that much
of the description of the kit assembly is no longer relevant. The finished plane looks
almost the same, but the construction process is very different. Perhaps at some point
this review will be completely rewritten to describe the new kit, but for now please keep
in mind that a kit that you order today will have most, if not all, of the problems
corrected. If you have questions about the improved kit, please contact Bill, and I am
sure he will be glad to help you.
</blockquote>

 

An Overview of the Rocket 

<blockquote>
The Bill Griggs Models (BGM) ROCKET is a balsa and foam Speed 400 class pylon racer. It
is available as a plan only (US$10), a plan with foam wing cores (US$20), or as
a laser cut kit (US$65), including all of the airframe components. BGM also offers
good deals on combinations of the kit and a drive train, so check their web site for
current prices. 
<blockquote>
<address>
Bill Griggs Models 
RR2 Box 64, Whitelaw Rd. 
Canastota, N.Y. 13032. 
(315) 697-8152
</address>
Email: <a HREF="http://rcgroups.com/shared/nospam.php?u=bgriggs&d=aiusa.com">bgriggs(at)aiusa.com</a> 
Website: <a HREF="http://www.aiusa.com/bgriggs/">http://www.aiusa.com/bgriggs/</a>
</blockquote>
I built my ROCKET from a kit that was given to the E-Zone for review purposes by BGM.
It was one of the kits put together for sale at the KRC meet in September 96, and Bill
told us that there may be some mistakes in the kit contents due to the frantic pace of
assembling the kits at the meet. The instructions I received are in fact the wrong
instructions, and have a number of mistakes. If your instructions seem confusing, call BGM
and get a new set. 
I have spoken with Bill Griggs on the phone several times, and perhaps the most
interesting thing he told me is that he has built 7 ROCKETs. I don't think this is a
testament to poor flying, but rather a determination to tweak the design until he was
happy with it. This is really nice to know, and is far less common than you may realize.
Many construction articles in magazines are based on a single prototype, and I think there
are many kits available for which only a single prototype was built. It would be nice if
the prototype came out perfectly, but they rarely do, so it is good to know that the
designer has made a serious effort at testing his design before releasing it to the
public. 
The ROCKET is a small airplane. The lead-in photo shows my son Samuel, who is 3
1/2 years old, holding the unfinished airframe, and it looks like a good size for a
child's toy. The above photo shows the finished ROCKET sitting on top of a 16"
toolbox. 
Don Belfort came in 2nd in the provisional Speed 400 pylon racing event at the '96 AMA
Nationals flying a ROCKET. Plans for the plane will be featured in a forthcoming article
in Model Airplane News. 
While my notes here are specific to my experiences with the ROCKET, many of them apply
to Speed 400 class pylon racers in general. They are by their nature small, fast, and
fragile airplanes. Light weight is required for speed, so it is just not practical to make
this sort of model very sturdy. The only alternative seems to be the pre-built composite
models that cost 4 to 5 times as much money - and may not be any more rugged. 
</blockquote>

 

What you need in addition to the kit 

<blockquote>
The ROCKET is not supplied as a complete kit. No linkages or hinging materials are
supplied, and neither is the wing hold down bolt. You will need: <ul>
<li>1/16" music wire for aileron torque rods </li>
<li>1/16" inside diameter brass or aluminum tubing for aileron torque rod bearings and
ends </li>
<li>Sullivan cable housing, smallest size, for elevator pushrod housing </li>
<li>0.025" music wire for elevator pushrod </li>
<li>antenna tube </li>
<li>0.7 oz fiberglass for wing trailing edge reinforcement </li>
<li>0.7 oz fiberglass and 2 oz fiberglass for fuselage reinforcement (see below) </li>
<li>1/32" plywood for elevator control horn and various reinforcements </li>
<li>Nylon 4-40 bolts for wing and stab holddown </li>
<li>velcro to hold the battery in place </li>
<li>glue (I used Ambroid and epoxy for almost everything) </li>
<li>covering material (I used Sig Supercoat, and some Fluorescent Oracover for trim) </li>
<li>adrenaline </li>
</ul>
</blockquote>

 

Fuselage 

<blockquote>
The kit box contained not merely two, but a bonus of three fuselage sides. This was
undoubtedly due to the kitting errors that crept in due to the frantic pace at KRC.
Unfortunately, one of these appeared to be made from depleted uranium sheet, painted as
faux balsa, (it weighed about 13 grams, more than the other pair) so I left it in
the box and proceeded with the largely matched pair of lighter sides. Other than this one
piece of depleted uranium, all of the wood in the kit seemed appropriate for the purpose,
or even a little too light. The fuselage sides, like all of the pre-cut pieces, are
actually hand cut from patterns. The sides matched each other, but not the plans, so I had
to adjust the shape a bit. 
There are three points of alignment relative to the fuselage side: the firewall, the
wing saddle, and the horizontal stabilizer platform. The sides did not really match the
plans at any of these places, so I drew extension lines on the plans for the stabilizer
and firewall, and marked and trimmed the sides to match the lines. The wing-stabilizer
incidence and thrustline are not specified on the plans or in the instructions, so I
called Bill Griggs and asked. He told me that everything is setup 0-0-0, so as best I
could, that it what I did. The final adjustment and alignment was done later, as
described below. The positions for the bulkheads were marked on the fuselage sides, and
the corner triangles installed. 
There are air inlets on either side of the fuselage. The construction of these is
rather novel, because the inlet backing is cut away from the fuselage on only three
sides, and then bent away. I have no idea if they are necessary, but they should be
effective at cooling the battery. A similar outlet is built into the fuselage bottom,
behind the wing. 
<img src="http://static.rcgroups.com/articles/ezonemag/1997/../images/kran1.jpg" ALIGN="LEFT" WIDTH="360" HEIGHT="226">The fuselage is assembled in several
steps, starting at the rear. The fin assembly is actually a sandwich of 3 layers, and the
middle layer includes the elevator pushrod housing and an antenna tube. I attached both of
these with PolyZAP, which produces good plastic to wood bonds. These 3 layers are
essentially flat to about the leading edge of the fin, except at the bottom, and the
fuselage tapers out into a box from there. The corner triangles must be tapered to allow
the fuselage sides to come together. This should be visible in the photograph. I clamped
the fuselage sides and fin together with pins and clamps, and made sure that the sides
were aligned up at the nose. This assembly must fully dry before additional assembly. 
Installation of the bulkheads into the assembled sides is a bit tricky, because there
really aren't any straight edges on the fuselage to pin to the building board. The
construction is essentially 'castle in the air', although I was able to pin the fuselage
down once I accepted that it would only touch the board in the middle. Other builders must
have problems with this step, because Bill asked if my fuselage came out 'banana' shaped.
It did not; I am a fairly careful builder, and my fuselage is straight. I think it would
be much more difficult to get a straight fuselage if you are just gluing the bulkheads in
with CA. I installed the bulkheads with epoxy, and clamped the assembly together until it
cured. This allowed me to make adjustments to ensure a straight fuselage. Nonetheless, it
is very difficult to align the firewall for the thrust line. 
I recently built a pod for an HLG fuselage that also had no straight edges. After some
thought about how to assemble it, I dug out my old Adjust-o-Jig, and used the fuselage
jigs to assemble it. When I build another ROCKET, I think I will build it in the
Adjust-o-Jig. 
The fuselage has three bulkheads: a firewall, which is actually one of the Tim
McDonough Speed 400 motor mounts, a bulkhead at the leading edge of the wing, and another
at the trailing edge. The firewall is supplied with cutouts for mounting the motor, but
must be cut to the appropriate shape and size to fit in the nose of the fuselage. The
bulkheads are cut from 1/16" plywood, and were a rough fit at best. The forward
bulkhead is actually an inverted U shape, so that it has no crosspiece at the fuselage
bottom. If the crosspiece were present, it might get in the way of the battery.
Unfortunately, the lack of a crosspiece contributed to the collapse of the bulkhead when
I tried to dry-fit the fuselage together and hold it with clamps, so I could see how
everything fit. Rather than try to repair the broken bulkhead, I decided to replace both
of them with new ones that were made to fit better. I made the forward bulkhead with a
crosspiece a the bottom, and added 1/32" plywood crossbraces at the top and bottom of
both bulkheads, to protect the fuselage from being crushed.. I also drilled the bulkheads
for the wing holddown dowel and the elevator pushrod, because it is much easier to do
while they are still flat on the bench. 
The top and bottom of the fuselage are sheeted with cross-grain 1/16" balsa.
Remember that the plane has no landing gear or skid - so the bottom sheeting IS your
landing gear. Don't sheet the top of nose until after the wing is finished and has been
drilled for the the holddown dowel - if you have a long 1/8" drill bit, you can pin
the wing to the fuselage and use the hole in the bulkhead as a drilling guide. This makes
for a tight fitting wing. 
My first introduction to Speed 400 pylon racing was watching Jim Bourke fly his SSP 400
last summer. The SSP 400 has a fiberglass fuselage with an  integral fin and a
balsa sheet stabilizer, and Jim had simply glued the stab in place at the top of the fin.
On one occasion, his flying was cut short for the day because the stab was knocked loose
on landing. On another occasion, Jim did not notice that the stab was again loose until
the plane was in the air, and this ended flying of the SSP 400 permanently. (editor's
note: Not true, Steve-o! I donated the plane to the local glow club and I have no doubt it
will fly again- probably with an OS 40 bolted to the nose!) 
I took this as both a lesson and a warning, and decided to modify the ROCKET to make
the horizontal stabilizer removable. This actually has several advantages: it was easier
to build, easier to cover, stores much more compactly, and can survive bumps and sloppy
landings without actually breaking the stabilizer-fin joint.  Jim concluded
that the failure of the stab attachment on the SSP 400 was actually caused by hangar rash,
so storing and transporting the ROCKET with the stab removed entirely prevents this
problem. I prefer removable stabilizers for the above reasons, and build most of my models
that way. 
The fin is actually 3/16" thick, so I made two holddown blocks from 3/16" x
3/16" spruce. I drilled and tapped them for 4-40 bolts, and then epoxied them into
notches in the top of the fin. I then shaped two pieces of 3/8" balsa triangle stock
to fit the curved surface of the fin, and epoxied them in place with a layer of 0.7
oz fiberglass between the triangle and the fin. Needless to say, I do not want the
mounting blocks to come loose! 
I also added some 0.7 oz fiberglass reinforcing where the rear bulkhead is attached to
the fuselage. I should have reinforced the front bulkhead, too, as we shall see later. 
When the fuselage and wing were completely assembled, I adjusted the wing-stabilizer
incidence to 0-0 by setting the plane  level with my Robart Incidence Gauge on the
wing, and using a level to check the angle of the stabilizer. I sanded the stabilizer
platform until the both the wing and stab were level. I am not sure if the motor mount -
and thus the thrust line - are aligned properly. After some flying, I have come to the
conclusion that I must have inadvertently built in some rightthrust that will have to be
removed with shims on the motor. 
</blockquote>

 

Wing 

<blockquote>
The wing is built from a hot-wire cut white foam core and 1/32" balsa sheeting.
There is no internal structure or spar. The ailerons are initially built as part of the
wing, and cut free and faced after sheeting has been applied. 
The wing sheeting is supplied as a number of 3" wide sheets that must be glued
together to make up sheets wide enough to sheet the wing. There is just enough sheeting
supplied to make up properly shaped wing skins, and there is NO scrap left over when you
are done. I assembled the sheets with Ambroid glue, and held them together with tape until
the glue dried. I like to use my Porter Cable 330 pad sander to get a really smooth finish
on both sides of the sheeting. It does a much better - and faster - job than hand sanding.

The supplied instructions describe how to sheet the wing using 3M 77 spray contact
cement. I don't really have any place to spray this sort of stuff indoors, and it was too
cold to do it outside, so my preference was to attach the wings with epoxy and use a
vacuum bag to hold them in place while the glue cured. According to Bill Griggs, this is
actually the preferred method, but he felt that recommending it in the instructions would
make the kit appear too complicated to people who have not used a vacuum bag. He said that
a lot of his customers have never built a foam wing before. The ROCKET would make a good
first foam wing project because its small size makes it easy to handle. 
The leading edge of the foam core was rather wavy, so I straightened it with a long
sanding block and attached the leading edge. The general instructions for vacuum bagging a
wing may be found in my review of the NSP Neon, so I will not repeat them here. The only
thing I did differently was that I tried to follow BGM's instructions about putting
spruce stock along the trailing edge overhang while the glue dries. This was a lot of
trouble in the vacuum bag, and I think it was unnecessary. If you are using contact
cement, I think it remains a good idea. 
The aileron torque rod linkage is not supplied and must be fabricated from 1/16"
music wire and 1/16" inside diameter brass tubing. One piece of tubing is used as a
bearing, and the other is used as a linkage end, and flattened and drilled to accept
a clevis pin. I soldered these to the music wire so that I do not need to worry about
them coming apart. 
The instructions suggest installing the torque rods before even attaching the wing
panels together, but I was concerned that the center trailing edge area would be so
weakened that it would be difficult to work on. I decided to completely assemble the wing,
including the fiberglass reinforcing and fairing blocks, before cutting the ailerons free
and installing the torque rods. The rear fairing block acts as a reinforcement for the
trailing edge area, and this prevented any problems with structural weakness or distortion
(twisting) while the torque rods were installed. I smeared Vaseline around the ends of the
brass tubing so that glue would not get into it during installation, and I epoxied them
into slots in the wing. 
The instructions and plans give no idea of how the torque rods are supposed to be
attached to the ailerons. I was very concerned that the torque rods would bind if
they were glued in, so I drilled the ailerons for the torque rods, and then added a small
piece of 1/32" plywood on the top and bottom of the aileron to reinforce this now
very flimsy area. 
The wingtip blocks and wing-fuselage fairings must be shaped from balsa blocks.
The holddown screw goes through the rear fairing, so I added a small circle of 1/32"
plywood to reinforce this area. A single 1/8" dowel holds the leading edge in place. 
I used my standard covering material hinges to hold the ailerons in place. The
aileron leading edges are tapered towards the bottom, and initially held in place
with a 3/4" wide strip of covering material that wraps around the leading edge of the
aileron and the trailing edge of the wing. The top covering secures the aileron in place.
I have never had this sort of hinge fail. 
I cut slits in the trailing edge at the wing tips and glued in small pieces of carbon
fiber as reinforcement. The completed wing is very solid. 
</blockquote>

 

Empennage 

<blockquote>
The horizontal stabilizer is precut from 1/8" balsa sheet, although the elevator
must be cut away from it. I made the stab removable, as described above. It is held in
place with two 4-40 nylon bolts. I added a 1/32" plywood plate on the top to
hold the screwheads, and provide some additional strength at the maximum stress point. 
I sanded a taper on the front edge of the elevator and simply used the covering
material, top and bottom, as the hinge. The control horn was cut from 1/32" plywood
and epoxied into a notch filed into the underside of the elevator. 
The fin is completely integral with the fuselage, so there is nothing more to do on it.

</blockquote>

 

Control Linkages 

<blockquote>
The elevator pushrod is housed in the outer tube from the smallest size Sullivan cable
pushrod, #507. The housing must be installed at the beginning of the fuselage assembly. I
made the pushrod itself from 0.025" music wire, which fit with much less binding than
0.032" wire. I did not provide any sort of adjustment, because my transmitter has
electronic sub-trims to adjust the neutral. I drilled a 0.025" hole in the servo arm,
and made a  Z bend in the pushrod. I then installed the servo and pushrod, and made a
simple L bend at the elevator horn. The bent over part is long enough that it is not
possible for it to come out of the control horn, other than to remove the stabilizer from
the stab platform. Folks who fly big power planes may gasp at such an arrangement, but for
a tiny electric, it works just fine. 
I used specially made 2-56 threaded 1/16" rods and mini plastic clevises to
connect the aileron servo to the torque rods. These linkage rods are hard to come by; I
think Goldberg is the only company that sells them, and no one seems to stock them. The
aileron linkage requires some abrupt bends that would horrify a power plane flyer, but
again, for a tiny electric, it works just fine. 
The aileron servo is almost directly above the elevator servo, but I did not have any
problems with interference between the linkages. 
No control throws are specified. I set my ROCKET up for <ul>
<li>ailerons  +3/16", -1/8" </li>
<li>elevator  +-1/8" </li>
</ul>
</blockquote>

 

Power System 

<blockquote>
The recommended power system is a Graupner Speed 400 6V motor. I purchased from
BGM the Graupner 6064 direct drive package, which includes the  6V Speed 400 motor, a
'Precision Spinner', and CAM 5-5 prop. 
I used a Tarling Microstar 20 motor controller. This is also available from BGM. It is
a very small unit and works well. 
The Graupner props are expensive and apparently very brittle, so I have not been brave
enough to use one yet. I am told they add about 10 MPH to the speed, which, frankly I
don't need yet. I have used instead the Master Airscrew 5.5-4 and 5.5-4.5 props. These
must be drilled 3/16" to fit the spinner shaft, and need to be held carefully
during drilling. I would highly recommend using a drill press for accurate drilling. These
props do need to be balanced. 
This plane should be flown with a 7 cell battery pack. There are basically two
types of cells to use in this plane: the KR600AE cell, and the N500AR cell. The 600AE cell
may actually have a little more capacity, but I think the output from the 500AR is
flatter, and does not drop off as much during flight. I have both types of packs, and
prefer the 500AR. Plan on buying a number of packs if you want to do much flying, because
it takes much longer to charge a pack than to put in a flight. These cells cannot handle
very high charge currents, so "quick charge" is a relative term. I currently
have 4 packs, and charge them overnight on an ACE DigiPulse, which can charge up to 6
packs. 
</blockquote>

 

Equipment Installation and Balancing 

<blockquote>
I used the following radio equipment: <ul>
<li>FMA Micro 2000 receiver, installed behind the wing </li>
<li>Tower TS-11 servos, which come with horizontal mounting brackets </li>
<li>Tarling Microstar 20 motor control, mounted right behind the motor </li>
<li>JR XF622 Transmitter </li>
</ul>
This is actually a very different equipment setup from that shown on the plans. Bill
used a Futaba MCR-4A AM receiver with integral motor control, installed behind the wing,
so he has less weight in the nose, and more in the tail. With my smaller receiver, and a
motor control in the nose, my plane was seriously out of balance. I had to add 0.5oz of
lead to the tail, which can be seen in the top photo as an orange blob on the side of the
fin. I felt that the correct balance was far more important than any possible weight
savings, so I have made no attempt to fly the plane without this trim weight. When I build
another ROCKET, I will shorten the nose a little so that the tail weight is not required. 
The Tower TS-11 servos come with a pair of brackets that slip on to the mounting lugs,
and allow the servo to be easily mounted on its side and held in place with 4 screws. (The
TS-11s appear to be repackaged RCD/Hitec HS-80s, which also come with the same brackets.)
Both servos are installed using the side mount brackets - the aileron servo is mounted on
the underside of the wing, and the elevator servo is mounted on the fuselage floor. I put
1/8" spruce mounting blocks in both locations so the screws have something to go
into. Actually, I drilled the blocks and attached them to the servos, and glued the whole
assembly in, so that I would not have to align them by hand. 
</blockquote>

 

Weights 

<blockquote>
I covered the ROCKET with Sig Supercoat low temperature film. It was selected for its
low weight, although the low temperature films are well suited for sheeted surfaces -
especially sheeted foam. It is not as nice to work with as Oracover, but it is light. The
fluorescent red stripes on the top of the wing and stab are Oracover. The Supercoat on the
bottom of the fuselage has not stood up well, and will be replaced by Oracover. 
Subassembly weights: <ul>
<li>Wing, with torque rods: ready to cover 45.9g, covered 56.5 g </li>
<li>Stabilizer and elevator, ready to cover 4.1g, covered 6.2 g </li>
<li>Fuselage (after repairs), ready to cover, 38.3g, covered 42.0g </li>
<li>Tarling Microstar 20 including wiring, 140g </li>
<li>FMA Micro 2000 Receiver, 25.5 g </li>
<li>Tower TS-11 Servo, 17.5g </li>
<li>Speed 400 6V motor 72g </li>
<li>Total weight, ready to fly, 450g or 16oz, including balancing weight. </li>
</ul>
</blockquote>

 

Flying 

<blockquote>
My first attempt at flying the Rocket was not really intended to be a flight, but
rather a straight hop across the field - Howard Hughes Spruce Goose style. The plane was
ready, and I thought I was ready, but it was a bit too windy for a first flight. So my
intent was to simply fly the plane in a straight line across the field and set it down on
the grass. This would tell me if it tracked straight, and whether or not the pitch control
was appropriate. 
<img src="http://static.rcgroups.com/articles/ezonemag/1997/../images/kran6.jpg" ALIGN="LEFT" WIDTH="361" HEIGHT="233"> Well, it did track straight, and pitch
stability seemed ok, but the landing - which was basically straight, with a tap on the
wingtips as it stopped - did a lot of damage to the fuselage. In retrospect, this landing
was actually a lot better than many of my later 'arrivals', so if it did not break on this
flight, it would have broken soon after. The photo shows a crack in the fuselage at the
leading edge bulkhead. There is also a similar crack at the trailing edge bulkhead on the
other side of the fuselage. What is not visible is that the fuselage broke completely into
two parts at the leading edge of the fin. The two pieces were held together only by the
elevator pushrod, and the movement around the pushrod caused the elevator horn to break
off. 
This is actually a very weak spot in the structure, and I should have realized it and
reinforced it when I built the fuselage. I did notice that the fin-fuselage
junction seemed to be rather flexible, but rather foolishly assumed that it would be OK.
To get an idea of just how bad a weak spot this is, take a toothpaste tube box and
try to fold it over, end toward end. You really cannot do it without breaking the box,
because of the box structure. Flatten the box and try it again. Now it is easy to fold
over, because there is no open box structure to prevent it. Well, the leading edge of the
fin is where the fuselage structure changes from a box to a flat plate, and that is why it
is so flimsy here. 
The wing and stab were undamaged. I stripped off almost all of the fuselage covering to
prepare it for repairs, as described below. 
</blockquote>

 

Repairing the Damage: Reinforcing the Rocket 

<blockquote>
The fuselage cracks were glued back together with slow epoxy. I wrapped the worst
damage, at the leading edge of the fin, with 0.7 oz fiberglass and gave it a thin coat of
epoxy. I knew the plane needed tail weight, so I saw no harm in adding material to repair
it. These repairs restored, but did not stiffen the fuselage. 
<img src="http://static.rcgroups.com/articles/ezonemag/1997/../images/kran5.jpg" ALT="Rocket with carbon fiber strips visible" ALIGN="LEFT" WIDTH="370" HEIGHT="170"> I considered fiberglassing the entire fuselage, but after some thought I
decided to stiffen it with carbon fiber strips. I cut 1/4" x .007" fiberglass
tape in half lengthwise, so that it is only 1/8" wide, and applied it to
the fuselage with slow setting gap-fill CA. The carbon fiber is visible in the photo
as the black lines on the side of the fuselage. I had to use several pieces, because
carbon fiber tape is very stiff, and will not follow a curve. I used a piece of wax paper
to rub it out and make sure that there was a good bond. This modification has dramatically
stiffened the fuselage, and I have had no further problems with it. 
I would highly recommend that some sort of stiffening be added to the fuselage during
construction. If you have never worked with carbon fiber tape, this would be a good place
to start. The tape is available from Hobby Lobby and all of the composite material
suppliers, such as ACP (Aerospace Composites <a HREF="http://www.acp-composites.com">http://www.acp-composites.com</a>)
and CST (Composite Structures Technology). Hobby Lobby <a HREF="http://www.hobby-lobby.com">http://www.hobby-lobby.com </a>sells 4 feet of the tape
I used for US $2.20, so it is not particularly expensive. Just be careful handling it -
you do NOT want to get carbon fiber splinters in your fingers! 
I was very concerned that in a sloppy landing, the battery would demolish the fuselage
floor, so I reinforced the inside of the fuselage bottom from the wing leading edge to the
elevator servo with 2 oz fiberglass and epoxy. While there was wet epoxy in the fuselage,
I installed two 3/4" x 1/4" balsa 'buttons' for the battery to rest
on. When everything was dry, I put pre-cut velcro 'dots' on top of these, so the battery
attaches to them, but air can still flow underneath. 
I have also added 0.7oz fiberglass reinforcing at all the corners of the wing saddle,
and under the wing holddown bolt plate. I would also recommend reinforcing the fuselage
'chin' - the area under the nose, and the underside of the wing tips. 
By the time I was done, I had added a lot of little reinforcements, almost all in the
fuselage: <ul>
<li>1/8" carbon fiber tape on the fuselage sides; see above photo </li>
<li>2 oz fiberglass on the inside fuselage floor, from leading edge bulkhead to elevator
servo </li>
<li>0.7oz fiberglass at bulkhead-fuselage side joints </li>
<li>0.7oz fiberglass at holddown screw plate - fuselage side joint </li>
<li>0.7oz fiberglass, cut into small pieces, at motor mount - fuselage side joint </li>
<li>3/8" triangle blocks under holddown screw plate and at front bulkhead-fuselage
joint, top 1/2" or so </li>
<li>3/16" spruce 'tail skid' at bottom rear of fin </li>
<li>0.7oz fiberglass on fuselage bottom just behind spinner </li>
<li>1/4" carbon fiber tape, about 1/2" long, glued into wing tips at trailing edge
(as ding-proofing) </li>
<li>0.7oz fiberglass on the bottom side of the wingtips, especially at the trailing edge
(really takes a beating) </li>
<li>fiberglass tape at wing center joint </li>
<li>1/32" plywood on aileron, top and bottom, at torque rod entry </li>
</ul>
I would also recommend, and will soon add to my ROCKET: <ul>
<li>0.7oz fiberglass on the entire bottom of the fuselage (it really takes a beating!) </li>
<li>0.7oz fiberglass around air inlet and exit, inside fuselage (cracks easily) </li>
</ul>
While the above reinforcing may look like a lot of work, it is these details that make
the plane sturdy without making it heavy. If you do not initially reinforce these areas,
you will have to repair them later - I speak from experience! 
</blockquote>

 

Subsequent Flying 

<blockquote>
After repairing and recovering the fuselage, I ran into a long period of uncooperative
weather. We have had a sloppy, but not particularly snowy winter here in the northeast US.
I was initially concerned about landing on frozen ground, and tried to fly only when the
ground had thawed (and was VERY muddy!). I have subsequently flown from frozen ground, and
watched as the ROCKET skipped like a stone on water while landing. 
I was not sure what to expect of the ROCKET. What I have found is that it is a pylon
racer, and nothing else. It is at its best in go fast-turn left mode, and trying to do
anything else only seems to get me into trouble. I have tried to do some simple aerobatics
- loops and rolls - and haven't done well at either. Perhaps part of it is me, and perhaps
the CG needs to be moved, perhaps the thustline is off, but I think that most of it is
simply that the plane is really optimized for one thing - racing. The control response is
adequate - which I think is all you want - and does not result in the plane getting ahead
of you. The only problem with control response is that it gets VERY sluggish when the
plane slows down. I need to revise my dual rate setup so that I have MORE throw for
landing. 
Launching is really very easy  - the important thing is simply to keep it straight
and level. If there is any breeze, throw it straight into the wind, regardless of the
layout of your runway. I keep a long piece of videotape on my transmitter antenna so that
I can always tell what direction the wind is going. I think a crosswind launch would
re-kit any Speed 400 pylon racer, because launch speed is so far below flying speed.
Anyone want to build a rail launcher? 
The plane will accelerate away from you, and once it gets 'on step' it will start to
climb. The climbout is surprisingly quick, especially compared to my Speed 400 sailplane.
Once in the air, the important thing is not to let the nose go up - it is possible that my
plane needs a bit of downthrust. If the nose goes up, the control response just
disappears. Fortunately, years of glider flying has made it instinctive to feed in some
down elevator when the control response is slow. Unfortunately, years of glider flying
have also made it instinctive to add up elevator in a turn, which the ROCKET does not
need. Now try flying circuits of your flying field. It is tough to do with any fast plane,
and this little plane moves around FAST. The ROCKET must be flown at all times; do not
think about taking a break or just watching it. 
So far I have rarely flown the plane at full throttle. Flying at a bit more than half
throttle stick is fine for me, although I have increased the throttle when the plane was
getting tossed around in the breeze and when the battery starts to run down. You
will probably notice when the battery starts to go, because the plane starts to descend
quickly. I always try to land before the battery gives out, because I want to have some
power left in case I need to do a go around. 
Landings took some getting used to, because the glide is very fast compared to a
glider. If there is any breeze, turn into the wind for landing - it will help to slow down
the plane. I have not experienced any problems with stalling on the final turn into
the wind. Just try to keep the plane straight and level, and set it down. My log sheet for
the ROCKET has a column marked L/A for Landing or Arrival. I seem to finally be doing more
landings than arrivals. 
Now all I need is someone else to race with, and someone who is willing to get
together all of the people required to run a race. 
Check this page in a month or so for an update on flying. 
</blockquote>

 

Recommendation 

<blockquote>
This is not a kit for a beginning builder, but then it is not a plane for a beginning
flyer, either. It is certainly the most demanding and challenging plane I have flown
in the 2 years since I 'returned' to RC flying. 
If Speed 400 pylon racing strikes your fancy, the ROCKET is a low budget but serious
and competitive path of entry. This is a really fun airplane, but it is meant strictly as
a pylon racer. It requires your constant attention while flying, and really seems to be at
its best in go fast-turn left mode. At full throttle it will cover a schoolyard very
quickly, and if you point the nose down, it really accelerates. The limited flight
time isn't really the problem I thought it would be; 2.5 to 3 minutes is enough -
I would like a chance to at least blink my eyes. 
If you want a sport flyer or micro-pattern plane, you should probably find something
with a larger wing. Perhaps BGM could sell a larger wing for this purpose. 
One notable thing about the ROCKET that distinguishes it from many other Speed 400
pylon racers is that this is a very serviceable airplane. It is very easy to get all of
the equipment in and out of the plane, and I have done so several times. Many of the
composite construction pylon racers require that equipment be installed permanently. 
If you don't like to select wood and cut out parts, buy the whole kit. Actually, BGM
can sell you everything you need for the plane except a transmitter and charger. If
you are very picky about wood and weight, buy the cores and plans. If you are really picky
about foam cores, just buy the plans. The kit is not complete, and instructions are not
comprehensive. I hope these notes are a help, but I really think that model designers in
general could do a much better job of sharing their knowledge about their planes. I
purchase kits so that I will not have to work out all of the details, but this kit, like
many others, leaves a lot of details to be figured out. I certainly learned a lot on the
first one that I will apply to the second one. 
The instructions for the ROCKET do include Bill Grigg's phone number. Not some office
phone number, but his home phone number. If you have a question about the plane, you can
call the designer. This sort of access to the designer of a kit is unusual, and is really
appreciated. Bill always seemed to be very interested in talking about the model. 
Bill Griggs Models is a part time cottage industry, as are many of the companies
serving obscure corners of the model airplane field. BGM and their compatriots deserve our
support for supporting us, because without them it would not be possible buy a lot of
interesting materials and kits. The quality and accuracy of the kit is affected by the
realities of very small scale cottage industry production methods - that is, by hand. A
lot of free flight cottage industry kits are not even pre-cut, but rather arrive as
printwood - literally patterns printed on balsa. 
All things considered, this is a OK kit of a really neat airplane. I hope that in the
future, BGM can supply more accurately cut balsa and plywood, and a complete hardware
pack. 
There is something truly amusing about flying a ridiculously fast airplane that is
barely larger than my transmitter tray. The ROCKET looks like a toy, but it is a serious
racing plane. 
The next time you are planning to travel the roads of upstate New York a bit above the
posted speed limit, be sure to keep a ready-to-fly ROCKET visible in your car. If you are
ever stopped by New York State Trooper Griggs, the ROCKET may not keep you from getting a
ticket, but at least the officer will understand your need for speed! 
</blockquote>

 

<big>Copyright</big>

<blockquote>
This document is copyrighted (c) 1997, 1998 by Steven Kranish, and may not be copied or
used in other forms of publication (electronic or paper) without written permission from
the author. I will probably grant permission, but I would really like to know about
it, so go ahead and ask. 
</blockquote>

<big> </big>

<big>Contacts</big>

<blockquote>
If you have any questions, please feel free to contact me at <a href="http://rcgroups.com/shared/nospam.php?u=skranish&d=ezonemag.com">skranish(at)ezonemag.com</a> 
</blockquote>
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