The SR Bantam Monoplane
Kit and Accessories Available
from:
SR Batteries, Inc.
Box 287
Bellport, NY 11713
Phone:
631.286.0079
Fax: 631.286.0901
http://www.srbatteries.com/
Review by Ken Myers
July 2002
The largest growing area of the R/C model
airplane hobby seems to be the slow and "backyard" flying segment, at
least according to the ads appearing in the general model aviation hobby
magazines. Almost ready to fly (ARFs) dominate this group, with the
majority being fabricated outside the United States. While some of these
ARFs appear to use "typical" model aircraft construction, many do not. For
those of us that like to build our own, there are not a lot of choices.
Fortunately, and I do mean fortunately, Larry Sribnick has come to our
rescue with the Bantam monoplane and Bantam Bipe.
For those of you who’ve been following
what I have built over the last few years, it may seem that I am biased
towards SR Batteries’ planes. Well I am! Every time that Larry introduces
a new plane, I get very excited. Why? He designs planes as I would. He
executes them into beautiful laser-cut kit form for all modelers to
duplicate, provides a place to purchase all of the necessary additional
equipment in a plug-and-play form and educates the builder with his well
executed construction manuals.
I must
admit that I’ve not had a lot of personal interest in this segment of the
hobby, but after having read Bob Aberle’s great book, Getting Started
in Backyard Flying, my interest was piqued.
While those of you who’ve read my Cutie
and X-250 reviews know that I modified the power systems to my personal
preference, I must make it clear that the "stock power system" versions of
the Cutie and X-250 are excellent aircraft as designed. They meet a
certain type of flying criteria intended by the designer. All this past
year I’ve been flying my Cute with the stock power system and having a
ball both inside and out. The X-250 is my most flown plane. It’s my gotta
fly whenever I go flying plane.
Since I
had no practical experience in the slow fly/backyard fly type aircraft, I
used the Bantam monoplane as a project to introduce me to, and educate me
about, this types of aircraft and flying.
The kit contents, all 145g/5.1 ounces of
it, come neatly packed in a couple of plastic bags. Full size plans are
used to build the wing on the board, and once again Larry has provided an
extremely well written instruction manual. The manual contains a lot of
pointers and warnings. This time I managed to build a right and left wing
panel. (Thanks for the reminder Larry!)
The only deviation I made during the
building was to use the "build on glass" method, instead of the "pins into
the building board" method. That should be obvious from the photos.
The construction was very easy, thanks
to the plans, well-written instruction manual, clear construction photos,
and my understanding of how Larry "puts stuff" together.
I used single-edged razor blades to
relieve the little "tabs" on the parts left after the laser cutting. I
cleaned up the lightly "burned" edges using the fine Midwest Permanent
Sanding Block. (I purchased all three grits of these when doing the Cutie.
They are very useful.) The parts diagram at the end of the construction
booklet was useful in identifying the parts needed for each step of the
construction.
Wing construction
and sanding was completed in 125 minutes.
The fuselage
parts were relieved, assembled and sanded in 90 minutes, while the tail
feathers took just another 15 minutes to get them ready to cover.
Another 40 minutes was used to bend the
landing gear wire and tail skid with needle-nosed pliers, reinforce the
landing gear holes with CA and do some final sanding.
The whole construction of the airframe
was finished in 270 minutes. Four and a half-hours to have a completely
finished airframe, ready for covering, is fantastic. (I’m beginning to see
why so many people are "into" these little planes!)
Larry recommends
Ultracote Lite for covering and is able to supply this product. I’d never
used this type of covering before, so I did have a few minor problems with
it. Removing the backing material was more difficult than I had
anticipated. With the backing removed, it is about the same thickness as
heavy-duty Saran® wrap, and like Saran® wrap, it
loves to fold over on itself! It seems to be more prone to static cling
than other iron-on coverings that I have used. Once it has folded onto
itself, it is difficult to convince it to unfold. It sounds like I don’t
like it. WRONG! After working with it for a while, I learned to remove the
backing and to be very careful about not letting it fold over itself. The
end result is a good looking, very light covering that is easy to apply
and shrink. The end result is well worth the little extra effort put into
working with this material. Larry has even included his volume of SR
Techniques on covering. The information in this volume can be very helpful
to those who’ve never covered with iron-on covering before, and even
"pros" can learn neat little tips from it.
The wing took 60 minutes to cover.
Before covering, the completed wing structure weighed 20g/0.71 ounces.
After covering with Ultracote Lite, it weighed only 30g/1.1 ounces. That’s
only about 10g/0.35 ounces for a surface area of about 420 sq.in., or
about 0.12 oz./sq.ft. for the covering!
Once the wing is covered, lay it on a
flat surface and check to see that there are no warps, and that you’ve not
inadvertently added washout to one tip and not the other. (Okay, don’t
ask how I know about this one!) Larry recommends no washout for outdoor
flying, and ¼" washout for indoor. If you want to keep it in tight, do
close figure eights, I’d recommend the washout in the outdoor version as
well.
The fuselage and tail feathers
took 85 minutes to cover. The covering went easily, as I’d learned to be
careful about the tendency of the film to roll over itself and stick.
The tail surfaces
were hinged with Larry’s special hinging tape. I used the larger diameter
of the two supplied pieces of wire to set the gap in the tail surfaces,
but, when I do it again, I’ll use the smaller diameter wire as the tool to
set the surface gap. The tires were glued onto the wheels. Unfortunately,
when I affixed the wheels to the axles, the glue stuck the left wheel to
the axle. When I tried to remove the wheel retainer, I ended up smashing
it. I made another one for the inside of that leg, a real bother, and used
the one that was on the inside as the "new" outside retainer. It would be
nice if Larry included more of these retainers. He has the "extra"
material already there. The extra ones could be used to fix a "mistake" or
on new landing gear, should they become necessary. I’d also recommend
making the axle part of the landing gear about 1/8" longer than shown on
the plan. Both motor sticks were assembled and fitted. The landing gear
was fitted to the fuselage along with the tailskid. I’d recommend that you
be sure to "double" glue on the tailskid and then cover the part of the
tailskid wire that is glued to the fuselage with some covering material.
All this took about 135 minutes.
The
motor was fitted to the motor stick and placed in the airframe. The
windows and dowels were added. The battery stop was fabricated and glued
in place and the servos mounted to the servo/receiver tray. I put a very
small piece of Velcro® at the front of the battery pack and on
the front of the battery floor. The battery is replaced through the bottom
of the firewall, under the motor. This is very handy and gives a great
escape route for the pack when the plane stops suddenly. I also chose to
use Velcro® to secure the receiver to the tray. All this took
about 90 minutes.
Battery packs
showing small Velcro
square
Instead of
using my fingers to set up the CG, I marked the CG on the wing saddle.
Next, I poked a straight pin through each side of the fuselage at the
marks on the wing saddle. I held the pins and adjusted the Rx/servo tray
before gluing it into place for the proper CG.
The pushrods were
fitted and radio installation was completed. I used scrap balsa and a
clothespin to hold the surfaces while constructing the pushrods. The Dubro
Micro E/Z Links supplied in the kit work very well, but they didn’t show
up well when dropped onto the concrete floor of a basement. It would be
nice if there were an "extra" package of these included in the kit. For a
few more cents, it certainly would save a lot of aggravation! The receiver
antenna was run out the fuselage side to the horizontal stab. The graphics
were added to the wing, and everything was given a final going over to see
that all screws were in place and everything tightened and ready to go.
Finishing up took 95 minutes.
The total, ready
to fly time, for this project was 745 minutes, or 12 hours and 25 minutes.
That’s about as fast as I’ve ever built any plane, complete and ready to
fly.
As I’d built the plane over a
two-day period, the two SR Batteries 150 mAh packs had both been slow
charged to prepare them for flight. Chris helped me range check, and
everything was ready for the test flight.
Flying
Session 1
The test flight was
done in the evening. The field chosen was about the size of two baseball
fields. The wind was not "ideal." It was about 7 - 8 mph and gusting to
10+. That is really the top limit for this type of plane. The first flight
was a bit "bumpy", as the gusts bounced the plane around. There was
nothing unusual about the flight or the plane’s flight characteristics. It
leaped into the air from a simple hand flick. Plenty of power! It is
probably the easiest plane I’ve ever hand-launched. It was flown close and
tight and high and out. The Focus 4 never missed a beat transmitting my
desires to the MPI receiver. Four more flights were completed that
evening. Each flight got better, as the wind decreased. While not an
aerobatic model, it will loop and barrel roll when both are initiated from
a dive. Flight times in the higher wind velocity were about 5-6 minutes
and when the wind slowed down the flight time increased to 7+ minutes.
Session 2
While not a
perfect morning for a slow flier, I decided to give it another go. I drove
to the local park, less than one minute away. I scanned the ball diamond
backstops, soccer goals, fences, tall light poles and other obstructions,
and decided to have a go at it. Even though the sun was in the wrong place
in relationship to the wind and obstacles, three more flights were flown
without incident. The third flight was at the very edge of flyability for
this plane. The red aircraft frequency identifying flag on the transmitter
antenna was standing straight out, and the whole flight was a "bumpy"
ride. This was not unexpected, as the plane only weighs 8.3 ounces and has
a wing loading of 5.69 oz./sq.ft.
Session 3
The Perfect Evening!
The perfect evening finally arrived,
after the less than perfect morning. As I arrived back at the local park,
there was no wind. I flew four long and enjoyable flights. The 150-mAh
pack easily gets more than the six minutes advertised by SR Batteries in
this windless environment. A few people wondered to the back of the park
where I was flying and stopped to chat. One fellow, that lives right next
to the park, said he’d seen lots of folks try to fly there, but no one had
succeeded. I filled him in on why. It is still beyond me as to why people
believe they can fly an R/C plane with no help or instruction. Oh well, I
digress.
Because of the total lack of
wind, I few one flight as if I was in the Oakland Yard, our local
soccer/golf dome. Easy as pie. Close in figure eights, circles on the left
tip, circles on the right tip, low and slow, and never going much over my
head in height were all easy to do. Indoors or out, this is one relaxing,
enjoyable plane. It is Fun with a capital F.
The Bottom Line
Larry Sribnick
has designed a slow flyer with good looks, great engineering and very nice
flying characteristics. It is easy to build and enjoyable to fly lazily
about the sky. It doesn’t require a trip to the local R/C field, as any
decent double soccer field size area will do, when safety of others is
kept in mind, as well as the location of local R/C club fields. With SR
Batteries ability to complete the package, it becomes an excellent value
as well.
This plane could not be
considered a trainer, as it is too light to allow flying at any given
time. But, if a nice calm morning or evening came along, I would certainly
consider letting a newcomer have a hand at flying it.
This is exactly the plane I dreamed of
having in 1962 or 1963. I wanted to fly my Minnie Mambo in the park at the
end of the street, but it was just too unpredictable. I could never
remember how many turns I had left on the escapement rubber, so I always
let if fly a long way before making a turn. There just wasn't room in the
small park to do that. The park is still there, and with the Bantam, I
could fly it there, but they no longer mow the grass. It's a place of a
bygone era. Still, I thank Larry for making one of my childhood dreams
come true.
Weights:
Kit components: 145g/5.1 oz.
Wing before covering:
20g/0.7 oz. - after covering: 30g/1.1 oz.
Fuselage before
covering: 30g/1.1 oz. - after covering: 35g/1.2 oz.
Tail
feathers before covering: 5g/0.18 oz. - after covering:
10g/0.35 oz.
Total airframe weight w/motor stick, Rx/servo
tray, LG and skid: 85g/3.0 oz.
GWS/MPI
Motor/gearbox/spinner/leads: 30g/1.1 oz.
9x4.7 Prop:
5g/0.18 oz.
Jeti 05 ESC w/leads: 5g/0.18 oz.
MPI 6800
micro receiver w/crystal: 5g/0.18 oz.
MX50HP Servo w/arm:
10g/0.35 oz.
150 mAh SR NiCad pack: 65g/2.3oz.
RTF (AUW)
weight: 235g/8.3 oz.
Wing Loading: 5.69 oz./sq.ft.
Power System Info & Observations
RPM:
measured at beginning of flight: 3,750 RPM
Approx. Airspeed:
3.75 * 4.7 = 17.6 mph
Approx. Stall Speed based on above: 3.7 *
SQRT(5.69 oz./sq.ft) = 8.8 MPH
Observations: Airspeed at full
throttle "probably" closer to 15 mph. Cells don’t seem to "knee" at this
low amp draw, but they seem to just run down in a linear fashion. I’ve had
to land every flight before the BEC shuts down. It is just out of "power"
to maintain flight. This is not "bad", but just an observation.
Manufacturer’s Data:
Wing area: 210 sq.in.
Span:
39 in.
Other items used but not supplied in the kit:
Motor:
GWS/MPI, Gear Ratio: 5.9:1, Prop: 9"x4.7"
Battery Pack: 7 cell,
SR 150 Series
ESC: Jeti 05 Speed Control with JST connectors
installed
(Note: the complete power system above can be
purchased ready to go from SR Batteries - Also, the complete Airborne
Radio system can be purchase from SR Batteries and includes: the MPI 6800
micro receiver w/crystal and two of MX50HP servos)
Charger: SR
Batteries Smart Charger (no longer available)
Dremel with
cutoff wheel
Electric hand drill w/1/16" bit
Single-edged razor blades
Digital scale
Needle-nose pliers
Midwest Permanent Sanding Blocks
Covering Iron
Heat gun
Scissors
Thin CA
Thick CA
30 Minute Epoxy
Baking Soda
Straight pins
Wire cutters
JST to Sermos Charge Jack adapter (can be supplied by SR)
2nd SR 150 mAh pack (can be supplied by SR)
Bag of
assorted rubberbands
Larry, you devil you! Let's see, the
Minnie Mambo has about a 36" wing span, about 212 sq.in. of wing area,
humm, I wonder? To be continued?
Could this be
a future project for Ken?
Unlike other sites,
there is NO paid advertising on this site! When you see an ad link, Ken
Myers uses and recommends the product(s), supplier or manufacturer. He
uses the "stuff" or supplier himself!
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