the authors of this article had a crystal ball to see into the future,
they would have been disappointed to learn that their prediction
for a resurgence of CO2-powered model aircraft was not going to
come true. Today it is difficult to get a CO2 engine other than
to buy a used one on eBay.
Return of once popular CO2 flying brings improved and lighter engines
and all-new compressed-gas jet- here used on the Micro-Jet Delta.
Howard Mc Entee and Bill Brown Jr.
This is an old 005 engine modified by McEntee for convenient
top-of-cylinder refilling. New engine not yet in production.
OLD-TIMERS who remember the late 1940's will recall the interest
in CO2-powered (CO2 in this article means carbon dioxide) model
planes, for sport flying and competition (there was at least one
AMA class). These remarkable powerplants were developed by Bill
Brown Jr., already famed for the development of the Brown Junior
gas engine (that's gas, not glow!) which revolutionized model aviation,
and brought on the continuing development of tiny model glow engines
which have reached such perfection today.
Never one to rest
on his laurels, Bill then dabbled with CO2 power. In the post-war
1940's he perfected three sizes of these engines. One was a rather
large job (relative to his others), which turned an 8" prop with
lots of power. It used an entire Sparklet CO2 cartridge for each
flight. These cartridges were used then, as they are now, for specially
equipped bottles that turned plain tap water into "soda water" for
drink mixing. This engine had a displacement of .018 cu. in. Really
interested in much smaller units, Bill sold all rights to the big
engine to Herkimer Tool & Model Works, who marketed the engine
under their "OK" label as late as the early '60's.
Larger engine, an 018 Herkimer OK, is shown with the 005
mill and its light-weight aluminum supply tank. Note aspirin
Next came Bill's favorite - the tiny A-100. The complete powerplant,
less prop, weighed about ¼ oz. A low-pitch 4"-dia. prop was recommended.
It flew planes ranging from 1-2 feet span, which weighed about 1½
oz. maximum. It was flown very successfully in tiny all-balsa scale
planes of 12" or so. The displacement was only .0015 cu. in.! The
final engine in the series was the "B," with a displacement of .005
cu. in. and total plant weight (including tank but less prop) of
about .65 oz., for planes up to 30" span. Production on both of
the smaller engines ceased around 1950.
Those of us who
were active with CO2 had a high regard for Bill Brown's developments,
but we (and Bill, too) freely conceded that some detail improvements
were needed. Tank filling was a bit unhandy. You screwed the cartridge
holder into a valve in the tank, a simple but fussy operation. The
A-I00 crankshaft bearings wore rapidly. Some of us put in brass
bushings - but this thinned the crankcase nose so that it broke
easily. Basically, the plants worked fine, and the incentive for
improvement came when the late Jim Walker became interested in them.
With such backing, Brown developed a much simpler, faster and
more convenient filling system. The tank is fueled through a tiny
nipple on the engine cylinder head. Crankshaft bearings were greatly
improved and the case beefed up considerably. A much better valve
material was found for the engine. CO2 gas is admitted to the cylinder
through a tiny ball valve. Great things were looked for with the
improved design but Jim's death brought a halt to CO2 progress.
Over the years, Bill Brown Jr. has run his machine-tool business
in central Pennsylvania for a living- but continued to dream of
marketing better CO2 powerplant. We're happy to report that such
marketing may not be too far off. Bill has refined designs for three
engines, with .001, .005 and .02 cu. in. displacement.
Jet is easily filled through outlet nozzle using CO2
cartridge and holder - which has pressure fitting. This
fitting also is the launch-release device. Thrust nozzle
adjustable for power output and duration. Delta is exciting
fun job. Jet can be mounted in dime-store, 29c gliders.
There is also a tiny jet engine. Due to its relative simplicity,
it doubtless will be marketed first. However, all components of
this plant will be worked into the piston powerplant to come later.
We show here with a little delta profile jet plane Bill has been
flying. Thrust doesn't last long-about 5 seconds (replaceable nozzles
with different-sized orifices will be offered for varying thrust)-but
the plane gets high enough for a fine glide.
Brown has chosen
the middle-sized .005 engine as his first piston job of the new
series to be marketed, but its difference from the old "B" is amazing.
About the only similarity is the .005 cu. in. displacement. The
plant will weigh little more than the old A-100, and the engine
itself isn't much bigger than the A-100 engine (which was only about
7/8" from top to bottom) . This engine will be marketed with the
same tank used for the jet engine (larger or smaller tanks may be
used, however). The jet engine itself (with proper nozzle to act
as a filler valve) may be employed to "gas up" the piston plant,
if you want to bury the engine in an inaccessible spot - inside
a scale plane cowling, for example.
While the .005 and .02
engines offer ample power to fly outdoor F IF models of all types,
the .001 job sounds ideal for the tiniest indoor designs! All the
engines can be adjusted easily for thrust. Thus, the .005 should
do fine indoors. Furthermore, with the very tiny and light gear
we have today - it sounds like a natural for indoor R/C flying.
Just think of the possibilities: No smoke, no smell, very little
noise, no fire hazard, instant starting every time, low fuel cost
(we used to get up to six flights from a single Sparklet cartridge).
Larger cartridges that are refillable reduce even this cost, allow
many dozens of flights before refilling. You can even recharge these
larger cartridges yourself, from the CO2 fire extinguishers and
tire inflators sold in some garages (and these too are rechargeable
for a nominal fee). We wish to emphasize that these CO2 power
units are not on the market yet - so don't write and. ask where
you can get them. We don't know where - or exactly when. But it
appears that Bill Brown Jr.'s long wait to market perfected tiny
CO2 powerplants is about to end. You can be sure we'll keep you
posted as to when he has something ready to sell. It shouldn't be
Micro-Jet Delta: Full-sized plans for this tiny speedster aren't
necessary. Just use the dimensions noted on our reduced plan. Be
sure to use the lightest 3"-wide Contest balsa throughout. You can
fudge a tiny bit when laying out the wing, even though when scaled
to full-size, our plans show that 3½" wide sheet is required for
the rear portion of the wing. Cement the three sections of wing
sheet together first on a flat surface, then slip the sanded assembly
into the fuselage slot and cement firmly. Note there is a slight
curvature in the wing; the center (at about the CG point) is 1/8"
lower than the leading and trailing edges. Bill just drew a radius
for a very large circle for the wing section. You can probably eyeball
this. The exact curve isn't vital, just as long as there is 3/32"
to 1/8" difference, as noted.
The tank must be cemented firmly in place. Feed tube to the
jet engine is shown going into the fuselage slot, but could just
as well be under the wing. It is vital to have the jet nozzle pointed
correctly. This might require adjustment. The jet unit must be cemented
to the fuselage firmly, since the entire plane is supported by the
jet nozzle, when you are charging the tank. The "Load-N-Launch"
filler holds the CO2 cartridge, and has what appears to be a small
knurled "chuck" at the forward end. The knurled portion is turned
until the filler is a snug, but not tight, fit on the jet nozzle.
Once this adjustment is made, you will not have to repeat it. The
filler can be slipped on and off the nozzle with light pressure.
special filler for the jet engine has a further sliding tip that
fits over the chuck end. After you have charged the tank in the
plane, you point the whole works up at a moderate angle, holding
the filler with one hand, the sliding tip piece with the other.
The plane is supported entirely by the jet nozzle fit in the filler
chuck. Now push the sliding tip piece smartly forward. This disengages
the jet nozzle from the filler chuck, and gives the little jet a
launching shove, whereupon the CO2 takes over to provide rapid acceleration.
No finish is needed on the plane. Remember, there is no
oil or dirty fuel involved. Keep it light for the best results.
Note that as this is written we do not have information on exactly
when the jet units will be marketed, or what the price will be.
But when they reach the hobby shops, you can be all ready to fly
one with this simple delta. Bill Brown has found it to be a fine
flier, and you should too!