The Hummelbird is all aluminium construction, built
from plans, some parts available
MAXIMUM PERFORMANCE - MINIMUM MONEY
by Ken Armstrong
is cute. I didn't want to say it but, it seems the best way to
describe a diminutive, single-place plane that cruises close to 100
mph on half a Volkswagen engine and costs less than $2222.00 to
Lets face it,
how expensive can a plane be when seven 4' x 8' sheets of aluminium,
several feet of aluminium angle, a few instruments, undercarriage
pieces and half an engine are just about all it takes - plus 1200
hours of your "spare" time. Built from plans that are the finale
to a story in itself, the Hummelbird is the successful conclusion to
an evolution from the Teenie 2 and Windwagon designs. A builder,
William J. Spring, likes the Hummelbird so much, he built two of
them (a taildragger and tri-geared version). True to the history of
refinements on this evolutionary design, Bill has modified his
second Hummelbird with a wider cockpit and aerodynamically enhanced
and extended the wing tips thus improving performance and handling.
beginning, Gary Watson built a Teenie 2. Wanting to try his hand
at design, he created the Windwagon with its open cockpit and
tricycle gear. While the design wasn't overly popular, nonetheless,
Morry Hummel bought the plans, added a canopy, reduced the weight,
streamlined the shape and converted the bird to a taildragger.
Enter Bill Spring. Dissatisfied with having to go through the
mental gymnastics of combining Watson's and Hummel's plans, he
photographed "every conceivable detail of Morry's plane at Oshkosh"
making construction much easier. Future builders have it easy as
the plans have been consolidated, updated and improvements
incorporated in a very professional presentation.
As far as the
all metal construction is concerned, Bill claims, "the parts are
easy to make and assemble. With the exception of 4 or 5 rivets,
riveting is a one-man job and a skill that is easily acquired", so
says this first time builder and electrical engineer. Bill pointed
out that the wing panel can be removed in twenty minutes and the
whole plane can be transported on a small skidoo or motorcycle
trailer and stored in a one car garage.
Spring calls his
half-engine's reliability and economy of operation -"amazing". In
the past, the various sawed-in-half VW conversions on the market had
more than their share of minor and major problems. Morry Hummel,
of Bryan, Ohio, has accomplished fixes for the glitches after a
great deal of developmental work on these two-cylinder, four-strokers.
Now a number of the VW engine conversion companies consult with
him for advice. The powerplant began life in 1971 pushing a
"pregnant roller skate" along Canada's roadways. Bill was only
able to salvage the crankcase, heads and connecting rods, although a
crankshaft was obtained from another engine. To transform the VW
engine, some machining and modifying is required with a handsaw (or
hacksaw) and lathe plus a little TIG welding to secure the
counterweights on the crankshaft. This addition largely overcomes
the "rocking-couple" created by the two crankshaft throws, leaving
only a small imbalance in the 2000 RPM range.
counterweights are added, "an external counterweight mounted on the
prop hub may be required to fine-tune the overall balancing",
according to Spring. He claims the half engine is more reliable
than the whole because it is better cooled and the "heads are single
units on this engine eliminating the constant valve clearance
problems that plague many of it's 4-banger relatives." The single
mag is directly driven by the crankshaft, eliminating the need for
an accessory drive system.
A 26 mm POSA
carb, with mixture control was combined with oversize cylinders,
pistons, high-lift camshaft, bearings and prop hub that were
available from HAPI engines (now Mosler Motors in Hendersonville, NC).
So far, this half engine has given l30 hours of trouble free,
quiet operation on less than 2 gph fuel consumption. This equates to
50 mpg on cross country flights! (No muss and fuss with fuel cans,
as owners can use their coffee thermos to take auto gas out to the
airport for their daily, after work, flight fix...)
In answer to an
oft heard question, Bill says that a 40 hp Rotax with a larger fuel
tank might prove suitable, although he cautions readers that the
aircraft might exceed the red line speed in level flight. (One is
flying in Australia but no performance data is available.)
Moreover, designing engine mounts and the installation of
accessories within the tight confines of a cowling are challenging
and time consuming jobs that should not be undertaken by first time
builders without engineering experience.
By the way,
Spring strongly recommends the installation of a carb heat system as
he has first-hand proof that this powerplant can ice up, although
other experts have claimed otherwise. Bill's home-made 46"x34"
prop seems perfectly suited to the bird as it gives a maximum cruise
airspeed of 100 mph at 3200 rpm and a rate of climb of 600 fpm.
(For flyers willing to crank up the VW to higher RPM's, 120 mph or
so is possible.)
Although all of
his flight experience was on tricycle geared aircraft, mostly the
Cessna 150, he decided to check himself and his new taildragger out
at the same time. Seven hours and several close calls later he was
able to keep the aircraft straight enough, long enough, to make a
take off. Substituting springs for the direct connection tailwheel
steering arms helped reduce the sensitivity and initial
over-controlling. His buddies around the airport advise that Bill
has mastered the conventional gear very well even though he chose to
build the second Hummelbird with the up front "training wheel".
Apparently, he is thinking of others who might want to introduce
themselves to the flight of the humming Hummelbird.
of the Hummelbirds seats on in turn proved that the two inch
widening of his second prototype was a good idea. The tall,
side-hinging canopy provides plenty of headroom for a six-footer and
allows easy enough ingress, once you learn the technique. The panel
has just enough room for a few "fun VFR" flying gauges and a
portable 720 channel nav/comm. The main cabin bulkhead forms the
aft-slanted seat back and a small hat rack will carry your goodies
for a day's outing. Averaging 307 pounds, the TD and TG versions
are within a few pounds of each other. Considering my 200 pound
bulk we could only fill the five gallon tank to the half-way mark to
keep runway legal.
flips of the prop and the VW danced to life. With one magneto and
a simple on/off fuel system, there wasn't much to check on the way
through the ankle length grass at the hidden Flamborough, Ontario
airstrip. Bill doesn't like the engine noise, but then he hasn't
flown any of the amateur-built mega monsters now available. After
all, how much sound pollution can 28 hp develop? It seemed mighty
quiet to me with a good headset holding my ears on.
made me grin so hard, I nearly swallowed the miniature microphone.
Honest, visibility is exceptional (even in the taildragger and this
thing can turn on a penny and give change (a British half-pence).
When you consider the 18 foot wingspan of the Hummelbird, you'll
realize you can park it between the main gear legs of numerous
aircraft. Although they aren't often needed, two small,
hand-actuated levers provide differential braking and turns so sharp
that all amounts of currency are too large to describe the tight
trouble with the tiny 500x5 tires and minuscule tailwheel in the
tall grass, it was surprising to feel how well they handled the
reasonably smooth turf field.
power (perhaps "full" is too strong a word for the amount of thrust
developed), this bantamweight taxis faster and faster until the
magic four-zero appeared on the clock. The controls are very light
with virtually no static friction and direction control on the
runway, while a little sensitive, is not difficult compared to the
average conventionally geared aircraft. (This could largely be due
to the low horsepower and small propeller blade diameter not
creating a lot of torque.)
awesome acceleration, the low lift-off speed of 40 mph had us
skimming through the long grass in less than 800 feet and climbing
600 fpm at the gross weight of 525 pounds.
This is high
performance, compared to staggering upwards at 350 fpm in a
Volksplane with a full VW engine. Accompanied by the "half-engine"
purring at 3000 RPM and enthralled with the unobstructed view a
autumn leaves, the Hummelbird zipped along at 85mph. Tugging the
throttle back for 2600 RPM only reduced the speed to 75mph at a fuel
flow that is slightly more than insignificant. Top speed is in the
100-120 range depending on the RPM you want to twist out of this
airborne auto engine.
The trim system
wasn't necessary as the stick forces are very light with these
harmoniously balanced controls. The bird feels as good as any I've
had the opportunity to thrash the air into submission with, and that
says a lot. Sure! it's not an F-18 Hornet, nor a Questaire Venture,
but, for those of you who cannot afford to buy, never mind fly, some
of the high performance kits currently available, this could be your
dream machine. Bill described the lines as "fighter-like" and his
unique tongue in cheek humour forced him to paint a warning on the
taildragger's open-ended tail cone, "Caution - Jet Blast".
cruise and high speed handling feels fighter-like, from back in the
days when 'fly-by-wire' systems weren't part of the vernacular.
When it comes to
slow-speed flying, the first thing one notices is that it takes a
long time for this aerodynamically clean machine to slow down. When
the stall is reached, this flap-less floater simply nods, slightly
nose down, at 40mph.
Without a VSI,
I'm not sure what the rate of sink was, but, it was better than most
aircraft's glide. Not much to it, nothing more to report.
As you might
expect, the hardest part of flying this microlight bird is getting
it to slow down and go down. Not wanting to super-cool the engine
in the cold fall weather, the RPM was left at 1800 and moderate
amounts of sideslip used to maintain the shallow glidepath that
terminated in the soft grass.
How is this
lightweight, low-wing bird in a crosswind? Well, according to
Bill, he landed while the windsock was horizontal to the ground,
pointing across the runway, with no problems.
or what? Remember, the wing tips are rather close to the ground,
and that's without any sideslipping. Seems that the maximum
crosswind limit would be in the 15 mph range.