The Hummelbird is all aluminium construction, built from plans, some parts available


by Ken Armstrong

The Hummelbird 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 build.

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.

In the 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.

After the 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.

Strapping each 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.

Three finger-fed 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.

Just taxiing 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 radius.

Anticipating 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.

Applying full 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.)

While lacking 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".

Indeed, the 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.

Beginner's luck 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.

fun 4 one

By way of conclusions, the Hummelbird's drawbacks are easy:  It's single-place and not available as a kit.  However, when you consider the low construction cost, the undercarriage options, portability, economy of operation and the durability of aluminum, the Hummelbird could be called a best buy amongst single-place amateur builts.  That should be enough of a reason to build this aircraft.  Moreover, once you've flown this lightweight, you'll call it a great deal.

For $130 you can order l7 detailed sheets of 24"x36" drawings, a materials list and a builder's manual from Mr. Spring at 4493 Tremineer Ave., Burlington, Ontario, Canada. L7H 1H8 or phone (416)632-7693.  You can also contact Mr. Hummel at (419)636-3390 as Bill says, "Morry is always willing to talk about his favourite subject."  From my observations, he can be justifiably proud of such a sweet design.  The Hummelbird allows dreamers to become builders with less money than it takes to go on a two week vacation!

wing span
wing area
empty weight
useful load
gross weight
fuel capacity
1/2 VW   37/30-40 hp
63sq ft
7 US gal


takeoff distance, ground roll
rate of climb
max speed
cruise speed
landing distance, ground roll
service ceiling

limiting and recommended speeds

design manoeuvring speed (Va)
never exceed speed (Vne)
stall, power off (Vsl)
landing approach speed

All specifications are based on manufacturer's calculations