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Thumper Delta & Stratus

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Thumper Delta

On Friday, May 17, 2009, I got the opportunity to test fly the new four-stroke Thumper motor mounted to a TrikeBuggy Transformer frame flying the North Wing Stratus trike wing at the El Mirage Ultralight Aircraft Flight Testing Grounds.

The Thumper Delta redrive is made by Terry Lutke in Dorr, Michigan, and is a remarkably nice package mounted to the Briggs and Stratton 23 hp V-Twin motor. Here is a breif excerpt of a recent email Terry sent to one of my client's inquiries:

"The engine is 100% stock (no hotrod parts), so engine parts and repair can be accessed where ever you are, and far into the future. The engine we use is not over-worked and we limit the RPM to increase longevity.

The important features about 4 strokes are their potential for longevity, reliability, low noise, ease of repair, and very low fuel use. Compared to 2 strokes, the 4 stroke is perfect for flyers who do not wish to learn to perform engine repairs and tuning. 2 stroke engines have a reputation for quitting at the wrong time..not a good thing when you're on a cross-country flight far from your car. The Thumper also comes with a very reliable propeller speed reduction system."

Starting this motor is as simple as turning the key, and the electric start breathes life into the Thumper. When the engine is idling, you can hold a normal conversation while standing right next to it, it is so quiet! Bring the RPM up to 3800, and you have the sound of the GSC 3-blade 62" propeller moving some serious air.

Seating is comfortable in the TrikeBuggy Transformer, as there is a back support along with the cloth seat suspended from the stainless steel trike frame. This seat buffers some of the vibration from the mighty 4-stroker, as it is a fairly heavy motor. Wrap-up is slightly slower than the MZ-34 (313cc Compact Radial motor), but the thrust becomes immediately evident, as the large prop grabs some serious air. I was able to launch using only about 2/3 throttle, engine RPM around 3800 and air speed of right around 28 mph. I did not change the position of the Hang Block from the setting installed at the factory, it worked just fine.

Thumper Delta Specifications
TrikeBuggy Model Transformer
Motor Briggs & Stratton V-Twin
Propeller GSC 3-blade 62" Ground Adjustable
Horsepower 23hp
Fuel Consumption Approx 1 Gal/Hour
Peak RPM 3800
Starter Pull Start (e-start optional)
Materials Stainless Steel & Aluminum
Weight 168 (no wing)
Width 58"
Length 78"

The pilot barely needs a ear protective headset, as the motor has a pleasant low timbre sound similar to that of a car's engine runing. Cruising with this trike is very pleasant for a variety of reasons:

  • First and most evident is the peace of mind that comes from flying an aircraft using this stock motor, expected to run for literally thousands of hours with little to do but change the oil.
  • Second is the noise, or lack of loud sound! I let Joey fly this trike, and was in awe as he repeatedly fley by us with little more than a whisper of sound from the aircraft. Even the videos seem loud, as they tend to amplify noises. You have to hear this one in person to believe it. The trike pilots from the Flying J Ranch said they thought it was quieter then Jim's trike, considered to be the quietest trike at the ranch.
  • Third is the North Wing Stratus glider, which I will comment more on.

From the moment you unzip the Stratus, you can see the quality of construction used by North Wing on this extraordinary wing. Set up is straightforward, and while there are more battens than the Wills Wing Falcon 225, the wing is a very different animal as a result. It is a true double surface glider, with the cross tubes completely covered by the very smooth lower surface of the glider. There are 11 upper ribs (battens) and 4 lower surface ribs, and once this glider is assembled and tensioned, it looks sleek and tight. The rear wires are abbreviated, made for use with a trike, and it comes with the split shaft collars already installed and ready for the Hang Block.

Stratus 17 Specifications
Speed Range 21 - 47 mph
Trim 28 mph
Wing Area 182 square feet
Span 34.5 feet
Aspect Ratio 6.6 : 1
Double Surface 75%
Nose Angle 132
# of Ribs - top 21
# of Ribs - lower 8
Rib Material 7075-T6
Weight 84 lbs.
Weight Range 240 - 500 lbs.

It was simple to attach the trike to the TrikeBuggy Delta, and lifting the 84 lb glider to the ready position is easily done by one person using wheel chocks behind the rear wheels of the trike. After installing the front compression strut and tightening the bolts, I am ready for Preflight and first flights!

I was surprised at how quickly the trike began flying after starting the takeoff run. I was expecting a much longer roll-out, but this combination of motor thrust and glider efficiency caught me off guard. I was in the air so quickly and everything was so well balanced, that I could hardly believe that I was flying. It felt very solid and perhaps heavy, compared to what I am used to, but the glider was just a joy to fly. The speed range is truly remarkable, as I played with touch and go practice for about an hour. Flare timing is very intuitive with this wing, and the retained energy lets you skim the ground in ground effect almost effortlessly.

One of the seasoned pilots from the Flying J Ranch commented on the wing after seeing it from the air. He said that it looked like a very high performance wing and was impressed with the smooth surface and sleek lines of the glider. He thought it looked like a "knife" just waiting to cut the air!

  • Photos of the trike on the ground
  • Photos of the trike flying and instructing a student
  • Video with no music featuring the sound of the Thumper
  • Video with soundtrack

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