Crazy electric flight Full scale flying lawn mower By Philipp Gardemin

When I was just a 14 years young boy I saw them flying at a model-air show in Germany : Lawn-mowers, build in wood and styro-foam, equipped with a 10-cc-motor and a tuned pipe. They were loud, fast and very impressive – in the eyes of a young boy like I was.

Today, 20 years later, I browsed on a lazy Sunday afternoon in the World Wide Web. Suddenly – I hope nobody will ask me how – I reached the website of a small model-shop in eastern Germany, named Flugwerft Brendel (www.flugwerft.com). That company offered a kit for a flying lawn mower, nearly the exact same model, which I’ve seen as a young boy. The mouse click on the order-button was almost instantaneous and several days later I received a package with a lot of plywood- and styro-foam-parts. While studying the plans and the parts, old childhood-dreams were coming true. But that the model will be as big as the plans were exciting, I haven’t forgotten this over the years.

Philipp Gardemin (Aufwind's editor) show this lawn mower is really a full scale model !

You can see a small video by switching the camera (630 ko, format wmv)

The central section of the flying lawn mower is the wing, with an S-profile and two big flaps on the trailing edge. Built with plywood-ribs, pine-wood-stringers and a balsa-planking; it’s a very stable and impressive piece of wood. The RC-components, the battery and the motor are included a big plywood-box in the middle of the wing. The design-elements, which everybody can see that this is a flying lawn-mower, are made from foam and glued on the central-section with white glue. Three servos of the standard-class are operating the two flaps with a delta-mixer and the front-wheel. The whole model is moving on three wheels of 70 mm diameter. The four wheels on the side of the lawn-mower are just dummies without any function. The big handle on the back of the lawn-mower is made from 6-mm-balsa. It looks very realistic, but it’s very susceptable to breaking. If the handle has some aerodynamically functions I haven’t found out until yet – and I’m not willing to test it! The colour-scheme is scale: The famous German company Wolf-Garten is using the same colours on their lawn-mowers. Acryl-colours and “Orastick”-foil were used.

Two big flaps are mixed for elevator and roll function.

The lawn-mowers 20 years ago were flying with 10-cc-motors. Today it sounds better with an electric-motor. I used a “Compact 490”-outrunner from Graupner with 18 cells and a 12”x6”-APC-prop. To my biggest surprise it was no problem to fix the centre of Gravity at the right position and the flying-weight was exactly in the area which the manufacturing company suggested before.

Engine is electric : better for the lawn... Compact 490 from Graupner, with 18 cells.

The controller is fixed outside. At the end of the fuse, we can see the flaps'servos.

3 wheels are used. The front onel is moved with a standard servo.

But there was a final question : How will that crazy thing fly ? On one of the first warm evenings in Germany I put that flying lawn mower on my grass-airfield and gave it full power. Much earlier than I expected the model took off and climbed fast and in a stable manner into the sky. My surprise was such that I nearly forgot to control it. The first round gave me a good feeling, how the rudder function is : smooth but direct, never critical. For two minutes I flew that crazy lawn mower around the airfield. All spectators were more than amused by the flight-image and the sound, which the model sent back. The first landing was no less impressive : With 30 per cent power I flew the lawn-mower to the strip and with a deep “bump”-noise the flying lawn mower was back on earth. My old childhood-dream came true !

Each time on the field, this simple lawn-mower make the show...

Several days later I visited an electric-flight meeting with 50 pilots and several hundred spectators. And what shall I say : Between the most expensive and biggest model-airplanes, my cheap and simple lawn-mower stole the show. I flew many more times on that weekend – each flight was a show stopper !

Contact :phgardemin@freenet.de

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At a glance : Wingspan : 780 mm Length : 900 mm Height : 950 mm Weight : 2990 g Motor : Compact 490, Graupner Battery : 18x CP-1700, Sanyo Flight-time : 3 minutes Propeller : APC 12”x6” Kit-price : 49,- Euro Address : Flugwerft Brendel, www.flugwerft.com