Langhors, a recumbent tandem

Langhors, my tandem -recumbent for loaded touring

Technical data:
Construction:        Carbon monocoque, positive laminated on PU-foam core
Suspension:          Front: central in the headset (a bit like Canondale, but not quite) / Rear: carbon swingarm
Wheels:                 Front 406-32 / rear 559-40
Brakes:                   Magura
Length:                  Just under 3 meters
Weight:                 Ca. 26 kg
Length of riders:   Front 170 cm to 200 cm / rear 160 cm to 195 cm
Panniers:               2 ortlieb back-panniers on the rear lugage-carrier / two cilinder-kanoobags below rear seat

Remarks:
The frame is extremely stiff. I believe this to be a requirement for safe high-speed driving. Handling is excellent: very light shimmying around 45 km/h, at higher speeds absolutely straight. One hand driving possible up to 75 km/h (may be even faster, but my courage does not allow it).
Brakes are a problem on longer downhills. Due to the high loaded mass (about 220 kg) the rims get very hot. You have to brake as little as possible, and to stop every few km to allow the rims to cool. With these brakes I do not go into larger mountain ranges like the alpes. Fitting a good disk brake could solve the problem, and I will try this in the future. If anybody has experience with disk-brakes: please mail me.

Some pictures of the animal, and of her birth Click on the pictures for a larger version Touring in France(74 kB) A side view (36 kB)

Front part of the core Rear part of the core Laminating Vacuum bagging Note: Plywood/aluminium inserts Skin protection (15 kB) (26 kB) (21 kB) (22kB)

Detail of the front suspension (111 kB)

Spoke problems On of the most common problems on tandems are broken spokes. Tandems exert huge loads that bicycle wheels are not designed for. So I decided to make both rear and front suspension to avoid spoke problems. Rear is a simple swing arm. To avoid unequal spoke tensions the rear wheel is not dished, and the hub is set at a little offset from the centreline of the bike to compensate. The front suspension is the most difficult part of this bicycle.
Construction of the front suspension Around the stem of a conventional fork a stainless steel tube is bonded with epoxy. This tube can move vertically in two POM bearings that are mounted in an aluminium intermediate tube. The intermediate tube is mounted in the frame by means of two industrial thin section ball bearings. These bearings can not withstand large axial loads, so for the vertical movement of the fork a simple but ingenious construction was designed:
A short stainless steel swing arm is mounted to the underside of the frame by means of a ball link. The other side of the arm ends exactly in the middle between the fork legs. At this side a thin stainless steel wire is mounted (bought in a yachting shop). This wire goes upwards trough the fork stem and is connected to the top of the stem. The wire allows rotation of the fork, so the steering is not influenced. For the suspension a rubber element is mounted between the frame and the swing arm. This element restricts the upward movement of the arm, and hence also the upward movement of the fork.
The POM bearings have to be fabricated to close tolerances, and provide a little damping. This suspension is simple yet effective, and very durable, even under the high (tandem) loads. I hope to provide a sketch soon, for better understanding.
I tried to use the POM bearings also for the rotation of the fork, however this arrangement had to much friction, and the handling of the machine was horrible.
And the name of the machine After a horse from a Dutch childres book. The horse was so extremely long that two wheels were mounted in the middle under her belly, and a whole family could ride her together.

Last changes: 17-3-'98 Back to index page