Customer: Colin Chapman (Group Lotus, Ltd.)
Type: ultra-light single-seat canard prototype
Program: Lotus MicroLight aircraft (proprietary)
Powerplant: 2 x 23 hp KFM 109 ER engines
First flight: 17 December 1982
With his love of flying to encourage him, Colin Chapman, the man behind the famed Lotus automobile company, "got into" microlights very quickly when ultralights/microlights began to appear on the scene. Chapman believed that Lotus composites technology could be applied to build an aircraft that still met ultralight rules, would be cheap and easy to fly, and very attractive to buyers. After reading up on German glider technology, Chapman approached the Rutan brothers in 1982 to study the feasibility of the project and commissioned Burt to design a new type of microlight based on Rutan's love of composites, efficiency, and the use of the "canard" wing layout for which Rutan is famous. Several designs were envisaged, one being the Rutan Model 91 ML (for MicroLight), a one-person 300 lb. ultralight aircraft, powered by two 25 hp jet engines. Despite Burt Rutan's dismissing the idea as complicated, Chapman insisted that the new plane should be a two-seater.
By June 1982, the final configuration was chosen out of nine different studied designs, and in December, the prototype Lotus MicroLight (Rutan Model 97M), built by Scaled Composites Inc. and appropriately registered N97ML, arrived at the Group Lotus airfield at Hethel in Norfolk, England. It was a side-by-side two-seater with a pointy nose, an enclosed cockpit, a retractable front wheel, and is of a unique design with a canard foreplane and a swept back wing, and a pusher propeller behind the cockpit. Tragically and ironically, Colin Chapman, the visionary who championed the Lotus MicroLight, died December 16, 1982 at the age of 54, the day before the prototype's first flight. It is said that being in desperate need of funds to finance his state of the art F-1 Designs and the Lotus Cars factory output, Chapman had got unknowingly involved with some exceedingly shady characters. To this day, his death is still shrouded in a number of conspiracy theories.
It is often said that the program was shelved by Lotus due to the death of Mr. Chapman. This was not so. Prototype trials continued with a little Italian KFM 109 ER two-stroke 23 hp engine, up to the end of the proof-of-concept phase. Specs for the Lotus MicroLight are lacking, but a 25 hp engine was originally planned for it. A Lotus engine that was being developed by Tony Rudd (a senior officer at Lotus), the 50 hp Magnum 4.5, was to have been installed in the production aircraft (see details left). The plane was assembled and flown for the first time in public in August 1983. It arrived in a crate at Hethel in August 1983, two days before the Lotus Open Day. It was assembled on Friday and Saturday, and was taxied in daylight on Saturday afternoon, and "accidentally" hopped in the dusk. Its first proper flight was Sunday morning, and the demo flight was in the afternoon for the crowds. It was now registered as G-MMLC.
The Lotus MicroLight was apparently a technical success, but a marketing failure. Despite both Lotus's and Rutan's credentials, the business arrangements didn't work out. Lotus wanted to build a business for the MicroLight, and sought backing to continue alone. When that wasn't approved, Lotus went looking for partners and teamed up with the Eipper company, a big ultralight builder in those days (now no longer in business) to distribute it in the USA, while Malcolm Lawrence's Aviation Composites of Thatcham in Berkshire, was to distribute it in the UK and Europe.
Lotus originally planned to build the basic structure themselves, with Aircraft Composites finishing and distributing it. It was then decided that the materials (epoxy glass) and the quality control techniques were not part of the Lotus core business, and Aircraft Composites agreed to take over the development and build, with the help of Peter Jackson's Specialised Mouldings (a well known firm in motorsport). Since Lotus was struggling to cope with the aftermath of Colin Chapman's death, the Aircraft Composites move into taking over the whole project was heaven sent. Instead, Aviation Composites used the design's features as a basis for a different aircraft. The company employed VariEze builder Ivan Shaw, and built a similar but much heavier version, the Mercury prototype (G-INAV), which incorporated various modifications from the Rutan design and had several problems with it.
The MicroLight was de-registered and returned to the USA in 1988, but it was lost in an accident in which both the owner and test pilot of the aircraft were killed. All in all, the Lotus aircraft was a nice dream that didn't get its proper chance. The nice twist to the story is that one of Lotus's former employees, Glenn Waters, was so taken by the whole MicroLight thing that he became the world's first kit builder of the Rutan Long-EZ's best derivative, the Berkut 360, and his own G-REDX, which incorporates many innovations taken directly from the Lotus Formula One cars, is considered to be the finest example of them all.
Population: 1 [N97ML, later G-MMLC and N7038W]
The Lotus engine
At the same time as the MicroLight was being developed, Lotus started designing a small lightweight 4-stroke aero engine, which would fix the inherent two-stroke problems of noise and gas-guzzling. (Ian Doble, the engineer who was given the task, went on to lead the LT-5 engine program, the Elan program, and has finished the Vector in Florida.) The engine was a brilliant concept - a modular monobloc design (crankcase half, barrel and head cast in one piece) which could be built as a two- or four- cylinder (25 or 50 hp). To keep the weight down, the castings were intricate with minimal fixings and parts count. The prop drive was off the camshaft to use the inherent 2:1 reduction drive (you need a big prop turning slow for efficiency, and a small engine turning fast for good fuel economy).
However, Lotus didn't have the sophisticated CAE systems that they have now, and the engine experienced severe torsional vibration problems. Lotus has one of the 4-cylinder engines on display at their factory—it is still a gem and sits proudly alongside the LT-5 engine and the 1.5 litre compound-supercharged F1 engine that Lotus was working on about the same time. Lotus were close to supplying the engine for use in target and reconnaissance drones (some flight testing was carried out) but it didn't happen. After further developement, Lotus got up to 150 hour durability (way below the hoped-for 1000 hour goal) about the same time that GM spotted that Lotus had a connection with the aircraft business. The engine project was closed down very quickly to prevent any possibility of aviation-sized product liability lawsuits. That was sad, because the world still needs a light, cheap, four-stroke aero-engine, and the Lotus is considered by some to be the all time best regarding 4 stroke ultralight engines. The Rotax is nearly there, but even Porsche failed with the PFM aero-engine based on their 911 motor.