The Daedalus Project
Pilot Frank Scarabino got his breath back after the prize winning flight of Monarch on May 11th 1984, the Monarch made a few more flights and was then displayed in the Museum of Science at Boston, Mass. Then they all wondered "What next ? " Some of them had helped to make the last desperate attempt to get BURD to leave the ground. Many had been involved with both Chrysalis and Monarch or with all three machines. BURD could no more fly than could a caterpillar. They had been through the "Chrysalis" stage and on to the prize winning butterfly stage of the Monarch. What could follow that ? The next stage above emulating real living creatures must surely be nothing short of emulation of the gods, or the mythical heroes of ancient legend who consorted with them. The archetype of mythical fliers were the father and son team of Icarus and Daedalus. Could they possibly have crossed the Aegean Sea then ? Could it be done now ? For a year, they asked this question. Then they decided to find out for real.
May 1984 to April 1985 By the end of May, five of the Monarch team, Juan Cruz, Mark Drela, Steve Finberg, John Langford and Barbara Langford were studying charts of the Aegean and starting to calculate what sort of plane would be needed. They concluded that if the flight could be made, it would not be done in the same sort of frantic rush as was used to get Monarch into the air, and it would not be done using the simple technology of MIT's three previous machines. Maybe, it was felt, it could not be done at all, and therefore it was proposed that a year be devoted to a feasibility study. In February 1985 the Smithsonian Institution gave the group some initial backing on the basis of this proposal.
PHASE 1 April 1985 to April 1986 Feasibility Study The official start of the Daedalus project with students at MIT making a preliminary design. The only major difference between this first design and the eventual aeroplanes was the propeller position which was shown at this stage as behind the pod. The classical Greek texts were studied in an attempt to pinpoint the route of Daedalus and Icarus. A trip to Crete set up weather stations and made contact with authorities. Efforts were made to get further sponsorship. In the group's study of the likely power available, it was realised that up till then all experiments on the power that a human can output had not recorded the weight of the person producing it. Clearly a choice of pilot will be based, amongst other factors, on both power-output and weight.
STANDARD FOR MEASURING POWER REQUIREMENT
Drela showed that if an airframe has half the weight of the pilot, then a reasonable approximation, within the range of practicality, is that the power needed is directly proportional to the weight of the pilot. Therefore the parameter most relevant to pilot physical fitness is power-output per weight. Drela chose to quantify this in watts per Kg. This value could be expressed in ft lb/sec per lb weight. This reduces to ft/sec (implying 1g conditions). One could then get a feel for the magnitude of this parameter by comparing it with, for instance, how fast one can run up stairs. This is readily measured in ft/sec and is also equal to the person's power-output per weight. Watt-units become relevant if there is electrical-energy-storage. As a result of the Daedalus project, watts/Kg has become the standard measure of HPA power-requirement. In April 1986 the group decided that a crossing of the Aegean was possible, but that technology would need to be developed, and that a prototype aeroplane would need to be built to determine the form of the final plane.
PHASE 2 April 1986 to April 1987
Michelob Light Eagle With sponsorship from Anheuser Busch Inc, makers of "Michelob Light", construction started on the Eagle. An Eagle is one of the trade marks of this company.
Mark Drela had written the program XFOIL which enables the design of aerofoils and which can accurately predict the performance at any Reynold's Number. It is actually superior to a wind-tunnel test of a proposed section, because tunnels suffer from turbulence and interference from the tunnel walls and model supports. A series of sections was produced to suit the varying Reynolds numbers along the wing due to wing-taper.
A computer-driven foam-cutter was built, based on a hot-wire stretched between the pen-holders of two plotters. This was used not only to cut the ribs, but to cut the nose skinning panels from solid blocks. The wing sections never existed on paper, either as lists of numbers or as drawings; the information came out of the design program onto disc, and this guided the cutter. The spar of the MLE (Michelob Light Eagle) was three tubes aligned vertically. This scheme was abandoned for the final Daedalus design where the more usual single tube was used. Construction of Light Eagle took 15,000 hours work by 18 members of MIT.
PILOTS SELECTION, TRAINING & TESTING
Because of the sheer distance to be travelled on the cross-Aegean flight, pilots had to be selected on athletic stamina, based on a carefully set up test which measured heart-rate at 70% maximum oxygen uptake during prolonged exercise. Being athletes rather than pilots meant that they needed to be trained to fly. Many other projects, faced with a plane with a high power-requirement have asked the experienced pilot to step out, and asked a cyclist to step in - with disastrous consequences. On the Daedalus project the quality of the flying-training, and the piloting-ability acquired by those that flew the three aircraft,(MLE, Daedalus87 and Daedalus88), is evident in that in all the flights made there were only two crashes, both in local weather conditions against which no amount of experience would have availed. Like most HPA, both Eagle and Daedalus are single-seaters, and a flight simulator was built to familiarize pilots. Other than on the simulator which had the same seating as the aircraft, the pilots kept physically fit by training on upright unfaired bicycles.
A special drink was developed by Ethan Nadel to refresh the pilots during flight. Nadel calculated how much fluid, glycogen and sodium would need to be replaced per hour, and found that no available drink would provide this. His own concoction was tested by the pilots on the ergometer and all who tried it could keep up a sufficient pedalling rate for six hours, except one who gave up after four hours because he had been sitting on the uncomfortable seat of the rig long enough, not because his legs were tired. It must be mentioned that this was done in the spirit of engineering in order to find a satisfactory solution to a problem, not as pure research, since no comparative tests were done with other drinks.
JANUARY 1987 TEST FLIGHTS
The Eagle first flew in October 1986 at Hanscomb Field. The wingspan was then increased to 114 ft (34.7 m) and the first series of Michelob Light Eagle test-flights were done at NASA Dryden during January 1987. On January 22nd with Glenn Tremml at the controls the distance record previously held by the Gossamer Albatross was reset at 36.5 miles (58.7 Km). The World Distance Record for a female pilot was set at 10 miles (16.1 Km) by Lois McCallin, in 37 minutes 38 seconds. McCallin's flight also established Duration-Female and Closed-Course-Distance and Closed-Course-Distance-Female records recognised by the FAI.
But the main purpose of these January 1987 flights was to gather data to guide the design of Daedalus itself.
To discover whether the flow on the wing surface was laminar, the team used the following technique. Immediately prior to flight, the wing surface was painted with a powder/liquid mixture. As the liquid dried off, the type of flow could be detected by the streaks that remained. This was photographed during or immediately after flight. On the Eagle it was seen that the flow was indeed laminar in all the areas expected, including at some points on the lower surface where the Melinex had been deflected up to touch the carbon fibre spar, but not at the wing-tips. This turbulence at the wing tips was attributed to the coarseness of the texture of the foam skin-panels on the relatively sharp leading edge. Accordingly, a denser foam,(pink-coloured), was used for Daedalus.
The pilot's heart-rate and breathing-rate were recorded during these flights and results confirmed those obtained on the training-rigs and the simulator.
Attempts were made to determine how much power was needed to fly Light Eagle. These were not very conclusive. It is notoriously difficult to use gliding angle as a measure, as any slight upgust will affect the results. The other method used was to fit a strain gauge to the propeller shaft, and use readings from this in conjunction with recordings from the airspeed indicator and altimeter to determine power-required. Altimeter readings were necessary so that the power absorbed by any height increase during the test-period could be subtracted to obtain the net power for level flight. This system gave consistent results. Surprisingly perhaps, it even gave fairly consistent results when the mean height was varied between 10 ft and 25 ft (3 m and 7.6m). The best measure of required-power still seems to be the subjective estimate of pilots, backed up by the records of their heart-beats during prolonged flights after the effect of take-off on heart-rate has subsided. This can be quantified as a power value from the records of each pilot's performance on a ground-rig on the same day. One snag with this system was discovered later, when on any pilot's first Daedalus flight, there was an increase in heart-rate which was due to the excitement of flying the new plane.
An attempt was made to make an autopilot, as had originally been envisaged for Daedalus. This did not prove possible because neither the artificial horizon display nor the sensors ever showed the degree of reliability necessary for autopilot operation, possibly because of a buildup of an electrostatic charge on the aircraft as it flew. This meant that the crossing of the Aegean would need to be made in daylight when there is more wind and turbulence.
PHASE 3 April 1987 to April 1988
The Daedalus airframe was considerably lighter than Eagle because it was designed to a lower load-factor, 1.75g instead of 3g, and because a higher grade of carbon was used for the spar. There were no ailerons on Daedalus, whereas on Eagle the tip 12 ft (3.7 m) had rotated. This more than offset the slightly heavier wing-skinning foam used. Parts for two Daedalus airframes were made simultaneously.
The United Technologies Corporation backed the project with $500,000, and there were many other sponsors.