Electrically- and Solar-powered Aircraft

To all concerned with electrically- and solar-powered aircraft

Since a couple of years the FAI Amateur-Built Aircraft Commission (CIACA) has been monitoring the developing movement of Electrically- and solar-powered aircraft. As initial result, preliminary definitions had been introduced into the 1996 FAI sporting code update. In the course of the recent 90th FAI General Conference in Rio an additional refinement has been applied in the sporting code; in the same occasion further discussions on this subject have taken place.

In particular FAI President encouraged initiatives aimed at promoting the development of these emerging categories of flying machines and the future organisation of proper competitions , possibly in the frame of the FAI World Air Games.

Reason of this message is that of informing all concerned with electrically- and solar-powered aircraft about the preliminary results achieved so far and the foreseen initiatives within FAI.

Some comments are also included, related to the technological trend of these new disciplines, collected from different sources.

All of this is also intended as a basis for discussion and contributions which will be welcome ( see subsequent point 4: specialised mailing list).

1) C.I.A.C.A. questionnaire on electrically- and Solar-powered Aircraft

First of all let me thank all those who contributed, either by replying to my questionnaire or by providing comments and suggestions, to the investigation carried out so far on the subject of electrically- and solar-powered aircraft.

The questionnaire's circulation has been as large as possible, involving approximately 60 people/groups in the world (hopefully most of all concerned have been reached...). Twelve replies have been collected so far. We expect that this figure will progressively increase once this second message will be circulated (to this aim the distribution via the newly established mailing list shall help ). A short summary of these replies has been reported in the meeting of FAI C.A.S.I. Commission in Rio and is hereinafter presented:


Number of persons/groups contacted: Approx. 60

Number of replies/contacts considered : 12

General comments:

There is a general agreement upon the need for some kind of "initial" definitions. According to the majority this need, in addition to be useful for opening the path to sporting competitions, is motivated by the necessity to make flight of prototypes formally feasible (some people suggest that weight limitations be applied, thus including these machines within the ultra-light group..).

In addition to electrically- and solar-powered aircraft/motor-gliders, also unmanned and airships shall have to be considered ; there are in fact around good examples of such kind of flying machines, the record breaking of which shall have to be subject of proper rules.

It is an almost general opinion that actual competitions are still a few years ahead, particularly for those "solar-powered" machines. The economical issue, in this case, heavily affects the development of the movement and only those groups which can afford significant budgets are in a position to proceed expeditiously (somebody is suggesting that some sort of grouping is made taking into account the installed panels efficiency level (and/or covered surface), thus differentiating in terms of money invested ...).

The category of pure electrically-powered aircraft ("motor-gliders"..) is obviously considered the most mature one, being more economically affordable and therefore suitable in a shorter time for actual competitions.

This is also confirmed by the fact that, after the prototyping experience carried out in Italy with an electrically-motorised homebuilt motor-glider (Monerai), in Germany the electrically-powered light motor-glider "Silent AE", powered with a 13 kW electric motor performed its first flight in Aachen last August. According to "Fliegermagazine (Nov.'97") the performance was quite interesting, with a 2.4 m/s climb rate and a climb up to 500 m. It is now being certified and a small series is being produced to be put soon on the market. The manufacturer is also considering the possibility of organising a preliminary competition for these machines (expected a first series of 10 units).

Furthermore recently interesting developments have been performed in the field of batteries, which seem to offer very good power-to-weight ratios. An electrically-powered motor-glider is today feasible !

The German glider manufacturer DG Flugzeugbau GmbH have presented on the web a very interesting proposal about a possible DG-800E 18 m high performance glider, which might be put on the market in an electrically-powered version if it will be understood that the market is actually interested ( in their message in Internet they, in fact, ask for comments... see www.dg-flugzeugbau.de/Elektroflieger-e.html).

There are no doubts that a precise definition for this category is more urgent.

Among the questions to be considered are the following:

  • shall autonomous take-off be required ? (In this case a very limited "spare" energy would remain on board, at least if one considers the today available batteries performance)
  • what about winch and/or aero-tow launch? (In this case one could "save" the energy for being "assisted" to get home in case of necessity...)
  • shall the kind of batteries (e.g. Ni-cad) be specified for classes/competitions ? (it is obvious that, leaving open the choice of type of batteries would give advantage to those able to spend a fortune for buying very advanced (light, durable and efficient ) batteries.
  • in perspective, shall other electrical accumulation means be allowed or shall they be grouped in a different category/ies ? (e.g. fuel cells, fly-wheels integrated with elctr.engine...)
  • could solar cells be considered just a means of increasing the batteries duration for an electrically-powered aircraft(or motor-glider)?

My personal opinion is that something could be done with the aim of speeding up also the process of developing a class of solar-powered aircraft (I would rather say "motor-gliders") which could be suitable for sporting competitions and actual entertainment not too later than the "pure" electrically-powered ones. In particular, instead of requiring level flight under sun radiation power, a solar-powered motor-glider would be a machine capable of taking-off autonomously after charging (on ground) through sun radiation its batteries (it is unlikely, for long time, that take-off and climbing without help of batteries will be possible, particularly if a "normal weight" pilot were required) ; flight after take-off and climb would be either a simple gliding flight or a sun-power-panels assisted flight (this could be a designer’s choice; in both cases there are advantages and disadvantages depending on the weather conditions).

If the requirement of level flight under a pre-defined sun-radiation were maintained, a significant economical discrimination would exist between those who can afford high efficiency (e.g. gallium arsenide) solar cells and those who can not. At the same time it would be arguable which is a "correct" sun radiation reference level. (For instance, the reference level of 500 watt/m2 prescribed by the "Berblinger prize", is such that no aircraft today would meet the requirement ; in practice, according to this rule, Icare and Sunseeker would not be classified as "solar-powered aircraft")

The following questions, therefore, shall be replied to:

  • could solar-powered aircraft (or ,better, motor-gliders) belong to the more general aforementioned category of electrically-powered ones ? (may-be a sub class of them ?).
  • shall level-flight be a firm requirement and reference be made to a well defined sun - radiation level ?
  • If the previous requirement is not applied, which criteria shall be used to define a solar-powered aircraft/motor-glider ? (in fact any aircraft fitted with even a single solar cells on its surfaces would be a "sun-powered one"... )
  • somebody proposes to differentiate between those solar-powered aircraft fitted (also) with batteries and those which are not (it has to be kept in mind, however, that if no batteries are fitted, take-off and climbing phases would result quite problematic if a 90 Kg pilot is considered and standard airworthiness requirements for structures are applied).

2) Paper presented in the XXV OSTIV Congress in Saint Auban, with the title: "Electrically- and solar-powered gliders: Do they require the definition of new FAI classes?"(P.Duranti)

The paper presented a discussion mainly based on the result of the aforementioned questionnaire , with several considerations by the author. Aim of it was to provoke discussions and comments from anybody interested, in order to make the debate more lively. The paper shall be published on "Technical soaring" (OSTIV Magazine).

3) FAI Sporting code definitions for Electrically- and solar-powered aircraft

The initial definitions, introduced for the first time in the Sporting code during the 89th FAI General Conference (1996, Bled, Slovenia) have been modified based on discussions held in Rio (which referred to the questionnaire’s results too), in the course of the 90th FAI General Conference (Rio, Brazil).

The philosophy followed has been that of leaving in the General part of the Sporting code just very simple definitions, transferring to other paragraphs (still to be developed) the relevant details.

At present, therefore, the following definitions are present under "Class C: Aeroplane":

  • Electrically-powered aerodyne - one which can be sustained in level flight in the atmosphere using solely an electrical motor(s).
  • Solar-powered aerodyne - one which can be sustained in level flight in the atmosphere using solar energy impacting on its airframe as its energy source.

The above definitions should be read very carefully; in fact they imply, for instance:

  • that Solar flight is a subset of electrical
  • that at present no restrictions are applied to take-off and climb phases/means
  • that "solar energy impacting on its airframe as its energy source" can also be stored (e.g. on ground) and utilised later-on in flight...

4) Dedicated FAI mailing list

Any comment to the aforementioned information are of course welcome. In fact we hope that all concerned with electrically- and solar powered flight will feel motivated to further contribute in these discussions, regardless whether they are interested in aeroplanes, motor-gliders, unmanned, airships etc.

In order to make this exchange of opinions more effective, a dedicated mailing list has been established. Click here to subscribe to the list.

Please pass on this message to any person/group that you are aware of, involved in electrically and/or solar-powered aircraft, suggesting that they subscribe to this mailing list.

We will monitor all the messages circulated and, whenever necessary, will post the results of any FAI discussion/initiative on these subjects.