We often get questions and requests for technical support from pilots who are interested in attaching some form of motor system to one of our hang gliders. The following is intended to provide pilots with answers to their questions, to the best of our ability.

The format of this information is a series of simple statements in bold face type, each one of which is then further amplified with additional explanation. If you’re in a hurry, read the bold type statements. If you want a more in-depth understanding, read everything.

The information below is NOT provided for the purpose of protecting us from liability, but rather for the purpose of giving our customers accurate and important information. Please take it seriously.

Wills Wing does not recommend that any motor system be used with any Wills Wing hang glider.

All Wills Wing hang gliders have been designed, developed and tested for foot launched gliding and soaring flight. None of our gliders has been designed, or tested with any consideration of the use of a power system. We cannot, therefore, recommend the use of any such system with our gliders.

Wills Wing does not provide any technical support for the use of any power systems on Wills Wing hang gliders.

Beyond what we have written here, we cannot answer your questions about attaching a power system to a hang glider. We would like to be able to provide unlimited technical support on any subject to all of our customers, but in practical terms, it simply isn’t possible with the resources we have.

We don't have any specific information about what might be required to attach any type of  trike to any of our gliders. The manufacturer of the trike system may be able to answer questions of this type. If a manufacturer of a power system chooses to take the position, based on their experience, that the use of their power system on one of our gliders is appropriate and airworthy, then to the extent that you are willing to accept their authority as the designer, and manufacturer of the entire system, including the hang glider, and place your faith in their qualifications in design, engineering, developmental flight test and product support, you can give whatever weight to their opinions you choose.

We don’t have any specific information about attaching or using a Mosquito harness to any of our gliders, other than the common general information that it is necessary, according to the Mosquito manufacturer, to remove any part of the keel which extends more than 1200 mm (47 inches) behind the hang point. We do not have the resources to, and will not provide answers to questions about which of our gliders would require relocation of the rear wire attachment, or modifications to the sail in order to comply with this, or what other problems may or may not arise in attempting to use a Mosquito or mosquito-like harness.  In very general terms, we do know that with regard to the 1200mm requirement, the Falcon 195 and 225 don’t work, and that most high performance gliders do “work” in the sense that the rear wire junction is less than 1200 mm aft of the hang point. Because requests for custom parts require an inordinately large allocation of technical support resources to process, we do not and will not provide custom wire sets, or custom keels, or sleeving “kits” for  “Mosquito modifications.” 

If you decide to put a motor package on a Wills Wing hang glider, you have made the decision to become both an aircraft designer and an experimental test pilot.

It is our opinion that it is not possible to develop a motor package separate from the wing to which it is to be attached, and end up with a tested, proven, airworthy flight system. Unless a full engineering study and developmental flight test program has been conducted specifically on a given model hang glider fitted with a specific motor package, then, in our opinion, the combination of that glider and that motor package is a purely experimental device of no known level of airworthiness. Please note that a simple flight test, as in "Yes we have flown the xxx model hang glider with the yyy model motor system and it flies fine," does not qualify as a developmental flight test program. Nor does the experience of five, or even twenty other people who may have flown a given glider and motor system combination, prove anything meaningful about the airworthiness of that combination. Please note that this is not idle or hypothetical speculation on our part. We have personally witnessed numerous real world cases of seriously dangerous results of incomplete engineering or inadequately tested systems in the application of various power systems to hang gliders. If you install a power system on a Wills Wing glider, you have chosen to become an aircraft designer and an experimental test pilot. We support the right of anyone to choose to become a designer and test pilot. (That is, after all, what we chose to be.) However, we are very much opposed to people becoming designers and test pilots when they are not aware that this is what they are doing.

Wills Wing cannot provide any meaningful information about what modifications may be necessary to a hang glider in order to safely use a motor system.

There are many possible considerations regarding the effect of using a power system on the airworthiness of the glider, including possible effects on static and dynamic stability, damping, control response, and structural integrity. These effects can be very complex, and in some cases difficult to evaluate, and we have not made any attempt to conduct any such evaluation.  Most pilots seem most concerned with the issue of whether the glider is strong enough to carry the extra weight of the motor system. In general, while this can be a concern, it is probably the least significant concern, since certified hang gliders are typically designed to a 100% structural safety factor when operated within the normal placarded operating limitations. There may be important structural concerns that relate to changes in the manner in which the glider is loaded, or to vibration, fatigue, or other factors introduced by the application of a motor package. Pilots interested in using trikes, for example, usually ask how strong the keel is, and how much sleeving do they have to add to the keel to make it strong enough. This is a question for which no simple answer exists, and any answer at all to this question, even if  “correct” would carry the implication that addressing this concern would address any and all potential structural issues, while in truth, it does not.

Proceed With Caution

All of the foregoing is not to say, or imply that it is not possible to use a trike, or a Mosquito type harness on a hang glider safely. Nor is it to imply that there is no value in the experience of someone else who has used such a device on a hang glider. It is to say that such experience has value only to a very limited extent, unless and until it reaches the level of a full, competent, professional developmental testing program. It is to say that the enterprise of aircraft design and testing is, even for qualified professionals, measurably more hazardous than is the normal use of a fully tested aircraft system.

If you decide to use a power system on a Wills Wing glider, please proceed with extreme caution, and get as much information about the proper use of the system as you can before you try to fly with it.