Hello Everyone,

I've been working on a scratch built, solar harvesting, UAV design at the University of Michigan for the past 2 years. Over those two years our design has matured from something that shouldn't be allowed to fly, to a very unique, sophisticated airframe. Our current design has a predicted endurance of 18 hours during a typical northern Michigan summer. This number should rise if we travel south. We have been working with MIT Lincoln Laboratory to deliver this aircraft to them where they will then outfit it with a payload.

Our goal is to complete two airframes by the end of May, with sufficient flight tests having been done to accomplish a long endurance flight in June and even possibly set some records. I won't go into too much detail about the history of the project as most of that information can be found on our website (http://solarbubbles.engin.umich.edu/...s/index-2.html)

What I do plan to do with this thread is to publish updates every few days on our build progress, a description of some of our unique weight saving construction techniques, and some of the coolest pictures and videos we take. Below is a short description of our design.

Wings

Our wings are of the built up, rib and spar variety. Our spar is constructed in a similar fashion as most F3J gliders, carbon spar caps on top and bottom of a balsa shear web. Carbon fabric is wrapped around the spar to secure the spar caps in place. This results in an extremely stiff and extremely light main structure. Balsa ribs are slotted on to this spar using a squaring jig. We carry 10 6S lithium ion packs in the leading edge of our center section. This forces the C.G to be remain forward with a full payload of batteries. The trailing edges are reinforced with thin carbon panels to carry some torsional loads as well as to protect from hangar rash. Since solar panels will cover the top of the wing, there is no monokote on the top surface to act as a torsional element. The loss of torsional rigidity is compensated for by the carbon spar and the carbon trailing edge. Aileron linkages are completely internal resulting in a fairly clean wing. Solar trays are removable and will be replaced with dummy trays for the majority of flight testing

Fuselage

The fuselage is a keel and bulkhead design. The skin is only used as a fairing in the rear of the fuselage and carries some of the load in the nose section. Kevlar live hinges are used in the fuselage skin to provide easy access to the electronics within. Shelves are installed in the fuselage to support the avionics. Using the weight saving keel and bulkhead design, we were able to greatly reduce the weight of this fuselage compared to conventional bladder molded designs.

Tail

The tail components are largely comercial off the shelf. For the horizontal and vertical stabilizers we are using tail surfaces from the Icon 2 F3J glider. The tails promise to provide reduced drag and greater controllability due to larger surface area and a better airfoil over most similar designs such as the Super Ava Pro. The tail boom was provided by Troy Lawicki, a well known builder in the sailplane forums.

More details will follow, including detailed performance parameters (once I gather the information) and descriptions of some of our unique weight saving construction practices.

Feel free to ask any questions about the development of a solar UAV including the power harvesting system, charging system, autopilot, drivetrain and construction techniques. Be gentle to my baby

Reserved

Here are some of our videos!

Solar Sight Highlights (1 min 29 sec)

Solar Sight 1.9 Onboard Camera (10 min 2 sec)

Solar Sight 1.9 Maiden Flight (14 min 35 sec)

Have you reached a point where the energy generated from the solar panels exceeds the draw of the motor? Very neat project.

We're getting there. The last airframe we flew was over built and over weight. This time we are shaving out enough weight to get the wing flying at its peak performance weight. We used an AXI 2820 with a Mega 5:1 gearbox and that averaged around 150 watts which is about 30 watts more than we collect in Michigan.

Currently we are wind tunnel testing a Lehner 1015/40 and 1520/40 with a Reisenauer Micro Edition gearbox. We expect one of these to reduce our power to 60 watts which will allow us to charge on sunny days. Unfortunately this is still not enough to fully charge the packs and we would have to come down after 18 hours (according to our models). We will see how well this models compares to reality when we attempt our summer endurance flight in June.

Thanks for the info.

When the plane is flying autonomously are you going in a specific pattern like a 1 mile radius circle?

Currently the plan is for 0.25 mile circles or so. The project was focused on putting a gimbal up in the air and orbiting around a point on the ground. That isn't to say our autopilot won't be able to do waypoint to waypoint flight paths, return to launch, ect.

The biggest challenge is getting our PCB's working correctly which right now is not always the case. If we get too far behind with debugging those issues we will use a black box autopilot like Arduplane just to do some endurance flying.

Hey everyone,

Today we spent some time testing motors in the wind tunnel and hingeing the aileron. We molded some solid core ailerons using a hot wire cutter, foam, 2 oz spread tow and a vacuum bag. The aileron was sized for the wing tip and then hinged using a kevlar live hinge. The hollow built up structure makes it easy to install and entirely internal drive for the aileron. This makes for a very slick wing.

A selection of Lehner and AXI motors are being tested in our wind tunnel to determine the most efficient drivetrain using AeroCam folding props. Currently we have tested the Lehner 1520/40 with a Reisenauer 5:1 Micro edition gearbox and are finding very promising results for charging battery packs during well lit days.

A more detailed update to our website will follow soon.

-mike

Here's a time lapse video of the tip section being assembled.

Built-up Tip Section Wing Time-Lapse (U of M Solar Drones Team) (3 min 42 sec)

Fascinating project.Did you consider a pure wing at the design stage?

A flying wing was the groups first design prototype back in 2006. Ever since then the idea has been tossed around but in the end gets cut out of the running due to more literature and data about conventional setups. Theres definitely something to gain from losing tail surfaces and a fuselage in terms of drag, but it limits how much internal volume we have for electronics.

The current plane that I have been posting about uses up all of the fuselage volume with components that are either too tall or inconvenient to be mounted inside the wing. After running revised performance parameters through a model developed by Lincoln Lab, we are looking at breaking 20 hours of endurance, going as high as 24 hours.

Subscribed

Totally subscribed! Very cool project. Keep the updates coming please.

-John

Very cool..

Tim

Originally Posted by Lost Oracle

The current plane that I have been posting about uses up all of the fuselage volume with components that are either too tall or inconvenient to be mounted inside the wing. After running revised performance parameters through a model developed by Lincoln Lab, we are looking at breaking 20 hours of endurance, going as high as 24 hours.

Flying wings can still have a fuse. Check out the Nurflügel forum

http://www.rcgroups.com/nurfl-gel-762/