Showing posts from April, 2021

Facebook group Solar RC Airplanes

  I created a Facebook group called Solar RC Airplanes .  I am hoping to find other people interested in this topic.   If you are and use Facebook please join that group.

Nature's Flyers Tricks For Efficient Travel Over The Ocean

  Nature's flyers (Birds, bats, and insects) have some tricks they use to travel over the ocean without using much energy.  Some travel long distances over the ocean while hunting (sea birds) and others mostly for migrations.   I am collecting some of the tricks nature's flyers use to save energy here with the idea that maybe drones could use some of these eventually. 1. Dynamic Soaring         By moving back and forth between two layers of air that are moving at different velocities an Albatross can soar for long distances over the ocean.  The video below explains how it works.           This trick is a bit like sailboat.  A sailboat has a sort of wing in the air and then a sort wing in the water (keel) and gets energy from air while the keel keeps it from being pushed downwind.   An Albatross gets energy out of the air when it is up high and then pushes off the low air to keep from going downwind.  The Albatross is very efficient in that it uses the same wings for both jobs. 

MPPT in iNav software

  Solar panels produce the most watts when operated at some ideal voltage called Vmppt. Normally people use special hardware called an MPPT controller to draw power from the solar at that voltage and then convert it to the right voltage for a battery. We have worked out a program for iNav so that this extra hardware and weight won't be needed.   The idea is to adjust the throttle higher if the voltage is higher than ideal and to lower it if the voltage is lower than idea.   Since we already have a computer onboard that knows the battery voltage and controls the motors, we can get things operating at the ideal voltage just using some software.  This will help keep weight down on solar airplanes we make.   We also save any conversion losses or power limitations of the MPPT hardware.   You can see this in the video and the picture after that.     Here is a shot of the program: A shot of the supercapacitor, flight controller, volt meter: The solar out the window: The power mete

Putting Solar on Opterra 2M

  The manufacuter of our F2X5S solar panels, , said they use Super Glue (with Cyanoacrylate) to glue them on foam planes.   The nice thing is it dries really fast.  We got some Gorilla Super Glue.   Here is a video the company made about how to attach panels to a foam wing and wire them up: To fit the solar panels on our Opterra we needed to remove some bumps on the top of the wing and cut a bit off the edge of the ailerons.   To remove the bumps we used a couple guides and a small hotwire as shown below: We cut out a piece of the aileron and glued it in the old gap to make end section fixed to the rest of the wing, so there was a bit more room for the solar panel. We taped one edge of the solar panel so it could act like a hinge and make the solar panel in the right spot as we were rushing to do the glue.   We lifted it up, put the glue on the foam close to the hinge side, then folded down the solar panel and held it for a minute.  Then we lifted up a bit and put

Bird Wingtips

  There are birds, like this Great Blue Heron, that have several separated feathers at the wingtips.   This is a bit like having propellers pushing the air down at the wingtips.   It helps prevent higher pressure air below the wing from sneaking around the end of the wingtip to the low pressure area above the wing.  Click pictures to enlarge them.     Thanks to David Stokely for the two pictures above.  A few other pictures showing this type of wingtip. This video shows some large birds with this type of wingtip.

Wingtip Propeller Theory

  There have been a number of studies of how efficient putting propellers on the wing tips would be.   We will try to collect some good ones here.   Below is a video of a simulation: Below is a list of papers:   Analysis and Design of a Small-Scale Wingtip-Mounted Pusher Propeller   Aerodynamic Analysis and Optimisation of Wingtip-Mounted Pusher Propellers  Experimental and numerical study on wingtip mounted propellers for low aspect ratio UAV design If you want to place solar panels on a wing, it is easier to have a rectangular wing.  I think for this shape wing the wing tip losses as a glider would be more severe and so having wing tip propellers makes for a bigger win than normal shape wings.

Solar Panel Unboxing

  We got our solar panels from !   They were very well packed and all seem fine.  The cost was $1.90/watt.  They are so small and light that express shipping from Taiwan to the USA was very reasonable.   They also included 2 MPPT boards and some wire good for solar panels for free.  The solar panels are about 15 inches by 5.5 inches. We got 18 solar panels and the total weight for all 18 was about 528 grams or 29.3 grams per panel. The side view showing how thick a stack of 18 solar panels is: The back of one panel showing wiring: These panels are their F2X5S panels.   The MPPT voltage for these is 5.72V and at that voltage it produces 2.04 amps for a total of 11.66 watts. Next to get them on a plane and into the air.   These seem like a very good product for solar RC airplanes.   Very happy with them so far.     We will probably put 4 on an Opterra (46.4 watts) and then 8 on a custom airplane (93.3 watts).

First iNav Build - Opterra 2M

    In working toward solar airplane development we first want to try out iNav.   We have chosen the following set of hardware to do this:    1)  Airplane:  Opterra 2M    2)  Flight controller:   FuriousFPV F-35 Lightning    3)  Radio/FPV/Camera:   DJI FPV  V1 (Remote Controller, Goggles, Air Unit)   Below are some notes that we think would help us do it next time and might help someone else get through this process. For each of the 3 parts, DJI Goggles, DJI Remote, DJI Air Unit, we had to get them connected to the computer and registered with DJI before they would work.  The F-35 has less soldering than most fixed wing flight controllers but it does have some.  The F-35 has an online manual .  Here were the wiring instructions for DJI.  Note that Air Unit is NOT the same as DJI Ocusync but they use the same wiring picture for the cable to either. And here is our real result.  It is only soldering 6 connections, but I look forward to a flight controller where I don't need to do a