The glider now has 12 pounds of lead shot and epoxy added to dead space in the very end of the tail boom.

My initial estimate of volume indicated that I could add 8 - 10 pounds this way. I'm pleasantly surprised, and I didn't make a chocolate covered mess of things as I was pouring this goop into the tail.

I need to add a few more pounds to the tail. Phase two of this project will use lead plate, bolted to the vertical fin spar. (I need to unroll the 1/4-inch plate first, then develop a template to cut the lead.)

I could not add the epoxy/lead shot mix all at once because of the exothermic reaction of epoxy. When mixed epoxy is in a thick blob (instead of a thin layer), it generates enough heat to warm itself...which accelerates the chemical reaction...releasing more heat...further accelerating the reaction.... I have seen epoxy smoking hot because of this, so I added a bit, waited a half hour, checked temperature with an IR non-contact thermometer, added a bit more when it was clear that the exotherm was only very mild, etc. That took a while, but turned out well.

I note that Roto Metals has a discount on some 1-inch lead plate. Get your fork lift ready. No free shipping!

https://www.rotometals.com/lead-sheet-plates/sheet-lead-1-64-lbs-sq-ft/

#AvGeek #Aviation #ElectricAircraft #Homebuilt #Glider #DIY #EAA #Ballast #Math #Density #Exothermic #Chemistry #Thermodynamics #Lead #Epoxy

The glider's 3rd battery now has a sewn carrying handle that makes it easier and safer to install in the crowded battery box.

Next, I need to devise a retaining system for it and finish the wiring harness that connects it to the rest of the system.

Progress will slow for the next day or two because the things I have ordered (epoxy, lead shot, etc.) will be delayed while we ride out a snowstorm that should end tomorrow.

#AvGeek #Aviation #ElectricAircraft #Homebuilt #Glider #DIY #EAA #Safety #Battery #Sewing

Where does the 'typical' glider battery go in this electric glider?

In the battery box, next to the high voltage motor batteries.

My final decision on this battery location depended on the weight and balance measurements I made last week. It shows that I need to add weight to the tail...so, the heaviest batteries are full-aft in the battery box, and this 3rd battery goes in front. All of this is aft of the tail in the fuselage/tail boom.

I now need to sew some sort of sack and carrying handle for this battery. It's not a heavy battery, but I want a secure way to handle it as I install/remove it.

Above my hand is a black/gray marbled-pattern object. It's a yoga block. That semi-dense foam will be cut to size to take up any dead space along the sides of the battery box to prevent the batteries from banging side-to-side if the other retaining systems fail.

#AvGeek #Aviation #ElectricAircraft #Homebuilt #Glider #DIY #EAA #Safety #Battery

My glider will use a tow rope that is too strong. That rope, when under maximum pull, may damage the glider.

I need to install a weak link as a mechanical 'safety fuse'.

Here is one weak link system I can use:
https://wingsandwheels.com/tost-weak-link.html

But which weak link is appropriate for my glider?

Federal Aviation regulations require a tow rope (or weak link) to have a certain breaking strength with regard to the maximum operating weight of the glider:

"The towline used has breaking strength not less than 80 percent of the maximum certificated operating weight of the glider or unpowered ultralight vehicle and not more than twice this operating weight."

https://www.ecfr.gov/current/title-14/chapter-I/subchapter-F/part-91/subpart-D/section-91.309

To complicate matters, my glider can carry 400 pounds of water ballast. When I'm flying 'dry', I would prefer to have a weak link that is just strong enough for the dry glider, and when flying 'wet' I would prefer a (somewhat stronger) weak link appropriate to the heavier operating weight.

See the second graphic, which shows which Tost weak links I can use in the dry or wet ballast condition.

I will start out getting the weakest weak links allowed (green, yellow, and white) and see if that launches me well without premature weak link breaks.

Pro-tip. Try not to lift the rear end of the ground launch car.
https://youtu.be/kd9QxRPb3hk?t=33

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