They are getting crazy close to going supersonic. The next build will include swept back wings to help it punch through the sonic barrier. I wonder what a sonic boom would sound like when generated by such a small craft? And since it's going back and forth in such a small area will the sonic boom perceived by the guy flying it be constant or repeat with each pass? There are student built rockets that go supersonic but they do it in one direction and at extreme height. I see why they have college professors studying this.
Those chemical changes from electricity going into a battery or coming out of a battery are further bottle necked by extreme cold or heat. Here's another link to the type of battery in the video with a proper way to charge it, prevent it from being over charged and monitor it. https://youtu.be/bj7abaCrwvI One important factor about this type of battery is they do not like cold weather at all!
I was watching a very fast nitro powered RC airplane and had seen some very fast electrics and asked which is the fastest, nitro or electric powered? The answer I got was neither. Wind power beat them both and then I watched the clip he included. For others that have never heard of dynamic soaring there are some links in the description in the video and more in the comments for the video. https://youtu.be/MoaWlKC3wIM
I'll give you it's a slightly different compound that's less of a fire hazard than other lithium battery compounds but it's still not a battery that can't catch on fire from extended over charging. He's got that setup to charge at lead acid battery voltages and rates. Fix that as I mentioned earlier and it might be worth a shot. The fire proof bags are so cheap and light weight that I don't see any reason to experiment without one. Unlike a car you can't pull over and pop the hood at first sign of smoke. Since many of the 2 strokes run without batteries just fine I think they show more promise over an engine that relies on a battery. Magneto systems would be another safe platform to test these with.
If you take the "Fe" and the "4" out of the info on the battery you get "LiPO" and that's why I included a link to the Lithium polymer battery. Lipo is a common abbreviation for Lithium Polymer batteries. And yes I did see it in the video and instantly recognized it as an RC hobby battery. The title of the video even states it's a Lithium battery. He also mentions a protective case for the battery. He flies RC so he has played with these batteries like many of us in the RC world. Yes the device has a built in charger but he's not using it. Nowhere in the video did he plug in an adapter to the charging port on the device. He snipped off the original electronics that may or may not have been designed to prevent charging from an electrical system. I can't see the component names or I may be able to back engineer what he snipped off. I do know with a direct feed to his airplane charging system his power pack will be getting constantly charged from the alternator charging system. At the very least I'd put a cheap charging bag around the whole unit such as one of these: https://www.banggood.com/search/protective-battery-charging-bag.html
I think you will be fine with the industrial models. I didn't give a specific part number mostly because I calculated what I needed. I took the total weight of my motor, propeller, gear box, muffler and starter and added it up and divided by 4 to give me the static load for each bushing. Then I browsed through the sizes I needed until I found one with the weight and size requirement. Is that the right way? Maybe, maybe not. An airplane in a flight can pull several G's and a heavier rated mount may be needed. There's a range to these things so I guessed using the static weight as the low limit. I also think you could slightly vary the mounts with two of a different density to play with dampening sub harmonic vibrations from the propeller at low rpm's. If you guess too high you defeat the purpose of rubber mounts and the vibrations get passed along to the air frame. Did you notice the video on the "Lord" mount website that had a camera watching the mount in an aerobatic airplane? The G forces do come into play on these mounts. A camera may be handy in finding the best rubber shore number for our type of aircraft.
Those of us that fly RC charge our batteries in fire proof containers for a very good reason. I'm not saying NOT to use a Lipo battery but if I did I'd be putting it in a fireproof battery container. They have battery charging bags that are cheap and light and you could fashion a protective case easy enough. The charging system on a normal car or airplane is not designed for the special requirements needed to properly charge and maintain a Lipo. If the charging system is altered for a Lipo battery and a fire proof box added you might end up with a safe and reliable system.
The experts; the lab manager and store manager at the eye glass store I made glasses at swore there was no way to remove scratches from customers glasses. They were partly correct. My father was a watchmaker when I was a child in the 60's. People would bring in their watches to get new crystals put in because they were so scratched you could no longer read the dials to tell time. I heard him say 100's of times "You don't need a new crystal, I'll buff that out for you." And he did! He used jewelers rouge and a light touch. The glass lens he could apply more pressure but you can easily melt a polycarbonate lens and end up with distortion. While the eye glass place didn't buff customers prescription glasses, I often buffed out my cheap readers while working there to get a few more miles out of them. I melted a few pair too! Even a little buffing will change the prescription but with readers it's not a big deal. If I had to see out of them full time I'd have to agree that they should not be buffed to remove scratches. As far as the scratch remover kit were talking about, yes it will work. It will fix cd's and dvd's if the scratches are not too deep also. I've used plastic polishes for motorcycle helmet shields too to get a few more years of life out of them. If your new to the process I'd suggest doing the front and center sections last to give you time to practice on the less important sections. The drill attachment will work fast. It can destroy a window fast too. Heat is your enemy when power polishing plastics. Keep the tool moving to prevent heat buildup and clean the window a couple of times before you start. Any grit not washed off your window before you start will work against you and put more scratches in than your removing. I've often taken my regular jewelers rouge and a buff on a drill out to fix a headlight on a car that's dulled more white than clear. It fixes them right up. If you get carried away and distort a section, stop. You cannot fix it and any attempt to do so will only dig your grave deeper. That's about when I decide I need a new pair of glasses or a new shield on a helmet, a mistake makes up my mind for me. The cast material is far easier to buff than the extruded but you can bring either material back some. Don't try to get it perfect or you will run the risk of going too far. You will be surprised how much yellow you can buff out too.
I've worked as a machinist for decades and two of those years I made eye glasses for Vision 4 Less. We sold mainly two types of lens material and all the "experts" including the store manager and lab manager referred to them as "plastic" and "polycarbonate". I was the "old" guy that had a hard time teaching these kids in their 30's and 40's that I might know something about their field that they didn't know. They don't understand that "polycarbonate" IS a plastic! While their "plastic" lens were a lower grade material than the "polycarbonate" lens they are in fact both plastics. We have a similar situation going on in this conversation concerning "Lexan" and "polycarbonate" for windshields. For the record; they are both "polycarbonate" plastic. "Lexan" is a trade name for "polycarbonate" made by a specific vendor. The biggest difference in "polycarbonate" material from any vendor is if it was made by "casting" or "extruding" the stuff. To machine the stuff or bend the stuff or scratch the stuff all varies from vendor to vendor but cast verses extruded needs to be looked at depending on your application. I can machine it on a lathe or mill all day long if it's cast. If it's extruded it melts at a lower temperature and likes to stick to the tooling making it hard to get a good finish. I wish I could say "this is best" but the truth is "best" is a whole can of worms I don't want to open. For eyeglasses we used "cast" material. Most of your "shooter" glasses and safety glasses are "polycarbonate" material for impact resistance. Heat works for tight bends but depending on if it's cast or extruded, the amount of heat will vary. If you want a uniform thickness then you will chose one over the other. You want the cheapest one, you will choose one over the other. There's no one size fits all. Just like airplanes, one kind cannot do it all. Link here to a plastic vendor: https://www.acplasticsinc.com/informationcenter/r/what-is-lexan I'm not recommending them, it's the first link I found with info on Lexan for you. This site does not go into the difference between cast and extruded but you can find that online in many places too.
New or old the first thing I would check is static balance on a home made string and hub center prop balancing device. Second while not usually a problem but I'd also check tip tracking from blade to blade. Set up a board or pole or tall back chair next to the prop and tape a pencil or some other pointy device at the tip of the prop and move the blade around until the other blade comes by and see if they are tracking exactly the same. With a couple of marks of bright marker or paint on the blade tips you can also start the engine and observe the marks from the side of the plane to see if one blade flexes more than the other causing the tip tracking to be different. Some composite blades don't get manufactured with the same amount of resin and even if balanced one may flex more than the other. One blade dialed into a slightly different pitch will also cause the tracking to vary from tip to tip while under load. Probably not your problem but it's something you can check if you run out of options. Sometimes the tracking issues are blade related and other times it could be a hub that was machined out of spec. You can mark the hub and swap the blades from side to side in these cases and see if the tracking issues follow to the new blade locations. If it does it's the blade, otherwise it's the hub or gearbox.