Mjolnir

Introduction:

This is another 600mm class mini wing. The frame from the strawberry strudel was simply amazing as it was able to take hit after hit without breaking down. I took all the frame construction concepts from that wing and doubled down on it to make an even stronger (albeit heavier) frame. The shape is the same as a DW mini rainbow, but with more sweep, but less so than the Strawberry strudel. The reason I needed an even stronger frame was because this is going to be the next class up of wings for me that are going to be using more powerful motors capable of producing 1kg+ of thrust. This is going to open up a new chapter for me in fast wings, hence I'm naming it after Thor's hammer (fast and heavy).

Components: (~$40)

• Dollar tree foam board & different size bamboo skewers & Duct tape & packing tape & gorilla glue & hot glue
• 2x 9 gram servos (don't want to mess with anything less powerful) & piano wire
• Cobra 2206 2100kv motor with 6030 BN prop
• Sunrise model 20amp ESC Little Bee 30a esc & 3amp bec
• Battery velcro strap
• DSM2 micro receiver

Conclusion:

The build was fairly straight forward as usual. The frame itself only took a couple of hours to make. Most of the time was spent performing thrust tests with different ESCs. Unfortunately, the 30amp escs I ordered for this wing never came in the mail (must have been lost..sigh). I didn't want to wait to build it, so I pushed ahead with another esc in my inventory. The plan is for this wing to run 3s & 4s batteries and on 4s, I need a esc with high switching rates. I actually have lots of 30amp+ escs, but most are for airplanes and cannot support the switching rates on this motor. The only one which was able to do it was a 20amper. I decided to complete the build with the smaller ESC until the more appropriate ones come in later. Of course the drawback of using the 20amp esc is that I was also limited to using a smaller prop than what the motor is capable of handling.

The build came out heavier than I expected at 200grams without the battery. With the 3s 800mah Graphene I will be flying it with initially, the AUW is 280grams. This is around 100grams heavier than my previous wings of the same size, so I expect that the flight envelope of this will be just one size - FAST. This is an acceptable trade off as the 1806 motor is already the perfect candidate for this class of wing for all around fun and I already have others wings with that motor.

My bench tests put the thrust at about 720grams with 21amps on 3s. Yes, I realize that 21amps is already overstraining the ESC, but keep in mind that even if the motor is capable of handling this high of an amperage, the battery is probably not capable of sustaining that level of performance long enough to burn out the ESC (or so I'm hoping). The motor should be capable of 1kg of thrust with a higher prop, so until I can get a more suitable ESC, I will only be flying at 2/3 of the limit for this motor. Even at just 720 grams of thrust, it should already be a beast as long as the drag for the wing is not too great. Of course the only way to find that out is on the field. If the motor does prove to be overkill for this wing, I have already ordered some 1408 class motors which I think may be the perfect balance for this wing when it comes to speed and weight.

Update 1/9/18:

As fate would have it, the 30a escs I ordered for this plane showed up the day after the maiden flight. Unfortunately, the maiden flight didn't go so well as the CG was a lot closer to the leading edge than I expected. Basically, I had to pull the 1000mah 3s battery all the way to the tip of the nose for it to fly well. I guess that's why they call these prototypes? In a nutshell, this is the fastest plane I have built/flown to date. It was pretty windy, so I didn't dare give it full throttle for anything more than a second. However, I did get a good sense of what she was capable of. I will need to fly her again in a larger field to truly find her top speed. Landings are another problem I'll need to solve...thankfully there was a foot of snow on the ground during the maiden to soften the blows. As of now, it's pretty difficult to gauge the landings so that I can bleed off most of the speed before bringing her down. She doesn't like to fly slow at all. Max thrust with the 6030 props right now will pull about 700+grams. The motor is capable of 1kg and unfortunately, finding a prop that will give that thrust and fit in a small wing such as this will be difficult.

This is why I have decided to build another wing so that this motor can be pulled forward in order to achieve the proper CG without moving the battery so far up. I will however repurpose this wing for the upcoming 1407 motors I bought which are a lot smaller, but can produce similar thrusts with a 6030 prop. This would allow me to use the same batteries without moving them all the way to the nose.

In conclusion, Mjolnir is going on a diet and the 2206 cobra will live on in another form.

Update 3/18:

I tried it on a 4s battery which weighed 100grams and it balanced out the wing perfectly. I also tried it on a 3s battery that weighed the same to compare the flight characteristics. Overall, the wing flew well on 3s, but amazing on 4s. The extra power made it feel like it was on rails. The baseball park I flew at was too small to contain this wing. I'll need to go to a larger field to truly test her out. Landing was also a challenge as every landing was pretty much a crash landing. It is a hefty wing built for speed and it is hard to bleed out all the speed for a soft landing. Luckily, I built her to be tough and she has survived all the crashes so far with no damage. I'm talking about nose first into the ground at speed type landings as well. I've only flown her a handful of times, so I assume that much better landings can be obtained with practice. :)

Update 9/18:

So the weakest part of the wing is really the motor mount. It broke on a bad takeoff which resulted in a crash nose first. Amazingly, the frame held up and the only other damage was to a small part of the foam on the wing which wasn't taped up. I ended up switching the motor mount to an x type mount made from injection molding. The new mount should easily outlast the wing. I also swapped in some larger elevons for better handling on 4s. The inherent flaw of this model is that it is not easy to balance unless a bigger battery is used.