chuckaaaaa
New member
I wanted to get some use out of some old cheapo 1000kv 2212 motors and 30A ESC's I had lying around. I liked the idea of seeing how much performance could be squeezed out of these traditionally slow-fly entry-level motors and ESC's on 3s voltage. Since I've already done a couple of traditional twin motor planes, I wasn't looking to go that route.
Anyway, I don't know if I saw it somewhere online or what, but the idea of using two motors to drive one shaft (thus being able to swing a 10x8 prop to give me some speed) came up.
So I got some 3.17mm shaft and configured the motors as you see in the photo, with one "outboard" (in front of the firewall) and the other inboard. Thinking that the inboard motor would be in danger of overheating without the propwash/airflow a motor normally gets, I made an internal heatsink out of some scrap aluminium and put a chopped-off prop on the back end of the shaft to draw some air over the motor internally.
To complicate things, though, I also got it into my head that I'd like to build something reminiscent of the U2 spyplane (but with a prop up front rather than a pusher prop or EDF).
I like working with duct-tape-covered foamboard, which is great for durability but does get fairly heavy. And with two 50g motors, 25g heatsink, and two ESC's, it came in fairly heavy for its high-apect ratio 44-inch wingspan - about 890g with a 1300mAh battery. Wing loading worked out to about 19oz/sq ft.
Admittedly the 19oz/sq ft wing loading is at the higher end of what I've flown, but I think the high taper of the U2-esque wingshape made this thing more tip stally than I was prepared for (apparently the real U2 was similarly scary to fly).
How it flew on the first try:
Though I had built in some right thrust angle on general principles, the torque roll tendency on this baby was much more of a bugger than I had anticipated. 10-inch prop, the mass of two motors spinning, and then with the narrow U2 wing tips not providing as much anti-torque-roll as I was used to, meant that she pulled majorly to the left the whole flight. She absolutely just laughed at me when I tried to bank right.
(Question to you experienced guys: would the fact that the nose on this U2 shape is so much longer than the average single-prop plane serve to make small changes to the motor's thrust angle have a greater effect than usual - located that far forward does give it more moment arm with respect to the cg, right?)
I got her back down on the ground - barely - and remounted the motor to give her more right thrust, which did help on the next flight.
I thought I'd "take it easy" speedwise on these first flights, so flew it on a 10x5 prop instead of the 10x8 - big mistake. After a minute or two of tipstall/catch/recover events, physics and gravity eventually won and she spun to the ground. Crunch.
After a rebuild/repair, the second try went like this: on the 10x8 prop she flew fast and true until excessive vibration (from a wonky prop adapter) caused the motor mount nuts to unscrew themselves, and/or the prop starting slipping on the shaft, and possibly the rear motor overheated (version one didn't have the internal cooling fan) and seized. Right roll over (result of the left torque tendency suddenly disappearing and me not realising what was happening and reacting in time?) Crash.
Anyway, I'm rubuilding with a shorter nose and have grafted some extensions onto the wings to increase area and reduce the taper. Not as sexy as the U2 shape, but hopefully one that will fly a bit less scarily.
Anyway, I don't know if I saw it somewhere online or what, but the idea of using two motors to drive one shaft (thus being able to swing a 10x8 prop to give me some speed) came up.
So I got some 3.17mm shaft and configured the motors as you see in the photo, with one "outboard" (in front of the firewall) and the other inboard. Thinking that the inboard motor would be in danger of overheating without the propwash/airflow a motor normally gets, I made an internal heatsink out of some scrap aluminium and put a chopped-off prop on the back end of the shaft to draw some air over the motor internally.
To complicate things, though, I also got it into my head that I'd like to build something reminiscent of the U2 spyplane (but with a prop up front rather than a pusher prop or EDF).
I like working with duct-tape-covered foamboard, which is great for durability but does get fairly heavy. And with two 50g motors, 25g heatsink, and two ESC's, it came in fairly heavy for its high-apect ratio 44-inch wingspan - about 890g with a 1300mAh battery. Wing loading worked out to about 19oz/sq ft.
Admittedly the 19oz/sq ft wing loading is at the higher end of what I've flown, but I think the high taper of the U2-esque wingshape made this thing more tip stally than I was prepared for (apparently the real U2 was similarly scary to fly).
How it flew on the first try:
Though I had built in some right thrust angle on general principles, the torque roll tendency on this baby was much more of a bugger than I had anticipated. 10-inch prop, the mass of two motors spinning, and then with the narrow U2 wing tips not providing as much anti-torque-roll as I was used to, meant that she pulled majorly to the left the whole flight. She absolutely just laughed at me when I tried to bank right.
(Question to you experienced guys: would the fact that the nose on this U2 shape is so much longer than the average single-prop plane serve to make small changes to the motor's thrust angle have a greater effect than usual - located that far forward does give it more moment arm with respect to the cg, right?)
I got her back down on the ground - barely - and remounted the motor to give her more right thrust, which did help on the next flight.
I thought I'd "take it easy" speedwise on these first flights, so flew it on a 10x5 prop instead of the 10x8 - big mistake. After a minute or two of tipstall/catch/recover events, physics and gravity eventually won and she spun to the ground. Crunch.
After a rebuild/repair, the second try went like this: on the 10x8 prop she flew fast and true until excessive vibration (from a wonky prop adapter) caused the motor mount nuts to unscrew themselves, and/or the prop starting slipping on the shaft, and possibly the rear motor overheated (version one didn't have the internal cooling fan) and seized. Right roll over (result of the left torque tendency suddenly disappearing and me not realising what was happening and reacting in time?) Crash.
Anyway, I'm rubuilding with a shorter nose and have grafted some extensions onto the wings to increase area and reduce the taper. Not as sexy as the U2 shape, but hopefully one that will fly a bit less scarily.
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