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Nov 13, 2019, 02:14 AM
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Phaedra's Avatar
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Originally Posted by StatGSR
That looks like a pretty cool mod and I hope it works out, why would you Y the motors though, if they to calibrate the same you wont be able to adjust, and if they were separate you could mix in differential thrust for rudder control.

I tried to add a second throttle channel last night, but apparently on this receiver it is a bit more complicated. A receiver with stabilisation has designated channels for rudder, aileron, throttle, etc. When I choose the rudder channel to be throttle too, the motor kicks in at half throttle only, so there must be some programming left to do before this works as it should. Getting there....
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Nov 13, 2019, 02:33 AM
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edwen303's Avatar
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Have anyone converted this loud pusher into single EDF (64 or 70mm)? Been thinking about it for while, how unscale it will be...
Nov 13, 2019, 03:20 AM
Youtube channel : solentlifeuk
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Quote:
Originally Posted by edwen303
Have anyone converted this loud pusher into single EDF (64 or 70mm)? Been thinking about it for while, how unscale it will be...
With care in weight ... what about twin smaller EDF's ? Then you can base on the existing model ?
Nov 13, 2019, 11:07 AM
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Originally Posted by Phaedra
I tried to add a second throttle channel last night, but apparently on this receiver it is a bit more complicated. A receiver with stabilisation has designated channels for rudder, aileron, throttle, etc. When I choose the rudder channel to be throttle too, the motor kicks in at half throttle only, so there must be some programming left to do before this works as it should. Getting there....
dont use the rudder channel on the RX, use an aux channel, then mix the aux channel and throttle to your rudder and throttle stick on your transmitter. this is similar to how any differential thrust plane would be set up.
Nov 13, 2019, 12:54 PM
An unexpected error occurred
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Quote:
Originally Posted by StatGSR
dont use the rudder channel on the RX, use an aux channel, then mix the aux channel and throttle to your rudder and throttle stick on your transmitter. this is similar to how any differential thrust plane would be set up.

Well, I didn't have much of a choice: I used the aux channels for ailerons (could have done that with one channel, agreed).
But meanwhile, I found a solution: when I reduce the weight for the throttle signal to 66% for channel 4, I get the normal response. I noticed that I had a sort of a dead-band between -100 and -70 (and the same on the positive side), so it had to be something like that.
I don't quite understand how this works, it would be way off-topic in this thread anyway, but it seems to work just fine now.
Nov 13, 2019, 02:05 PM
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just make sure you turn of stabilization for the rudder channel, with the rx you said you had, i believe that is possible. i dont have any first hand experience with that though.
Nov 13, 2019, 03:08 PM
An unexpected error occurred
Phaedra's Avatar
Quote:
Originally Posted by StatGSR
just make sure you turn of stabilization for the rudder channel, with the rx you said you had, i believe that is possible. i dont have any first hand experience with that though.
Yep, correct. I turned the gain for the rudder channel stabilisation down to 0.
Nov 15, 2019, 07:22 AM
An unexpected error occurred
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While doing some motor tests, the thing that was most apparent was the lack of structural integrity and stiffness of the airframe.
First thing was the horizontal stabs: they showed a lot of torsion; this airframe was not designed to be used with motors on the elevators. When I first built it, I only glued to bottom half to the top half without any further thought. I now filled the gap between the engine ducts and the fuselage (see second picture) with expanding PU glue. This improved the torsional strength impressively, I feel no need to further strengthen the tail part of the fuselage.
Second thing I noticed was the structural weakness caused by the original slot for the propeller and by the fact that I didn't glue the bottom of the battery bay part to the top of the fuselage. With the more extreme forces that can be expected from the thrust vectoring action, the fuselage is most likely to break in two pieces at that exact spot. I decided to first glue in a couple of hard balsa strips (see first picture) across the bottom gap. Next I will be filling in the gap completely with 6mm depron. That should hold....


Next step is to tweak some sort of landing skids at the back, to protect the propellers. And when I add something alike at the front, I might even take off from the ground, instead of hand-launching.
Nov 17, 2019, 02:29 PM
An unexpected error occurred
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She's ready to fly again.
First thing I did was to fabricate landing skids for the tail. I laminated two layers of balsa into tiny skis, glued them to the tail fins, and glued the latter to the fuselage.
To strengthen this construction, I used stirring sticks (from Starbucks, if this could be relevant to the story in any way). I made a groove into the front and the back of the fins, inserted the stick into those grooves, and let the sticks protrude straight through the fuselage (see pictures).
The front posed a bigger challenge. After a couple of experiments that failed, I used a wooden stick (that is normally used to support flowers), and inserted it into the front belly, pointing backwards. This should provide enough damping and shock absorbing on rough landings.
This combination of skids should also give me the means of a rolling (sliding) takeoff....curious if this works out.


Next challenge is: decent re-maidening weather.
Nov 23, 2019, 04:39 AM
An unexpected error occurred
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Had a quick test outside yesterday afternoon, in the garden.
First conclusion: rolling (sliding) takeoff won't work; I tried it on our lawn (hasn't been mowed, long grass): the model didn't move at full throttle.
I then tried holding the model vertically and throttling up: it has over 1:1 thrust-weight at less than full throttle, so hand launch will be easy.
I also experienced some (torque-?) roll that needs to be investigated (I have counter-rotating props, so it must be a difference in thrustline).
Looking at the telemetry data, I had a peak current of 32A (per motor), which is good news (40A ESCs, 3000mAh battery).

UPDATE:
I thought about measuring the thrust angles, and decided to use one of my older tricks that I learned while restoring crashed models :-)
I taped a straight stick of wood to each motor, to better visualize the thrustline by extending it. When looking from the side, I could clearly see a difference in angle when all controls were at neutral. As it is very hard to precisely adjust the pushrods for the elevons, I decided to make an exception to my rule of always centering everything mechanically, and adjusted the aileron trim to compensate for this.
I then took it outside again for a new test, and this did the trick: no more roll on throttling up.
I could also measure that it hovers at 25A. I let it hover into the gusty wind (still holding my hand around it for safety) for a minute and a half, and it consumed 500 mAh. This means that theoretically I can hover it for 6 minutes and have 30% of battery capacity left, which is nice.
The gusty wind allowed me to set the stabilization gain at a good starting point for the re-maiden flight, and it seems to work just fine.
Can' wait to fly this one again...should be a treat.
Last edited by Phaedra; Nov 23, 2019 at 06:01 AM.
Nov 24, 2019, 11:24 AM
An unexpected error occurred
Phaedra's Avatar
She flew!
For the first flight, I asked for a helper to launch it. He launched it in an overhead throw, and I shouldn't have worried: she flew off like on rails.
I selected the low rates setting for this flight, and that appeared to be a good choice. Control sensitivity was just right, no bad behavior experienced.
I just did a general flight check without any aerobatics, really uneventful. After almost 3 minutes fo flight, I consumed about 500mAh only, which is promising.
I topped up the battery again, while I went inside the clubhouse to warm up.
For the second flight, I decided to just throw her up vertically at WOT, and she climbed away easily from my hand; I didn't even have to throw.
This time, I explored the flight envelope a little more. This model handles really well at slow speeds, and there is almost no speed change between half and full throttle. It adds thrust, lots of it, but almost no speed. A looping is slower than expected (need more throw I guess), but rolls are powerdrill-speed (elevons combined with ailerons...), and they need to be toned down for me. Lots of expo here, which makes for a nice roll control in normal conditions.
Hovering goes really well, with the tons of thrust, combined with the stabilization function of the S6R receiver. This also got rid of the pitch-up reaction from the throttle; it now stays perfectly level at any power setting. Slow and low passes are a breeze, with a vertical climbout to top it off.
It appeared to be a real crowd pleaser, my little Sukhoi. And the noise level is so much better compared to the screamer it used to be.
After 4 minutes of this kind of flight, I only consumed about 600mAh, so 10-minute flights should be easy. But the cold made me quit early.
This has a lot of potential, that's for sure.
The landing skids proved to be very solid, no complaints there.
I can now start to make it a bit prettier, and give it a new color scheme. And maybe a couple of lights to help me in orientation....
Dec 01, 2019, 04:50 AM
An unexpected error occurred
Phaedra's Avatar
Had another couple of flights yesterday, cut short due to the cold this time.
I changed the throws and expo settings, and snap loopings are better now, roll is less powerdrill-style.
The best part of this mod is that I can now have it take off from my hand, without having to throw. Thanks to the stabilization of the S6R, it climbs like on rails...no stress at all. It was a bit windy, but that wasn't any problem at all. The stabilization also took care of the pitching up when throttling up, so now every flight is like a walk in the park.

After the second flight, I noticed that the inner hinge of the right elevator had come loose, so end of flying for the day.
This didn't really surprise me, given the great forces on this part now.
To repair and strengthen it, I punched a couple of holes in the foam and glued some bbq skewer sticks straight through the stab and hinges, accompanied by some expanding PU glue. It is solid as concrete now, I only have to cut off the ends of the skewer sticks and it's ready.


During the week, I also closed the center gap, where the prop used to be, with some 6mm depron. Can't hurt, aerodynamics-wise.


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