Dualsky Extra 260

[Tom Foreman]

Finally got my Dualsky Extra 260 on Thursday, had been waiting for the motor and ESC to ship fom China, looks like everything is go slow until after the olympics. Still thanks to Als Hobbies for sorting it out. This is my first mid size model since I had a Progress 40 Trainer back in the 80's. Gave up flying 20 years ago and then started again last year with electrics.

Anyway she is 54" span, 2 - 2.5 Kg weight, will be powering with 4s2p 5200 LiPo, Spektrum Digital Servos, and Futaba 6EX 2.4 Ghz radio.

Build photos and captions to follow. 

[Andy Harris]

Tom

Welcome back to flying ... the Dualsky does fly very nice, but be careful its quite fragile.  Als Hobbies supplied me with a larger motor capable of 1.1kW, I think they may have been short of the one specified in the combo deal.

Mine literally pulled itself apart in flight Friday night, a mid air disintegration.  Before that it had been easily out pacing 40 powered IC models in the circuit.

So have a look at the motor part number and if its a biggy (you'll have to mod the cowl).  Think about propping the model so that it can't use all the available power.

Andy 

[Tim Mackey]

I think this is somewhat of a testament to being very careful about expecting lightweight "fragile" ARTFS to handle such very large powertrains.

[Tom Foreman]

Hi Andy, I got the recommended motor, XM4250CA-6, its a 900W one. Unfortunately the manual is a bit confusing as it recommends a 15x6 prop, I had a 14x8 but the motor pulls 68A and 880W on 4s1p. Now the max current is rated at 60A 15s burst, fortunately I shut down before the 60A ESC smoked it self.

On closer inspection the manual recommends a different XM4250CA-7 motor which is a lower Kv suitable for 5s, this explains why the recommended prop wouldn't suit my motor. So I'm grounded at the moment until a smaller prop turns up.

 It is very lightly built so I can understand its fragility, what broke yours out of interest? High 'G' manouvers or did the motor break free?

[Tom Foreman]

Anyway on with the build

Got the ailerons and aileron servos, undercarriage and rear stabiliser on.

Close up of the fragile light plywood and balsa structure

Nice translucent underwing covering to help with the orientation, beefy big spektrum digital servos, hope they don't blow the 5A Bec on the ESC

Nice short track rods and carbon fibre horns for slop free linkages, furry myler hinges seem adequate. Not a lot of wood in the wing or ailerons.

[Tom Foreman]

Spent ages gluing and truing up the rear stab, only to ruin it all when I had to manhandle the elevator onto its joiner, my fault for not trial fitting it dry or waiting for the stab epoxy to dry. I don't find out until later on.

Fin trimming before gluing, I could have got this straighter as well, it was perfectly square but didn't line up perfectly to make the rudder easier to hinge.

Looks good, but it could be better

Tail wheel also on as well.

Arggh! I now found out the rear stab has moved, after much soul searching and anger management, I decided to butcher it and put it right, its only out by 5 deg but it would bug me for the rest of the models life!

[Tom Foreman]

Plenty of room for the rudder servo

Elevator servo is a tight fit, the covering bulges out on the other side

Oh b****r, I can't find any motor screws in the model box or the motor box. Will have to use nylon wing bolts for now, but won't be able to fly it until I get the proper metal bolts.

After a long day of model heartbreak, I gave up with just the ESC to solder and fit, prop and spinner to ream, and install batteries and reciever.

Still its a nice size

Even the colour scheme is starting to grow on me, I think I like it!

[Andy Harris]

Tom

I'm envious you have some great flying ahead !

The 'accident investigation' thread is here:

Catastrophic Failure

My baseline thoughts are that it was the control horns that failed first, others feel that the hinges needed to be pinned.

I've ordered another airframe since all the expensive bits survived!

Andy 

[Tom Foreman]

I might look at a bit of strengthening then, how many flights did you manage? A week or so a go a bloke down our pitch turned up with a beautiful brand new Harmony Twin (IC) it flew really fast and looked great in the air. Our club expert took it up for the maiden and pronounced it a keeper with a big smile on his face, this thing sounded mint in the air. However when it came to its 2nd flight of the day by the owner it managed 3 fast laps of the field when one of the motors cut out. He panicked, tried to land on one engine came in too quick and Bang Bang thankyou mam the end of a beautiful plane. It cartwheeled in at his feet a big pile of smouldering wreckage, bit twitchy on the ailerons

[Andy Harris]

Tom

11 flights, two test flights, two for the 'A',  six for practicing slow rolls and the final flight.

As a postscript I was using Electrolite batteries that seemed to get better and better. Therefore the 820 Watts that I measured before the test flights could have become the full 1100 Watts in subsequent flights.

The first two flights were very short, but I put this down to a fair sized model and 3700mAh batteries.

When I mention quick, I really meant quick, With a Funtana 50 in the circuit I could see not just a difference but the ability to catch up within half a circuit.

Timbo has warned in this very thread of over powering.

I've looked at the remaining wing, can't see where pins would go on the aileron side without causing a weakness.  Next time I'll double up on the number of hinges.

I really enjoyed the 'point and squirt' locked in feel of the model in the air, the landings were really easy.

You're going to enjoy this one ...  Andy

[Garry Pollard]

Andy

With all due respect if you drill and glue in cocktail sticks it is impossible to weaken anything, the reverse I think . You must have more strength

[Tom Foreman]

Sorry to keep pestering you Andy, but how much throw did you have at the time? Mine has too much on high rates with about 50-60 deg throw. Going to get my protrator out and set them up properly as per the manual.

  

[Andy Harris]

No problem!

I set mine up exactly as the manual states, which is a good 60 deg on maximum deflection.

Apart from a 30 second try-out I didn't fly on high rates. The roll rate is akin to watching a food mixer!

The elevator on high rates was really sid vicious, looked like a loop in its own length.

Can't comment on the rudder, never got round to doing any knife edge. ...Andy 

[Tom Foreman]

Cheers Andy, will hopefully get some flight photos at the weekend, and will pin the ailerons as well. Good luck with the new airframe.

[Barnesyboy]

Knife Edge on manual settings is very good, fine required very little coupling even with a forward cog

you WILL enjoy this plane

B

[Tom Foreman]

Set the throws last night, 30deg low 40 deg high on ailerons and elevator, 40 deg low 50 deg high on rudder. Should be enough for now, all though it could go further, I don't have any 3D skills yet.

AUW is coming out at 2.18 Kg or 4.796 lb, that's with 560g of 4s2p 5200 Lipo, if I bought a new 4s1p 3700 Lipo that would bring the weight down to 2Kg!

Projected power when I get a smaller prop of 800W should give me a respectable 166W per lb, should go ballistic! Set CoG at 27% of MAC, 103mm from leading edge, had to move the heavy battery pack all the way back to the spar, so thats pretty much the heaviest battery I can fit in my setup without moving the CoG forward.

Hopefully will maiden on Saturday, want to do it down the club where there is plenty of space, as I don't want to maiden this monster in my local park!

Tom

[Tom Foreman]

Well it fly's! Managed 3 flights until the landing gear collapsed, definitely a weak point on this model. But it fly's beautiful, really locks in well and is graceful. Flew it on low rates, and it was nearly twitchy but not quite. Lost the canopy the first time I did a roll, should have done what the instructions said and screwed it on. The first landing was perfect, just took her out a long way and then bled all the speed off, cut the throttle at the last moment and flared for landing.

Did some basic rolls, loops, cuban eights, stall turns and inverted flight, all really easy. She picks up lots of speed as she growls around the sky. I was surprised that I was only getting 7 minutes out of 4s2p 5200 battery, but the battery might be knackered as I only put back 2000 mAh, and the charger reckoned the battery had 10% left.

Tried to hover, but it kept rolling out, but it nearly hovered! More practice required. Excellent ulimited vertical it dissappeared quite quickly!  

Anyway need to fix the undercarriage before I can fly again, will need to reinforce it for my rough landings

Off to see Batman now with the Misses.

Beautiful flying weather today!

Tom 

[Tom Foreman]

Video of some flight

http://www.youtube.com/watch?v=moECx3OoJMo

[Garry Pollard]

Hi Tom

The flight seemed quite smooth and controlled. What were the throws you were using high and low airolon and elevator. Would just like to compare

Thanks for video

Garry

[Tom Foreman]

Hi Gary, just used low rates as in the manual, 20 deg aileron & elevator, 30 deg rudder. -25% expo aileron and elevator, -30% expo rudder.

Set high rates to 30 deg aileron & elevator, 40 deg rudder, but never tried them out or felt the need.

There's plenty of negative expo though so she is quite controllable, very smooth and responsive just on the verge of going out of my comfort zone to begin with, but I soon got used to it and liked it!

Tom

[Garry Pollard]

Thanks Tom

Slightly different set up to me I used pos expo and found it a little lazy. Maybe your way is better, will try it next trip

Thanks

Garry