KV Duo Discus X - 1:3.75 scale at 5.33 meter span - build thread

[Steve P]

While I dearly love my wood/foam/carbon winged EMS Duo Discus, I've been wanting two things... flaps for full trailing edge camber / tow settings and the ability to push the airframe even harder in speed runs and a bit of fooling around.

Enter the KV Duo Discus X. Schempp-Hirth added flaps and turned up tips to the later versions of the venerable Duo and marked those planes the X and the XL. So here we have the X model sporting those features and exactly meeting my desires. In all candor, I don't prefer the look of turned-up tips on the Duo, but performance considerations win.

Span is 5.33 meters (210") Wing area is 109 dm2 (1689 sq. in.), airfoil is HQ 3/15-12; loading @ 96 g/dm2 (52 oz/sq. ft.), fuse length is 2.3 meters (91") flying weight approx.: 10.5 kg (23 lbs). I've come to prefer 1:3 and 1:3.5-sized sailplanes, so this Duo is perfect! Each wing is also two-parts with a short outer panel with one aileron and integral turned-up tip. So, this will be even easier to transport. REVOC bags, of course!

Like most all beautifully-molded all composite sailplane kits, this is really a matter of assembly, not build per se. I'll be going all HV servos and PowerBox power supply. A few orientation photos...



Main wing panel


Tip Panel


Horizontal stab

[Steve P]

A few more orientation shots...

Fuselage side showing anti-rotation pins and joiner slot. Note the CG mark already on the fuselage


It's the real deal


Fuselage side carrying the X designation



Big photo for the big reason: Huge carbon-wrapped joiners, carbon roots. Wiring and Hanson connectors shown are my own.

[Steve P]

Some servo install shots...

Ailerons are Spektrum 5060HV in frame. All frames are installed with Hysol 90EP and then after that cured, an additional bead of Hysol around the frames. You will note the cut away of some of the lip for the servo cover so as to get a servo and frame inside while still being able to access the frame screws. A small price to pay and will make zero difference once the covers are installed. Heavy duty metric clevises/connectors are my own. The kit came with no hardware.



Airbrakes are JR189HV in frames and flaps Spektrum 5060 in frames


JR 398HV rudder servo tucked in under one of the seat mounts


Retract servo is Spektrum A6220HV


Decided to make life easy and flexible with Hansen snap connectors - one 6-pin and one 3 pin.

[Mark9]

Steve, I'm curious where did you source the Spektrum A6220HV? I couldn't find a HV low profile servo on this side of the pond that I wanted to pay for to put in my KV 4.8 meter Ventus.Nice work! OOH, mine has the same label as shown earlier, it is mostly covered by the seat pan mount though...

[Steve P]

All of the Spektrum servos came from Horizon Hobby. Found it on their website.

[Steve P]

https://www.horizonhobby.com/product/radios/aircraft-radio-systems/aircraft-servos/a6220-hv-dig-low-profile-hi-torque-mg-aircraft-sx-spmsa6220

[Steve P]

Finally, gap sealing. One thing this model does not have is wipers. So, there is a reasonable gap on the bottom surfaces that might make a cool noise, but rob performance. The exceptionally thin Ripmaxx gap tape is a great product but not available in the U.S. Hyperflight in the UK was out of stock so a roll was sourced from Sussex Model Center.

In the photo the 4-40 Sullivan airbrake hardware and nice double thickness HD flap horn sourced from Esprit Model can been seen. The flaps get the HD metric hardware same as the ailerons.

[Steve P]

I had questions about where I found Spektrum servo frames. Switzerland! Jeremy would be so proud.

The Spektrum frames can be ordered direct or from Ali at Flite Comp. One of the very best sources of servo frames is in Germany — www.servorahmen.de Easy to order and pay online. They were the source of the airbrake and rudder frames for the JR servos in the Duo. I have their external bearing frames in other planes. Nothing from Spektrum yet, but they’ve got a great range of other frames and also IDS / LDS units.




I plan to adapt one of the Type 19 frames for the tow release...

[Swiss1]

Well done Steve!

[Stew2]

Servo frames and servos, the never ending abyss of combinations and permutations...where the cost of tooling will forever create a year lag behind the servo that has just been discontinued!!

None the less, I think, and though most times nothing happens, I think that the Servorahmen Type 19 frame will also fit the Spektrum 6300....

Interested to see what you come up with for fitting the 6150 into it. And maybe Servorahmen makes a type 19 with the external bearing??

[Steve P]

So true. How does one know the size or durability of the market for any one servo? There is a Type 19 Lager but the frame is huge and inside the curve of the nose it’s a tough fit for the tow release.

[Steve P]

Took the time to build a combination ballast box and tow release mount into the nose. Modifying the Type 19 servo mount just took a bit of coaxing with a Proxxon handheld belt sander...

[Steve P]

Getting closer. No more shop time for a couple weeks, but the punch list is short...

[Sinkhappens86]

Looking good Steve. Nice clean install!

[Steve P]

Thanks, Kevin. Hope to see you on the mountain in March.

[Steve P]

Seems the Duo developed a drinking problem? I found it in the basement downing Solo cups full of lead!?!?

Even with that, it seems to be balanced and not “tipsy” at all.

[Steve P]

It was pointed out to me today that I left this thread cold. So, suffice it to say, the Duo is done, has been flying for about a year and a half and continues to be a great performer!

I've had the EMS Duo in the past and this sailplane performs similarly well!

It now flies on a PowerBox CORE radio with 2x 26D receivers. A set of Revoc wing bags and it has a permanent home in my fleet. Wouldn't think about parting with it.

Here's a photo of the boys taking a rest after a flight at Cumberland this summer...