Killerwatt (oz13085)


Killerwatt (oz13085) by Colin Usher 2010 - plan thumbnail

About this Plan

Killerwatt. Radio control sport aerobatic model. Wingspan 1485 mm, for .40 engines.

Note this is a clone of the Chris Foss Acro Wot design.

Note this plan was previously available as a free download, from the now-defunct Colin Usher website. We found this file in 2021 using the Wayback machine, see datafile link.

Quote: "The Killerwatt (Kilowatt) is a perfect follow on model from a Watt Four. It is a low wing design, slightly bigger at 1485 mm and uses a modified shape of tailplane & fin similar to a Watt Four. In fact the wing is so similar a friend uses an old Watt Four wing on his Killerwatt. Apart from the added 50mm it is more or less identical, even using the same airfoil.

As with the Watt Four a plan for the ACROWOT was never issued, so if you crash, need a spare or just like building you have a problem. Again the Killerwatt is not, for copyright reasons, identical to any other design.

I am reliably informed that this model will fly very well on a good 25 but a 40 is probably better. The prototype was fitted with an OS 46 MAX FX. The constructional details are my own and the outline shapes vary slightly, as does the airfoil. This is an NACA 63 0 18 at the root & 63 0 15 at the tip.

Electric Version hence the Killerwatt (Kilowatt): The plan as drawn is for an OS 46 MAX FX, but a version is flying with an AXI 4120/14 660 kv Brushless motor, a JETI 70w Advanced SB ESP, together with a Winforce 5 cell Li-Po pack running a 12 x 8 prop. Cheaper alternatives are a KSM 4120/06 660kv with a Wasp 70W Opto ESP from BRC. A 4 cell Li-Po also works but without the extra power of a 5 cell. You will need to put a hatch in the fuselage in front of the canopy for battery access.

Flying: The model has now flown more or less straight off the building board. A small amount of up trim was required but otherwise perfect. No signs of a tip stall, even on tight slow turns, ** nice flat even stall with no wing drop and a very flat glide on tickover. Very stable with an almost vertical climb. Needs plenty of aileron for Rolls, Loops and Stall turns no problem. A nice docile model all round.

** The original Acro Wot had a tendency to tip stall I am told but the slight dihedral, and most importantly the 2° washout seems to have cured this often fatal problem.

Update 12/7/2022: Added new rib files, thanks to Miguel, in both pdf and dxf format. Hopefully these correct the problem with the fit of the original ribs (see comments).

Quote: "Hi Steve, I have finally finished the new rib set for this model. There are two A1 PDF sheets, and I'm enclosing a DXF file in order to make life easier to whoever may wish to machine cut their own. If you find anything not up to scratch, please set the war beacons afire :)
Kind Regards, Miguel"

Supplementary file notes

Ribs Mig.
Ribs Mig dxf (zipfile).


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Killerwatt (oz13085) by Colin Usher 2010 - pic 003.jpg
Killerwatt (oz13085) by Colin Usher 2010 - pic 004.jpg
Killerwatt (oz13085) by Colin Usher 2010 - pic 005.jpg
Killerwatt (oz13085) by Colin Usher 2010 - pic 006.jpg
Killerwatt (oz13085) by Colin Usher 2010 - pic 007.jpg
Killerwatt (oz13085) by Colin Usher 2010 - pic 008.jpg
Killerwatt (oz13085) by Colin Usher 2010 - pic 009.jpg

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User comments

Thanks to Geoff Wise who mailed in to point out there is an issue with this plan - the fit of the wing ribs along the main spar (see pic 003). It seems the plan contains errors, as it stands. Also the supplement ribs file seems suspect. Me, I have no skills with these vector format plans. Does anyone out there have a way of drafting something that will fix this, make it buildable? The dihedral brace as shown would demand a flat/straight main spar, ie not swept-back, right?
SteveWMD - 30/06/2022
Has anyone ever built a model from this plan? I am curious how this issue was solved. Looking at the other plans we have on here, the same issue will also have to be solved if anyone is planning to build the Mega Watt (oz13092) or the Watt Four (oz13084). All 3 plans have been drawn in the same way.
SteveWMD - 30/06/2022
Hi Steve, it appears to me that both the leading edge and main spar are 'straight', i.e., perpendicular (or right-angle) to the fuselage centreline, while the T.E. iis obviously swept-forward. In a set-up like this - paralell L.E. and main spar - the location of notches for the spars on the ribs will be "travelling" backwards as the ribs go from middle to tip. For instance, the notches start at roughly 1/3 of the root rib and end at 1/2 the tip rib.
All this is eyeball measurement, I can try and do a full wing rib geometry study to corroborate or negate what's in the plan, and at the same time take a look at the spars and dihedral braces. I haven't looked at the other two plans but I'm not expecting any catastrophe. "Sc itur ad astra",
Miguel - 01/07/2022
Thanks Miguel.
SteveWMD - 01/07/2022
The Watt 4 has the same errors in the wing rib drawing. I can make 3D models and plans for both designs without the errors as well as dxf.
Jonathan Noon - 01/07/2022
"For instance, the notches start at roughly 1/3 of the root rib and end at 1/2 the tip rib." Miguel: maybe you meant to say "end at 1/4 the tip rib"??? In any case, to me, that is not the issue. If the main spar (MS) and the leading edge (LE) are meant to be parallel (and judging by the plan, that would seem to be the case, like you said) then the length between the MS and LE of both, the root rib and the tip rib (and every rib in between) MUST be the same. The way the side-view of the root and tip ribs is drawn, it is clear that the length from MS to LE of the tip rib is much shorter. This would suggest that the LE sweeps back as it goes towards the tip. So, in other words... either the root and tip rib are used as shown and the wing is built as double tapered, or, the location of the MS intersection has to be made equidistant in both of the rib templates. Comments? Reactions? Did I miss something?
RC Yeager - 01/07/2022
Jonathon, that sounds great. But be aware Miguel (see prev comments) is working on this right now, so it's up to you if you want to risk duplicating the same work. Up to you.
SteveWMD - 01/07/2022
I think the LE of the wing is surely meant to be straight, and not swept back. That is definitely the way the original Acro Wot looks, when I google for pics. And this here Killerwatt was designed as a clone of the Acro Wot (see the datafile link to to see the designer's notes). Have added a couple of pics on here now of the Acro Wot [004, 005] just for reference. Granted, these show a modern ARF version. Interesting that pic 005 if you look at the reflections in the covering, you can see the LE and mainspar are both dead straight, parallel.
SteveWMD - 01/07/2022
Jonathan, I don't mind if you pick this up, I believe you can do much faster work than I, I suppose the Hare and Turtle moral tale applies, not the pub :)
I hate speaking ill of a fellow air modeller, but the fact is that this plan has a number of irregularities I wasn't expecting to see in a CAD drawing. Still speaking of the unfortunate ribs, they are supposed to be symmetrical but aren't, the airfoils are described as "NACA 63" series but these are very far from what is depicted. I could go on but no, thank you.
Concerning Colin U., I hope I haven't been offensive, I am grateful for his tremendous job doing an Aeromodeller T.O.C. visible in HipPocketAeronautics, for one.
Miguel - 01/07/2022
Hi, I'm Geoff, the guy that started this, sorry. I have to admit that I'm building this half size 1/2 a 049 or a big mig 072. I do have 2 full size templates made by a cabinet maker which are spot on accurate. I can get these photo copied and perhaps put on a PDF. Hope to enclose a couple of photos in the next couple of days. Thanks again and will be in touch as soon as I can.
Geoff Wise - 02/07/2022
Thanks Steve for your work, this is my Accrowot [006, 007]. I will send you the wing templates for anyone interested. As its only a small model I'm building, I'm going to go with the drawings I have just for fun and alter the main spar so it fits at the highest point on both ribs, which actually is parallel with the leading edge [pic 008]. Job done. If you wish I can carry on with any updates as I get them. Thanks again to all your members, I'm very impressed and have been for a long time with the plans I've built from you, big and small. Thanks again,
Geoff Wise - 03/07/2022
Added new rib files now, thanks to Miguel. See pic 009 for a thumbnail image, and supplement download files.
SteveWMD - 12/07/2022
Hi Steve, Can you pass on to all the skilled helpers for all the outstanding work in producing a magnificent set of templates, much appreciated. Keep up the good work, thanks, Geoff :)
Geoff Wise - 20/07/2022
Well, that would just be Miguel. I'm not sure if anyone has ever called Miguel skilled or indeed magnificent before, but there's a first time for everything :)
SteveWMD - 20/07/2022
Neither did I, people normally use a different vocabulary range, but you have to admit there's a ring to it.
Miguel the Magnificent, wow!
Miguel - 21/07/2022
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Download File(s):
  • Killerwatt (oz13085)
  • Plan File Filesize: 1487KB Filename: Killerwatt_oz13085.pdf
  • Supplement Filesize: 25KB Filename: Killerwatt_oz13085_ribs.pdf
  • Supplement Filesize: 92KB Filename: Killerwatt_oz13085_ribs_mig_1.pdf
  • Supplement Filesize: 44KB Filename: Killerwatt_oz13085_ribs_mig_2.pdf
  • Supplement Filesize: 55KB Filename:
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