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'Nextra (An Extra)


Having built the And Now? on David Theunissen's Fly Electric site, I wanted something a little better looking. David's site also has an 'Extra' with the same overall dimensions and I decided to build one with a few mods. David offers the plan in four different formats here.

I did a little fiddling with the side view to my own taste but retained the moments. Having seen several examples of the Ikarus 'Shock Flyers' I was rather taken with the idea of adding a horizontal profile to stiffen up the fuselage and increase the 'presense' in the air. I also liked the idea of the profile spats on the end of the axles. Both of these ideas were incorporated.

I terminated the spruce motor stick in the area of the spar to save a little weight. Initially, I used a wire U/C bound to the motor stick, but really couldn't get the spats to stay in the position I wanted because the wire changed its shape after any contact with the ground. I resolved this by using 1.5mm carbon U/C legs Cyano'ed into the motor stick. The wire stub axles are attached to the legs with heatshrink tubing. Once you are happy with the position you can cyano the axles to the legs. For this to work, it is essential that you bend the wire back on itself where it goes inside the heatshrink tubing. Cyano will bond well to carbon, but not to wire!

Nextra U/CNextra U/C

Original wire undercarriage and modified carbon version.

It is also a good idea to glue a disc of 1/64" ply to the inside of the spat where it will be attached to the axle. Otherwise you will keep knocking the spat off, leaving a small piece of depron attached to the axle! The ply can be coloured with Tipex, as can the other ply bits that are used.

I already had a 7:1 ratio IPS drive unit which gave poor performance in a 'Pico Stick' and reasonable (but not great) performance in the 'And Now?'. I used this for convenience with a 9 x 7 prop (the pictures were taken when I was experimenting with one cut down to 7 inch diameter) and was surprised to find that it worked very well (horses for courses). Initially, I used various combinations of 6 and 7 cell 300 mAh NiMH packs, but am now using a 2 cell pack of 340 mAh Kokam Lithium-Poly's. All up weight, with 3 servos (2 x Hitec HS-50 and 1 x Saturn 4.4g) is 137 g and performance is very good for 10 minutes plus.

7:1 ratio IPS unitIn flight

Cutting the motor stick short may not have been such a good idea. Despite the horizontal brace, the fuselage can twist quite a bit and the disposition of the rudder, mainly above the thrust line, makes the fuselage twist noticably in knife edge flight which causes various interactions between the elevator and the ailerons. The Shock Fliers use full length 1/4" triangle section balsa stiffeners but these don't really make them any stiffer. I plan to add stiffening webs from 3mm Depron with the edges shamfered so they can be fitted at 45 degrees between the vertical and horizontal profiles.


I did eventually buy a Shock Flyer to see if they were any better but powered it with a dual motor IPSD unit. The Shock Flyer performs better because it is stiffer and doesn't have any camber on the wing. It also flies considerably faster. The two have different appeals and I like the 'Nextra because it is slow and will perform effortless aerobatics. The particular setup of drive unit and mounting makes it sound like a well silenced Rotax engine.

I must resist the urge to build all of David's other designs!


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