So finally got to the slope today. 30 km/hr and gusty to boot on the N side. It was quite chilly and I needed to fly with gloves. She slope flies OK but I only got 1 flight as I made the mistake of letting her come too close to the ridge, and she went downwind into the turblence on the lee side. I lost control in the turbulence and one stabiliser came off on landing. So that was it for the day. Luckily I had the Halfbad with me too and had several short flights while Ann took some video and pictures. The stabiliser broke off cleanly at the joint, so no problem to fix.

Looking forward to better weather to put her through the paces.

I still haven't managed to get the Sogwing to the slope. I will do this weekend if the weather is right before the Club meeting.

While you were all on your way down to Toledo, I had a good flying morning at the field and played with the Sogwing for a short time. I'm happy to report that the tow hook works sufficiently to get a good enough flight (45 secs) to assess trim. I was concerned about the hook integrity in the foam, but no problems from that point of view. By effectively adjusting the hook position with some material in the knee of the hook (i.e. moving it back), I might be able to get her to stay on the line longer. Not that this is intended to be a Hi-Start launch model.

On a separate note, judging by my typical poor ratio of catching thermals to number of launches, the new field is definitely thermally active.

Finishing touches, more trim and feedback?

I finished off the cosmetics with a couple of decals. These are created in Paint Shop Pro, printed on tissue, adhered with a glue stick or 3M Super 77 and covered with page protector clear plastic covering. The SOGGI decal is scanned from a larger professionally printed plastic decal and reduced in size.

It was too windy to venture to the slope most of this weekend, but I managed to get a few more trimming glides one early morning when it was calmer. It still needed more uptrim but managed a 40 paces glide without any bother. I figure it is probably best to leave it there until I get to the slope, as it may need penetration rather than float. BTW I've reduced aileron and elevator travel on the Tx to 60% and 75% respectively for now.

I also added a nylon thread retainer for the hatch cover. On one quite heavy nose landing during the trim flights the hatch cover sprang off. At the slope in the long grass it might be difficult to find it. And also BTW the nose reinforcement is essential.

The caption ("spot the mistake") with the middle photo in the "Battery and Receiver Installation" post was an attempt to solicit some feedback. As that didn't work, I'm hoping that the photo of the SRB launch system for the SOGWING below might get some comment?

Maiden flight test glide:

Despite the fact that I am typically very nervous on maiden flights, I ignored one golden rule for a test glide - choose a calm day. The wind was blowing at 20 km/hr. But I figured this is a very durable model and it will to have to survive at least that strength of wind on a slope much rougher than my local soccer field.

The first throw, despite the up trim, went straight into the ground. Second and third throws were progressively better with more up trim each time. She would not penetrate the 20 km/hr wind with a hand throw, but would glide nicely crosswind. Even with the 50/60% expo, she is ridiculously sensitive to just minor elevon movement. So I'll reduce elevon travel, increase expo and choose a calm day before the next test flight.

Despite some very wobbly landings she came home with no damage.

I'll keep posting with the really interesting parts to come.

Balancing and control surface set up:

Nothing much to say on balancing. As described previously I have slinging points at 21, 23 and 25% of MAC. Balance at the 21% point gave nose slightly up. At 23% it was slightly down by about the same amount. So I just left it where it was at ~22% (217 mm from the nose). No lateral balancing was needed. So bottom line, no ballast added at this stage. It is possible that fore/aft balance may need to change after a few flights.

All Up Weight is 366 gm (12.9 oz). Wing loading is 11.8 gm/dm2 (3.8 oz/ft2).

To start with on controls set up I just copied all the settings from my Halfbad. That is;

Ailerons: full travel 50% expo (decreased sensitivity near neutral)
Elevator: full travel 60% expo

The Halfbad needs reflex (up trimmed elevator) for a level glide. So I set up neutral elevon position with some up trim and used some judgement on the amount.

Battery and Receiver installation:

The battery (Duracell 223 non-rechargeable) and Rx are attached with a Velcro type fastener and double sided tape respectively. Some dense foam will be added in the small gap in front of the battery to absorb shock on heavy landings if the Velcro should let go. The battery connector is scratch built and just attached to the battery with strong masking tape, see photos. I don't use a battery isolation switch if I can avoid it, as it is just another component that is a potential source of unreliability. To power the model on/off I just connect/disconnect the Deans plug.

For folks interested in using non-rechargeable batteries for non-powered models, see my article in the Feb 2012 issue of Task.

The Rx antennae run through 1/16” holes to the wing lower surface and will be attached flush to the wing with covering.

As noted previously I had already checked the wing tips for being parallel. So the only remaining alignment check prior to stabiliser attachment is to ensure they are perpendicular to the wing. It turns out no adjustment was needed for this and a big thanks to Ray for cutting the edges of the foam square. I attached the stabilisers with medium CA and used kicker to ensure they adhered rapidly. As noted previously clamping the stabilisers to the wing would not be easy.

Covering:
Before deciding on covering, I made a preliminary balance check. If the model is very tail heavy and needs up front ballast, I did not want to add more rear weight from the covering. The wing area behind the CG exceeds that forward of the CG, so covering will result in a net movement of the CG rearwards. It turned out that the preliminary balance was almost perfect at 21% of MAC. So I was not not overly concerned about the effect on balance from covering. Note covering on the wing is really only cosmetic, but does add some strength to the stabilisers.

I decided to use Coverite Microlite, which I like and have had success with on several models. It is light, advertised at 0.6 oz/sq yd (though I suspect heavier) and easy to apply. I tested application to ensure it does not melt the foam under the Kevlar. It does not at a medium iron setting (#5 on a Hobbico iron).

The only problem I had, that I had not experienced before with this covering, is that it tended to curl inwards, towards the adhesive side, after removing the backing. I suspect this may be a function of humidity. I had not covered at this time of year before when the humidity is relativity low and static may be higher.

For complex shapes I use a paper template to cut out the optimum covering shape. This enables some experimenting with the shape before cutting out and applying the covering.

A functional advantage of the covering I realized after applying it is that it seals the cut edges of the Kevlar. I did not overlap the Kevlar at the edges as it is not easy to do neatly.

The covering added 18 gms to the wing and 1 gm to each stabiliser. So I reckon the covering is roughly 40% heavier than advertised.

In retrospect covering would have been easier if I had masked the area where the pushrod tubes are attached, then removed the covering local to the tubes so they could be attached afterwards. Covering around the tubes/rods was fiddly. I also realized that I could have buried the pushrod tubes beneath the wing surface.

I've often thought that aeromodelling is a building exercise in which all the angles involved have to absolutely accurate. Attaching the V stabs on a tailless wing is no exception. The stabs have to be square to the wing in the vertical plane and parallel to the wing centreline.

This is the procedure I used to to ensure the stabs are aligned parallel. It is complicated by the fact that the wing tips where the stabs are installed are behind the trailing edge of wing root. So one cannot measure from the wing tip to the centreline without extending the centreline rearwards.

1. On a flat surface mark a straight line at least as long as from the wing nose to the rear of the wing tip measured along the wing centreline.
2. Lay down the wing (upside down as the ventral fin gets in the way otherwise) with its centreline on the drawn line.
3. Measure the distance from wingtip to drawn line and wingtip to wingtip at both leading and trailing edges of the tip.
4. Repeat the above but from the other wingtip.
5. Average the tip to centreline and tip to tip measurements.
6. Determine the differences between tip to centreline at all 4 points (LE and TE at each tip).

In my case the differences (mm) were as follows:

Left Right
Tip LE 597.5 595
Tip TE 597 593

From the above it is deduced that I need to add 2 mm to the right tip TE to ensure the stabs are parallel. There will still be a 2 mm difference between left and right half spans, but as this is only a 0.3% difference it is not worth bothering about.

The stabs will be attached to a 1/32” balsa airfoil shape shims glued to the foam wingtips. The main reason for this is that I don't have a fast acting adhesive to attach the balsa stabs to the tips. We need a fast acting glue because it is difficult to clamp the stabs to the tips. But it is easy to clamp a shim to the tips using tape.

The 2 mm difference is dealt with by shimming the right airfoil shaped shim at the TE by a small 2 mm shim. The gap between the airfoil shaped shim and the foam is then filled in with 1/32” stock sanded to fit.

The stabs will not be attached until after covering both wing and stabs, as the covering process is much easier with these as separate pieces.