AVRO 539B – New Year Flight

by alibopo | January 18, 2014 | (0) Posted in Just Fun

AVRO 539B – New Year Flight

Though the low Winter sun was a bit of a nuisance, conditions were near perfect for this flight. Winds peaked at about 7mph with only a little turbulence coming over nearby treetops.

For my own ‘flyer satisfaction’ I was aiming for slow flight in this session. Flying slow with this plane means less bank-and-yank and more controlled rudder turns - which I’m still far from comfortable with. Sometimes I ‘got it’ – quite often I lost concentration and reverted to bank-and yank - you’ll spot more than a few turns where I let the wings dip too much and the plane loses altitude and accelerates. Fortunately the plane is pretty stable, so it was easy enough to catch.

Overall it was a great morning’s flying. I think I managed to capture a few ‘scale-ish’ moments, with the plane ‘bumbling along’ serenely - which isn’t bad for a plane this size and weight. There’s no slo-mo film effects in the video – what you see is what it does. 

CG is currently at 25% of wing chord, but I’m still trying to decide whether to push it forward a tiny bit more. I recently ‘munged’ the numbers through a CG calculator on this webpage;

http://www.willingtons.com/aircraft_center_of_gravity_calcu.htm

The results, depending on how ‘twitchy’ or ‘mushy’ I wanted the plane to fly (by adjusting the % static margin), were CG figures from 26% through to 22% - which was ‘interesting’.

On the maiden and first flights the plane was very responsive to the elevator, but I’ve tuned that right down, which has made the plane manageable and pleasant to fly. However there’s always room for improvement, so any comments on CG and the plane’s observed flight characteristics would be welcome.

Cheers, alibopo.

UPDATE 02/03/2014; the plane had a 1700KV 28A motor to start with, but current draw was quite high with the 9x3.8 prop I was using. Time in the air wasn't really that good. I tried a smaller prop, 8x4, to allow the motor to use its revs to produce the thrust - hoping for more efficient use of the motor - but I think too much thrust was lost pushing air against the blunt nose. A bigger prop pushes more air out beyond the blunt nose, so not so much thrust is lost. With all that in mind I decided to try a slower revving motor, better suited to turning a bigger prop. I went for an EMAX GF2215/20 1200KV which theoretically draws about 20A with a 10 x 4.7 slow flyer prop. I only had 9 x 4.7 prop around, so tried the plane with that. It flew fine, with plenty of get-up-and-go for the take-off. I'm guesstimating my max current draw from this 'under-propped' setup is somewhere around 15-16A. This should give me much better flight times, though I've still to get a chance to confirm this. Last outing, with the new motor and prop, shortly after I got the plane in the air the wind picked up and I was happy (relieved) just to get it down without mishap! 

COMMENTS

dreamwalker on January 18, 2014
A wonderful video and a beautiful flying airplane. Your cabane strut assembly inspired me to try and build one of own. I'm using it on a parasol design. It seems to work very well.
I'm still working out how to build the wing struts, probably use carbon arrow shafts.
How is the O-ring suspension working out? Does it handle the impact well?
Thanks again for another informative and enjoyable article.

Tom
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alibopo on January 19, 2014
Hi Tom, thanks for the kind words. I think this cabane assembly would be fine for a parasol design, but I wouldn't underestimate how much strength and stability the bottom wing lends the top wing. I'd definitely want wing struts as well. Have a look at my Velie Monocoupe, which evolved into the morphocoupe! :) - that has functional wing struts. They are made from BBQ skewers with wire ends bound-on with thread and CA. At the outboard end the wire has a right angle bend that fits neatly into a servo horn that is embedded into the wing. A swing-in keeper stops the wire popping out, and makes the assembly easily dismantled to allow the wing to be removed. At the inboard end I made up a little 'V' shaped piece of wire and shaped the tip of the V into an eye. After a bit of bending and shaping to take the wire around the edge of the fuselage I used a screw through the eye to locate the inboard end of the strut assembly onto the MDF pad on the underside of the fuselage. There's good pictures showing how it fits in the Monocoupe article. Though obviously vulnerable to direct impact, these struts have lasted through many crashes and are still in use on the latest version of the model. I wrapped brown PVC tape around the skewer to give it depth. In the AVRO article I show how to securely embed the servo arms in the wing so that the ends project enough to be useful. Carbon struts would work fine, but maybe a bit of overkill? I suppose it depends on the scale of your model :) You'll know your flying style and likely demand on the struts. Sometimes I think TOO rigid is an invitation to damage weaker components elsewhere. In a crash situation, 'd rather have a strut break than tear the fuselage in two.
The suspension works fine, though I did recently have to replace the O rings - I think they deteriorate with daylight. I find the same problem with elastic bands - they harden-up after a while. I use this suspension on both the AVRO and the Monocoupe/Morphocoupe - but I recently made slight change to the AVRO detail at the bottom end where the wire forms a V - I turned the last 1/4 inch or so to make it vertical. As the axle rode up the wire frame, the pointy end of the frame was projecting into the wheel and catching the wheel spokes (and making a mess of my 'old style' wheels). I might do a little article on those 'design failures' - I've had a few along the way. I'm looking forward to seeing the Parasol version - there's something special about that bit of air under the wing, between the wing and fuselage. Cheers, alibopo.
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AVRO 539B – New Year Flight