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Mar 20, 2019, 02:33 AM
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FX-706 Slope Glider Mods: "FINALLY--A Wee Bit 'O Progress!"


Having spent January & February hunkered down amidst rain /wind...
...several trips to L.A. & back...the odd bout of sickness & fatigue...and a spending a couple '$$$K's worth & on taxes, unexpected car repairs and vet bills for my dearest, stalwart companion Ehrlah...

I DID slowly get back to modding this FX-706 Glider!
What should have taken a few weeks...along with the inherent 'trial & error' of unconventional building off ill-defined 'plans'--has taken me 2+ months.
Oh, well...I've still 'enjoyed' the journey/challenge.

One issue slowed me down initially: the Vertical Tail as I designed it didn't have enough torsional stiffness. When I mounted the stock, foam stabilizer in position, I could waggle and twist it with my hand quite easily. Aerodynamic flutter--"waiting-to-happen"!

This was after I had routed & embedded the elevator cable guide to its 'exit' point & thought I'd be ready to mount the rudder, stab then skin over everything. I'm still determined to do as much of this build WITHOUT carbon & minimal glassing, as using this shoddy, Harbor Freight 2-part epoxy is a PITAS to get right!
Only '5 min.'-working time--thats when it is cool outside!

Of course, weight budget for this tail end looms over everything. I haven't put it on a scale yet but I'm watching how far the 'CoG' creeps back behind the wing saddle T.E., when balanced on my finger or ruler's edge!

I briefly considered creating an 'ersatz honeycomb' block of material: corrugated cardboard strips...stacked together...soaked w/thinned resin...and shaved/shaped into a filler matrix, fitting the open space within the vertical's structure.
The idea being that it might mimic that brown paper honeycomb seen in disposable packaging for large appliances & the real composite matrix used in aircraft tail surfaces. Its pretty light, stiff stuff when done right.

However, a pair of stir sticks upon each face of the vertical fin...in an 'X'-brace pattern...proved better. As well as adding an angled vertical brace, just ahead of the rudder post--using a strip of this stir-stick wood laminated to acrylic 'blister pack' plastic.

A tiny amount(..maybe 2 deg..) of misalignment/'twist' showed up at the top of the vertical fin, versus the fuselage long axis--probably the wood stick components drying out and setting somewhat. It got corrected with hot water + jigging 'under-the-sun', while I added these braces.

Some judicious sanding & shaping to blend its contours resulted in a blotchy[..all the DTE + 'Gorilla Glue' foaming!..] but satisfactory fin structure. Turned out stiffer & lighter than anticipated, no need for that cardboard block!

Rudder build--as simple as it SHOULD have been--was a mess! I had thought it out well, but execution was all over the place & didn't go as planned...probably due to a lot of rain, plus car issues & relocating.
After a lot of redundant, over-'built/over-weight' missteps; I got it 'mostly' the way I wanted....still isn't quite the right shape?!
I had decided the stock kit foam stabilizer was GROSSLY oversized and 'thick' sectioned for the job. I drew up a few different shapes that complemented the aesthetic I 'think' I've got going while examining other slope & HLG model with T-tail arrangements for hints.

I didn't find satisfying dimensions for the tail moment & span I was aiming for until I actually spent a few evenings playing around with 'Sailplane Calc'...whereupon I ended up DOWNSIZING my planned wingspan extension as a result!

The stock stab was 467 mm in span; I settled on just 386 mm, with a 'forward-swept' shape.

Originally this plane was to be increased from it's stock '1210 mm/'1.2 metre' span--> out to '1635 mm/'1.6+ metre'. I've walked it back down to only '1490 mm/ ~1.5 metre', although I might change my mind again once I get to the wings.

After all this correction & re-measurement, I quickly made my stab template from a large piece of acrylic, 'blister pack' plastic(..Discarded packaging = AWESOME versatile stuff!..) and cut out the parts for my rudder, thinking I would get it all built & mounted just as quickly.
Last edited by Spaaro; Mar 20, 2019 at 05:38 PM. Reason: Title, plus more content/context added to photos
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