Jonathan M

Andy, that sounds alarming! Did the tailplane half just fold at the root?

Thanks Nigel, very helpful! I found the article I'd seen before, it was by Peter Miller https://www.modelflying.co.uk/woodnt-you-know which complements your advice above. Thanks also for the heads-up on tail servos ?

I'm finally about to make a start - my first plan build - with foam wings from Cloud Models. Will keep as close to the plan/article as possible, but take advantage of modern RC gear to help keep the weight down, and reckon a 2/3AA 800mAh NiMh will be ample for a normal flying session. Power will be a new OS35AX with standard silencer. Servos will be HS85MG in each of the wings (original design had a single central standard and torque rods). Thinking of fitting the same for the tails , or perhaps the beefier HS225MG for these? My main opening question is what density balsa should I be selecting for the main fuselage components? The sides are 3/32" (with a 1/32" ply doubler, a 3/32" wing-seat doubler and 1/8" x 1/4" spruce longerons), while top decking is 1/16", etc. The 3/32" sheets I have range in weight from 8 to 16lbs/cubic ft (i.e. from fairly light to really quite heavy), but I have several in the medium range. I simply don't know what the norm is - not just for the fuselage but for the various major components (different built-up wing parts, tail parts, etc) across a whole traditional power model. The old website had an article by one of the regular columnists, but I cannot find this anymore. Any suggestions?

Can't say I really noticed... ?

Example pictures. Propped up TE etc (easiest with non-tapered wing): Ribs pattern and jig described in my post above (tapered wing):

Another method I've seen is to accurately bore two small holes of the same distance apart in each rib (doesn't matter if the wing is tapered as long as the holes are all in line) then suspend the ribs with two stiff tubes fastened to blocks at each end, then add LE, TE, spars, etc until the assembly is stiff enough to remove from the jig. But most modern plans seem to opt for the tabs method - if the ribs are laser-cut then so much the easier!

I'd go for the solution that is most future-proof.

I have a very nice, broken-in but very little used ASP70FS (was briefly in an ARFT Acrowot then serviced by Just Engines after its early demise - caused by radio failure courtesy of a brand beginning with the letter 'S') for which I don't have a foreseeable use. Pm me if you're interested.

Aidan, just buy a set of four saddle-clamps for 8SWG wire, and screw into the existing ply U/C base.

Just used standard slot-headed bolts, washers and nuts, plus split-washers. Easy to keep an eye on things as it's an open-access bay.

Aidan, it's a fairly heavy model with a trainer-sized engine, so it will take longer to overcome inertia and gradually accelerate than a more lightly-loaded model with a more powerful engine, and the landing roll-out is similarly longer. For me that - and also its less acute climb-out angle - actually makes it seem more realistic. I've never measured the length of take-off run but I'd guess (assuming you open the throttle smoothly) you should allow a good 30-40m...?

Set up a programme on the Taranis for servo-cycling (with RX battery telemetry logging) and ran some NiMh tests. Slightly differently to the video instructions above, I set the speed to 2.5secs each way with no pauses at the end-points, so 5.0 secs complete cycle. This is more similar to but very slightly slower than a standard servo-tester cycle. Used the five servos I'm due to fit to the Chilli Breeze (which are now well burnt-in!) 2 x Hitec HS225MG (rudder and elevator) 2 x Hitec HS85MG (ailerons) 1x Emax micro (throttle). All three batteries were fully discharged to 4.0v then re-charged using my standard routine for consistency, and this was done the night before so they were rested. The graphs below are self-explanatory. They were the second set of tests which were almost exactly the same as the first set. The AA 2000mAh Eneloop (graph shown in the raw without annotation) finished the hour with the voltage still nicely above 4.9v. The 2/3AA 800mAh held the voltage above 4.8v for about 50 minutes. The AAA 800mAh Eneloop dropped below 4.8v after only 20-25 minutes. So the answer is to fit the 2/3AA 800mAh (no point in fattening the 48" CB with an unnecessary extra 2oz that comes with a 2000mAh). This is the spare for my Ahi (usually flown for extended periods in bouncy conditions on high-rates with large/frequent surface deflections off four 12g metal-geared 2.4Kg.cm servos), so I'm sure will be fine in the CB for several 8-10 min flights off a full charge. I can check the current voltage at any time by just glancing at the large telemetry screen on the TX. My normal charger also runs off 12v from the field-box Pb and would take say 30mins to top-up, else I can carry a spare.

The Chilli Breeze plan shows 1/16" sides, a 1/32" ply doubler, and an additional 3/32" short doubler at the wing-seat - which all seems an entirely appropriate assemblage, especially for IC. By contrast, my Gangster 63 Lite only had - as designed - 3/32" sides and nothing else except a short 3/32" balsa doubler between the ply firewall and the lite-ply tank former. I beefed this up with three extra 3/32" pieces as far back as just aft of the former above the TE, especially as I felt the wing would be happier with a thicker seating etc.

Yes the CB. Just lining up all my ducks before getting properly stuck in! Mind you, here's one I made earlier...

Coming along very nicely!

Thanks for the input fellas. It makes sense that any water-based glue will soak much faster into the more porous balsa as opposed to the plywood, which is both of denser grain and has an impermeable barrier before the next ply. Then, as the glue dries through evaporation, the stage is set for a differential shrinkage! (A parallel is when veneering grown-up wood over a ply or MDF base: balancing veneers are always laid on the opposite side for exactly this reason, even though the base is always a much thicker and therefore technically more rigid partner.) I've dug out an old tin of Evostick contact adhesive... ?

Other aspects of this model which will effect climb etc, and which may well be quite different from your other models, are it's wing section, incidence angle of wing, etc. But also check your CG: if the model is nose-heavy you might then have a bit of up elevator trim dialled in to maintain S&L at half throttle; give it more beans and your up-elev will be quickly pushing the tail down, and so she'll immediately start climbing at a quicker rate than if your elevator was neutral.

Very nice indeed Tim! Re climbing under power, that is completely normal after a few seconds of increased revs from a baseline of S&L flight at around half throttle, and I wouldn't do anything to alter that with any fancy mixes, else you'll acquire confusing flying habits which won't translate to other normal models. But if it climbs immediately you blip the throttle open, then it is definitely due to insufficient down-thrust. What does the plan state and what do you actually have have? Can you measure it accurately? In the free fight world short-nosed models (e.g. WW1 types with rotary engines like the Camel, Eindekker, etc) need an awful lot more down- and also right-thrust than more conventional designs with longer noses. While you're about it you might also look at its right-thrust. Some pull to the left is okay when opening up power (e.g. at the start of the take-off run) but if that is really excessive then add some (more?) right-thrust. (Some would say just learn to use rudder, which I agree with, but if your model isn't nicely mechanically set up in the first place, then it'll retard your skills and enjoyment.) The test for this is to fly S&L (wings must be level) into wind then increase throttle to say 2/3 power then pull smoothly to verical climb. As the model slows (due to gravity not throttle which you keep at 2/3 power) if it yaws to the left this indicates that it needs a bit more right thrust. PS: 2/3 power is just a suggestion, try 3/4 and full throttle as well and repeat tests (both down- and right-thrust ones) until you're sure there's a noticeable consistent deviation. Then, if you do alter thrust lines, run your tests in the air again and observe the difference.

Why is contact adhesive traditionally used to glue ply doublers to fuselage sides, and are there alternative glues?

It isn't a question of not holding (even small rubbish screws have a significant area of thread), it's about one or more screws not working even slightly lose under vibration, and also about the risk of stripping the plastic thread if over-tightening or misaligning on repeat screwing.

My own battery is already bang under the TE... yet still needed some tail-weight (for me, not for learners). Good job Aidan didn't go with the four-stroke!

I'm at 100mm to the rear of the prop. No point in going any further forward as it'll just mean more horrid tail weight!

That sounds ideal for my application.

Thank you Jon - I have a weakness for proper jobs...! ?

John, that was exactly the Modelfixings page I was looking at, which prompted me to ask the question. I have an 0S35 to fit into a 48" aerobatic with a fixed balsa cowling, so won't have easy access for nuts etc on the underside of the mount. Sounds like I'll be fine with 3.5mm self-tappers then.