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Jonathan M

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Posts posted by Jonathan M

    Chilli Breeze 48" Build (IC)

    in Classic Aerobat Build Blogs

    Posted · Edited by Jonathan M

    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?

     

    • Like 1

    wing building

    in All Things Model Flying

    Posted · Edited by Jonathan M

    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!

     

    WHICH ENGINE?

    in All Things Model Flying

    Posted

    4 hours ago, Ernie said:

    Hi, and thanks for all that..Just what I wanted to find out.  So it looks like a 60 to 70 four stroke is what I need.  Anyone need a brand new OSV95,

    to buy, swap, or some sort of interesting deal..

    ernie

     

    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.

    Seagull Boomerang or Arising Star - any difference at all?

    in Trainer kits

    Posted

    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...?

    High Voltage equivalents for Hitec HS85MG and HS225 servos for 2s LiFe RX battery.

    in All Things Model Flying

    Posted

    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.

    1818551420_AA2000mAh4.8vcopy.thumb.png.3a4bcc5ae3eaafbbd59070ab74d0c9bf.png

     

    1907796475_23AA700800mAh4.8vcopy.thumb.png.d82f4926d059fd49cc5c572cb82e4053.png

     

    544342125_AAA800mAh4.8vcopy.thumb.png.5301226364a07ee7dec6f0ae8d7b5535.png

     

    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.

    • Like 1

    Gluing ply doublers

    in Building from Traditional Kits and Plans

    Posted

    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.

     

    DSC_0509.thumb.jpeg.73d448af89cf0bcf5c6a4eaad2dc91a6.jpeg

    Gluing ply doublers

    in Building from Traditional Kits and Plans

    Posted

    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... ?

     

    Forum members' new models: Let's see them.

    in All Things Model Flying

    Posted

    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.

    Forum members' new models: Let's see them.

    in All Things Model Flying

    Posted · Edited by Jonathan M

    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.

     

    Nylon engine-mounts: self-tappers or through-bolts?

    in All Things Model Flying

    Posted

    29 minutes ago, Paul De Tourtoulon said:

    Here we are a rubbish HK 2.2mm screw halfway screwed into a piece of plastic, 21 kilos and still holding, so x 4 screws =84 kilos for an OS 25 fsr, prop 9 x 6 @ 12.000rpm = 1.8 kilos static thrust,,,

     

     Still worried that it won't hold ,.?

     

    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.

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