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Jonathan M

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Everything posted by Jonathan M

  1. For normal glow 2 or 4 stroke, say from .30 to .80 sized engines, what is the norm? I can see that for installations with little or no access to the underside of the mount then self-tappers are convenient. But I've always so used bolts with spring-washers or similar simply on the basis that (a) it feels more secure, and (b) if I strip a thread by over-tightening then its easier to replace a bolt etc than the whole engine-mount.
  2. No worries Aidan. I used the clobber supplied in the kit, which is robust enough for the job. The only mod I did for IC was to fuel-proof thoroughly in the open engine-bay (on top of whatever the manufacturer used) and all around inside the tank-bay as far as the wing-seating, then I used silicone sealant to (semi-permanently) bond the tank-bay (i.e. Lipo-bay) hatch in place, including replacing the nylon screw and wooden-block inside with a metal self-tapper etc, as the original block and protruding screw was fouling the front of the tank. It will be nose-heavy unless you position your 4.5v NiMh as far back behind the servos as possible. Flying-wise, I reckon a 46 pulls it around absolutely fine for a medium-heavy trainer-type. I estimated mine (pre-obesity due to crash-repairs) to be about 135 W/lb, with a wing-loading of 23.5 lbs/sq in. (For comparison my Wot4 with an Irvine 47 comes out at about 165 W/lb and a loading of 21 lbs.sq in.)
  3. 11x6 works best. Tried an 11x5 to help slow it for landings, but found it was then too slow for normal smooth flying. Note that my Boomerang has gotten heavier by 10% after earlier repairs, and because it (also/then) needed a good dose of tail-weight for a closer-to-neutral CG.
  4. If it is metric (it looks like it may well be) then just lightly try any spare metal ones for an easy natural fit that won't damage the threads in the female part, then order nylon ones in your chosen length from Modelfixings.
  5. EB, I didn't know if you double-clicked the photo in the editor before posting that you can re-size it here. So I've reduced the test photo to 500 wide using the editor, which is half the normal width I usually post. But this (on my laptop screen) comes out as a bit small really - and I'd rather not have to click the picture so it opens at a bigger size in a new window, as I want to view it along with the text it refers to. So perhaps a compromise size of 750 wide is best: I don't know how big these come out on other people's screens.
  6. Train sets are very useful... if you want your model to fly on rails! ?
  7. Firstly, I try to take photos in 'landscape' format in the first place, which fits the computer/forum screen better. Here I have a picture taken in 'portrait' format, so lots of wasted space either side, and if you want to see large-scale detail then you have to scroll down: So, if the picture can be rotated either way into 'landscape' format (without making the viewer seasick) then I do this. At the same time I reduce the file size to 60 pixels across (which makes best use of the default space on the forum without being either unnecessarily large and wasteful of storage, or too small and harder to see without zooming in? I also tweak the picture to make it as clear as possible, either automatically, or by individual adjustment of exposure, contrast, etc. Here I just used the auto option: Finally I always make sure there are line spaces between each photo, but also between photos and text. Not having spaces makes it harder going for the poor viewer! This then is the final result (which I also cropped slightly top and bottom to lose some unnecessary space): It is of course a lot quicker just to bang photos in without adjustment or line spaces etc! ?
  8. Very nice build Mark - look forward to seeing more! Jon PS - it's always easier to follow builds if there are line spaces between the photos (just a little visual pedantry I admit!) ?
  9. Thanks Matty, that's great. The programming looks quite straightforward, and I like the idea of being able to monitor the RX voltage in real time (having calibrated the telemetry to the battery first of course). I expect this to simply read 5.5v until the LiFe supply voltage drops below 6.0v, after which it'll be very interesting to see what happens. Will the BEC output voltage then drop below 5.5v or will it cease supplying any volts at all? All this can be done on the bench as part of the pre-build cycling exercise on the four main servos (wings and tails); the throttle one doesn't need any real torque so will be a diddy little EMAX one to save weight which can be cycled on the tester separately. John, I hear your warning! My only observation is that your UBEC failure was about letting 24v through the gate, whereas my concern here is whether the UBEC simply works per se to supply 5.5v from a more modest maximum of 7.2v, and then keeps working once the LiFe is below half-capacity and for how long.
  10. The input spec for the 4-Max 5A ubec is 6-33V DC (2-8 LiPo), output is 5.5v. A 2s LiFe is fully-charged at 7.2v and fully-depleted at 5.0v, which means (assuming for simplicity a more or less straight line discharge gradient) that the voltage will have dropped to 6v after having used about 55% of the capacity, call it 50% to be on the safe side (and ignoring any peak demands). For my 1600mAh LiFe, this then equals 800mAh usable. Good advice! Do you run the tests on each servo independently or as many as you can fit on your tester (mine does 3 max)?
  11. I did consider that, but the 800mAh NiMhs are based on AAA sized cells and I'd be concerned that they mightn't deal with the load. Savox are mightily expensive, and although I could find a Mini equivalent I couldn't see any for the Micro size. Good to hear of that experience. However I've just discovered an unused 5.5v BEC I'd previously bought (from 4-Max). What would be the downside of playing safe and just fitting this? Do good quality BEC's ever fail? After all they're incorporated in the vast majority of ESCs for electric power-trains!
  12. I was going to fit HS85MG and HS225 servos in my next build (48" Chilli Breeze IC, original used 1990s standards) but looking to save (further) weight by using a 2s 1600mAh LiFe instead of a 2000mAh NiMh. However I don't know whether these can take 7.2v fully-charged? If this isn't safe I could always fit a BEC to step down to 5.5v, but would rather keep the supply as direct and with a few components as possible. So, any recommendations for good quality (not crazily expensive) alternative high-voltage servos I could consider to the 85MG and 225?
  13. Good idea Peter, and easy enough to fit the nipple, but I'll leave this refinement for a future model where I can plan it in from the outset. Aside from moving the battery back and fitting the bigger engine, all that remains is to scribe in new wing-saddles to fill the surprisingly large gap that's grown (been using masking-tape as a temporary dodge), then I just want to do nothing more except fly it! (And build the next model!) Although it's quite big, it just squeezes fully-assembled into the back of my car with the seats down (old-style Honda CRV) which is really convenient. It's easy to clean in the pits (snug fit on the flight-box cradle) with slightly diluted spray de-icer and kitchen-roll, but frankly the combination of exhaust-deflector and Bekra fuel (5 normally but 10 in cold weather) means that there's precious little residue on the airframe. Might stow it (in knife-edge orientation) on the wall... ?
  14. Plenty of clearance for the 53 to spin a 12x6 with the larger wheels I've fitted ✔️ The other thing I'm going to do once the fuselage is back on the bench is see if I can get rid of at least some of the 50g of tail-weight by relocating the battery back one bay from its current spot around the CG mark to its original berth above the wing TE. Just some rough guesses in my head right now rather than any accurate measuring yet, but moving the 125g NiMh back say 200mm is broadly equivalent to losing 30g (that's an ounce in old money) from the tail 800mm away, i.e.: Battery: 125 (g) x 200 (mm) = 25000 Lead weights: 30 (g) x 800 (mm) = 24000
  15. This looks much nicer - and no more wobble! The OS one (with correct OS washer) from Just Engines:
  16. So this afternoon's flying (cold but sunny!) proved the following: Normal elevator rate needed to be a tad higher than 50% so increased it to 55% (+7/-8mm, appx 11° each way) with expo reduced from 35% to 30% to make things less sudden towards full stick travel. High 'Stall' rate worked at treat at 100% (20° deflection): model slowed to idle, nodded and then rudder alone triggered an immediate spin whichever way I chose, with exit right on the money the instant the sticks were neutralised, and no ailerons needed at any time. So I experimented with dialling the rate down to find the optimum amount: 80% (16°) produced the same wallowing rubbish as normal rates. 85% (17°) reliably produced a stall and spin but only to the right (the right wing has some wash-in toward the aileron corrected by a tad of right-aileron trim - which explains why only the left wing will stall at this borderline rate). 90% (18°) reliably produces a stall and spin either way - the sweet-spot! Re landings, I'm finding that I can consistently flare out at the normal rate, so don't need to mess around (or risk a premature stall!) with the rate switch. Afterwards I asked an experienced club-mate if he'd like a go. He flew the B Test schedule beautifully, except his attempt at the spin (because I hadn't briefed him on the rate switch malarkey), and his stall-turn was just about okay (I hadn't mentioned the need for a modest blip of throttle to encourage the rudder over). He thought the Gangster had plenty enough power on the 46 generally, but found that knife-edge (he does it all the time on his own models without mixes) gradually lost altitude: maybe there's some blow-back on the rudder (which is heavily geared for travel not torque), or maybe this would just work better with the extra thrust from the 53 (which I'll be fitting next). Looks like the weather's going to close in from tomorrow onwards... but I've had a complete ball trimming out the Gangster and huge thanks for all the advice and discussion! Learnt loads! ???
  17. Gangster Point well made guys. Not averse to using rate switches (use them aplenty on my DLG for launch and flight phases) so after a bit of fiddling with moving the elevator clevis closer in and setting up a sprung two-way switch (top-left, same as my DLG launch one), this is what I've got to flight-test next: Normal Rate 50%: +6.5/-7.5mm (appx 10° each way) - recently proven for smooth flying with rearward CG etc. 'Stall' Rate 100%: +12/-13mm (appx 30° ea way) - previously proven for prompt stalling, spinning and immediate recovery. I'll leave setting up a switch for landings till later - my brain can only handle one variable at a time! ? Andy, I had considered whether the rudder had a part to play? Whether it's gearing resulted in any blow-back, but this wouldn't a factor at such very slow speeds. And whether it's travel wasn't sufficient, but its got an easy 50mm each way (same as the MR instructions and the original Gangster) whereas it binds at 55mm, so ruled this out. Thanks for the advice to alway spin left and for the reasons why... I do like to understand why! ? Breeze This really ought to be in a separate thread (I think I've already got one somewhere!) but you're completely right Nigel. No point in me overthinking things or making more work for myself - just get cracking with the foam wings! I think with the slightly heavier foam wings I'll stick the OS35AX in it. I can always limit throttle to say 80-90% at first, but it would be good to have the reserve power.
  18. That makes sense: the increase in wood weight would equal the increase in wing area, but the weight of all the other major parts (engine, fuel, servos, battery, etc) would stay the same. As these are a big percentage of any AUW a lighter loading would certainly ensue, and my guess is that the OS35AX would then be just the right engine...? Andy, that's now gone. However I also have a NIB SC32 in my very modest collection, which was the original plan if I was to do a built up wing at 48". The prototype flew with an OS32 on such a wing but used the Irvine 36 with the heavier foam wing. I actually have a set of foam wings at 48" good to go, but am wary of either being impatient (my reason for ordering the wings) or having too heavy a model.
  19. Peter Yes, the original setup produced an immediate classic nose-drop and spin. I realise now that this specific problem has almost nothing to do with incidence or CG changes as such, as it also had 12mm of elevator travel each way. I'd decreased this progressively (as I moved the CG aft) to a latest range of 6mm up and 7mm down, which is simply too little! As I'm happy with the overall setup and don't want to move the CG again (was 96mm, now 111mm), the solution is to start increasing the elevator travel back in 1mm steps until I get a clearer nod and proper stall, with the model falling into a rudder-only spin as before. If it won't, then I'll have to start fiddling with aileron-assistance. Aha, the inverted spin... I'd best leave that for a little while! ? Cheers Jon
  20. In the meantime, after another half dozen flights today with the the Gangster, I'm slightly flummoxed by the fact that - now with proper wing incidence of 0.8° and the CG 15mm back (to 111mm) from where I originally started (96mm) - it no longer falls naturally into a spin with just full up elevator and rudder. Unless I apply aileron to help instigate a proper immediate spin, the model just wallows and flops around in all sorts of chaotic ways, even with less than a quarter of a tank of fuel left, until I eventually stop embarrassing myself and restore normal flight. Have I simply got too little elevator (+7/-8mm) for the job? Or is this something to do with having progressively tuned the model from a negative wing incidence, nose-heavy starting point (where I had no problem entering the spin on just elevator and rudder) to where it is now?
  21. Thanks Nigel, interesting plans to peruse and analyse - and look forward to seeing your Aussie Challenger build! But here's a question: aside from foam-cored wings giving faster build times and more robustness, how complicated would it be to design and build a lighter built-up wing structure? As to the OX35AX being potentially over-powered for the Chilli Breeze (Andy, or not, Nigel) what would happen - in terms of model aerodynamics, P/W ratio, structural strength, etc - if I got the plans scaled up by say 10% from 48" to 52/53" but kept all material thicknesses etc the same?
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