Jonathan M

On the basis that I like to have redundancy (and a 12v field power source for my Fusion charger), I've ordered an identical replacement 7Ah Pb for £21 delivered (as it happens from the same retailer I bought the original from): Yuasa NP7-12S. Will also of course keep the simple adaptor I made up for the starter's banana plugs and the 3s 3300 on half-charge in the field-box as a backup. Nonetheless today the knackered 12v still managed to start the Irvine 46 half a dozen or so times in pretty cold weather while also powering the glow-plug - although as Peter reports (and as mine has always done) did need to turn up the dial once the starter was spinning to keep the plug glowing at 1.5v.

I'm now happily talked out of building the Acrowot! The Chilli Breeze will most likely be my next build, and my first from a plan (keen also to know when Mike Delacole's new lighter wing design will be ready). The larger Wind would probably be the more sensible size, but I want a suitable model for my OX35AX, and also interested to see how I'd get on with pattern aeros with a smaller model. Another future build could be from the original Loaded Dice plan? Although the original is quite big at 66" and heavy at 8.25lbs with foam wings etc, maybe a 90% scale version and/or constructed slightly more lightly with a built-up wing (with/out retracts) etc would prove a good stable-mate to the Gangster with a similar-sized engine? Out of interest, I ran the cubic wing loading numbers for the different options - lightest at top, heaviest bottom (conventional loading in brackets): Gangster 63 Lite - 5.45 lbs - 7.7 (17 oz/ft2) Loaded Dice 66" - 8.25 lbs - 8.9 (22 oz/ft2) Chilli Wind 58" - 5.25 0lbs - 10.7 (21 oz/ft2) Chilli Breeze 48" - 3.30 lbs - 10.8 (18 oz/ft2) Tornado 62" - 6.25 lbs - 11.1 (23 oz/ft2) Bullet 50" - 4.75 lbs - 12.9 (23 oz/ft2) However one cuts it, the Bullet is the heaviest by far, followed by the Tornado! The Breeze looks quite respectable despite its small size, and a very slightly smaller or just lighter Dice would be an interesting proposition...

Useful discussion. On reflection I'm inclined to buy a new sealed lead-acid battery as my main field-box power source, and keep the Lipo version as a backup for the starter (left on a not unsafe 50-60% charge for occasional use) rather than put all my eggs in one basket. Charging and storing the lead-acid is altogether much less fraught - just overnight after or before a day's flying then unplug and forget. But I think the standard 7Ah battery is excessive in its capacity, and could easily save weight by dropping to 5Ah or even 3.5Ah - what do other folk have?

Thanks Peter and Andy Peter, I appreciate the advice on fitting the 53 and now understand from that the reasons why. Yes it has the silver carb (as does the current 47). The guy I bought it from was using it to pull around an Acrowot with a 12x6 prop, says an 11x7 also works well. With the slightly bigger wheels now on my Gangster I should have clearance for the 12x6, which should also be the quieter of the two. Andy, trimming will probably prove to be the easy part, because that was just a question of studying the theory and then being methodical with each component part almost every day over a week. Whereas practicing flying any given schedule - without hesitation, deviation or repetition - that will really test me!! To be honest I have little interest in just pottering a powered model around the sky. But more to the point I repeatedly became frustrated with my previous attempts to make any progress with traditional aeros. In part this was because I was trying to improve my skills by flying less than suitable models (after learning with a Riot, I then had an ARTF Acrowot with a 70FS which unfortunately splintered into hundreds of pieces early on in its life when my then Spektrum TX failed, then an ARTF Wot4 first on electric then with a 40, also an ARTF Boomerang with a 46), but also because I didn't really understand how to set them up optimally in the first place. Building the Gangster has been a bit of a journey (to say the least!) but I learnt a huge amount in the process. And on its first few flights, even before fine-tuning the trim, it was immediately clear that it was such a different beast to the other models. I have an Acrowot kit to build one day for the 70FS or a Laser 80, but my next power-build (some time in 2022?) is likely to be the Chilli Breeze for an OS35AX - 2/3rds the size of the Gangster but a not dissimilar type of model - and at least I'll be working off a proper plan and proper magazine article. Cheers Jon

After several sessions of trim flights over the last week, this is where my Gangster is now at: As built and first flown, the model needed a good amount of up elevator. But before going large with tail weights to move the CG aft etc, I fished out my incidence meter which showed that the wing had a default incidence of almost 1° negative! So I made up two pairs of temporary hardboard and MDF shims (could eventually use lite-ply but wanted a quick method for initial tests) to fit between the wing and the rear mounting-plate with holes for the nylon screws: two at 2.2mm thick each and the other two at 2.9mm each. Combined in pairs, these give a total thickness of 4.4mm, 5.1mm and 5.8mm, resulting in positive incidences of 0.2°, 0.5° and 0.8°. Not having previously - methodically - set up and fine-trimmed a proper aerobatic model, I printed out the GBRCAA Trimming Chart and worked through this repeatedly on several series of short flights (half-tanks of fuel to keep the nose light), at each of the 0.2°, 0.5° and 0.8° wing incidences. Straight & level flight revealed a need for slight right aileron trim (there's a very slight warp in the right wing resulting in a tad of wash-in), while the as-built 0° down-thrust was perfect. Other tests on the chart showed a need to increase right thrust from 1 to 2°, and lateral balance was achieved by sticking a 10g weight on the left wing-tip (i.e. opposite the sidewinder engine cylinder). Aileron differential I'm still fine-tuning (it doesn't seem to need much if any) and my rates are currently set for a complete roll-rate of 2 secs. Both aileron and rudder have 20% expo (rudder can probably use less). Which just left the two usual suspects of CG and wing-incidence to deal with (with elevator rates to suit!). But, while these are separate issues, I found it quite tricky in practice to juggle the tests, make incidence, tail-weight and elevator trim/rate changes (one at a time) and interpret the results correctly without getting confused! But the net result of all these methodical tests has left me with (aside from a knackered brain, a bad back and a week's worth of stubble!) a working result of: 0.8° wing incidence CG at 4-1/4" (108mm) via 40g of tail weight very slight down trim on the elevator (travel range of +7/-8mm on 30% expo) At these settings: incidence test (gain height, vertical dive at idle) remains vertical ? CG test (both versions: 45° down-line on half-throttle and 45° inverted up-line on full-throttle) gives only the slightest arc towards the canopy ? I'm now finding the Gangster a dream to fly. It goes precisely where I want to put it, and accelerates and decelerates with the Irvine 46 (11x6 prop) exactly as needed. Stalling on full up elevator for spinning produces a good amount of nodding before it eventually falls off (usually to the right) but clear rudder input works immediately to instigate spin and neutralising it gives instant and accurate heading recovery. Inverted flying is very comfortable and assured with only a very slight forward pressure on the stick. Landings are consistently accurate (touchdowns within 10m of chosen spot) sometimes a three-pointer, sometimes on main UC before dropping onto nose-wheel, but without any worry of dropping a wing in whatever conditions of wind speed and direction. Happy Chappy ? PS - just taken delivery of a good Irvine 53 from a bloke giving up IC.... ?

PS - The second option above comes from slope aerobatics where 4-Axis is employed for extreme flying (all at the polar opposite of things compared to the Blackburn Monoplane!) but such a system would give you the ability to trim the wing-incidence slightly (in flight using a slider?), still employ rates and differential, etc - until you've tweaked the model for best and safest control. https://www.slopeaerobatics.com/2007/04/13/an-introduction-to-4-axis-flying/

Did the full-size wing warping work in just one direction (down)? If so then no wonder (along with then other primitive design features) it is a handful to fly! Re the model: I can't see how one could effectively "hide" any sort of conventional ailerons. But here are three possible starting points: Completely re-design the wing for warping as per the full-size; this would require functional bracing to support the delicate structure. Mount the wings in a way that they rotate as a whole but in opposite directions on their main spars via servos in the fuselage (would only need a fraction of movement for effective roll-control). Stiff transparent plastic trim tabs on the last few inches of each wing, operated by push-pull wires to servo(s) in the fuselage. The first option would be a major engineering challenge, and would result in a dangerously delicate wing for RC flying. The second option would provide maximum "hiddeness" without the loss of structural strength. Maybe rigging would still need to be functional (but working in the same direction as the wing-rotation, or slightly elastic?). The third option would be visibly obvious but the easiest to achieve.

Won't they roll around on the building board...?

3s Lipo hotwire hack (didn't want to lose the starter's banana plugs just yet) worked a treat at the patch today! Used 10% capacity of the 3300mAh - as I was doing lots and lots of repeated but short CG and incidence trimming flights on half tank to keep nose light.

I understand. So even a smart-charger that has a desulfator function won't be able to resuscitate a modern gel-based lead acid that has been physically distorted by massively overcharging at 0.85C.

Thx Peter. My starter is a Just Engines one with a 4:1 reduction gearbox and rated for 12 – 15 Volts. JE add that "under certain conditions the use of LiPo batteries can overpower the starter and cause the switch contacts to weld on. Many use LiPos without problem..." but I assume this is where folks are using 4s LiPos? At full charge my 3s 3300mAh will deliver 12.6v, down to 12.0v at 80%, etc. In the meantime the 7000mAh has accepted a charge of over 1500mAh (20% of its capacity), which doesn't bode well given that a lead-acid is only normally flat when it is approaching down to 50% capacity.

I'm hearing all the preferences for switching to LiPos so (as I'd like to fly this weekend) I'm going to try that route - at least as an interim solution! I've got a pair of good but completely redundant 3s 3300mAh LiPos - I assume 3s would be the correct voltage rather than 4s?

That makes sense Keith. The alarm system type would have thin plates (like a marine leisure battery, for nav and cabin lights, electronics etc), whereas the drill type would have thicker plates (car and boat engine start batteries for cold-cranking).

Thanks folks - I realise that I've properly cooked it! Don't want to down the LiPo route, prefer the simplicity and safety of Pb, and weight isn't really an issue (the 7Ah 12v balances the 1/2 gallon tank at the other end of my field-box/stand). This one actually lasted me very well (until I recently attempted batterycide - twice at least! - by charging at 0.85C) and they're not dear, so I'll just order a new one. But one question for Cuban8: you say charge at 0.1C which my Fusion charger can do (just set it to 0.7A), but I can't change the voltage end-point on it to less than 14v. Surely this is safe enough for fairly regular overnighters as I did for years?

12v 7000mAh starter battery failed at patch today - had started Irvine 46 a couple of times but fell off a cliff the third time, glow meter dropped to almost nothing when using the starter. Had been fully-charged a few days ago, used for starting and glow plug maybe a dozen times since. Back home on the multimeter it read 12.28v. I'd always previously charged on 1A but found my charger set to 6A from the last time. Have I damaged the plates?! It is a Yasua NP7-12S, about five years old with very light use over that time. Currently re-charging at 1A. If it is damaged would repeated gentle cycling recondition it to health, or time to buy a new one?

Will there be scallops on the fuselage... or clams?

Got to use my patent wire-bender for the first time ever making new 8 gauge U/C for the new 2.75" wheels (with a bigger internal diameter than the original smaller 10 gauge ones). Quickly discovered that the trick was to hold the first bend (axle) flat on the plate to ensure an accurate parallel second bend: And a similar dodge for the final bend which is at 90° to the rest: This all now looks like it'll cope with our patch much better: Needless to say weight crept up by 5oz (from 5.1 to 5.4lbs) and there'll be a tad more drag, but can live with all this: Turns out that the heavier gear didn't change the CG at all, which is still at 3.75". But while it was on the stand I experimented with adding 10g weights to the tail and noted how much the CG moved aft - 1/8" (3mm) each time - which would be helpful for my next flying tests at the patch:

That's not good to hear. The only Radient LiPos I have are a couple of single cell 700mAh ones for a new bungee 2mRES, so far unused. Swelling won't be a problem on 1s, but will be interesting to compare their in-flight capacity and longevity to my old but still good Nanotech ones.

Proper job Stephen! I also really like it when people insert spaces between their photos - makes the visuals much easier to read than continuous reels! ?

Gents, you've all risen to the challenge admirably! I've had a long day away from home, but in a brief quiet moment I called Just Engines. It turns out that the Irvine 46 (at least the OS produced ones like mine) used exactly the same prop driver and thrust washer as the OS 46AX, 53AX, etc - so I've ordered these from them. Had this not been the case, then I'd have set about one side of John's double-flatted one with a file - however thanks so much for looking, really appreciated!! Had John not unearthed his one, then I'd have gone with Robin/Martin's suggestion of a new brass key (I have suitable stock) with baked epoxy. Had I done nothing, then, as Jon says, it wouldn't have looked pretty but it would probably have continued working (the thin hex nut is actually a good fit on the shaft and against the front bearing) until the original bodged key eventually wore away entirely... Thanks to all for the help and advices! ???

That sounds like it'll do the trick. But take care to lightly abrade the piano wire first. Also worth doing a test run on a piece of scrap wire first to test the process; you can always re-heat the joint to liquidise the solder and remove, but will need to clean the socket before final soldering. Get yourself a solder-sucker, which is cheap but effective. Agree totally about doing the covering in one sitting. Tack film panels down around the outlines on low temp as you go, but only shrink at higher temp once the whole lot is on both sides. If there are any warps (keep checking carefully by eye as you go) then give the opposite side a careful blast with a heat gun, then weigh down overnight. Try to only tack the film to the internal ribs and sheeted areas once you've got a smooth warp-free surface overall.

Thanks Denis, that can be Plan B. Will see what John comes up with from his stash first... and/or if I can find an old Irvine 40/46/53 for spares?

Andy I suspect that the one I have isn't an original like the one pictured above (out-of-stock at the usual retailers). The engine is obviously well used and was given to me complete with a very tatty Boomerang (no doubt not it's first airframe) which I binned. There's also a thin hex-shaped nut used to pack it forward from the front bearing, which I'd ideally replace with a proper thrust-washer (if that's what it's called). But it is a good runner and ideal for my Gangster. I don't have access to any welding kit. If I can't get a suitable replacement, occurs to me that I could either use J-B Weld metal epoxy to build the flat up (if that'd prove robust enough?) or tap in a steel grub screw with grippy threads (assuming that wouldn't unbalance things too much?)... or both?!

Interestingly a mate sent me a flying spec for the original Gangster 63: 5.75lbs (15% heavier than my 5lb Lite) Enya 60 with an 11x7.5 (that's coarse and fast, mine is an 11x6) CG at 110mm (mine's currently at 95mm, going to try 100mm next - but only if it needs it) 1° of down-thrust, 3° of right (mine was no down, 1° right - but I've just now shimmed it out to give 2° right as I think initial tests showed a tendency to still roll a bit left when the power comes on). Jon PS - Hope I'm not boring the parish by going on and on!! Just that I'd like it if anyone else who decides to build a Gangster Lite can benefit from what I've learnt etc.

Cheers John The prop-driver is 9.4mm thick, has a maximum diameter of 28mm and the ID of the hole is 10mm. The prop-shaft is 1/4" (6.4mm on the smooth part) and the diameter of the thicker part nearest the bearing is 9.5mm (the flat is 1.6mm lower). Jon