John Rickett 102

Danny, In hindsight it looks like the flexy pipe which was rigidly anchored at both ends, may have contributed to its early failure. If you make up a new pipe which is rigidly fixed at the engine end and only pushes over the stub on the exhaust manifold (with a short length of silicon on top to act as a seal) you may find that the flexy pipe does not have to work so hard. With the fracture occurring only a couple of inches from the engine, the exhaust is still going to be hot at that spot and I doubt silicon will last very long, possibly two flights! You could try inserting a brass sleeve inside the flexy before sliding on the silicon, this will prevent the hot gasses from directly impinging on the silicon, conduct the heat away from the upstream bit of flexy and will also act as a support. Without a support, the silicon is going to take all the load just where its hottest so I'm sceptical that it will afford any kind of long term solution. Unfortunately while silicon will stand up to 2 strokes, a 4 stroke exhaust is much hotter, although it cools quickly along the length of the pipe, but where yours has broken, the heat is possibly at the limit of what silicon can withstand. Yes, put a tiny drop of threadlock on the screws, but don't over do it if you want to remove the same screws in the future. One final thought, a wooden prop will dampen engine vibration better than a glass filled one.

For anyone who has grappled with 'conditions' in modern Futaba transmitters, the dawn has just broken for me - in any 'condition' that is going to be changed from the Normal (Condition 1) setting, the Group/Single setting has to be set to Single, the default is Group. This now make sense in that the changed condition will only be applicable to that one (single) condition. The engine controls are now set so that the inners and outers all work together in 'Normal', or by operating a switch, will bring the outers to idle regardless of the throttle stick position. I've also set up a 3rd condition which will stop all four engines when the throttle cut switch is operated. It does away with using dual-rates to achieve the same end, there's no difference in practice but to me its a neater and more logical way of doing things. I'm getting to be a fan of the SX radios, the conditions facility is a powerful provision.

I’ve had five more flights now, unfortunately the left outer has stopped on two of them. On each occasion, the throttles were closed and the model glided in. The main needle needed opening half a turn prior to the first flight of the day, which seemed odd as I hadn’t touched the needles after the previous flights. All ok after that until the most recent flight when the left outer stopped again, and glided in narrowly missing a tree! At home, after a blast of carb cleaner, I found some debris between the main needle and the spray bar. When an outer cuts, its impossible to maintain revs and turn into the cut engine, (when an inner cuts it’s not nearly as dramatic) so up to now the only course of action is to go to idle and glide down. The throttles are all operated from the main throttle stick through individual servos each having their own channel. My hoped-for solution was to be able to chop both outers (so it doesn’t matter which outer stops) when necessary, leaving the inners running, I’m sure the model will maintain height on the outers alone. The Futaba set I’m using is a 16SZ which has ‘conditions’ settable for various flight modes. I wanted to be able to have a condition where the left slider would activate a second condition and become the throttles for engines 1 & 4. It doesn’t appear as if that can be done, once a function is assigned to a stick or switch, it stays that way – I thought that within a condition, everything could be altered just as in setting up a new model memory. I’ve now ended up with assigning an unused switch as a dual rate switch and set the alternate rate, using the ‘point’ graph in the AFR menu to bring throttles 1 & 4 to idle regardless of throttle position. This will have a similar affect as the first method but I still find it odd that not everything is re-assignable under a new condition. As an experiment, I tried altering the servo speed under the second condition – that doesn’t work either, whatever is set for the first condition stays that way…unless anyone has better knowledge of the radio? I did manage to get the conditions renamed as Normal & Idle 1&4 which will read on the main display and be switched by the dual rate switch but am a bit confused as to why only certain parameters can be changed within a flight condition.

Thanks for the compliments and pleased you liked the refurbishment blog. This is the first time I've attempted to record a build or repair sequence though might try another, I see Mr Fenton's efforts are popular and if it encourages people to get building, or help to stem the decline in building which is more to the point, it can't be a bad thing. Thanks for the tip regarding the use of fibreglass Manish, of course that won't burn so will be stored in the grey matter for possible use.

Hopefully, the problem with the inner engine exhausts has now been fixed. This picture shows the gap between the exhaust flexy pipe and the silencer stub; exhaust heat directly onto the silicon tube bridging the gap soon destroys it and if the flexy touches the tank, that too is melted. The simple solution was a short length of K&S thin-walled brass tubing, the silicon now forms a bit of a seal between the flexy pipe (which is slightly smaller than the silencer stub) and the brass tube but does not come into direct contact with the hot gasses. With there now being a metal bridge, there should be improved heat conduction. As an additional safety measure a piece of thin aluminium sheet has been glued under each tank. The 3rd flight was captured on video, still shaky in parts I’m afraid, but proves that the model has successfully flown again. The day was fine enough though a little choppy leading to the model being buffeted at times. The speed was kept slightly on the high side, I’m sure this can be reduced in better conditions to create a greater sense of realism but the greater aileron movement afforded by a one-servo-per-aileron installation showed that the model can now cope with a bit of turbulence. Resized, edited DH86 3rd flight.mp4 The little Lasers started easily and performed faultlessly, once again thanks to Jon Harper at Laser Engines for working his magic. From building three other deHavilland twins and multis, I’ve found there is a slight disadvantage (for the modeller) to their designs. The adoption of a single fin/rudder puts it out of the propwash. With the DH86 the outer engines are a considerable distance from the centreline, less than perfect engine synchronisation causes a tendency to swing on the take-off run which is difficult to correct with rudder alone. To counter this, each engine servo has its own channel with the outer engines slaved to the rudder. Full rudder output will advance the opposite outer engine by about 10%, ie right rudder will open the throttle of the left outer engine. The right outer engine in this example is not reduced by 10%; modern radios make this mixing very easy as Side A and Side B, in Futaba parlance, can be programmed independently. The cost of the restoration hasn’t been kept but it will have been a few hundred pounds, cheaper and quicker than starting from scratch I suppose. Cynically it could be described as mutton dressed as lamb, however I’m pleased with the final result and hope now that it has proved itself. it gets flown a bit more often than when first built. I’ll admit that it has been a more enjoyable project than I first thought, given that I reluctantly carry out repairs and this restoration was essentially just that. In building a model from scratch most are effectively prototypes as a subsequent one doesn’t usually get built to correct the inadequacies of the original, so a first for me on that score. This was the second of a two-model refurbishment I had tasked myself to do (the other was an equally old DB SE5) to prevent unairworthy models from taking up valuable space in my shed. In truth that was only buying a bit of time as now they are complete, I feel the need to tick off another attractive subject on an ever growing list. I’d better sweep out the workshop and worry how I’m going to squeeze another project into the shed.

Thanks for the compliments, its well appreciated. The little engines are bedding in nicely, even after only about 1/2 hours running, thanks to Jon Harper for getting them back to health. Here's a shaky bit of video, in my haste I had fitted a nearly flat battery into the camera instead of a charged one, so the camera cut out after a minute of so. The sound change when the exhaust blew can be heard as it comes overhead. Here's one more of Mike Mennell's photos from a different angle - now I really ought to get those homemade exhausts fixed so that flying can continue. 457295767_DH86PostRestoration1stFlight.mp4

Larger magnets have now been fitted to the (outer) tank hatches and spinner adapters, courtesy of Just Engines, have also been fitted. A bit of time was spent at the field getting the engines to run in sync, a job made much easier nowadays with the aid of point adjustable curves for the servo outputs. Each engine has its own servo and servo channel from the receiver so its possible to use one engine as a reference and adjust the servo curves of the other 3 using the (9) point adjustments in the AFR settings - I'm using a Futaba transmitter, though imagine that most comparable radios will have a similar facility though it might not be called Adjustable Function Rate (AFR). Mixed fortunes on the first flight. Son Steve was pressed into service as the test pilot and did a splendid job, the good news is it flew with only minor trim adjustments required, the bad news (not really), a silicon exhaust coupler failed on the first circuit and the flight had to be terminated. The inner engines each have a bendy pipe leading from the exhaust port to the homemade silencer. Short lengths of 1/2" silicon tube were used to make the couplings but the silicon cannot stand the exhaust heat for very long and one failed. This has happened a few times in the past and I haven't come up with an alternate solution, but one is needed as the fuel tanks are only millimetres above the exhaust pipes. When a silicon tube fails, the hot exhaust can be directed onto the bottom of a fuel tank and deform it. I'll have to think of another method to connect the two parts together which will allow a degree of vibration protection and also not allow any of the silicon tube to come in direct contact with exhaust gases. Fellow club member Mike Mennell takes excellent pictures of member's aircraft and lived up to his standard on Friday when these were taken.

Thankyou for all the supporting comments along the way. Having stared at it for so long I'd almost forgotten the drab clothes it previously wore - hopefully its new bright finish will be an aid to my failing eyesight. I discovered yesterday during the engine runs that the magnets holding the tank covers for the outer engines were not up to the job; I think the old magnets will have to be cut out and replaced with stronger ones. Another fault to be overcome is the lack of thread remaining on the crankshafts when using aluminium spinners. I believe Laser Engines recognised this oversight some years ago and made the crankshafts a bit longer on subsequent engines so its no longer a concern. Shaft extenders used to be available from Laser but aren't listed anymore so perhaps a call on Monday to Just Engines is required.

Thanks for the support and the information Steve, yes that is what I wanted originally but being a novice at Youtube...... I won't be bringing it at the Easter weekend, the engines need to be set up which will take a while and then I'd rather do 2 or 3 test flights when there are few around.

Couldn't resist a picture with the wings fitted, before taking it apart again to put back in the workroom.

Thanks Graham, throttled back Lasers have a muted note, much less harsh than their contemporaries. About 18 months ago I bought a new transmitter, (Futaba 16SX). The features blurb said it had a multi engine function but whatever that feature is, is not in the manual. I was hoping it would carry the throttle cut to any other channel which was designated a throttle…but it doesn’t. In the end I got round the problem by assigning dual rates to each throttle channel, and only extending the range on one side. So now, pulling up the throttle cut switch, puts a high rate to each throttle servo and brings the throttle arms back just that bit further. I think I need to play with them a bit more to close the throttles completely - its all part of the pre-flight preparations.

If I've done this correctly, the link should show the little engines singing in harmony! The engines had only been run for a few minutes prior to this so there is still some setting up to do, but run they do and much the better for being overhauled by Jon Harper. The No:1 engine is really tight in the bore but even after this run it was loosening nicely. https://youtu.be/NPNurI4riOw

Thanks Ron, its taken a lot longer than originally expected but we're nearly there. Hope to have 4 dinky Lasers running by next week.

With painting complete its time to get on with the engines, tanks and undercarriage installation. The trousers completely enclose the inner engines so to allow for glow connection, a mini jack-socket is located just behind the cowl. With the cowl in place the male connector can access the female jack-socket. The one below is for the an outer engine, these are a bit more accessible so only needs a bracket to hold similar jack-sockets. The bracket then fits almost flush with the bottom of the cowl. In each case the glow plug connector part is a few turns of spiral wire with the lead soldered on and covering with heat shrink to take the load away from the solder joint. I used to use the old nylon wire curtain rods as they were a good fit on the plug posts of a few years ago. With a standardisation for all my Lasers to using OS 4 stroke plugs, which have a wider than normal post, the wire that is used for a certain type of stationery file folder, is a pretty good fit. Buy a couple of these if you find them in a stationery shop and you'll be set up for years! With just one turn snapped over the plug, they are not going to let go very quickly.

Sorry Danny, I've only just picked up on the question. The tape I used is from a company called Physical and its simply labelled as Sports First Aid. Its says its zinc oxide tape and latex free. Putting that into the search came up with this: https://firstaid4sport.co.uk/?gclid=CjwKCAjw0a-SBhBkEiwApljU0g3RbuTuy_ZffS68-sNzfI3rAhdGHARn-yS0a6kwHK2qHxgRPQZLHBoC63IQAvD_BwE It looks the same but can't be sure being out of the wrapper. The wrapper on the stuff I have says its distributed by Physical Sports Ltd, 17 Dam Rd, Barton-on-Humber DN18 5AS. If you are looking for a sharp saw-tooth edge, this won't give that. At first it looks to have a good edge but by the time its been stripped of adhesive and applied to a surface (I use fabric cement) the sharp saw-tooth edge is lost, but its passable from a distance.