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Robin Colbourne

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  1. Diagonally crossed bands are less likely to come off in a cartwheel, so are more likely to result in damage to the leading and trailing edges. Parallel bands do come off so protect the model better. Diagonal bands put their load on the thickest part of the chord at the dihedral beak, whereas straight ones do so outboard of the fuselage side, so they support the wing better too. If you are concerned about the bands sliding off before you want them to, then your dowels should be longer.
  2. The Iranians must have a sense of humour.
  3. A lip on the cooling air exit helps reduce the pressure there, otherwise the departing air meets high pressure air and doesn't depart. When on the ground, it is not unknown for the airflow through the cowl to reverse and get drawn out the front by, I suspect, spanwise flow along the propeller. A friend with a BMW flat twin in a SkyRanger microlight proved this with a smoke test.
  4. MFA / Como Drills do a range of gearboxes and gearbox accessories aimed at modellers wishing to experiment. MFA / Como Drills Gearboxes
  5. Martin, a free flight or radio controlled model allowed to circle will fly a steady state turn whilst moving downwind with the body of air in which it is flying. The circle will perfect relative to the body of air, e.g .when viewed from a balloon also moving iwht that body of air, but from the ground the model will appear to slow down when heading upwind (ground speed = airspeed - windspeed) and faster downwind (groundspeed = airspeed + wind speed) . A control line model, on the other hand, is circling around a fixed point on the ground, whilst the body of air in which it is flying moves downwind. The suggestion to gently turn into wind in the event of a problem is incorrect. Get the nose down and turn at a 45° bank. The shallower the bank the more height is lost, as more time is spent in the turn. One must also remember wind gradient. When landing into wind, the air's friction with the ground results in the wind speed reducing closer to the ground so the model needs to accelerate to maintain airspeed. The way to do this is to get the nose down. A downwind landing is less likely to result in stalling on approach as the model will gain airspeed as it descends into relatively faster moving air. The landing will also be faster relative to the ground and will result in more damage if it goes wrong.
  6. Always store cyano in the fridge when not in use. Fortunately my girlfriend used the stuff at work in a production environment and doesn't question my doing this. Your experience may vary. Aliexpress do applicator nozzles in packs of 100, for under £2 (although VAT will be added): 100 Cyano nozzles Tacking with cyano, then going round all the joints with Super 'Phatic (from Deluxe Products) gives the speed and accuracy of the cyano, plus the long term strength of an aliphatic joint as it wicks in between the mating parts. Don't forget that birch ply has an oily surface, and really needs cleaning with a solvent, and lightly abrading, before gluing with what ever you use.
  7. Martin, a genuine LOL from me when I read that!
  8. PatMc, this Merco 35 test refers to the ball-headed plug as being KLG Merco 35 Engine test with KLG Plug There is always the possibility that Merco sold them at some stage marked up as their own. I've just read in that Merco 35 test that it was run in on fuel with 30% castor oil. We had better not tell [email protected] engines!
  9. Rich, Pat & Andy, thank you for the replies. Rich, yes I did see the Merco exploded diagram, however I couldn't read the writing on it. I will take care with cleaning. I doubt small amounts of petrol would damage glowplugs, as Merco recommend adding 5% petrol to ordinary glow fuel to improve starting and throttling. I'll probably give my as yet untested ultrasonic tank a try. What we used to do at work if something was really grubby, was to put the solvent and part to be cleaned in a glass jar, and then put that in the tank surrounded by clean solvent or just water. By doing this, only a small amont of solvent would be made dirty. Pat, I hope you are right, as 1/8 Whitworth shouldn't be a problem. Dad did his apprenticeship at Short Brothers in Rochester at the end of the war, converting miltary Sunderlands into civil Sandringham airliners. 1/8" Whitworth screws were used in lieu of Cleco fasteners to hold parts together before riveting. After removal they were thrown on the floor and swept up by the cleaners. Dad must have intercepted quite a few on their way to the bin and there is a jar of them somewhere if only I can find it. Andy, I have some of those ball-headed glowplugs, but hadn't made the link to them being Merco. As far as I can see, all the Merco 61 tests on Sceptreflight use conventional looking plugs.
  10. Andy, all this talk of twin plug Mercos inspired me to have a look at the twin plug 61 I picked up many years ago. It was minus the carb, the backplate screws and one cylinder head screw. It was seized solid, and had clearly had some sort of grips on the prop driver at some time. At least there are no signs of crash damage though, and both glowplugs work. It took a number of attempts with lots of heat from the hot air gun, some automatic transmission fluid and glow fuel to get things to start moving, but eventually they did. The next step will be to get it apart for thorough cleaning and in all probability, bearing replacement. When I eventually was able to remove the backplate, the inside was reminiscent of opening a very old tin of golden syrup. I'm guessing this engine has seen an awful lot of castor oil! Questions I'm hoping you may be able to answer are: What threads is this engine likely to use? I've tried what I think are M3 and 6BA, but neither seem to want to go in. The only review which mentions these threads is the one on the late Premier-made Merco 61 which were M3, but I guess by the time they were made, older sizes of production taps may have been getting expensive or difficult to obain. What grade of bearings do you use? The Sceptreflight review of the Mk1 says the original used an FBC (UK) 1/2x1 1/8 x 1/4 rear bearing and a Fafnir (UK) 8x22x7mm front one. What would be appropriate bearings without going overboard on quality or price? Can you tell from the pictures which Mark mine is? I'm guessing a Mk2 or a Mk3? How interchangable are the carburettors between the various Marks? I'm likely to a have a Merco carb somewhere, but before I go rummaging it would be nice to know.
  11. It is a long bolt which screws in from the top of the quill to pull the chuck or collet into the quill. By being in tension it prevents the chuck or collet loosening and dropping out if you experience chatter on the cutter. A vertical slide is the usual method for converting a lathe to do milling. It enables three axes of movement at the cross-slide, so you mount the workpiece there and have the cutting tool fitted in the headstock.
  12. Don, if only it were that easy!
  13. Rich, Would this be adequate for your needs? Compumill
  14. Rich, If you haven't already looked there, Lathes.co.uk has detailed info and history on Milling machines (going back to the year dot) too, plus classified ads. For instance, this is the entry about the compnay that made my friend's mill Lathes.co.uk -Centec 2A
  15. Rich, sadly that's usually the case once you delve deeper! If you buy a good used milling machine and look after it, you will probably get the majority of your money back when you sell. I recently helped a friend get a Centec 2A milling machine, which does horizontal and vertical milling, plus a Boxford AUD lathe. He had just retired and having had access to lathes and mills throughout his working life, he wanted one of each at home. The machines had been bought by an also recently retired chap taking up model engineering, who sadly died soon after getting them. Neither machine was new by a long way (1960s/70s), but both were in excellent condition (except the mill needed a new traverse motor which we already knew). My friend intends to fit digital readouts (DROs) to both machines, so the machine being metric or imperial isn't an issue. By buying secondhand, there's a good chance you will get the machine plus all the tooling, which can add a lot on if you buy a new machine. Plus, if you read about the Chinese ones, any attempt to improve them is generally attempting to make a silk purse out of a sow's ear. If you join your local model engineering society you will most probably hear about estate sales and people selling to upgrade etc. Beware when looking online, there are a lot of ex-factory machines around that have been 'serviced' with little more than a pot of paint, so don't go too much by first impressions. Get someone who knows a worn machine when they see it to take a look, even if you have to pay them for their time.
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