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Martin Harris - Moderator

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Everything posted by Martin Harris - Moderator

  1. Martin Harris - Moderator
    An 18 x 6 prop on an ASP 160 is exactly 1/4 scale diameter and suits a 1/4 scale Cub perfectly so not all i.c. models need non-scale props! However, as you are very unlikely to notice the prop in flight, why not just have a nicely detailed display prop? Edited By Martin Harris on 14/01/2011 19:32:04
  2. Martin Harris - Moderator
    As others have said, the only safe electric model is one with the main battery leads disconnected so fitting a switch could lead to sloppy safety procedures. Having said that, I've set up my transmitter so that all my electric models have a throttle isolating switch which I leave safe until I'm on the flight line but I still regard the model as live and dangerous from the moment the battery is connected until it's disconnected again.Edited By Martin Harris on 13/01/2011 13:50:20
  3. Martin Harris - Moderator
    Great news - especially now that you've got that load off your mind! Keep up the good work and let's hope you get back to your old grumpy self soon!
  4. Martin Harris - Moderator
    Posted by Steve Hargreaves on 12/01/2011 08:53:27:  I do recall that the original Irvine 40 (from the late 80's) had a custom made rear bearing (as in custom made for Irvine) & was a slightly smaller od than the "standard" size bearing. When Irvine stopped making the engine supplies of spare bearings ran outr pretty quickly too. The solution was to Loctite a circular shim around the outside of a smaller bearing to make it the correct od to fit the housing.......didn't work very well though!!! Why Irvine insisted on a custom sized bearing is anyone guess!!! When I spoke to Irvines about spares for my ancient Irvine 40 (bought around 1976 so they pre-date your estimate a bit!) just after returning to the hobby after a 25 year break they explained that the bearing used had been dropped by the bearing manufacturers and was a mixed imperial/metric one so I'd imagine that when they specified it all those years before it was a standard item. In addition, I'd have thought that the cost of getting custom made bearings for the relatively small volumes would have been prohibitive?  P.S. IIRC the "official" solution was to specify a bearing with an oversized bore and sleeve the crankshaft.which, on thinking about it, would allow a correct width bearing to be obtained.Edited By Martin Harris on 12/01/2011 12:05:59
  5. Martin Harris - Moderator
    Posted by Tony Prince on 12/01/2011 10:42:51: Hogster, if the OD is too big why don't you get an engineering grinders to skim it down for you. Get them to measure the bearing bore in the engine first, they will be able to recommend the correct final size. When you get the bearing back, wash it well in Meths, then Laquer thinners, then petrol, then meths again. Then lubricate with after run oil before fitting. This is to be absolutely sure you get all the grinding nasties out before you fit it.  Are you serious Tony?  Quite apart from the cost of getting the bearing ground, I'd have thought this would be an absolute last resort as the chances of contamination must be horrendous!  Perhaps you were in a "needs must" situation but I really wouldn't recommend this solution to the average modeller with the alternative of returning a bearing to get the correct one! Edited By Martin Harris on 12/01/2011 11:36:21
  6. Martin Harris - Moderator
    I think some of us are missing the point here - Scruffmeister seems quite aware that he can buy by internet/phone/post but is looking for a local supplier - not necessarily a model shop and wants generic suggestions where to look...Edited By Martin Harris on 12/01/2011 11:10:45
  7. Martin Harris - Moderator
    Unfortunately we've mostly got ourselves to blame.  Using Ebay, Giant Fish (great service BTW), mail order from HK, ARTFs and other forms of instant gratification, parking restrictions, greedy landlords, computer games etc.etc. have all conspired to making it extremely difficult for traditional model shops to survive.  Of course, back when I were a lad, most decent sized towns had 2 or 3 model shops...and thee could buy enoof balsa to mek 7 quatter scale replicas of 't Spruce Goose, a gallon o' tissue pest, a pint tin o' Diesel fuel and still have change from haff a crarn...those days are sadly gone but the compensation is that this hobby has actually never been so affordable.
  8. Martin Harris - Moderator
    Posted by Andy Harris on 10/01/2011 00:43:14: @Martin.H  I'm assuming we're discussing as if the Eflite SU 26M (480 Motor) version was being flown.   No - I was talking in general terms...
  9. Martin Harris - Moderator
    The odd thing is how little some people use the rudder on the ground run - I'm fairly sure that most clubs have their share of "it takes off in whatever direction it ends up" fliers. Watch their rudder inputs and I can almost guarantee that you will see no movement whatsoever in many cases as the model wanders off line - even from some very established club fliers.  Unfortunately, you can pass an A test without touching the rudder - perhaps taxying out and lining up should be a required maneouvre?  Helicopter fliers are far more aware of their (Mode 2) left thumbs, having learnt to make precise height adjustment and heading changes right from their first attempts, as opposed to fixed wing fliers who learn to use the ailerons/elevator first and often tend to use the throttle rather digitally and as John says, have little involvement with the rudder after being introduced to it at a fairly late stage in their training.
  10. Martin Harris - Moderator
    I'd just like to add a note of caution to BEB's very informative posting earlier. The suggestion to use rudder to turn when low and slow sounds to me to be a recipe for a wing drop/incipient spin. I was always taught (and in turn taught pupils) to perform all turns (in full sized gliders where use of the rudder to counteract adverse yaw is a basic requirement) in a balanced condition.  If you yaw an aircraft with low airspeed, you slow the inner wing and this can result in it stalling - the reaction then to pick up the wing with aileron adds more drag to the inner wing and effectively increases the AoA (as the chord line is measured from the aileron TE to the wing LE) deepening the stall. The result often involves a cartwheel and a plastic bin liner...  Incidentally, in a sidelip, most aircraft find their elevators are less effective due to airflow being shaded by the fuselage and very often, in a fully developed sideslip, you can find you have full, or large up elevator delections in order to keep the nose up and airspeed under control so stalling off a sideslip is not usually a problem.  In practical terms, use of the rudder is less important in turns on the average power model, particularly when flown at typically over-scale speeds but if you watch the model in the turn and the tail appears to hang low, that's an indication that you need some rudder to balance the turn.  In a light aircraft, the primary use of rudder is to trim out yaw due to power changes and very little rudder is usually required to balance turns - and without some form of seat of the pants or slip ball telemetry slip (or skid) would be very difficult to detect from the ground.Edited By Martin Harris on 09/01/2011 22:34:07
  11. Martin Harris - Moderator
    Absolutely, BEB and particularly on the approach some extra speed is the key to arriving at ground level under control but in this case I suspect the opposite!  If it (not knowing the model) is a typical trainer with a healthy positive AoA a good armful into a gust could cause a zoom climb and the complications of flying while looking over your head backwards makes it very tricky to sort out in the few moments.
  12. Martin Harris - Moderator
    Simon, I'm wondering if you're trying to shape the profile before building the wing? That would be tricky to do accurately...  I don't know how the others do it but 'd guess, like me, they would build the wing with appropriate plain strip and plane and sand it in situ - mark a straight line at the most forward projection and smoothly blend to this, finishing that part last to get an even profile.  If you're on a budget, get yourself a balsa stripper and cut your own strips from sheet - buying them pre-cut is a VERY expensive way. For instance, from a randomly selected supplier, a sheet of 1/2 x 3 is £2.42 and a single strip of 1/2 x 1/2 is 75p (L.E. is £1.65) so you could cut 6 strips at a cost of @40p each so a balsa stripper like this (my favourite type) would soon pay for itself - as well as giving you any size you need without delays or wasting petrol or postage!  P.S. Don't pay too much attention to the 1/4 inch sheet mentioned in the link - 1/2" is 1/4" from both sides but I'm sure it cuts deeper than this anyway and on thicker sheet still it starts the cut beautifully for finishing with a knife and straight edge.  P.P.S. Just checked mine and it goes out to almost 13/16 width and will cut as deep as I can set a scalpel blade - maybe 3/4" although I'd make several cuts for this depth... Edited By Martin Harris on 08/01/2011 23:43:39
  13. Martin Harris - Moderator
    ...and another check is to try rocking the prop - if there's any noticeable play the bearings are shot.
  14. Martin Harris - Moderator
    Posted by Biggles' Elder Brother - Moderator on 03/01/2011 17:30:47:   Regarding connectors - the two main choices seem to be "Deans" connectors, like two blades at right angles to each other, or "Bullets", basically cylindrical plugs and sockets. Bullets come in a range of sizes - typically from 3mm up to 6mm+. Its a personal choice but you really need to standardise on one type for interchangability. Personally I use 4mm bullets. If you use bullets should also adopt a "convention" like "plugs on the battery positive, sockets on the battery negative" and do all systems like that. That way any battery will fit (electrically at least) any model. You'll need a similar convention for Deans connectors if you use them - like battery positive always goes to the "horizontal" blade or whatever.    Just a quicky BEB, as Timbo pointed out to me a while back - and I didn't believe until I checked - all Deans - and every clone I've checked - have polarity markings moulded on them (which may be tricky to spot once they have been soldered up) so there is already an established convention. The way I remember it is positive is a cross (across) - look at one and you'll see what I mean... Edited By Martin Harris on 04/01/2011 23:35:41
  15. Martin Harris - Moderator
    Was that the forerunner to the "trigonic" profile as used for TT100 (K81) tyres back in the days when bikes were proud to show off their engines and didn't hide everything under plastic shells?  Lovely grippy tyres in their day with very progressive breakaway but the back one would only last 4000 miles on my Bonnie.
  16. Martin Harris - Moderator
    From the description, some work with a drill, various Dremel tools and scalpel to remove the bearer material from the ribs, cutting back carefully to the glue line?  
  17. Martin Harris - Moderator
    Have most of us got a old bike tucked away somewhere? Like Tony's, mine's virtually the same age as me (same month/year) and I've owned it on and off since I was 16 and a couple of months. I can't claim it's up to the exotic standards of the bikes featured so far - it's just a little Triumph Terrier - but I restored it from a total wreck after recovering it (and draining the rusty water from the crankcase/gearbox) from a friend who'd lost interest (or was told he had perhaps?) after starting a rebuild a decade or so before.     I did have my ideal bike before that which I'd intended to keep indefinitely - a '68 Bonneville - but it was stolen and I only got the frame, seat, back wheel and mudguard back some years later so that's probably destined to be just a memory. Edited By Martin Harris on 03/01/2011 21:41:22
  18. Martin Harris - Moderator

    Martin Harris - Moderator posted a gallery image in Member Albums

  19. Martin Harris - Moderator
    First proper (IC) flight of the year today with the trusty Seagull Extra 300S - thought it was about time to give it an airing after so much electric flying while my finger recovers from its workshop mishap.  Glad to find out that the amazing knife edge spin still works (I say amazing because all I do is hold the sticks in the top left corners while sometimes hearing people admiring the manoeuvre - don't tell anyone!)
  20. Martin Harris - Moderator
    I think I'd be asking myself questions if I thought my tailplane wasn't strong enough to retain the model...the average tailplane has about 5 inches of epoxy in shear attaching it against the thrust. I'd be surprised if there was much more than 10 lbs of static thrust from a 120 4 stroke or 90 2 stroke at full bore.   
  21. Martin Harris - Moderator
    I'm not going to put it to the test but I'd guess that given that as there is virtually a dead short while the motor is stationary and the back emf is not being generated, if the motor isn't turning due to a wire off then it won't take long for a magic smoke pipe to burst! The brushless motor (outrunner or inrunner) is a 3 phase motor which has bursts of energy fed to the relevent windings at the right time by the ESC - sensed by the back EMF generated by the motion of the magnets past the coils or vice versa.  A very different concept to a brushed motor which simply stops running if a wire breaks.Edited By Martin Harris on 03/01/2011 13:37:59
  22. Martin Harris - Moderator
    Odd - I just posted to a different thread - sorry!  Posting deleted....Edited By Martin Harris on 03/01/2011 13:34:24
  23. Martin Harris - Moderator
    Does this apply to electric powered models as well? 
  24. Martin Harris - Moderator
    Several clubmates use the line system (although I'm a restrainer user myself) which is pretty safe as long as you move behind the model to unhook it.  I always teach people to remove the glow from this position anyway so there's nothin additional to do. I hate seeing anyone reach over a running prop for any reason!
  25. Martin Harris - Moderator
    Posted by Spice Cat on 02/01/2011 23:18:50:   Harris' Snug  (Feel free to drop a load)   I hope that's not a comment on the quality of my postings! Given the musical content (a subject I claim full ignoramous status on) how about "Pilot's Notes"?   
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