fly boy3 Posted April 21, 2013 Share Posted April 21, 2013 Hi all, damaged my bipe on t/o yesterday, when my OS 46 LA cut on take off and nose dived into the tarmac.Is its Sods Law that it should cut at this important position ? The engine has never faltered previously. Apart from some dirt in the the carb, what could the reason be. Old timers at patch spoke of "surge" but could not enlarge on this.I know I am asking a lot, but any ideas out there. Thanks Quote Link to comment Share on other sites More sharing options...
Mowerman Posted April 21, 2013 Share Posted April 21, 2013 I Dont know about surge but I think its called 'sods law'. Quote Link to comment Share on other sites More sharing options...
Paul Williams Posted April 21, 2013 Share Posted April 21, 2013 check clunk rattles as it should and do a nose up before take off every time. has clunk pipe come off in tank? Was it running lean, loads of reasons for this mate just gotta work through them. Quote Link to comment Share on other sites More sharing options...
fly boy3 Posted April 21, 2013 Author Share Posted April 21, 2013 Thanks both. Clunk ok, and needle is never touched, but I should have checked the nose up test as it was thr 1st flight of the season for the bipe. I think I can call this "pilot error" Lol Cheers Quote Link to comment Share on other sites More sharing options...
Rich too Posted April 21, 2013 Share Posted April 21, 2013 I'm surprised that you have never touched the needle as well!! I would normally tune, and then carry out the nose up test...Rich Quote Link to comment Share on other sites More sharing options...
fly boy3 Posted April 21, 2013 Author Share Posted April 21, 2013 Hi Dickster, you could be right re. the needle, being first flight of the year. What I meant was I am not a needle fiddler as such.Once set I leave we'll alone. Should have taken more care. Thanks Quote Link to comment Share on other sites More sharing options...
crispin church Posted April 21, 2013 Share Posted April 21, 2013 your problem is in the first line LA bin it NOT GOOD what size bipe is it LA ok for little 30size trainner not much else Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted April 21, 2013 Share Posted April 21, 2013 OS LAs not good!!!!??? Couldn't agree with that Crispin.....the LAs are superb beginners engines. Not the most powerful it is true but once set they hold their tune until the next Ice Age (as long as you don't change the fuel) It does sound like it might have been just a touch weak FB3....the "surge" the old boys mentioned probably refers to the fuel sloshing about & might just have made the difference between running (just) & a lean cut. What fuel are you using? If its castor based & its the first flight of the year (as you mentioned) the needle jet might be slightly gummed up which could account for the possible lean run... Another quick point to note with the LA series is the rear mounted NVA.....you should always allow around 20-30 seconds for the mixture to stabilise when adjusting the needle.....it takes a while for the "new" fuel metering setting to "reach" the engine & affect its running.... Quote Link to comment Share on other sites More sharing options...
fly boy3 Posted April 21, 2013 Author Share Posted April 21, 2013 Hi Steve. 5 percent nitro, model has given no trouble for over 12 months, and was designed for an Enya 32. Have not used Castor for years. Thanks on the adjusting tip Steve. Over 20 years of flying I have always had OS engines in my fleet, but if I need all out power I prefer Super Tiger.Cheers Quote Link to comment Share on other sites More sharing options...
John Olsen 1 Posted April 22, 2013 Share Posted April 22, 2013 One thing to bear in mind is that the engine will tend to lean out as the plane accelerates, because the loading comes off the prop and so the engine speeds up a little. So it pays to set them a little on the rich side on the ground to allow for this. We played with telemetry and found that an OS 56 was speeding up from about 10,000 rpm on the ground to 11,000 in the air, both readings at max throttle and in level flight in the latter case. John Quote Link to comment Share on other sites More sharing options...
cymaz Posted April 22, 2013 Share Posted April 22, 2013 Plane was sitting on the strip and it begins to roll...did you rapidly open the throttle? Could be that the plug gave out or is giving out. Though not flying for hundreds of years I find most engine cuts or poor running is due to an old duff plug or too lean a mixture. Hope this gives food for thought. Quote Link to comment Share on other sites More sharing options...
fly boy3 Posted April 22, 2013 Author Share Posted April 22, 2013 Hi John, very interesting info regarding leaning out in the air. Could never completely under stand the theory. Ok. prop unloads a little when in the air, but how does this effect the amount of fuel getting to the carb. must be less fuel being sucked up, so if the engine was very lean to start, it would get less fuel then cuts ?. Cheers Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted April 22, 2013 Share Posted April 22, 2013 As the engine speeds it up it draws in more air but cannot draw any more fuel because this is restricted by the needle valve. More air for the same liquid fuel equals a leaner mixture.... Quote Link to comment Share on other sites More sharing options...
fly boy3 Posted April 22, 2013 Author Share Posted April 22, 2013 Thanks Steve, even I could follow that explanation.! Quote Link to comment Share on other sites More sharing options...
fly boy3 Posted April 22, 2013 Author Share Posted April 22, 2013 Hi Cymaz, we are on the same wavelength. As I filter my fuel I thought dirt in carb would be low on the list for engine cuts. Most probably it was a lean tune that caused the problem, although a duff or dodgy plus is also high on the list. This brings me to another question, how often should we change a plug, and have they a "sell by date" from new. I normally use OS, FS8 plugs. cheers. Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted April 22, 2013 Share Posted April 22, 2013 Dirt in the carb certainly can cause a lean run....if the dirt retricts the fuel flow you've got a lean run!!! How long does a plug last? About as long as a piece of string really.....consider the way it can fail...the coil can get damaged & fail, the sealing can fail so the plug leaks compression (bubbles around the centre post usually indicate a problem) & the coil can become contaminated. Basically if it glows OK, doesn't leak & the element is a nice coil & looks shiny its probably a good plug....a contaminated coil will look dull & "flaky" Oh & dead plugs don't improve with keeping.....bin 'em!! Quote Link to comment Share on other sites More sharing options...
cymaz Posted April 23, 2013 Share Posted April 23, 2013 If it looks like these two then see how far you can throw it , or better, put it in the recycle bin Quote Link to comment Share on other sites More sharing options...
fly boy3 Posted April 23, 2013 Author Share Posted April 23, 2013 Nice pics. Cymaz, no the plug in question is a new Enya No 3 or 8 , and it tests ok. Cheers Quote Link to comment Share on other sites More sharing options...
PatMc Posted April 23, 2013 Share Posted April 23, 2013 Posted by Steve Hargreaves - Moderator on 22/04/2013 15:20:58: As the engine speeds it up it draws in more air but cannot draw any more fuel because this is restricted by the needle valve. More air for the same liquid fuel equals a leaner mixture.... No it doesnt, the ratio stays the same. The needle valve is a means of automaticaly metering the ratio of fuel to air depending on the air pressure in the carb throat. Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted April 23, 2013 Share Posted April 23, 2013 So you are saying the volume of air drawn into the engine doesn't depend on how fast it is turning over Pat? Quote Link to comment Share on other sites More sharing options...
PatMc Posted April 23, 2013 Share Posted April 23, 2013 No, I'm saying that the ratio of fuel to air doesn't change. Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted April 23, 2013 Share Posted April 23, 2013 So why does an engine run lean as it speeds up then? Or are you saying it doesn't? Edited By Steve Hargreaves - Moderator on 23/04/2013 22:45:54 Quote Link to comment Share on other sites More sharing options...
PatMc Posted April 23, 2013 Share Posted April 23, 2013 If it speeds up because the model is travelling faster with the same throttle setting then it doesn't lean out. Quote Link to comment Share on other sites More sharing options...
Lee Smalley Posted April 23, 2013 Share Posted April 23, 2013 Sorry pat but that's just wrong, if engine is set a tad rich and is ran at full throttle it runs rich,put model in a dive it speeds up, throttle is still in same position engine leans out and power increases, model slows down and engine starts to run rich again of course the ratio changes in flight, as we can not change the mixture we have to set up for a compromise Quote Link to comment Share on other sites More sharing options...
PatMc Posted April 23, 2013 Share Posted April 23, 2013 I've no idea how you work that out Lee but sorry, it doesn't make sense. Anyway we aren't considering the engine speeding up in a dive. We are considering Steve's explanation arising from John Olsen's earlier post. Edited By PatMc on 23/04/2013 23:39:23 Quote Link to comment Share on other sites More sharing options...
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