Martyn K Posted March 16, 2015 Author Share Posted March 16, 2015 Thanks Alec - our posts crossed - I'll take a look Martyn Quote Link to comment Share on other sites More sharing options...
Martyn K Posted March 16, 2015 Author Share Posted March 16, 2015 That is great Alec! According to the chart, my pipe length should be 515mm = 20.27" which is just outside my calculated value. I'll cut the header so I get a 22" pipe length and start from there. Martyn Quote Link to comment Share on other sites More sharing options...
Martyn K Posted March 17, 2015 Author Share Posted March 17, 2015 I measured the battered supplied header and pipe combination (just butted together) and amazingly it was just over 500mm long so it appears that my measurements and assumptions my be fairly accurate. So, a lot of messing about last night - cutting the header down, fitted the engine then spotted that the throttle linkage alignment didn't align so engine out, mount out, redrill etc. put it all back together and the engine is now in. The header was a bit too near the deck, so that came off again, out with the blowtorch, softened the aluminium and gently bent it up (in reality down - its an inverted engine) by about 15mm and the pipe now fits a treat. (Ignore the mass of blue pipes, they will be cut down when I sort out the refuelling arrangments The observant will have noticed that the undercarriage legs are no longer skinny and heavy 6swg piano wire but a carbon fibre item from Carbon Copy. I just wasn't happy with the spindly legs so have gone for this. I humbly apologise to the purists amongst us I have used the same mounting points - which were 5mm holes drilled into long hardwood blocks glued up the fuselage sides. I have epoxied a pair of 5mm steel threaded rod in place and it seems quite secure. The first heavy landing will probably prove me wrong though. Not really that visible on this overexposed shot is the two hardwood blocks extending back behind the undercarriage . These are just glued to the fuselage sides and provide a torque bearing point. Finally, I covered and attached the rudder last night which was removed again this morning as I wasn't happy with the Robart hinges that I used. I do have (at least) one problem that I have got to sort out. The throttle linkage arm on the carburettor is a ball link. I have fitted the (nylon) linkage arm, bit it is very stiff - a servo will operate it but I need to free it without compromising the link security. Any suggestions would be welcome. I have cut away the back of the ball arm which has obviously helped but it is nowhere near free enough to operate smoothly. More to come.. Martyn Quote Link to comment Share on other sites More sharing options...
Paul Jefferies Posted March 17, 2015 Share Posted March 17, 2015 It really shouldn't be that stiff...... Are you sure the ball/link arm are a pair? You could try some silicone grease as used by plumbers...... Quite cheap and seriously slippery! If that doesn't do the trick, buy a new ball link. Paul Quote Link to comment Share on other sites More sharing options...
Martyn K Posted March 17, 2015 Author Share Posted March 17, 2015 My thoughts entirely Paul. The ball end is steel and definitely part of the carb assembly, but no linkage was provided with the engine. There is no spares list available for the engine so I cant find out what was supplied. The link piece is a nylon end like this - looks like a Dubro part but really could be anything. It seems to fit OK, a decent push on snap off without too much effort required. It is just very stiff. I'll try your suggestion of some silicone grease in a few minutes Martyn Edit: Forgot to mention. The Ball end on the carb is definitely non standard - it has a dog leg in the arm so that by twisting it you can make it adjustable (if you can visualise that). I have got another ball end but its the same brand as the first, I'll see if that is better. I wondered whether the ball end I am using is imperial and the ball metric.. Edited By Martyn K on 17/03/2015 13:36:17 Quote Link to comment Share on other sites More sharing options...
Sam Wragg Posted March 17, 2015 Share Posted March 17, 2015 Great to see Concept nearly there. Re OS61, Martyn I suspect you may have throttling problems due to the large throat area and a pump may be required due the lack of suction of fuel because of this fact, although I may be wrong. I have read that with this Engine modelers have had success in changing to front induction with an increase in power over the RF version . Nevertheless I would run the engine using 10% nitro and see how you go on as it shouldn't stop you from tuning the engine to the pipe (after a period of running in). Leave the pipe slightly long as the engine unloads in the air if you suffer poor throttling try a smaller choked Carb as idealy this will give you more torque and suction. Revs..... aim for the mid ten thousands as this keep the noise down and go for an Apc 12x9 minimum, I feel the 12x8 you intend to use will be too fine a pitch for your OS. The OS61 in my Magic was new at the start of last season and the pipe was set long, by the time we last flew at Montfort Bridge I noticed that the engine had come on song and suspect I may have to go up in pitch to a 12x10 to maximise the power. Welcome to the delights of tuning piped 2 stroke engines Sam Quote Link to comment Share on other sites More sharing options...
Martyn K Posted March 17, 2015 Author Share Posted March 17, 2015 Thanks Sam, if I am going to drop the revs slightly then I'll need to lengthen the pipe. I have allowed an extra 50mm just in case - and have space to go longer if needed. I think I have a spare 12x10 and 12x9 prop (APC) available. I need to get the airframe fuel proofed or the paintwork will look even more of a mess.. Because its a rear carb/rear induction, the fuel feed to the tank is actually quite short - about 50mm as the crow flies.. I hope I can manage without a pump - they are expensive beasts and there isn't much space to place it. We will have to see and I'll probably regret that decision on the first dead stick Looking forward to getting it going.. Just out of interest, why does everyone specify APC props particularly? Those very narrow tips cant be dong very much - although I agree that they wont be making much prop noise either.. M Quote Link to comment Share on other sites More sharing options...
Sam Wragg Posted March 17, 2015 Share Posted March 17, 2015 Apc I believe are designed to be quiet Sam Edited By Sam Wragg on 17/03/2015 15:29:25 Quote Link to comment Share on other sites More sharing options...
Martyn K Posted March 17, 2015 Author Share Posted March 17, 2015 Yes - I think I can see why that would be the case. Thanks Martyn Quote Link to comment Share on other sites More sharing options...
Peter Android Posted March 17, 2015 Share Posted March 17, 2015 **LINK** Interesting Concept , This link may help Martyn ? not an expert myself. The usual U.S.A pedal to the metal style of flying appears to predominate ( mega -Rpm ) was ( sadly) curbed over here many years ago. the rest you know. Many fond memories of watching the F3A Guys extract every last rev out of their motors ............ I notice in the UKCAA photo - thread ( which is excellent reading ) that a few individuals make reference to employing an " O.S V " motor , in happier days past. Your " Timing Disc " has some happy and , sometimes painful memories from my own motorcycle days . The O.S " badge " engineering appears to be very confusing over different world markets . I had to read a few threads to try and understand , and still not sure , of the subtle differences twixt an O.S >V, VF, and VFR motor ? As a very wise Flyer has previously mentioned , who has considerable mechanical expertise over many years of competition flying, although his dress - sense is questionable Hi - Sam. T'Owdlad Workable r.p.m range may be very narrow ? for most * reasonable purposes anyway. Maybe put the power setup on a test rig using larger / higher pitch props ? before you start chopping further lumps out of the header ? I wonder if anyone reading this Forum has actual - user experience of using this particular engine themselves ? Be great if you could get it workable on @~ 10K r.p.m , unless you have access to a suitable flying site. Good Luck. Quote Link to comment Share on other sites More sharing options...
alec james Posted March 17, 2015 Share Posted March 17, 2015 If you go to manuals.hobbico.com/osm/61vf-manual.pdf you will find information on the OS 61 engine. I remember a few years back when I was running an OS 61 'pumper' (Not a Hanna Special) I was aiming for 10000rpm on a 12x10 APC prop. I also found that the motor needed at least 10% Nitro. I can't help thinking that with the choke size on your OS you will have fuel draw problems as the motor looks more suited to ducted fan use than aerobatics! Quote Link to comment Share on other sites More sharing options...
Paul Jefferies Posted March 18, 2015 Share Posted March 18, 2015 Martyn, if you do have fuel-draw problems, before messing about with pumps you could try sleeving the barrel. OS used to supply a variety of sleeves that fitted inside the throttle barrel to reduce the throat diameter. I think I have one or two of them out in my shed and I will try to find them a bit later and post a picture...... actually they would be very simple to make. Paul Quote Link to comment Share on other sites More sharing options...
Martyn K Posted March 18, 2015 Author Share Posted March 18, 2015 Morning all, thanks for all the advice and links. Pater A - that is a very useful link - thanks... I think that my original estimate of 12000 on a 12x8 wasn't a million miles out, I agree that I need to get it to run a little slower although I just love the sound of a howling 2 stroke.. (Shouldn't really admit that here - I'll probably get moderated.. ) I did wonder whether it would run on a 13x6 - 13x8 - that would slow it down a bit and the additional flywheel effect would help with slow running... your thoughts on that please,. Alec - thanks for the link. I have seen the VF manual before, I couldn't find one for the RF although apparently some parts are interchangeable and the engine performances are comparable It's interesting to see your comments on the use of the engine for DF. The valve timing on this engine is actually quite tame at 145 degrees. This compares with 140 degrees for a typical sport engine - e.g. the SC46 that I use on the Gangster. My genuine OS91 Ducted Fan engine (instructions say run it in at 18,000 rpm!) has an exhaust valve timing of 175 degrees. (That little timing disk is really quite interesting to use). I suggest that the engine is probably OK for this use although not ideal in the modern world. Apparently it is 1982 vintage or thereabouts.. Paul - OK on sleeves , this is something I have done before with restricting power on motorcycles, you can actually get away with a washer although the airflow post venturi may not be ideal but does assist with atomisation. I agree, they should be simple to make, I'll take some measurements. A bit more progress yesterday, the rudder is back on again, the throttle linkage is a bit freer (Silicone grease - thanks) and the throttle and receiver servo tray has been glued and fitted.. The throttle servo seems to operate the throttle OK with no buzzing so some progress there. Best wishes M Quote Link to comment Share on other sites More sharing options...
Martyn K Posted March 18, 2015 Author Share Posted March 18, 2015 One thing I forgot to mention. The image on the OS engine History site.. Mine has a slightly different carb. This one has a conventional throttle arm and pilot jet arrangement, mine has a lock nut on the pilot and is far more inaccessible, which is a bit of a shame.. Apart from that it looks the same. Martyn Quote Link to comment Share on other sites More sharing options...
Jon Laughton Posted March 18, 2015 Share Posted March 18, 2015 Martyn - its looking great! I really like your colour scheme / design and may pinch that idea for something in the future! Looking forward to see how things develop.... Jon Quote Link to comment Share on other sites More sharing options...
Martyn K Posted March 18, 2015 Author Share Posted March 18, 2015 Hi Jon I have copyrighted it .. Nah only kidding, I must admit that I am quite pleased with it though, just don't look too closely.. Glad you like it. Martyn Quote Link to comment Share on other sites More sharing options...
Paul Jefferies Posted March 18, 2015 Share Posted March 18, 2015 As promised a pic of the OS sleeve...... These are the only two I could find, one is thicker walled than the other. Very simple to make out of a bit of brass tube though the diameter/wall thickness could be an issue. The tube needs to very slightly oversized and then the slit down the side makes it possible to squeeze it slightly and push it in. You have to remove the spraybar to get it in there and then when you put it back the spraybar holds the sleeve in place. I found it did not significantly restrict the power but it certainly did improve the "suck"! Paul Quote Link to comment Share on other sites More sharing options...
Martyn K Posted March 18, 2015 Author Share Posted March 18, 2015 Thanks Paul. I can see now that it sits in the barrel. I thought it would have been located on the carb outlet like we do on motorcycles. It should be fairly easy to make one of those up. If I have some suitable tube, I'll have a go tonight By the way, that barrel has the same pilot jet and ball link that my carb has. Regards Martyn Quote Link to comment Share on other sites More sharing options...
Paul Jefferies Posted March 18, 2015 Share Posted March 18, 2015 "By the way, that barrel has the same pilot jet and ball link that my carb has" OS No.7 used on my 61VF........ 'Bit grubby I'm afraid because they've been sitting in my bits box for rather too many years! Paul Quote Link to comment Share on other sites More sharing options...
Peter Android Posted March 18, 2015 Share Posted March 18, 2015 Hi Martyn. No actual user experience on this motor, my observations stem from common interest., not a critic either. Used a tuned pipe many years ago ( correctly called an expansion chamber) as you know. Wealth of experience amongst F3A flyers , not always on here though. try to add a couple of links just as a general guide , not teaching egg sucking. **LINK** **LINK** It may be fair to say that unless you are able to alter all port timings - width - height - shape to suit a particular application , you are left chasing the effect rather than the cause .. Bit off topic - but related. Eons it seems , ago. we sent most of our( motorcycle) barrels away to be ported which often involved new pistons , apart from taking a file and die - grinder to a few Bantams , Lambretta;s etc. remember crankcase stuffers ? Manufacturers regularly try to re - invent the wheel in order to gain market share , an example of this is when we ( Joe Public) were allowed to walk around the pits at race meets . circa @1976 I I was lucky enough to examine Mr Sheene's new RG500 square 4 with it's fairing removed . , the motor looked like 2 x stepped twins joined together in a square-ish layout , and looked vaguely familiar . Fast forward 40 - odd years , and the net' - via Wikipedia & Motorcycle News revealed it was effectively 4 x MZ 125cc's joined together in a stepped 4 config.now produced by Suzuki. In a very minor way , I was able to help out some of the penniless club racers ( we all were) by cutting apart their expansion chambers periodically , in order to remove the accumulated baked on clag & oil , then rewelding by hand. Sometimes the lads wanted the design modifying to their own design( at their risk ) where they obtained the designs from was a closely guarded secret , exept that everyone journeyed to Louth on a regular basis , and produced improvement on occasion , accompanied by 100% terror for fear of seizure , on all occasions. bore and length of the stinger .having a marked effect , a few mm. the wrong way and you ( they ) were kissing tarmac. We were the complete inverse of restriction , and despite this planet's bunny - hugging fraternity I don't think we have seen the last of the 2T strokers quite yet , I hope. You are not alone Martin, in relishing the mournful wail of an on - song stroker and I hope you can make this motor work effectively . at a more moderate rpm. As a long time customer of MCN, I was a bit alarmed to read last weeks 60th Anniversary edition , and staggered that I had been a punter for 42 of those years , Time & Tide innit . I watch , ask and learn with great interest about making a fundamentally wrong tool for the job - operate . some of your fellowes employ un - standard piston / liner combinations in their own motors , which is encouraging. Be interesting how the disc valve induction works with a pipe . Never mind, you can always put a 2CV engine in , and listen to Mantovani records between flights ? that should please the bunny - huggers , who's numbers will be reducing due to toxic waste from used batteries ? Thin Lizzy does it fer me. Vive Le Revolution . Cheers. Quote Link to comment Share on other sites More sharing options...
Martyn K Posted March 19, 2015 Author Share Posted March 19, 2015 Hi Peter I am sure you really mean 'Spannies'.. very nice on a 350LC I started tuning Bantam engines when I was 17 yo. Usually made them very peaky and totally unusable on the road but it was a fun learning curve. Mind you, we could pick up bantam parts for next to nothing in the early 70's - unlike the extortionate prices requested today.. You need to go and see Limehouse Lizzie as well - excellent (one of the best) tribute band. I have lost count of the number of times that I have seen them - probably the best was at the BMF show a few years ago Not much progress on the model yesterday. The rudder is off again. and the Robarts have been ditched.. Just not happy with them for this application. I also applied one thin (NOT thinned) coat of Rustins Fuel Proofer on the wing last night. Looking OK so far. Martyn Quote Link to comment Share on other sites More sharing options...
Martyn K Posted March 19, 2015 Author Share Posted March 19, 2015 Regarding the Carb Type - its a 7E. Just by pure chance one is available on FleaBay at the moment I wonder if I can buy the ball link separately. Martyn Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted March 19, 2015 Share Posted March 19, 2015 Martyn, have you tried fitting your slightly tight link onto the ball, then heating the arm under the ball with a soldering iron? It should (with luck) soften the link enough to fit itself to the ball. Got to be worth a try. Quote Link to comment Share on other sites More sharing options...
Andy Green Posted March 19, 2015 Share Posted March 19, 2015 I think a heli pilot trick is to squeeze the assembled ball link, this stretches the plastic slightly. Andy Quote Link to comment Share on other sites More sharing options...
Martyn K Posted March 19, 2015 Author Share Posted March 19, 2015 Thanks both. I'll try both suggestions although now I have the servo in place and the ball greased it isn't too bad. Still a bit stiff for comfort though Martyn Quote Link to comment Share on other sites More sharing options...
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