cymaz Posted October 22, 2017 Share Posted October 22, 2017 Now that I have a 4 engine plane, I have been thinking, what if? There must be some wizard at aerodynamics or someone good at plane design who could answer this question..... " My plane has 4 x OS 40la 2t engines. They currently all use APC 10x6 props. What would be the effect of running 10x6 on the inner engines and 11x5 on the outer engines....or vice-versa for that matter. Would there be any advantages to do this and would it help in the event of an engine stopping". Anyone come up with a good idea for this? Or otherwise for that matter. Quote Link to comment Share on other sites More sharing options...
PatMc Posted October 22, 2017 Share Posted October 22, 2017 They are matched engines so why would you want to run them at different rpm ? The ones on outer pair would need to run 20% faster or the inners run 16.6% slower for the props to have matched the "pitch speed". Edited By PatMc on 22/10/2017 17:54:05 Quote Link to comment Share on other sites More sharing options...
Jon H Posted October 22, 2017 Share Posted October 22, 2017 I agree with Pat, there is not really any advantage to this. If you need more thrust run them all on 11x5's, if not leave well alone! Quote Link to comment Share on other sites More sharing options...
cymaz Posted October 22, 2017 Author Share Posted October 22, 2017 I will see what the 10x6 props are like. Thanks for the advice. I will change all 4 should the need arise. Would it do any harm? Quote Link to comment Share on other sites More sharing options...
Jon H Posted October 22, 2017 Share Posted October 22, 2017 what model is it? Quote Link to comment Share on other sites More sharing options...
Stevo Posted October 22, 2017 Share Posted October 22, 2017 4 engines eh... c'mon, tell all!! Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted October 22, 2017 Share Posted October 22, 2017 Blogs been on here a while. Edited By john stones 1 on 22/10/2017 18:26:12 Quote Link to comment Share on other sites More sharing options...
Stevo Posted October 22, 2017 Share Posted October 22, 2017 Thank you John. Hmm a wierd one. He's from Cornwall, y'know... Quote Link to comment Share on other sites More sharing options...
Jon H Posted October 22, 2017 Share Posted October 22, 2017 ooo 10x6 will be fine Quote Link to comment Share on other sites More sharing options...
cymaz Posted October 22, 2017 Author Share Posted October 22, 2017 Just an thought . 10x6 gave 3200 idle, 10k @ WOT Quote Link to comment Share on other sites More sharing options...
Jon H Posted October 22, 2017 Share Posted October 22, 2017 thats a very fast idle. i would expect 3k at most, 2500 would be better. Quote Link to comment Share on other sites More sharing options...
cymaz Posted October 22, 2017 Author Share Posted October 22, 2017 Cheers Jon. I realise it's a quick one. There's still a bit a fine adjustment to do. Considering all four engines are working off 1 servo - I've got them within 200/250 rpm of each other...nearly there. I will do the final idle on end point, there is enough of that to complete the job. They are also several years old, not that should make any difference! Just a couple of minor bits of work to do. Finally fit the remote glows and get the cowls on. Range check and failsafe to do. Next Sunday looking good for the fly- off. Quote Link to comment Share on other sites More sharing options...
Jon H Posted October 22, 2017 Share Posted October 22, 2017 Dont forget that the air bleed carb slow run tuning works backwards Quote Link to comment Share on other sites More sharing options...
cymaz Posted October 22, 2017 Author Share Posted October 22, 2017 Posted by Jon Harper - Laser Engines on 22/10/2017 22:04:17: Dont forget that the air bleed carb slow run tuning works backwards No I hadn't...pick up from idle to WOT is good. Checked the price of remote needles for OS 40 la.....about £17. Daylight robbery Quote Link to comment Share on other sites More sharing options...
Martin McIntosh Posted October 22, 2017 Share Posted October 22, 2017 Many years ago I guy by the name of Robin Lehman pioneered some multi engined models and set each one to give out thrust so that a single motor running would result in straight flight. Seemed to work. Quote Link to comment Share on other sites More sharing options...
Geoff S Posted October 22, 2017 Share Posted October 22, 2017 Posted by cymaz on 22/10/2017 22:34:10: Posted by Jon Harper - Laser Engines on 22/10/2017 22:04:17: Dont forget that the air bleed carb slow run tuning works backwards No I hadn't...pick up from idle to WOT is good. Checked the price of remote needles for OS 40 la.....about £17. Daylight robbery If the needles are remote then can't you use any needles and fit them in convenient places? I suppose they'd all have to be the same but not necessarily. I've use remote needles with 50mm long fuel lines to the carb which worked OK - to my surprise! Geoff Quote Link to comment Share on other sites More sharing options...
Robert Berger Posted November 24, 2019 Share Posted November 24, 2019 Is there a thread on this site on how to plumb up a four engine IC fuel tank system. I am into a B17 Marutaka Kit and I have 4 OF FS26 engines that I have set up on a test board with 4 throttle servos on 4 channels running through 2 SBD-1 Futaba Decoders. Would I use 4 tanks, a pair of tanks or just one tank and how would I set up the tubing, vents and pressure tubes from the mufflers if multi engines were of one tank. Thanks if you can help. Quote Link to comment Share on other sites More sharing options...
Frank Skilbeck Posted November 24, 2019 Share Posted November 24, 2019 4 tanks, keeps all the plumbing short, tanks should be in each nacelle, and adjusting each engine independent of the others. Quote Link to comment Share on other sites More sharing options...
cymaz Posted November 24, 2019 Author Share Posted November 24, 2019 The fewer the number of tanks the more complicated the plumbing, joins etc. With any multi engine, keep it simple, keep it easy to maintain and trouble shoot. Great tips HERE Edited By cymaz on 24/11/2019 08:50:00 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted November 24, 2019 Share Posted November 24, 2019 cymaz Reading through those tips highlighted in your last post "long tail moment" and "a thin wing" stand out. I wonder how well your plane meets these criteria if you are worried about the effect of an "engine out" . I certainly favour a long tail moment and a big fin on my multi engine jobs so if an engine dies things happen slowly enough for me to contain the situation. Quote Link to comment Share on other sites More sharing options...
cymaz Posted November 24, 2019 Author Share Posted November 24, 2019 With the Seagull Dual Ace, engine out is a bit of a drama but not a handful if you stick to your engine out game plane. On my G-CYRL, 4 engine, your can fly around on 3 and not even notice it. The wing is a thick as your forearm and a huge fin !! Quote Link to comment Share on other sites More sharing options...
Robert Berger Posted November 24, 2019 Share Posted November 24, 2019 Thanks Guys, I got my answer and will use 4 tanks. That's a great article by Frank but a bit scary. Sounds like a maiden flight might only include a take off and that's only a "might". If you do get it up then that's only the start of it. However if you don't have a crack at it you will never know the experience. Quote Link to comment Share on other sites More sharing options...
Allan Bennett Posted November 24, 2019 Share Posted November 24, 2019 Remember that cutting all engines, or at least reducing throttle significantly, is sometimes the best way to deal with an engine out. Quote Link to comment Share on other sites More sharing options...
Jon H Posted November 24, 2019 Share Posted November 24, 2019 People get very hysterical about multi engine models and there is an awful lot of nonsense out there about what to do if you loose an engine. Frankly, they are a non event if you take a few additional steps vs a single engine model. The first is to make sure you have everything set up nicely. Are the engines tuned correctly so that each is happy, are the tanks right, is the cooling ok... When it comes to engine tuning dont bother matching top end rpm. Its more important that they are happy. +- 100 or 200rpm is not important. Also make sure the engines are nice and warm before takeoff. A good 15-20 second blast at full power is a good idea and dont just firewall the throttle. Open smoothly to 80% and leave it there. With engine failures (which are rare if the engines are set properly) the key is airspeed. If you are fast loosing an engine is not a problem as you leave the other flat out and correct with rudder. Many correct the yaw induced roll with aileron and this is really not good. Fly the rudder by hand, dont trim it as you will be out of trim again when you throttle back to land. Once guaranteed to make the runway you can throttle back and 'glide' home. Beyond that i split my flights into a few categories and have already decided what to do in advance if an engine dies. 1. Takeoff - If im on the ground and an engine fades abort takeoff. Dont try and coax it. If its sick abort and try again. 2. Climb out - This is the dodgy one. If you are low it might be best to chop throttle and land ahead. If there is a hedge or something in the way you might get away with throttling back (this might save the fading engine) and trying to hop over it on the good engine but be on the ball with the rudder and if it starts to swing chop the other engine. If you are higher and with some speed get the nose down a little, gain speed, get the power up and fly back and land. Be very careful and dont expect a decent climb rate or to climb into circuit. Climb just enough to avoid hitting anything. IF that means a flat circuit 2 feet off the ground then do that. Dont force the climb if you dont have to. 3. In flight - Generally if i loose one in flight i open the other up to about 90% power and just keep flying. As i said before, if you are fast enough for the rudder to overcome the dead engine then its a non event. Get too slow, or get lazy with your rudder and its not likely to end well. That said, if you do get in a spin chop the other engine and recover. Its no different to a normal spin so just get out of it as you normally would. Most accidents, single or twin, come from poor preparation. Pilot skill is a factor, but you can be a good pilot and still be caught flat footed if you dont have a plan in already in mind when something goes wrong. Equally, a careful pilot of moderate skill will do well if they have considered all their options in advance and made all of their choices ahead of time. Chopping all the power immediately just turns the model into a brick. Its a far better idea to fly yourself out of the problem than abandon the model to gravity Edited By Jon - Laser Engines on 24/11/2019 21:08:38 Quote Link to comment Share on other sites More sharing options...
cymaz Posted November 24, 2019 Author Share Posted November 24, 2019 Following on from Jon....thoroughly superb by the way....I have a certain routine for start up. Run each engine at once. Check at full throttle and pick up. Then run them altogether If any of them is not 100% , DO NOT FLY. Go home and check out and fix the problem Quote Link to comment Share on other sites More sharing options...
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