The Wright Stuff Posted July 13, 2018 Share Posted July 13, 2018 Posted by Jon - Laser Engines on 12/07/2018 16:21:03: Its a pointless test that dates back to the early days. With modern engines that have considerably better fuel draw and/or are pressurised its really redundant. Jon, what do you mean specifically by 'early days'. All the OS manuals appear to recommend pointing the nose 15 degrees up (as opposed to vertical). I always like to try to reconcile difference of experience - it's the scientist in me, I guess, but is it possible that (due to your experience) your engine tuning is generally pretty good to start with, whereas there may be some benefit to the 'nose up' practice if it is grotesquely out of tune (or badly plumbed)... Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted July 13, 2018 Share Posted July 13, 2018 I tune my motors 1st week in October, then the 1st week in March the following year Regularly is the key. Quote Link to comment Share on other sites More sharing options...
Ron Gray Posted July 13, 2018 Share Posted July 13, 2018 As per Manish, if it makes you feel good then do it, no harm. I’ll stick to not doing it if that’s all right with you ‘nose uppers’. Quote Link to comment Share on other sites More sharing options...
David Davis Posted July 13, 2018 Share Posted July 13, 2018 Posted by Jon - Laser Engines on 12/07/2018 16:21:03: Its a pointless test that dates back to the early days. With modern engines that have considerably better fuel draw and/or are pressurised its really redundant.... What about us cheapskates who use old engines to power our models, e.g, the Meteor 60 I have in the Boomerang trainer? Quote Link to comment Share on other sites More sharing options...
Jon H Posted July 13, 2018 Share Posted July 13, 2018 Posted by The Wright Stuff on 13/07/2018 14:35:31: Posted by Jon - Laser Engines on 12/07/2018 16:21:03: Its a pointless test that dates back to the early days. With modern engines that have considerably better fuel draw and/or are pressurised its really redundant. Jon, what do you mean specifically by 'early days'. All the OS manuals appear to recommend pointing the nose 15 degrees up (as opposed to vertical). I always like to try to reconcile difference of experience - it's the scientist in me, I guess, but is it possible that (due to your experience) your engine tuning is generally pretty good to start with, whereas there may be some benefit to the 'nose up' practice if it is grotesquely out of tune (or badly plumbed)... Early days being the un silenced days with things like the original os max engines. You remember the type with a plate over the exhaust to alter the backpressure with the throttle. Also I accept that I am probably better at tuning engines than many, but part of the reason for that is by ignoring the test as there are many other factors that cause issues for the tuning. In the case of Extra Slims example, which is a common one, the issue is likely to be heat and not the original tuning of the engine. This is because the required tuning changes with engine temperature and the long run at full power on the climbout heats the engine up to a point where the tuning it held on the ground is no longer viable and she goes out. To be clear, the engine has not overheated at this point, its just too hot for that tuning. If the engine was run for a longer period of time before tuning it on the ground then it would be hot and any adjustments would be appropriate for the engine at its operating temperature. Equally, upon the restart the engine will not return to full power, because its hot...its retuned and off it goes. in this case, the nose up test is again not proving anything, retuning the engine at its higher temperature was the thing that actually fixed it. Its very important to run engines up to full temperature before tuning them. Quote Link to comment Share on other sites More sharing options...
Jon H Posted July 13, 2018 Share Posted July 13, 2018 Posted by David Davis on 13/07/2018 16:57:34: Posted by Jon - Laser Engines on 12/07/2018 16:21:03: Its a pointless test that dates back to the early days. With modern engines that have considerably better fuel draw and/or are pressurised its really redundant.... What about us cheapskates who use old engines to power our models, e.g, the Meteor 60 I have in the Boomerang trainer? As pointed out on the other thread, they should stop burning their money on a stash of kits and buy some new engines Quote Link to comment Share on other sites More sharing options...
Gary Manuel Posted July 13, 2018 Share Posted July 13, 2018 Posted by Jon - Laser Engines on 13/07/2018 14:03:35: Pleased to hear it Gary but please dont mistake the facts i present here as opinion. All you guys still claiming it will give indications of XYZ im telling you it simply will not do that. Hmmm - interesting definition of "facts" Jon. Here's a few facts. If the engine is tuned for maximum revs and the carburettor fuel pressure is reduced, the engine mixture will become leaner. The static pressure at the carburettor will drop whenever the (unpumped) carburettor is lifted above the fuel tank - even with a pressurised tank and a good fuel draw. The further the carburettor is lifted above the tank, the greater the pressure drop will be. When a model is pointed nose up, the horizontal distance between the fuel tank and the carburettor will be converted to vertical distance, which will reduce the pressure at the carburettor. All of these facts, work to answer Dai's original question. Posted by Dai Fledermaus on 12/07/2018 15:33:23: If the fuel tank is pressurised, what difference does holding the nose up make? To answer the question by saying that it makes no difference is simply wrong. It goes against these facts, which are based on fluid dynamic principles - and by observation of a model tuned for maximum revs having it's nose pointed upwards. I would be interested to hear if you disagree with any of these facts. Please note that the original post was not asking whether the nose up test affected straight and level flight, which is what I believe Jon is talking about. It was about the affects of raising the nose as per taking off, steep vertical up lines and other nose-up manoeuvres. If simple circuits is your kind of flying, then I'm sure that tuning for peak revs will be just fine. The minute the model's nose is pointed up, whether it's in flight or not, the mixture will be weakened. Jon actually consedes this point. Posted by Jon - Laser Engines on 13/07/2018 12:39:58: Sure the engine you saw at the weekend stopped, why wouldnt it? the conditions it saw were beyond what it could cope with and certainly beyond what it would see in flight. Not many models sit stationary with their nose held high while screaming flat out. I am sure that most of my engines would stop if i did a nose up test with them, but in flight they are no problem and im sure that if your example took flight it would not stop. Yes Jon, a lot of models do sit stationary (or slowly climbing) while screaming flat out during flight. Most aerobatic and all 3D models are capable of this. I could understand your argument against doing the nose up test if you were to qualify by saying that it applied to gentle aerobatics and scale / sports flying. As it stands, I believe that you are offering incorrect advise and incorrectly claiming it to be fact based. Edited By Gary Manuel on 13/07/2018 18:03:54 Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted July 13, 2018 Share Posted July 13, 2018 Sorry if some of this repeats with advice in the previous post which I overlapped with. What I have difficulty reconciling is advice that a tank may be too low for reliable operation but the same tank located correctly somewhere behind the engine can happily cope with a 45 degree or greater attitude in flight. I accept that some of my (and my clubmates' ) models' fuel tanks may have sub-optimal locations. I tune my engines on the bench and do warm them thoroughly. Very occasionally they falter slightly during a subsequent nose up test. I richen them slightly and they perform perfectly. While I may be able to modify a model to locate a tank better than the designer or ARTF manufacturer, not everyone may have the means or inclination to do so. While I am happy to accept that engines installed and tuned by some experts may never miss a beat in the air, I see no reason to deviate from my practice and if a nose up saves a lean cut and deadstick for anyone else, I see no reason to discourage them. I also see little danger if the nose up is done sensibly away from others and away from the operator's face - in Chris's hypothetical example (I've yet to see it happen...touch wood) a prop going back overhead into the pits should lose a great deal of its energy before arriving anywhere sensitive and I wouldn't advocate holding the model at 90 degrees to the horizontal anyway... Edited By Martin Harris on 13/07/2018 18:21:47 Quote Link to comment Share on other sites More sharing options...
Ron Gray Posted July 13, 2018 Share Posted July 13, 2018 @Gary - I tune my engines on the ground much as Jon advocates. I fly a lot of ‘stupid’ 3D type manoeuvres with lot of vertical including prop hanging. Using your ‘facts’ how come my engines don’t falter when in these attitudes (Laser engines plus others)? Must be luck I guess........... Quote Link to comment Share on other sites More sharing options...
Paul Marsh Posted July 13, 2018 Share Posted July 13, 2018 I still do it. Its a test, fail to do that and your model stuffs in if the engine cuts on a climb out, especially a twin. Best to do all the test, even on a petrol, don't do it and it could matter. Don't get many, if any climb-out dead sticks. raising the nose will tell you if either the mixture is out, or there is a leak in the fuel system. You won't know there is if don't do it... Quote Link to comment Share on other sites More sharing options...
Gary Manuel Posted July 13, 2018 Share Posted July 13, 2018 Posted by Ron Gray on 13/07/2018 19:11:50: @Gary - I tune my engines on the ground much as Jon advocates. I fly a lot of ‘stupid’ 3D type manoeuvres with lot of vertical including prop hanging. Using your ‘facts’ how come my engines don’t falter when in these attitudes (Laser engines plus others)? Must be luck I guess........... I don't have all the answers Ron. Nor do I profess to be an expert on glow engines. I was merely answering the question posed by the original poster, who wanted to know what difference holding the nose of the model up made. I'm guessing that if your models can do the manoeuvres you list, it would also pass the nose up test. P.S. One other very important difference it makes is a psychological one - to give the pilot the confidence to launch his model knowing that he's done all he can to allow the model to be put into any manoeuvre. This alone makes it worthwhile. Quote Link to comment Share on other sites More sharing options...
Ron Gray Posted July 13, 2018 Share Posted July 13, 2018 Agree on the psychological aspect, if it makes you feel good, do it! @ Paul - the nose up test won’t show you that you have an air leak in the system. What will happen is the engine will falter when nose up so you will richen the mixture to stop it happening. Off you will go and you will congratulate yourself that the problem has been fixed because it climbs out no problem. You then decide to do a nice long, low, slow flypast and guess what, your engine cuts out and you have a dead stick at low altitude and low speed. Now why did that happen, because it was too rich and the plug went cold. You may say rubbish but believe me it will because that’s exactly what happened to me, the nose up test actually hid the problem but I listened to ‘wiser’ ‘more experienced’ fliers who said do the nose up test. Had I stuck to my guns on tha basis that I had the engine tuned correctly, the fault could only be down to fuel supply, which it was, due to air ingress to the feed to one of the carbs. Quote Link to comment Share on other sites More sharing options...
Gary Manuel Posted July 14, 2018 Share Posted July 14, 2018 I trust that your question has been answered to your satisfaction Dai. Most people are of the belief that it's worth doing and the facts support that belief. Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted July 14, 2018 Share Posted July 14, 2018 Ding Ding. Quote Link to comment Share on other sites More sharing options...
Don Fry Posted July 15, 2018 Share Posted July 15, 2018 Posted by Gary Manuel on 14/07/2018 21:22:45: I trust that your question has been answered to your satisfaction Dai. Most people are of the belief that it's worth doing and the facts support that belief. Round one. Sentence two is a Trumpism. No evidence available of what most people believe, and fact should never be confused, or viewed as interchangeable with, an opinion. (Ex nose upper, currently an abstainer, agnostic on the subject) Quote Link to comment Share on other sites More sharing options...
Gary Manuel Posted July 15, 2018 Share Posted July 15, 2018 Posted by Don Fry on 15/07/2018 06:49:35: No evidence available of what most people believe, I was referring to most people who have contributed to this thread. Posted by Don Fry on 15/07/2018 06:49:35: and fact should never be confused, or viewed as interchangeable with, an opinion. I couldn't agree more, which was exactly my point. Quote Link to comment Share on other sites More sharing options...
Jon H Posted July 15, 2018 Share Posted July 15, 2018 Gary my comments relate to all glow engine operation. In 3d flying you are never flat out while not moving, the engines in those models have sufficient power to prop hang the model at a considerably lower power setting than full throttle and the moment the throttle is raised the model begins to move. As soon as its moving, everything changes. Many 3d models also have mini pipes or other exhaust tuning and as Bob pointed out some time ago they change things considerably as well. in contrast, scale can in fact put greater load on the engine as loops (for example) need to be large and sweeping. That requires power and given that most warbirds are very heavy full power is often needed for a long period. I don't know if you have ever seen me fly, but those that have will tell you I don't spent much time straight and level. My big fat Sea Fury for example could climb vertically from ground level to around 800ft if I asked it too, my La7 could as well, both at full power. The engines in these dont stop, I would have to bring to model to a complete halt and stall it out before the engine would start to suffer from the mixture change. And even then, reducing the throttle by 20% would keep the engine running. It would sound that the engine was slowing down through the climb, and it would be as the airspeed bled off, but the effect would be made worse by the doppler component of the sound. This would lead you to believe that the darn thing was on the verge of throwing in the towel when in fact it is quite happy. I would try a nose up test with it to see if it would fall over on the ground, but there is no way im waving a 23 lb 58cc model around with its nose in the air. I am not for a moment suggesting that the effect of gravity on fuel flow make no difference, clearly it does, im simply saying that the test will not reveal how this will effect the engine in flight as the unloading of the engine in the air will more than cancel out the gravity effect. An airspeed of only 5mph can increase rpm buy as much as 500 depending on the prop. This is a significant load off the engine, more or less equal to an inch of pitch or dia depending on prop brand. As for being an expert, well, i would like to think i am better educated in glow engine operation than most given my current occupation. Given that fact, instead of giving me both barrels and accusing me of spreading false information, even though this is the same information i provide as a manufacturer to my customers, why not listen to me? give my method a go? forget the anecdotes, why not give it a try? Especially when Ron, who has followed my advice, tells you that it worked. I know that we modellers are often stubborn so n so's stuck in our ways but we all have to accept change some time. Start the engine, run it up to half throttle for about 20 seconds. run up to full power and tune for max rpm. The best way to do this is lean the needle until rpm drops (too lean), then open the needle until rpm drops (too rich). Anything in the middle of that arc can be considered optimum tuning so i set the needle in the middle of that optimum range. Hold this needle setting at full power for at least 10 seconds. By now, the engine has been flat out for a little while and is likely nice and toasty. If it made it through the 10 second power test without significant loss of power (more than about 50-100 revs) get it out on the runway and stick it in the air. Don't nose up test it, just fly it. If you are worried about the climb out, take off at 70-80% power as most models are plenty powerful and this will be more than enough. If you have done this correctly, and there is no other external influence screwing things up the engine will not stop. If it quits half way through the flight, then will not run up to full power again at that tuning without refuelling then the tank is too high and the mixture has gone lean as the tank level dropped and fuel head changed. Lower the tank, retune the engine for the new tank height and try again. If it stops after a while but will restart and hold full power at the original tuning then it overheated and the cowling design is poor and baffles need to be installed. Most engines will not deliver peak power indefinitely without overheating even with good cooling. Engine cuts in flight are always blamed on being lean and i suspect this is the root of this nose up nonsense. In reality, this is rarely the case and there are plenty of other explanations for engine flame out. Edited By Jon - Laser Engines on 15/07/2018 09:31:59 1 Quote Link to comment Share on other sites More sharing options...
David Davis Posted July 15, 2018 Share Posted July 15, 2018 Posted by Jon - Laser Engines on 13/07/2018 16:59:51: Posted by David Davis on 13/07/2018 16:57:34: Posted by Jon - Laser Engines on 12/07/2018 16:21:03: Its a pointless test that dates back to the early days. With modern engines that have considerably better fuel draw and/or are pressurised its really redundant.... What about us cheapskates who use old engines to power our models, e.g, the Meteor 60 I have in the Boomerang trainer? As pointed out on the other thread, they should stop burning their money on a stash of kits and buy some new engines I bought three from you last year. Just haven't found the time to build any of the kits for them! Quote Link to comment Share on other sites More sharing options...
Gary Manuel Posted July 15, 2018 Share Posted July 15, 2018 Posted by Jon - Laser Engines on 15/07/2018 09:28:00: If it quits half way through the flight, then will not run up to full power again at that tuning without refuelling then the tank is too high and the mixture has gone lean as the tank level dropped and fuel head changed. Lower the tank, retune the engine for the new tank height and try again. Can't you see the contradiction here John? In one breath you are saying that the relative position of the carburettor and tank make no difference once the engine is tuned for maximum revs - hence why the nose up test is pointless. In this paragraph you are saying that the tank position is critical to good running. Which is it to be? You also say that the tank should be lowered before re-tuning. Are you serious? How does one go about lowering the tank of a model that is already built with it's tank position dictated by the position of the inbuilt tank shelf? One other observation comes to mind here. Most glow engines are designed with the carb fuel intake close to the centre line of the engine to allow the engine to be mounted in any orientation. I note that the carb fuel intake on laser engines is at the top of the cylinder head. Does this mean that the fuel tank needs to be positioned at a different height depending on how the Laser engine is mounted? Quote Link to comment Share on other sites More sharing options...
PatMc Posted July 15, 2018 Share Posted July 15, 2018 Posted by Gary Manuel on 15/07/2018 10:18:14: You also say that the tank should be lowered before re-tuning. Are you serious? How does one go about lowering the tank of a model that is already built with it's tank position dictated by the position of the inbuilt tank shelf? One raises the nose of the model the engine's mounted to. Quote Link to comment Share on other sites More sharing options...
Don Fry Posted July 15, 2018 Share Posted July 15, 2018 Posted by Gary Manuel on 15/07/2018 09:24:32: Posted by Don Fry on 15/07/2018 06:49:35: No evidence available of what most people believe, I was referring to most people who have contributed to this thread. Posted by Don Fry on 15/07/2018 06:49:35: and fact should never be confused, or viewed as interchangeable with, an opinion. I couldn't agree more, which was exactly my point. Sorry mate, explanation is also a Trumpism, don't like what you said first time, pretend you said something else. Anyway, I'm off to sort out the engine installation in my new hack. With adjustable tank position built in. In an ARTF. Quote Link to comment Share on other sites More sharing options...
Richard Wills 2 Posted July 15, 2018 Share Posted July 15, 2018 I am not a believer in the nose up test. In fact i'm not a believer in any sort of ground tuning beyond setting for max rpm for a baseline that the model will fly safely at. Tuning on the ground with a stalled prop at a completely different rpm and load than in actual flight is not going to get you anything other than somewhere near. Once in the air, the engine will tell you what it needs, you just need to take note, and try tiny changes over a few flights depending on what you see and hear. Some end up leaner than baseline, some richer, but seldom is ground tuning absolutely correct. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted July 15, 2018 Share Posted July 15, 2018 It could be argued that doing a nose up will guarantee sufficient air time to make those assessments! Quote Link to comment Share on other sites More sharing options...
Ron Gray Posted July 15, 2018 Share Posted July 15, 2018 Re-positioning of an incorrectly installed tank is important Gary and yes, I have had to cut out tank shelves, Wots Wot XL, Seagull P40, Great Planes U CanDo, to make sure that the tank is in the best position possible. Indeed, in some cases the use of the 'chicken hopper' system maybe necessary. Get the tank position correct and tuning for flight becomes a lot easier. Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted July 15, 2018 Share Posted July 15, 2018 Tuning for flight is easy, very rarely had to move a tank, you're masking a simple task sound like rocket science, no wonder glows in decline. Quote Link to comment Share on other sites More sharing options...
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