Ron Gray Posted May 2, 2021 Author Share Posted May 2, 2021 (edited) Lovely day today so took the Sportster out and had 3 flights of +10 mins each. Have to say that the engine ran a bit better but still not 100% so plan B is to continue with the direct air feed to the carbs. Edited May 2, 2021 by Ron Gray Quote Link to comment Share on other sites More sharing options...
Ron Gray Posted May 2, 2021 Author Share Posted May 2, 2021 Fitted air feed pipes to the carbs, they will get air from within the fuse. Both air feeds are the same length If it works then the next step will be to make an airbox with an external ram air feed to it (pressurised air box?). 1 Quote Link to comment Share on other sites More sharing options...
Chris Walby Posted May 2, 2021 Share Posted May 2, 2021 (edited) Hi Ron, I think your hose pipe solution may create more problems than it solves with carburetion after all if it was that good wouldn't all manufacturers advise doing it, but I'll leave Jon to have his view. Edited May 2, 2021 by Chris Walby Quote Link to comment Share on other sites More sharing options...
Ron Gray Posted May 2, 2021 Author Share Posted May 2, 2021 It may well do so Chris, but that's what it's all about, experimenting and it's no great effort to put it back to what it was beforehand! Hopefully I'll get a chance some time tomorrow to run it up in the garden. Quote Link to comment Share on other sites More sharing options...
Eric Robson Posted May 2, 2021 Share Posted May 2, 2021 Hi Ron, I was thinking of a deflector over the intakes .something like a channel that would deflect debris away from the carbs but not impede the air flow. I hope you don't pull in any balsa dust with your pipes, I would test it tomorrow morning as it is forecast heavy rain in the afternoon. Quote Link to comment Share on other sites More sharing options...
Ron Gray Posted May 3, 2021 Author Share Posted May 3, 2021 The problem I’m experiencing is that with the cowl off the engine is sweet (as a nut) with it on it’s not quite so nice ( and I’m being hyper-critical as the plane flies fine, it just doesn’t sound quite so nice). Therefore it is the cooling baffling that is causing the problem which I put down to air disturbance and I’m guessing that it mainly affects the rear carb as that is close to the bulkhead. My experiment with the air pipes takes the air intake from a calm air mass, inside the fuse but may, due to the restriction imposed by the pipes, create a fuelling issue which I may, or may not be able to tune out with mixture tweaks. If it works then I may then make an air box out of an old fuel tank which the pipes can be connected to. Agree with you about balsa dust Eric and I’ve blown the fuse out with compressed air to remove as much as I can. However, the airframe is several years old and has been flown many times over the years so most dust will, I think, have been blown out. Quote Link to comment Share on other sites More sharing options...
Ron Gray Posted May 3, 2021 Author Share Posted May 3, 2021 Had some time, just before the rain comes, to test the air pipes on the engine. 2 vids, the first with the tuning unchanged, the second with some bottom and top end adjustments. Video 1 - bit lumpy at low revs and swinging an APC 16x8 topping out at 8.1K Video 2 - tweaked both bottom and top, a lot smoother and tops out at 8.5K. Whilst I will leave my final judgment for in flight testing, I am very pleased with these results. Another side benefit is that the engine is a lot quieter than before (difficult for you guys to tell when I'm wringing the neck off it in front of a building) but I noticed it as soon as it started, the lack of carb induction noise! 2 Quote Link to comment Share on other sites More sharing options...
Ron Gray Posted May 3, 2021 Author Share Posted May 3, 2021 Sorry, typo in the previous post, in should read an APC 18x8 not 16x8! Quote Link to comment Share on other sites More sharing options...
Dwain Dibley. Posted May 3, 2021 Share Posted May 3, 2021 What about with the cowl on Ron. The object being, you shouldn't notice a difference. ? Good fun fiddling with stuff, and it keeps us off the streets, where I suspect, we would only get into trouble. D.D. 1 Quote Link to comment Share on other sites More sharing options...
Ron Gray Posted May 3, 2021 Author Share Posted May 3, 2021 Put the cowl back on but then the wind and rain arrived so couldn't test it again. Like you say D.D. cowl on shouldn't make any difference on the ground or in the air but who knows until I test it? Planning on in flight testing on Wednesday if the weather allows. Tis good fun fiddling with stuff and there are times when I enjoy it more than building or flying! 2 Quote Link to comment Share on other sites More sharing options...
Dad_flyer Posted May 3, 2021 Share Posted May 3, 2021 (edited) Both videos will play at the same time on my phone. The sound of a twin using inline twins ?. That would suit Child_flyer's current favourite plane, but it would need to be a big one... (CF's picture from yesterday) Edited May 3, 2021 by Dad_flyer Add photo Quote Link to comment Share on other sites More sharing options...
Tim Flyer Posted May 3, 2021 Share Posted May 3, 2021 I’m enjoying watching the thread too . Regarding air intake to carbs it certainly should be in free flowing air and free from firewall restrictions. A velocity stack or bell mouth helps airflow considerably. I don’t think any sort of “air ram” would be beneficial. This is because the Lasers generally don’t use pressure fed fuel, and ramming with its extra air pressure might lean out the engine on full throttle. Quote Link to comment Share on other sites More sharing options...
Ron Gray Posted May 3, 2021 Author Share Posted May 3, 2021 The proof to see if this works will be when I fly it with the cowl in place, as I said above this 'shouldn't' be any different to that which I've seen on the ground in my tests. I also think that with a better design of air cooling baffling I could probably got rid of the turbulence that I believe to be the root cause of my problems but the air intake pipes has so far proven to be a good solution with the added benefit of a reduction in noise! Tim I still like the idea of the air ram creating a pressurised air supply, who knows if it will increase performance but unless you try you don't find out! But that will have to wait as I just want to get it running to my satisfaction first. Quote Link to comment Share on other sites More sharing options...
Ron Gray Posted May 3, 2021 Author Share Posted May 3, 2021 2 hours ago, Dad_flyer said: Both videos will play at the same time on my phone. The sound of a twin using inline twins ?. That would suit Child_flyer's current favourite plane, but it would need to be a big one... (CF's picture from yesterday) I've got the Tigercat powered by twin V twin Lasers, now that does sound good but have to agree that something like a Mossie powered by twin in-line twins would be awesome! Quote Link to comment Share on other sites More sharing options...
Jon H Posted May 4, 2021 Share Posted May 4, 2021 In your 2nd video Ron are you dropping down to 1 cylinder at idle? It sounds like one might be absent at idle even though it picks up on both. I am going to have to have a crack at this air box situation myself i think. I have been meaning to try it out for ages but never got round to it. As my La7 is currently engineless due me abandoning my efforts to use a radial in the front (due to the engine being a useless steaming pile) i can refit a laser 300 and see if i can come up with an air box/filter for the carbies and try cooling it in the same way as the argus V8 in a storch. On ram air, the effect is likely to be very small as the ram air pressure of what, 70mph? over a hole the size of the carby is likely to be quite small vs the induction cycle of the engine. That said, its another fun thing to test! One final note on this is cooling. By drawing cold air from outside the cowl into the combustion chamber you are giving yourself additional cooling right where you need it. The cooler air is also denser and in theory offers you more power. Again, i suspect the effects of both will be small at our scale but its still going to help a bit. Quote Link to comment Share on other sites More sharing options...
Tim Flyer Posted May 5, 2021 Share Posted May 5, 2021 I think it really depends on what we mean by air ram . If we have a large say 1.5 inch aperture directly facing the oncoming airstream, and feed that with a silicone seal directly into the carburettor stack I think that would have an adverse effect by leaning mixture at higher speeds. If by “ram air” we mean bringing in air to flow towards the carburettor with no seal so excess air can spread and pressure will not substantially change I think that would be positive. However the proof is all in the pudding as you both say. I certainly remember how important good airflow is on an RC boat engine despite water cooling. Performance massively deteriorates without good flow. Quote Link to comment Share on other sites More sharing options...
Frank Skilbeck Posted May 5, 2021 Share Posted May 5, 2021 Many years ago, my 3rd year project at University was to set up an engine on a dyno (a MZ250 piston port two stroke) and evaluate the length of an inlet tube on the carb, as expected there is a resonant length where you can get a slight boost effect and more power. I did the calculations at the time looking at the port timing and resonant length to get the pressure wave to arrive at the port at the right time. If you know the valve timing on the Laser it might be possible to get a similar effect. Note get the length completely the wrong length and it could sap some power. Quote Link to comment Share on other sites More sharing options...
Chris Walby Posted May 5, 2021 Share Posted May 5, 2021 IMHO the discussion about tuned length for inlet and exhaust ports is a bit off topic although interesting and I could .....off topic! The issue was around ingesting unwanted foreign objects causing engine damage and how to prevent it. The most important thing is not to upset the engine across its RPM performance range (no disrespect intended, but the Laser engine is not a hyper-performance design) and are operated by a wide range of owners and skill sets They do need to be set up correctly and will then reward the operator with performance and reliability. Their reliability is well known and IMO messing around with bits of rubber tube is likely to end up with sub optimal results and overall reduction in performance/reliability. Perhaps a wire mesh thimble over the front of the carb is all that is needed to solve the issue. I can just see this ending up with chasing the tail of odd issues which are installation related and would not be found on the test bench or a different model installation. Its like the never ending debate Jon has about tank location "someone puts the tank in the wrong place and then complains the engine is unreliable" as if they are surprised. Keep up the good work as its an interesting project. Quote Link to comment Share on other sites More sharing options...
Ron Gray Posted May 5, 2021 Author Share Posted May 5, 2021 Just watch this space Chris as I will be posting a couple of videos of the Sportster flying today with the air feed pipes in place once they have uploaded to YouTube! Quote Link to comment Share on other sites More sharing options...
Jon H Posted May 5, 2021 Share Posted May 5, 2021 The idea of this intake digression is purely to look at preventing debris ingestion. While possible to tune intakes for performance it is not what we are looking for and all of this is a bit of an experiment. Ron has benchmark performance from the stock engine so any performance issues will be immediately apparent. I always aim to offer solutions that will always be guaranteed to work. That may be cooling, fuel tank placement, fuel choice, plug choice, props..whatever. I dont recommend things that can work, only things that will. With things that can work, so much is down to the individual that its unrealistic to expect everyone to be able to get the same result. For that reason, things like tuning exhausts or intakes are not on my radar, but testing something that may prevent debris ingestion is worthwhile, especially if its as easy as some old tights and a bit of pipe! Quote Link to comment Share on other sites More sharing options...
Ron Gray Posted May 5, 2021 Author Share Posted May 5, 2021 (edited) OK, the proof of the experiment I believe can be seen in these 2 videos (one now, one in a bit), and the vids are from the starting of the engine to show I'm not 'cheating'. Also please take a look at the windsock to show the conditions we were flying in!!!! And yes, the front pot is running a tad rich! Edited May 5, 2021 by Ron Gray 2 Quote Link to comment Share on other sites More sharing options...
Ron Gray Posted May 5, 2021 Author Share Posted May 5, 2021 Second vid, mainly as this showed a landing. In all I had 5 circa 8 min flights today, thoroughly enjoyable. 4 Quote Link to comment Share on other sites More sharing options...
Steve Dunne Posted May 5, 2021 Share Posted May 5, 2021 Very nice, Ron. Good to see it perform so well! I had four good flights today, one of our members (stand up, Phil) took some footage on his phone. I will try to post it once I get a copy. Steve. Quote Link to comment Share on other sites More sharing options...
Ron Gray Posted May 5, 2021 Author Share Posted May 5, 2021 Thanks Steve, yes, I’m really pleased with how it’s running with the air pipes in place. You can’t really tell from the vids but they have also really cut the noise down. But the main thing is that the pipes have not had a detrimental effect on performance and proves that the cooling baffling was causing the fuelling problem. I’ll look at that again but I’m in no rush as what I’ve done works and only involved drilling a couple of holes in the bulkhead and the fitting of 2 silicone pipes. 3 Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted May 5, 2021 Share Posted May 5, 2021 Nice Strafing runs Ron, someone starched yer windsock ? 1 Quote Link to comment Share on other sites More sharing options...
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