2 Stroke Engine tuning For 3D

2 Stroke Engine tuning For 3D
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2 Stroke Engine tuning For 3D - 2/1/2007 5:41:37 AM

efish

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Hi, I've just started learning 3D about a month ago with a Magic powered by an Enya 35X (it's equipped with a 2 needle carb). It's been a great learning experience not just about the flying, but also about engine tuning and prop selection.

Anyhow, I've found that in a sustained hover (I'm guessing after 30secs), the engine needs a richer HSN setting otherwise it seems to sag a little. Which is fine except that this richer setting is a lot richer than what I would typically consider my usual "slightly rich setting" for my 2 stroke engines mounted on sport planes. At less than half throttle, the engine sounds noticeably rich (it's 2 stroking and there's still enough power). I find significantly better performance for normal aerobatic flight with a slightly leaner setting, though if I try hovering with the leaner setting, the engine will sag after a period of hovering. The LSN is about as low as I dare to go - just a barely discernible increase in revs when I run the pinch test. Also check it by pointing the prop straight up and gunning the engine up from idle.

The engine has otherwise been great - I was surprised that it took about a gallon to really break in (even though its an ABC of sorts), but its got enough power (hovering just past half throttle), has never forced a deadstick and the twin needle carb seems to provide better throttle response than the fixed airbleed OS 32 SX I had been using.

So, am I doing anything wrong? Is there something else I could try to make things better or is engine tuning on a 3D plane, like most things, a judicious compromise where some desideratums have to be sacrificed for others? As an aside, would a 4 stroke (with its higher torque) be very much superior (I have my eye on the next plane already)?

I seem to be getting the hovers lower and lower all the time, so I want to make the engine is tuned to its max potential.

Thanks.

Post #: 1

RE: 2 Stroke Engine tuning For 3D - 2/1/2007 7:14:53 AM

warrend

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From: , SOUTH AFRICA
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Hi efish

I had a similar problem with a supertiger engine more or less the same size. I eventualy found the fuel I was using was of poor quality. What was happening was in hover after a few seconds or even in a steep climb the engine would over heat and drop power. My fuel mix is now 75% Methenol, 15% cool power ( or a good known brand synthetic oil ) 5% caster, 5%nitro. I've never had the problem again.

(in reply to efish)

Post #: 2

RE: 2 Stroke Engine tuning For 3D - 2/1/2007 7:21:11 AM

efish

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Hi Warrend, thanks. I'm running straight 5% Omega - from the same company that makes Cool Power.

Don't think its the fuel, because the engine's fine even on vertical rolls and long uplines. I noticed the richer setting is only necessary when I want to do extended (more than a few seconds) hovering.

Could be I need higher nitro to desentsitise the HSN, but in fact, the plane/engine combo is flying really well as is. But.... Can't help but feel there's still a little smidgin of room to tweak it to perfection. So perhaps I'm just being a nit picker....

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Post #: 3

RE: 2 Stroke Engine tuning For 3D - 2/1/2007 9:18:44 AM

j.duncker

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What prop are you using.

IMHO one of the tricks to getting a good 3D engine set up is to slightly underprop the engine. You should be flying on the throttle anyway so will rarely use full throttle in level flight.

What you want is reasonably high RPM in the hover. This improves fuel draw and will make the transition and spool up times better.

Try a 10x4 or an 11 x 3.

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RE: 2 Stroke Engine tuning For 3D - 2/1/2007 9:24:29 AM

efish

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Thanks, J dunker.

I've found that the Enyas like a slightly larger prop compared to their OS counterparts. After running through about 1/2 doz props, I'm now using an APC 11x4. Tried a Top Flite 11 x 4 - much better throttle response, but couldn't help but feel that I was over reving the engine. Certainly seemed to have a little less thrust compared to the APC. Had a MAS 11x5 for a while, but the throttle response on that prop was a little too slow.

But you raise a good point - will put the top flite back on and see if that changes anything. Perhaps my engine tuning skills have improved a little since

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Post #: 5

RE: 2 Stroke Engine tuning For 3D - 2/1/2007 9:42:16 AM

Kweasel

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I you are hovering at half throttle then open the LSN. The engine is drying out in this range and then sagging when you open the throttle. Tuned pipes make this situation even worse, the key to good response is in having a slightly rich mixture before the throttle is opened since we have no accellerator pump to compensate.

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Post #: 6

RE: 2 Stroke Engine tuning For 3D - 2/1/2007 9:45:33 AM

efish

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Thanks Kweasel, will give it a go.

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RE: 2 Stroke Engine tuning For 3D - 2/1/2007 10:08:36 AM

XJet

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From: Tokoroa, NEW ZEALAND
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quote:

ORIGINAL: Kweasel

I you are hovering at half throttle then open the LSN. The engine is drying out in this range and then sagging when you open the throttle. Tuned pipes make this situation even worse, the key to good response is in having a slightly rich mixture before the throttle is opened since we have no accellerator pump to compensate.

The only problem with this is that many 2-stroke engines will load up if the bottom-end is too rich. That is to say that there will be an accumulation of fuel in the crankcase that gradually increases. Then, if you've been at a low throttle setting for any length of time (even 15 seconds is sometimes enough) the engine will cough and splutter as it "clears its throat" before transitioning properly.

I tuned my 3D engines so that they're as lean as possible (without hesitating during transition) on the bottom and slightly rich on the top.

There's no way to turn a sow's ear into a silk purse though and for that reason I am careful to choose a good engine for my 3D planes. If it's a 2-stroke then I use only the Thunder Tiger 46Pro. If it's a 4-stroke then I use only Saitos. Both these provide unbeatable throttle response and 100% reliability.

I've tried other engines (GMS, ASP/Magnum, SuperTigre, etc) and none of them hold a candle to the TT or Saitos when it comes to the precise throttle response that 3D requires -- although those other engines are fine for many other types of flying.

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RE: 2 Stroke Engine tuning For 3D - 2/2/2007 9:42:55 AM

efish

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Thanks X Jet. I have to say that the Enya is about as good as any 2 stroke I've ever used. To be fair, there's nothing really I could objectively fault the engine on. In fact, most of my flying mates think it performs beautifully. But the reality is I'm not that good a flier and can't help but want to get things as good as I can.

Tried the richer LSN today, and I think I'd have to agree with you - much prefer it with the LSN as lean as possible and the HSN rich; seems to work better at least for my setup. Could be personal preference too.

As it happens, I bought a lightly used TT 46 Pro recently. Was debating between that and a Saito 56 to put in my next 3D plane. Can't say your comments have made my choice any easier ....

Was wondering if I shouldn't have saved up for an OS 46AX instead of the TT but I guess each has its fans.

As an aside, I have noticed that hovering is a lot easier with the HSN on the rich side. On a leaner setting, the plane becomes a little twitchy in the hover and is hard to get it to sit still. A few clicks rich, the smoke trail thickens and it becomes much better behaved. I was just wondering why. I don't think the engine is running lean since all these settings still produce smoke and the engine is running very much rich when tuned on the ground.

(in reply to XJet)

Post #: 9

RE: 2 Stroke Engine tuning For 3D - 2/2/2007 11:24:48 AM

Ed Cregger

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From: Ringgold, GA, USA
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quote:

ORIGINAL: efish

Thanks X Jet. I have to say that the Enya is about as good as any 2 stroke I've ever used. To be fair, there's nothing really I could objectively fault the engine on. In fact, most of my flying mates think it performs beautifully. But the reality is I'm not that good a flier and can't help but want to get things as good as I can.

Tried the richer LSN today, and I think I'd have to agree with you - much prefer it with the LSN as lean as possible and the HSN rich; seems to work better at least for my setup. Could be personal preference too.

As it happens, I bought a lightly used TT 46 Pro recently. Was debating between that and a Saito 56 to put in my next 3D plane. Can't say your comments have made my choice any easier .... Was wondering if I shouldn't have saved up for an OS 46AX instead of the TT but I guess each has its fans.

As an aside, I have noticed that hovering is a lot easier with the HSN on the rich side. On a leaner setting, the plane becomes a little twitchy in the hover and is hard to get it to sit still. A few clicks rich, the smoke trail thickens and it becomes much better behaved. I was just wondering why. I don't think the engine is running lean since all these settings still produce smoke and the engine is running very much rich when tuned on the ground.

----------------

Forget that nonsense about "over revving" a conventional two-stroke (non SK). That doesn't happen in the real world - no valves to swallow.

Sagging occurs because the timing is too far advanced for the load. One can richen the mixture a tad (which you don't like doing), back off a tad on the prop load, lower nitro (you're low enough now), lower compression OR change to a glow plug that runs a bit cooler in heat range. That would probably be the easiest thing to do.

Also, a helicopter heatsinked cylinder head would be a help, if you can find one at a good price. When flying competition fun fly models my OS.32F-H never sagged out, like my competition's engines did. That heli cylinder head was well worth the extra weight it added.

Thunder Tigers are good engines, but they are not in Enya's class at all, XJet.

Ed Cregger

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Post #: 10

RE: 2 Stroke Engine tuning For 3D - 2/2/2007 11:26:40 AM

speedster 1919

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You have to keep in mind on a long hover your fuel is as far away from carb as possible and you have to pull it up fighting gravity 100% One thing to check is all seams in muffler sealed and exhaust flange has RTV silicone to achieve 100% muffler pressure. Check muffler nipple too. Do not use an exhaust gasket.

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RE: 2 Stroke Engine tuning For 3D - 2/2/2007 4:09:18 PM

asmund

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I adjust my engines in 3-d planes a bit richer on the top than I do on my sport planes. Usually on sport planes I peak the engine and then richen it up just a bit (plane level) On my 3-d planes that do a lot of hovering for extended periods I point the nose to the sky and peak the engine and then richen it up a bit. This causes a really rich takeoff, but once in the air it is good and in hovering things are perfect

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Post #: 12

RE: 2 Stroke Engine tuning For 3D - 2/3/2007 1:21:32 AM

efish

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Hi Ed, many thanks for the insightful explanation and many helpful suggestions. On the glow plugs, have you ever tried running Rossi glow plugs? I've got an OS 8 on at the moment which I think is a medium-cold plug and I guess I should try an Enya 3 which I think is a little colder. But the Rossis are cheap locally and come in an extensive range of temps. Suspect they were designed for use on car engines though. I do have a heli engine, but its an OS 50 hyper. Got it cheap slightly used. Was just thinking of sellling it, but in light of your comments perhaps I will keep it for use on a plane.

Thanks speedster. Understood the part about fuel draw but didn't think to check the exhaust pressure system. One question: Why should I not use an exhaust gasket? Forgive me, as I have no formal engineering/tech training, but wouldn't an exhaust gasket promote a better seal?

Asmund, thanks. Actually, I've more or less arrived at the same tuning method you described. As you say, the take offs are really rich, and after prolonged periods near idle (e.g. flat spins etc), the engine does run noticeably rich. Just wondering if there was a better way to tune up the engine and make it run better.

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Post #: 13

RE: 2 Stroke Engine tuning For 3D - 2/3/2007 1:28:13 AM

Ed Cregger

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