3W 70cc single Prop size / rpm??

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stuart knowles 1611
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3W 70cc single Prop size / rpm??

Postby stuart knowles 1611 » July 6th, 2017, 12:36 pm

Hi All,
I have a 3W 70cc single (side exhaust / rear carb) The manual on the 3W site suggests props in the 23x8 to 24x10 range. On these props I am only getting 5700 rpm. I have checked the carb tuning and there are no more revs to be found there. It starts and runs well at idle, mid range and full throttle.

My guess is that the manufacturers prop sizes are a bit over ambitious? A Zenoah 62 would be using a 22x10.

Is there anyone out there using this engine that could comment??

The airframe is a 100" 28lb WWII type.[img]
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Cary Bailey
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Re: 3W 70cc single Prop size / rpm??

Postby Cary Bailey » July 6th, 2017, 2:00 pm

Stuart, 3W are slightly ambitious in their rpm info. On the basis that you have your cooling of the motor sorted and the general normal things needed to run this engine then there are several things to note, fuel/oil ratio, type of oil you are using plus the ignition module.
3W say use 50 or even 80:1 fuel oil ratio, I always use around 50:1. 50:1 and lower can actually reduce the rpm in 2 factors, too much oil around the needle bearings can actually make them "slide" as opposed to roll. This causes excessive heat and the engine rpm drops due to this even though you have increased the oil thinking the engine will benefit from this and the cooling property of the oil. This causes the heat, the heat then richens up the fuel setting and the rpm drops off!
I use a good quality 2 stroke oil such as Bel-Ray, Redline, Castrol. Using the cheaper oils can cause problems and higher levels of carbon deposits.
3W ignition unit, here I have a problem in that I have 2 3W 55i's that I could never get them to perform at higher rpm's. I was only getting as you are around the 5700-6000 rpm on a 22x10 Menz or Falcon prop. I changed the 3W ignition unit to the Rcxel unit and immediately got an additional 1000-1300 rpm!
Just some pointers that you probably know but that is my experience with them.
Cary

stuart knowles 1611
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Re: 3W 70cc single Prop size / rpm??

Postby stuart knowles 1611 » July 6th, 2017, 5:15 pm

Thanks Cary, I'm presently using 'Stihl' oil at 40:1 - I was using 50:1 until this year when I upped the oil content because I ran a big end bearing out last year on a different engine. The Ig Unit in use is the 3W original. I have had good experiences with the RcXL until as a replacement for a Zenoah 20 engine. I'm inclined to give both your suggestions a try.

I had one flight last night which ended in a dead stick - surprised me because it had been running well right up to the moment it stopped, running well and then just died without a splutter of warning.
On retrieval it started and ran well again but I decided against further flight until it had a good coat of looking at.

This morning I made sure that the ignition battery was fully charged and then retuned the carb on the ground, just edging toward 'rich' on the high end. A good ground run with no sign of distress so further flights this afternoon. First was too rich and barely flew, tweaked.... better, tweaked again ... better still and ran well AND kept going. Still maxing out at 5700 /800 rpm with a small increase in the air. Presently running a 24x10 cut down to around 23"

Three flights - on the same prop and nothing fell off so nearly there....If it had another 1000 rpm it would be spot on. I'm pretty sure that there's no more to be found in this engine 'as is' I'm going to put in a bit of flight time and then try the Ignition swap.

Thanks for the suggestions - much appreciated. Anyone out there with the same engine?
cheers,
stu k

stuart knowles 1611
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Re: 3W 70cc single Prop size / rpm??

Postby stuart knowles 1611 » July 7th, 2017, 8:59 pm

Just want to bump this thread..... Anyone using a 3W 70cc single who could comment on what prop sizes you have found useable.
thanks

stu k

stewart clifford
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Re: 3W 70cc single Prop size / rpm??

Postby stewart clifford » August 9th, 2017, 8:16 pm

I had one and ran it on a 24 x 10, I got just about 6000 rpm. 3W's seem to be hit or miss, I've seen some roaring models around the sky and plenty of others running flat and seemingly gutless. My 80 was the same, maybe it's something I was doing wrong?? But I did try lots of things to try to improve it. In the end I cured the problem with the 70 by replacing it with a Zenoah 80 and cured the 80 by replacing it with a DLE 85.

stuart knowles 1611
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Re: 3W 70cc single Prop size / rpm??

Postby stuart knowles 1611 » August 9th, 2017, 10:20 pm

Thanks Stuart, that's good to know. I have flown it a few times now and it is showing a marginal improvement. I think that the basic problem is a lack of cubes for the size of model.

Do I gather that you found a DLE85 single better than the Z80 twin?? - surprising, I was thinking that the Z80 would fit the cowl, may I need to think again?

Thanks for the info, much appreciated.
stu k

Cary Bailey
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Re: 3W 70cc single Prop size / rpm??

Postby Cary Bailey » August 10th, 2017, 9:58 am

Stu, have you changed the ignition yet & thrown away that rubbish oil you use???
Cary

stuart knowles 1611
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Re: 3W 70cc single Prop size / rpm??

Postby stuart knowles 1611 » August 10th, 2017, 4:39 pm

Ha! No not yet, I picked up the oil but not used it yet, can't help but think that there is a large element of snake oil in the said two stroke oil..... something has to account for the price!
I did find that the more it has run there has been a marginal improvement to the 'barely adequate' category but at this time of year its not the time to be ripping it apart. I'll keep it going until things wind down a bit and then decide what to do.

stewart clifford
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Re: 3W 70cc single Prop size / rpm??

Postby stewart clifford » August 15th, 2017, 8:46 pm

stuart knowles 1611 wrote:Thanks Stuart, that's good to know. I have flown it a few times now and it is showing a marginal improvement. I think that the basic problem is a lack of cubes for the size of model.

Do I gather that you found a DLE85 single better than the Z80 twin?? - surprising, I was thinking that the Z80 would fit the cowl, may I need to think again?

Thanks for the info, much appreciated.
stu k


No, I got rid of both 3w's. The Dle has much more power but that and the zenoah are great engines and fly both models how I want them to.

stuart knowles 1611
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Re: 3W 70cc single Prop size / rpm??

Postby stuart knowles 1611 » August 15th, 2017, 9:30 pm

Thanks Stewart, I appreciate the feedback.

martinwaller4
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Re: 3W 70cc single Prop size / rpm??

Postby martinwaller4 » August 15th, 2017, 10:53 pm

Hi
I have a 3W 70i in a quarter scale ME109 black 6. I use a 24x10 mejetlk (spelt wrong) carbon prop and get around 6,400 static. I get 6,300 on the 3W 60 with the same prop.
I use 40 to 1 Silkoline Comp2 synthetic. Similar to Stihl oil.
Motor is very sensitive to the exhaust system and if restricted will drop performance. I have three 3W60 engines and all were 6200 new and up to 6500 run in static on 24x10 mejetlk carbon prop. I have had your problem but exhaust improvements brought revs to minimum 6200 for new engine. On my Zirolli Mustang I doubled the exhaust outlet with a third large bore pipe revs lifted from 5,800 to 6200. The revs you have indicate a problem needing sorting especially cooling or most likely a restrictive exhaust system. Revs on the Metz 24 x 10 wood props about same as Mejetlk but carbon prop 50% more thrust. Zenoah 62cc 4.6bhp while 3W70i is 6.5bhp. In my well run in 3W60 in my Extra I get 6500 static on the 24x 10 Mejetlk carbon prop. The 70i with its rear disc induction is greatly superior to the side induction 3W60 especially as it unloads in the air. Fitting a tuned pipe will really push up the power on both engines.
Martin


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