Ringed engines vs. ABC engines.

Ringed engines vs. ABC engines.

Postby scottl0413 » Tue Feb 18, 2014 7:08 am

I was wondering what the performance difference would be of a ringed engine vs. the same engine that is ABC. Any thoughts would be great!

Scott
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Re: Ringed engines vs. ABC engines.

Postby ffkiwi » Tue Feb 18, 2014 4:21 pm

There are not a lot of options for doing a fair comparison-ie where two versions of the same engine model exist one ringed and one ABC-with no other changes to porting timing etc-but IIRC the HP 2-strokes (for certain) and one or two Super Tigre models would be good candidates. Generally the ABC version has more power. In most cases, ABC has superseded an earlier ringed model so the comparison is not necessarily valid, as other internal changes may have occurred. The HPs are definitely available as a ringed (Silver Star series) and ABC ('Gold Cup' series) in 20, 40 and 61 capacities...
On reflection, the Cox Conquest .15 would be another candidate-the current model that is, as manufactured by MECOA, though it is not ringed-but IS available in ferrous and ABC P/L options.......

ChrisM
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Re: Ringed engines vs. ABC engines.

Postby scottl0413 » Wed Feb 19, 2014 6:33 am

Chris, I have two ST 25 series X engines, both are in excellent condition. Again one ringed and one ABC. I was planning on putting one of them on a 580 Shocer for Classic A/B.

Thks, Scott
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Re: Ringed engines vs. ABC engines.

Postby Gnu » Wed Feb 19, 2014 8:41 pm

I believe that the difference lies in the limitation of RPM set by the tendency of a piston ring to float or flutter at high RPM thus being unable to achieve a seal between the cylinder wall and the piston in this state. Dykes style rings are effective at higher RPM than standard rings, but they too have limitations. If a ringed engine makes the power you need and you don't need a high rev engine, the only difference to be concerned with is the weight of the engine, since a smaller engine at higher RPM can equal the power of a larger engine at low RPM. If you don't like screamers, ringed engines will suffice.
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Re: Ringed engines vs. ABC engines.

Postby ffkiwi » Thu Feb 20, 2014 12:59 pm

Scott you have the perfect opportunity for some comparative testing then....! Actually it would be not quite as easy as we've made out-gnu has touched on some of the issues-the other point is that I would not expect the porting to be identical in a ringed and ABC version of the same engine. As well as 'floating' mentioned above by gnu there is also the issue of 'ballooning' whereby the ring tends to expand outwards (as it should) under combustion pressure and has the potential to get caught in the ports-so ports are bridged in a ringed engine to restrict the amount of ballooning that can occur. Rings are sometimes 'pinned' to prevent them rotating and the gap catching in the ports. Bridges in the ports automatically means that incoming and outgoing gas flows are going to be slightly altered versus those in the ABC engine where the bridges are not present. This I would expect to have some effect, though probably small-and an ABC piston I would expect to be lighter than the equivalent ringed one-so less inertia, and possibly slightly better balance.
Actually when I suggested ST as a possible candidate in my first response to the thread I was thinking of earlier ST models-I didn't realise the X25 came in ringed and ABC variants.....

ChrisM
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Re: Ringed engines vs. ABC engines.

Postby scottl0413 » Mon Feb 24, 2014 7:19 am

Chris and Gnu, thanks for your thoughts on the subject, all are very valuable points of interest. I will probably build a new fuselage and mount the ST Series X 25 on it and see how things go. Chris, as you mentioned earlier the use of ST engines, I have a no. of A/B classic designs with ST 23's on them and they do quite well. My only concern is that generate quite a bit of vibration!!! I fly them with an 8x4 APC prop. I've been told that allot of the older loop scavenged engines weren't design to run at the rpm's that we run them at in FF. I was thinking of trying a 9x3 APC to see if I can slow down the engine a little bit and reduce the vibration without diminishing the pwr. output. I have also discussed balancing the ST 23's with Bob Mattes and I will be sending him an engine to see what he can do!. The ST series X engines are great engines and they are at a par with the K&B's, i.e. 3.5, 4,9,6.5, etc.

Scott
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Re: Ringed engines vs. ABC engines.

Postby ffkiwi » Mon Feb 24, 2014 1:06 pm

Scott-you make a fair point.....and in response I'll make the point that I seem to have to keep reiterating from time to time- horsepower and revs don't fly aeroplanes-THRUST flies aeroplanes-and whilst there is a connection between all three it is neither linear nor directly proportional-and we forget that to our peril. NFFS over the years has published several articles on thrust measurement tests-and IIRC the highest thrust for any particular engine-prop combination rarely if ever coincided with the max revs and the smallest prop......
There is never any point at all in propping an engine to run faster than the BHP peak-in the air! And if you accept (and it is generally accepted-and partially verified by in flight rpm measurements) that our engines unload by approximately 10% in the air-then you want to be propping the engine for 10% less revs on the ground than the BHP peak. Of course if there is no published data for the engine, all you can do is go by the manufacturer's recommendations (which are often conservative) or see what similar sized engines are being loaded with (equally fraught given the variations in design and performance). I tend to go for the larger props-on the basis of efficiency if nothing else-and in the case of diesels (which I use quite extensively) ease of starting as well. Our forbears in the 50s used to use props as part of the trimming process on FF duration models-altering both diameter and pitch to fine tune trim (and often cropping diameter by 1/8" at a time) which we seem to have forgotten in the decades since. [mind you they had far fewer prop options available to them then]
As regards the ST23 I can't comment from any personal experience with them-but I do know they had a less than stellar reputation-but that may have arisen through ST pushing the boundary a bit-with the classic 'quart in a pint pot'-when you shoehorn a .23 into a case designed for a .15 things are bound to be a bit less than optimal......as for the vibration-well it would seem to me that this is one of the outcomes of that action-the crankshaft size and throw are already determined by the 15 case size-which effectively determines the balance factor-so fitting a larger and heavier piston in the 23 will increase the reciprocating weight-and the degree of imbalance-hence more vibration. I'm sure if anyone can do anything to improve things, Bob Mattes can-but I suspect his options are fairly limited-there's not a lot more you can do to restore the balance factor-apart from lightening the piston and rod-or adding tungsten inserts to the crankweb......
One thing I have noticed over the past few decades-is that engine crankwebs have got a lot thicker and heavier in modern engines-even as pistons-thanks to the near universal use of ABC, AAC or ABN cylinder technology-have become lighter.....and modern engines seem far less problematic when it comes to vibration..........

ChrisM
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Re: Ringed engines vs. ABC engines.

Postby scottl0413 » Wed Jul 16, 2014 2:30 pm

Well finished the new Big Dog Fuselage yesterday and mounted the Dykes ringed S.T. Series X 25 on it. Took it outside to fire up the engine much to the neighbors "destane" (sp). It took a little work to get it fired up since I hadn't run it before and had to play with the NV in order to feed it enough(it is a thristy engine). But once I got it figured out it was very enlightening!!! With a 9 x 4 APC Prop on it, it was turning 20k RPM!!! Really pulling hard. I think the difference in the std. ringed engine and a dykes ringed engine will be noticeable. Going back to my cross country dessert motorcycle racing in the late 60's and 70's Most of your hotter 2 strokes where dykes ringed engines, i.e. Husqvarna's, CZ's, etc. The difference being is that on the compression stroke the dykes ring expands and the normal rings relay on the spring forcer of the ring its self thus giving the dykes ring a tighter seal to the cylinder wall. Anyways enough of this theory stuff it runs very good and has tons of thrust.

Regards, Scott
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Re: Ringed engines vs. ABC engines.

Postby scottl0413 » Thu Jul 17, 2014 6:17 am

Well, took out the ST 25 ringed out last night and flew a 500 sq. in. Geodetic Galaxy and the pwr. was great! Took 3 test flights to get the pwr. pattern figured out than ran out of daylight!!! But all and all very pleased with the pwr. plant.

Scott
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Re: Ringed engines vs. ABC engines.

Postby John Buskell » Thu Jul 17, 2014 8:44 am

It's good to hear you are getting some flying in, Scott, well done.

Did you perhaps make a typo in the previous post? Did you run your X.25 on a 9x4 APC - or did you mean 8x4?
20k RPM on a 9x4 means something like 2 hp - forgive me, please, but I kind of doubt that!

best regards
John
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Re: Ringed engines vs. ABC engines.

Postby scottl0413 » Thu Jul 17, 2014 8:55 am

John, yes it is a 9 x 4 APC prop. I will verify the RPM again but it pulls harder that an K&B 3.5 with 7.8 x 4.5 APC on it!!!

Scott
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Re: Ringed engines vs. ABC engines.

Postby John Buskell » Thu Jul 17, 2014 9:36 am

Sheesh, that's really something!
What are you putting in the fuel tank?

The late George Fuller had an X.25 in one of his Unlimited models (in the UK). I watched several fly-offs from a distance down wind, and his model always peeled past the big 40 models, and the F1Cs on the way up, so those engines can certainly 'haul the freight' as they say!

John
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Re: Ringed engines vs. ABC engines.

Postby scottl0413 » Thu Jul 17, 2014 10:34 am

John, I too was surprised how hard it pulled when I first fired it up! Fuel is 35% nitro 25% lub. (50/50 castor/klotz). This is what i use in all my ball bearing engines. Plane bearing engines is 25% nitro 20% lube (100% castor oil).

Scott
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Re: Ringed engines vs. ABC engines.

Postby Dan Berry » Thu Jul 17, 2014 9:12 pm

Try a Master Airscrew 8 x 4.
I'm not joking.
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