ABC versus AAC

[Andrew Tinsley]

Hello again,
Randy still has stock ABC and his special AAC P/L liners for the OS 46VF (at least I think that was what he said?). This got me thinking about the two types of P/L setups. I know that you need a special piston alloy (hypereutectic aluminium / silicon alloy) to match the expansion of the brass cylinder liner.
The hypereutectic alloy seems to be expensive and not all that readily available, so why do most manufacturers stick to ABC (or ABN) setups? It would seem logical to use the AAC system where both piston and cylinder should have similar expansion coefficients. It should be both lighter and cheaper this way.
The fact most manufacturers don't use AAC tells me that I am missing something, but I can't quite figure what! Anyone got the time and knowledge to enlighten me?

Thanks in advance,

Andrew.

[Richard Koehler]

Andrew, what I've heard mostly from people I trust is that the only people in the world that know how to make an AAC engine are the Eastern Europeans that make both Double Star and Brodak engines.  This would seem to make sense since they are the only AAC engines available here in the States.  I love my Double Star 40 and two Brodak engines.

[Mike Greb]

Jett and Nelson have been manufacturing AAC stunt engines for quite a few years.  Great engines and made here in the USA. 

[Tim Wescott]

I'm not sure what exact alloys are used for the liners, but 2024 aluminum and 260 cartridge brass have nearly identical coefficients of thermal expansion (21.1 um/m vs. 19.9 um/m).

My understanding is that you need a piston that will expand less than the liner, rather than one whose expansion is matched, both because the liner tends to get better cooling, and because you want the liner to expand away from the piston when the engine gets hot (this is why an ABC engine will "squeak" at TDC until it's broken in).

Brass is something like the second easiest metal to chrome plate (copper is easiest, and is often used as a "primer" for high-quality decorative chrome and maybe hard chrome as well).  Aluminum is difficult and expensive to chrome well.

So I suspect the big difference is the difficulty and expense of chroming aluminum -- and those former Eastern Bloc modelers will have post-cold-war weapons manufacturing facilities available to them that can be used, as well as less environmental regulations on the chrome shops, plus exchange rates that lets them put more labor into their engines and sell them at a profit over here.

[Chris Wilson]

Good reply Tim and I note that the Eastern Bloc made R+B 75 has an AAC setup as well and is incredibly light for its size.

But on the flip side I believe that brass can be squeezed back to regain lost pinch whereas aluminum can not be.

[RandySmith]

Andrew, what I've heard mostly from people I trust is that the only people in the world that know how to make an AAC engine are the Eastern Europeans that make both Double Star and Brodak engines.  This would seem to make sense since they are the only AAC engines available here in the States.  I love my Double Star 40 and two Brodak engines.

Flat wrong, AAC p/s have been made here and sold for decades, good as anything made anywhere

Regards
Randy

[RandySmith]

Aero Tiger 36  AAC
all PA Engines AAC
many Jett engines AAC
I have made many many  HP, OS VF SF AAC   OPS AAC, there have been other made here in the US also
Plus 100 or 1000s of OS RC rebuilds AAC
I did many rebuilds on VF 46 AAC engines

Randy

[Brian Hampton]

AFAIK the first mass produced AAC engine was the Enya 60X from late '74 and many of the later Enyas were also AAC. The old Bluebird engines (known as Brat in America) were all AAC from their .21 to .46 although for some reason their .51 is ABC.

Chris, my understanding of AAC is that it doesn't bell mouth like ABC does so repinching is never needed.

[Andrew Tinsley]

Hello All,
I was aware that AAC setups have been made in both the US and ex USSR countries. What intrigues me is that nearly all the AAC engines are small run, specialist types (with the exception of the Brat series that I was unaware of). So what are the pros and cons of ABC vs AAC setups? It seems that chroming aluminium is perhaps not all that difficult, perhaps a keying layer of an intermediate material between the aluminium and chrome? Why do the mass producers stick mainly to ABC (N) types. I would think it must be a cost decision, but can't figure out why the AAC should cost appreciably more.
Forgive my curiosity, in the big picture it hardly matters, but these odd little issues just fascinate me!

Regards,

Andrew.

[ash]

Why do the mass producers stick mainly to ABC (N) types. I would think it must be a cost decision, but can't figure out why the AAC should cost appreciably more.

Could be a warranty avoidance issue. I understand that AAC liners are quite easily distorted by hamfisted tinkerers.

[Brett Buck]

Andrew, what I've heard mostly from people I trust is that the only people in the world that know how to make an AAC engine are the Eastern Europeans that make both Double Star and Brodak engines.  This would seem to make sense since they are the only AAC engines available here in the States. 

   I don't trust anyone from Eastern Europe to build anything the same twice in a row. All of my AAC engines are made right here in America - Utah/Georgia and Texas.  US-Built AAC motors have won something like 15-16 of the last 20 NATs.

[Andrew Tinsley]

Hello again Brett,
Now come on and tell me why AAC engines are so good at winning Nats! Couldn't be anything to do with the pilots I suppose? Seriously what advantages do the top draw pilots see in AAC setups?

Thanks,

Andrew.

[RandySmith]

And Worlds wins also

A couple of big advantages are weight, the AAC engines weigh about 1 ounce less, which is near 10% of the weight of the motor.
Al. sleeve , al. piston, al. case .... very good rate of expansion similarities in having al. everywhere,  Al. is also pretty strong and holds it shape well.

Randy

[Tim Wescott]

A couple of big advantages are weight, the AAC engines weigh about 1 ounce less, which is near 10% of the weight of the motor.
Al. sleeve , al. piston, al. case .... very good rate of expansion similarities in having al. everywhere,  Al. is also pretty strong and holds it shape well.

Since you make AAC sleeves you know exactly how much it costs and what the problem rate is -- am I correct in my impression that it is a more involved and expensive process than plating brass?  I recall that when I used to work with mechanical guys who had to have such stuff done, a suggestion to plate brass was usually a "ho-hum, we'll get a price on that", while suggesting that one plate aluminum was "oh horrors -- can there be another way?"

[RandySmith]

Since you make AAC sleeves you know exactly how much it costs and what the problem rate is -- am I correct in my impression that it is a more involved and expensive process than plating brass?  I recall that when I used to work with mechanical guys who had to have such stuff done, a suggestion to plate brass was usually a "ho-hum, we'll get a price on that", while suggesting that one plate aluminum was "oh horrors -- can there be another way?"

Hi Tim

There is not any measurable difference in fail rate as they both are excellent. as far as the problems making them, It is only a problem for people that are inexperienced in AAC technology, one that are  have no trouble

Randy

[RDJeff]

Check out CZ pistols sometime.  Very well made!  I'm also partial MVVS diesels...

   I don't trust anyone from Eastern Europe to build anything the same twice in a row. All of my AAC engines are made right here in America - Utah/Georgia and Texas.  US-Built AAC motors have won something like 15-16 of the last 20 NATs.

[RandySmith]

Check out CZ pistols sometime.  Very well made!  I'm also partial MVVS diesels...

LOL  are they AAC ?      

Randy

[Brett Buck]

Check out CZ pistols sometime.  Very well made!  I'm also partial MVVS diesels...

    I was referring to model engines.

     Brett

[Tim Wescott]

There is not any measurable difference in fail rate as they both are excellent. as far as the problems making them, It is only a problem for people that are inexperienced in AAC technology, one that are  have no trouble

So, as an engine builder, do you have any theories why the big operations seem to favor ABC over AAC?  I'm interested to know.

[RandySmith]

So, as an engine builder, do you have any theories why the big operations seem to favor ABC over AAC?  I'm interested to know.

Hi Tim
Cheaper and quicker?  The only "BIG" operation..whatever that means, that is doing ABC maybe the Magnum plant in China

Randy

[Tim Wescott]

Cheaper and quicker?  The only "BIG" operation..whatever that means, that is doing ABC maybe the Magnum plant in China

OK, then allow me to expand my question to ask how ABN fits into the mix, and why those 'biggies' like OS and Enya that use it might use it instead of AAC?

Fox, by the way, seems to offer steel, ABC, or "ceramic plated" (which I assume means a hypereutectic piston in a hard-anodized sleeve, but I don't know for sure).  But I'm not sure whether Fox counts as "big"  Where they say at all, Saito seems to be a mix of AAC and ABC.

[RandySmith]

There are less problems (cost of the entire process from start to disposal) with nickle plating although the OS nickle is far inferior to real chrome. The Enya nickle is much  better than the type OS uses.
Maybe the biggest ABN factory now, is Thunder Tiger and OS, they use 2 different types of plating
The acid in chroming may cause OS  problems and that is why the use nickle.
There is a lot of acid used in chroming and Japan may have environmental laws making it much more expensive.

Randy

[Andrew Tinsley]

Hi Randy,
Thanks for your input , it has been very interesting to learn some of the behind the scenes reasoning. The 64 thousand dollar question remaining is how do the two processes compare with each other? Say an OS 46VF ( for obvious reasons, I just purchased one!). How does the standard OS piston / liner compare with your AAC piston / liners?
I can probably fill in some of the comparison boxes, i.e. your AAC setup will probably outlast the OS product by a good margin. The engine will be lighter. How about performance? Although if you put the engine in a piped ship, then the performance will probably be the same? Other applications may prove different?

Thanks again,

Andrew.

[RandySmith]

Hi Randy,
Thanks for your input , it has been very interesting to learn some of the behind the scenes reasoning. The 64 thousand dollar question remaining is how do the two processes compare with each other? Say an OS 46VF ( for obvious reasons, I just purchased one!). How does the standard OS piston / liner compare with your AAC piston / liners?
I can probably fill in some of the comparison boxes, i.e. your AAC setup will probably outlast the OS product by a good margin. The engine will be lighter. How about performance? Although if you put the engine in a piped ship, then the performance will probably be the same? Other applications may prove different?

Thanks again,

Andrew.

Hi Andrew

If you go with just a pure allout 2 cycle you can get  a little more out of teh chromed engines because you can fit them tighter/better, but that would not translate to more when running as a stunt engine
What you will get is a tougher ,longer lasting sleeve/Piston, and about 1 ounce less weight, maybe a little better transition between 4/2 or cycling

Randy

[Andrew Tinsley]

Thanks Randy,
I think you have about answered all my queries on the ABC vs AAC theme! Thankks for your time and input, it is much appreciated.

Regards,

Andrew.

[Brett Buck]

OK, then allow me to expand my question to ask how ABN fits into the mix, and why those 'biggies' like OS and Enya that use it might use it instead of AAC?

  It's inexpensive, the process in forgiving, it breaks in almost immediately, and for stunt purposes, lasts longer than you need it to. There is no need for concern of wearing out an ABN liner in normal stunt use - Paul Walker and I each wore out *one* 40VF liner but that was after more flying that most people do in their entire lives. Any of these types, properly implemented, will outlast most of us, and are *far, far* better than something like a iron ring like an ST46. And are much more forgiving.

   The big difference between AAC and ABC or N is that the AAC (properly done) keeps its fit at all temps, the ABC is tight when cold and loosens up when hot. For stunt purposes that's pretty irrelevant but for other applications it matters.

   Brett

[Lauri Malila]

Hello again,
Randy still has stock ABC and his special AAC P/L liners for the OS 46VF (at least I think that was what he said?). This got me thinking about the two types of P/L setups. I know that you need a special piston alloy (hypereutectic aluminium / silicon alloy) to match the expansion of the brass cylinder liner.
The hypereutectic alloy seems to be expensive and not all that readily available, so why do most manufacturers stick to ABC (or ABN) setups? It would seem logical to use the AAC system where both piston and cylinder should have similar expansion coefficients...

 Andrew,

 You assumption about materialrequirements is wrong. AAC system does not work if both piston and liner are made of similar alloy, piston must have a smaller expansion coefficient.
 Classical rule is that there should (in AAC) be a difference of 10...12% in the Si contents of piston- and cylinder alloy.
Normally for the cylinder, the alloy with best thermal stability is chosen. Usually this means an eutectic mix of Si in alloy, which is something around 10..12%. And of course the chromium plating requirements must be considered too.
 So, for piston, the Si requirement is about 20%, but in modern engines with more power and "pinch" even more depending of running requirements. Even 30% Si consentration is used in some cases, like in our MB stunt engine.
High Si content is also good for friction coefficient against chromium.

Regards from Kiev, Lauri

[Andrew Tinsley]

Hello Lauri,
I don't think I was clear enough in my original statement, I did however say "similar" which I take to be not the same! I appreciated that the piston was going to have a somewhat higher concentration of silicon than the liner, but I wasn't too sure of the respective percentages ..... hence my use of "similar".
Apologies if I didn't make that too clear.

Regards,

Andrew.

[Lauri Malila]

 You don't want "similar" coefficients, the piston must have less. Both ABC and AAC need the piston alloy that you call "special", so materialwise the price difference comes from the price of brass (or some bronze) and aluminium.
 Chrome plating brass is really a lot easier that Aluminium because the pre-cleaning is more simple. With Aluminium, you must get rid of the oxide layer, basically this means that to prevent re-oxydation, the surface must remain wet all the time during the process. This tends to pollute the chromium bath and that's why many plating companies refuse to plate aluminium. At least that has been the explanation when some plating companies have refused the work.
 Of course it's possible to ease the work by using gradient layers of other metals, but I understand that especially in the racing engines of highest quality they prefer very thin chrome directly on aluminium. L

[Brian Hampton]

The Enya nickle is much  better than the type OS uses.

The Enya instruction sheet for the 61CX (more specifically for my 61CXLRS...thanks Randy ) says that the liner is brass, nickel-plated of silicon carbide composite which would appear to be Nikasil or similar as used in very high performance car engines. AFAIK this is a first for model engines. Personally I think the way of the future will be the so-called ceramic (Norvel's AAO) when the rest of the world learns how to do it.

[Dennis Moritz]

Orestes used an American engine?

[Steve Fitton]

Orestes used an American engine?

Orestes used a PA I thought until he defected to the Retro powered Yatsenko Shark.

[Dennis Moritz]

Orestes won the NATS with a Shark and a Retro. The Yatsenko Combos do all right in the Worlds. Probably the dominant choice. I believe the engines/planes arrive sorted out and ready to fly. Doubt the brothers could do that, if the Retros were of indifferent quality. All that said. I sure wish Randy would get a new supplier for castings. The big PAs my club members use, run real sweet.

[Brett Buck]

I believe the engines/planes arrive sorted out and ready to fly. Doubt the brothers could do that, if the Retros were of indifferent quality

    Well, they have personal control over each one, since they make it. The big problem I have seen is when Iron Curtain companies make OEM motors for others.

    Using the airplanes/engines as RTFs works, and the engines and airplanes work nicely, but it's a sort of pointless activity.

    Brett

[Dennis Moritz]

Aren't first quality combat engines made in the Ukraine and elsewhere in what was the USSR. The combat engines run at ridiculous rpm and are durable. 

[Bill Little]

Orestes won the NATS with a Shark and a Retro. The Yatsenko Combos do all right in the Worlds. Probably the dominant choice. I believe the engines/planes arrive sorted out and ready to fly. Doubt the brothers could do that, if the Retros were of indifferent quality. All that said. I sure wish Randy would get a new supplier for castings. The big PAs my club members use, run real sweet.

Before Orestes got his Sharks he used a Randy Smith designed airplane and a PA engine.  I don't remember exactly which one he used to win NATS Advanced.

BIG Bear
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