I love my 2-Strokes but I start feeling like the designers need to do a little "catching up" when I see Saito .82 and 100's in the same weight class as 2-Strokes half their displacement. Brodak has a non throttle .40 at 6.7 ounces the listing says it comes with a muffler but doesn't specify if it is included in the 6.7 ounces. Saito's advantage in weight is due in large part to their AAC design also. Why don't we see AAC 2-Strokes of 1.25 displacement in the 20 ounce range? O.S. is among the lightest that I know of with the 1.20 AX just over 31 ounces. That makes it heavier than a Saito 1.80.

Many high performance 2 cycle engine are of the ringless AAC construction, Enya, Nelson and Jett come to mind. In the high performance class 2 cycle the benefit of the AAC is in dimensional stability at heat (power).

The proper measure is power to weight not displacement to weight. As for power to weight the 2 cycle has nothing to fear from the 4 cycle.
The 120AX is 3.1 hp @ 21 oz and the OS200 is 3 hp @ 31 oz with muffler 35 oz. Not that I'd rely on any data from OS to make my point or purchase.

You do make a good point that engine size restriction for classes where one wishes to limit engine power should be called out by mass not displacement. Duke Fox proposed this as a means to control the HP race we saw in many competition classes like pattern. But the AMA did not like the idea of a low RPM 15cc engine that only weighed 10 oz. Think of all the fields that engine could have saved being low rpm low power yet rather high torque if made correctly.

That is a interesting observation. yeah the 2 stroke engine have grown huge and became quite powerful compared to their older smaller cousins.
it used to be that a Saito 80 competed against the .60 2 stroke engines. Now the large 52 and 55 two stroke engines are almost as powerful as the .60 engines. So actually the  Saito .82 is now competing against large 46, 50, 52, and 55 engines. You have to go with a .90 to 1.25 four stroke to compete with the more powerful .61 size two stroke engines.

But now in recent years, in a effort to reduce the noise, the two stroke engines are being tuned to turn slower RPMs as a slower larger propeller makes less noise. Plus they are using much larger mufflers than the engines did in the past. All to reduce the noise levels being outputted by the two stroke engines. So the two strokes are more or less becoming more like four stroke engines. But still a 2 stroke is putting out between 40% to 60% more power than a same size four stroke engine can. Which means you still have to increase the four stroke engine displacement to match the smaller two stroke engine.

I have been impressed with how Saito has managed to reduce the weight and size of their newer four stroke engines. I have a couple of Saito FA-40a engines, and they weigh slightly less than the Thunder Tiger Pro 36 engines do. But a lot of weight is arguably in the huge mufflers that the two stroke engines use nowadays to get their extra power with. But the TT Pro 36 still outpowers the nifty little Saito 40's by quite a bit though.

Since r.p.m. is a large part of the horsepower equation does Konrad's horsepower to weight comparison also follow the same scale when you compare thrust to weight ratio of a 2-stroke vs. 4-stroke? Is AAC a much more expensive process than say ABC?


I have to admit that the weight idea has been rolling around in my head since I started a post that had people commenting about the low weight of their older loop ported .60's etc. I then thought if the same engines had been produced without the brass or steel liners they would really be light.

Just a stray thought, here, if I may...

Earlier glow engines were lighter, yes, but at the expense of compromising some things: durability, smooth (less vibrating) operation, and overall sturdiness.

More recent engines are sturdier - ruggedly structured to withstand the power protential of the schneurle porting layout. They are better balanced for smoother running largely because the crankweb has been beefed up considerably from earlier practice. That acts as a vibration-damping flywheel.

And, as a by-product of the potentially greater power available with advanced metallurgy and the schneurle porting approach, they are built strong enough to meet those demands.

A more frail engine will flex during operation, and that compromises the metallurgy and machining possible today. The precisely tapered fit cut into most CNC produced engines is irrelevant if the case flexes under running loads.

I don't know the weight difference between ABC, ABN and ABC pieces, but those deal only with the sleeve. The piston is of similar metallurgy for all three, and it is the piston which moves, not the sleeve. A crankcase solid enough to prevent unwanted distortions from running heats and loads IS more substantial than the Fox 35s, K&B 1950's green-heads, and other much earlier engines.

That we have 4-cycle engines of comparable weight and power output is a blessing from careful and effective design, IMHO, not a condemnation of any other engines...

I've seen and flown both approaches. Either way still works, if allowance is made for the intentions of the designers.

This is just an assumption on my part but I think RC engines have gained a lot of weight simply to make them strong enough to survive crashes. Similar sized CL engines are very much lighter because all up weight of the model is important. The Brodak 40 mentioned in the OP was designed as a CL stunt engine and its all up weight with muffler (of my engine) is 8.2 ounces. I have an ABC rear exhaust CL stunt 60 that weighs about 13.5 ounces with muffler. There's also a lightweight version of that engine too and a RE 81 that weighs 13 ounces without muffler. Jett has a rear exhaust 60 that weighs 13 ounces (without muffler) so it can be done.

That is true for almost all manufacturers statements if you are looking for a flyable set up.

Flyable (whatever that is) or not, OS's ads are VERY optimistic! I have only measure two OS engines that meet their claimed power output. One was the OS 1.08 and the other I can't recall. I choose to focus on the OS line 2 cycle vs 4 cycle just to keep the variables of how the units were derived under a little more control.

Power is power, now if you are talking about torque and the RPM band it is generated in, then we have a more realistic representation of the engine's application. But unfortunately this doesn't help the "AD HYPE" as this a lower number than the calculated value OS prints. True the issue is not just OS's but rather ours ,the buying public that believes AD HYPE!

Edit: to change power to RPM as in "RPM band"

The newer two-stroke designs are generally lighter than the first generation schnurle engines of the 70s. They have basically taken durable high RPM designs and traded that durabillity for displacement and the torque at lower RPMs. The newest/lightest designs like Webras P5 series are too expensive for the average flyer. All the cheap engines are just OS clones that are not exceptionally light weight.

Having the lightest weight engine is not always best, a engine with some mass also tends to dampen vibration better, all else being equal of course. I certainly would not give up my rossi engines and they are as beefy as they come.

The brodak control line engine you refer to is a special purpose engine, it's much less powerful than a similar BB R/C .40 and turns about 5000 fewer rpms than we are used to.

What makes an engine a clone? Looking at the OS of the 70's they actually look design wise very much like a McCoy. Even the OS of today still looks like a McCoy just that the materials are worse.

That was Duke's point. That at some point the trade off for thermal stability and mechanical reliability would limit the power output of the engine. A displacement limit really doesn't limit anything for example an OS LA 40 might put out 1.1hp on 15% nitro yet a Nelson FAI 40 might put out 3+ hp on zero nitro fuel both engines are of 6.5 cc displacement.

Just a point, the Fox 25BB puts out more power than the old Fox 35 stunt on close to the same props. This is "flyable" power in a smaller engine displacement!

Now the Rossi and Webra are real performance engines. I agree all things being equal I wouldn't give up a Rossi for what passes as a high performance engine at most distributors today. I will admit that the Nelson was a competition engine and therefor way outside the scope of most pilots. Today's OS AX series is having thermal stability issues with the collapse of the cylinder mounting flange as the engine gets near its performance potential (hot). This is because there is little thermal mass and the case, head and cylinder configuration is not optimized for such a light weight engine.

You use the mass of the engine to dampen vibration? Why not balance the engine correctly to begin with for its anticipated rpm? The mass might be better placed elsewhere for mechanical or thermal integrity

All the best,
Konrad

The Webra P-5 that was mentioned above is a compact, "dense" engine in that it is physically small yet has a lot of meat in it. It is designed to turn props from 14x12 to 16x8 at sub 8,000 to 8,500 rpm. It is built strong and in my mind has the extra mass to handle the heat. It is a very smooth running engine and has a very cool purr when doing its best work.

http://www.youtube.com/watch?v=lBp5ag6SJH4

Hobbsy,
i recall you had some photos of that P5 that show how massive looking the engine is. The apparent size gives the case a lot of geometric stability for its given mass.

All the best,
Konrad

Why remove the comment offering to help you understand the mass issue? There was nothing offensive in the comment just a helpful offer.

Here is a shot of the wrong side of it to show the compactness. A view from the other side shows it better. I sold the engine so can't show it along side the old .91

I see nobody has addressed these questions. So at flight speed yes the thrust (dynamic thrust) issue is much the same as the HP issue. There is no value in a static thrust number for our airplanes. Every lift equation I know of use velocity. So if velocity is zero (static) the ship won't fly. You need to keep your eye on the concept of pitch speed. As to the smart a****, of which I have been accused, yes static thrust can play a part in the acceleration to flying speed. Not sure I see your point about 2 cycles vs 4 cycles as far as thrust. Thrust is a prop issue not an engine issue.

Yes, AAC is a little more expensive to produce as there is a need for a metal strike (usually zinc) to protect the aluminum from the chromic acid. Now both ABC and AAC are much more expensive than ABN/ABL as they need a mask and second machining operation (grinding the chrome to size). Electroless nickel is plated to size. No need to machine the plated nickel.

I see nobody has addressed these questions. So at flight speed yes the thrust (dynamic thrust) issue is much the same as the HP issue. There is no value in a static trust number for our airplanes. Every lift equation I know of use velocity. So if velocity is zero (static) the ship won't fly. You need to keep your eye on the concept of pitch speed.
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Good to see there is at least one other person who realizes how unimportant static thrust is. If static thrust was so important we'd all be flying with helicopter rotors bolted to the nose of our aircraft. Dynamic thrust potential depends on power and efficiency of the propellor system.

A sport (high performance rossi like) engine is expected to be smooth running at all rpm, and single cylinder engines like this are inherently unbalanced, we can balance the engine rotation at 12 and 6 oclock but it will be out at 3 and 9, I am probably just repeating stuff you already know here. The extra mass of the case will help dampen and mask the inbalance.

OTH I have a Enya VT-240 and it is a V-twin in a 80 degree layout, this configuration can be made very smooth because one cylinder will balance the other at the 3 and 9 oclock position, neat. I have thought of selling this engine, but it is one of the best engineered glow engines out there, so cool, I just can't bring my self to part with it.

To answer my own question before I post it, I think cost is the reason.
The 2011 Ford Shelby GT500 engine is over 100 pounds lighter than the 2010 GT500 engine. Why? Ford used a process where the steel liner is actually heated and sprayed onto the cylinder walls on the 2011. The 2010 had steel sleeves. So why not do this for a model engine?

David

The only time there is no velocity is when the engine isn't running. You are wrong when you say static conditions produce zero velocity. Equations use the velocity of the prop (rpm) for one measurement (static), and a flying (moving) propellor uses two types of velocities (v and V).

There is no real value in static thrust, rpm, power, etc.

That is a neat trick, I wonder how they spray in a steel liner?

My motorcycles (honda & suzuki) have some sort of liner applied directly to the aluminum cylinder and unless they are scored or chipped will last almost forever.

Last I looked HVOF and/or Praxair "D" gun Metal/Plasma spray is limited to bores that are 2 inches or larger. I know nothing of the process Ford uses.

Sorry HVOF = High Velocity Oxy-Flame
http://www.praxair.com/praxair.nsf/d63afe71c771b0d785256519006c5ea1/2471692e3b79f13485256ef600676b10/$FILE/HVOF%20HardFacts.pdf

If the wing is not moving there is no lift. Static thrust means no change, no motion as in the airframe. So whatever value you get for thrust with the airframe static (at zero velocity) has no bearing at flight speed.

I did not say there was no work being done at zero velocity. The prop is moving a lot of air mass even even if the ship is standing still. Again thrust in our toy airplanes is a product of the prop, not wether the engine is a 2 cycle or 4 cycle

Yep. My little FAI F3D 6.5cc Pylon engine probably couldn't pull the wrinkle out of an oil soaked rag statically, yet could drag my over weight racers at over 300 KPH. Now that was real "flyable" power!

All the best,
konrad