OS FS .26 and .40 Surpass Tech Info...

While browsing the 2002 Tower Hobby catalog, I spied a bit of tech trivia that some 4-stroke enthusiast might find interesting. We all know that the 4 strokes are RPM limited, torquey sloggers, right? The aircraft versions of the OS .26 and .40 Surpass are rated at .41 BHP @ 11k rpm and .65 BHP @ 12k rpm with "practical rpm" maximums of 12k for both. However, on p. 231, in the R/C car engine pages, the "C" versions are rated at .5 hp @ 17k and .9 hp @17.5k rpm respectively with upper rpm limits of 22k and 21k. If I were to own a .26 or .40 Surpass, I would carefully compare parts numbers of the cam, rocker arms, springs, valves, head, and carby to see if there are different part numbers that provide the extra HP and RPM range. They LOOK the same, externally. FWIW, Steve

Is this a warning against or a suggestion for? What you are doing is swapping torque for high rpm horsepower which will not be useful to us in our applications. Even a pipe engine isn't going to be winding that high (although we could use a shorter pipe then) and high rpm ducted fans aren't an efficient use of horsepower, either.

Leonard Neumann

"a bit of tech trivia that some 4-stroke enthusiast might find interesting." I thought that was clear enough. Somebody might find it useful or interesting, or it might dispell some myths. Steve

Hi steve,

This is interesting info. Clearly, higher revs and thus horsepower can be dialed into four stroke engines with alternative timing. You can get all the revs you want with 4 bangers...just go to Indy.

Len brings up an interesting proviso, however. One of the things that appeals to me about four strokes for stunt is the ability to prop them for approximately max revs in maneuvers. The beauty of doing so is that when the winds blow and try to speed up the ship in consecutive maneuvers the timing of the engine limits the revs to which it will go and thus helps to retard speed build-up.

right now my intention is to develop a two stroke to fly at lap times I desire near its max rev limit. At first blush this will require at a minimum playing with props and intake size. Might well require some investigation of head clearance and valve clearance and even timing eventually. If maneuver revs are, say, 11K and max revs due to timing are 11.5K acceleration due to winds will start to be combatted by the engine once it unloads to that rev limit.

If, on the other hand, the engine was capable of, say, 15K, the airplane would happily accelerate to an airspeed which allowed the engine to unload to that limit. This isn't desirable for stunt flying.

Another aspect, although not published, is the consideration of the torque curve. Ideally, like with a pipe, we'd like the unloaded level flight RPM slight over max torque. Thus, when loaded...as in maneuvers...torque would increase so as to maintain airspeed while doing so.

>Hi steve,
>
>This is interesting info. Clearly,
>higher revs and thus horsepower
>can be dialed into four
>stroke engines with alternative timing.
> You can get all
>the revs you want with
>4 bangers...just go to Indy.
>
>

True, but I don't think they use pushrods and rocker arms. F1 motors spin something like 18000 rpm, but they have pneumatic valve actuation, 4 valves per cylinder and mega-dollars behind it. The most amazing thing is the absurdly small size.

I'm still pretty impressed by the old unlimited-boost F1 motors. 1.5 liter 4-cylinder, 1200+ HP, turbo boost in the high 2 digits PSI. I heard one run on SpeedVision the other day, and it sounded like a funny car motor - barely ticking over compared to current F1/CART motors.

Scaling it down to model size helps a lot. I have never heard of valve train float as an issue.

How long do you suppose it will be before we end up with a cult of "magic secret cam numbers"?

>>Hi steve,
>>
>>This is interesting info. Clearly,
>>higher revs and thus horsepower
>>can be dialed into four
>>stroke engines with alternative timing.
>> You can get all
>>the revs you want with
>>4 bangers...just go to Indy.
>>
>>
>
> True, but I don't
>think they use pushrods and
>rocker arms. F1 motors spin
>something like 18000 rpm, but
>they have pneumatic valve actuation,
>4 valves per cylinder and
>mega-dollars behind it. The
>most amazing thing is the
>absurdly small size.
>
>
>
> Brett

No pushrods---overhead cams pretty much eliminated those. I've never heard of pneumatic valve actuators--I suppose they do.

There were recent stock block push-rod Indy engines i think but the latest competitive "normal" engine I believe was the Olds Aurora V8.

I predict that the 4 stroke setup that Ted describes above will be available shortly using a form of EFI--similar to the new OS system. I think they are simply monitoring revs and egt now and setting the mixture to suit. Sensor technology is there, its just a matter of the demand.

Automotive Powertrain Controllers are highly capable. Even a subset could provide a "dial-up" configuration that would compensate for density altitude, fuel mix, and prop loading.

Come to think of it, the controller could control the prop also.

Interesting winter projects!

Interesting, indeed. Given the particulars of the differences, one could make custom parts to get the run one wants-- an 8,000-RPM stunt engine that turns a 14" four-blader or a honkin' .60 for combat.

I kinda like diesels better...except for the smell. Leonard's SSW engines put out diesel-like torque without the smell and other negatives of diesels. I just thought the different specs for the OS car engines might give somebody some ideas for some R&D for some use, maybe not stunt. But certainly not Combat, Howard!
Ted's response has me confused..."right now my intention is to develop a to fly at lap times I desire near its max rev limit. At first blush this will require at a minimum playing with props and intake size. Might well require some investigation of head clearance and and even timing eventually. If maneuver revs are, say, 11K and max revs due to timing are 11.5K acceleration due to winds will start to be combatted by the engine once it unloads to that rev limit. " The <> are mine. Ted meant , I think.
I believe that 4 stroke model engines are in a relatively young state of development...lots more to do...but not much of that is within the ability of even the best equipped engine tuner. Cam grinding, rocker arm ratios, light pushrods, high flow porting, and oversized valves are going to be developed by the engine manufacturers over a period of time, as required by marketing departments, not modelers. Being able to mix parts from the manufacturer's parts bin is a place to start experimenting, which interests me more than competition at this point. Steve

Steve http://www.nwskyraiders.com/index.html

Steve,
About the only thing the airplane version and the car version share are the case and piston/liner assembly. They run about $70 more than the airplane version also. I have the .40 in a 4x4 truck that absolutely hauls hiney, and there is tons of torque, you will shred a stock tranny. If you were to try to put one of the car motors in an airplane you would probably have to replace the crankshaft as the car engines generally have a shorter shaft. Fuel economy is a big plus, especially with car fuel running $25 a gallon (not to mention the $8 glow plugs).
Kiiski

These motors are in no way alike except for the name on the side of the case. the insides of the highdollar highreving 4s are top of the line. The head has copper inserts and as far as I can tell multiangle valve jobs. The seat the rocker arm and the springs must all be top dollar high quality material to get that kind of revs without damage or float. The cam has to be ground at totally different timing and seperation point to get those rpms. Just try to push your airplane motor that high. It simply will not do it. Even on a little 6 inch prop. the valave train(include cam shaft) is not setup to run in this fashion. Just like cars the cam and the valve train(springs etc...) will only allow for a certain max rpm. I personally would love to get one of the high rev 4s. I just dont know where I am going to get a crank built and installed.

As far as the F1, probably the most dominating disply of technological advancement. These motors are non turbo charged now. They do spin 18000 rpms and range in 1000 hp. They have solinoid/pnuematic operated valves(read that no camshaft, no valve springs, no lifters, all computer operated adjustable on the fly). It is the engines small size that gives it the abilty to rev so hard and sustain it for 200 miles. By the way these guys drive their cars over 200 mph on 13" wheels. Money is never an issue with these teams. If you won the 100 million dollar lotto you would not have enough money to build and race an F1 car in ONE race. The technology from these machines slowly makes it way down to our cars and that is why a new altenator for your new chevy truck cost a whopping 350 bucks. The computer in your car makes it all cost alot more. I for one say give a my a 68 camaro with good ac and I am happy.

DMoon

I for one
>say give a my a
>68 camaro with good ac
>and I am happy.
>
>DMoon

Yep..Z28 cross ram dual quad intake.....