Power curves

Here some real power curves.

Wow! Look at the OS 60 FS (4 stroke).

Drops off like a stone at 12,000! I bet the Saito 72 is very close to that!

Now that is what I am takling about! Look at the spiked curve, as compared to the non piped 2 stroke.

The piped (I assumed non baffled) 2 strokes look like the edge of a cliff.

Thanks Igor.

I just note that it is old OS engine. New surpass looks more flat (little). I note also "out of sence" type YS120 foucycle - everything depens on valve construction / timing. The YS120 picture contains also newer Surpass as well as Enya curves.

Hi Igor,

When looking at these power curves, it seems they were taken with different props. I wonder wheter they have been leaning out the engine for max RPM every time they've put on a new prop. This would completely ruin the graph with respect to our needs. What we need is a graph where with different loads, the needle is NOT touched.
Perhaps for the 4 strokes this is less important, but still...

Paul

Yes, but what to do? Did you see measured rich engine? I remember I saw it somewhere sometimes, but my memory ... you know ... too much butter or what ... I really do not know where I saw it.

I hoped it was here on this forum, but I did not find it ...

Igor,

Sorry to be redundant to your dictionary <G>

Mike Billinton, years ago in Aeromodeller, made some noises about trying to find a valid way to test the middle-middle type of performance we use in stunt. (About the middle of the power curve, and beyond the torque peak, with variable loads from small to pretty large.) I don't recall if he ever came up with anything. I didn't catch Brett's SSW thread, either.

Of course we usually test in ways we can repeat pretty dependably. For engines, ultimate power at RPM on several different loads can give us points on the curve of maximum potential from the engine. Some in these threads may not have realized that. Any other way of testing is too variable, and has no standard to base upon.

As always, I enjoy your comments and have high regard for the way you have reached your conclusions.

Mike Billinton's test of the FP 40 did contain a graph for the engine in 4-stroke mode. From memory it peaked at something around 0.35bhp when run like this! Regret my mags are in chaos at the moment, and will not be sorted for some time.
Something I drew up once but never built was a 35 size stunter for a Cox TD15. It seemed to me that the traditional 35 4-stroking produced less power than the Cox was capable of, so it should have been adequately powered.

>Mike Billinton's test of the FP 40 did contain a graph for
>the engine in 4-stroke mode. From memory it peaked at
>something around 0.35bhp when run like this! Regret my mags
>are in chaos at the moment, and will not be sorted for some
>time.

I believe it was a bit higher. Even the Fox 35 puts out more than that, as I recall.

>Something I drew up once but never built was a 35 size
>stunter for a Cox TD15. It seemed to me that the traditional
>35 4-stroking produced less power than the Cox was capable
>of, so it should have been adequately powered.

It is controlled power that we are after. Any engine can be made to scream, which is just exactly what you have to do with the Cox TD 15 to produce power. So if you are going to scream the engine, why don't you just scream the 35 and have more power?

Hi Leonard. Conceerning my mention of an old (unfulfilled) idea to try e.g. a TD15 in a 35 size stunter:-
We are aware of how a marginally powered f/f model can frequently be improved by fitting a larger prop, albeit that the engine will run lower down the power curve. Similarly a stunter can sometimes be omproved by fitting a larger prop. A typical prop on a TD15 combat model at the time would have been a 7 x 6. I agree this would be unsuitable on a 35 size stinter. For the controlled power you mention my thought was to use a prop more appropriate to the model, something like a 9 x 4 or even a 10 x 3 or 10 x 2.5. Certainly rather exotic props at the time, more easily achievable today.
Concerning my comment on the FP40 power in the Billinto test, clubmate Dr. John Dixon, whose mags are better sorted than mine at the moment, has kindly looked up the info for me.
Conventional test :- Open exhaust unsilenced 0.59bhp@11k rpm. Muffled 0.55bhp@10k rpm. 4 stroking muffled :[email protected] rpm.
John made the point that this last test must have been virtually as rich as possible, unlikely to be a lean 4-stroke such as we might use. I guess my guess of 0.35 might not be too far off.
I still think this would make a viable project, but so many others to do first. Best wishes,

Interesting, got one for an LA 40?

Giffy

Why does the fuel consumption drop with increasing RPM towards the end of the curve? They do not seem to be brake specific fuel consumption, but direct fuel consumption in liters/hour. Not what I would have expected. Or are the engines running really lean at this point?

Suman

>>>Why does the fuel consumption drop with increasing RPM towards the end of the curve? <<<
Good point, I am also surprised. It is obvious that if you make less power (even past the power peak) the consumption should be lower, but it does not answer why consumption goes down even before power peak. I think the magic could be in fact that optimal power at high rpm is possible only with little lean quickly burning mixture, while high torque at lower rpm is easy to get with rich fuel which may be does not burn very well (there is more time at lower rpm), but safely uses all available oxygen (means richer than stechiometric).

That is only my feeling, but I would really say that it is not “too lean at high rpm” – it is rather “too rich at low rpm”.

Possibly because the engine is so underloaded that it can make that RPM using little fuel. The ports are probably opening and closing so fast that the fuel/air mixture has no time to overcome inertia, and less of it gets sucked into the engine.

Sorry it is all in German language.

Verbrauch – consumption
Larm – noise
leistung – power
drehmoment – torque
schalldampfer – silencer
drehzall – rpm

Len, do you know where?

>>It is controlled power that we are after.
>>Any engine can be made to scream, which
>>is just exactly what you have to do with
>>the Cox TD 15 to produce power.
>>So if you are going to scream the engine,
>>why don't you just scream the 35 and have
>>more power?

>>Leonard Neumann

>Because then you'd need a .46 size plane..

I missed the point here, Iskandar. I wasn't advocating screaming the .35, by the way, but he was trying to compare the power of a screaming 15 to a stunt run 35. All of the Cox .09 and .015 stunters that I have seen (which isn't many) were all way underpowered and not very well controlled. They were outclassed by the .35/.40 size stunters that they were competing against. But if you do run the engine in a high rpm range, all you need do is use a lower pitch prop to maintain good stunt speed.

And for those who think you are overpowering, I keep reminding people we run a 35FP with a 12.5 inch 2-blade prop on a 570 square inch plane. We used an overweight 570 square inch plane as a test bed for the .53 with a 13 inch 3-blade prop. Same size lines (about 66 feet) and same lap speeds. Great combination, however. Although we were just testing the engine, we kind of proved to ourselves that a little more engine (and prop) on even the smaller size planes isn't all that bad. I have been considering building a plane (purposely) around that size for that engine. It hauls freight in a very controlled manner.

>Absolutely facinating. But I was hoping for some curves out
>of Playboy.

Ty, thous shalt not. For then the moderator would have to throw another curve by pressing the magic delete button.

Oh, and this reminds me of a time I was in a supermarket perusing through a magazine when one of my parishioners walked by. She jokingly said, "I hope you aren't looking at models" (implying the "girlie" type. I showed her that I was, indeed, looking at models...airplane models.

>That is true, but why is the consumption lower also at peak
>of delivered power??? It is not unloaded, it delivers
>maximal power, so also consumptin in liter/hour should be
>high. ... ???

Not if the engine leans out. We tend to run our engines rich, so they consume (throw out the exhaust) more fuel. If you lean them out, they can develop more power AND burn less fuel (less mixture per stroke). I had a Fox 40 on a Magician once that I ran at nice liesurely 5.2 second laps or thereabouts for about 6 minutes on a tank ful. I was using the stock Fox muffler (BAD design) on muffler pressure. One day the Fox muffler blew apart shortly after take-off. The engine went screaming lean. I can attest to the fact that it was developing more power--much quicker laps--and the thing managed to continue to run that way for 15 minutes! I think we can safely say it was burning less fuel. An autopsy later on also revealed that it has fried the piston and rod.

Sometimes we get a little of this effect for the last lap or two of the pattern. I know typically on our FP wet up, we would be running 5.3 second laps until about the last two laps where the "bubble" would break on the uniflow and then the plane would speed up to about 4.5 second laps for about 2 laps and then shut off. It was a good indicator to let you know you were about done, and also gave you good flying speed to enable you to pick your spot for landing.

I understand Len, but those chards are not measured "rich", they are measured "optimal", so the only answer can be that it _needs_ to be rich to deliver high power at low RPM.

>As the power increases, I would like to see the fuel
>consumption increase, so that more fuel and oil are pumped
>through the motor. This has simply never been the case. As
>far as all of my practical trials are concerned, it has
>always been the opposite. The higher the RPM the less fuel
>is consumed, even at richer settings.

Are you saying you can't set it richer, or doesn't it want to run at the higher rpm with it set rich? Again, I repeat that I have little knowledge about the 4-cycle engines.

>Are you saying you can't set it richer, or doesn't it want
>to run at the higher rpm with it set rich?

Both... it simply does not work well. It sputters and the power jumps up and down.

One interesting observation. Increasing the oil content does not appear to increase fuel consumption either, as would typically be seen on a two stroke. The fuel consumption just appears to stay the same, and now the engine is running leaner with less power. This may explain why 4 stroke fuels generally have lower oil content. The drop in RPM was substantial.

It also points to the fact that the oil content is less of a factor in removing the heat from the engine. Any increase in oil for cooling appears to be almost nullified by the increase in heat generated by the leaner condition resulting from the volume of the oil.

I am chasing my tail again. I am starting to think "you can't get there from here". I am getting pretty picky I guess... need to be to beat these guys, huh?