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Author Topic: 4 Stroke and Climate Change  (Read 280 times)

Offline Martin Quartim

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4 Stroke and Climate Change
« on: March 15, 2021, 06:59:21 PM »

I have used an OS 70 Ultimate 4S with a fixed sized venturi for the whole year at contests in 2008, 2009, and 2011.   I have flown at Brodaks in summer at 1000ft,  and in Brazil in cities from 2300ft msl to 4600msl.  My Os 70 Ultimate never changed its performance and fuel consumption with varying Density Altitude. Always used 90ml and got 6:30 min flights. As far as I can tell same laps speed.

I am puzzled why that engine was not sensitive even to drastic changes in density altitude.

Have you guys also experience the same thing with your 4S engines?

Does anyone know why 4S engines performance do not change with density altitude?

Martin
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Online Dan McEntee

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Re: 4 Stroke and Climate Change
« Reply #1 on: March 15, 2021, 08:17:38 PM »
   You might not get too many answers concerning an OS .70. My main experience is with a Saito .56, but last summer inherited a Hawker Typhoon with a 65" wingspan and powered by an OS .7 FS. It has an R/C carb that I have closed the throttle down to about half open in order to get the patter in on a 4.5 ounce tank on muffler pressure. After experimentation using what I have learned with the Saito, I finally settled on 15" Cool Power for fuel and can shout tank it down to 4 ounces I think for a 7 minute run swinging a 14-6 prop at about 7800 RPM . I plan to try a 7 inch pitch as soon as weather allows. If I converted correctly, you are using about 3 ounces, so your venturi must be quite small. My UEWAG ( Uneducated Wild Ass Guess!) is that we have to run the intake on these beats so small, that the air part of the mixture is small enough that the density doesn't affect it and the nitro content makes up for any difference. I couldn't get the pattern in on YS-20/20, so that is why I dropped down to 15% If you are up there in nitro content also, that may help explain it.
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Offline Martin Quartim

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Re: 4 Stroke and Climate Change
« Reply #2 on: March 18, 2021, 10:39:49 PM »
   You might not get too many answers concerning an OS .70. My main experience is with a Saito .56, but last summer inherited a Hawker Typhoon with a 65" wingspan and powered by an OS .7 FS. It has an R/C carb that I have closed the throttle down to about half open in order to get the patter in on a 4.5 ounce tank on muffler pressure. After experimentation using what I have learned with the Saito, I finally settled on 15" Cool Power for fuel and can shout tank it down to 4 ounces I think for a 7 minute run swinging a 14-6 prop at about 7800 RPM . I plan to try a 7 inch pitch as soon as weather allows. If I converted correctly, you are using about 3 ounces, so your venturi must be quite small. My UEWAG ( Uneducated Wild Ass Guess!) is that we have to run the intake on these beats so small, that the air part of the mixture is small enough that the density doesn't affect it and the nitro content makes up for any difference. I couldn't get the pattern in on YS-20/20, so that is why I dropped down to 15% If you are up there in nitro content also, that may help explain it.
   Type at you later,
   Dan McEntee

Hi Dan,

You have a very good point.  My venturi is .285 same as I used on my Saito 72. The OS 72 Ultimate seems to have a higher compression ratio, thus more efficient with fuel.


May point is if the guys using 4 Stroke of whatever brand and model had the same experience about Density Alt.

Martin


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Online Dan McEntee

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Re: 4 Stroke and Climate Change
« Reply #3 on: March 19, 2021, 08:11:44 AM »
   I don't get to fly mine at different altitudes very often, so don't really know for sure. I have flown mine in a lot of different temperature ranges and have found that I need to make allowances for that with the screw that runs into the venturi. About 1 turn in when the weather gets cold and bac out the same when it warms up, but I haven't had to do that a lot either. If I had really experimented a lot and kept some notes, I might have found that if I left it in the middle of that range, it may be OK to leave it there year round. That model is due for a recover and freshening up and I may get back to that. You can probably get to a point where the fuel required amount is so low as it flows through the venturi, the ambient air just doesn't matter as long as there is enough for combustion.
   Type at you later,
   Dan McEntee
AMA 28784
EAA  1038824
AMA 480405 (American Motorcyclist Association)


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