Great Planes Extra 300S - 60 (64") - Too much power?
12-07-2004, 11:54 PM
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Great Planes Extra 300S - 60 (64") - Too much power?
Hi,
I am gearing up to begin the build on this plane. Looks like a fantastic kit. My question is one of power choice. How much power can this plane handle? In cruising RCU I see many have gone with a 120 four stroke.
I've done a little research. The full scale Extra power to weight ratio is around 0.2 hp per lb. The Extra I am building should come out 7.5-8.5 lb. So I figure I need a minimum of 1.6 hp to be scale. That's your base 91 four stroke / 60 2 stroke.
However, my goal is to be overpowered for access to 3D capabilities. So at +50% that would be a 2.5 hp engine. Therefore I am looking at a Saito 150-180 four stroke or a 1.08 - 1.50 2 stroke. Overpowering it would boil down to diligent throttle management.
So, what is the maximum power ever installed and tested in this kit?
I am gearing up to begin the build on this plane. Looks like a fantastic kit. My question is one of power choice. How much power can this plane handle? In cruising RCU I see many have gone with a 120 four stroke.
I've done a little research. The full scale Extra power to weight ratio is around 0.2 hp per lb. The Extra I am building should come out 7.5-8.5 lb. So I figure I need a minimum of 1.6 hp to be scale. That's your base 91 four stroke / 60 2 stroke.
However, my goal is to be overpowered for access to 3D capabilities. So at +50% that would be a 2.5 hp engine. Therefore I am looking at a Saito 150-180 four stroke or a 1.08 - 1.50 2 stroke. Overpowering it would boil down to diligent throttle management.
So, what is the maximum power ever installed and tested in this kit?
12-08-2004, 12:54 PM
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RE: Great Planes Extra 300S - 60 (64") - Too much power?
This is a 60 sized kit. The modern trend is to overpower it. At our feild, there are a few. I think one has a good 60, while the others are 90's or 120's: 4 bangers. I beleive a .90 4 banger to be ideal. My buddy's Extra with its OS 120 Surpass, he consideres just a bit too 'over the edge'.
12-08-2004, 04:40 PM
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RE: Great Planes Extra 300S - 60 (64") - Too much power?
The big "Canadian Buck" solution is the YS 1.10 which weights (27.5 oz) just a little more than an OS.91 4 stroke and puts out a lot more power. Despite the Extra's excellent engineering it is a little overweight for 3D work.
12-08-2004, 04:42 PM
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RE: Great Planes Extra 300S - 60 (64") - Too much power?
The big "Canadian Buck" solution is the YS 1.10 which weights (27.5 oz) 4-5 ounces less than your average 1.20 and puts out a more power. Despite the Extra's excellent engineering it is a little overweight for 3D work.
12-09-2004, 05:11 AM
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RE: Great Planes Extra 300S - 60 (64") - Too much power?
I have done two of these and put hundreds of flights on each plane. I happened to use a hot OS .91 fx 2 stroke and with proper prop it did the job in high style.
The engineering question is a good one and I agree that it is not the best choice in this size airplane ( the same is true of the full scale version) I now fly a widebody 60 and the difference is easy to see.
In my experience the HP rating is not a very reliable way to discuss the power side of the Thust to Weight relationship. The HP numbers do not have a standard measurement system that relates to the ability to move the plane. I like to just measure thrust in pounds and relate that to the weight of the plane in pounds. Hook the plane to a fixed pbject and use a good fish scale to read the force the motor is delivering at full speed........ The plane it is on is not important (except for the fus crossectional area) and this is the good way to preview changes in props or fuel. Once I knew that the .91 gave me 9.2 lbs of thrust with my setup of props and fuel, then I used the same scale to weigh the plane and it will give the thrust to weight ratio. For 3D, I need reserve power ( not very good at it yet) so I am looking for more than 1.5 to 1.[:-]
The engineering question is a good one and I agree that it is not the best choice in this size airplane ( the same is true of the full scale version) I now fly a widebody 60 and the difference is easy to see.
In my experience the HP rating is not a very reliable way to discuss the power side of the Thust to Weight relationship. The HP numbers do not have a standard measurement system that relates to the ability to move the plane. I like to just measure thrust in pounds and relate that to the weight of the plane in pounds. Hook the plane to a fixed pbject and use a good fish scale to read the force the motor is delivering at full speed........ The plane it is on is not important (except for the fus crossectional area) and this is the good way to preview changes in props or fuel. Once I knew that the .91 gave me 9.2 lbs of thrust with my setup of props and fuel, then I used the same scale to weigh the plane and it will give the thrust to weight ratio. For 3D, I need reserve power ( not very good at it yet) so I am looking for more than 1.5 to 1.[:-]
