Air Cylinder Diameter Size?
07-11-2008, 01:47 PM
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Air Cylinder Diameter Size?
Gentlemen,
Is there any advantage or disadvantage to the diameter of the gear door air cylinders? I am not sure which size to use in my JL F18. I see them in 1/4", 5/16" and 7/16" diameters.
Any comments or suggestions would be appreciated.
Wayne
Is there any advantage or disadvantage to the diameter of the gear door air cylinders? I am not sure which size to use in my JL F18. I see them in 1/4", 5/16" and 7/16" diameters.
Any comments or suggestions would be appreciated.
Wayne
07-11-2008, 02:49 PM
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RE: Air Cylinder Diameter Size?
the larger the diameter, the more force it will have to move, and hold doors open and closed. the formula is force (lbs) = pressure (psi) x area of cylinder (sq. in.)
you can find the area by diameter x diameter x .7854, so for a 3/8" dia it would be .375 x .375 x .7854 =.110
now to use the formula, .110 (area) x 130 ( air psi) = 14.3 pounds of force the cylinder can devolop during extension. on retraction its a little less because you have to subtract the area of the rod from the area of the piston to get the net retract area.
you can see that going up in size or pressure changes things pretty fast. of course these are standard formulas that work for any cylinder, air or hydraulic.
geezze, guess what i do for a living....[
]
kirk
you can find the area by diameter x diameter x .7854, so for a 3/8" dia it would be .375 x .375 x .7854 =.110
now to use the formula, .110 (area) x 130 ( air psi) = 14.3 pounds of force the cylinder can devolop during extension. on retraction its a little less because you have to subtract the area of the rod from the area of the piston to get the net retract area.
you can see that going up in size or pressure changes things pretty fast. of course these are standard formulas that work for any cylinder, air or hydraulic.
geezze, guess what i do for a living....[
]kirk
07-11-2008, 05:28 PM
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RE: Air Cylinder Diameter Size?
Wayne,
The other thing of note to increasing the cylinder diameter is scale door speeds. As Kirk said the force available is directly proportional to the area of the cylinder. If you use a larger cylinder, it takes less air pressure to move the doors or gear with the same force. This can also really help with slowing the gear/door speeds down.
Having to use the maximum pressure available in the air system usually results in hung gear, doors or anything else that uses air pressure to do work, eventually. Since parts have a tendency to change tolerance as they age, get dirty, bent or whatever; a malfuntion is usually inevitable.
If you can get away with a larger cylinder size, it's always better to have more force than you need. You can use airline restictors or speed valves to slow down things without sacrificing the end force available. Also, if you have a slow leak and you're using larger cylinders, chances are they'll still be enough force available to do the job, so long as the air volume remains adequate.
Dan
The other thing of note to increasing the cylinder diameter is scale door speeds. As Kirk said the force available is directly proportional to the area of the cylinder. If you use a larger cylinder, it takes less air pressure to move the doors or gear with the same force. This can also really help with slowing the gear/door speeds down.
Having to use the maximum pressure available in the air system usually results in hung gear, doors or anything else that uses air pressure to do work, eventually. Since parts have a tendency to change tolerance as they age, get dirty, bent or whatever; a malfuntion is usually inevitable.
If you can get away with a larger cylinder size, it's always better to have more force than you need. You can use airline restictors or speed valves to slow down things without sacrificing the end force available. Also, if you have a slow leak and you're using larger cylinders, chances are they'll still be enough force available to do the job, so long as the air volume remains adequate.
Dan
07-13-2008, 01:20 PM
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RE: Air Cylinder Diameter Size?
Kirk, thanks for the in depth explanation on how they work. I have filed the formula in my RC accessories notes. It does go up fast as you increase the diameter of the cylinder.
Thanks Kirk for taking the time to explain this.
Dan, you bring up a very good point on the speed of the gear and doors. I am looking for the more “scale” look. I really don’t want the doors to snap open and the gear fly out. As far as the fit of a larger cylinder, I guess I will start with the 5/16” diameter and see how they work.
The pictures I have seen on RCU build threads, on the F18, the cylinders look like the 1/4” ones. I guess looks can be deceiving.
If there are any F18 owners out there could you please suggest what size cylinders work for you.
Kirk and Dan, thanks so much for your input. I really appreciate it.
Wayne
Thanks Kirk for taking the time to explain this.
Dan, you bring up a very good point on the speed of the gear and doors. I am looking for the more “scale” look. I really don’t want the doors to snap open and the gear fly out. As far as the fit of a larger cylinder, I guess I will start with the 5/16” diameter and see how they work.
The pictures I have seen on RCU build threads, on the F18, the cylinders look like the 1/4” ones. I guess looks can be deceiving.
If there are any F18 owners out there could you please suggest what size cylinders work for you.
Kirk and Dan, thanks so much for your input. I really appreciate it.
Wayne
