I've been doing a bit of research lately, exploring my options for a 2-4 place aircraft that would go on wheels, skis and (potentially) floats. I have Solidworks and have been using it now for several years, so I tend to run these types of things through it for study. So here's my question: What do you guys tend to use for lower longeron thickness for your PA-12/-12/-18 builds or re-builds?
I have the Super Cub drawing USB stick, and also plans for the Wag Aero Sport Trainer and Sportsman 2+2 aircraft, and have notice that the longeron tubes tend to be 3/4 x 0.035" in size. So is that thick enough for float use, or would you go with the 0.049" wall thickness on an E-AB aircraft?
For reference, Solidworks tells me this:
3/4 x 0.035":
# Per foot
Density = 0.284 pounds per cubic inch
Mass = 0.268 pounds
Volume = 0.943 cubic inches
Surface area = 54.067 square inches
# 18' longeron
Density = 0.284 pounds per cubic inch
Mass = 4.816 pounds
Volume = 16.982 cubic inches
Surface area = 970.532 square inches
3/4 x 0.049":
# Per foot
Density = 0.284 pounds per cubic inch
Mass = 0.367 pounds
Volume = 1.295 cubic inches
Surface area = 53.070 square inches
# 18' longeron
Density = 0.284 pounds per cubic inch
Mass = 6.610 pounds
Volume = 23.309 cubic inches
Surface area = 951.591 square inches
7/8 x 0.035":
# Per foot
Density = 0.284 pounds per cubic inch
Mass = 0.314 pounds
Volume = 1.108 cubic inches
Surface area = 63.519 square inches
# 18' longeron
Density = 0.284 pounds per cubic inch
Mass = 5.658 pounds
Volume = 19.950 cubic inches
Surface area = 1140.206 square inches
So it seems then that there's a ~40% increase in weight by going with the thicker-walled tubing, which translates to about 3.6 pounds more weight for two 18' lower longerons (for example). An alternative to that weight penalty would be to use short sections of inner sleeve reinforcement(s) only where needed.
I've looked around in the forum archives a bit, but didn't find a whole lot of information on this question, so I thought I'd just start a thread. Any input would be appreciated.
Thanks!
TB
EDIT: Added the 7/8 x 0.035" tubing mass data from Solidworks. Compared to the 3/4 x 0.035" tubing, this represents only a 17.4% increase in weight. So it's a definite improvement compared to going to a thicker-walled 3/4" tube.
I have the Super Cub drawing USB stick, and also plans for the Wag Aero Sport Trainer and Sportsman 2+2 aircraft, and have notice that the longeron tubes tend to be 3/4 x 0.035" in size. So is that thick enough for float use, or would you go with the 0.049" wall thickness on an E-AB aircraft?
For reference, Solidworks tells me this:
3/4 x 0.035":
# Per foot
Density = 0.284 pounds per cubic inch
Mass = 0.268 pounds
Volume = 0.943 cubic inches
Surface area = 54.067 square inches
# 18' longeron
Density = 0.284 pounds per cubic inch
Mass = 4.816 pounds
Volume = 16.982 cubic inches
Surface area = 970.532 square inches
3/4 x 0.049":
# Per foot
Density = 0.284 pounds per cubic inch
Mass = 0.367 pounds
Volume = 1.295 cubic inches
Surface area = 53.070 square inches
# 18' longeron
Density = 0.284 pounds per cubic inch
Mass = 6.610 pounds
Volume = 23.309 cubic inches
Surface area = 951.591 square inches
7/8 x 0.035":
# Per foot
Density = 0.284 pounds per cubic inch
Mass = 0.314 pounds
Volume = 1.108 cubic inches
Surface area = 63.519 square inches
# 18' longeron
Density = 0.284 pounds per cubic inch
Mass = 5.658 pounds
Volume = 19.950 cubic inches
Surface area = 1140.206 square inches
So it seems then that there's a ~40% increase in weight by going with the thicker-walled tubing, which translates to about 3.6 pounds more weight for two 18' lower longerons (for example). An alternative to that weight penalty would be to use short sections of inner sleeve reinforcement(s) only where needed.
I've looked around in the forum archives a bit, but didn't find a whole lot of information on this question, so I thought I'd just start a thread. Any input would be appreciated.
Thanks!
TB
EDIT: Added the 7/8 x 0.035" tubing mass data from Solidworks. Compared to the 3/4 x 0.035" tubing, this represents only a 17.4% increase in weight. So it's a definite improvement compared to going to a thicker-walled 3/4" tube.
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