Snelson5254
New member
6/10/2021
The Nano Goblin is super cool, but the airframe isn't particularly efficient. Sure, its sleek, but it doesn't have a very high aspect ratio. I know its flight times are pretty darn good, but how much better would they be if it had a more efficient glider-like airframe, like the Volantix Ranger?
I want an sub-250g RC plane with extremely long flight times, at respectable speeds, 30 mph give or take. To maximize the weight allowance for a big battery, I'm going to need to use building techniques that are a bit more advanced than my usual FliteTest / Experimental Airlines style. I think my best bet is to use fiberglass over a foam fuselage and wing cores. I've done a lot of experimentation with different types of foam for hotwire cutting, and I've found that most insulation foams (XPS) are too dense to be of much use for such a small plane with tight performance criteria. Most XPS foams seem to have a density of ~0.03 g/cm^3. EPS is a bit lighter, with varying densities. The one's I've been able to measure range 0.008 g/cm^3 to 0.017 g/cm^3, depending on the source. It should be noted that denser foam is stronger.
My foam of choice for this project is EPS, with the 0.017 g/cm^3 density. I chose it based its ideal strength-to-weight ratio, Young's modulus, and it performed well in the impact simulations I ran. Haha, just kidding. My mom found a bunch of it for free by the side of the road.
I drew up this CAD model, and applied the densities of the foam and other components to the parts, so that I could get an estimate on the weight and CG.
My plan is to use a 6mm roll-wrapped carbon fiber tail boom (8 grams), hotwire-cut EPS for the wings, tail, and fuselage (30 grams) covered with 2-4 layers of 3/4 oz fiberglass (more or less layers depending on weight available). The motor nacelle will be 3D printed, and mounted on a balsa + fiberglass pylon.
My electronics setup should be pretty similar to the Nano goblin's:
Motor: T-Motor 1408 3750kv
Prop: Gemfan 3052 Tri-blade
ESC: 12a (or 6a to save a few grams, if I can find one at a good price)
Servos: FliteTest 5g (Flaperons + Elevator)
FPV: Spotter V2 all-in-one
The battery options are a little open-ended. I have some 2s 850mah LiPos that will work just fine. I used an online power system calculator called eCalc, and it said that they would last for 40 minutes to an hour if I fly conservatively. If I used an 18650 3000mah 2s1p li-ion pack, I could get more than 3X the capacity. That means I could get 3 hours of flight time! Unfortunately, I don't think that there will be enough weight allowance for an 18650 pack. Most likely, I'll use a 2s 1200mah LiPo pack, or a DIY 18500 2s1p li-ion pack, which would be 30-35 grams lighter than an 18650 pack. But I'll start off with the LiPos until I feel the need to fly for 2+ hours without landing.
These are uncharted waters for me in terms of building techniques, and I'll probably mess up and learn a lot in the process. My goal here is to document my process so that you can maybe learn something too, and mess up a bit less!
The Nano Goblin is super cool, but the airframe isn't particularly efficient. Sure, its sleek, but it doesn't have a very high aspect ratio. I know its flight times are pretty darn good, but how much better would they be if it had a more efficient glider-like airframe, like the Volantix Ranger?
I want an sub-250g RC plane with extremely long flight times, at respectable speeds, 30 mph give or take. To maximize the weight allowance for a big battery, I'm going to need to use building techniques that are a bit more advanced than my usual FliteTest / Experimental Airlines style. I think my best bet is to use fiberglass over a foam fuselage and wing cores. I've done a lot of experimentation with different types of foam for hotwire cutting, and I've found that most insulation foams (XPS) are too dense to be of much use for such a small plane with tight performance criteria. Most XPS foams seem to have a density of ~0.03 g/cm^3. EPS is a bit lighter, with varying densities. The one's I've been able to measure range 0.008 g/cm^3 to 0.017 g/cm^3, depending on the source. It should be noted that denser foam is stronger.
My foam of choice for this project is EPS, with the 0.017 g/cm^3 density. I chose it based its ideal strength-to-weight ratio, Young's modulus, and it performed well in the impact simulations I ran. Haha, just kidding. My mom found a bunch of it for free by the side of the road.
I drew up this CAD model, and applied the densities of the foam and other components to the parts, so that I could get an estimate on the weight and CG.
My plan is to use a 6mm roll-wrapped carbon fiber tail boom (8 grams), hotwire-cut EPS for the wings, tail, and fuselage (30 grams) covered with 2-4 layers of 3/4 oz fiberglass (more or less layers depending on weight available). The motor nacelle will be 3D printed, and mounted on a balsa + fiberglass pylon.
My electronics setup should be pretty similar to the Nano goblin's:
Motor: T-Motor 1408 3750kv
Prop: Gemfan 3052 Tri-blade
ESC: 12a (or 6a to save a few grams, if I can find one at a good price)
Servos: FliteTest 5g (Flaperons + Elevator)
FPV: Spotter V2 all-in-one
The battery options are a little open-ended. I have some 2s 850mah LiPos that will work just fine. I used an online power system calculator called eCalc, and it said that they would last for 40 minutes to an hour if I fly conservatively. If I used an 18650 3000mah 2s1p li-ion pack, I could get more than 3X the capacity. That means I could get 3 hours of flight time! Unfortunately, I don't think that there will be enough weight allowance for an 18650 pack. Most likely, I'll use a 2s 1200mah LiPo pack, or a DIY 18500 2s1p li-ion pack, which would be 30-35 grams lighter than an 18650 pack. But I'll start off with the LiPos until I feel the need to fly for 2+ hours without landing.
These are uncharted waters for me in terms of building techniques, and I'll probably mess up and learn a lot in the process. My goal here is to document my process so that you can maybe learn something too, and mess up a bit less!
