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u/celkemdenis

r/RCPlanes r/CFD
▲ 3 r/CFD

Why is ANSYS Fluent lift 3x SMALLER than XFLR5? (Same conditions, massive discrepancy)

Hey everyone, I’m running into a massive roadblock with my glider design and could really use a sanity check.

I’ve been designing a glider in XFLR5 and was honestly pretty happy with the numbers. Today, I decided it was time to do a "proper" 3D CFD analysis using ANSYS Fluent. After about 4 hours of intense struggling (this is my first time doing any CFD), the simulation finally converged.

However, under the exact same operating conditions (same velocity, density, and angle of attack), my lift force in Newtons is literally three times smaller in ANSYS than it is in XFLR5.

Is it possible that I screwed something up during the setup or are results like these expectable?

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u/celkemdenis — 8 hours ago
▲ 2 r/RCPlanes

Sanity Check: 3.2m Solar Glider Design (XFLR5 vs. eCalc Numbers) — Is perpetual flight realistic here?

Hey everyone,

I am currently designing a 3.2m solar-powered glider with the ultimate goal of achieving perpetual (day/night) flight. I’ve done some preliminary aero and powertrain modeling, but I want a quick sanity check from the community to see if my numbers are realistic or way too optimistic.

Aircraft & Solar Specs:

  • Wingspan: 3.2 meters
  • Wing Area: 0.71m2
  • Solar Array: 28 cells (each 12.5x12.5cm, aiming for premium Maxeon-style cells flat on the wing). Total active area approx 0.44m2.
  • Battery: 270Wh 3S Li-ion pack.

Performance Estimates:

  • Aerodynamic Power (XFLR5): Estimates 12W required for sustained level cruise.
  • Electrical Power Draw (eCalc): Estimates the motor will draw around 20W from the battery during cruise (accounting for ESC, motor, and prop inefficiencies, roughly a 58.5% total powertrain efficiency).

The Strategy:

At a continuous 20W draw, the 270Wh battery should theoretically give me about 13.5 hours of endurance, which should safely get the glider through a summer night. Once the sun comes up, the solar array needs to sustain flight and fully recharge the battery back to 270Wh for the next night.

My Questions for you:

  1. Do these XFLR5 12W and eCalc 20W numbers look achievable for a 3.2m airframe, or am I overlooking real-world losses?
  2. For those who have built solar planes, what kind of real-world degradation should I expect on the solar cells due to wing curvature and heat?

Thanks in advance for any feedback or advice!

u/celkemdenis — 1 day ago