Airplane drive setup with propCalc and perfCalc

“Fits in the cowl” is not a drive design. You need thrust for takeoff and climb at real AUW, efficient cruise, thermal headroom — and a sense of resulting performance. eCalc splits that: propCalc (motor/prop/battery) and perfCalc (performance).

Roles

Iterate the drive in propCalc → feed numbers into performance → verify CG. Demo vs membership: see current signup.

Mechanism (short)

Props make thrust from rpm and blade geometry; the motor supplies torque at a current set by Kv, voltage and prop load. Airplanes typically care about:

• Static / takeoff thrust vs AUW (many trainers sit roughly ~0.5–1:1 thrust/weight — class-dependent; always calculate)
• Continuous current in climb/cruise vs motor/ESC limits (Overheating, Marginal)
• Prop rpm within manufacturer limits; pitch matched to speed

perfCalc places the drive in flight context — document aero assumptions.

Rules of thumb

1. Lock AUW including pack.
2. Size prop for spinner, ground clearance and cowl.
3. Vary cells/motor/prop in propCalc until current and temperature are sane.
4. Feed results into perfCalc.
5. Confirm CG with cgCalc before maiden.
6. Never invent custom motor parameters.

Worked example: ~2 m e-glider / hotliner-ish

Assumptions:

• AUW 2.8 kg
• Pack 4S 4000 mAh
• Prop 14×8 folding (effective diameter)
• Motor ~ 500–600 Kv class on 4S (exact DB entry)
• Cooling Medium to Poor depending on fuselage — be honest

In propCalc check WOT current, efficiency, est. temperature, prop rpm. Keep long climbs out of the red; peaks only brief. Then estimate climb/speed in perfCalc with the same AUW.

Steps

propCalc

1. Open propCalc.
2. Enter battery, ESC, motor, prop D×pitch.
3. Set weight/environment and cooling.
4. Calculate — peak vs continuous, temperature, rpm.
5. Adjust prop or Kv/cells until advisories are acceptable.

perfCalc

1. Open perfCalc.
2. Transfer aircraft and drive inputs per the form fields (no invented deep links).
3. Read performance; if off-target, return to propCalc.

More practice: from drive numbers to expectations

After propCalc you should be able to write three sentences:

1. What current at full throttle and in a typical climb?
2. Is estimated motor temperature acceptable for the cooling grade you chose?
3. Does the prop fit diameter (ground/spinner) and rpm (manufacturer)?

Take those answers into perfCalc and to the field. If the model climbs far less than expected, verify AUW and prop first, then the motor — don’t instantly buy “the next stronger one”.

EDF and helicopter drives have their own eCalc tools in the bundle; copying prop logic 1:1 often misleads. For multicopters, stay in xcopterCalc — this article focuses on airplanes.

FAQ

Is propCalc enough alone?
For part selection often yes; for “how will it climb?” you need performance context plus honest aero inputs.

EDF?
Use the dedicated fan-oriented tools in the RC bundle — don’t mix pure prop logic blindly.

Hotliner with no vents?
Select very poor cooling and take temperature seriously.

Iterate like a checklist

Treat propCalc like a checklist you re-run after every hardware change: new pack, new prop brand, different altitude flying site. Small changes stack. When perfCalc and field feel disagree, trust measurement of AUW and amps first, then revisit assumptions — not marketing thrust graphs.