Choosing the Right Trial Weight for Rotor Balancing

Every single-plane or two-plane balancing job starts the same way: pick a trial weight, bolt it on, fly, and see what changes. Pick wrong, and you pay for it — too small a trial weight and the change in vibration is too subtle to read accurately; too large and you risk overcorrecting or exceeding structural limits on the mounting point.

It's a Calculation, Not a Rule of Thumb

There's a real relationship behind the right trial weight, based on the rotor's RPM, radius (where the weight will be mounted), and your estimated existing unbalance. A trial weight is meant to produce a vibration change that's clearly distinguishable from measurement noise without swinging the rotor into a wildly different vibration state — which means the right size scales with how fast the rotor spins and how far out from center you're mounting it, not a flat number that works for every job.

What Happens When You Guess Wrong

• Too small: the vibration reading barely moves between the original and trial run, so the sensitivity you calculate from it is dominated by measurement noise rather than the actual trial weight's effect — and every correction downstream of that sensitivity inherits the error.
• Too large: you risk a correction that overshoots, or in the worst case, exceeding a fastener or mounting point's rated load for that trial run.
• Either way: you've spent a flight cycle collecting a data point you can't trust, and you're doing the whole trial run again.

Calculate It Before You Fly

BalancePro's Trial Weight Calculator takes your rotor's RPM, radius, and estimated unbalance and returns a recommended trial weight in seconds — free, no account required. It feeds directly into BalancePro's single-plane and two-plane balancing calculators, so your whole workflow — trial weight, correction, hole-by-hole weight distribution — runs in one place, in your browser.

BalancePro is an experimental, unofficial calculation aid provided for reference purposes only. It has not been certified, approved, or endorsed by any aircraft, engine, or component manufacturer, nor by any civil aviation authority, and is not a substitute for approved maintenance data or manufacturer-published sensitivities. Independently verify all results before use.