The Cracked Prop We Missed: How to Inspect and Replace Props Before Your Next Flight

Quick Answer

After every crash, check your propellers for hairline cracks at the hub, chipped tips, and bent blades. A cracked prop causes violent vibration at 20,000 RPM and can destroy motor bearings in a single flight. Replace any prop that shows damage. We keep a pack of ABS 5x3 spares on the bench permanently.

The 30-Second Inspection We Run After Every Flight

We have a workshop rule: no prop flies twice without a check. Spin each prop by hand, feel for wobble, then flex each blade gently at the root. Props hit the ground, branches, and fence posts on every crash. They hide damage better than any other component.

The most dangerous flaw is a hairline crack where the blade meets the hub centre. Invisible from arm's length, it opens when you flex the blade. That crack propagates under load in flight. When it fails, the imbalance rips motors from their mounts. We have pulled FCs off frames with sheared standoffs because someone skipped the prop check.

Check three zones on every blade: the hub root for cracks, the leading edge for nicks deeper than 1mm, and the tip for bends. If any blade fails, replace the whole prop. Do not save "the good blade" from a damaged set.

CW vs CCW: The Direction Error That Throws Props Mid-Flight

The most common mistake we see (from experienced builders, not just beginners) is fitting a prop with the wrong rotation. Every FPV quad uses two CW and two CCW props. The nut thread direction matches the rotation so the prop self-tightens. Fit a CW prop where CCW belongs and it spins off the motor at throttle.

Here is the reliable method: hold the prop with the lettering facing up. If the blades curve clockwise (like a clockwise staircase), it is CW. The threading confirms it: CW props use standard right-hand threads, CCW use left-hand threads. When in doubt, check the stamping. Most manufacturers mark CW, CCW, or R (reverse). Our ABS 5x3 packs come in labelled bags for each direction.

What We Stock: The Workshop Prop Rack

For 5-inch freestyle we run bi-blade ABS. Cheap, they survive most low-speed impacts, and produce clean thrust. For 7-inch long-range rigs we use tri-blade props like the 7x4.5 tri-blade for extra grip at lower RPM. See our 5-inch props and the full propellers range.

The mistake most pilots make: buying one set of carbon fibre props and nothing else. Carbon performs well but shatters on impact instead of flexing. For learning and everyday freestyle, plastic survives more crashes at a fraction of the price. Run carbon on race day.

The Post-Crash Prop Checklist

1. Spin each motor by hand. Listen for scraping. Feel for resistance.
2. Remove each prop. Inspect the hub from underneath for cracks radiating from the centre hole.
3. Flex each blade 10 to 15 degrees. Watch the root for separation.
4. Check the leading edge for nicks deeper than 1mm.
5. Check tips for bends. A bent tip changes effective pitch and causes vibration.
6. Bin the whole prop if any blade shows damage.
7. Replace with a fresh set from the same manufacturer and pitch. Mixing types creates asymmetric thrust.

This takes under two minutes. For a deeper vibration diagnostic, see our jello fix checklist.

FAQ

Q: How many flights should a set of FPV props last?

A: Clean freestyle flying, 20 to 30 flights. Learning and crashing regularly, 3 to 5 flights. We replace ours as soon as we see visible wear or after any ground contact at speed.

Q: Can I fly with a chipped prop tip?

A: No. A chipped tip creates imbalance that worsens with RPM. At full throttle on a 5-inch build, even a small chip produces noticeable vibration and makes the quad pull to one side.

Q: How do I know which prop size fits my build?

A: Match the prop to your frame size. A 5-inch frame takes 5-inch props. See our propeller size guide for the full breakdown by frame class.

Q: Bi-blade or tri-blade for everyday flying?

A: Bi-blade for freestyle and learning. Cheaper, more efficient, more crash-tolerant. Tri-blade for racing where thrust response matters. Our blade count guide has thrust data for each type.