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The size range across petrol and glow aerobatic models is wide, and it’s worth understanding roughly how the classes relate to each other if you’re moving up (or down) in scale.

30-size to 50cc class covers a lot of popular sport and lighter scale aerobatic models — generally lighter, more portable, and typically the entry point for pilots moving from trainer-style models into dedicated aerobatic or 3D types. Gear, wheels, and general hardware at this end of the range are correspondingly lighter-duty, sized for the lower weights and loads involved.

80cc to 100cc class represents a genuine step up in both scale presence and structural demands — models in this range are often serious club-level or entry competition aerobatic machines, and landing gear, fasteners, and fuel system components all need to be specified accordingly rather than simply scaled up casually from smaller-class parts.

150cc and above is squarely the large-scale end, where models start to genuinely resemble their full-scale counterparts in size and presence, and where every component — gear, fuel system, ignition — needs to be selected with real margin rather than minimum-spec, given both the values involved and the consequences of a failure at this scale.

Moving up in class isn’t just “buy bigger everything.” Weight, structural loads, vibration characteristics, and fuel system demands all scale in ways that aren’t perfectly linear, which is part of why manufacturer size brackets (see Day 1) exist rather than a single universal formula — a component correctly sized for 50cc use doesn’t necessarily scale proportionally and safely to 100cc just because the numbers look related.

If you’re moving up a size class for the first time, it’s worth treating it as a genuinely new specification exercise for gear, fuel system, and hardware — rather than assuming your existing knowledge and component choices simply scale up alongside the model.

Take a look at our EXTRA 300 26cc – 35cc Carbon Fibre undercarriage for a solid example of correctly sized gear.

A well-stocked field box saves more flying sessions than almost any other single habit, and it doesn’t need to be expensive or complicated to be genuinely useful.

Fasteners first. A small assortment of the bolt sizes your models actually use, plus a spare tube of thread-lock, covers the single most common field fix — a loosened gear, cowl, or engine mount bolt discovered during a pre-flight check (see Day 17).

A spare glow plug or spark plug, matched to whatever engines you’re actually running that day, is cheap insurance against a session-ending failure that would otherwise be a simple two-minute swap.

Basic ignition spares if you’re running petrol — a spare kill switch lead and, if you’ve got the budget for it, a spare ignition module for your most-used engine, since ignition failures tend to be sudden and total rather than giving you warning.

A spare prop or two in your common sizes, since a strike serious enough to end a flying session but not serious enough to be an obvious safety issue is a genuinely common occurrence, and there’s little worse than driving home early over a five-minute prop swap you couldn’t make because you didn’t have a spare.

Basic landing gear spares are worth considering if you fly regularly from grass (see Day 9) — even just spare mounting bolts and a spare wheel or two, since these are exactly the components taking the most repeated, unpredictable load on a typical flying day.

A simple field checklist, even a basic one, catches more issues before they become spares-box problems than the spares box itself ever will — the two work best together, not as alternatives to each other.

None of this needs to be elaborate — a genuinely useful field spares kit is more about consistency (always having the basics, every session) than about having every conceivable spare part on hand.

For a real-world example, have a look at our Protective RC Wing Bag 50-70cc size.

Fuel systems don’t get the glamour of engines or gear, but a poorly specified or poorly plumbed tank causes more mysterious “engine problems” than almost any other single component.

Size for your typical flight duration, with margin. Running a tank close to empty regularly isn’t just inconvenient — it increases the chance of uneven fuel pickup and air getting into the line as the fuel level drops and sloshes with manoeuvres, which shows up as intermittent lean running or cutting out, often blamed on the engine rather than the fuel system.

Placement affects feed consistency through the flight envelope. A tank mounted too far from the engine’s ideal fuel level, or positioned so that aerobatic manoeuvres regularly uncover the pickup, will cause exactly the kind of intermittent fuel starvation that’s maddening to diagnose in the field. Following the airframe designer’s recommended tank position (rather than fitting the largest tank that physically squeezes in) avoids most of this entirely.

Clunk placement and free movement matter as much as tank size. A clunk that’s snagged, kinked, or restricted in its movement inside the tank defeats the purpose of having one at all — it’s worth a visual check (tank empty, clunk moving freely through its full range) whenever you’re setting up a new tank or troubleshooting inconsistent running.

Fuel line condition degrades gradually and easily gets overlooked. Silicone fuel line can harden and crack over time, particularly with petrol rather than glow fuel, and a line that looks fine but has lost flexibility is a common, easily-missed cause of intermittent air leaks into the fuel system.

A full fuel system check belongs in the same pre-season routine as gear and fasteners (see Days 14, 15, and 17) — it’s an unglamorous job, but fuel system issues are among the most common causes of in-flight engine problems that have nothing to do with the engine itself.

Our Petrol conversion fuel tank bung and fittings is a good reference point if you’re shopping around.

Propeller selection is its own deep rabbit hole, but a few fundamentals apply broadly across most gas and electric sport and scale setups.

Diameter and pitch are doing different jobs. Diameter is broadly related to how much air the prop can move (and therefore how much static thrust it can generate), while pitch relates to how far the prop would theoretically travel through the air in one revolution, which affects top speed and how the engine or motor loads up at different RPM. Manufacturer-recommended combinations for a given engine or motor are a sensible starting point rather than something to second-guess without good reason.

Gas engines generally want a specific pitch range for the engine to run happily, and going too aggressive on pitch can load the engine down below its efficient RPM range, hurting both performance and engine longevity — this is one area where following the engine manufacturer’s recommended prop range genuinely matters, rather than being an overly cautious suggestion.

Electric setups have more flexibility but more room to get it wrong, since motor, ESC, battery, and prop all need to work together within safe current draw limits — a prop that’s fine on one motor/battery combination can be genuinely unsafe (overheating the motor or ESC) on a different combination, even at the same nominal size.

Balance and true running matter as much as size selection. An out-of-balance or slightly warped prop introduces vibration that affects everything downstream — engine mounts, fasteners (see Day 17), even radio gear reliability over time — regardless of how correctly sized the prop otherwise is.

When in doubt, start conservative and work up, particularly on a new engine or motor combination you haven’t run before — it’s easier to notice a prop that’s slightly too small than to recover from over-stressing a new power system with too aggressive a first choice.

You can browse our Carbon Fiber Propeller For RC Fixed Wing Airplane 19×8 19×10 22×10 23×8 23×10 24×8 24×10 Propeller to see this in practice.

Spinners are often treated as a purely cosmetic finishing touch, but a poorly fitted or unbalanced one can genuinely affect how a model runs.

Balance matters more than most flyers expect. An out-of-balance spinner, spinning at engine RPM right at the front of the model, introduces a genuine vibration source — one that’s easy to blame on the engine or prop when the spinner itself is the actual culprit. A quick static balance check before fitting (balancing the spinner alone on a suitable fixture, checking for a consistent rest position) is worth the couple of minutes it takes.

Backplate fit affects prop and spinner alignment together. A spinner backplate that isn’t sitting flush and square to the prop driver introduces run-out that no amount of careful prop balancing alone will fix — it’s worth checking backplate seating specifically, not just assuming a snug fit means a square fit.

Match spinner diameter to cowl, not just to prop size. It’s a surprisingly common mismatch — a spinner sized correctly for the propeller but slightly wrong for the cowl opening either leaves an unsightly gap or requires more cowl trimming than expected. Checking both dimensions against the spinner’s spec before ordering saves a return or a rework.

Carbon fibre and composite spinners generally need less balancing correction than some alternatives, thanks to more consistent manufacturing tolerances, but “generally less” isn’t “never” — it’s still worth a balance check rather than assuming a premium material guarantees a perfectly balanced part straight from the packet.

A well-fitted, properly balanced spinner is one of the cheaper, quicker upgrades available for both looks and smoothness — it’s just worth doing the fitting properly rather than treating it as a five-minute bolt-on job.

Our 1.75″/44.45mm Drilled Alu Prop Spinner for DLE30/55 MLD35/70 DA50 EVO54 Engine is a good illustration of the kind of fit and finish to look for.

It’s easy to dismiss a few grams here and there as insignificant, but on the models where weight matters most, small savings genuinely compound.

Power-to-weight ratio is the whole game on 3D models. A model built for hovering, torque rolls, and other low-speed, high-power manoeuvres lives or dies on its power-to-weight ratio — every gram saved anywhere on the airframe is a gram the engine or motor doesn’t have to work as hard to move, which directly affects how “floaty” and controllable the model feels at low airspeed.

Landing gear is a good place to look, because it’s unsprung, extremity-mounted weight. Weight at the end of a gear leg, well away from the model’s centre of gravity, has a disproportionate effect on how the model handles gear-adjacent manoeuvres compared to the same weight saved somewhere near the CG — which is part of why carbon fibre gear (see Day 2) is such a popular first upgrade specifically for 3D-oriented models.

It’s not just the gear itself — wheels matter too (see Day 7), since wheel weight is rotating mass at the very end of the gear leg, arguably an even more sensitive location than the gear leg’s own weight.

Diminishing returns are real, though. Chasing grams on landing gear while ignoring far larger weight savings available elsewhere on the model (battery selection, unnecessary scale detailing, control horn hardware) is a common mistake — gear upgrades are worth doing, but they’re one part of an overall weight-conscious build, not a silver bullet on their own.

If you’re building or upgrading specifically for 3D or serious aerobatic flying, it’s worth thinking about landing gear weight as part of the same conversation as motor, battery, and prop selection — not a separate, purely cosmetic decision.

Take a look at our Carbon fibre undercarriage for 70 size nitro or electric models – narrow for a solid example of correctly sized gear.

Every flyer has one occasionally — a landing that’s harder than intended, whether from misjudged flare, a gust, or just an off day. What matters is what you do immediately after.

Don’t fly again without checking, even if it “felt fine.” Carbon fibre’s failure mode (see Day 2) means damage isn’t always visually obvious or immediately apparent from how the landing felt — a leg can retain enough residual strength to survive taxiing back and look fine sitting on the bench, while carrying damage that fails on the next hard landing rather than this one.

Check both legs, not just the one that looked like it took the impact. Asymmetric hard landings still transmit load through both legs via the airframe, and it’s easy to focus attention on the obviously-affected side while missing developing damage on the other.

Look specifically at the mounting area first — this is the highest-stress point on most gear designs and the most common location for hairline cracking to first appear, before it’s visible anywhere else on the leg.

Do a hand-flex test comparing both legs, similar to the fitting check in Day 5 — any noticeable difference in how the two legs flex under equal hand pressure is worth taking seriously, even without visible cracking.

When in doubt, don’t fly it. Landing gear is one of the cheaper components to replace relative to the cost of what happens if it fails on a subsequent landing — a cracked leg that lets go on touchdown risks the propeller, cowl, and potentially the whole airframe, well beyond the cost of the gear itself.

A hard landing doesn’t automatically mean replacement — plenty of hard landings are shrugged off without issue by gear that’s correctly sized and in good condition. It just means the checks above are worth five minutes before your next flight, rather than assuming everything’s fine because it looked fine going onto the ground.

For a real-world example, have a look at our 120 size profile carbon undercarriage (60-70″ models).

Carbon fibre is a genuinely robust material for storage compared to some alternatives, but a few sensible habits over the off-season will keep your gear in the same condition you packed it away in.

Avoid prolonged direct sunlight or heat sources. Carbon fibre itself is largely unaffected, but the resin matrix holding the fibres together can be more sensitive to prolonged UV and heat exposure than the fibre itself — a garage shelf out of direct window sunlight is a better long-term home than a spot that bakes in summer sun through glass.

Store gear unstressed, not under load. If gear is left bolted to a model that’s stored resting on its wheels for months, particularly on a soft surface, it’s sitting under a small constant load the entire time — not usually enough to cause visible damage, but there’s no benefit to it either. If you’re storing a model long-term, supporting it so the gear isn’t bearing weight is a sensible, low-effort precaution.

Keep it dry. Moisture ingress isn’t the concern with carbon fibre that it is with some wooden airframe components, but any bare cut edges (see Day 11) are more vulnerable than factory-finished surfaces, and a damp storage environment is never doing any RC equipment favours generally.

A pre-season check still applies even to gear that’s been “just sitting there.” Carbon fibre doesn’t degrade the way rubber or foam can over a winter, but the fastener and inspection checks from Day 4 and Day 17 are still worth doing at the start of the season — not because the gear itself will have changed, but because it’s a good moment to catch anything you might have missed at the end of last season.

Off-season storage for carbon fibre components is genuinely low-maintenance — a bit of common sense goes a long way, and there’s no special treatment or product needed to keep it in good order.

Our Carbon Fibre Undercarriage for 50cc models – suits Yak and others. is a good reference point if you’re shopping around.

It’s an unglamorous topic, but a genuinely high proportion of landing gear problems trace back to fasteners rather than the gear itself, so it’s worth a post of its own.

Over-tightening is at least as common a problem as under-tightening. Carbon fibre mounting plates and gear legs can crack under excessive clamping force, particularly around bolt holes, well before the bolt itself reaches its rated torque. “Tight” doesn’t mean “as tight as you can physically make it” — a firm, secure tightness by feel, with a drop of thread-lock for security, beats over-torquing every time.

Thread-lock matters more on vibration-heavy setups. Petrol twins in particular (see Day 13) generate enough sustained vibration to walk fasteners loose over a season, even ones that were properly tightened at the start. A medium-strength thread-lock (rather than a permanent, high-strength grade you can’t remove later) is the right choice for most gear-mounting applications.

Check, don’t assume. A fastener that was correctly torqued at initial fitting isn’t guaranteed to still be correctly torqued three months and a dozen flights later. Building a quick fastener check into your regular pre-season and post-hard-landing routine (see Day 4 and Day 9) catches loosening before it becomes a genuine failure.

Match the fastener to the job, not just to whatever’s in the spares box. Landing gear mounting bolts see cyclic shock loading, which is a different demand to a purely static fitting — using an appropriately rated fastener, rather than the nearest bolt that happens to fit the hole, is worth the extra five minutes of checking.

It’s not the most exciting maintenance topic, but it’s one of the highest-value ones — most fastener checks take moments and catch problems while they’re still easy and cheap to fix.

You can browse our 26-35cc Carbon Fibre Undercarriage for Petrol / Gas / Nitro models. to see this in practice.

Main gear gets most of the attention, and understandably so, but the tail wheel does genuine work on every flight and deserves more attention than it usually gets.

It’s your primary ground steering on most taildraggers. A worn or loose tail wheel linkage doesn’t just cause a wobbly taxi — it directly affects take-off tracking and landing rollout control, which matters more on a crosswind day than most flyers give it credit for.

It takes real load on landing, particularly on a slightly tail-low touchdown or a three-point landing style — the tail wheel spring or mounting bracket is doing genuine shock-absorbing work, not just providing ground clearance.

Common failure points are small and easy to miss: a worn steering arm pivot, a spring that’s lost tension, or a mounting bracket that’s slowly working loose from vibration are all things that develop gradually and rarely announce themselves clearly until ground handling noticeably deteriorates.

A quick functional check is genuinely quick. With the model on the ground, gently push the rudder stick fully each way and watch the tail wheel respond — it should move smoothly, promptly, and return cleanly to centre with no noticeable play or delay. Any looseness, binding, or delayed response is worth investigating before it causes a ground-handling surprise.

Replacement is usually simple and inexpensive compared to most other gear-related items, which makes it one of the easiest maintenance wins available — there’s rarely a good reason to keep flying on a tail wheel assembly you already suspect is past its best.

Our Carbon Tailwheel bracket for 120 / 20cc models is a good illustration of the kind of fit and finish to look for.