TL;DR: The Sling TSi’s 14V system works, but a 28V setup — common in modern certified GA — would double electrical capacity, allow lighter wiring, and improve cold starts. It could make big loads like A/C or TKS easier to handle and reduce the need for an external alternator, but would require the 28V Rotax B-model and a few component changes.

In aviation, you can start an argument faster than a Lycoming on a summer day just by asking pilots about their favorite oil, tire pressure, or whether teardrop entry to the pattern is a sin. But bring up 14 volts versus 28 volts, and you’ll get an entirely different kind of debate — one that quietly shapes how modern airplanes are designed, equipped, and flown.

Most general aviation aircraft live in one of two worlds: the 14-volt camp, with its simplicity and parts availability, or the 28-volt camp, with its extra electrical muscle and efficiency. Certified manufacturers have been steadily moving toward 28V in new models, especially those with glass cockpits and high-demand systems. Meanwhile, much of the experimental and light sport world — including the Sling TSi — still runs on 14V, just like the family car.

The question is: does that make sense in 2025 for a cross-country, IFR-capable kitplane like the TSi? And more provocatively… what could a 28V Sling TSi do that today’s can’t?

Before we start imagining upgraded alternators and high-powered accessories, let’s lay the groundwork and talk about what voltage really means in the cockpit.

1. Electrical Systems 101: 14V vs 28V

At its core, an airplane’s electrical system has a simple mission: get power from the alternator and battery to everything that needs it — from your G3X displays and autopilot to pitot heat, lights, and yes, the USB charger for your phone.

The big choice for designers and builders is what voltage the system will run at. In general aviation, there are two standards:

• 14V systems — lighter-duty, simpler, and still the most common in smaller or older aircraft.
• 28V systems — more common in modern, high-performance, or complex airplanes.

The Core Physics

Here’s the one equation from high school physics that actually matters in your cockpit:

Power (watts) = Voltage × Current

Double the voltage, and for the same current, you double the available power. Flip it around: for the same power requirement, a 28V system carries only half the current of a 14V system.

This single fact has ripple effects all over the airplane:

• Lower current → thinner wires → less weight
• Lower current → less voltage drop over long runs → more efficient
• Lower current → less heat in the wiring and connectors → better reliability
• Higher voltage lets you deliver more total power before tripping breakers or maxing out the alternator.

The Starter Motor Bonus

There’s also a performance perk: a 28V starter motor spins faster and with more torque than a 14V one, making cold-weather starts easier and quicker. Less cranking time also means less strain on the battery and starter.

So Why Not Just Use 28V Everywhere?

Because in aviation — especially in the experimental world — nothing is truly plug-and-play.

• Many small-aircraft components (flap actuators, trim servos, LED lighting modules) are built specifically for 14V.
• While many avionics have both 14V and 28V versions, 14V gear is often cheaper and more readily available in the kitplane market.
• Switching an aircraft to 28V isn’t just about changing the alternator — it means rethinking the battery, starter, breakers, wiring gauges, and sometimes even which variant of the engine you use.

In short, 28V systems bring engineering advantages, but 14V remains popular because it’s simpler, cheaper, and compatible with the huge catalog of GA components — which is exactly why the Sling TSi, like most LSAs and experimentals, ships in 14V form today.

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2. What the Sling TSi Has Today

From the factory, the Sling TSi’s electrical system is built around the 14-volt Rotax 915iS or 916iS A-model engine. That means:

• Main Bus Voltage: 14V
• Alternator A: 30 amps, engine-mounted, dedicated to the engine’s ECU and ignition (can’t be used for airframe loads)
• Alternator B: 40 amps, also engine-driven, powers the airframe and avionics
• Battery: 12V AGM or lithium (EarthX is a popular builder choice)

Optional External Alternator

For builders who plan a full-IFR avionics suite and extra accessories — such as air conditioning — Sling offers an external belt-driven alternator.

• Output: ~40–50 amps
• Price tag: just under $3,000 USD installed
• Requires a custom bracket, pulley, belt, and a small cowl modification
• Typically feeds a second electrical bus for high-draw accessories and redundancy

Want to see what adding more alternator output looks like in today’s 14V Sling world? We covered that in detail this post:

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Why Sling Stuck with 14V

The decision to keep the TSi on a 14V system is driven less by avionics compatibility — since virtually all modern avionics suites work just fine on 28V — and more by the supporting hardware in the airframe.

From a Sling technical representative on the Sling Pilots Forum:

“We are not offering it as an option currently. The limitation lies with some of the equipment used (flap actuator, trim servo, lights, etc.). We will consider it as an option in the future, but it will be some time still.”

Switching to 28V from the factory would mean:

• Finding 28V versions of these airframe components, or adding step-down converters for each one.
• Sourcing, testing, and validating new parts for reliability and longevity.
• Updating wiring diagrams, harness kits, and builder documentation.

For now, sticking with 14V keeps the build process simpler, avoids mixing voltages in the airframe, and aligns with the majority of Sling’s current mission profiles — even if it means some builders add an external alternator to handle bigger electrical loads.

For most Sling TSi missions — cross-country VFR, light IFR, or even moderately equipped glass panels — the stock dual-alternator 14V system offers plenty of capacity and redundancy.

The moment you add a string of high-demand systems (e.g., A/C, heated propeller, TKS de-icing, dual independent avionics buses), the margins get thin. That’s why so many fully-loaded IFR TSi builds add the external alternator — not because the airplane can’t run without it, but because it’s nice to avoid running at 90–100% electrical capacity in cruise.

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3. What Other Aircraft Use

To see where the Sling TSi sits in the bigger picture, it helps to look at the electrical systems used across general aviation — both certified and experimental.

Certified GA Aircraft

Aircraft	Electrical System	Notes
Cessna 172 (pre-1996)	14V / 12V battery	Common in older six-pack trainers
Cessna 172 (G1000 models)	28V / 24V battery	Factory 24V to support glass cockpit and modern avionics
Cessna 182 Skylane	28V / 24V battery	Higher-performance single with greater electrical demands
Cessna 206 / 210	28V	Supports heavier loads for utility and IFR missions
Piper Cherokee / Warrior	14V / 12V battery	Legacy VFR/IFR trainers
Piper Archer LX / TX (G1000)	28V	Modern trainer with glass cockpit
Piper Saratoga / Lance / Mirage	28V	Complex singles and twins
Beechcraft Bonanza (G36)	28V	High-end single with full-glass and TKS options
Cirrus SR20 / SR22	28V	Heavy IFR and optional A/C, TKS de-icing
Mooney M20 series	Mostly 28V	Especially turbo and glass-equipped variants
Diamond DA40/DA42	28V	Modern composite singles/twins
Tecnam P2010 / P2006T	28V	New-generation trainer/twin designs

Experimental & LSA Aircraft

Aircraft	Electrical System	Notes
Van’s RV-7 / RV-10 / RV-14	14V (typical)	Some heavy-IFR builds go 28V
Sling TSi	14V	Rotax 915iS A-model
Sling High Wing	14V	Same as TSi
Sling 4	14V	914UL-based
CubCrafters XCub / CarbonCub	14V	Simplicity-focused designs
RANS S-21 Outbound	14V	Popular STOL kit
Glasair Sportsman	14V or builder’s choice	Experimental flexibility
Zenith CH 750 / CH 650	14V	ULPower or Rotax powered

Trends and Takeaways

• In modern certified GA, especially with glass cockpits and high-draw options like TKS or A/C, 28V is now the default.
• In the experimental world, 14V still dominates — partly because of component availability, partly tradition.
• The Sling TSi is in the same camp as most experimentals, but it’s also a high-performance cross-country aircraft that could benefit from the extra headroom of a 28V system — much like its certified peers already enjoy.

Got it — here’s Section 4 rewritten as a concise bullet list, with Section 5’s “external alternator” analysis folded into the last bullet.

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4. Why 28V Would Be Interesting for Sling

A 28V electrical system wouldn’t change the Sling TSi’s aerodynamics or fuel burn, but it would:

• Double the usable wattage at the same current – Alternator B on today’s 14V system outputs ~40A × 14V ≈ 560 W; at 28V, the same current delivers ≈ 1,120 W, giving far more headroom without upsizing the alternator.
• Make high-demand accessories easier to integrate – Air conditioning (38–46A @ 14V), heated propellers, TKS de-ice, and high-power lighting would consume half the amps, freeing capacity for avionics and safety systems.
• Allow smaller, lighter wiring – Halving current means thinner wire gauges for the same loads, saving weight throughout the airframe.
• Improve starting performance – 28V starters spin faster and with more torque, improving cold-weather starts and reducing wear on batteries and starters.
• Increase redundancy headroom – More total capacity makes it easier to support dual-bus or dual-battery IFR setups without bumping against alternator limits.
• Reduce reliance on the external alternator – For light-to-moderate IFR loads, a 28V system could make the belt-driven alternator optional; for heavy IFR plus accessories, it would still be desirable for redundancy, but less for raw capacity.

Alright — here are the final two sections for the post.

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7. A Path Forward

If Sling ever decided to offer a 28V option, it wouldn’t require reinventing the TSi — but it would need a focused redesign in a few areas:

• Engine choice – Spec the Rotax 915iS/916iS B-model, which comes with 28V alternators from the factory.
• Airframe components – Either source 28V versions of flap actuators, trim servos, and certain lights, or use robust step-down converters for those loads.
• Wiring and breaker updates – Adjust wire gauges, circuit protection, and harness diagrams for the new voltage.
• Builder documentation – Update wiring diagrams, load analysis examples, and optional equipment guidance.
• Options integration – Leverage the new headroom to package features like A/C, TKS de-icing, and heated props in a factory-supported configuration without requiring an external alternator for most builds.

This wouldn’t turn the TSi into a “different airplane,” but it would align it with what most modern certified high-performance singles are already doing.

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8. Closing Thoughts

The Sling TSi has always been marketed as a modern, efficient cross-country aircraft — and in most ways, it delivers. But its electrical system is still firmly in the 14V camp, alongside legacy LSAs and kitplanes with much lighter missions.

As more builders equip their TSis for serious IFR flying, long-range travel, and comfort upgrades like air conditioning, the electrical load margins get thinner. A 28V option could change that equation overnight — doubling available wattage, lightening wiring, improving cold starts, and, for many builds, eliminating the need for a belt-driven alternator.

Certified GA made this transition years ago for the same reasons. The question for Sling isn’t whether 28V works — it’s whether the factory wants to offer builders the same flexibility that certified manufacturers now consider standard.

So… is it time for the Sling TSi to go 28 volts?