Wag-Aero Sport Trainer (CUBy)

The Wag-Aero Sport Trainer — originally called the CUBy — is a homebuilt replica of the Piper J-3 Cub / PA-11 Cub Special, designed by Dick Wagner and marketed from Lyons, Wisconsin. Wagner first flew the prototype on 12 March 1975, and by mid-2001 Wag-Aero had sold roughly 4,193 sets of plans and kits, making it one of the most successful Cub-alike homebuilts in the U.S. The aircraft exists because genuine Cubs became expensive and antique-fragile; the CUBy lets a builder end up with a brand-new airplane that looks and flies like a J-3 but is built to modern standards and registered Experimental-Amateur-Built.

Structurally the Sport Trainer departs from the original Piper in several ways: the fuselage is welded 4130 chrome-moly steel rather than the Cub's 1025 carbon steel, wing ribs and spars were originally wood (spruce) with aluminum later offered as an option, and fuel is carried in two wing tanks (13 gal each) rather than a single fuselage header tank. That wing-tank layout is the headline functional difference: unlike a real J-3, the Sport Trainer can be flown solo from the front seat, which is a big deal for visibility and for low-time pilots. See piper-j3-cub and piper-pa11-cub-special for the originals.

Wag-Aero expanded the line into a whole Cub-family: the Acro Trainer (clipped-wing semi-aerobatic), the Super Sport (enclosed cowling, up to 150 hp, Super Cub alternative), the Observer (PA-18 lookalike), the Wag-a-Bond (PA-15/17 Vagabond replica) with a Traveler sub-variant, and the Sportsman 2+2 / CHUBy (PA-14 Family Cruiser four-seat replica). The Sport Trainer is the anchor of the family and by far the most-built.

Note on the company: In May 2024, Aircraft Spruce acquired Wag-Aero's parts distribution business, moving inventory to Georgia. The manufacturing/kit side was not part of the sale and continues to operate. This matters for builders: consumable Cub parts (fittings, fabric supplies, hardware) now flow through Aircraft Spruce, while airframe kits, plans, and proprietary Wag-Aero components remain with the original company. See maintenance-ecosystem.

This page covers the Sport Trainer proper. The Sportsman 2+2 and Wag-a-Bond deserve their own pages eventually; the Acro Trainer and Super Sport can be treated as variant notes here unless demand grows.

Published Sport Trainer numbers (C-85, 85 hp): 85 mph cruise, 38 mph stall, 450 fpm climb, 375 ft takeoff roll, 420 ft landing roll, 310 nm range. Those are very close to a real PA-11 and marginally better than a J-3 owing to the wing tanks (no fuselage-tank CG penalty) and slightly cleaner cowl/firewall work.

Real-world observations from builders on SuperCub.org and backcountry forums:

• With a 100 hp O-235 — the sweet-spot engine for most builders — you'll see ~85–90 mph TAS and ~600 fpm climb solo. Adding a passenger drops climb to ~400 fpm on a hot day, exactly like a J-3.
• With a 150 hp O-320 Super Sport build, performance approaches (and in some respects beats) a stock PA-18-150 Super Cub: 800+ fpm solo climb, shorter takeoffs, and more reserve at density altitude. This is the build for anyone who actually wants to use it for mountain or bush work.
• The flat-bottom USA-1 airfoil and 178.5 sq ft wing yield a low wing loading (~7.4 lb/sq ft) which makes the airplane float in ground effect and land short.
• Builders consistently report that the Sport Trainer is slightly heavier empty than a pristine J-3 (~720–760 lb vs 680 lb) because of the heavier 4130 tube, wing tanks, and modern hardware. Useful load therefore depends heavily on how disciplined the builder is about paint and panel weight.

Density altitude behavior is classically Cub: high and hot is survivable with one pilot and half fuel, miserable with two adults and full tanks.

The Sport Trainer's useful load of ~580 lb (100 hp build, aluminum-wing, reasonable panel) plays out as follows:

Scenario A — Solo + full fuel (26 gal = 156 lb)

• Pilot 200 lb + baggage 25 lb + fuel 156 lb = 381 lb, well under the 580 lb useful load.
• Range at 5 gph: ~4.5 hours + reserve = ~340 nm no wind.
• This is the airplane's happiest loadout.

Scenario B — Two adults + full fuel

• 2 × 180 lb = 360 lb + fuel 156 lb + baggage 25 lb = 541 lb, still under useful load (barely).
• Same ~340 nm range at reduced climb performance (~350 fpm at sea level, less at altitude).
• Two 200-lb adults + full fuel = 556 lb — still legal on paper but climb becomes marginal on hot days.

Scenario C — Two adults + short fuel

• 2 × 200 lb = 400 lb + 15 gal fuel = 90 lb + 25 lb baggage = 515 lb.
• Range ~180 nm, which is a reasonable weekend hop to a fly-in or grass strip.

Scenario D — Super Sport O-320 build (useful load ~700 lb)

• Two 200-lb adults + full 26 gal + 50 lb camping gear = 636 lb. Works comfortably and climbs at ~700 fpm even loaded. This is the build that turns the Sport Trainer from a solo-fun airplane into a two-person light-bush airplane.

MOSAIC eligibility: With a clean stall speed of ~38 mph (33 KIAS) and gross weights of 1320 lb (baseline) to ~1500 lb (Super Sport), the Sport Trainer comfortably meets the draft MOSAIC rules (published stall ≤54 KCAS, no gross-weight cap for LSA operation). Sport pilots should be able to fly all Sport Trainer variants under MOSAIC once the rule takes effect. See mosaic.

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Local Fun Flying (9) — This is what the airplane exists for. Open door, 500 ft AGL, grass strip to lake cabin, sunset pattern laps. Scores as high as anything in the wiki for pure recreational enjoyment. See local-fun-flying.

Backcountry/Bush (7) — With big tires and a 100+ hp build, the Sport Trainer is a credible backcountry airplane. The Super Sport variant with O-320 and bush tires rivals a Super Cub for short-field work, though wood spars (if chosen) make some builders nervous about rough loads. Not as strong as a purpose-built cubcrafters-carbon-cub or backcountry-super-cubs-bcsc, but much cheaper to own. See backcountry-bush.

Flight Training (6) — Legally only usable for pilot-owner training under Experimental-Amateur-Built rules (no rental, no paid instruction in someone else's airplane without LODA). But as a personal tailwheel/taildragger trainer for a builder-pilot, it's ideal — forgiving, slow, honest stall. See flight-training.

Surveying (5) — Slow speed and good visibility are assets; limited payload and range are liabilities. OK for short pipeline or fence-line runs, not for serious mapping.

Aerobatics (3) — Standard Sport Trainer is not aerobatic. Only the Acro Trainer clipped-wing variant is semi-aerobatic, and even then it's a gentle-aerobatic trainer, not a competition airplane. See acro-sport for Wag-Aero's actual aerobatic line and aerobatics.

Cross-Country (3) — 80 kt cruise and 310 nm range make any XC a commitment. Fine for a weekend fly-in two states away; unrealistic for routine travel. See cross-country.

Business Travel (1), Cargo Hauling (2) — No.

As an Experimental-Amateur-Built, the Sport Trainer has no avionics certification requirements — the builder can put in anything from a single airspeed indicator to a full Garmin G3X Touch. Typical configurations by budget:

Budget / Vintage (~$500–$2,000 panel) — Airspeed, altimeter, slip ball, oil pressure, oil temp, tach, mag compass. No radio, no transponder. Legal for day VFR outside controlled airspace. Most traditional J-3-lookalike builds go this route to preserve the period feel.

Sport VFR (~$3,000–$8,000) — Add a handheld or panel-mount VHF com (Icom A220, Garmin GTR 200), a portable ADS-B in/out solution like uAvionix tailBeaconX or SkyBeacon, and a basic 7-inch EFIS like a Dynon D3 or Garmin G5. This is the modal 2026 build.

Full Glass ($10,000–$20,000) — Dynon SkyView HDX or Garmin G3X Touch 7" with ADS-B in/out, com radio, intercom, GPS nav. Overkill for the mission but popular with builders coming from glass-panel certified airplanes. IFR flight is legal but operationally impractical given performance and airframe characteristics. See avionics-pricing.

Because the Sport Trainer is Experimental-Amateur-Built, STCs do not apply. Builders modify freely within the limits of their operating limitations and their builder/A&P judgment. Common modifications:

• Engine upgrades: C-85 → O-200 → O-235 → O-290 → O-320 is the typical progression. The 150 hp O-320 Super Sport build is the most common "hot rod" path. No paperwork beyond weight & balance and operating-limitations review.
• Aluminum wing spars and ribs — Wag-Aero began offering aluminum as an option after initial wood-only kits. Aluminum is more durable and slightly heavier; wood is lighter but demands climate-controlled storage.
• Bush tires — 26", 29", or 31" Airstreaks / Alaskan Bushwheels. Install cost ~$3,000–$5,000 for the larger sizes.
• VGs (vortex generators) — Micro AeroDynamics-style kits, ~$500, lower stall speed 2–3 kt.
• Enclosed cowl (Super Sport conversion) — Improves cooling and looks with higher-HP engines.
• Extended baggage — Extra tubing aft of the rear seat, ~50 lb baggage capacity gain.
• Skylight and extended windows — Common visibility mods.
• EarthX lithium battery — Weight savings of ~10–15 lb, popular in experimental Cub clones.

Note also wag-aero (as a company) historically held several J.A. Myers STCs for certified Piper Cubs; those STCs are now owned separately from the kit side and do not apply to Experimental builds.

The Sport Trainer is one of the easiest E-AB aircraft to maintain because:

1. It's built from Piper J-3 / PA-11 / PA-18-compatible parts wherever possible. Cleveland wheels and brakes, standard Piper-style fittings, Lycoming/Continental engines, McCauley/Sensenich wood or metal props. Any A&P who has touched a Cub can work on a Sport Trainer.
2. Aircraft Spruce now stocks all former Wag-Aero parts as of mid-2024, meaning fittings, hardware, fabric supplies, and Cub-specific bits are readily available nationwide.
3. Annual condition inspection (not an annual inspection in the Part 43 sense — E-AB requires a "condition inspection" at least every 12 months) can be performed by any A&P, or by the original builder if they hold a Repairman Certificate for the aircraft. Typical shop condition inspection: $800–$1,500.
4. Typical annual operating cost for an owner flying 75–100 hrs/yr: $4,000–$6,000 including fuel, oil, condition inspection, insurance, tiedown, and reserve for fabric/engine.

Expensive items to plan for:

• Fabric recover every 20–25 years: $8k–$15k in materials, 300+ hours of labor (or $20k–$30k done by a shop).
• Engine overhaul: $15k–$22k for O-235/O-290; $20k–$28k for O-320.
• Prop refurbishment or replacement: $1.5k–$4k.

Mechanic familiarity is common rather than universal — any Cub-experienced A&P is immediately comfortable, which is most rural/GA shops but may not include urban jet/turbine shops. See maintenance-ecosystem.

Sport Trainer pricing on Barnstormers and Trade-A-Plane 2024–2026 ranges roughly $22,000 (project or tired 65 hp wood-wing) to $55,000+ (nicely built O-320 Super Sport with fresh fabric and a modest panel). Typical flying example is $30,000–$40,000.

Major valuation drivers:

• Engine time and model — O-235/O-290 at mid-time adds ~$5k over a runout C-85; O-320 build can add $10k+.
• Aluminum vs wood wing — aluminum spars add ~$3k–$5k because of perceived longevity.
• Fabric age — fresh Poly-Fiber adds ~$8k; tired fabric subtracts by similar amount because recover is ~$8k–$15k in materials and ~300 hours of labor.
• Bush tire package — adds $3k–$5k to value and expands the buyer pool.
• Builder reputation — a Sport Trainer built by a known A&P/IA is worth 20–30% more than an unknown builder's otherwise-identical airplane.
• Documentation — complete build logs, photos, and weight & balance records add ~$3k and shorten time-on-market dramatically.

New kit cost from Wag-Aero (post-acquisition kit operation) runs roughly $20,000–$30,000 for the airframe kit plus engine ($15k–$30k used Lycoming), prop ($2k–$4k), instruments, fabric, and paint — total build cost typically $50,000–$75,000 with a used engine, ~$90,000+ with new engine. Build time is quoted at ~1,200 hours and realistic for an experienced builder; first-timers report 2,000–3,000 hours. See valuation-methodology.

Experimental-Amateur-Built aircraft are not subject to Airworthiness Directives on the airframe. Engine and propeller ADs still apply if certified parts are used (nearly always the case — Continental C-series, Lycoming O-235/O-290/O-320). Watch for:

• Lycoming O-320 / O-235 crankshaft and oil pump ADs — standard Lycoming fleet issues.
• Continental C-series cam and lifter wear — common in low-utilization Cub-clone engines.

Common Sport Trainer-specific problems and pre-buy red flags:

• Wood spar condition — on older (pre-aluminum) builds, inspect spars for moisture damage, glue-line cracks, and hangar rash. This is the #1 deal-breaker for used examples.
• Tube rust at cluster welds and lower longerons — classic fabric-airplane issue. Pull inspection panels and look, especially around the tailpost and gear attach points.
• Fabric condition — Poly-Fiber or Ceconite systems last 20–30 years depending on storage. Punch test at pre-buy.
• Builder quality variance — this is the single biggest risk with any amateur-built. A well-documented build by an experienced builder is worth a significant premium; a half-finished project or an obscure builder's work can be dangerous.
• Logbook traceability — E-AB logbooks can be incomplete or lost; insist on seeing the builder's photos, condition inspection history, and any STCs/alterations.
• Engine mount cracks — especially on higher-HP (O-290/O-320) conversions where the original J-3-style mount was beefed up but not always correctly.

The Sport Trainer falls into the experimental taildragger underwriting bucket. Typical 2025–2026 premiums:

• Liability only (smooth $1M): $400–$700/yr for a qualified tailwheel pilot with 200+ hours and 25+ tailwheel hours.
• Hull + liability on a $35,000 hull: ~$1,200–$1,800/yr for a proficient pilot, rising to $2,500+ for low-time or zero-tailwheel pilots.
• Some underwriters (Avemco, BWI, Falcon) quote Cub clones readily; others decline E-AB entirely.

Underwriting quirks:

• Minimum tailwheel hours — typically 10–25 required, with dual in make-and-model or a transition checkout.
• First-year hull exclusion during flight test phase is common — builders often fly off Phase 1 (25–40 hrs) with liability-only coverage.
• Agreed value vs stated value — most carriers write stated value; agreed value is rare and expensive on E-AB.
• Builder = first owner discount — some carriers give a small discount to the original builder on the theory that they know the airplane intimately.

See insurance-underwriting for the general E-AB premium structure.