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Model  Interstate L6


Type   Tube and fabric tandem seat bush plane/warbird.  Controls front and back.  Large baggage area.  Tail wheel configuration.  Float fittings.

Seats  2

Engine  To be determined,


Somerset, California

For Sale, The Mercury Project Interstate L6

The Mercury Project originated from a 1943 Interstate L6 Military liaison aircraft. Subsequently, this airplane model underwent modifications to become the Arctic Tern Bush Plane. Numerous existing models underwent conversion before the new owner of Interstate aircraft, who rebranded as the Arctic Aircraft Company, began building them new.


The building of this project involves configuring it into a bush plane while reinstating the original military observation windows. Earlier owners had removed these windows, opting for a conventional straight design. The aircraft lacks original paperwork and is being constructed for registration in the Experimental category. We've named the plane the Mercury Traveler, giving rise to the title "Mercury Project."

Some modifications are complete including  Aeronca landing gear purchased new and new tail wheel, float fittings and more.  The wings are ready to cover with new spars, new pulleys and new control cables.  New control cables throughout. New aluminum above windscreen fairing, original and new carbon fiber below windscreen cowl and two firewall aft cowls.  No firewall forward cowl.  I have part of the original cowl, but we were going to do an engine upgrade and make a new cowl.  All control surfaces included. 

Several modifications have been finished, including the installation of new Aeronca landing gear and a new tail wheel design, along with float fittings and various other updates. The wings are nearly ready to cover and feture new spars, pulleys, and control cables throughout. Additional parts include a new aluminum fairing above the windscreen, a combination of original and new carbon fiber for the cowl below the windscreen, and two aft cowls behind the firewall. While there is no firewall forward cowl at the moment, part of the original cowl is available; however, plans include an engine upgrade and the creation of a new cowl. All control surfaces are part of the package.



I have fabric (Ceconite) to cover the airplane and tape for the seams etc, but it is 15 years old.  It has been stored well and should be fine but I would recommend doing a strength test.  I am not considering this in the price.  But it comes with the project.   This project uses fabric clips, not rib stitching.

Many more parts and spares.

We had the late Pete Knedinger (Christen Eagle shop foreman) and Vaughn Lamb helping us with the project.  It was going to be similar to Pete's L6, the Yellow Swan.  A couple of photos of the Yellow Swan are included.

This will be a great bush plane similar to a Super Cub.  But with more baggage room.

Aluminum firewall

Aft firewall cowlings (2 sets)

Fuel tanks

Inspection plates

Fabric tape

Fabric clips

Some Parts and features;


Cleveland wheels and brakes.

Aluminum fuel tanks.

Original control cables included.

Original and new instrument panels.

Fuselage sandblasted and painted with PMI.

Very large baggage compartment.

Float fittings.

New hardware.

Professionally made wing spars.

Expected performance with 150hp. 

This will vary of course depending on construction methods and engine models


  • Empty weight: 1,000 lb

  • Gross weight: 1,900 lb

  • Maximum speed: 120 mph

  • Range: 650 mi

  • Service ceiling: 19,000 ft

  • Rate of climb: 1,275 ft/min

  • 'Stall mph 34.

  • Takeoff (50′) 500. Landing (50′) 350.

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​​​A little L6 history.

In 1940, Interstate Co. ventured into the aviation industry with the S-1B "Cadet," a tandem seat liaison aircraft. As the United States joined World War II, the U.S. Army Air Forces commissioned Interstate for 250 S-1B planes, designating the prototype as the XO-63, marking the final use of the "O" (for observation) designation. Subsequently, the USAAF assigned the production aircraft the L-6 designation.

Despite its capabilities, the aircraft grappled with significant overheating issues that were only partially resolved. Notably, the L-6 had the distinction of being the least-produced liaison aircraft by the USAAF. Its role encompassed utility transport, liaison, and training within the United States, without deployment overseas. Following the war, surplus L-6s were sold off.

Engine: Franklin XO-200-5 115 hp
Maximum speed: 105 mph
Range: 540 miles
Span: 35 ft. 6 in.
Length: 23 ft. 5.5 in.
Height: 7 ft. 3 in.
Weight: 1,650 lbs. loaded 
Serial number: 43-2680


In the late 1960s, the Type Certificates and tooling were acquired by the newly established Arctic Aircraft Company. Transforming the S-1B1 into a bush plane, Arctic Aircraft enhanced structural elements of the fuselage, landing gear, and wings. The resulting aircraft, designated the S-1B2, featured a Lycoming O-320 160 HP engine and an 82” McCauley propeller for improved performance. Certified in 1975 as the Arctic Tern, production continued from 1975 to 1985.

The company embarked on refining the Arctic Tern into the ultimate STOL aircraft, implementing several improvements to the original S-1B2:

  • Replacing wooden wing spars with aluminum box extrusion for enhanced capacity and improved service life.

  • Substituting steel lift struts with aluminum to reduce weight and enhance service life.

  • Upgrading from a fixed-pitch propeller to a constant-speed one for improved takeoff performance and higher cruise speeds.

  • Modernizing the instrument panel, instruments, avionics, and electrical system to meet contemporary standards.

  • Incorporating Dual Seaplane doors for increased safety and convenience.

For extreme bush flying, nothing rivals the performance of the Tern.

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