This site is dedicated to anyone with an interest in Thorp T-18 and/or Sunderland S-18 experimental aircraft.

T18.net is not associated with any company manufacturing parts/kits for either the T-18 or S-18, and mention of companies and/or products are not endorsements....

About the T-18...

The T-18 design was originally developed with the Lycoming 0-290G (ground auxiliary power unit) in mind, by John Thorp. Which was easily converted to a Lycoming 0-290D engine producing 125 HP.

The T-18 is an all metal 2 place side-by-side high performance aircraft. Control response is exceptional and control forces are well harmonized. The T-18 is a very capable cross-country airplane. It will carry 2 people, 80 lbs. of baggage, and depending on engine and prop, can cruise around 180 mph. Powerplants range from Lycoming O-235 (115hp) to IO-360 (180).

The T-18 was designed to be built from twelve 4' x 12' sheets of aluminum ranging in thickness from 0.016 to 0.040. Ribs and fuselage frames were designed to be hand formed with a mallet over plywood form blocks. Simple aluminum angle extrusions are used for stringers and longerons. The main wing spar caps are made from 1/4 "U" channel on top and angle on bottom with flat sheet for spar webs.

John Thorp designed the aircraft to be small, yet strong with excellent take-off and climb performance. The landing gear is a simple "A" frame of heavy wall 4130 steel tubing, heat treated to 180,000 lbs./sq. in. and bolted to the firewall with (3) 3/8" bolts. The engine mount is also attached to the "A" frame allowing landing stresses not to be transmitted directly to the fuselage. This landing gear system has proven to be rugged and durable. The T-18 incorporates the "flying tail" which John Thorp held the patent for. This design also incorporates a sliding bubble canopy, like a fighter style.

The T-18 is a very historic aircraft. It was one of the first all metal homebuilts. It was the first homebuilt to use the stabilator or all-flying-tail. The stabilator was designed by John Thorp and was later used by Piper on their line of Cherokee aircraft. Today you can see the extensive use of this design on military aircraft. The T-18 was the first homebuilt aircraft to fly around the world. It was also the first homebuilt airplane to fly to both the geographic and magnetic north poles. The legendary Don Taylor completed all of these feats in the early 1970's. His famous T-18 is now on display in the EAA museum in Oshkosh, Wisconsin. 

T-18 plans are available again through Eklund Engineering. They are also developing a kit version, using laser cut parts and of course John Thorp's matched hole tooling concept. The laser cut parts are beautiful and it promises to be a wonderful kit. For more information contact Eklund Engineering at: thorpt18@jps.net or by phone at: (209)727-0318

No other homebuilt has done all the things that have been done by this airplane. It is no doubt one of the best designed aircraft in the world.

T-18 Designations / Models

T-18        
The original design by John Thorp in about 1963

T-18C
The original T-18 fuselage design, but incorporating Lu Sunderlands new Convertible or folding wing. Plans were available through John Thorp. The folding wing was a supplement to the original T-18 drawings. The plans were taken off the market in 1984 when John Thorp retired.

T-18W      
Not many of these exist, but is the wide body version of the fuselage as designed by Lu Sunderland, using the standard T-18 wing platform. Plans were available through John Thorp. The wide body modification was a supplement to the T-18 drawings. The plans were taken off the market in 1984 when John Thorp Retired.

T-18CW
This is the predecessor to the S-18. It is the wide body version of the fuselage, and also the Convertible or folding wing as designed by Lu Sunderland. Drawings were available from John Thorp and they contained supplements for the fuselage and wing modifications. The plans were taken off the market in 1984 when John Thorp retired.

T-18L
This is my own designation for this model and I hope it will be accepted. This model uses both the standard fuselage and the standard wing plan form, but incorporates the LDS airfoil designed by Lu Sunderland and used on the S-18. There are no actual drawings for the "L" version, as builders have taken it upon themselves to make the airfoil change.

S-18
This is the redesigned version of the T-18 by Lu Sunderland. A complete new set of drawings were done and offered in 1985. It is basically the T-18CW.

About The S-18...

John Thorp retired in 1985 and took the T-18 plans off the market. Lu Sunderland, having worked with John on a wider fuselage and folding wing option for the T-18, did a complete rework of the drawings and produced plans for the S-18. The S-18 is then a redesign of the Thorp T-18. The fuselage body is 2" wider and 5" longer than the standard T-18. Also it has a newer NASA computer designed Wing Airfoil, which is stated to lower the stall speed by 6-8 knots. This airfoil also allows a more gentle stall with adequate warning. The top and cruise speeds remain the same. An S-18 with an 160hp Lycoming IO-320 and Hartzel Constant Speed propeller will cruise around 180 mph at 8500 ft (MSL) on less than 7 GPH (gallons per hour of fuel).

The S-18, like the T-18 is an all metal 2 place side-by-side high performance aircraft. Control response is exceptional and control forces are well harmonized. The S-18 is a very capable cross-country airplane. It will carry 2 people and 80 lbs. of baggage. Powerplants range from Lycoming O-235 (115hp) to IO-360 (180).

Parts can be provided with matched holes so that parts fit together saving a lot of time in construction. Also parts are scribed to outer mold-lines or trim lines. No jigs are required. The airplane is built using 1/8" solid aluminum rivets, but can be built using 1/8" stainless steel pop rivets (but not recommended).

The S-18 has a folding wing designed by Lu Sunderland which can be swung around parallel to the fuselage making the airplane less than 8 feet wide. So that it can be trailered home or stored in small spaces.

The S-18 is available in kit form from Classic Sport Aircraft. Pieces and parts for both the T-18 and the S-18 are available here also. For more information contact them at:
s18thorp@lightspeed.net or by phone at: (559)539-2755

• Wingspan .................................. ......... 20' 10"

• Wing chord ........................................ ...... 50"

• Wing Area ......................................... 86 sg. ft.

• Wing loading, 1600 lbs .................18.6 lbs/sq. ft.

• Span Loading, 1066 lbs ......................8.9 lbs/hp

• Length .................................................. 18' 11"

• Height ...................................................... 5' 1"

• Wheelbase ............................................ 13.3 ft.

• Main gear track ........................................ 62.8"

• Normal empty weight (0-290 engine) ....... 900 lbs.

• Design gross weight (0-290 engine) ....... 1500 lbs.

• Acceleration limits at 1250 lbs ............ +6 / -3 G's

• Ultimate G-Load at 1250 lbs. ....................... 9G's

• Recommended engines .. Lyc. 0-290, 0-320, 0-360

Airspeeds Per N42KB Owners Manual, IAS

• Never exceed, Vne ......................182 kts/210 mph

• Maneuvering, VA ........................138 kts/ 159 mph

• Best rate of climb, Vy ..................................... NA

• Best angle of climb, Vx ................................... NA

• Stall, clean at 1500 lbs ..................... 56kts/65 mph

• Stall, landing at 1500 lbs ...................50 kts/58 mph

• Flap speed, Vf ................................95 kts/110 mph

• Best glide ......................... .... aprox 87kts/100 mph

For more technical information on the T/S-18 please see the Technical Info page.

And now, for the mandatory small print...
All information presented here is for entertainment purposes only. Any attempt by a reader to apply any of the information presented herein is done at his/her own risk. Use as directed. Under 17 not admitted without parent. If skin irritation occurs, discontinue use. For external use only. Remove before flight. No live animals were hurt during the construction of this Web site (or dead ones either).