The thorp T-18 story

Background & History

There's always a story behind each airplane. This story begins with a design that was introduced in 1963 by John W. Thorp. My father was an early adopter who became interested in the experimental Thorp design within a year of introduction. At that time he had been a Delta Air Lines pilot for three years and knew he would upgrade to Captain shortly. New Captains are often placed on reserve, an on-call position where pilots wait at home to be called in for trips. So he thought – what better thing to do with the wait time than build an airplane? He bought plan set number 347 in 1965 and started building.

Me and my brother in Rockford, IL 1965 in front of one of the first three Thorps to be finished
Me and my brother in Rockford, IL 1965 in front of one of the first three Thorps to be finished

Fast forward in the story to spring of 1971, N110JH has its airworthiness certificate and is ready to fly.

N110JH completed by Jack Hagle in 1971
N110JH completed by Jack Hagle in 1971

Unfortunately at 87 hours the engine failed (carb ice suspected) on takeoff in August 1972 and we lost the airplane to a post-crash fire. I was with my father and still sport evidence of burns on my right leg. The surviving parts and a bunch of new material was purchased from Ken Knowles and N45881 flew in 1978. I got to solo the airplane in 1979 and it stayed in the family until 1986. N45881 is currently owned by Rich Shoup and lives in West Virginia.

Time away from experimental aviation

N45881- Summer 1984
N45881- Summer 1984

Once my father sold N45881, I became busy with my career and was away from general aviation for years. In the late 90s I was in between flying jobs and created my best flying job ever by hopping rides in a Waco YMF-5 in Destin, Florida. After a season and a half, it was time to get a real job so I joined Atlantic Southeast Airlines to fly the EMB-120. That was followed by the CRJ-200, CRJ700 and finally the ATR-72. In 2006, I moved my employment to Airtran Airways and flew the 737-700 on all the Domestic and International Routes.

After years of commercial airline experience, I felt a nostalgia for my early days in aviation and those Thorp experimental airplanes. In December of 2012, I purchased two Thorp projects from JW French.

New Thorp Projects in 2012

N66WT Tail Numbers
N66WT Tail Numbers

N66WT, S/N 1066 had flown previously, but had been disassembled for paint. I found numerous not-to-plans issues with WT and spent time returning the fuselage to plans specifications. The second one (what became 218TH) was pretty far along, but had not been finished.

I set a schedule for completing WT first. Since it had flown previously, I could finish it, fly it and sell it to make room for what will be N218TH. There were some unique challenges in getting WT back in flight status, but that story is for another time.

planning & Building a thorp t-18

I can relate to what my father went through as I make the decisions for what is to become N218TH. It's exciting to dream and plan out what I want in the panel. I have a set of design goals for TH. Being able to choose the engine, propeller and interior design is like spec building a house.

Side of a Thorp t-18
On it’s gear when it arrived

Although the design predates the Vans series, there was not a “quick build” kit for the Thorp. Thorp Central now provides excellent support for the Thorp Community. Many of the large items are relatively easy to get. Others must be fabricated using other builders' ideas found on the Thorp Forum.

N218TH is unique in that I selected a Superior Cold Air induction system for my Lycoming XIO-320-B1A. I sent the engine to JB Engines for overhaul prior to aircraft completion. It now has 9:1 compression ratio pistons. The idea being that I can get the power of an O-360 at the weight of an O-320. The cross over exhaust system that is commercially available for Thorps cross in front of the fuel servo for the fuel injection. Because of this, the crossover exhaust system would not work for TH.

XIO-320B1A with 4 into 1 exhaust system
XIO-320B1A with 4 into 1 exhaust system

A custom exhaust was the only way to go on this. I have equal length pipes going into a common collector. I wasn’t sure what to expect with regard to how the engine would sound. Most Thorps I have heard with the crossover system have a distinct pop pop sound as the airplane goes by. This 4:1 seems to smooth the exhaust pulses and the exhaust sound is actually less than the crossover exhaust. As I prefer to not have a scoop, I have a NACA duct on the bottom of the lower cowl for intake air.

For propellers- N45881 was equipped with a Lycoming O-360 and Hartzell CS prop. This combination required 13lbs of lead in the aft fuselage for weight and balance. By selecting an IO-320, I saved 15 lbs of engine weight. I also have a Sky TeK starter and B&C alternator. The big weight savings came with the selection of GT propeller blades. These are designed to fit in the Hartzell hub but weigh 22 lbs less than the aluminum Hartzell blades. I have calculated that because of this, I require no lead in the tail.

The design goal was to have the airplane weigh about 925lbs empty. Actual weight after paint is 940lbs empty.

In thinking about how to paint the airplane, I could have used the scheme my father came up with for N45881; however, my oldest daughter is a graphic art and design major. I handed her a 3D drawing and she designed the paint scheme for TH.

There are 3 generations of input for this airplane. My father, who was passionate about the design, my reinvolvement after numerous years away from the Thorp Community and my daughter’s input on the paint scheme.

First rollout of 218TH, but before the cowling was reinstalled
First rollout of 218TH, but before the cowling was reinstalled

Equipment list

2019 Thorp T-18

  • Lycoming XIO-320B1A (178hp)

  • Hartzell hub, GT composite blades

  • Sky TeK starter

  • B&C vacuum pad mount 20 amp alternator

  • Grand Rapids Sport EX 7 efis

  • GRT autopilot servos

  • Garmin GTR-200 comm

  • Garmin GTX-327 transponder

  • Echo UAT ADSb

  • 406 ELT

  • Electric elevator trim on stick

  • Electric flaps on stick

  • Electric aileron trim on stick

  • Pressure recovery wheel pants

  • Oregon aero seats and side panels

  • Infinity stick grip

Empty weight: 940 lbs

Gross weight: 1650 lbs

Useful: 710 lbs

Luggage: 90 lbs

It takes a team

From left to right - Rick Hills, Tom Hills, Doug Vayda, Terry Hagle
From left to right - Rick Hills, Tom Hills, Doug Vayda, Terry Hagle

The acknowledgement of friends cannot be overlooked on this build. I had great help from Rick Hills and his Brother Tom Hills. Rick is an electrical engineer and responsible for the workings of the Instrument panel. Tom is the fiberglass and epoxy guru. Changes were made to the cowl for form and function. I learned an immeasurable amount from both these guys. Additionally, Doug Vayda was responsible for the first flight of 218TH as well as application of the Glasurit Paint and Clear on 218TH. The process took all four of us and a great time was had by all.

The finished product is an awesome flying Thorp T-18.

Original stabilator counter balance weights
Original stabilator counter balance weights

victory flight to Oshkosh

I graduated from Embry Riddle in April of 1983. That was also the year that I would get to fly Dad’s Thorp to Oshkosh. Unfortunately, those plans changed when a brake failure caused some damage to an outer wing panel. And there was not enough time to make the repair and get the airplane to Oshkosh. The consolation was that my ride to Oshkosh was Dad’s North American T-28A. Again, that’s another story for another time.

So now here I am, in a Thorp that I put together completing a goal of flying a Thorp to Oshkosh. A goal that was planned to happen a bunch of years ago finally checked off the bucket list.

If you have any questions about building a Thorp T-18, leave a comment below or contact us.

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