I'm posting this on behalf of Tom Hunter ...
From: Tom Hunter
Where: Somewhere in Thailand
Subject: Thorp postings re: ways to go faster in a Thorp.
I notice that a number of Thorp owners are questioning ways to go faster In a Thorp.
The following is a review of the various steps I made in that pursuit.
1. Complete new wet wing using the Lyle Trusty wing as a model. Lyle lent me his master rib profile and I used it to make the tooling necessary to make a new wing. This entailed making all new ribs since the entire profile is different than the front and rear ribs in either the original Thorp wing or the modified Sunderland wing. By making the center inner D section wet, the total fuel load was increased to 52 gal.
a. The skins were modified so that they covered the aileron and flap "gaps" on the bottom surface of the wing. It was with a certain trepidation that I did that to the flaps since it would seem that the Fowler functionality would be diminished if you add these gap seals. I was very pleased to discover that the flaps were still extremely effective.
b. The main spar to skin joint was " adjusted" so that there is no disruption in air flow. You can check to see if your wing has a "bump" span wise at the main spar to skin joint. This is common with the Thorp structure if the builder did not take steps to eliminate it in construction. The reason for removing this bump is to reduce the drag of the wing.
c. Wing tips that "blend" into the modified airfoil.
d. The entire top of the wing and the bottom to the spar filled and blended so that there is no distortion when the wing is "at rest". Due to the light structure of the Thorp wing, one wonders when flying and noticing the continual deformation of the outboard panels how worth while the time and labor of rivet filling is in a practical sense.
e. Roll trim tab within aileron. The straightness of any wing can be intuitively verified by the amount of roll trim needed to maintain a wings level attitude at cruise speed. However, if you are still relying on the adjustable left flap for roll trim, you are tossing away some cruise speed due to extra drag with a flap partially deployed. Note, in my "new" wing, the flap was reflexed in relationship to its T.E. position on the standard or Sunderland wing.
f. Custom wrap around wing to fuselage fairing. This was added after the plane was flown. No measurable increase in cruise could be noted. It is possible that in some unusual attitudes that fairing could have positive benefits other than cosmetic.
That is about the sum of the changes to the wing.
2. Fuselage:
The side skins were changed to .032. Care was taken to achieve a smooth intersection between the windscreen and the canopy. I was fortunate to enlist the talent of a former Lockheed experimental shop worker who had worked on the P-80 (T-33) canopy fit and made the assembly line changes to solve in field issues. It took approx. 3 months of work to complete the fit of the canopy.
Fit of windshield. It is probably true that the best fit of windscreen is putting the glass UNDER the upturned lip on the forward skin. However, for ease of removal this was not done. It was deemed that quick removal of the windscreen would be of benefit in maintenance of instrument panel.
The fuselage rivets were filled back to the pilot station. A few words on body filler and the Thorp. I used only the best quality auto body filler. While several people informed me that it would crack and break off,
(especially on the wing) no such thing occurred. Of course if you do not follow good practices in application your results may vary.
The leaf spring and tail wheel were changed to a Trusty designed rod spring. The Aviation Products 6 inch tail wheel was faired in a split tail wheel pant with the general profile of the pressure recovery RV style main wheel pants. A number of these small pants are flying on T-18's and RV's.
The main wheel pants on the T-18 were originally from Rudy Adler. I worked on them to eliminate any surface waviness. The brake fairings were old parts as well. Eventually I made new female molds for slightly larger brake fairings so I could house Cleveland 500X 5 Heavy duty wheels and brakes. These fairings are made in a two part mold and are formed with no seam. The builder adds the split so that the fairings can be fit very tightly to your pants (if your pants are the original profile). Since the plane was tested both without and with the wheel pants and brake fairings comparable speeds could be determined. These fairings were originally molded with Carbon Fiber, but that was changed since Carbon Fiber is so difficult to cut and fit.
Since I was never pleased with my internal induction system to the IO-320, I designed a new system to take advantage of Ram Air as well as create a direct induction path to the Servo with a High Capacity Filter. The result of that effort can be seen flying on Jonathan Levi's T-18 as well as several T-18's in Australia and an RV-7 in San Diego. I happily noted an increase in inches of mercury and less "stumbling" of the engine on approaches.
Summary:
Reducing drag on the T-18 can give you long term rewards. It can allow you to cruise the same speed at less horsepower thus allowing your motor to work less and effectively extend its life span. Also, lowering drag can allow you to cruise climb at a higher speed. It will also allow your decent to land to be at a lower throttle setting and higher speed.
I still supply fiberglass parts for the following applications:
!. Tail wheel pant for the Aviation Products 6 inch tail wheel.
2. Brake Fairings manufactured in fiberglass.
3. Air scoop for an injected 0-290. 320 or 360 Lycoming.
4. Drop tanks to extend your range with an additional 10 gals of fuel. See Vimeo video:
http://vimeo.com/2985919 I can be reached at
thunter007007@yahoo.com or 805-769-2047 my Skype number.
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My main goal in flying is how fast I fly over the ground ! 
My fastest GS was 698 kts ! BOOM ! OH MY ! 
The only thing that saved me was the $60.00 HP hand held calculator my Mom bought me to take to boot camp . A hand held calculator that solved math problems was big News back in 1976 ! 