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Had a call last night from a discouraged Thorp owner (new owner). Seemed he was not getting near the Airspeed he was expecting. Turned out he had removed the gear fairings for ease of maintenance.
Remember fellas those gear fairings are not for looks, they add 8-10 mph in cruise, next to a flat plate there aren't many things less aerodynamic than a tube ...
Here's an excerpt from SA's 1976 article on T-18 cruise performance ...
"Relatively clean, modern versions of the T-18, such as Roemer's N18TT, will indicate better than 210 mph at sea level with 180 horsepower, while a good T-18 less some fairings, such as Henderson's N600HH, will indicate more than 195 mph. Under the same conditions, the original "basic" T-18 without pressure cowl or canopy would indicate 155 mph and the intermediate "sport" would indicate 188. Our tests show that these performance differences can be accounted for by both streamlining and engine details. The canopy and pressure cowl add about 33 mph. Landing gear tube fairings raise the speed by 8-10 mph, and wheel pants, gear tube-wheel pant junction fairings, and the tail wheel spring fairing each account for 2-4 mph. The use of lower aileron gap covers adds about 3 mph and down pointing exhaust pipes cost 3 mph. The use of a wooden propeller also costs 3 or 4 mph. Together the stated differences in 600HH and 18TT account for about 10-13 mph of a 15 mph plus difference in sea level top speed with 180 HP input. The remainder can be attributed to smaller details such as the canopy windshield junction, epoxy filled rivets, etc. In closing, we should point out that any small improvements in air frame streamlining have pronounced effects in fuel economy, and operating costs as well as on cruise speed. For the T-18 an increase of only 10 mph in top speed is the equivalent of nearly 25 extra horsepower
_________________
Lee Walton
Houston, TX
N51863,N118LW
KEFD
Last edited by Anonymous on Tue Aug 09, 2011 8:27 am, edited 1 time in total.
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