Author: B. Hager
Edition: Model Aviation - 1987/08
Page Numbers: 54, 154
,

Radio Control: Pylon Racing

By Bill Hager

BY NOW all of you should have some races under your belts. Some of you are getting ready for the '87 Nats to be held at Lincoln Municipal Airport, Lincoln, NE on July 11–19.

This year an added Q500 event should prove interesting. For those who didn't like flying into the sun in the evening, we will be flying in the mornings. Anyway, with all of the interest this year, we should have a really good turnout.

Whenever I can, I try to pass on any items of information which might be of help to the racer. If you have anything which might interest other fliers, send it to me and I will put it here in the column.

Supertigre/Como .40 engine information

John Kilsdonk reports on the 1987 Supertigre/Como .40 changes:

"After almost seven years without any major changes, the 1987 model Supertigre S-40 has undergone some changes. I assume that these changes are similar on the Como .40, also.

"External appearance has changed due to a different bead-blasting of the crankcase. The engines have a new carburetor body that is about .200 in. wider and has a correspondingly longer rotating barrel. However, the venturi diameter is unchanged. The carburetor also has the rubber boot on the right side, as introduced on other carburetors a year or so ago. The other obvious external change is the new 'swing-arm,' two-piece muffler.

"Internally, the engines have some major changes. They feature dramatically reduced exhaust timing and slightly reduced bypass and crankshaft timing. After testing one of these engines, it appears that the changes may be geared toward the sport flier who might want to run a larger prop. Another, less obvious conclusion might be that they tried to make the engine more like the Rossi. This is just speculation on my part, but the apparent limitation in matching Rossi's bypass timing might have been caused by the crankcase casting."

Engine comparison (dimensions and timings)

  • Exhaust Timing — Old S-40: 157°; '87 S-40: 145°; Rossi .40: 147°
  • Bypass Timing — Old S-40: 124°; '87 S-40: 120°; Rossi .40: 130°
  • Boost Port Timing — Old S-40: 110°; '87 S-40: 110°; Rossi .40: 130°
  • Crank Open — Old S-40: 44° ABC; '87 S-40: 39° ABC; Rossi .40: 39° ABC
  • Crank Closed — Old S-40: 60° ATC; '87 S-40: 51° ATC; Rossi .40: 52° ATC
  • Total Crank Duration — Old S-40: 196°; '87 S-40: 193°; Rossi .40: 192°
  • Carb Bore — Old S-40: .350 in.; '87 S-40: .350 in.; Rossi .40: .300 in.
  • Muffler Outlet Diameter — Old S-40: .300 in.; '87 S-40: .300 in.; Rossi .40: .300 in.
  • Muffler Volume — Old S-40: 86–94 cc; '87 S-40: 86–94 cc; Rossi .40: 145–147 cc

Muffler and performance tests

"The following performance tests were run with the new 'swing-arm' muffler to evaluate its characteristics. The muffler was tested both with a new S-40 and with an older Como .40. In each case, rpm is given as rpm/1,000."

Test No. 1 — Muffler "exit" from closest position (in.). Positions: 0, 1, 1 1/4 (rpm in thousands)

  • New ST S-40
  • Prop A: 174 / 174 / 174
  • Prop B: 161 / 162 / 173
  • Prop C: 143 / 142 / 142
  • Old Como .40-S
  • Prop A: 178 / 175 / 174
  • Prop B: 160 / 163 / 162
  • Prop C: 140 / 143 / 142

"The following test was run to evaluate the performance of the old muffler and to evaluate the new ST S-40 in comparison with the older Como .40-S. Once again, engine rpm is given as rpm/1,000 and is listed as ST/Como."

Test No. 2

  • Prop A: 177 / 184 (ST/Como)
  • Prop B: 164 / 164 (ST/Como)
  • Prop C: 146 / 140 (ST/Como)

"Next test was run to investigate the effects of the Rossi muffler and to compare the new ST S-40 with the Rossi. Engine rpm is rpm/1,000 and is listed as ST/Rossi."

Test No. 3

  • Prop A: 173 / 191 (ST/Rossi)
  • Prop B: 160 / 173 (ST/Rossi)
  • Prop C: 140 / 160 (ST/Rossi)

Conclusions

  • The new (standard) ST/Como muffler is not tuneable (Test No. 1).
  • The performance of the new ST/Como engines is essentially the same as previous models (Tests Nos. 1 and 2).
  • The new ST/Como "swing-arm" muffler is roughly equal to the previous standard muffler (Tests Nos. 1 and 2).
  • The Rossi muffler does not work as well as the stock ST muffler on the ST (Tests Nos. 2 and 3).
  • Despite the timing changes made to approximate Rossi timing in the new ST/Como .40s, the Rossi still appears to hold a decided advantage (Test No. 3).

Editor's note

Please remember that these tests were all run using only one sample of each engine. It is the experience of many modelers that performance can vary widely between different samples of engines of the same manufacturer and model. Time will tell whether John Kilsdonk's test results are statistically meaningful. (RMcM)

Engine cleaning and break-in

Preparation

  • Mount engine in Q500 aircraft, preferably using a metal engine mount.
  • Affix 9 x 6 Master airscrew prop.
  • Open carburetor idle screw two turns (from present position).
  • Open main needle valve five turns.

Cleaning steps

  1. Submerge the front housing and swish the crankshaft while listening/feeling for rough spots — this may indicate the presence of metal particles. Repeat the process until the crankshaft spins freely.
  2. Apply Marvel Oil liberally to bed the rings and crankshaft.
  3. Do the same for all other parts.
  4. Reassemble the engine — head-bolt torque should be even.
  5. From this point onward, the engine must be kept clean (wrap in cotton).

Ground break-in procedure

  • If possible, run no muffler.
  • Run the engine very rich for one minute, then hit it cool; repeat this process three more times. (The engine is running cool if you can hold the cylinder head while it's running.)

In-air break-in procedure

  • Install the muffler.
  • Be sure the engine is set very rich (but still flyable). Two-minute flights should kill the engine due to the overly rich idle setting.
  • Fly the engine for three or four flights with shallow climbs and dives only, and mostly flat, gentle turns.
  • After four or five flights, begin doing large reverse Cubans: climb at 20°, roll inverted, large half inside loop, then continue 20° climb in the opposite direction, and so on. Continue the process, gradually leaning out the needle and adding stress to flight maneuvers.
  • After 12 to 15 flights (four to five minutes per flight), the engine should be race-ready.

Keys to success

  • 1) Cleanliness
  • 2) Patience
  • 3) A little luck

Hey, gang! It really works.

Q500 kits and sources

  • Thunder Q-11 — Paul's Flying Stuff, P.O. Box 121, Escondido, CA 92025; phone (619) 743-5458.
  • China Clipper — Model Tech (available in hobby stores).
  • Talon — California Speed Pros, 32221 Alipaz, P.O. Box 15, San Juan Capistrano, CA 92675; phone (714) 661-7430.
  • Spickler — Spickler Models (available in hobby stores).
  • Texas Outlaw — Dixon Aircraft, 4101 Lamar, Houston, TX 77026; phone (713) 661-5458.
  • Scat Cat — Flite Line Models (available in hobby stores).
  • Yellow Jacket — Mills Airplane Models, 2688 Hambleton, Rica, MD 21140; phone (301) 956-3308.

See you at the races.

Bill Hager 706 Glen Haven Dr. Conroe, TX 77385

Transcribed from original scans by AI. Minor OCR errors may remain.