a set. It’s still a good idea to loosen the mount screws if the plane is going to be sit- ting more than overnight, but forgetting is unlikely to cause problems. That was the tough part. The rest of the
mods are fairly straightforward. The 25 en- gine is 1–1.5 ounces heavier than an F2D engine. Most folks handle this by fitting a large stabilator made out of fairly heavy, ta- pered, ¼-inch balsa sheet. For starters try a stab 15 inches span and 2.5 inches wide. Ta- per the leading edge outboard of the hinges back about ¾ inch at the tips. This works okay, but is not ideal. The larger stab puts more load on the pushrod so the stock bell- crank may run out of leverage when the plane is up high and heading into the wind. If there is room, put in as large a bellcrank
as you can. Maybe even install a platform sticking into the left wing and mount a 3- inch bellcrank or mount it on top of the wing with a bolt going all the way through the center rib. You just have to look at how much wood, and what kind is used to figure out if it will be strong enough and where it needs strengthening. The next step is to move the leadout
Stock F2D planes can be used with minor mods (above). Depending on the exact speed limit a piece of 1⁄4-inch bladder tubing over the intake, maybe a piece of 5⁄32-inch or 1⁄8-inch brass tube wired in a plastic prop like the 6.5–3.5-inch Master Airscrew Scimitar prop will do the job. Watch out for overcontrol. With long lines and low wing loading an F2D plane can turn considerably tighter than you may want at times! One way to convert an F2D to Speed Limit (below). This changeover simply used the .25 engine and a larger stab. It’s not perfect, but flew close to the best. Moving the leadouts back a half-inch helped a lot when Phil finally did it. Add some to the wing tips to get 48-inch span and a half-inch strip to the trailing edge for more area and you’ll have a real .25 powered Speed Limit ship. The plane has to be designed to fulfill the job it has to do.
guides back. Longer lines make the plane less stable and have more weight and drag. As a ballpark estimate, switching from 52.25-foot lines on a 14-ounce plane to 60- foot.×.018 lines on a 17-ounce plane means the leadout guides have to move back ~1⁄2 inch. The midpoint between the leadout guides should be about 1.8 inches behind the center of gravity (c.g.). Another tack on using F2D for Speed Lim-
it is to go with a regular F2D engine. This works depending on where you fly. The AMA rules allow .15 engines to fly on .015- inch lines. Some CDs don’t go for this and re- quire .018 lines for everything. If this is the case, don’t bother. The plane is just too light, going too slow. The extra weight of the .018 lines will swing the plane around erratical- ly in tight maneuvers. It’s fairly easy to slow the plane down on .015 lines. The simplest is to use a 7–3 APC type propeller. Restrict the intake with a short piece of 1⁄4-
inch bladder tubing pushed onto the ven- turi. Restrict it further by wiring a short piece of 1⁄8-inch brass tube in the rubber tub- ing. Be sure to flare the tubing a bit so it can’t get sucked down into the engine. This usually is enough to get the speed down to 75 mph. Due to the light weight of the plane the leadouts should be moved back to about 21⁄8 inches behind the c.g. It’s also a good idea to add some offset to the engine. Mill or file the mounts with a taper of about 1⁄16 inch along a stretch of 1.5 inches. This will help guarantee the plane stays out where it belongs. But in the last analysis, the best way to
adapt an F2D ship to Speed Limit is to fig- ure out how to fit it with a 5–6 inch boom and a 25–30 square inch stabilator, along with wing tip weight, engine offset, and get- ting the engine mount fit properly.
FLYING MODELS 45
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