TOW PLANE CG
Reprinted from ISSA website
There was a recent thread about optimizing the CG of a tow plane for aero-tow. The ISSA Pegasus with the Brison 5.8 started out extremely nose heavy, but towed everything just fine. The airplane was a little tough to land, as the nose dropped when the power came off, even with flaps extended. That had nothing to do with the design of the Pegasus, however, but is a common trait of any nose heavy power plane. Tony Elliot’s 3W 120 powered Peg, which I spent the day flying at Visalia, however, landed like a trainer – and didn’t have flaps. The difference was in the CG – Tony’s was much further rearward than the ISSA’s tug, and it also towed the big stuff just fine. When the ISSA Brison 5.8 was replaced with a Desert Aircraft DA-100, almost three pounds of engine weight was taken out of the nose. Immediately the airplane flew better, and landed very much like Tony’s. The CG was about 40% of the wing chord, (waaay back) but the airplane remained predictable and stable. At 40% we towed 4-meter “slippers” with no problem. But the larger sailplanes create far greater loads on the tow plane, and 40% is probably too far rearward for good tow stability, so we need to add some weight. (All the batteries are already forward). The consensus from the more experienced tow pilots is that a forward CG helps under tow. And we know from our experience that even a really forward CG tows fine, it just requires a little finesse when landing. So with those ideas in mind, we’ll move the current CG of the Pegasus forward while trying to retain good landing characteristics.
