cmbined displacement on multiengine planes

[George Waters]

What is the total disp allowed on a multiengine stunt ship? I have two 40's on the A26 and was curious if one could use two 46's or would that be too large. I thought .91 was the limit but I was told that new rules are in place for both disp and lines sizes.  George

[Steve Helmick]

The new limit is 15cc's (or about .915 cu. in. ). Two .46's would be very close to, or over, the limit. It would take some careful measuring and calculating, to determine if those two .46's would be legal or not.

Most engine makers exaggerate a little, (no offense, Bill) but then there's the OS ".21FP" situation.  I'd say that if your two .40's aren't enough power, then you have the wrong two .40's on your twin. Most .40's are slightly over .40 Cu. In., because they're a metric size (6.5cc's). Most .36's are over .36 (.365 cu.in.) for the same reason. I believe .46's are 7.5cc's (more or less), so they might just be legal, since 7.5 x 2 = 15.

Some of this problem is caused by the simple fact that sport fliers don't care about rules (understandable, but they "drive" the market, being a huge part of it), plus the ever popular marketing ploy of "bigger is better".  I'd look at the manufacturer's spec sheets. You might find them online. If you find the mfg.'s spec sheet for the engines you want to use, plan on bringing one along to contests. You'll also need to bring .021" (braided) flying cables. Yikes!              Steve

[Paul Smith]

Tower Hobbies carries detailed spec sheets for the engines they sell.

LA 46 = .467 cubic inches, or in the French unit of measure, 7.64 cc.

Is 15.28 over or under 15?

You fly one of these brutes on .018" lines, would you still feel safe flying TWO of them on the same lines?

You could use two LA 25's and safely fly the plane on .018"'s.