Sm Tall alk H
ere we are right in the middle of windy season in the desert south west, so once again, shop time far outweighs air time. Hopefully the season won’t last more than the usual six weeks or so and blow on through, but until then, it looks like we’ll be doing the dawn pa- trol and getting what flying in that we can before the gale ensues.
Getting things in balance As long as we’re on the subject of shop time, one of the most important facets of set- ting up a new model is getting the c.g. (Cen- ter of Gravity), or as it were, balance point right. I can tell you from experience that there’s nothing on this planet more exciting than tying into a small, tail heavy model. It’s been said that “a nose heavy model will fly poorly, but a tail heavy model will only fly once.” Believe me, that is no doubt a true statement.
So how do you set the c.g.? Well, there are several ways, but first you need to deter- mine where the c.g. needs to be. On most models 30–32% works fine. However, the heavier the wing loading the less aft c.g. tol- erant the model will generally be, so it’s best to opt for the forward side of the range to start.
The procedure for finding the location varies from airplane to airplane depending on the wing configuration. Constant chord wings are easy; it’s simply the chord × .30– .32 to get the dimension back from the lead- ing edge to the balance point. Figuring the location for tapered wings, biplanes, and sesquiplanes can get a little in depth, too much so to go into it here, but generally speaking, the recommended c.g. will be shown on the plans, or the case of ARFs, in the instructions. Again, for the early test flights, a little forward is better than a little aft.
The method for actually setting up the balance is to first mark the location of the c.g. on the wing itself. Simply measure back from the leading edge and mark the location PHOTO: CHRIS STARLEAF
by pat tritle You can reach Pat Tritle at 10313 Snowheights NE, Albuquerque, NM 87112 or via e-mail at
patscustommodels@aol.com
PHOTO: PHILLIP AGNOLETTO
Phillip Agnoletto built his Ryan Navionfrom enlarged Earl Stahl plans and converted the model to 4-channel R/C. Stahl’s freeflight models always fly well, so using his basic designs will pretty well guarantee Phillip will have a great flying R/C model.
with a dot on the wing. Then place your fin- ger tips on the dots and lift the model off the table. If the nose is low, it’s nose heavy. If the tail is low, it’s tail heavy. Wet fueled models should be balanced with the fuel tank empty. Then to get a level balance, add either nose or tail weight as required. Electric powered models work the same way, but the “fuel tank” weighs the same full or empty, so you can shift the battery loca- tion to best accommodate the balance point. Now, as a point of interest, to determine about where the c.g. is going to end up, when you do that final “ready to fly less cover” dry run, set the c.g. 10% forward of the recom- mended location using battery placement so
you can work out the access as needed before the model is covered. Then once the cover goes on, the weight of the cover will have you pretty close, if not spot on where the c.g. is supposed to be.
And there’s one last thing, when setting a high wing monoplane the model should be right side up. A biplane should be set up us- ing the top wing as the point of contact. A low wing model, on the other hand, should be balanced inverted so you get the same pendulum effect as you will on a high wing or biplane configuration. Then once the model is set up, changes can be made during flight trimming to get the optimal point. However, when changes are made, make
PHOTO: RALPH SNOW
Chris Starleaf, who has mastered the art of large freeflight models, is converting the 60-inch span DC-6 (at left) from R/C to rubber powered freeflight. And having seen what Chris can do, there’s no doubt that the DC-6 will be a winner too. Ralph Snow has done a terrific job on his Westland Whirlwind (above) R/C conversion built from enlarged Cleveland plans and finished in Doculam and acrylic colors.
56 APRIL 2013
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