Skyscraper (oz403)

About this Plan

Skyscraper. Control line stunt model. Wingspan 60 in, for .45 power.

Quote: "Introducing to you the 'Skyscraper' a 60 inch .45 powered stunter plane. Trends in hobbies do change and Stunt had a major one in 1949. I was connected with that change and in the past few years, have thought a .45 stunter would be still better. With the advent of the .45 RC engine designed by Clarence Lee and the fact that Lew MacFarland won in 1961 with a .45 powered Shark (oz4557) design, also, Brian Horrocks's Australian design, started me seriously considering BIG STUNT.

What I had in mind was to have a model fly slower than a .35 as it will only slow down so far, to fly any slower a pilot really would have to work. A model should fly clean through all the stunts without hesitation, therefore a .45 running at full 4-cycle would fly slower and still have reserve power to fly clean stunts. Also, a .45 running at full 4-cycle should run at constant speed at all times going up or down. This constant speed will improve flying as timing is always the same when turning the model. So with this in mind, started to design the model and must say that, of all the models I have designed, more drawing and redrawing as well as figuring were needed to produce this one design.

I wanted this one to really work so put in everything I knew that had worked in the past, checked it carefully for warps, balance and lead out yaw. I started flying the model, carefully working up to doing the full pattern. looking for any weakness in design, and bad characteristics and found none. I put the model near the 70 ft limit and went to regulation .018 line. Started flying again and brough the engine up to a little taster 4-cycle extra line diameter and length made hardly any difference in line pull and performance. I have flown the ship quite a number of flights now and have found it to be what I was looking for in BIG STUNT. Longer lines and constant speed have resulted in precise stunts. It does not over control and doesn't jump like a .35 model, all movements are precise. Even after not flying for awhile, then flying again. I noticed that if you know how to stunt very little practice is necessary to get hack in the groove. Once you have flown slower and have thoroughly taken the model through all stunts, your practice time can be cut.

This model is equipped with differential flaps. I have had this idea for sometime now, experimenting with every model I have built since the idea first came to mind. Some modelers have gone along with the idea and some have not. I first put it into the Thunderbird (oz6238). I was out of town at the time the T-bird plans were finalized and the way l had hooked up my controls and the way the plans for the kit were drawn were quite different. But even my method in the beginning was not as good as it might have been. After some criticism as to why it wouldn't work, I began looking for a solution, for in my opinion, the idea is still an excellent one.

The hook-up method was what was wrong. I had put my flap control horns close together and this helped my models. The main trouble was the rotation of the bellcrank which cut down the inboard flap travel, therefore destroying the desired action. So, I turned the control rods to flaps in aft position and I have no trouble now with the rotation of the bellcrank. I have also been experimenting with just how much differential can be used. I find that 3/32 difference between holes is too much. It causes the inboard wing to jump up when full control is suddenly applied. If a fast 35 powered model is used 1/32 is just right and also for a slow .45 powered model.

With differential flaps you can feel the pull change as you do horizontal eights. It will tighten as you turn both ends of the eights. This system also allows the lead out position on the wing to be moved forward. Since we now have differential flaps helping to hold the model out we can cut down the yaw which makes for cleaner stunts and also helps keep the speed up in corners. Doing two square eights is hard on a model as well as on the engine as it must keep its power and speed to carry on through the stunt..."

Update 15/01/2019: Added article, thanks to JMP_blackfoot.

Update 11/1/2023: Replaced the article with a clearer copy, thanks to Mike Foster.

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