I am about to begin a project of converting a 4 Star 40 into an Air Tractor 502 crop duster. I have had one other 4*40 (stock) and it flew like a dream. I have been more than enthused with Air Tractors since I was a kid and have always wanted to build a scale R/C version of one. I have seen where a gentleman on this board converted a 4*120 into an Air Tractor 802 and it looks very nice. Now, onto my questions. I have acquired three view drawings with dimensions from Air Tractor's website ( www.airtractor.com ) and have taken measurements form my stock 4* and started planning out what needs to happen to make the plane scale.(BTW, I am going to start with an entirely new kit, not going to try and hack up the already built one.) First of all, the wing chord on the Full Scale is 6' with a 50' span, so that means that I need to lengthen the wing from the stock 59.75" to a whopping 83" to make the correct proportions. The stock model also weighs approx. 4.75lbs and I estimate that mine (with the modifications) will weigh around 6lbs. at the very most. I have figured the wing loading with those numbers and it will actually be about 3oz./sf lower than the stock configuration. The stock plane calls for a .30 to a .40 2-stroke and I plan to power mine with an .O.S. .46SF. Now that seems like a big plane (83") to pull with a .46, but it still will only weigh in the neighborhood of 6lbs and the span itself is really the only dimension that is getting enlarged to this extent. Do you guys think that the .46 with a 3-blade prop will be up to the task? I'm not looking for a speed demon here, just a scale flying plane. Also, can you forsee any potential problems with the flight characteristics by extending the length of the wings this much? The only other modifications that will be needed are some changes to the shape of the horiz./vert. stabs and the shape of the nose on the fuse. I would love to hear any advice that you guys have for me or any problems that you think I may encounter on this project based on my plans. Any help would be greatly appreciated. Thanks,

Zach

Zach,

I converted a 4* 120 to a sorta scale Thrush S2R in 1996 to use as a practice plane for Top Gun. I wanted an airplane about the right size and profile although the cross section and power-to-weight were way out of scale with a Saito 1.50. The way I accomplished a reasonable chord to span ratio was to leave off the strip ailerons and build "scale" barn door ailerons and flaps into the rear of the wing. This was a fairly simple mod by just trimming off the ribs and capping them with subspars to hinge to. I doubt you will be able to make a very accurate scale plane out of the rest of the kit either considering the width and cross section of the fuselage. You may want to check the cropduster r/c link- http://www.rcuniverse.com/forum/m_16...mpage_4/tm.htm
elsewhere in this forum for other plans and kits that are available.

David Hayes

I feel very privelaged to get a reply from the "master of R/C dusters". I have admired your planes for years, Mr. Hayes. I hear exactly what you are saying about the 4* probably not turning out truly to scale, but I just don't believe that I have the ability to design and build one from the ground up. I would love to buy the kit that Duane Habets has available for the AT502, but I figure that I would end up with over a thousand dollars invested in it before all was said and done, and that's just not in the cards for me at the moment! So, I guess the only option that I have left is to bash a 4* into a "somewhat scale" AT. As I said, I would love to be able to design and build my own, but I just don't have the building knowledge and experience to take on a project like that. I even thought of resizing the wing on the 4* and building my own fuse from scratch, but I am afraid that I may not get the incidence and all the geometry correct on the tail. With the ideas that I have to "bash" the 4*, I won't be fooling with any of the angles of incedence or geometry, just resizing the wings and reshaping the tail feathers and fuse a bit. I think that's about all that my skill level will allow at this time! Thanks again for the reply Mr. Hayes.

Zach Jaynes