Jumby

What do you all think about the new Scratch built plane in the newest Model Aircraft magazine called the Clean Cut. Looks like a fun winter project? Opinions?

--Eric

Walter D

My Feedback: (16)

What!? Nobody answered your question yet, they must be very busy flying, it is almost the end of the season for most of the people.
Anyway, yes, I too think the Clean Cut, design of Dick Sarpolus is a good, sound design, the only thing I believe is a bit out of place is the canopy, a bit too big, it would however help it when doing kife edge flying, but some allowances could be made there.
This man has been in this hobby for a very long time, and he's always provided us with very good designs, easy to scratch build, always with the type of construction that anyone can tackle succesfully, wing ribs with alignment tabs, straight forward construction methods, this type of building and design are great for those new in the hobby that would like to get involved in scale scratch building and design, definetely a building project that would be fun from beginning to end, it takes a lot of planning and work to bring designs like this to life, so let's all get together and say: Thank you Mr. Sarpolus!

LLRCFlyer

The Clean Cut design was designed by Dick Sarpolus and plans were issued in 2002. It is a sport pattern style aircraft and spans 90 inches. I finished one in August 2022 that had been started about 20 years ago by my friend Clyde. At some point he had purchased a beautiful new Brison BA32 engine for it (3.2 cubic inch or about 53 cc) to power the Clean Cut. He then developed macular degeneration and lost sight to the point he could not see to fly and abandoned the project. When I was visiting him one day he asked if I would like to finish the project. I agreed it would be a fun project and then proceeded to finish it over the course of a year. Clyde did make a switch to a fixed landing gear for grass runways rather than install retracts. The finished Clean Cut weighs in at 20 pounds fully fueled and ready to fly with redundant batteries. This yields a wing loading of 33 ounces per square foot, which is not bad for a large thick airfoil. It actually slows up very well for gentle landings with no tendency to tip stall. The Brison BA32 engine is fitted with a Bisson Custom Pitts style muffler and a Zoar 20x10 wood propeller and will pull the Clean Cut straight up as far as I care to take it. Flying characteristics remind me of a .60 size Kaos pattern plane. It is smooth on the controls, tracks well and will easily do any of the full advanced pattern routines. It is not a 3D plane, but is a very fun and relaxing sport pattern aircraft. Dick Sarpolus used a Quadra engine on his original version. The Brison BA32 must be considerably lighter than the Quadra because I had to move the Brison forward 4.25 inches of the firewall in order to get it to balance. If you can't find a Brison BA32, a 40-50 cc engine should work well. Just find something that produces over 20 pounds of thrust. I think it should fly very nicely with a DLE 40 twin.

LLRCFlyer

Here is the Clean Cut I completed in August 2022. Powered with a Brison 3.2

carlgrover

Your pic did not show up. The Clean Cut looks a whole lot like the Prime Cut which is a plane I've always wanted to build. It looks like the major differences are the retracts and possibly only the foam construction in the Prime Cut.

Carl

LLRCFlyer

Carl,

I just looked up the Prime Cut plans on the AMA Plans Service. The two-sheet plans set is still available for $24.00, same as for the Clean Cut. I could not determine the wing span from the small preview drawings, but from the scale ruler, it looks like 80-85 inches versus 90 inches for the Clean Cut. The Prime Cut calls for a 35-40 cc Quadra whereas the Clean Cut calls for a 50 cc Quadra. The main differences I observed are: The Clean Cut was designed for retracts; The Clean Cut uses all built up surfaces instead of foam; The rudder and elevator are a larger percentage on the Clean Cut; The Prime Cut fuselage is wider percentage wise, the Clean Cut has flat tail surfaces whereas the Prime Cut has airfoil shaped tail surfaces; The tail surface outlines on the Clean Cut more resemble those of an Extra 300; The cowl shapes are different.

My Clean Cut uses the same type of fixed landing gear as the Prime Cut. This gear works very well on my grass runway. For this type of airplane, I think retracts would just add unnecessary weight with negligible gains in performance. I suspect the Prime Cut would fly very well. If it flies anything like my Clean Cut, it would definitely be worth the effort to built it. I also suspect the Prime Cut will have the same center of gravity issue I experienced with my Clean Cut. The old Quadra engines made 20+ years ago used a very heavy magneto flywheel which made the engine total weight much heavier than today's lighter engines equipped with electronic ignitions. Consequently, the plane will probably be tail heavy if not modified. I had to use 4.25 inch long engine mount stand-offs with the Brison 3.2 cubic inch engine to get it to balance. If a modern 35 cc engine like a DLE is to be used, I suspect the firewall will need to be moved forward significantly to get it to balance. This is also important because the specified fiberglass cowl would probably be too short to reach the firewall once the engine is mounted far enough forward to get the plane to balance. If I were to build the Prime Cut, I would first determine the weights of the 40 cc Quadra and engine to be used and then do the math to calculate the new engine location needed to make it balance. The distance from the CG to the center of the Quadra engine times weight of the Quadra engine yields the moment due to the engine. Divide this moment by the weight of the engine to be used to determine how far forward of the CG the new engine must be mounted. Then increase the front fuselage length accordingly to get the firewall in the right place to make the CG and cowl work.

Hope you enjoy the build.
David

LLRCFlyer

More Clean Cut photos.

Clean Cut bottom view

Clean Cut top view

Clean Cut left rear quarter view

carlgrover

Thanks so much for the write up and extra pictures. Very nice looking plane for sure. I'm going to order the plans, cowl, and canopy this October when the AMA plans service has their annual fall sale. I'm also likely going to put a Quadra 50 in mine (I picked one up at Perry a few years ago). I always wanted to build a Prime Cut but wasn't crazy about all the foam. I doubt my foam cutter is that long but I would rather build up conventionally anyway. And I agree, no retracts.


Carl

LLRCFlyer

Carl,

When you build the Clean Cut, I suggest adding tail bracing wires. After about 4 hours of flying time I noticed a little flexing in the vertical fin. It was not broken or cracked, probably had flexed like that all along, but just had a little more give in it than I would like when flying knife edge and snap rolls. I modified the tail by gluing on some plywood attachment plates and installed four 2-56 bracing wires. Now the tail surfaces are very rigid and it did not hurt the looks of the airplane at all. In fact it makes it look a little more realistic. It would have been much easier to have included this modification while laying up the horizontal stabilizer when it would have been much easier and cleaner to install the plywood attach plates internally instead of externally as I had to do after it was built.

Concerning the CG, my Brison BA32 (53cc) engine with ignition (excluding battery), muffler, 20x10 Zoar wood prop and True Turn aluminum spinner weighs 4 pounds 10 ounces. It is mounted on 4.25" standoffs. From the pictures, you can see that I could not find standoffs that long and had to resort to stacking them. Surprisingly, there were no adverse vibrations or harmonics with this setup. It runs very smooth at all throttle settings. Perhaps this information will help in estimating where to mount the Quadra 50 and determining if the firewall needs to be relocated during the build to make the cowl installation work.

I hope you enjoy the build.

David