After a few too many "gonks" and repairs, my first Su35 MK2 just wasn't flying right, I could never seem to get it balanced and trimmed just right anymore, so I decided it was time to recycle it and built another.
I love the profile of this plane and how it flies, but being on the wrong side of 50 years old, I wanted to see if there were some build mods I could make to it to smooth things out a bit to prevent having to put such insane amounts of expo (like 70-80% in the roll axis) to make it a little gentler on my old nerves!
I did a lot of studying of plan views of the real Su30/Su35 and wanted to put a couple of little scale tweaks of my own on this plane as well.
So here are a few thoughts starting from the back of the plane -
- I made the elevons a bit smaller, bringing them a bit more in scale proportion with the wingspan. It was about a 3/4" total reduction in span and I trimmed the edges a bit, adjusted a couple of the angles and also fashioned a bit of a centre boom between the "nozzles" like on the real plane. Mine is not as long as it would be to be totally scale, but I hope it gives the appearance of it. In the first picture below, you can see the difference between stock and my mods. In the second picture, I overlaid my elevon over the stock elevon. I think in total I reduced the total elevator/elevon surface area by about 15%. This should still give me amazing authority, but hopefully a little more gentle.
- Borrowing an idea from the RC Powers Mig29 V3, I decided to angle out the vertical stabs from front to back about 2 degrees. As Dave Powers has discussed, this subtle "wedge" shape seems to give a lot of self stabilizing qualities to the Mig29 V3 and it will be incorporated in the new V4 series as well, so I thought why not give it a try here as well. Since the angle is so subtle, it is hard to see, but the pictures below might show it. In order to prevent interference with the prop slot, I widened the back deck from the back of the wing root to the elevon hinge by 1.2 cm in total and I had to angle the slots for the tabs on the bottom of the vert stabs. So it will be a lot of dry fitting and experimenting, but I'm up to the challenge!
- In an effort to also help reduce the sensitivity in the roll a bit without needing a bunch of expo, I will also be reducing the chord width of the ailerons by about 1/2". I kept them the same shape as I had made the ailerons on my previous Su35 straight rather than flared at the end and it rolled funny in quicker rolls, like it was trying to use a hula hoop! I used the standard shaped ailerons on my Su37 MK2 and it rolled much cleaner and crisper, so perhaps the shape is important. Also by having the hinge line a bit further back, I won't interfere with the bottom airfoil of the Kf airfoil. In the bottom picture, you can see where I had to trim a little bit off the end of the bottom airfoil to prevent it from interfering with the hinge. Nothing major, but this time I won't have to trim it.
I am also planning on making the top Kf a little larger to encompass the leading edge extension. It is not a big area, but I have been noticing in other planes, the FRC F15 MK2, the RC Powers T50 V1 and the RC Powers F22 V1 that extending that Kf forward like that makes for a much smoother flying plane. So we shall see... :)
The last new technique I am going to try is to taper all the trailing edges, ailerons, elevons and vertical stabs/rudders.
As a testbed plane I will take care in the build aspects that affect performance, but won't worry about a fancy paint job, probably just some color and contrast with magic marker like I did on my testbed F18 V3. In my experience, test planes don't mind being ugly and they seem to fly awesome for a long time...I have over 250 flights on my F18 V3 and she is still going strong!
I will continue to update my blog as the build progresses along. I'm excited to see what results I get... :)
Cheers,
Scott
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