FRC Su35 MK2 NAMCV3 build - initial thoughts

Hi everyone -

While I had two of my favorite Russian park jets at the field yesterday, I got busy with the ruler again and made a few more measurements to make some comparisons.  I know it has only been a month since I built the last FRC Su35 MK2 NAMCV2, but with what I have experienced with the Mig29 V4 NAMCV3, I am excited to transfer some of those ideas to another airframe once again... :)

As I have already written at length, the red, white and blue Mig29 V4 NAMCV3 has taught me a real lesson on the importance of concentrating as much mass as possible around the CG to allow physics to help my plane fly smoother and more precise as it rotates better and more efficiently (i.e. with less control input required) around all three axes, roll, pitch and yaw.

The current Mig is now heavier with the NTM power setup, but I was able to keep the weight within a pretty small span (11.25") on a 39" plane.  So not including pushrods, etc, the weight of the battery, ESC, Rx, six servos and the motor is 15.6 oz.  Total weight of the plane is 24.7 oz, so I have 63% of the plane's total weight located within 29% of the plane's total length.

So when I start to make some of the same measurements on my yellow, tan and brown Su35 in the picture above, things get interesting... :/  From the front of the battery to the rear of the motor when balanced on CG, the weight is spanned over 13.5" which on a 35" long plane is 38%.

So using the same criteria to factor the weight of the battery, ESC, Rx, servos and motor on the Su35, the weight is 13.2 oz, total weight of the plane is 21.5 oz, so 61% of the plane's weight is spanned over a much longer portion of the plane, making that "lever" much longer that the plane has to move to rotate around CG.  The back of the battery which is 32% of the plane's total weight is at 2.75" ahead of the CG.  On the Mig, this weight starts only 1" ahead of CG.

So although I don't plan or shortening or lengthening the Su35, I don't know if the center of lift will get moved as much when I move the center of thrust and center of mass, but my main goal here is to get the motor forward considerably to allow me to pull back the battery and other components closer to CG and also see how moving the motor forward helps slow flight and possible high alpha which it did with the NAMCV3.  

So I looked at a couple measurements on both planes.  The motor mount on the Mig29 NAMCV3 is 61% from the nose, on the Su35, this same measurement is 71%.  To have the motor the same percentage from the nose on the Su as I have it on the Mig, I would have to move the motor mount 3.4" forward which I honestly think is a bit drastic and would really affect some structural integrity.  So I looked at where the motor mount is in relation to the CG on the Mig, it is 3" behind.  So if I go with that measurement and scale it down as the Su is 89% the size of the Mig, I end up with about 2 and 5/8" which I think is far more manageable and realistic.  This puts my motor about 63% away from the nose, so still very close to the Mig setup.

To prevent a huge gaping hole in the middle of the plane, I will also move the back edge of the prop slot forward by about 2".  Comparing ratios of size of the back plate on the Mig NAMCV3 this should still be small enough so that I should not have too much problem with elevon polar pitch effect or wind vaning in cross wind turns.

Also, I will move my aileron and elevon servos forward about an inch or so so that they are also concentrated more closely to the CG as they are on the Mig NAMCV3.  Other than that all the mods I have made to this point WRT elevons, vert stabs, ailerons, KFs will remain the same, but this will be another ambitious round of mods with that much adjustment to where the motor and other airplane weight is located.  Hopefully it will only be for the best... :)

So lots of measuring and adjusting of the plans still to do, but I am excited to see if it will further expand the Su35's flying envelope to suit my flying style.

Cheers,

Scott