RCP Mig29 V4 NAMCV2 and V3 flyoff

Hi everyone -

I was blessed with another calm, dry late fall day today, so a great opportunity to keep dialing in and fine tuning my new RCP Mig29 V4 NAMCV3 (which is the white plane on the right which I will call the V3 for the rest of this post) and do a flyoff with it and my Mig29 NAMCV2 (which is the blue camo plane on the left which I will call the V2 for the rest of this post).

These two planes are much more alike than the V3 and the stock Mig29 V4 I flew when I maidened the V3.  The rudders, ailerons and elevons are essentially the same size, the biggest difference being length and motor position which then affect several other portions of the flight envelope.

This was an excellent session of testing as it showed me how having simple physics working in my favor with respect to how the weight is centred on the V3 combined with how the CG (center of gravity), CT (center of thrust, referring to where the motor is located in the plane), CM (center of mass or where the bulk of the weight is located) being moved around by my modifications affected the plane's performance.  I am also sure that the CL (center of lift) has been moved on the V3 as well, but I'm not sure how I could test for that.  The other three, CG, CT and CM I can measure which I will do and discuss later in this post.

I also did a little research to reassure myself where a plane rotates and with a simple diagram and a little help from my friends at NASA ;)  relearned that an aircraft's point of rotation for all three axes is the CG.  http://www.grc.nasa.gov/WWW/k-12/airplane/rotations.html  I think this link was designed for kids, so it is barely within my grasp of understanding... ;)

Today was again a calm day, so still no real assessment on how the V3 handles the wind, that testing will have to wait for another day.  In calm conditions, both planes I would say are equally stable at middle to high speeds, there is a difference however at lower speed which I will discuss later.

Turns and general handling

The V3 requires about 10% less control input to perform a turn of the same rate/radius as the V2.  This is also considering that I have 10% less throw on the elevator input on the V3 than I do on the V2.  Aileron throws and expo are the same on both planes.  Rudder throw is the same on both planes, but to tame down the rudder responsiveness on the V3, I increased the rudder expo by 10% over the V2.  Both planes really carve through turns, track exceptionally well, but if I had to give a slight nod it would be to the V3.  Because of how it is better balanced WRT weight distribution, it just feels smoother and tighter with no wasted movement or loss of energy at all in turns.

Loops and pitch maneuvers

The V3 is more responsive and smoother through loops and other pitch maneuvers.

Rolls

As I said in my post flight, the V3 rolls like there is a rod right down the center of the plane that it rotates around.  Because the weight on the V2 is spread over a much larger area, sometimes in rolls it will twirl slightly like a drum majorette would twirl a baton.  In other words, the nose does not stay as level throughout the roll on the V2 as it does on the V3.

Yaw

The V3 is much more responsive in the yaw, as mentioned I had to down tune the expo a bit to keep from getting too aggressive in the yaw in high alpha and moves like a stall turn.

Slow speed and high alpha

This is where the V3 really sets itself apart from the V2.  In level slow flight with the throttle at about 35-40%, the V2 is very stable, but still feels like it is on a bit of a razor's edge from a standpoint of control and stability.  The V3 actually felt today a lot like my stock RCP F18 V3 at slow speed, almost like it had some sort of self correcting mechanism as it flew along, it felt noticeably more solid.  In high alpha, both require about the same amount of power, the spoilerons on both are identical at 5/8" travel, but to hold the nose at the same AOA (angle of attack) for both, the V3 needs about 10% less up elevator.  Because it rotates so well in the yaw axis, about 10% less rudder input is needed to bring the nose around in high alpha as well.

Before going any further, I don't want it to sound like every new Mig I build is amazing and all other Migs I built before that are no good, but it is a logical progression as Stephan and I think, design, test and validate each new sets of mods.  As I have mentioned before, this was definitely the most ambitious set of mods attempted thus far as a lot of things got moved around as a result of shortening the plane and moving the motor forward.

So of course, I had to get out the ruler (it never lies... :) ) and my dollar store calculator and put some numbers to what I was seeing and feeling at the field today.

During the first couple flights with each plane, I double checked that all my control surfaces were still dead center at zero trim and rechecked the CG on both.  The CG on the V2 is now 1" ahead of stock and the CG on the V3 is about 1/8" ahead of stock.

V2

Wingspan - 27"
Length - 40"
Distance of CG from nose - 20.5"
Nose to motor mount - 24.75"
From front of battery to rear of motor when balanced on CG - 14.75"
Distance from the CG to back of battery when balanced - 3.75"
Distance between CT (back of motor mount) and CG - 4.5"

V3

Wingspan - 27.5"
Length - 39"
Distance of CG from nose - 21.25"
Nose to motor mount 23.75"
From front of battery to rear of motor when balanced on CG - 10.75"
Distance from CG to back of battery when balanced - 1"
Distance between CT (back of motor mount) and CG - 3.25"

So when I look at these numbers, I admit I have always known that having as much weight as possible concentrated around the CG is better for overall balance and handling, but because of poor planning or the plane, I was never really able to get the weight concentrated as well as ended up on the V3.

So let's look at the weight of the planes.  The V2 is a bit lighter at 20.9 oz, the V3 is 21.5 oz (even though not painted it has much more carbon reinforcement and 10 gr extra in servo weight).

Total weight of battery, Rx, ESC, motor and servos for the V2 - 13.2 oz.  Same combination for the V3 - 13.3 oz.  Because the battery is the heaviest part of this equation, the battery for each weighs 6.9 oz, over half the total weight of the electronics gear.  This will become important again later on.

So the gear on the V2 makes up 63% of the plane's total weight and is spread over 37% of the total length of the plane when balanced.

The gear on the V3 makes up 62% of the plane's total weight, but is spread over only 28% of the total length of the plane when balanced, so it is concentrated in a much smaller area.

A couple other measurements that become quite interesting is when I look at where the batteries, which make up 33% of the total weight on the V2 and 32% of the total weight on the V3 are located WRT to the CG on each plane.  On the V2, this weight starts 3.75" ahead of where the CG is on this plane.  On the V3, this weight starts only 1" ahead of the CG.

In my opinion, this alone easily explains some of the differences in both the yaw and pitch axis on these planes.  The controls have to work much harder to pull the nose up in the pitch or bring it through on the yaw axis as the weight on the "lever" is much further from center explaining why more control input is needed on the V2 in both the pitch and roll just to lift that heavier weight further from the rotation point.  This may also explain why the V3 is more solid in rolls as there isn't that big bunch of weight so far out ahead of CG as it rotates on the roll axis.

Since although I shortened the back end of the V3 by 1", I also moved the motor mount ahead by 1", so the distances between the prop and the elevons and rudders are the same on both planes.

So looking at where the motor and CT of thrust are now located on both these plane and how it affects the CG.

If we break the length of the planes into percentages, the motors are essentially in the same location with respect to total distance of the plane.

V2 - motor mount 24.75" from nose divided by total length of 40" = 62%

V3 - motor mount 23.75" from nose divided by total length of 39" = 61%

If we look at where the CG is located on each plane WRT to total length.

V2 - CG 20.5" from nose divided by 40" = 51%

V3 - CG 21.25" from nose divided by 39" = 54%.

So if we then look at a couple other numbers, the distance between the CT and CG on both planes, they are quite different, the CT and CG are significantly closer on the V3 than the V2 by 1.25".

So although the CG is closer to the very centre of the airplane on the V2 than the V3, the CT on the V3 is about 40% closer to the CG which I think helps make rotation in all axes more efficient and effective.  Also, by bringing the CT forward, it brings the CG back and when coupled with how much closer the main body of mass on the plane (the battery) is located to the CG, it makes sense that the airplane is not only better balanced, but rotates that much better as the CT, CG, CM (center of mass) and I assume CL are all much closer together.  Quoted from the link above

"In flight, any aircraft will rotate about its center of gravity, a point which is the average location of the mass of the aircraft."

I hope that I am following a logical path with this thinking, there is certainly some serious mojo going on there with these changes that were made, I'm sure all working together to make this plane better balanced, more responsive in all axes and overall more stable and self correcting.

Another fun and educating day at the field today for sure.  Amazing how a few manageable changes on a plane can make such significant differences in how they perform.  That and I just love how this V3 looks in the air, more compact, more solid and more scale looking and flying.  I am truly happy and satisfied how all these changes have worked out... :)

Next up will be to paint it, change the power system and then do some more testing with higher wing loading and speed... :)

Cheers,

Scott