Mig29 V4 and Su35 MK2 NAMCV2 flyoff

Hi everyone -

The weather gods were on my side today and I managed to actually get out and fly... :)  Calm winds, cool, dense air, perfect day to put a couple of jets through their paces.  Took my two favorite Russian park jets out to the field to do a bit of a fly off.

The blue camo Mig on the left is the RCP Mig29 V4 NAMCV2 (I'll just refer to it as the Mig for the rest of this post).  It is modified quite a bit from stock, you can read the build details and modifications here http://migsrus.blogspot.ca/2014/09/rcp-mig29-v4-namcv2-build-complete.html

The yellow and brown camo Su35 on the right is the FRC Su35 MK2 NAMCV2 (I'll just refer to it as the Su for the rest of this post).  It is highly modified from stock, you can read the build details and modifications here http://migsrus.blogspot.ca/2014/10/frc-su35-mk2-build-complete.html

I know some of this comparison is kind of the old comparing "apples and oranges" dilemma, but I learned a lot today about motor position in the airframe and how the distance between where the prop is in relation to the rear control surfaces (elevons and rudders) impacts flight performance.  This couldn't come at a better time for me as I am playing with some pretty significant modifications on my latest Mig29 NAMCV3 build that I am kind of "morphing" into a Mig35.  Part of that modification involves adjusting the motor position forward and shortening up the distance between the trailing edge of the wing and the tail assembly.

I will present my impressions of how these planes handle in relation to each other, then if you are interested, I am going to dig a little deeper into some measurements and try to see if I can put some scientific logic and explanation as to why these planes handle how they do.

Firstly, both these planes are about the same weight, very close to the neighborhood of 21 oz with a 2200 battery.  Both have the same motor, the FP 2700 with 6x3 EMP prop, same controls, elevons, ailerons and rudders.  In fact the rudders are essentially identical in size and shape as I used the Su rudders as a guideline when I modded the Mig rudders on that plane.

The throws are essentially the same in all axes within about 5%.  Where the big difference is that in the pitch and roll, I have about 10% more expo on the Su than on the Mig.  I may have mentioned it before, I am kind of a "muscle memory" flier in that I have kind of a certain amount of stick movement programmed into my brain and thumbs to generate certain pitch and roll rates especially.  To accommodate this, I adjust my throws and expo so that as I transition between each plane, my stick movements remain very much the same without over banking, over pitching, etc.  Hopefully that makes sense, if not please ask and I'll try to explain it more clearly.  Anyway, to keep the Su a bit more docile so that I don't flail it around too badly in turns and basic maneuvers, I threw in a bit more expo to accommodate my muscle memory and soften it's responses.

Speed and stability

Above half throttle, both planes are very stable, so close that as John Wayne once said "I wouldn't want to have to live on the difference" :) .  They are both very stable in calm and windy conditions. They are essentially the same speed at full throttle.  The Su however is a bit more susceptible to a bit of torque roll on occasion when hammering on full throttle.  Doesn't always happen and nothing that can't be corrected with a tiny bit of opposite aileron, but it is noticeable.  On the Mig, I don't think I have ever seen it torque roll.

Where the big breaking point comes with respect to speed and stability is when you start to get slow, below half throttle.  The Mig stays very stable down to about 35-40% throttle, very few bad tendencies unless you get too aggressive with the sticks when you are slow.  The Mig is also capable of very good high alpha, with angle of attack (AOA) of about 35-40% fairly easy to maintain with the aid of a bit of spoiler deflection.  

Slow speed is where the Su really starts to drop off in performance, it is flyable in calm conditions like I had today down to about 35-40% throttle, but you really have to stay on top of it.  If you lose focus for a few seconds, it can become a very unhappy park jet very quickly... :/  I have never really played around with any serious high alpha with the Su as I find as soon as I get slow and get about 25 degrees AOA, wing rock comes on quickly and violently and the only course of action is to drop the nose and fly out of it, no bringing it back right away like I often can with the Mig.

Pitch axis

The Su is more responsive and aggressive in the pitch axis in turns, loops other maneuvers that are "pitch centric".  It does however require a bit more finesse on the sticks with respect to control input and power management or it can very easily "over pitch" or even get to the point of thrust vectoring (TV) stall (when speed gets low and with too much elevon deflection they act as speed brakes rather than elevons).  The Mig is also very responsive in the pitch, just not quite as aggressive and is more forgiving through loops and other pitch maneuvers not requiring as much finesse or focus on power and control inputs.

Roll axis

The Su again even with more expo is quicker and tighter in the roll axis than the Mig.  Slightly shorter wingspan might contribute to that performance, but it is more responsive in the roll than the Mig.

Yaw axis

Both are very responsive in the yaw, rudder authority is excellent in both, in fact I used Su inspired rudders on the Mig, so that is probably logical.  The Mig still occasionally has a bit of "rudder roll" when executing stall turns, the Su not so much.  However, if the rudder is held over too long through a stall turn with the Su, it will start to seriously spiral and do some pretty funky things...all while heading straight at the ground... :/

Overall handling and impressions

Both these planes in their current configuration are a lot of fun to fly and it might just be a matter of what you are looking for on a given day.  

The Su that I am flying now is highly modified from stock, many of the features I added were to build in more stability to come into line with my flying skills and abilities.  I used the toed in vertical stabs and split horizontal stabilizer and elevon from the RCP Mig29 V4 to enhance stability and am pleased to say it does work really well to tame this plane down from it's stock configuration, at least in my experience and at my skill level.

Both planes track exceptionally well, really carving turns with no hesitation, both are very precise and crisp in their maneuvers.  As already mentioned, above 50% throttle, I would give the slight nod to the Su as being the more agile and aerobatic, but a bit more focus and concentration is required when flying it to prevent problems. 

The Su tends to slow down more quickly and lose energy in aggressive maneuvers if I don't anticipate correctly and manage it's speed correctly.  The Mig tends to not need as much throttle management through the same maneuvers and maintains and regains it's energy better than the Su.

As already mentioned, where the real difference in performance and versatility happens is in the slower flight regime, less than 50% throttle.  The Mig wins there hands down.  It stays predictable and forgiving even down to about 35% throttle and does high alpha very well.  The Su can be managed down to about 35% throttle, but if I lose focus for one second and don't anticipate adding some power in turns, it can bite me, stalling out and dropping a wing or it's tail very quickly.

From a standpoint of versatility in power setups, I would also give the nod to the Mig.  I have built and flown the Su with the NTM 2700 and I know lots of folks have had success with it using that bigger motor, my experience was that it (in stock configuration mind you) did not like the extra power and weight and was a real handful to fly.  This weight of about 21 oz with the FP 2700 motor is the perfect setup for me where the Su is concerned.

So again, it boils down to what you like or what you want.  In the configurations I flew both these planes, the Su is more nimble and aerobatic above 50% throttle, although it does require a bit more focus and concentration when flying and is not as forgiving as the Mig.  The Mig is more forgiving and more versatile over a much larger speed envelope than the Su from my experience, so again, all depends on what you want.  I often take one of each to the field and fly them both as I mentioned, both are a real blast to fly in their NAMCV2 configurations.

As I was flying and after I got back from the field, I really started wondering what was going on between these two planes and how their setups affected their performances.

So just a few quick measurements and a couple more pictures that might put things into perspective on the differences and similarities between these two planes.  I took the time to measure all these distances on my planes as they are rather than using the stock measurements off the plans since both my planes are modified.  I know some of the measurements may seem a little weird and I may or may not use them in my discussion, but since I had the ruler out anyway, what the heck?

Mig

• Wingspan - 27";
• Length - 40" (one inch shorter than stock);
• Distance of CG (based on where I found my CG to be which is about 3/4" ahead of stock on the plans) from the nose - 20.75";
• Distance between trailing edge of the wing and the horizontal stabilizer - 2.25";
• Distance from the nose to the motor mount - 24.75";
• Distance from the prop to the elevon hinge line - 8.25"; and
• Distance from the prop to the rudder hinge line - 6.5"

Su

• Wingspan - 26";
• Length - 35" (one inch shorter than stock);
• Distance of CG from the nose - 20";
• Distance of trailing edge of the wing to horizontal stabilizer - 1.5";
• Distance from the nose to the motor mount - 25";
• Distance from the prop to the elevon hinge line - 4.875"; and
• Distance from the prop to the rudder hinge line - 3".

A couple things to note right away, compared to the real Mig29, the Mig is very close to scale, it should be about 41" long (which it is stock, not with smaller elevons like I have).  Compared to the real Su35, the Su is 2.7" too short based on my current build.  Even stock it is almost 2" too short to have scale proportions.

Some interesting measurements when you look at how much shorter a distance there is between the elevons and rudders and the prop on the Su.  I think this has a lot to do with it's snappiness in the pitch.  Also, in relation to the whole length of the airplane, the CG on the Su is further back, pretend the airplane for a minute is measured in percentages from front to back, the CG on my Su is at 57%, the Mig is at 52%.  

Also, if you look at this picture (I tried my best to take a bird's eye view from the top) you can see that the motor on the Mig is almost completely centred in relation to the chord of the wing.  Whereas with the Su, the motor is almost at the trailing edge of the wing.  For the sake of this discussion, lets call the motor/prop location the centre of thrust (CT).  Not only from the picture but when I do the math, there is a significant difference where the CT is on each plane in relation to it's total length.  There is 38% of the Mig behind the centre of thrust, but only 29% of the Su behind centre of thrust.

I know perhaps this might all be getting too complicated, but when you think of where the CG and the CT are in relation to the length of each airplane, I think it has a big impact on why they perform and respond how they do.  For me, it is a simple matter of levers really.  There is a lot more of the Su ahead of it's CG and CT, but once you get that lever moving, it rotates more aggressively than a more equally balanced (front to back in relation to it's CG and CT) Mig.

The relationship of where the prop is compared to the control surfaces also has quite a bit to do with it.  Also, if you look at the pictures above and below, the prop on the Mig is ahead of the leading edge of the vertical stabilizers while the prop on the Su is between the vertical stabilizers.  On the Mig, the prop wash has more chance to dissipate after it comes off the prop, on the Su it is funneled directly back between the vertical stabilizers, hitting the elevons with much more concentrated force than the Mig.

Just spitballin' here, but I think that both these situations are good and bad.  The Mig is still getting good thrust vectoring (TV) authority, but responses are not quite as immediate and aggressive as they are on the Su and while still very responsive, the Mig is a little more forgiving in the pitch especially.  While the Su is more aggressive, this also has it's downside as without managing the power and control input properly, the Su can TV stall much more quickly than the Mig, causing the plane to slow down very quickly, lose energy and then well...things can get very ugly from there... :/

Also, when looking at how much of the plane is ahead of the CT and CG, it might explain why the Mig is better balanced in slow flight and high AOA situations.  I remember Dave Powers in one of his old videos demonstrating how when you try to balance a long stick vertically on your finger, it is very hard to do and very unstable as the long stick is acting like a big lever.  However, if you balance a pencil, it is a much smaller lever and much easier to balance vertically.  

Perhaps this is what is going on between these two planes.  Much less of the total length of the Mig is ahead of the CG and CT than with the Su, so when you try to balance the Su at a high AOA, there is a much longer lever to balance on the pivot point.  This does make for some very nice flips over the top on slow loops, but it might be an interesting experiment to move the motor/CT a bit further forward and see what happens.

Not that I am interested in hovering a park jet by any means, but when I watch the promo and hovering video of the RCP Su30 V4 with it's motor very far forward, it again confirms that less lever above the CT is easier to balance at higher AOA.

Getting out my dollar store calculator once again, to bring the CT on the Su closer to that of the Mig, means moving the motor forward by at least two inches.  Perhaps that might be a bit drastic, so more measuring, calculating and assessing will have to be done.  Here I go again, talking myself into another project... :/  But I am up to the challenge and very interested to see what the results will be.

So I guess in conclusion, it all depends on what you are looking for.  To get the Su I am flying now to where it is, there was certainly a lot more modification required to get it to be smoother and more stable over stock, with the Mig not so much.  The Su being smaller and with a CG and CT further back tends to be more nimble and aggressive at higher speeds, but performance drops off at lower speeds compared to the Mig.

I am thinking that there could be still more mods done on both, as mentioned I am kind of currently "morphing" a Mig29 into the more modern Mig35 and I can see more potential with the Su35 by not only moving the motor forward a bit, but perhaps also stretching the back out a bit further...oh dear, the wheels are turning now...how much more depron do I have?!  :)

Cheers,

Scott