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

Polar Moment Epiphany

I was going to add this comment to my original "dissertation" on Cg and polar moment of interia.  But after my epiphany at the flying field, I thought I would start a new post.

Scott really got my brain churning with his new NAMCv3.  I started reading and realized I had ignored the importance of the polar moment.  Simply put, the less torque needed to rotate the pitch/roll/yaw axis around the the Cg, the plane will rotate easier, faster, and more efficiently requiring less control surface deflection.  I can't believe I have ignored this basic law of physics.

So today at the flying field, I tested the plane with the same Cg but with different polar moments.  How did I do this?  I usually placed the ESC wherever it would fit and "looked" right.  This usually meant as forward as possible. Today, after a couple of flights, I moved the ESC as far back as possible which then allowed me to bring the battery aft and closer to the Cg.  I could feel a difference and the plane was more responsive in all 3 vectors of rotation.  The bigger the ESC, the more noticeable the difference will be.

After "centralizing" as much as possible the battery and the ESC, I then started to play with Cg.  As mentioned in a prior post, I test the Cg by flying at 40-50% throttle nose up at 30 degrees and cut the throttle.  I want to see the plane continue to climb and then slowly and gently drop the nose completing a nice arc.  Note: I read about this but can't remember the citation.  So I did this today and kept moving the battery aft.  A tail plane is a crashfest, so I stopped before it got tail heavy.  Wow, what a difference.  The plane in pitch, yaw, and roll is so much smoother and looks more scale like. Induced spins and recovery were better as well.  I used to like nose heavy for high alpha, but today it was much easier and wing top rock onset was more gentle and not so violent.  Best way I can describe it is that as speed bleeds off in a tight turn or climb out the plane appears to be sliding through the air as the lift decreases.  Make sense because as lift decreases, you are not adding more control surface input to counter act a forward Cg.

I really felt like I saw the "light" today flying.  Gasser RC day habits of nose heavy planes is a hard habit to break.

My Cg is now 22 3/8 inches from the nose, 2 1/8 forward of the spar,  which is about 3/4 aft of stock.  Remember this plane does have a higher wing load than stock with a downsized LERX and leading edge.

Video will come, one day, I promise.

Thanks you Scott for my epiphany today!  Song of the day from Archie Bell & the Drells "Tighten Up".  For us that means your battery and ESC!

Stephan

RCP Mig29 V4 NAMCV3 is amazingly fast!

Hi everyone -

Had my two favorite Russian park jets at the field today, my new red, white and blue Mig29 V4 NAMCV3 on the left and my yellow, tan and brown FRC Su35 MK2 NAMCV2 on the right.

It was a very exciting day at the field to say the least... :/  I have the NTM Prop Drive 2700 motor in the Mig29 V4 NAMCV3 now (I took it off for the picture below to make the repairs a little easier).  I had done three flights on 3S (more on that later) and one flight on 4S (more on that later too... :) ) and was just getting ready to shoot some video, when I noticed that the foam behind the glue joint on my motor mount was cracked :( !  The glue joint held up just fine, but the foam cracked all the way across.  I guess the serious stress the NTM on 4S put on it pushed it beyond it's structural limit, but no fear, plane otherwise is fine.  I have marked where the fault line is below with black magic marker to make it easier to see in the picture.  So anyway, video will have to wait for another day  :(.

So as I continued to fly my Su35, I started wondering how to repair and strengthen this weak area.  So once again the dollar store came to the rescue as I had some popsicle sticks laying around and I cut some lengths of that, laid in a good coat of epoxy and so far, it is super strong...only field testing will prove if the repair is solid, but I'm pretty sure it will hold... :)

I will also swap out the prop I have on the motor, it was balanced, but has had some use, so time for a new one to ensure I am not still sending any vibration into the motor mount.  Anyway, a small setback and fortunately no loss of aircraft and a 10 minute repair and I think we are once again ready for some more serious speed... :)

So here is the really good news for us speed demons... :)

On 3S, I clocked four solid speed runs of 97, 92, 90 and 90 with this setup... :)  

On 4S, I clocked four runs of 115, 111, 102 and 100...wow!  

The speeds diminish as the battery loses it's punch from being fully charged, but four runs of 100+ mph on 4S is crazy!  The first two runs are faster than the top speed I got with the Mig29 M3e3, so this is a pretty quick little plane.  

I just looked back through my flight log, the top speed on 3S I achieved with the Mig29 M3e3 was 94 mph.  On 4S, my speeds were 109/108/104/102.  

So this is the first time I have broken 110 mph with a plane built with relatively stock setup...gets your heart rate up seeing something you built from foam and glue go by you that fast... :) 

So onto overall performance with the higher weight and heavier power system.

My CG ended up moving forward by about another 1/8", so it is now about 1/4" ahead of the stock CG marked on the plans.  The battery is moved forward about 1/2" over the FP setup, so this makes some sense to counter balance the heavier motor and the "average of mass" has been moved somewhat which will slightly affect the location of the CG based on the info at this link from NASA http://www.grc.nasa.gov/WWW/k-12/airplane/rotations.html

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

It has been awhile since I flew an NTM equipped plane, so perhaps some of what I am about to say is because I am a bit rusty on managing this kind of power, but since I also have the weight concentrated around CG much better than on any other NTM plane I have built, some of this makes sense besides my lack of skill... ;).

Everything happens faster with this plane with the higher wing loading and more powerful, higher torque motor and I don't mean just from a stand point of speed.  It is more responsive in all three axes without feeling heavier than it was with the Focal Price motor setup.  It does take a little more room in which to turn and fly as even at half throttle it is going fast, but "on the sticks" it didn't really feel like the wing loading had gone up a huge amount even though the overall weight went up by 15% with painting and the bigger power system.

So I actually toned down the throws in the pitch and roll by 10% and increased the expo by another 10% so that I didn't over control it.  At speed, it is rock solid stable and it almost seems like the faster it gets, the more stable it gets, it just screams ahead with no hesitation or bad habits.

So still more testing and another round of speed trials to come.  I'm not sure actually when the foam behind the motor mount cracked, if it was loose most of the time, I'm sure some of the speed could have been lost from that.  I hope to get back out again Friday, the forecast for the next two days is not good.  Very pleased with how well this plane flies at medium weight/power or heavy weight/power... :)

Oh yeah, did I mention it is fast?!  :)

Cheers,

Scott

Lessons learned from two years of park jets

Hi everyone -

It has been two years since I seriously started my journey to where I am now WRT park jet building and flying.  Although I still have much to learn and keep learning more with every build and every trip to the field, there are some general "big picture" things I might have done differently if I had to start over again.  So perhaps this post would be aimed more at a beginner in the hobby or in park jets for sure, but hopefully there is a little something for everyone.

I had actually dabbled a bit in RC flying about 5 yrs ago, I made the mistake of thinking I could learn to fly building 3D foamies from plans I got from RC groups made of "indestructible" EPP foam.  Well, nothing is indestructible and 3D planes are not good trainers in my experience... :/  Then I had a couple years off as I dealt with a bunch of life stuff.  So when I was able to properly commit to my dream of building and flying park jets two years ago, I kind of started all over again.  I still had my Spektrum Dx6i radio, some batteries and a couple receivers, but not really anything else.

So my first task was to learn to fly RC planes properly.  It was around this time that Dave Powers released a video on the Bixler 2 from Hobby King.  At the time, it was kind of the latest version of the Hawk Sky type planes and the price was right at $70, all I needed to do was supply a battery, radio and receiver, all of which I had.  So off I went.  It was about the best $70 I had spent in the RC hobby to that point.  I just kept taking that plane to the field and flying it over and over, practicing all the basics, it turned out to be an awesome training platform for me.  Even after I built my first park jet, the RC Powers F35 V2, I kept flying the Bixler til I had about 70 flights on it and I am very glad I was patient in doing that.

So here was my first park jet the RCP F35 V2 (which was free), elevons only, KF2, built way too heavy, but it flew and held up for about 60 flights before it just got too heavy to fly anymore.  Ugly as it was, it filled it's role in my park jet process.

So I progressed pretty quickly from there with my building, but not necessarily my flying... :/ building a total of 4 F35 V2s, the Mig29 V2 (my absolute nemesis, I built and wrote off three of these and got less than 50 flights among the three of them... :/)  My heavy building continued and pretty quickly as my control setups and mixing became more complex, I outgrew the capabilities of the Dx6i.  By the time I built my F18 V2, I had over an ounce of extra stuff (three mixers and three Y harnesses) in my F18 to get it to do what I wanted it to.  I was still doing a lot of what the "herd" on the forums was doing, chiseled leading edges on my KF4 wings, linked ailerons and elevons (2 servos running 4 surfaces or 2x4).  I was using uneven KFs, 6mm on tip and 3mm on bottom.

So enough rambling about how I got started, here are some of the things I would do different now right from the beginning if I could.  It would be a bit easier for me to commit to some of what I am going to discuss because I knew I wanted to build and fly park jets, perhaps this might not apply to other folks, park jets are a bit of a unique aspect of the RC hobby.

Choice of beginner plane

If I was learning to fly all over again, I would probably scratch build right from the start using free plans from Flite Test http://www.flitetest.com/articles?grid=true#/textSearch=FTScratchBuild  I think their power pod concept where you build one Power Pod that can be swapped among several airplanes makes a lot of sense for a beginner.  Inexpensive and easy to build planes from dollar store foam and hot glue is a simple, inexpensive way to get started.  You can learn scratch building at a very basic level, don't need to buy a whole bunch of gear, most of your build materials can be purchased at the dollar store or other inexpensive places like Walmart.  

Their beginner planes like the Nutball, FT Flyer and FT Delta are super simple to build and fly, you can build a few of them and then just swap your power pod between them or to your next one when you crash the first beyond repair.  A lot of planes can be built for the $70 I spent on my Bixler 2 and you get to start learning some basics of scratch building at a very easy level and their instructions and build videos are excellent.

Choice of transmitter

Knowing what I know now, I would have purchased a transmitter that I could grow into or could be easily and inexpensively upgraded as my experience and skills grew.  The Dx6i is an excellent radio for park and general flying, but the unique control setups on intermediate to advanced park jets max out it's mixing capabilities very quickly which led me to add weight and gear to my planes to get the mixing I wanted/needed.

After considerable research and a tight budget, I decided to buy another radio, the Turnigy 9x with the er9x firmware upgrade.  By the time this radio and parts were shipped to me, it cost me about the same as my Dx6i did from my LHS, but it's mixing and fine tuning capabilities are exponentially better than the Dx6i.  If you go to this post, I put links to all the goodies needed to have the Turnigy 9x with the er9x firmware upgrade http://migsrus.blogspot.ca/2014/10/my-park-jet-workshop-video.html  

This is certainly not the only radio available, the number of highly capable, easily programmable radios just gets better all the time.  I found You Tube an excellent source of information, lots of folks have taken the time to do reviews and comparisons of many of the popular transmitters.  RCmodelreviews has done many reviews on inexpensive Hobby King transmitters on his You Tube channel as well https://www.youtube.com/user/RCModelReviews

My main point here is if I could, I would have outlaid the cash required to buy a transmitter I can could grow into or was easy and inexpensive to upgrade rather than having to buy a second transmitter which in the long run was not only more expensive, but required I learn a whole new programming setup.

Choice of first park jet

If I had to do it over again, I would have started off with a profile park jet like the RCP Mig29 V1.  The Mig29 V1 was a real turning point plane for me in my park jet career, unfortunately I didn't build one until I had already written off about a dozen score and fold RCP V2 type planes.

The Mig29 V1 is super simple to build, one sheet of depron or it is even an excellent candidate for dollar store foam.  It flies amazing with elevons only, can be built in about a half a day and is super simple to repair because everything is a flat surface.  Even if you get a little "glue happy" and build a bit heavy, you can still use the D2826/6 motor from HK and have a lot of fun.  This was a real confidence builder for me after having a real run of bad luck crashing a bunch of V2 planes, so if I had to start over again, I would have built this first and just flew the wings off it before moving on to a score and fold plane.

Learning to build lighter sooner

I have joked many times about being a card carrying member of "overbuilder's anonymous", but this mentality of over building I'm sure cost me many planes early in my park jet career.  Of course my skills were not then what they are now, but my planes rarely survived serious impact like they do now because I failed to learn quickly enough that heavier is worse, not better.  Again, it is basic physics, more weight coming to a sudden stop causes more damage than less weight doing the same thing.  

Fortunately, I made another big turning point in my park jet career when the V3s were released by RC Powers as these planes were smaller, designed to be strong but light and didn't need big power setups like many of the V2s did to have any decent performance.  With all the flying and testing I have done in the past year I have found an overall ideal weight for the V3 size planes to be about 20-22 oz as this allows for best stability and wind penetration and when using the Focal Price type motor still gives great speed and aerobatic performance.  

Breaking from the "herd" sooner

This is probably a tough thing to do, many of us when first starting off see what the "hot shots" on the forums and You Tube are doing and fall into the trap of trying to follow that same path.  Now there is nothing wrong with that, but if it is not what you really want to do, it can lead to a lot of disappointment and frustration in my experience.  I know when you are first starting off it is tough to answer the question "what do I want my plane to do", but I think that if I had to do it over again I would ask myself that question much sooner as well as "how do I want to build and fly?" and then stuck to my guns as I moved ahead rather than trying to keep up with the pack.

  

Even though many of the things like 2x4 linked elevons and ailerons, uneven KF4 airfoils (thicker on top, thinner on the bottom) and chiseled leading edges on wings and elevons didn't make sense to me aerodynamically, I kept following that path because that was what was what the "herd" was doing.  So what happened?  I was building and flying my planes like other people did because I thought that was what I needed to do to become a good park jet pilot, not what made sense to me or fit in with how I wanted to build and fly.  How does that old saying go?  "Insanity is continually repeating the same behavior expecting a different outcome".

It took me awhile (probably a lot longer than it should... :/) to come to the realization that my building and flying should be measured by what gives me the most fun and satisfaction, not what others are doing.  Even if it is completely opposite what the "herd" is doing, if it means I am excited to build a new plane, go to the field and fly it and leave satisfied, that is what is important.  If I could give a new RC pilot any advice at all, it would be exactly that, don't worry about what others are doing, just do what gives you pleasure and satisfaction, no matter what that might be.

Fortunately since Stephan and I have been sharing ideas, I have broken free from that "pack mentality" and the fun and satisfaction I have from this hobby has taken another huge turn for the better.  With Stephan's help and encouragement, I have broken from many of the old paradigms of building and flying and the overall performance of my planes has instantly leaped to a whole new level of performance as has my flying fun and satisfaction.  

So while I think it is a good idea to experiment with new things, if something makes absolutely no sense to you, don't be scared to do it your own way.  One of the greatest things about building and flying scratch built park jets is each build is like a new artist's canvas waiting for you to experiment with a modification or a change that you want to test and evaluate, even if others haven't tried it before.  You just never know what might happen until you try.  Fear and common sense are sometimes highly over-rated... ;)

Another aspect of this "go your own way" (not the Fleetwood Mac song... ;) ) is not to be scared to try out new gear once in awhile.  Maybe it is a different power setup or even testing a different prop.  You don't have to go to the trouble of testing 10 different park jet motors like I have over the last year to find something very simple to breathe new life into your plane or your power system.  

Let's look at something as simple as changing a prop.  The 6x4 APC prop is without doubt the most popular park jet prop around and is an excellent overall prop.  Even though I knew people were using the 6x3 EMP prop, again I was worried about trying something new until I saw how a lot of motors perform with that prop.  I realized after trying out this different prop that I had been cheating myself of some real fun because I was scared to try something new for too long.

While with most of the motors I probably lost some top end speed, the increase in pop and acceleration for all round flying and aerobatics was truly eye opening for me, and that was a very easy and affordable change to make my plane fly differently.  The other good news is that my motors ran cooler and more efficiently with the 6x3 EMP prop.  So my point here is don't be scared to try out some different gear once in awhile, you never know when you will stumble on something simple that will better suit your building and flying style and your pocket book.

The research is never over nor should it come from one source

I know that Stephan and I get a lot deeper into research of aerodynamics and other things than you might be interested in and our testing is maybe beyond what you might care about, but I think always keeping an open mind in what you read or what you see your planes do is key to continually evolving your building and your flying.

The internet with Google, You Tube, the many RC forums and blogs like this one have an overwhelming amount of information.  Sometimes it feels like you might be trying to drink from a fire hose until you find good reliable sources of information.  But even then I think it is important not to "sole source" yourself to one person or one site.  I have always found collecting from many sources and then filtering through it from a standpoint of what suits how I like to build and fly always works best for me.

Even though Flite Test http://www.flitetest.com/ doesn't really do park jets, they make their living designing scratch built foam planes and I have picked up lots of little build tips from watching their build videos.  I have also learned several technical things from listening to some of their podcasts, so I do check their website quite often to see what is going on there, I never know when I might find a new nugget of info.  

Google and wikipedia are also good sources for theoretical research on aerodynamics, propeller performance, etc.  For gear research, including different people's testing and assessments or comparisons between other components, You Tube is a great source as lots of folks have taken the time to shoot videos of their findings.

Anyway, enough of my rambling... :/.  I guess of all the big picture lessons I learned from above that made the biggest difference in my park jet career was to do things my own way.  I try to measure my success by the fun and satisfaction I have when standing at the side of the field watching my plane fly around, not by how my build or my flying skills match up with what others have done or are doing.  It doesn't matter what I do, or what others on the forums or You Tube does, it should be about what you do... :)

Cheers,

Scott

RCP Mig29 V4 NAMCV3 - painted and powerful... :)

Hi everyone -

Just finished painting my RCP Mig29 V4 NAMCV3 and upgrading the power system by adding the NTM Prop Drive 2700 motor with 6x4 APC prop and 60A ESC.

Since the Mig35 is still in development and not yet operational (or at least I could not find reference to it being operational in any of my research), it has only been painted mostly grey for airshows and testing.  Grey paint schemes and my 53 yr old eyes don't get along well, so I went with a white, blue and red "camo" paint scheme in honor of the Russian flag.  Should be easy to keep track of, even at 100 mph... :)

Here are a few more pictures of the plane.

On the spine of the fuselage, I put our NAMC patch and the patch that RT designed for us with our motto in latin, Think, Design, Test and Validate.

Here is a picture of my new power setup and the layout in my electronics bay.  This shows battery position based on the current CG.

My overall weight is now 700 gr/24.7 oz with the 2200 battery.  My weight is now spread over 11.25" from the front of the ESC to the tip of the bullet nut on the motor.  This is only 1/2" more than the weight distribution with the FP motor which was 10.75".  As mentioned in a previous post, the NTM motor is about 3/8" longer than the FP motor and I needed the ESC to be that far forward to counterbalance the heavier motor.  As it sits right now, the bulk of the weight, the battery is in the same place as it was with the Focal Price setup.  This is pretty light for an NTM setup for me with full paint job and 6 servos, so I am excited to see what sort of speeds I will get, especially on 4S where my thrust to weight ratio will be theoretically 2.2:1.

I played around with thinning the paint a bit more since my Su35 MK2 build and found my paint scheme (I only painted the top) added only 18 gr/0.6 oz (I even painted the white areas to make the color "pop" a little better) which is about half what my old paint schemes used to weigh, so I am happy with that.

Weather isn't looking suitable for flying again til Tuesday, then the testing and evaluation with the new power setup will begin.

Cheers,

Scott

The NAMCv3 and Polar Moment of Inertia

I have been living large lately through Scott's design modifications, builds and flight reports.  Lately RC has had to take a back seat to my runaway freight train life these days.  Thanks to Scott and this page, I still get to daydream and think about aerodynamics and flight characteristics as I plan my next build.

Scott really hit on a basic concept of physics that we partially addressed in the past.  In our early days of the RPCv3s, we both we not happy with weather vaning and the EPPE (elevon polar pitch effect).  We fixed that by redesigning the elevons by decreasing their overall size to that more of a scale type craft.  In a natural progression, we both felt that the Mig was too long.  Scott has built and modified the FRC Su and vastly improved it as well by NAMCifying it as well.  Scott has posted his mods as well as as comparison of the length ratios as compared to the Mig.  Somewhere between the short Su and the stretched Mig was the sweet spot.  Scott found it in NAMCv3.

In addition to shortening the "wheelbase' of the Mig, Scott also brought the controllable mass of the airplane closer the center of mass and the Cg.  The center of mass is actually the integral of mass density. Meanwhile, Cg is the integral of force of gravity.  For my brain, center of mass is a static measurement while Cg is dynamic, i.e. plane at rest vs is the air.  By shortening the plane it, there is less plane to rotate around the Cg therefore the plane requires less energy to move in the roll, pitch or yaw axis.  This energy to rotate an object and overcome its inertia is referred to as torque.  The ability of an object to resist torsion is referred to it polar moment of inertia.  This is commonly abbreviated to a descriptor as an objects polar moment.  Basically, how is easy is to accelerate/decelerate an object.  I found a great example at http://www.avcanada.ca/forums2/viewtopic.php?f=3&t=94865.  I included his entire post:



As a pilot, you are taught to respect W&B. They
are tremendously important, and must be within
limits. Terrible things will happen if they are not,
you are told.

But then you hear about people flying over-gross
without incident (eg transatlantic ferry flights) and
the baby gets thrown out with the bathwater, and
people start disregarding W&B.

Despite what you have heard, weight is probably
the least important of the three topics of this thread.

You can increase the max gross of a 40-flap 172 by
150 lbs if you jigger the microswitch on the selector
so that you can't get more than 30 flaps. There's
even an STC for it.

I have flown airplanes that IMHO flew like they were
well over their max gross, they climbed so badly. A
fully loaded M20J on a hot day comes to mind, as does
a C150, which is frequently flown over max gross.

As I mentioned in the Accidents forum, an aircraft with
a forward C of G is going to be gentle and docile. It's
going to fly nicely and recover well from stalls and spins.

It is easy to develop contempt towards such an aircraft,
but beware that at the same weight, if you try to fly with
an aft C of G, like college girls on spring break, it's going
to behave badly. It's going to be sensitive in pitch, and
it's going to be a handful in stalls and spins. Might not be
recoverable at all.

tl;dr C of G is what matters, not weight. Weight just makes
your airplane climb like a pig, and a runway hog, which is
immediately obvious. A bad C of G, like your girlfriend off
drunk at Daytona on spring break, is not so obvious.


Now onto Polar Moment of Inertia (PMI) which is a measurement
of how the mass is located.

The best way to understand this is to take an egg carton with
four eggs in the center, close it, and spin it back and forth on
a shiny countertop, holding it from above in the center. See
how easy it is, to start and stop it spinning, with all the mass
in the center?

Now, open the egg carton and put two eggs in each end
and close it. Same weight, same balance, but a wildly
increased PMI. Now repeat the experiment, spinning it back
and forth, holding it at the center. See how much more torque
is required to start and stop it spinning?

This is why you want to centralize mass, which is actually
really hard on the wing spars, a subject for another time (ZFW).

So why did Scott notice such a hugh difference with the NAMCv3 vs prior Migs?
1. Overall shorter length
2. Most importantly, he put all of his eggs in one basket by centralizing the moveable mass of the plane (motor moved forward, centered the servos, battery, ESC)

Hope I didn't scramble (I know, corny attempt at humor) your brain!

Next it will be interesting to see how the NAMCv3 handles with the NTM and a markedly increased polar moment with a bigger battery as well.  The answer will be better the v2 with the same setup.  Why, because the fundamental law of gravity shall not be denied!

Stephan

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