North American Mig Consortium (NAMC) was formed to share ideas, build techniques and test results in pursuit of a park jet that suits our flying styles. This additionally will be a forum to freely post and share ideas and have a lot of fun! If you don't have gmail or google accounts and want to send us questions, please do so at scott@migsrus.com. Your e-mails may be re-posted in the blog to benefit other followers.
Puto, Consilium, Test et Convalidandum;
Think, Design, Test, and Validate
Made some more progress on my NAMCV2 Mig29 V4 today. Finished all the final sanding, cut out the holes for the servos, installed the motor and the control horns. All fussy work, but good to have done, now she is ready for paint... :)
As I mentioned in a previous post, I have found with both the previous Mig29 V4s that I have built that the CofG has ended up between 5/8" and 3/4" ahead of stock on the plans, so I wanted to move some weight forward to allow me the flexibility of using lighter 1600 and 1800 batteries. Here is where the aileron and elevon servos are on my current Mig29 V4s.
And here is where I will be installing my aileron and elevon servos on this plane. I moved them forward 1 and 3/4".
Rudder servo holes also cut out, the push rods will run outside the vert stabs and rudders to try and keep the prop slot and prop wash area as clean as possible.
Bottom view showing control horn positions. The aileron servos will be angled to meet up with the control horn that is almost in the centre of the aileron. I'm not sure how this will affect airflow over the bottom of the wing, moving the servos forward increases the length of the aileron and elevon push rods, thus causing greater angle on the aileron push rod, so it might be one of those "trade offs" you have to live with sometimes when modifying a plane... :/.
I also managed to score some paints at the dollar store today that are a pretty close match for my paint scheme. I will take pictures at each stage as I apply each shade for the three tone camo pattern to give an idea of the technique that I like to use. I hope to get started on the paint tomorrow. I already have my radio programmed, I essentially just copied the setup that I have for the Mig29 V4 NAMCV1 since it seems to work really well, then I will fine tune from there since the ailerons are slightly different and the rudders are about 55% bigger in moving surface area.
Then after paint, final installation of the Rx, ESC, all the rat's nest of wiring, etc, put on the decals/insignia and she will be ready to fly! Thus far I am about an oz lighter than I was with the NAMCV1, so as long as I don't goop the paint on too thick, I should get down around 20.5 oz with a 2200 battery... :)
Another very busy day in the NAMC workshop (Canadian Division). I managed to get the airframe completed including KF4 airfoils, time now just to let all the glue cure overnight before dry fitting the servos and doing the final carving, shaping and sanding.
I'm pleased with how the NAMCV2 modified vert stab and rudders turned out, looks pretty sleek and lots of control surface, can't wait to try them out.
During assembly, I noted that I had made a bit of a "boo boo" in cutting and ended up with a bit of a gap between the back plate and where it meets the vert stab and side fuselage in the back as you can see in the picture below.
As I am trying to build light, I didn't want to smear a bunch of glue in there to fill the gap, so I had a bit of a "eureka" moment fortunately and decided to bridge the gap with a strip of drywall tape reinforced with Foam Tac glue. I did this both on top and bottom. So not only did I cover that gap, but in the process I managed to strengthen up that critical joint considerably... :) Sometimes I would just rather be lucky than good... (which happens a lot, cause I'm not that good :/ )
So after cutting the holes for the servos, it will be time to give the plane it's final finish with razor knife and sandpaper. This process again is a bit fussy and takes some patience, but makes a huge difference not only in how the plane looks but how it flies in my experience. It also on average saves 15-20 gr or about half an oz or more in weight with the foam that is removed.
I have forced myself to be a bit more methodical in this build and take my time, thus far I have managed not to use any hot glue, just Foam Tac. I will use some epoxy for the motor mount and control horns, so hopefully as long as I don't go too crazy with the paint, I should keep it lighter than my previous Mig29 V4 NAMCV1. Not that the NAMCV1 is a pig by any means, but I am shooting to get as light as my first Mig29 V3 which weighed 20 oz with a 2200 battery. It will be tough as the V4 in foam alone is almost an oz heavier than the V3, but I'm doing my best.
Then after the finishing job, time to paint then mount the motor and electronics and then start the process of getting everything connected and sorted out before the maiden flight which I hope will happen early this week... :)
Managed to squeeze in a little more time in the NAMC workshop (Canadian Division... :) ) today. I put the Velcro down in the electronics bay, put the bulkhead and nose former in the fuselage and then did a considerable amount of sanding and shaping on the trailing edge of the wing, the back plate and elevons and the rudders and vertical stabs. The sanding took about an hour and 15 minutes, so after that I thought it better just to leave the nose forming and shaping til tomorrow when I have the energy. I find that nose forming is a bit of a fussy job, so I want to be fully committed before doing it so that my plane doesn't end up looking like Jimmy Durante... :)
In the next two pictures I wanted to show the comparison of before and after sanding of the tail plate. It does round off some of the sharp corners and scale angles of the Mig elevons, but at 20 ft in the air I'm not too worried about it. What I am pleased with is the reduction in drag that it gives me... :)
One thing I did note today when I was sanding the elevons was that there was a bit of flex in the small area between the main elevon surface and the "nozzle", so I put down a small piece of drywall tape and some Foam Tac and coupled with the drywall tape on the opposite side that acts as a hinge , it is now nice and strong.
I know I have rambled on about the virtues of symmetrical leading and trailing edges and paying attention to detail in doing a good job of sanding in previous articles and when I was still active on the RC Powers forum, but wanted to revisit it again today. Now I certainly was not the first one to do this, folks were shaping and sanding their foamy park jets long before I showed up, but as my building skills improved coupled with some great feedback from Stephan, I have taken my finishing skills to the next level of attention to detail and it is paying off considerably. Even on the first plane that I really modified, the FRC Su35 MK2, I was still going with the "chiseled" leading edge on my wing and elevons. Again, part of following the "herd" on the forums as that was what everyone was doing and was being recommended by RC Powers.
I really don't know why it took me so long and so many planes to convince myself that aerodynamically this makes no sense. I suppose if I was using a KF2 airfoil or had a cambered wing then maybe I might go for this shape of leading edge, but otherwise, I can't see the benefit. Again, thanks to Stephan for helping me break out of that rut!
I did do a "half hearted" job of tapering the trailing edges on this plane, but not to the point I do now, this was a pretty sloppy job with just a few quick swipes of the sandpaper... :/
So fast forward a few planes and here is the symmetrical leading edge on the wing of my stock RCP Mig29 V4.
Also, as you can see below, I took the time to properly taper and blend the trailing edge much more on the Mig as well.
So, why all this worry and fuss about shaping and sanding leading and trailing edges and the entire plane in general? Well, I guess it depends on how you like to fly and what you expect from your planes. I still have probably another hour of carving, shaping and sanding to go once the plane is all together, so that is over 2 hours just sanding.
Since buying into the tapered leading and trailing edges and truly taking the time to blend the taper by starting off with 150 grit sandpaper and then finishing with 220 grit, I have been amazed at how much slipperier my planes feel in the air.
Another bit of proof hit home the other day when I was flying the two planes show in the pictures above. I wasn't really testing or evaluating anything, just out thrashing around having fun, but I started to notice on approach and landing, that the Mig29 V4 with the symmetrical leading and trailing edges would dead stick glide over twice as far as the Su35 with chisel edges. Now I know I am comparing two different planes, but I had to keep power on much longer in the landing approach with the Su35 in order to maintain control whereas the Mig just kept gliding smoothly and efficiently for over twice the distance that the Su35 was capable.
So if you fly or have to land in a really small area, this might not be something you want your plane to do, but overall I think this proves how much more efficiently the plane glides and cuts through the air when the time is taken to really shape and sand the leading and trailing edges and the entire fuselage and body. It is almost like free speed, or free efficiency (other than a couple sheets of sand paper and a couple hours of time) without having to upgrade any equipment.
I'm finding that by taking the bulk of the foam away with the 150 grit and then gradually shaping it smooth with the 220 grit back about 3/8" from the edge, makes for a nice smooth transition rather than a rough, angular, blocky edge. Given that most foams are not the most slippery materials with which to build an airplane, anything I can easily do to cheat the air and gain speed and efficiency is a good thing.
Maybe that is too much fuss for you and that is fine, as I have said before, do what makes you happy and build and fly how you want to, that to me is the most freeing thing about this hobby of scratch building foam park jets. I know sanding is not one of my favorite parts of the build, but I have proven to myself it is crucial to really pushing my planes to their maximum performance. As both Stephan and I have mentioned, don't worry about what we say or anybody else says, the moment of truth is when you are at the field flying your plane and how much fun you have.
If however, you are looking to squeeze just that extra bit of performance from your plane, I encourage you to give some thought to really taking the time to sand and shape your plane to make it as aerodynamically sleek as possible including trying symmetrical leading and trailing edges on the wing, elevons, vertical stabilizer and rudders. You will be amazed at how much smoother and slipperier your plane feels through the air. I know I did the first time I tried it and I will continue to refine my sanding and shaping technique with every build.
There is a threat of rain here this weekend which will interfere with flying... :(, so I hope to keep plugging along on the build and maiden by next weekend.
I finally got my butt in gear and got some foam cut out this afternoon. Just need to cut out the KF4 airfoils next, but those can wait a bit as they are going on in a later stage of the build.
In the picture below you can see my carbon reinforcement setup. In the wing plate, I am using 4mm carbon rod for the main wing spar, the section as shown is 16.5" long. For extra reinforcement that has been working really well in my previous two Mig29 V4 variants, I am using 3mm carbon tube along the leading edge. I cut the channel about 5/8" back from the leading edge so that when I attach the KF4 airfoils and then bevel and sand them back for my symmetrical leading edge, the carbon tube won't be affected. Those two sections are 12.5" long each. You can also see my modified ailerons attached as well.
I am using 5.5" sections of 3mm carbon fibre tube on the elevons shown above, they are hinged with fibreglass drywall tape and Foam Tac. On the back deck plate, I have already cut off about an inch of foam to help prevent the Elevon Polar Pitch Effect (EPPE) or fish tail turns in crosswinds that can sometimes occur with the stock back plate. I also moved the tabs (indicated by the pencil in the picture) and corresponding slots in the side fuselage back about an inch to ensure good solid assembly when I get to that point since I removed an inch of deck plate in order to open up the prop slot considerably.
In this picture below, you can see that I have cut some triangular vent holes on the sides of the fuselage (behind where the bulkhead will attach to the fuselage) as well as one each on top and bottom of the fuselage to aid in air flow through the electronics bay. Cooler weather is on it's way before too much longer, but I always like to have good airflow going through the electronics bay anyway.
As I mentioned in a previous post I am really hoping to keep this plane good and light, so I used thinly spread Foam Tac glue opposite the score lines on the fuselage, they act as a very light hinge when I go to make the score and fold part of the assembly. I like to just make a very small impression in the foam and then run a thin bead along that line and then squeegee off the excess. You can see the shiny lines where the glue has dried and is ready for folding.
Since I like to have a little extra strength along the score lines of the intakes/nacelles, I have had really good success with using one inch strips of fibreglass drywall tape and Foam Tac glue, as I reported in my last post, 201 flights on my stock Mig29 V4 and that joint is as strong as the day I built it... :)
In the next picture, you can see the rudder setup I ended up going with, quite a bit larger than stock and my previous NAMC modified Mig29 V4. I didn't completely cut out the little slot that you can see below the rudder, next step is to symmetrically shape and sand the trailing edge of the rudder, wing and the leading edge of the vert stab as well as the front and back of the prop slot. I find this much easier to do when they are still flat pieces of foam before assembly. I left the little slot in as it is easier to sand that way and prevents small sections of foam like that between the slot and the bottom of the rudder from getting broken during sanding.
So quite a bit of work accomplished today, as mentioned, next is some fussy sanding of some leading and trailing edges, but I have been finding this well worth it. I find it makes the plane much quieter, more efficient and slipperier through the air.
Now that hopefully I am on a bit of a roll, I'll keep the build moving along at a good pace... :)
Another milestone for me today at the field, I flew my 200th flight (201 and counting) with my stock built RC Powers Mig29 V4. Here it is dutifully guarding the pilot's "jet fuel", a cup of black coffee from Tim Horton's which apparently is now getting bought out by Burger King worldwide for $11.4 billion USD... :/ Wonder if that means I can get a double Whopper and fries with my coffee and maple dip donut?! That will be great for the nutrition plan...yikes! But, I digress... :)
This plane has seen a lot of flying over the summer as I have evaluated it beside my Mig29 V3M3e3, my Mig29 V4M3e3 and my FRC Su35 MK2 NAMC V1.
I have mentioned several times that without a doubt this is the best stock (ie built to plans without major modifications) built plane I have ever flown and is a major improvement over the Mig29 V3 in all categories. You can read and see my comparisons between the stock Mig29 V3 and V4 in these two posts
One thing I have noticed now with this many flights accumulated is that the CofG seems best about 5/8" of an inch ahead of the stock CofG on the plans. On my modified Mig29 V4M3e3, it is actually more like 3/4" ahead of stock. As Stephan explained, this shift on the V4M3e3 is probably caused by us moving the center of lift due to modifying the back end and moving the trailing edge of the KF airfoil back about 1/4".
Here is a picture showing where my current CofG is on the plane. The hex driver is pointing to where the stock CofG is and the ziptie is pointing to where my CofG is now. I know not the best of teaching aids...but they are what I had handy... :)
So keeping in mind that this trend will probably continue, I will use this information to adjust a few things on my current Mig29 build in order to be able to use lighter weight 1600 and 1800 Mah batteries.
As you can see in the pictures below, I had to have this lighter battery all the way up against the bulkhead, quite far forward to get the plane to stay balanced in the pitch.
With fall approaching, we actually tend to have a lot calmer days wind wise, so I won't need to worry so much about having extra weight to help with wind stability in my planes. As such, I want to be able to use my 1600 batteries http://hobbyking.com/hobbyking/store/__9456__Turnigy_1600mAh_3S_30C_Lipo_Pack.html which are 18 gr/0.6 oz lighter than the yellow battery shown above to really be able to get some good speed and slightly lower wing loading when I want.
As such I think I will need to move some weight forward to allow the plane to still balance with the 1600 battery as I can't really put it any further forward without needing down trim. I have some leeway with my new build to move the Rx further forward as well as my aileron and elevon servos. The picture below shows where they are on the stock Mig29 V4.
Even though the modified Mig29 V4s that Stephan and I have been working on fly faster, sharper and more precise with less bad habits than the stock Mig29 V4 (at least for how we like our planes to respond and behave), this stock Mig29 V4 is still a blast to fly and I hope to have it around to compare with the Mig29 V5 if and when that should come out... :)
Well, I have started work on my new Mig29/35 NAMCV2 (making up new acronyms is fun... :) ) based on the RCP Mig29 V4. I am looking to experiment and evaluate a couple of things as shown in the pictures below. It won't be a speedy build as with the nice weather I do a lot of flying now and other summer activities, but I will plug along and keep the blog updated.
As Stephan and I have discussed a bit already in previous posts, I want to experiment with larger rudder surfaces to see if it helps improve right turn performance in high alpha without sacrificing clean, direct rudder response in the yaw axis, i.e. no rudder roll that has to be compensated for with opposite aileron when doing stall turns, wing overs, etc. So basing my rudder mod on the FRC Su35 MK2 stock rudder, I angled the rudder hinge and trailing edge back 3 degrees from vertical and then extended the hinge line right to the top.
I now have a rudder surface that is about 10.75 sq inches, an increase of 2.75 sq inches over the rudder I have on my Mig29 V4M3e3. I'm interested to see what happens, I'm sure it should give better rudder authority, but hopefully not cause any other problems that need to be compensated for. This should still give me that updated Mig35 look and since the hinge and trailing edge are still pretty much vertical, I should retain the good clean characteristics of this design that I like.
I have also decided to play with the aileron shape a little bit, pulling the hinge line aft about 3/8" and extending the length outwards about an inch. This actually gives me pretty much the exact same amount of moving surface as the V4M3e3 aileron, but I'm interested to see how or if there is any difference in high alpha stability and performance (when the ailerons are deployed as spoilers/spoilerons). This brings the aileron to about 50% of the total trailing edge of the wing. I will still leave 3/4" static along the fuselage to allow me to run my push rods externally without interference from the moving originally designed aileron.
LATE EDIT: In the process of cutting out the foam just now, I realized I mislabeled the picture below.... :( The length of the trailing edge of the aileron should be 4 and 3/4", not 5 and 3/4". Sorry for the confusion... :/
Another main goal I have in this build is to try and lighten it up a bit over the V4M3e3. I got a bit heavy handed with the hot glue in a couple spots in my haste to get it built, so I am hoping if I can lighten it up by about an oz, I might break the 90 mph barrier with the Focal Price 2700 motor on 3S with the 6x3 EMP prop... :) I clocked the V4M3e3 at 88 mph, so I'm hoping with a little weight reduction I can break the 90 mph barrier.
All other build techniques will be the same as my previous two RCP Migs including all the other mods I made to the V4M3e3 from stock. As I mentioned in my last post, I liked the blue camo pattern on my last stock built FRC Su35 MK2 which I think was inspired from a Kazakhstan Air Force paint scheme. So the other day a picture popped up from the MigFlug page I follow on Facebook of an Azerbaijani Mig29 and luckily it was on this website I like to use for Mig paint schemes http://www.mars.slupsk.pl/fort/mig/ I think the roundel looks kinda cool too, so this is the paint scheme I will go with.
As always, it is exciting to tweak and experiment a little bit more with this plane and if I don't fully achieve the goals I am look for, I still have a pretty darn cool plane to fly... :)
Reached a nice milestone today, flew my 200th flight (201 and counting actually :) ) on my FRC Su35 MK2 with NAMC mods. Here she was at flight zero before maiden.
Here she is today after 201 flights...I guess my magic marker "paint job" could use a little touch up, but I don't want to jinx her... :/
This is one of the first planes that I took the time to research and plan out a series of modifications to not only prove to myself that different ideas work, but also to stabilize and smooth out how the plane flew within the limits of my flying skills. I had already built two FRC Su35 MK2s and an FRC Su37 MK2, details on those are archived in this blog earlier in the year. The first one I built far too heavy, it just never flew properly from the outset, lesson learned.
So I built a second one much lighter with a lighter power setup and really enjoyed flying it, I got about 80 flights on that one shown in the picture below before the accumulation of "gonks" were just too much for it. But over those 80 flights and experimenting with all different setups of expo and throws, I found that it was susceptible to thrust vectoring (TV) and tip stalls and I also wanted to build in a bit more stability and tone down it's responsiveness, hence the research and mods. As a side note, this was an excellent paint scheme for visibility and orientation, worked in all sky conditions and against the dark background of the trees at my flying field...will use it again... :).
Fortunately around this same time, Stephan and I started sharing our ideas and philosophies on park jets and their setups and how we could modify them to best suit our styles of flying. At that time, Stephan was working on an RCP Mig29 V3 KNex (knife edge experimental) to see if he could get some good knife edge performance with the Mig29 V3. So that is basically when the North American Mig Consortium (NAMC) was born.
The following two posts have the details, pictures and video of the modifications that I tried on my Su35 MK2 with NAMC mods, so I won't repeat all of them now.
As I have mentioned in many posts, the mods that I tried were certainly not my own ideas, I borrowed them from what I had seen other folks doing on the RC Powers forum and elsewhere and modified them with input from Stephan and from what made sense to me aerodynamically. Many of the mods were posted and some were not, but apparently from what some folks told me afterwards, they had been tried before. I did borrow the angled out vertical stabs idea from the Mig29 V3 with permission from RC Powers which I don't think at that time had been tried on the Su35 MK2, but again, I could be wrong.
One of my biggest takeaways from building this plane and subsequent modifications I have worked on with Stephan and tried on several other planes, is not to be scared or skeptical that something won't work until I try it. Nothing proves or disproves a theory or a modification like seeing what happens after the plane leaves your hand. Even all the post flight reports I have written, videos I have done trying to pass on my experience or reading what others have done on the RC Powers or other forums can replace the satisfaction of trying something out for yourself.
Before I started working with Stephan and sharing ideas, philosophies and results, there were a lot of these mods we now enjoy and employ on our planes that I would not have tried until I took the leap of faith, broke down my own paradigms and tried them. Before that, I was stuck in a bit of a rut, doing things because that is what the "herd" on the forums was doing, so it must be right... :/ Imagine my surprise when I found out that trying some other things that in the back of my mind always made sense to me was what I should have tried in the first place! I'm not bashing the forums, they are certainly gold mines of information, but if you find your plane is behaving in a way you don't like or a certain popular technique does not make aerodynamic sense to you, go with your gut and try out what you think makes sense, you might be amazed at the results... :)
Without pounding my pulpit too hard, I am a firm believer that your plane should do what you want it to do, not what someone else wants their plane to do. If you have an idea that has not been tried before or "flies in the face" of the conventional theories or even any of Stephan and my theories, give it a try... :) It is only foam and you might be surprised at what happens.
Stephan has an excellent philosophy, take one of your older planes that might be near the end of it's life or you are thinking about recycling and use it as a test bed, get out your knife, tape, glue, some scrap foam or whatever else you need and try out a new mod or two. That way if it works on that plane, it might breathe a whole new life into it, or inspire you to try out that idea, mod or technique on your next plane. And at the end of the day, if the theory didn't work, you didn't build a whole new plane to end up being disappointed... :)
So now that I have probably bored you to tears with my personal testimony, I guess I just primarily want to pass along my biggest lesson in almost two years of building, crashing, rebuilding, modifying and oh yeah...flying park jets. I always try and remind myself that all the great builds, blog posts, You Tube videos and what is popular on the forums is great, but ultimately they should only be important to me if they help me achieve the goal of building and flying my plane to my satisfaction, not anybody else's... :)
Now granted, it took me almost a year and a half to fully realize this and have the courage to follow my gut if a certain build technique or plane characteristic didn't make sense to me, so we all find our way somehow. If you are just starting off, it doesn't hurt to try some of the proven or popular techniques, but if you find it isn't working for you, don't be scared to change the status quo and go with what makes sense to you.
Fear and common sense can sometimes be highly overrated, sometimes you just have to build it to your standards and satisfaction, take it to the field, toss it in the air and see what happens. You might leave the field with a huge smile on your face or end up going back to the drawing board, but the risk is definitely worth the reward in my experience... :) And don't forget at the end of the day, this is supposed to be fun... :)
Scott,
I just reread the flight gear references on torque. Excellent articles and written so it is easy to understand what is happening. In looking at your picture, I realized when in high alpha we only have one rudder doing all the work. The inboard deflected rudder is doing the thrust vectoring. The contribution of the outboard deflected rudder is minimal. I have always been surprised about how much rudder input I use in high alpha. Now it makes sense, I only have "one" rudder in high alpha to generate yaw.
For a design solution to improve right turns the answer is increase the surface area of the rudder and to increase the prop wash to the outboard deflected rudder.
On my next build, I would increase the rudder surface area. With the extended leading edge as we have now, it would be easy to add height and width. Going back to the stock leading edge, there is less room to increase the surface area. Definitely would need to glass the vertical stabilizer where it gets narrow. Here is what I was thinking doing on my next build:
Why not extend the rudders the length of the vertical stabilizer? I tried this on an earlier build but it made the plane very unstable in knife edge which is a flight characteristic I have been chasing. Leaving the top part of the vertical stabilizer adds lift and stability in knife edge.
Increasing exposure of the outboard deflected rudder in high alpha is more difficult. The v4 vertical stabilizers and tail plate are a half inch wider than the v3. In comparing the two planes, I don't think there is much difference in prop wash to the rudders. The ultimate solution would be a counter rotating dual engine setup. The torque issue would be negated and there would be equal prop wash to the inboard and outboard deflected rudders. This would be a great winter project.
Since my last post discussing my high alpha testing of my Mig29 V4M3e3, I have been doing quite a bit more flying, evaluating and reviewing further the difference in rudder performance between my stock RCP Mig29 V4, my Mig29 V4M3e3 and my FRC Su35 MK2.
As I have mentioned several times in previous posts, the more vertical rudder style on the FRC Su35 MK2 and the Mig29 V4M3e3 is definitely my preference for pure, smooth direct rudder response in maneuvers that require a lot of rudder input (other than high alpha which I will discuss in a bit). Both planes respond very well to rudder input without any adverse roll characteristics. The stock Mig29 V4 still has rudder induced roll in most maneuvers which must be countered with more opposite aileron input to prevent the plane from rolling over when large amounts of rudder are being used in stall turns, wingovers, even just coordinated turns.
This practice has been very good for me to hone my flying skills as I am finding now in windy conditions especially I am doing more coordinated turns with both elevon and aileron with a tiny bit of rudder working with it. I find just the tiniest bit of rudder helps bring the nose around a little smoother, then once I am through about the halfway point of the turn, I ease off on the rudder and just continue with aileron and elevon and my turns are turning out much smoother in windy conditions.
On the day I flew the stock Mig V4 and the V4M3e3, I was able to get a little bit of a high alpha comparison done. It was a tiny bit windy, so I couldn't manage sustained high alpha, but high alpha for 30 seconds at a time or so. I noticed that the stock V4 had good rudder authority both left and right, but when the rudder did "bite" in high alpha turns, it also caused roll, causing at times the low wing to drop quickly. Since I fly with spoilerons, I could give a little opposite aileron to correct or just let off on the rudder a bit and the roll lessened until I could get the nose around to where I wanted it.
The V4M3e3 was still at times challenging to get through a right turn, especially if I was turning in crosswind or trying to get the nose back into the wind, it would slow down considerably, requiring me to input some pretty significant rudder to keep it coming around and normally a shot of power so that more prop wash was going over the rudder surfaces. So although I have no wind tunnel proof, from what I saw, I think in my haste to redesign the vert stabs and rudders, bringing that leading edge of the vert stab forward for aesthetics is causing some airflow blockage problems... :/ (sorry Stephan... :( ) More on that in my previous post here http://migsrus.blogspot.ca/2014/08/mig29-v4m3e3-hi-alpha-testing.html
Again, perhaps I am wrong and something else is going on, but it is worth trying something else to prove or disprove my theory. So although I had just started another FRC Su35 build, I am putting that on hold and will work on another Mig29 V4M3e3/Mig35 NAMC to further research and evaluate another vert stab/rudder setup. The "M" in NAMC is Mig after all, so if I have the excuse/opportunity to build another Mig, I'm going for it!
I am going to go outside the box a bit and research Option C that I wrote about in the link above, a narrower but taller rudder surface similar to the Su35 which will have more total moving surface and almost vertical (angled back only 3 degrees) hinge and trailing edge. Also this allows me to eliminate almost all of the addition I made to the leading edge of the vert stab on the V4M3e3 that my gut tells me is causing blockage to the prop wash. Maybe I am grasping at straws and have evaluated this whole thing incorrectly, but sometimes I just have to follow my gut instincts and see where it goes. I should have flown my Mig29 V3M3e3 as well, but my memory serves it didn't seem to have such a challenge turning right in high alpha as we left the vert stab leading edge more stock than I did on the V4M3e3.
I already have Mig29 plans back from the print shop, and will leave everything else on the V4M3e3/Mig35 NAMC the same (unless Stephan thinks there is something else we need to try... :) ) other than a new vert stab/rudder setup, so back to the North American Mig Consortium work shop (Canadian division... :)). The FRC Su35 will still get built, just a bit later than originally scheduled... :/
Had two of my favorite Russian park jets out at the field again today blasting through several more batteries.
Fortunately, it was almost dead calm, so I managed to get some sustained high alpha testing with my Mig29 V4M3e3... :) Unfortunately, epic fail on my part as I didn't expect it to be calm so I forgot my camera at home to video any of the flying... :/ :(
As Stephan mentioned in his post with his excellent flying video, http://migsrus.blogspot.ca/2014/08/flight-highlights-of-mig-35-namc.html it is a bit more of a challenge turning right with this plane in high alpha than it is left. This is true for most planes in my experience, but this one seems to be a bit more of a challenge... :/
So, I did a little research to understand why this is common to all planes in an effort to figure out how we might go about alleviating some of the challenge of turning right in high alpha with this plane. Before I go any further, I must caveat by saying that I am certainly not an aeronautical engineer, so how I am interpreting things primarily just comes from my own logic, from considerable park jet flying experience and closely observing how my airplanes respond and behave in given situations.
I found an excellent website that explains a few contributing factors to why most planes are a bit more challenging to turn right in high alpha quite simply, or at least simply enough for me to understand it... :) http://wiki.flightgear.org/Understanding_Propeller_Torque_and_P-Factor Although these theories are primarily for front mounted or tractor prop type planes, much of it still applies I think to our mid mounted "prop in slot" park jets and in fact might be exaggerated a bit due to the stronger prop wash in close proximity to the empennage (tail assembly of rudders and elevons/elevators).
From what I have read from the link above, there are probably three main things going on that cause making it more difficult to turn right in high alpha with our park jets.
Prop wash - "A propeller pushes air not just horizontally to the back, but more in a twisting helix around the fuselage (clockwise as seen from the cockpit). As the air whirls around the fuselage it pushes against the left side of the vertical tail (assuming it is located above the propeller's axis), causing the plane to yaw to the left. The prop wash effect is at its greatest when the airflow is flowing more around the fuselage than along it, i.e., at high power and low airspeed, which is the situation when starting the takeoff run." This is quoted directly from the link above. Although in our situation we don't have a fuselage in the way of the prop wash, our prop wash when it hits the rudders is still fairly strong as it has not had much distance in which to dissipate. Also, perhaps high alpha exaggerates this behavior since it is a low airspeed situation, not necessarily high power, but certainly low airspeed;
Propeller torque effect - "Torque effect is the influence of engine torque on aircraft movement and control. It is generally exhibited as a left turning tendency in piston single engine propeller driven aircraft. According to Newton's law, "for every action there is an equal and opposite reaction," such that the propeller, if turning clockwise (when viewed from the cockpit), imparts a tendency for the aircraft to rotate counterclockwise. Since most single engine aircraft have propellers rotating clockwise, they rotate to the left, pushing the left wing down. Typically, the pilot is expected to counter this force through the control inputs. To counter the aircraft roll left, the pilot applies right aileron. It is important to understand that torque is a movement about the roll axis. Aileron controls roll. Prop torque is not countered by moving the rudder or by setting rudder trim. It is countered by moving or trimming the aileron. This correction induces adverse yaw, which is corrected by moving or trimming the rudder (right rudder)." Although when we turn left in high alpha, we don't normally want the plane to roll, having this added benefit does seem to make it easier to turn left and probably contributes to the challenge at times of turning right.; and
P Factor -
"P-factor is the term for asymmetric propeller loading, that causes the airplane to yaw to the left when at high angles of attack.
Assuming a clockwise rotating propeller it is caused by the descending right side of the propeller (as seen from the rear) having a higher angle of attack relative to the oncoming air, and thus generating a higher air flow and thrust than the ascending blade on the left side, which at the other hand will generate less airflow and thrust. This will move the propeller's aerodynamic centre to the right of the planes centreline, thus inducing an increasing yaw moment to the left with increasing angle of attack or increasing power. With increasing airspeed and decreasing angle of attack less right rudder will be required to maintain coordinated flight.
This occurs only when the propeller is not meeting the oncoming airflow head-on, for example when an aircraft is moving down the runway at a nose-high attitude (in essence at high angle of attack), as is the case with tail-draggers. Aircraft with tricycle landing gear maintain a level attitude on the takeoff roll run, so there is little P-factor during takeoff roll until lift off.
When having a negative angle of attack the yaw moment will instead be to the right and and left rudder will be required to maintain coordinated flight. However negative angles of attack is rarely encountered in normal flight. In all cases, though, the effect is weaker than prop wash."Again, this information is considering a normal tractor type airplane, but I had never considered that the prop itself might not be generating even thrust with both blades until I read this part of the article.
So, if you are still awake after reading this rather technical data, here are a few things I thought about after reading this that I have observed at the field over time when practicing high alpha with my RCP F18 V3 with which I have logged many high alpha flights
In an effort to keep this plane light, I did not reinforce the vertical stabs, so I often get a lot of "vertical stab flutter" on my right vertical stab where the left one stays static. This is in direct relation to the prop wash point above I think, showing that the right stab gets more prop wash and since the prop wash is going that way, when trying to turn right, perhaps there is less force on the left rudder surface.
Also, I notice that when in sustained high alpha that the prop sound is different, the power setting stays fairly constant, but the prop does sound different, perhaps this is caused by the P factor and the imbalance in thrust between the two blades? With this F18 V3, I normally had to keep a tiny bit of right rudder input in at all times when doing high alpha or the plane would naturally want to drift left to the point where I could do almost a complete wide 360 turn if I left the rudder alone and just kept the plane stable in the pitch and roll axes in high alpha.
So since these factors above are always going to be present in any park jet, I started to wonder if there was something in how I redesigned the vertical stabs and rudders on the Mig29 V4M3e3 that may be causing it to be a bit more of a challenge than other planes to turn right in high alpha.
So while at the field yesterday, I started to think about several things and decided to see what was happening. I don't want anyone to get the idea that this plane is impossible to turn right in high alpha, but it definitely requires more lead time, more steady rudder input to turn right than to turn left. Is this manageable? Of course it is. And considering that the way the rudders and vert stabs work so amazingly well in other parts of the flight envelope is it really a matter of great concern? Well, no probably not, but one of our cornerstones at NAMC is to constantly pursue that "perfect park jet", especially where our favorite park jet the Mig29 is concerned. While we understand this might not ever be achievable, when there are other options to explore, why not explore them?
So I wanted to see if the plane drifted left like my RCP F18 V3, so I set it up to fly high alpha and then just took my thumb off the rudder. It in fact stayed very straight and tracked true, only wobbling if a bit of breeze hit it. So, no bad tendency to drift left on it's own, but still a bit more challenging to get it to turn right. Now, comparing the F18 V3 to the Mig29 V4M3e3 is a bit of "apples and oranges" as the Mig29 vert stabs are perpendicular to the wing plate, while the F18's are angled outwards, perhaps this causes more left drift on the F18, but the F18 is also a bit easier to turn right in high alpha.
With my plane in particular with the CofG about 3/4" ahead of stock, I can almost pull the nose up to about 70 degrees for short periods of time (say maybe about 5 seconds or so). I am not trying to hover it by any means, I think a "hovering parkjet" is a bit of a stretch of scale performance (sorry RC Powers... :/), but that is just my humble opinion. What I did notice though was as I got the nose up that high, my ground speed came down to almost zero, putting into basically a "power stall". This in fact then did really funky things with the rudder control... :/ Not only was turning right then almost impossible, in fact I got reverse yaw several times where putting the rudder hard over to the right actually caused the nose to go left...yikes! Fortunately I was high enough to recover or that could have been costly... :/
So I started to wonder, did something I did in the design of the rudders/vert stabs help exaggerate the problems with prop wash, prop torque and P factor? As Stephan had mentioned in one of his build/walkaround videos, I had moved the leading edge of the vertical stab forward when redesigning the vert stabs/rudders. Unfortunately, this was not based on any kind of "aerodynamic epiphany", rather pure aesthetics so that the top of the vertical stab didn't look too narrow or "pointy"... :/
So I got out some of the most valuable tools of an RC park jet test pilot's arsenal, a copy of the plans, a pencil, eraser, ruler and protractor and got to work looking at what was going on and drawing up possible alternatives.
I drew up this diagram of the stock vert stab/rudders with the Mig 29 V4M3e3 vert stab/rudders drawn over them highlighted in yellow as well as maybe some other options highlighted in orange and blue. I tried to highlight the original leading edge of the stock vert stab in green, but it doesn't show up too well... :( However, hopefully you can see that there is quite a bit more surface area forward of stock with the adjustment in the angle of the leading edge.. So I started to wonder...does this extra surface now block some of the prop wash to the right hand rudder when trying to turn right? If the left hand rudder is already less effective because of the prop wash properties, maybe I have made matters worse by physically reducing the amount of air that flows to the right rudder when trying to turn right in high alpha... :/
So I started thinking about another plane I have been flying a lot lately that has very effective rudders, the FRC Su35 MK2. The rudders were one area that I did not modify when I built this plane. And since I already had a copy of the plans on my work table as it is a plane I am building right now, I did have a bit of an "aerodynamic epiphany"... :) Although I have said that the rudder hinge and trailing edge of the rudder on the Su35 are vertical, you can see in the picture below they are not purely vertical, they in fact tilt back about 3 degrees which is much less than the stock Mig29 which tilt back about 13 degrees. Now, before I go too far down this road, I must admit that I have not been able to fully assess the Su35 rudder design in high alpha as for me, the Su35 MK2 is not a good high alpha plane. I find that as soon as I get the nose up to about 25-30 degrees, wing rock comes on quickly and violently, that has been my experience with all three Su35s I have built (two stock and one modified), but again, just my experience.
So in the plan diagram (I just pasted it in below again to make it easier to follow), I drew a line that angles back 3 degrees from our V4M3e3 rudder, shown in orange. Then keeping the same dimensions at the top of the vert stab, this allows the leading edge to be angled back considerably, almost to stock (again this is shown in orange). Although it is angled slightly, it still gives an almost vertical appearance on the back edge, allowing me to keep the Mig29M/Mig35 profile that I really like and the still relative clean back end that reduces drag and turbulence over the much more angled vert stabs/rudders of the stock Mig29 V4.
I also drew in the 4" by 2" rudder that we have been using on the Mig29 V4M3e3, again shown in orange. Then for another option, I drew in the rudder styled exactly after the Su35 style rudder, the hinge line shown in blue. Although this option makes for a narrower rudder in relation to the V4M3e3 rudder, it ends up being approximately 8.5 sq inches, where the V4M3e3 rudder is 8 sq inches.
So here are perhaps a few options I am considering for my next Mig29 V4M3e3/Mig35 NAMC. I don't plan on cutting up my current plane as I think it is due for a motor upgrade to the NTM Prop Drive 2700 for some kick ass speed where high alpha performance is not as important as just "haulin' the mail" and doing everything else at greater speed and higher wing loading... :) Besides, if I modify the rudders and vert stabs on my next Mig, I want this to compare it to.
Option 1 - leave everything as is. This probably won't happen as I won't be able to test and evaluate a different setup if I did... :/ ;
Option 2 - angle the V4M3e3/Mig35 back 3 degrees and keep the 4" by 2" inboard rudder. This still gives pretty much vertical rudder hinge and trailing edge, but allows the leading edge to be pulled back closer to stock and hopefully prevent as much prop wash being blocked from the right rudder as I'm trying to turn right. This rudder design gives great crisp, clean rudder input without the adverse behavior of roll like the angled stock V4 rudder;
Option 3 - again angle back 3 degrees, but use the style of rudder that the Su35 uses, taking the hinge all the way to the top and not having an inboard rudder. This reduces the chord or depth of the rudder surface from the V4M3e3, but increases total rudder surface by 0.5 sq inches and perhaps extends the effectiveness of the rudder in the prop wash as it expands after leaving the prop. This design works very well on the Su35 as it provides very crisp, clean rudder input without adverse roll behavior. As mentioned before though, I have yet to be able to assess this rudder design in high alpha with my Su35 MK2 in any configuration.
So, in the spirit of testing and evaluation, it is going to be either option 2 or 3. As with any change or modification, there is always a risk of adversely affecting other performance qualities of the plane, but if we don't try, we won't know... :)
The Mig29 V4m3e3/Mig35 NAMC is still the best park jet I have ever flown, and even if neither Option 2 or 3 changes it's right turn performance in high alpha without adversely affecting it's other performance qualities, I will be very happy with it. As I said before, this is a small part of the whole flight envelope and it can be dealt with using the right anticipation and finesse in piloting. But then again, one never knows what might happen with that next little tweak...I think the risk is worth taking... :)
