I managed to get out flying yesterday, took two of my favorite planes to the field... :) The camo one on the left is my stock built Mig29 V4, built as close to plans as my building techniques will allow and on the right with the less than stellar paint job is my FRC Foamies Su35 MK2 which has been significantly modified from stock.
So I thought that since both these planes fly really well (at least for my preferences) but one is stock and one is not, why not discuss why we might modify our planes?
When Stephan and I first started discussing our builds through the RC Powers forum, he was working on a Mig29 V3 that he called the KNeX (Knife Edge experimental) where he was looking for a rudder setup that would allow him to fly knife edge maneuvers with his Mig. At the same time, I was working on trying to make my Su35 MK2 more stable. I had built and flown two versions of this plane previously and enjoyed it, but found I had to crank my throws down and my exponential on my radio way up in order to be able to handle it. So after looking at several different things that were making other planes more stable and talking with Stephan about several different ideas, I adjusted my build accordingly.
So in these situations you can see that most of it is about modifying the behavior of your plane to suit your flying style, not because the stock plane was horrible in the first place. Sometimes it is about enhancing a certain behavior to get your plane to do something better and sometimes it is about modifying something to reduce a bad behavior.
As Stephan has mentioned in a previous post, building and modifying a plane is all about aerodynamic trade offs sometimes. I think we would all like to have a plane that is fast, yet also flies well really slow, is rock solid stable but also incredibly nimble and agile for aerobatics. So as you might play around with the configuration and setup of your plane, you might find that you improve one area at the detriment to another.
Stephan took advantage of his KNeX Mig and in addition to the rudder mods and testing, he did a lot of testing of KFs and aileron and elevon shape and sizes. With the KFs he tested different combinations of thicknesses, taped the trailing edges to simulate tapered KFs and he learned and proved many things, that Mig he tested gave us a huge amount of groundwork for developing the Mig29 V3M3e3 which we both really love to fly.
At the same time, I had built an FRC Su35 MK2 with several mods to try and improve it's stability as I found it a bit too twitchy for my level of flying skill. I also found it suffered from tip stalling and thrust vectoring stalls where with too much elevon surface deflected at slow speed, the elevons would act more like speed brakes, cause the back end to drop, nose to pitch up and well...things could get bad real quick from there... :/
So we both ended up being very happy with the mods we tried and tested on these two very different planes and thus was born the "M3e3" effect that has since been applied to our Mig29 V3M3e3, an RCP F18 V3 with great success and now the RCP Mig29 V4 although the mods have yet to be field tested.
A few things we found were constant on all these very three different planes that we modded with respect to our flying styles.
We don't need huge control surfaces to make our planes fly well. Even at slow speed, there is still tons of response, but because we are putting less surface into the slip stream, there is less associated drag and turbulence. Responses are cleaner, crisper and the planes fly more precisely.
Extending the top KF airfoil along the intakes or leading edge extensions depending on what plane you are building adds great stability and seems to make the plane fly just that little bit smoother. While on the subject of KF airfoils, Stephan and I are both big fans of using paperless dollar store foam top and bottom. We both have to be prepared to fly in windy conditions where we live and the equal thickness of airfoil top and bottom makes a big difference in speed and stability. We both like to build our wings with 6mm depron, so rather than adding 12 mm extra thickness, the approximately 9 mm we add still gives the stability we seek, but cuts down on the thickness and drag of the wing. Besides, the dollar store foam is cheap and very easy to sand, saving some depron for other things. It is also easier to make the leading edge symmetrical when the thickness of foam top and bottom is equal.
With respect to the depth of the KF or it's width in relation to the wing chord, we have yet to find any definite percentage for what works best for swept wing planes like the Mig and Su families. I have found through experience that about 40% seems to work best for me which is a little larger than what most stock plans call for. Again, some folks prefer wider, some narrower, all a matter of experimentation and choice. For more straight wing planes, like the F18, I experimented with 50% which in testing was found to be the ideal thickness and it seemed to work awesome on my F18 V3M3e3.
We don't claim to be the inventors of any of the techniques above, they have all been tried by others before us, but these are some of the constants that we have been finding regardless of the plane.
Although the wheels are always turning between Stephan and I how a plane can be tweaked in pursuit of the "perfect park jet", one or both of us always have and always will build a new plane stock as close to plans as possible before we try modifying. That way I feel it maintains the integrity of what we are doing in being fair to the designer and also allows us to see what behaviors are good or bad that might need to be improved upon to tweak the plane to suit how we like to fly.
I know that building one plane stock and then building a modded version might not be for everyone, but Stephan has a great philosophy. If you have a plane that is getting ready to be "recycled" due to a few too many "gonks" or maybe you are just tired of it, try some mods, cut it up, tape it up, try some different control surfaces, different KFs, etc, you never know, it might breathe a second life into your plane. Or if nothing else give you some ideas for your next scratch build. The other neat thing is that doing all this stuff and then testing at the field is not only a lot of fun, but it helps us learn a great deal what little nuances impact just how our plane flies. That is the beauty of foam park jets, the material is cheap, and we all have scraps laying around to make new elevons, ailerons, whatever to try something new.
So in closing, we don't mod our planes because we think we are smarter than the original designer or it is a statement on what we feel is wrong with the plane, rather it is to modify how the plane performs to maximize our flying experience. At the end of the day, it is all about you standing at the edge of the field having the most fun possible with your plane, at least in my humble opinion. If tweaking a few things here or there to make your plane fly better without having to spend a bunch of money makes that experience even better, that is a pretty good deal to me and worth experimenting... :)
Cheers,
Scott
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