As promised, here is some video comparing the stock built RC Powers Mig29 V4 to the latest creation to come out of the NAMC, the modified Mig29 V4 M3e3. Some flight video follows proving that it flies... :)
Cheers,
Scott
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
Nice when a plan comes together
ReplyDeleteScott,
I’ll admit, there is always that moment of trepidation when testing new ideas. Especially since you are bearing the burden of the senior test builder and pilot. I’m ecstatic that our modifications resulted in a positive change in the flight characteristics.
Without being boring, I’ll try and explain why the CG moved forward. Unlike real airplanes and gas RCs, we have the advantage in electric RC planes of having fixed CG. The unfortunate crash of the 747 in Bagram is an example of the effects of a shifting CG. For a plane to fly stably, the CG must be within the center of lift (COL). The COL is sum of the lift forces generated by the wing, the fuselage, canards, and horizontal stabilizer. The lift forces change with the angle of attack. The wider the center of lift around the CG, the more “stable” the flight characteristics.
With the modifications we made, two produced changes in the COL. The horizontal stabilizer contributes lift and by reducing its size, we decreased its contribution to the COL. The increase in the KFs, moved the wing’s contribution to COL aft. So to obtain stable level flight, the COG had to move forward to counter the change in the COL. Simply put, we increased the stability of the flight envelope of the plane. Honestly, did I figure this out when we came up with the modifications? No, but we did figure this what modifications have worked since we started comparing flight data and testing. Trial and error. As I have said before, prior to retiring a plane, do some experimenting yourself.
Ever since I tried the vertical rudders on the KNEx, I could never understand why anyone would want anything else. I don’t want a rudder inducing pitch and yaw, at least minimizing the pitch effect. With the rudders on these park jets above the wing, there will always be some pitch effect. At least we have minimized the pitch effect of rudder input.
The last test will be up to Mother Nature to see if the EPPE is improved or needs more work. My gestalt is this plane will have more EPPE than the v3M3e3 simply due to surface area.
As always, great stuff!!
South of the Border NAMC partner,
Stephan
Excellent explanation of the CofG shift, Stephan, makes complete sense when shown in that light. This plane definitely does feel more stable and more solid in it's handling and characteristics. Not easy to explain perhaps, but just that "seat of the pants" feeling that I got flying it. The interesting thing is that every time I have flown a different plane with these mods or variations of these mods, I have felt the same thing when comparing them to the stock versions. It just seems that with these tweaks we have made it is like taking a race car that feels loose on the track and making it much tighter in it's performance and handling.
DeleteI'm with you, there is some trepidation just before launch when we have made these changes to a stock built plane we are already familiar with, but thus far on four different planes now, the FRC Foamies Su35 MK2, the RC Powers Mig29 V3, F18 V3 and now the Mig29 V4, it became immediately apparent to me that we have changed and improved the plane's characteristics to better suit our flying styles. So I am confident once again it is a winning combination of ideas we have here.
The forecast looks like I might have a bit more wind to play in today, but in all honesty, I am very confident that based on how the plane felt yesterday that we have eliminated most of the EPPE problem. I know that with planes that weigh only about 21 oz that it will never be completely eliminated, but I prefer my plane not to behave like a drift car every time I go into a turn... :) There might still be a little bit of room for adjustment in the back end surface area without making it too difficult to balance the plane. As I said in the video, I still had about 1/2 to 3/4" more room to move the battery forward and then we could also compensate by moving servos and other gear forward more to help with the balance. I placed my servos on the V4M3e3 in the same spots as I did on the stock V4 to make for an honest comparison, but there is still lots of room to move them forward or even put some extensions on the ESC and move it forward to help out with the CofG being moved forward, lots of options there.
I would venture to guess that the elevon surface reduction was about 10-15% of original and with moving the prop slot back another half inch, I reduced the tail plate surface area by about 3 sq inches. That and a 1/4" increase along the trailing edge of the KF definitely made the difference.
Another thought just popped into my head about the EPPE. Does it make sense mechanically that the tail will be less likely to drift out if the main weight of the battery is closer to the nose? Like a simple lever, if the weight of the battery is moved further out on one end of the lever (the nose), it would take more force on the other end of the lever (the tail) to move that weight, meaning the tail is less likely to wash out in a turn? Although granted this depends on where the actual pivot point might be on the plane, so maybe that theory doesn't hold any weight? Just spitballing there, hopefully I will get to see some actual proof today if there is a bit of a wind, but I just have this feeling that we have eliminated a large amount of the EPPE just with the mods we have made.
The vertical rudders are much crisper and direct, I would say that about 80% of the roll problem I found with the stock rudders has been eliminated. When I was practicing stall turns and wingovers which require considerable rudder input, I had to input very little opposite aileron to keep the plane from wanting to roll and yaw simultaneously. And normally I would get about 45% degrees of yaw before any roll would come on, then adjust accordingly. With the stock rudders I found I had to apply rudder and opposite aileron together right away or the plane tended to roll as soon as I input any significant rudder.
Anyway, many more test flights to come, but once again, just based on the 10 flights I got in with it yesterday, the NAMC ideas continue to work amazingly well... :)
Cheers,
Scott