Back out at the field again today getting some flights in with my F18 V3M :)
I managed to get 8 more flights in today before being chased away by some rain, but it was a very productive day none the less. I think I have the CG now dialed in exactly where I want it.
CG/PMI
I moved the battery back 1/2" from yesterday's testing and it just really gave me that locked in and almost perfectly balanced feeling when flying the plane. So my PMI is now about 9.5", not quite as tight as the NAMC Mig-35, but darn close. It certainly feels just right for this plane.
What was interesting today however was as I moved the battery back, the CG balance point moved back considerably from yesterday, either that or perhaps I was assessing it incorrectly, I'll be the first to admit I do make mistakes often :/
Anyway, today, the plane seems to balance perfectly at a point 1 and 3/4" behind the wing break or 1 and 3/4" behind where it is marked on the original RCP plans.
Here are a couple pictures showing where the CG is now located and how the battery is located in the electronics bay. In this first picture you can see the blue "+" indicating where my plane balances with the battery installed.
In this picture, you can see how far back the battery is compared to my first flight, hard to believe that I used to fly this plane with the battery 9" further forward than this :/ Just for testing sake, I did try it just a bit further (about 1/4") back, but then I could feel the plane tail heavy and harder to handle.
With the battery in this position, there was a significant difference in the arc tests, the plane actually floated a bit over the top of the arc before the nose dropped, which is what I am looking for. Then when I rolled inverted to cross check it, it only needed about 20% forward pressure on the stick to keep the nose level while upside down. Even though it would now be "top heavy" while inverted, it was very well behaved during inverted flight.
I know we all set our planes up a lot for how it feels to us, but as soon as I got the battery in this position, I could tell the difference. As I was flying straight and level, I could just let go of the sticks and it stayed true, smooth and stable and I have no trim required any longer in the pitch axis.
General flight characteristics
General handling and aerobatics are very smooth, yet very precise and the plane is quick and agile, but only goes where you point it, it doesn't over respond to the controls when it is balanced this well.
On launch, it just goes straight forward, I can see how well balanced it is as it starts to fly away and picks up speed. Then on landing, it just finds it's own natural sink rate, a little up elevator to hold it off at the end and I can touch it down almost like a feather, very impressive and satisfying to fly a plane when balanced properly.
KF adjustment
I am undecided as to whether I am going to play with the KF dimensions any further. I mentioned at the end of my last test session I thought I saw some "mushiness" returning to it's handling, but perhaps that was from a bit of wind or was "mushiness" of the brain and not the plane! :/ I'll further evaluate it's performance in the wind before considering whether to trim any more off the trailing edge of the KF. I have actually already removed about 3/8" from the stock KFs as I trimmed 1/4" off before installing them. Once I am satisfied the KFs are the way I like them, I will measure and report them based on their percentage of total wing chord at the wing root and wing tip.
Slow flight and high alpha
Although there was a light and variable wind today, I kept the plane up a bit higher and assessed it's slow flight and high alpha performance. I can see there is quite a bit more dialing in that will be required for the optimum high alpha setup which also relies on pretty calm conditions, so that may be a work in progress for awhile.
I could cruise around quite comfortably at about 40% throttle and still make easy turns with elevons and ailerons without danger of tip stalling, however with the plane being so well balanced and a tight PMI, it is far more responsive to the controls than I was used to with my previous F18s, so I had to be careful not to over control as I didn't have a lot of airspeed with which to help me recover. Fortunately, the 2212/6 2700 Kv motor and 6x3 EMP prop combo gives great pop to get me out of trouble if I do get too slow.
As I mentioned in my previous post, even with the battery all the way to the left of the battery bay, in high alpha the plane wanted to turn right on it's own all the time which defies normal performance where due to prop wash and torque the plane always wants to go left in high alpha. I did increase the throw on my rudders by 1/4" (1/2" total) which helped, but I need to experiment some more with "differential spoilerons" to help with high alpha stability and handling. Awhile back I wrote this article that might help you understand what I mean by setting up differential spoilerons for high alpha. http://migsrus.blogspot.ca/2014/12/differential-spoilerons-for-high-alpha.html
As you can imagine, the plane is much more sensitive to high alpha control inputs as the CG is much further back and the PMI is much shorter than the setup I used to have. It can hold very scale high alpha, about 40 degrees AOA (angle of attack), but I will have to train myself to be very smooth on the sticks to get the best high alpha performance, but I am up to the challenge. I've always found the F18 V3 to be one of my favourite planes when I feel the need to try a little high alpha flying and since the F18 does this a lot in airshows, it is nice to try and emulate the scale performance I have watched on many occasions live.
So a bit more testing to be done before I write my final synopsis, but thus far I am very, very pleased with the new life that seems to have been injected into the F18 V3, one of my favourite all time park jets :)
Cheers,
Scott
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