I managed to get this beauty out yesterday for it's maiden flight and to start getting it dialed in😀
I managed to get 10 solid flights done yesterday and think I have the CG dialed in pretty much where I want it and the throws are also just about there as well.
Here is some flight footage and discussion of yesterday's flight session, I did some more dialing in after I shot the video which I will discuss later in this post.
Center of gravity (CG)
As I mention at about 7:40 in the video, my CG ended up about 1/2" ahead of the middle of the black rectangle that RC Powers puts on their V5 plans. Here is a picture of what the CG spectrum looks like on the V5 plans.
Where the toothpick is on my plane shows where the center of this black rectangle is located and the "T" pin shows where my CG ended up for best balance, this has been a trend on all the RC Powers V5 planes I have built😕
Before I go any further on discussing the plane's flight characteristics, I will get the discussion on what I did wrong with my KF airfoils out of the way first.😉
As mentioned in the video, on the first couple flights, the plane felt quite twitchy and as it accelerated or slowed down, often the left wing would dip quite aggressively and the nose would pull left, just a bit scary!😲
I had quite a bit of left trim in at the time, but that shouldn't have caused the rather aggressive wing dips and yaw that I was seeing, so after the second flight I decided to double check that the trailing edges of my KF4 airfoils on both wings were even. Low and behold, the trailing edge on the bottom KF on the left wing was about 1.5-2mm further back than the one on the top...OOOPs! 😬
How I determine this is I push a pin through the wing right at the trailing edge of the KF as you can see in the picture to see if the trailing edges are aligned. When I pushed it through on the left wing, there was foam behind it on the bottom, you can see the part I trimmed off laying on the wing.
Once this was trimmed off, the nasty tendency to want to dip the left wing went away, fortunately the RC Gods were with me yesterday and I didn't lose the plane due to my inattention to detail in that part of my build😳 Big lesson learned and wake up call😓
Control surface throws
A couple flights after I shot the video, I did zero out all the trim on my control surfaces and found that my right aileron was deflected up about 2 mm when it should have been dead center, so I zeroed that and it helped me remove quite a bit of the left trim I had been flying with. There is still some there, but not anywhere near as much.
Here are my current throws which may get adjusted minimally as I get more used to the plane, but these seem to work best for scale flying and still allow me a little extra in the pitch if I need to avoid hitting something😲 Of note, I don't fly with a lot of expo, only 15% in the pitch and roll and 20% in the yaw, so the control surfaces react pretty quickly when I move the sticks. Pictures are below showing where I hold the ruler to measure for reference.
Pitch - 3/4" of travel one way;
Roll - 1/2" of travel one way in both the elevons and ailerons; and
Rudders - 1 and 1/2" one way.
Of note, the travel in the roll in the ailerons and elevons is equal. On most other planes, my aileron throw is considerably less (normally less than 50%) than my elevon throw in the roll axis. With these stealth style park jets, I find I need to have them closer to the same to get the rolls crisp and axial otherwise the rolls tend to be more of a barrel roll or the nose wanders around during the roll.
Launch
Launches were uneventful, I was a bit worried after downsizing and reshaping the vertical stabs and shortening the nacelles that I might have some torque roll issues, but none ever showed up. With the good mid range power of the EMAX RS2306 2750 Kv motor and the fact the plane is pretty light at 552 gr/19.5 oz, 50% throttle was sufficient to get it going and flying away nicely.
Turns
The T50 tracks really well in turns, in the calm wind conditions I had, I never really had to feed in any rudder input to keep the nose tracking true. However, it took me awhile to get the throws and my touch just right to keep it from "over banking". As I mention in the video, the battery sits up much closer to the wing plate, there is only about 3/4" between the bottom of the wing plate and the bottom of the electronics bay on this plane whereas with my modified F-22 V5, it is more like 1 and 1/4" which makes the F-22 more stable. Also, because I reduced the height of the nacelles, there is less resistance in the roll axis, so it sometimes wants to bank a little more quickly than a lot of other planes I fly. However, with time my thumbs will figure out the right touch😉
Rolls
As mentioned above in the section on throws, it did take me awhile to get the rolls sorted out to ensure they were balanced and axial. The T50 is very responsive in the roll axis and requires very little surface deflection to do a complete aileron roll.
Loops
As I mentioned briefly in the video, it takes a little gentler touch over the top of loops to let the up elevator input off at the right time. Since the battery does sit a little high in relation to the wing plate, the T50 is almost a bit "top heavy", so as it starts to go through pure vertical, it can fall over on it's back a little more quickly than some other planes, so when I was trying to go for a nice uniform loop, I had to be careful with this. Otherwise, the loop would look more like an egg where the plane went over the top too quickly and then the bottom of the loop would be wider.
Yaw response
Even though I did trim the rudder surfaces down quite a bit to accommodate my mod to the nacelles, they are still pretty responsive, of course I have pretty big deflection in them, but for keeping the nose true in turns, etc they do the job just fine. I like to pull up in the straight vertical and do stall turns to see how the rudders respond, thus far the T50 is not quite as quick in the yaw axis in a stall turn as the F22, but I can still get it to do pretty decent stall turns.
Slow speed
I took the plane up to about 100 ft a couple of times and reduced the throttle down to about 40% or so, it was not too bad, I had to be very careful in the turns or I would see adverse yaw on occasion. Essentially what would happen is I would be putting in control inputs to make a gentle turn in one direction and if the speed bled off too much, the plane would have a tendency to yaw in the opposite direction of the turn, sometimes quite aggressively. This was not a surprise as it is a common tendency with park jets with the stealth type wing like the F-22 and T-50. So lesson learned, don't get too slow in turns, speed management is crucial to ensure either the plane doesn't want to roll on it's back to suddenly yaw opposite to the direction of turn.
Cruising around
In the video I mentioned that this airframe style (T-50) likes to go fast. I didn't mean you need to fly it wide open all the time, it flies and behaves just fine at about 50-60% throttle all day long, but on occasion as the speed bleeds off too quickly or the throttle setting gets too low other than when coming in to land, it can misbehave somewhat😏
High speed
I would say RC Powers is correct in billing the T-50 as being faster than the F-22. The F-22 is pretty fast, but this T-50 is noticeably faster. Once I got the KF problem sorted out, it handled aggressive acceleration and full throttle runs just fine, I didn't see any torque roll, speed wobble or tendency to want to zoom or dive. Full throttle turns and aggressive vertical pulls were just fine, no bad tendencies, it felt locked in and solid at speed and the wing was strong, no flex even in high G turns or pulling out from loops and dives.
Glide/landing
The T-50 behaved itself well on approach to land, I did my normal approach routine, roll it out straight and level, chop the power and let it glide down at it's own rate from about six ft off the ground, feeding in a little bit of up elevator as needed. Once I had it balanced, it actually maintained a pretty steady and smooth rate of descent on it's own once the power was chopped. I fly with my brake off on my ESC, so the prop free spins as it is gliding, I have found this to give me the most stability. Then just as it started to break ground effect about 2 ft off the ground, I fed in just enough elevator to hold it off and it landed pretty smoothly on it's own. Once I fixed the KF problem I didn't notice any tendency for it to want to tip stall as it slowed down to land, which is good👍
So overall, the T-50 is fast, agile and very responsive, especially in the pitch and roll. Once I started to get the hang of it, it became more and more fun to fly with each flight although it did take a bit more dialing in than some other planes to get the CG and control throws just right. As I mentioned in the video, because of it's quickness, speed, adverse yaw habits if too slow in a turn and it's slight "top heaviness", I would not recommend this for a starter or even second park jet. Perhaps if your skills were coming along well or you had lots of flying experience before getting into park jets it might be a different story. I would say the F-22 is a bit more forgiving while still quick and aerobatic, so if you have never flown a stealth style park jet before, I would suggest flying the F-22 first perhaps with some of the mods I made as discussed in this video to help with stability.
Looking forward to many more flights with this little rocket of a park jet and as I get it dialed in completely and more comfortable with it, I will shoot some more video😊
Park Jet noise...the "other" sound of freedom😎
Cheers,
Scott
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