A couple of weeks ago I took my ARF T-Rex out for its first flight session, and I wanted to share some thoughts and observations and advice...
My T-Rex, the one from the "T-Rex progress thread" on Stunt Hangar, was the absolute best flying airplane I had ever flown, better than my current Time Machine, better than a host of other people's planes I have flown (including some top 20 and top 5 Nats planes). It was also the only plane I had ever encountered that was pretty close to "flying off the board", to the point that its second flight was a full pattern that would have fared quite well on a lot of Southeast contest scoreboards
It was the best flying plane I ever had, for 2 and 1/2 flights. It disintegrated in an outside square on flight number three, ending its career in a crumpled heap of contest balsa and ultracote.
Ranting about how bummed I am that my plane fell apart is not the purpose of this post though. I feel that this design has too much promise to be kept down by the issues of Chinese wood selection or quality control and I think events will bear me out over the next year or two, as more people see a T-Rex fly for themselves. I did want to share some thoughts on how mine flew, how it failed, and what can be done to rectify the structural issue.
Obviously, there is little new under the sun as far as stunt aerodynamics and design goes, and frankly, it doesn't really matter how exactly Brad Walker arrived at the numbers and configuration, but, as he would say, “I'm here to tell you” that it works. My example had brutally hard corners that could be entered and exited with perfect control, instant locking onto the flats, and yet executed rounds with uncanny ease. The round loops felt like they only required two inputs, one to enter the maneuver and another to return to level flight, with the plane almost saying "ok, I'll take over from here" as you entered the maneuver and giving you back the controls as it exited. The overheads were a joy to execute and the big jug style fuselage presented just awesome as you watched the ship go through its paces. This may be the very first truly competitive mass produced ARF in a .60 size. My only squawks about flying characteristics were that I felt that the vertical fin area was a tiny bit too small (I know, somewhere out there Howard Rush is probably laughing right now) it made me think that it needed a little dorsal strake like the later marks of the P-47 had, just something to help a little bit with the larger props. When I talked about this with Brad, we had a good natured argument about it and he pointed out (in fairness) that it was more likely the fact that the leadouts were not perfect yet, and in this case I defer to the designer. Another flight issue I have noted, not just in mine, but in all four different T-Rex’s I have flown to date, is that every one of them can be driven into a stall, especially in an inside pullout where you have the 1 g of gravity added to the normal pull for a corner. Brad’s extensive testing with his 67 ounce example did not find this problem, and I am guessing that the much lighter production versions are allowing the wing or flap to flex to the point of spilling air through the flap hinge gap. I didn’t tape the hinge line on mine, probably the one important bench trimming thing I left out. We are going to tape one of the other T-Rex’s in the club and see if it fixes the stalls-I’m betting it does. I might be clear here as well that these are slight stalls, and not on every corner-maybe one detectable stall per flight, just the sort of random funny that taping usually eliminates. I’ve been trying to get some good in flight photos to see what the wing is doing, but so far have not seen anything exciting, even on film covered wings. The flex is detectable by some skin wrinkling, but total deflection of the wing seems much less than say, a typical I beam ship.
The achillies heel (of the ARF version) is the fuselage just at the trailing edge of the wing. To my knowledge, there have been two failures of the fuselage where the top sheeting just behind the canopy fails under tension in an outside square, allowing the entire fuselage to split in half and making the airplane impossible to control. The picture I attached of mine shows exactly where the failure occurred. My buddy Eric down in Florida lost his T-Rex ARF to the exact same failure a few weeks before mine. We thought maybe his was a fluke (he lost his in about 30 flights), but when mine failed in three flights it pretty much confirmed at least some of the ARFs had issues. As Brad has commented on in some of the T-Rex threads, the Chinese evidentially discovered the mother lode of contest wood and started putting it in T-Rex’s, circumventing Brad’s elegant design that is made to give maximum lightness for the usual heavy wood the Chinese use. The use of contest wood in the critical upper skin, combined with the film finish of the ARF, is enough that some will fail. (some, but not all-one of my fellow club members has a T-Rex ARF that we abuse like a red headed stepchild, and through 91 flights it showed not the slightest structural issue anywhere.)
The short answer for the structural issue is to buy an ARC version, or strip off the covering of an ARF and redo it. My next T-Rex will be an ARC for the simple reason that I might want to fly it at the Nats some time, and under the current rules the ARC is legal, the stripped ARF is not. Two of the local T-Rex’s are ARC, covered in .5 oz glass cloth and epoxy on the fuselages and film on the wings, they have been flying with Saito and PA power for several weeks now without the slightest issue. My next T-Rex will use the glass on the fuselage, and silkspan on the wings-while the extra wing rigidity may not really be needed, it certainly can’t hurt.
For the person with an ARF, reinforcement on the inside of the fuselage upper skin with glass cloth and CA or epoxy would be highly recommended -why take a chance when you have a pretty expensive engine up front. In addition, some of the other recent T-Rex construction threads have some good tricks for extending the fuselage doublers past the trailing edge of the wing which will add greatly to the strength. If your ARF is already completed, you might consider removing the covering from the top of the fuselage from the back of the canopy to about three inches further back and glass the wood at that point, then replace the covering. It may not look pretty, but it will look worse if the fuselage lets go, trust me. Again, the picture of mine shows exactly where the fuselage fails and where reinforcement will do the most good.
Finally, lets hope this thread can be an exchange for better ways to address this and any other problems that might arise with the T-Rex. I have contacted both the manufacturer and the designer for this plane, and I know they will have engineering improvements for later generations of T-Rex’s down the line. In the meantime, we can debrief on our own experiences here on the forum so that losses of planes and engines are minimized. After all, as good as these things fly, you’ll want yours to hold together for a long time!
Steve
PS, I’m sorry for the rambling nature of this post, but its hard to write with a 2 year old climbing all over you. I hope some find this helpful.
Topic: T Rex flight report (Read 5766 times)