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Old 08-23-2013, 01:18 PM   #2076
a65l
Wise guy, eh?
 
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Joined: Aug 2004
Location: Where life is good and the air is sweet
Oddometer: 1,066
Quote:
Originally Posted by Saget View Post
15 seconds??? WTF happened? Hoping you have better luck the second time.

So I'll fill you all in on the whole sordid story. I bought the plane off a radio control website with the initials R.C.U, if you don't know it already. They have a buy/sell section, and I thought the plane was a good deal for the size plane and all. Sight unseen, I might add, other than the pictures. Well, when I got it, as usual for me, there were multiple things I didn't like. I was rushing a little bit, trying to get some flight time before a big event we were having. I could never get a straight answer out of the guy I bought it from if he had flown it or not. I'm guessing not, given the results of my first flight.
Anyhoo, I fixed what I didn't like, and modified a few things, but really wasn't overall happy with the plane. It's a big boy, 112" wingspan and the plans call for a flying weight of 26-28 lbs or thereabouts. This one was, I would guess conservatively, about 24 pounds. It was 24 pounds because the builder decided that it was better to not use the heavy and relatively pricey spruce and aircraft grade ply the plans called for and instead use Balsa wood and light ply. The next part is important. Of the same dimensions.

Let me repeat. Of the same dimensions.

Now, I'm not one to talk down other builders and hobbists. I don't know everything, and I'm certainly not qualified as a master aircraft builder. The guy I got this plane from had built qutie a few more planes than me, and as a matter of fact one of my club members had one. It was very nicely built, tight secuure joints, straight, fairly solid. But me, just me, if I'm going to substitute wood of, well, lesser strength in high stress areas, I'm going to increase it in dimension. I know balsa is strong wood, but if the designer calls for spruce of a certain dimension, I've gotta believe he knows what he's talking about.

Anyway. So I fix this and I fix that, and leave a couple things because, gosh darn it, he must know what he's doing, right? And let's not forget, I checked the CG as well, and wound up adding almost 4 pounds of lead to the nose to get it to hang level at the reccomended balance point. But that's OK too, I have another airplane that balances well behind it's CG point, and it flies fine. So maybee he did fly it like that, and likes it that way. Who knows. I don't, and I do like my warbirds to be right on or slightly nose heavy, especially on the first couple of flights.

Now I've got to talk about the wing attach method, because that's what failed. The Fokker D8 uses two sets of struts each side of the plane to hold the fuse to the wing. The fwd. struts are a tripod arrangement that bolts to a single point on the wing. The aft struts are single struts that bolt to the wing aft of the fwd struts. Convention would say that when bolting fairly important joints like that one would use either a block of hardwood, drilled and tapped, and a suitably long bolt, or a "T" nut with a bolt as well. The builder had, instead, installed a piece of 1/4" aircraft ply at the mount points, then drilled and tapped that to accept the bolt. I discovered this bit of engineering genius when I attached teh wing for the first time, and the bolts wouldn't tighten. Further, the foward struts (tripod arrangement, remember) consisted of three pieces of wire. The main wire was one piece from the bottom of the fuse to the bottom of the wing, where it fitted through a hole in a piece of angle aluminum. This was my failure point. Turns out that I should have put a wheel collar on that piece of wire before I tried to fly.
Now, I did see this as a potential problem, but with the plane on the ground I moved the wing around as much as it was possible to, and picked the plane uip by the wing, and did everythign I could to determine if a wheel collar was needed there. I never saw the wire move, so I figured I was good.
So, back to the maiden flight. AFter range check and multiple runs around on the ground, including a shutdown where I rechecked all the bolts and wires and wheel collars and control linkages, we were off. The takeoff was nice and straight, the engine seemed to make enough power, but just as it lifted off and passed out of ground effect I saw the wing "cock" to the left. The plane started to turn left, I applied corrective controls and it responded, at which time I started thinking about landing. I think I was starting to ease into a right turn when the wing seperated completly from the fuse. The fuse, of course, turned into a lawn dart. Good thing the ground at the field was soft, even though the prop broke I don't think the engine suffered any damage. The wing just fluttered down to the ground, unfortunately landing on a wingtip.

The moral is, and my lesson is, if you think it's wrong it probablly is. I have to wonder, though, if that plane had survived it's maiden flight how long it would have lasted. We tend to toss the WWI planes around a bit, scale stuff and all that, and I don't think the wing spar would have survived it's first loop. Not to mention the fwd. upper struts were simply screwed into balsa! stringers. Oh, and the horizontal stab was all 1/4" sticks. That thing spans almost 24".

This one I'm building is gonna come out heavier than the original, but that's fine. I'm pretty confident it's going to be under 30 lbs ready to fly, and at that weight it should do fine.

I've got a funny story about control reversal too, and it's the reason I always check the controls three times before takeoff....
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