MJD

My Feedback: (1)

But power doesn't make models go unstable, esp after flying 20 yards or so. Is it going berserk when you first apply control inputs, or is it after it seems to pick up a certain amount of speed, or..? Any chance CG is too far back? Everything straight?

vh2q

My Feedback: (5)

I think I figured it out, it is an intermittent battery switch ... at least that's what I think it is. The control surfaces were going into "freak out" mode due to low RX voltage. The controls tested OK in my hand just prior to launch so why they failed 20 yards out is still a bit of a mystery, perhaps vibration of just range. I cleaned the switch with electronic cleaner and now it seems to work. We will know for sure next time we have good flying weather.

skaliwag

My Feedback: (1)

Range test the radio?

50+AirYears

I had a similar problem some years ago. Plane going squirelly in the air just after launch. Second time, locked in up elevator, looped across the field without any control, ended up about 6 foot up in a tree. Thought it was the receiver, so I changed it out with one from another plane. Did a range check, engine off and engine running, while going through all throttle settings. After TO, the plane became a FF, with a gentle RH climbing turn. Thought I was in trouble, plane had a Fox .15 BB and a 4 ounce tank, good for about 21 minutes at full throttle. However, after about 1.4 minutes, plane went into a slightly descending banked turn, and ended up in a pear tree. Seems that as long as the plane was held by sombody, or in contact with the ground, there was enough vibration damping so the switch wasn't affected. Once in the air, the damping was gone, and the switch went full open, leaving the plane in whatever control settings last sent. I'm just glad it didn't hit anybody or anything, a 3.5 pound plane at around 55-60 mph can do some damage, especially with an 8-4 wood prop spinning around 14,800 rpm.

jonastecknare

I have tried to use small indoor recievers with the cox engines! Didnt work! I dont know if it was vibrations or something else. Anyway i have since stayed away from indoorstuff. Always use a fullrange reciever. I always had trouble with servos smaller than 5-6 g. The just couldnt take the beating they got!
Jonas

MJD

My Feedback: (1)

Still seems dodgy to me, if I had a troublesome switch I'd yank it out. In lieu of a switch there are options such as plugging the battery lead into a short servo extension from the receiver, but of course that requires internal access before flight.

vh2q

My Feedback: (5)

There isn't much room in this tiny model for a lot of wires, plugs and swiches etc, so I used a small Radio Shack two way switch hard wired into the battery circuit. In position A, it allows the battery to be charged via a pigtail that I can fish out via the window. In position B, it supplies voltage to the RX. I have used these switches before due to their terminals taking a standard futaba crimp-on terminal, with a little filing of the switch terminal. It seems to be making good contact now.

I have used the disconnect plug in a lot of other models but that's not foolproof either. I have had a Deans plug go bad putting my plane in the top of a very tall Redwood tree. And to conserve the very small battery in this plane, I don't power up until I have started the engine and set the needle.

50+AirYears

I'd be careful about using some of the cheaper switches. Often their contacts are little more than two maybe lightly spring loaded flat strips or balls pushing against each other. Think of just sliding your finger tips together. The best switches use a knife type contact. Think of holding the tips of the thumb and index finger of one hand close together, then sliding the tip of another finger between them, so that the finger tip is actually squeezed by the others. This gives a much more reliable, almost self-cleaning, relatively vibration proof connection. Found that out the hard early in my RC career, back with even tube type radios. One often had to build up the harness to fit, because even the switches were not supplied. You had to buy the wire, switch, battery box, and in-line connectors separately and solder everything together. Cheap switches quickly went intermittent.

We have it SO much better today.

Mr Cox

The small receivers are also very sensitive to disturbances. I had lots of radio problems on a J3 cub, with a pee wee. Turned out to be a nut I used to balance the front that was grinding on metal. That was enough to take the radio out in the air when the peewee revved out...

vh2q

My Feedback: (5)

The switch is rated to 15A I think so it should be OK. It is the sliding pad type though. I will keep an eye on it. I note that my RX picks up static every time I hook up the glow plug.

50+AirYears

Metal-to-metal contact, especially with dissimilar metals, can generate electrical noise that will be picked up by a receiver. The lower the receiver frequency, the more sensitive the rcvr will be. Add to this the fact that when the center post makes contact, there is a sudden flow of several amperes of current through a small coil, I'm sometimes amazed that I have had almost no trouble with this, except with the earlier 27 MHz radios back in the 1960s. Some were so sensitive to metal contact, just having a loose clevis on a threaded rod could cause problems throughout a flight. Or sometimes even too much looseness in carburetor parts on an engine, or a loose universal muffler.

vh2q

My Feedback: (5)

Well I changed the switch and while I was at it, also the battery pack (not because I suspected it, but I found a smaller pack and with only 2 servos this little plane doesn't need much battery). Tricky work, like building a sailing ship inside a bottle, as the only access I had was one side window and a small hatch for the RX connections. I ranged it and called it good. Planned to fly yesterday, Memorial Day, as we had a break in the rain, and also for personal reasons Mem. Day was a good day to maiden this plane. While doing test glides, I noted the control surfaces quivering at 20 yards range. Had absolutely no radio range. Back to the bench to change the RX. Finally got that done including some soldering in tight quarters in time for supper. After supper, with one hour of daylight left, I took her out for a test flight. Took me some time to get the needle on the Cox 020 right (ran at 7 1/2 turns!) and off she went. Flight was successful but short, due to small tank and futzing with the needle. Second flight off she went with gusto. Joy! She flew well with plenty of zip. I got over-enthusiastic and coming out of a steep bank I decided to loop her. The video tells the rest of the tragic story of this little rubber band Stinson.

[link=http://www.youtube.com/watch?v=Vh8xhb-KNXs]Memorial Day[/link]

It took all night (10 hours) to upload this 1.9GB video ... (: )

R/C Phile

Too bad about "structural issue" it was flying beautifully.

What did you use as covering? Do you have some pics of the breakage ? The fuselage looked pretty well triangulated from the earlier pictures.

I did not picture an .020 as an over-powering monster I guess I'll keep that in mind when I finally build the plane for mine.

vh2q

My Feedback: (5)

I used monokote. The weak point was the wing attachments, each wing was separately att and the struts were glued but obviously not well enough. Should have used some FG tape.

The new video, when posted, will show the aftermath. Not repairable unless I wanted to make a new fuse, and then I would have the same structural problem I suppose. And I don't have the plans ....

R/C Phile

I see, so there was no beam going along the spar from 2nd or so rib to the other side connecting the wing roots together. Instead, it was a "Butt join" to the center section shown on the prior picture right?

vh2q

My Feedback: (5)

There was just a short balsa stub on each wing that went to the fuse and if I recall I put an extra piece of balsa in the fuse at the attachment point, but there was no connection between the wings. It wasn't the butt joint that failed though. It was the strut attachment to the wing, and also to the fuse. I did reinforce the struts with unwaxed dental floss and CA. If I had glassed the strut root to the fuse, and the tips to the wing, I think it would have been OK. Stupid, I glassed the entire cowling to strengthen the motor mount, but I failed to do the struts. Live and learn.

You can still buy this model here, but's it's been updated since mine was built (a good 15 years ago). If I were to do it again, all it needs is a Cox 010 or an 020 Pee Wee. The Cox 020 Tee Dee was pushing the model beyond it's limit I think.

http://www.gravesrc.com/DUMAS_STINSO...R_p/dum203.htm

If someone does buy this model, I would very much like to get a set of plans (or a copy) so I can rebuild the fuselage from scratch. I don't have the heart to rebuild the whole model.

vh2q

My Feedback: (5)

Well since I now have an RX and 2 servos to spare, I have started to build an EDF version of Jonas' Saab Tunnen. I had to scale it up 20% to accommodate a 35mm EDF. The main design change will be to use custom made fiberglass air ducts on both the inlet and exhaust side of the motor. This will entail moving the electronics up into the upper half of the fuselage. Since we are only working with 10 oz of thrust here, we have to keep it light. The body will be monokote over balsa formers/stringers (as I believe Jonas built his) and the wings will be sheeted balsa over balsa spars.

I know it's not 1/2A any more but this is one situation where I like electric motors. For prop engines I still like noisy metal pistons that spray oil all over the place.

See pic for progress. The plan Jonas sent me calls for quite a bit of ad lib construction so we are learning as we go. Hopefully no do-overs.