Crash Box Special

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kittyfritters
Posts: 241
Joined: Tue Sep 27, 2016 8:13 pm

Crash Box Special

Postby kittyfritters » Thu Oct 27, 2016 7:12 pm

You do have a crash box, don't you? That's the box where you keep components from salvaged from expired models that you think may be of some use in the future. Usually they are hardware items, propellers, nose bearings, prop shafts, etc., but sometimes complete wings and tails.

I was printing some skins for no-cal orders and thinking about an upcoming R.O.G. contest. The skins take a while to print so I do other things while they are printing. My gaze fell upon the crash box. Rummaging through it I selected a wing, from an Alphonse Penaud style pusher that I made for demonstration flight at the AMA EXPO several years ago. It was the same dimensions and configuration as the first rubber powered model, but was all balsa construction. I also found a motor stick from one of my early A-7 no-cal prototypes, an elevator from one of my all balsa A-frame pushers, an 8" propeller from a Chinese foamy toy biplane that my wife gave me as a joke (Actually, not a bad flier, but double sided tape is no way to hold a model together.), and a landing gear assembly that came from an A-J Hornet (Yes, there is some old stuff in that box!). I could see an R.O.G. coming from all this junk simply by adding a wing pylon and a vertical tail.

First, I flattened the A-frame pusher stabilizer, creating a lifting stabilizer, and glued it to the end of the motor stick. I traced about 3/4 of half of the stabilizer outline onto a piece of scrap 1/32" sheet, cut it out, and glued it to the motor stick in front of the stabilizer to make a vertical tail. I attached the A-J landing gear to the motor stick, about an inch behind the prop hanger, and bound it with a little thread. The Chinese prop was given a Peck bearing along with a couple of brass washers and a glass bead on one of my own prop shafts.

The wing took a bit more thought. Since the motor stick was 1/8" thick I used some 1/8" X 3/16" stock, that I happened to have, to frame up the wing pylon. Two degrees of incidence seemed about right so I inclined the top of the pylon by that amount. Two pieces of 1/32" sheet were glued to the bottom of the pylon to provide a saddle allowing the pylon to be moved to find the balance point. The wing was glued to the top of the pylon and the whole model assembled. Using CA, and kicker, my whole design and assembly time was about 15 minutes.

I made up a motor of 3/32" rubber that was about 1-1/2 times the hook to peg (or in this case hook) length, installed it and test glided the model. As I had suspected, with the lifting tail, the wing went pretty far forward to get a decent glide. I took it to the next O.F.F.C. meeting for trimming flights.

The wing position needed some refinement to get the balance between power flight and glide, but after I found it a couple of drops of CA set it in place. It would fly stably, but I could not get a decent climb after I cranked a left turn into the prop hanger for the room. Moving up to 1/8" rubber didn't get much better results. I had a motor that I had made up for a different model that was 2 loops of 1/16" about twice the hook to peg length so I tried that. This was the correct power. It will now R.O.G. and climb steadily right up to the ceiling where it cruises nicely and comes down to a gentle landing just before the rubber completely unwinds.

Is it going to be in the R.O.G. contest? No. It flies very nicely, now that it's trimmed, but the best I can get out of it is about a minute. Fun it is, competitive it ain't!

Back to the building board!
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kittyfritters
Posts: 241
Joined: Tue Sep 27, 2016 8:13 pm

Re: Crash Box Special

Postby kittyfritters » Wed Nov 02, 2016 11:50 pm

Took the Crash Box Special to the O.F.F.C. meeting this morning just for fun to see what I could get out of it if I really pushed it. Best I got was 1 minute 19 seconds. not bad for something like this but still not competitive. In the upcoming ROG contest any model that can't do five minutes in that room will be an also ran. :o
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Guest

Re: Crash Box Special

Postby Guest » Thu Dec 01, 2016 2:51 am

Well, I know that I said the it wasn't going to the R.O.G. contest, but I didn't have the time to build anything else so I took it and finished 5th. As it turned out the heater came on in the gym and the staff could not turn it off. The wight of this thing (23 grams with rubber) kept it very stable in spite of the "breeze". My combined score was a little more than 1/3 of the first place finishers, but at least I was well on the board. This thing should fly very well outdoors. Of course, since it is a "junkyard dog" I probably couldn't reproduce it if I tried. Fun, anyway! ;)

kittyfritters
Posts: 241
Joined: Tue Sep 27, 2016 8:13 pm

Re: Crash Box Special

Postby kittyfritters » Thu Dec 01, 2016 2:58 am

How did it let me make that last post as "Guest"?
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kittyfritters
Posts: 241
Joined: Tue Sep 27, 2016 8:13 pm

Re: Crash Box Special

Postby kittyfritters » Fri Dec 16, 2016 6:38 pm

Oh, Yes! There is a video of it flying. ;)

https://youtu.be/8t-oDt3gByU
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