Posts: 4767
Joined: 7/21/2005 From: Greensboro,
NC, USA Status: offline
This stage was a lot of fun. I cut and fit the wheel wells and glued them in the wings. I did this after checking the wheels one last time by placing a level on the fuselage. The nose is set slightly down. The openings for the retracts still allow a good 1/8" of adjustment each way for the wheels, so I can still make minor adjustments. I temporarily hooked up the air lines and checked the system. It all works great. Next I will sheet the center of the wing. The nose wheel retracts completely into the fuselage with no part exposed. I was very happy with the way this turned out. This was the first time I've ever installed retracts and I think it went very smoothly. I'll admit I'm pleased! The only part that was a bit tricky was making sure I cut the gear legs to the proper length.
Posts: 4767
Joined: 7/21/2005 From: Greensboro,
NC, USA Status: offline
Instead of driving 45mins to my LHS for a $2 bit of hardware, I decided to fabricate my own tiller for the nose gear steering setup. I took a Hitec servo arm and cut off two of the arms and put a piece of brass tubing in it as a bushing. Then I slid a bolt through that and soldered a nut underneath tight against the bushing so that the servo arm spins freely. The bolt then goes through a piece of ply that will be glued inside the fuselage. For the cable connectors I soldered pieces of brass tubing onto lengths of threaded rod, flattened the ends of the tubing and drilled holes for the cable. The cable is Dubro pull-pull rudder cable looped through brass tubing which was crimped and covered with heat-shrink tubing. The other ends of the cables will be hooked up similarly to the tiller arm on the nose gear. Then, a regular adjustable nyrod pushrod will run from the homemade tiller back to the rudder servo. It was necessary to use cable since the distance from the nose gear tiller changes when the gear is retracted. The cable simply goes slack when the gear is up.
Posts: 4767
Joined: 7/21/2005 From: Greensboro,
NC, USA Status: offline
I got the nose gear linkage hooked up. It's not the prettiest job, but it works. I had to make a number of adjustments and modify a few things to get it to retract and lower correctly without anything catching or binding. The cable has to be taught enough that there's no slop, but just loose enough that it won't prevent the spring-down mechanism from locking. Since I'm new to installing retracts I decided that if it worked correctly 90% of the time it might as well not work at all. So, I added a piece of balsa over the retract since one time the cable snagged on the pin that secures the air cylinder. It might not happen again in a thousand cycles, but it will when something like a deadstick occurs. You see, I'm basically Murphy's poster child. I'm sure I'm boring you all with this minutia. All in all, it wasn't any more tedious than installing a steerable tail wheel. I really enjoyed fabricating the little tiller assembly, I like the stuff where you have to do a bit of basic engineering.
Posts: 57
Joined: 5/26/2002 From: Portage,
WI, USA Status: offline
Dave,
Still neat as a pin! I might suggest you harden the balsa under the cables with epoxy or CA so the cables do not carve into it under tension. Also, why not clip off the outer portions of the steering tiller on the nose gear strut and fill in the bottom block accordingly? Just a couple of ideas.
Posts: 4767
Joined: 7/21/2005 From: Greensboro,
NC, USA Status: offline
Thanks y'all! 8178, I've uploaded a pic of what I think you wanted to see. j26, those are both good ideas. Thanks. It's great having someone "proof" my work since I can get so lost in the details that I miss the practical improvements that another set of eyes will notice.
I didn't show it in my last post, but I cut away a lot of the underside of the balsa block so that the cables clear everything. One of the pics below tries to show how thin it is in places. The reason the red tiller is so far back is to allow room to get the tank in and out. Ideally, I'd rather have it up closer to the gear to shorten the cable runs.
I took three pieces of threaded pushrod, wrapped them tightly with copper wire and soldered them together, then covered it with heat-shrink tubing to make the elevator pushrod. I can still use a cf or fg shaft if I feel it's necessary.
I had been scratching my head about how to route the servo leads and air lines through the wing. I needed a way that would allow me to remove and replace them if needed after the wing is sheeted. I've seen giant-scale models with cardboard tubes in the wings for this purpose, but I had nothing around the house like that small enough. No worry, I soaked a sheet of A-grain 1/16" balsa with Windex and taped it around an aluminum pole and put it in the sun to dry. I'll admit the result looks a bit odd with the 90° bend, but it actually works very well. To remove and replace the wires and air lines I just have to tie a length of monofilament on the end before pulling them out. Then I use it to pull the stuff back through again. Installing these balsa tubes should have been done before the wing halves were joined. If you look close you can see how I had to cut the ribs and then replace part of them on top of the tubes. It's no less strong and it will all be covered with sheeting anyway. You can also see where I needed to cut out a curved section of the ply tongue that holds the wing to the fuselage. The nose wheel was hitting it before.
I just put the wing on my postal scale and I was sort of surprised. With the retracts, servos and all that extra "woodworking" I did it weighs 1lb., 13oz. The bottom sheeting and ailerons will add another 2 1/2 oz., but that's lighter than I thought it would be.
Posts: 628
Joined: 3/9/2002 From: East Berlin,
PA, USA Status: offline
I would go with the dave brown carbon fiber push rods, I think you may get to much flex with that set up. Remember this bird is fast. If that push rod flexes, you may end up with flutter. Just my 2 cents. Looks great. I realy like the blsa tubes used for the air lines and servo leads.
Posts: 4767
Joined: 7/21/2005 From: Greensboro,
NC, USA Status: offline
Paternguy, I was just looking at those today on the web. How would you modify them for dual elevators? Would you run one cf rod to the back of the fuse and then use heavier wire - like 4-40 - to branch off to the horns? Or is there a better way I'm not aware of. Pics would be great.
I'm using Dubro HD horns. I've already glued the end-grain blocks into the elevators, but I still need to drill them out and glue in the hardwood dowels.
Posts: 628
Joined: 3/9/2002 From: East Berlin,
PA, USA Status: offline
They come with an end cap for the rod that uses 2 4/40 rods in a "Y". I used them on my Tipo and it worked great. The carbon rod is very stiff, and with the end cap you can get away with running fairly short pieces of rod. There is very little slop in this set up. I am sure some of the other guys here have used them over the years, I first found them in the early 90's, and I use them on every plane I build. I don't like the nylon rods, they seem to get a little soft in the heat and change the trim of the aircraft from flight to flight. I have never used them for control surfaces, but I have flown other people’s planes with them, you can feel the slop in the air, again just my 2 cents.
Posts: 4767
Joined: 7/21/2005 From: Greensboro,
NC, USA Status: offline
Thanks, Paternguy. Well, I re-order all new control hardware today.: GP deluxe 4-40 pull-pull system, Dubro 4-40 Safety-lock Kwik-links, threaded 4-40 rods and the Dave Brown fg pushrods. It could end up being the best $26 I spend on this plane. I also ordered a 6v 1200mah Nimh rx pack. It actually weighs less than a 4.8v 1200mah nicad pack. This will add a little oomph to my servos (from 44 to 57in/oz).
Elvis Costello once said that every musician is a Magpie and a thief and he meant it in a good, complimenary way. I know I've borrowed my share of techniques and ideas from the better modelers. The Central Hobbies web site has a good how-to on installing MK horns. I basically followed their method for the Dubro horns I'm using. I cut out the surfaces and glued in balsa blocks end grain facing out. Then, I used a paddle bit (man, I need to buy some Forstner bits the next time I'm at Harbor Freight) to cut 7/16" holes in the blocks with a drill press. I drilled out some 1/2" dowel in the drill press and glued segments into the blocks. Then I sanded everything flush.
The UFO plans say to slant the elevator horns 15° forward for differential. The Dubro horns I'm using extend past the hinge line as is, so I think I'll go with the way they are. Does anyone know if needing more down than up is due to the anhedral stab, or was elevator differential common practice on all pattern planes?
< Message edited by rainedav -- 6/5/2006 2:16:03 AM >
Posts: 612
Joined: 2/26/2002 From: Durham,
NC, USA Status: offline
Beautiful work, rainedav! I especially like the formed balsa servo lead tubes- MITRED no less!!! You and 8178 must have some kind of competition going on to see who can build the prettiest airframe. Keep it coming- I love it!
Printable Version
All Forums >> RC Airplanes >> Pattern Flying >> Classic Pattern Flying >> RE: Bridi UFO Build (all wood) 
RE: Bridi UFO Build (all wood) - 
