First time scratch build-- Uravitch 81" OV-10 Bronco (Full Version)

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cmoore806 -> First time scratch build-- Uravitch 81" OV-10 Bronco (3/20/2008 5:01:32 PM)

Hey everyone. SO I bought all kinds of fancy tools in preparation for this moment. I spent most of my modelling time building planes on a building board on the dining room table. After moving to a home of my own a year and a half ago I put in a workshop in the basement. So I have a band saw, a scroll saw, a belt/disc sander, a spindle sander, and plenty of bench space. I also had picked out a couple of plans for planes and am saving them to build later. I put in my order at Balsa USA for the wood I need to build the Uravitch Giant Bronco and the order came to me in three days! What a great surprise. Anyways, I always read about how to transfer plans to wood and how to select the right wood, etc. Now I finally had a chance to build a kit from plans!

Here are some pictures of the ribs I cut out so far. Wish me luck!




cobi.p -> RE: First time scratch build-- Uravitch 81" OV-10 Bronco (3/20/2008 6:49:02 PM)

hello to you
let me be the first one to congratulat you with the best of luck and a happy build [:D]

you have choose your self a very good and well fly plane for your first progect and from a very excellent designer .

i will watch your post very close because i want to build this one too .

let's see your progress come ........

cheers - cobi



CanDo -> RE: First time scratch build-- Uravitch 81" OV-10 Bronco (3/20/2008 8:57:41 PM)

-Hi, I built my smaller Uravitch Bronco from plans, and the wing and horizontal stabilizer on my 80" OV-10. I also bought the 80" ARF (for the nacelles and fuse) and removed the covering to change its colors. This gave me a chance to see how it was built. The short story is build it light, especially any part of the plane that is aft of the CG (like the nacelles, vertical stabs, horizontal stab, etc. Some things you should decide early on is: one piece wing or 3 piece wing?; which gear to use? (fixed , retracts); which motors to use? (2 stroke, 4 stroke, electric); etc. These decisions will determine the details of your design. Note, as far as I know every 80" Bronco built (including ARFs) was tail heavy, some more so than others.
-If you go to " CanDo " at:
http://www.rcuniverse.com/community/profile.cfm?section=profile&forum=1&memid=237938
you can see what the Bronco ARF looks like without the covering. Notice that the ARF substituted balsa for lite ply in the fuselage and nacelles, and it is a one piece wing.



fancman -> RE: First time scratch build-- Uravitch 81" OV-10 Bronco (3/22/2008 11:16:43 AM)


quote:

ORIGINAL: CanDo

-Hi, I built my smaller Uravitch Bronco from plans, and the wing and horizontal stabilizer on my 80" OV-10. I also bought the 80" ARF (for the nacelles and fuse) and removed the covering to change its colors. This gave me a chance to see how it was built. The short story is build it light, especially any part of the plane that is aft of the CG (like the nacelles, vertical stabs, horizontal stab, etc. Some things you should decide early on is: one piece wing or 3 piece wing?; which gear to use? (fixed , retracts); which motors to use? (2 stroke, 4 stroke, electric); etc. These decisions will determine the details of your design. Note, as far as I know every 80" Bronco built (including ARFs) was tail heavy, some more so than others.
-If you go to " CanDo " at:
http://www.rcuniverse.com/community/profile.cfm?section=profile&forum=1&memid=237938
you can see what the Bronco ARF looks like without the covering. Notice that the ARF substituted balsa for lite ply in the fuselage and nacelles, and it is a one piece wing.

Exactly right. Ditch the ply sides for balsa as they did for the ARF. My kit built Bronco was much heavier than the ARF because the ARF doesn't use ply sides or the thick bass wood formers in the fuselage. Build the nacelles as light as possible and you will still need about a pound of weight in the nose to balance.



CanDo -> RE: First time scratch build-- Uravitch 81" OV-10 Bronco (3/22/2008 7:07:44 PM)


Cmoore806, you picked a good project to work on. Rich put a lot of effort in this design to make it enjoyable to build. To be honest, I enjoy building as much as I enjoy flying his planes! When you bring it out for the maiden flight you will have a plane to be proud of, plus you will have a plane that makes you look good when you fly it. Don't tell any anyone, but as long as you tune the motors carefully (happy motors = happy owners!), check the CG, etc, this plane is not difficult to fly. It's not a trainer, although it was my twin trainer, but it is a smooth and predictable plane, especially for landings. If you scan through some of the other OV-10 threads, you will learn a few more helpful hints from guys like Fancman. These guys have "been there, done that" and they know what they are talking about. Good luck...have fun!



cmoore806 -> RE: First time scratch build-- Uravitch 81" OV-10 Bronco (3/23/2008 12:08:54 AM)

I wont be switching the ply with balsa as recommended for two reasons, one, I cut out the ply already and two, it just wouldnt make me comfortable. The ply cant hurt and the lite ply is, well, not that heavy. I will save weight elsewhere: two stroke engines instead of four, spring-air retracts not scale struts, one piece wing instead of three piece....Cutting is going well now...I took a little break to build an edge-truing fixture! Thanks for the words of support and advice!



cmoore806 -> RE: First time scratch build-- Uravitch 81" OV-10 Bronco (3/23/2008 3:25:00 AM)

Does anyone have experience with Spring-Air retracts? I ordered the mains and nose gear but need to pick out an air valve, tank, and fittings. I plan to use a robart air valve for the three way gear. What did you use?

Here is a picture of the edge truing fixture I built today. I cant use it yet since the polyurethane is still drying.



cmoore806 -> RE: First time scratch build-- Uravitch 81" OV-10 Bronco (3/23/2008 3:26:05 AM)

And here are some misc. parts I cut out yesterday.



fancman -> RE: First time scratch build-- Uravitch 81" OV-10 Bronco (3/23/2008 3:38:06 AM)

quote:

ORIGINAL: cmoore806

Does anyone have experience with Spring-Air retracts? I ordered the mains and nose gear but need to pick out an air valve, tank, and fittings. I plan to use a robart air valve for the three way gear. What did you use?

Here is a picture of the edge truing fixture I built today. I cant use it yet since the polyurethane is still drying.

I have a set of Spring Air Retracts that I used in my kit built Bronco. With the weight of the Bronco in the kit built form you're probably going to be at about 20 lbs and if you're flying off grass you're going to find the spring air retracts and the music wire gear lacking. I've been there and done that. Gear had to be straightened after every flight. I'd be more than willing to sell them to you for a good price if you would like.
The Spring Air Retracts are very easy. all you need is the fill and retract valve and a very small air tank.



cmoore806 -> RE: First time scratch build-- Uravitch 81" OV-10 Bronco (3/23/2008 1:50:58 PM)

Is there anything I can do to the 3/16" struts to help them not bend?




fancman -> RE: First time scratch build-- Uravitch 81" OV-10 Bronco (3/23/2008 2:54:00 PM)

I couldn't figure out anything to do to stop the bending. Others have said that there was no problem with bending if the model is kept to 17 lbs or so but I don't see how you get there with the plywood and such. The ARF is built with balsa sides and no heavy formers in the fuselage. You'll just have to see how things turn out.




Fili -> RE: First time scratch build-- Uravitch 81" OV-10 Bronco (3/23/2008 3:14:05 PM)

I also had problems with the spring air struts bending. I just ordered the scale struts from Lenny at www.shindinmachine.com/ I wasnt too worried about the bending, just wanted to make a few changes for this upcoming season.

To help with weight I drilled lightening holes in the ply fuse sides and the nacelle sides all the way to the tail. She still came in at 19#



CanDo -> RE: First time scratch build-- Uravitch 81" OV-10 Bronco (3/23/2008 4:09:43 PM)

-Because tail weight is often 2 or 3 times the distance from the CG, it may require 8 to 12 oz in the nose to balance the plane; tail weight is not your friend. If you are building from scratch, it pays to do your homework.
-Because the Bronco's motors are essentially mounted on the leading edge of the wing, they have little effect to counter balance any tail weight; you will need weight in the nose of the fuselage.
-With careful wood selection and some design changes, my scratch-built 3 piece wing actually weighs slightly less than my ARF's single piece wing!



cmoore806 -> RE: First time scratch build-- Uravitch 81" OV-10 Bronco (3/24/2008 2:07:02 AM)

What are we talking about here as far as ways to cut weight (other than cutting holes). The design could use balsa instead of lite ply but where exactly is it worth compromising strength? We've talked about fuselage and nacelle sides as a place to cut weight and I can see myself laying out some lightening holes aft of the CG on the nacelle sides. I plan to use the wire and bellcranks by making my own graphite/carbon fiber plate bellcranks. Did any of you guys build your own bellcranks?

Regarding engine selection. I wont stray from OS engines, and I am looking at either the .61 FX or the .75 AX. With two engines in this bird I would save 5.72 ounces by using the .61 FX engines instead of the .75 AX engines. When light weight is the priority would it be worth lowering the power output to save almost 6 ounces?



rrudytoo -> RE: First time scratch build-- Uravitch 81" OV-10 Bronco (3/24/2008 4:01:32 AM)

Hi Guys,

I'll jump into the fray as I'm building the Uravitch 81" Bronco, too. I got the short kit and plastic accessories from Hobby Hangar. I splurged and got the Sierra Giant Scale retracts which are not only light in weight but of beautiful workmanship. ( I have Sierra gear in my Yellow P-47, too, and I am sold on Darrell's talent and products. )

I know I'm going to get slammed for this but I'm using the same engines that Rich did when he wrote his review in Model Airplane News.......OS .46 FX's. I've read where guys are stuffing all sorts of power into these Broncos and I was tempted to use a pair of .60's after reading so many comments regarding engine sizes. Tell you what, once I maiden this bird I'll give you my honest opinion as to how the .46's performed.

I have the central fuse and both nacelles framed up, gear mounted and the empennage is done but not attached. The next step is starting in on the wing which will be a three-piece affair. I intend to leave everything assembled except for the outer wing panels for transportation. The horizontal stab will be permanently attached to the vertical stabs for strength. The interesting part will be setting the incidence of the horizontal stab. I will wait until I have the wing built and mounted then set the two surfaces to 0 degrees.

This should be a lot of fun!

Al



CanDo -> RE: First time scratch build-- Uravitch 81" OV-10 Bronco (3/24/2008 4:05:22 AM)

-Someone probably has written a book on how to build model planes, but I'll try to keep it short. I've substituted balsa for lite ply before in fuselage sides and top and bottom sheets and it works great. Note, the 80" Bronco ARF is all balsa skins.
-I would start by buying a cheap cooking scale that measures in oz and grams. When you buy sheets of balsa, use your scale to select the lighter wood for tail feathers, aft fuselage pieces, etc. Note too which balsa sheets are really flexible and which ones are pretty rigid. The flexible sheets are good for wing leading edges and the rigid ones are good when you need more rigidity (possibly for fuselage sides). When you cut parts and glue pieces together, try to make all pieces fit well to minimize the amount of glue/epoxy you need. Try to limit where you use epoxy and the amount you use, it's relatively heavy.
-Because I made my wing from plans and the ARF's dimensions were slightly different, I needed to make a new horizontal stab. The ARF's stab seemed a little heavy, so I pealed off the balsa skin and found the wood that framed up the stab was pretty heavy. After building my stab out of lighter balsa, it was 2 oz lighter that the ARF's. It's details like this that reduce tail weight, which reduces nose weight, which reduces overall weight of your plane. Remember, it's easier to design a lighter structure in the beginning rather than try to take weight out of a heavier structure.



fancman -> RE: First time scratch build-- Uravitch 81" OV-10 Bronco (3/24/2008 5:09:52 AM)

quote:

ORIGINAL: rrudytoo

Hi Guys,

I'll jump into the fray as I'm building the Uravitch 81" Bronco, too. I got the short kit and plastic accessories from Hobby Hangar. I splurged and got the Sierra Giant Scale retracts which are not only light in weight but of beautiful workmanship. ( I have Sierra gear in my Yellow P-47, too, and I am sold on Darrell's talent and products. )

I know I'm going to get slammed for this but I'm using the same engines that Rich did when he wrote his review in Model Airplane News.......OS .46 FX's. I've read where guys are stuffing all sorts of power into these Broncos and I was tempted to use a pair of .60's after reading so many comments regarding engine sizes. Tell you what, once I maiden this bird I'll give you my honest opinion as to how the .46's performed.

I have the central fuse and both nacelles framed up, gear mounted and the empennage is done but not attached. The next step is starting in on the wing which will be a three-piece affair. I intend to leave everything assembled except for the outer wing panels for transportation. The horizontal stab will be permanently attached to the vertical stabs for strength. The interesting part will be setting the incidence of the horizontal stab. I will wait until I have the wing built and mounted then set the two surfaces to 0 degrees.

This should be a lot of fun!

Al



I don't think you will find making the horizontal stab permanent to be a good idea. When you have to seperate the nacelles from the wing, not twisting the horizontal stab will be a real chore. It's easy enough to make the horizontal stab removeable. With the Sierra Retracts and three piece wing your plane will brobably be like mine was and come in at at least 21+ lbs. Good luck with the .46 engines.



fancman -> RE: First time scratch build-- Uravitch 81" OV-10 Bronco (3/24/2008 5:17:22 AM)

The engines in the Bronco are only four inches or so in front of the CG therefore they have little effect on the balance of the finished airplane. If you save five ounces of weight there you'll just have to add more weight in the nose of the fuselage to balance the airplane. Engine weight within reason isn't a problem at all. I use twin Saito 82's on mine turning 13X8 APC props at about 10,000 rpm. They give good power but not what I would call over powered expecially when you have an engine quit and you're flying a 20 lb airplane on one little engine.



CanDo -> RE: First time scratch build-- Uravitch 81" OV-10 Bronco (3/24/2008 3:56:02 PM)

If you check previous OV-10 threads, you will see that although Rich did fly his first Bronco with OS .46 engines, his motors were working pretty hard and the plane weighed ~18lb. With a 20 lb plane you probably would not be able to hold altitude on one .46 engine to get back to the runway. At our field, landing off the runway would severely damage a 20 lb plane; a strong .60 2 stroke or .80 to .90 size 4 stroke should help get you home in one piece.



rrudytoo -> RE: First time scratch build-- Uravitch 81" OV-10 Bronco (3/25/2008 6:21:40 AM)

I look at it this way, If I lose an engine I'll idle back the running engine or kill it completely and dead stick it in. I've known guys who have lost their twins by trying to coax it "home" on one engine and losing it. In hind sight they each said that they had wished they had just dead sticked it in like any single engine. I've kept in mind the possibility of switching to .60's should the .46's prove inadequate but I just wanted to give them a chance.

As for the permanently attached horizontal stab, the wing will be pretty much permanently attached to the central fuse and the nacelles as I don't see a need to disassemble the main components. Transportation will not be an issue as I have a trailer so only the outer wing panels will be removable.

Those of you who have made your wings with removable outer panels, what diameter tubes and sockets did you use? I got 7/8" tubes but they now look like overkill.

Al



CanDo -> RE: First time scratch build-- Uravitch 81" OV-10 Bronco (3/25/2008 3:52:26 PM)

-Yeah, it's a matter of personal preference for the single engine flameout. The terrain is pretty rugged around our flying field; if you can't dead stick it back to the runway, you may need to extend your "glide" a bit to make it home. I'm comfortable flying a twin on one motor, so I'll give it a try in a pinch. I also like my motors loafing along at 1/2 throttle, but that's personal preference too.
-I used the 3/4" OD tubes in my wing and they are plenty strong. The problem you run into is if you already cut out the ribs, the joiner holes are 7/8". I made some lite ply pieces that filled in the holes so I could use the smaller tubes. Note, one fellow used wood joiners (like the Sr Telemaster ARF), which should be lighter and strong too. One of the questions you need to ask in the beginning of the design is, what kind of flying will I be doing with this plane? If you plan to make 20 G pylon turns, then you had better beef it up; if you plan to fly it more scale like, you don't have to redesign everything. I honestly believe most model planes are over designed for the guy who wants to put an oversized motor in his plane, thus you typically have a healthy safety margin for sport flying.



rrudytoo -> RE: First time scratch build-- Uravitch 81" OV-10 Bronco (3/26/2008 6:05:37 AM)

CanDo,

I'll be flying in a scale-like manner. I can't do aerobatics worth a bean anyway.

I saw that the wing ribs had a .950" diameter hole in them already and I selected the 7/8" tubes as the sleeves had an outside diameter of .960". Seemed like a good match at the time. I may just order a smaller pair and save these for another project.

Thanks for the input, guys, but we better let cmoore806 have his thread back. [;)]

Al



CanDo -> RE: First time scratch build-- Uravitch 81" OV-10 Bronco (3/26/2008 3:57:06 PM)

Al, they are a good match if you just lightly sand the holes in the ribs a wee bit. The 3/4" joiners require more time to install. Cmoore806, sorry for hogging your thread, I'll get back to building!
-Les-



cmoore806 -> RE: First time scratch build-- Uravitch 81" OV-10 Bronco (3/27/2008 3:39:05 AM)

I havent done enough building to warrant a picture. I am making the sheeting for the wing now and, well, it just isnt that exciting. I will get something up after this weekend if I can get enough time to start the wing building.





cmoore806 -> RE: First time scratch build-- Uravitch 81" OV-10 Bronco (3/27/2008 1:53:07 PM)

Hey guys, I figure I would snap a couple of pictures of the bottom wing skins as I make them. I read in Rich Uravitch's article that he layed out the sheeting this way before building the wing. It makes sense if you can do it and it might save weight since I can more easily sand the skins on my benchtop.



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