Posts: 46
Joined: 10/1/2007 From: Ellsworth,
WI, USA Status: offline
Hey Gang
I thought a build thread on my HOB Super Decathlon would generate some tips/suggestions, if not a little entertainment At any rate this is my second build, the first being a Sig Kadet LT40 that my stepson and I built last winter. Despite the mistakes we made with it it flew like it was on rails. Almost 0 trim adjustments. Very cool experience. We learned alot, but maybe by posting my mistakes I'll learn even more this time around. Please don't hesitate to post something even if I've past the point of no return as I'm starting this thread a good way through the build.
I chose the Decthlon because it looked like a fast build, a bit more aerobatic than the kadet, and it like a good candidate for an electric conversion that could be flown in the fairgrounds area behind my house. I purchased it from gravesrc.com for about $65 with shipping. Last I checked they didn't have any more. It was a hard one to find. Manufacturers link and box/content pictures below.
Posts: 46
Joined: 10/1/2007 From: Ellsworth,
WI, USA Status: offline
The instructions have you start with the wing which goes togethor easily. Most of the parts are lazer cut and and assembled easily. The biggest problem I've run into is the instructions, although they are pretty good, are not where near as in-depth as the kadets were. If you don't slow down, place the parts together for a trial fit and think how it'll work you mess it up. A lot of it seems left up to the builder. No hand holding I guess
Posts: 46
Joined: 10/1/2007 From: Ellsworth,
WI, USA Status: offline
WING
The wing went together pretty quick. The parts are laser cut and go together easily. It has ribs that have notches for the main spar, trailing edge, two more separate spars at the front of the ribs and a cedar dowel for the leading edge. The main spar and trailing edge are of a sandwich type construction. The notches were such that there was no need for sheer webbing on the main spar. I was a little concerned about CA's effectiveness on the cedar dowel, so I used epoxy. I used rubberbands to hold it in place while the epoxy dried. Any thoughts on this? Different methods? I used Titebond woodglue on the trailing edge pieces as I thought they would require sanding that CA would make difficult.
The wing tips were the hardest part. They slid into a notch in the main spar, but trimming the spar and the sandwich construction trailing edge wasn't easy. A saw, some sanding and pucker-factor later it came together. I stuck an extra piece of balsa in between the tip and one of the forward spars to make it reach to the wingtip. I think the plans had me cut it flush with the rib, but I thought it wouldn't hurt. Thoughts on this? Again, I used Titebond.
The first two ribs are smaller to allow for sheeting the center section of the wing. I learned in cutting out the sheeting that large curves over small spaces require the grain in the sheeting to be perpendicular to the bend.
The one main sticking point I had was the dihedral. The plans call for 7/8th at the tip on both wings. I could not seem to achieve this at both tips, only on one (one wing flat on the table and the other at an angle to it). Guess it’ll roll a little better than advertised. Thoughts? I made two plywood dihedral braces for either side of the main spar. The instructions have you simply glue the two halves and use some fiberglass tape. The kadet had these and I like the idea a little better. Thoughts? I need to attach the inner trailing edge piece/aileron torque rod assebly before joining the wing halves, which is where the wing construction is currently paused.
Posts: 46
Joined: 10/1/2007 From: Ellsworth,
WI, USA Status: offline
Trailing edge/Aileron torque rods
The kit has a pretty good hardware package, including aileron torque rods. The setup has you use a quick link to attach the servo pushrods to the torque rods. The kadet had torque rods with threads. I like this much better than a quick link. I didn't solder the kadets aileron pushrods either, but used threaded rods and links. I'm going to do the same with the decathlon. So far as the links go, any suggestions between nylon and metal?
Posts: 46
Joined: 10/1/2007 From: Ellsworth,
WI, USA Status: offline
Fuselage
This starts out with gluing the top and bottom halves of the fuse sides together, adding a very thin ply doubler and a 3/16th brace I assume is for the servo tray. I used CA. Next you add a differently sized firewall supports to the front of the fuse sides. These set a healthy angle to the firewall to help offset turning tendencies of the prop/motor. I was originally going to modify the cowl to a more scale like shape, but the firewall angle convinced me to leave it stock. I'll sheet around the cheeks and motor and leave it at that. And this brings me to my first (that I'm aware of) big mistake. I had a plan to use t-pins to hold the firewall supports and cheeks together for gluing instead of doing it in two steps as per the plans. I wound up with a gap between the fuse and the cheeks and had to use a heat gun to loosen the epoxy and reglue the cheeks. You can see the scortch marks on the fuse in the pictures, it really didn't take that much heat... Question; will epoxy redry to its former strength after being heated like that?
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Joined: 7/17/2006 From: Ann Arbor,
MI, USA Status: offline
I also have a House Of Balsa Super Decathlon comming from Graves RC, Kargo. I'm hoping to install an OS 10 LA for an engine. I'm looking forward to seeing your progress in this build, and how you are planning to do the covering. Keep up with the good work!
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Joined: 7/17/2006 From: Ann Arbor,
MI, USA Status: offline
quote:
I was a little concerned about CA's effectiveness on the cedar dowel, so I used epoxy. I used rubberbands to hold it in place while the epoxy dried.
I did the same thing with the ribs on my Great Planes Rapture 40. I'm thinking that I could have installed shims for the ribs that were slightly too short and used CA instead to save weight. However, I did manage to get a very strong wing that has stood up to a lot of abuse. The wing loading on this Super Decathlon is very light, so maybe the added strength isn't such a bad idea.
Posts: 1992
Joined: 4/21/2003 From: Hemderson,
NV, USA Status: online
I'm just teaching my youngest student to build, we are building the 4*60 and it has A lot of light ply that needs gluing. Most the time CA works well when used on balsa to hard wood but it almost never works on hard wood to hard wood. I let him try though. Most the time when I have to glue any parts to hard wood I go to epoxy or wood glue and stay away from CA if it shows any signs of not working. Most all builders have several types of glue on there bench and reach for what they have learned will work on what parts. Using the epoxy was A good idea on the dowel.
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Posts: 46
Joined: 10/1/2007 From: Ellsworth,
WI, USA Status: offline
Fuselage continued;
Next formers F12, F6, F8 are glued to the left side, and then to the right.
The bottom sheet C1 has a 3/16 stick glued to the forward end. This is to fit into the slots on the ply double, and for sanding smooth with the rest of the fuse. The bottom sheet is then glued in between the fuse sides. I used the formers to help line things up, and then rubber bands to hold the sides against the bottom sheet. Finally I used a straight edge to ensure it was all flush. I then tack glued on the inside of the fuse (for sanding purposes) moving the straight edge as I went. Once everything was in place I glued the entire length.
< Message edited by kargo -- 7/12/2008 8:39:28 PM >
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All Forums >> RC Airplanes >> Kit Building >> HOB Decathlon build 
HOB Decathlon build - 
At any rate this is my second build, the first being a Sig Kadet LT40 that my stepson and I built last winter. Despite the mistakes we made with it it flew like it was on rails. Almost 0 trim adjustments. Very cool experience. We learned alot, but maybe by posting my mistakes 
I'll learn even more this time around. Please don't hesitate to post something even if I've past the point of no return as I'm starting this thread a good way through the build. 
Question; will epoxy redry to its former strength after being heated like that? 
