kargo

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.

kargo

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

Sorry, forgot the link to the mfc website;

http://www.houseofbalsa.com/store/st...03lozkuQg9j9p0

kargo

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. [8D]

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.

kargo

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?

kargo

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?

kargo

swing and a miss...

kargo

2

NorfolkSouthern

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!

NorfolkSouthern

NorfolkSouthern

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.

NorfolkSouthern

Gray Beard

My Feedback: (-1)

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.

kargo

Sorry about the long absence... Cheeky issues pics continued;

kargo

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.

kargo

C1 Bottom sheeting with 3/16 stick, bottom sheeting glue process;

kargo

Bottom sheet glued, 3/16th stick and sheet sanded flush.

kargo

With the bottom sheet in place, its time to glue in the formers. The fuse sides are both marked with ALL the former locations, which was a big help.

buzzard bait

Regarding dihedral, since the plane has ailerons, you'll be fine.

For a plane without ailerons, you would need to get the dihedral right regardless of how the parts fit. I don't know what didn't fit. Sometimes you just have to modify or replace kit parts.

The fiberglass tape alone should have been enough for the joint - this is not the only kit to use that method.

I'd have used white glue on the dowel. Epoxy will build up weight faster than you think. Looks like a lot of reinforcement on the front end if you are modifying for electric. A common beginner mistake is to try to build strong, and the result is heavy and hits harder. When one part is very strong, it just means something else breaks.

Should be a nice little plane!

Jim

kargo

Fuselage continued;

Now that the firewall supports and cheeks are in place its time to glue in the firewall. The problem I ran into with this is that the "cheeks needed to be squeezed" to make the firewall fit properly. The firewall is 2 1/4 inches and the space is just under 2 1/2. I called HOB to get some advice. They seem like a smaller outfit, but provided great service and spoke to me at length about my project. They told me that the squeeze was part of the design, and intended to provide a taper to the front of the fuse. They answered several other questions and provided some advice about balancing the model with a screw eye (as opposed to the finger method). It seems as though this model needs a more accurate balance and I will be sure to do so. They also told me they sold similar kit that was intended for electric, the K71 Acrocub. Oops, I think I'll call the manufacturer before my next purchase!

kargo

I'll need to get the motor, a Great Planes 28-30-1450 drawing 17amps with a 7*4SF prop, before I install the firewall. Due to the angle the firewall installed at I will need to take great care in how I possition it. The picture shows the offset used to compensate for the angle on the firewall.

kargo

Fins

I'll let your imagination figure out the copious stupidity I employed with gluing the fins together[:@]. The pictures will tell my story. Again, you don't need that much heat off the heat gun.

The elevator uses a piece of hardwood to conect the two halves.

The rudder is optional, but come on, you can't have a Decathlon without a rudder[8D]!

Both are hinged with covering style hinges. I found a how to resource on wattflyer.com.

http://www.wattflyer.com/forums/showthread.php?t=34600

Again, Thanks Ron!

kargo

The power setup is going to be electric. To that end I've been receiving advice from one of the moderators on wattflyer.com. Thread;

http://www.wattflyer.com/forums/show...739#post440739

kargo

OK, been a bit. Thank you to those who have replied on this thread. The continued progress;

Motor and Firewall
I received the motor, a Great Planes 28-30-1250, and have since been able to mark the firewall with the motor offset from the plans and the marks for the motor mount holes. The dirty details are on wattflyer.com.

http://www.wattflyer.com/forums/show...d=1#post444245

I plan on using nylon spacer tube type mounts to bring the motor forward enough to fit through the cowl, and a setscrew style prop adapter to fit the prop. On the advice of one of the wattflyer moderators I intend to remove much of the firewall not used in supporting the motor, and to install triangular braces behind it to increase the glueing area. Not so much vibration on a electric motor. With everything marked I glued in the firewall with epoxy. It is installed flush with the top of the fuse side, leaving a 1/8th gap at the bottom to install the tank floor. There is a large amount of right thrust built in. This is per plans and from what I can tell those who have used it have had success flying.

kargo

http://www.hobby-lobby.com/motor-mount.htm

Thanks again for the link Sky Sharkester!

kargo

Back to the WING;

I left off with the aileron torque rods, the plywood dihedral braces, and the dihedral setting troubles. Thanks for the post on dihedral buzzard bait.

Aileron torque rods

I went to LHS (Hub Hobby Twin Cities) and the rc addict there said to use a Dubro Strip Aileron set for the servo pushrod link to the torque rods. They have a collar with a setscrew that goes in the middle of the nylon piece. I'll use some locking compound to ensure the setscrew doesn't back-off. I am very comfortable I can put this setup through its paces and have something other than it fail. At any rate one problem solved.

Issue solved, it was time to glue the torque rods into the trailing edge pieces (CA, medium I think). With that dry I used Titebond wood glue to attach the trailing edge/torque rod assemblies to the wings. There were slight gaps where I had not lined up the trailing edge "sandwich" of the wing quite right. I used the wood glue and a piece of scrap ply to fill the gap. The torque rods still move even, although I'm sure it wasn't the best technique for building light. The Titebond does sand well, it was not a problem to get everything smooth again.

The instructions call for 2 hardwood sticks at the aft center section of the trailing edges. I used Titebond.

Wing halve joining.

This is one of my favorite parts of the build process. It is very gratifying to see the wing come together. The pictures are self-explanatory. I had to make a notch (per plans) in the right trailing edge for the left aileron torque rod. The aileron servo is offset to the right. I don't know if I didn't set the torque rods deep enough or what, but I had to notch into the trailing edge of the wing to get enough travel on the torque rods. I used epoxy on the dihedral braces and root ribs. The ratchet style hobby clamps are awesome. To my surprise, the wing had the dihedral called for in the plans. I don't know what the problem was or where I screwed up originally, but I'll take the end result. The only problem was that the trailing edge pieces didn't touch. I tried filling the gap with Titebond again. Didn't work. I'll have to use epoxy. Buzzard Bait, hopefully I didn't create a strong part to break the weaker one. Only one way to find out...

I've deviated from the instructions some as I have not sheeted the center section of the wing yet. I want to make a bit stronger mount for the aileron micro servo, something underneath the sheeting. Since I don't have the servos yet I can't determine how to proceed. Probably some sort of brace between the ribs. Ideas?

kargo

pics

kargo

skipped two...