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Old 02-01-2018, 03:34 PM   #21
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Re: IMAC DR-107 One Design Build


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Thanks for the kind words but you guys should know that I just spout off the first thing that comes to my mind! It’s not my plane after all!
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Old 02-01-2018, 03:35 PM   #22
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Re: IMAC DR-107 One Design Build

BTW, it’s looking great Ken. Happy anniversary as well!
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Old 02-03-2018, 10:39 AM   #23
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Re: IMAC DR-107 One Design Build

The only thing about these clamps is that they will tend to crush soft and medium balsa. They work great on plywood, spruce, basswood, and hard balsa.
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Old 02-05-2018, 02:13 PM   #24
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Re: IMAC DR-107 One Design Build

What a great weekend! Tons of snow; city brought to a stand-still and a basement full of wood and glue… what else could you hope for!

With the forward fuselage substructure solid, it was time to add the plywood doublers. These stretch from the firewall to behind the wing and are notched to fit into the fuel tank floor. I did a little sanding of the structure first to ensure a tight fit between the doublers and structure. I used a couple of #2 screws to help locate and clamp the doubler to the firewall and lower half of F2 (the two ¼” ply formers). These were set in place with slow set epoxy one at a time with care being taken to ensure that the top of the doublers were parallel to each other.

While waiting for the epoxy to set up, I got the 3/16” fuselage sides finished up so that they could be installed. This meant laminating 1/8” ply doublers to the tail on either side to mount the servos to. I also glued in 3/8”x 1/4” spruce rails to the plywood for the servo screws.

With that done, and the ply doublers now firmly glues to the forward structure, it was time to tax my clamp supply and glue the 3/16” sides to the doubler; again ensuring that the top edges were parallel to each other. These were also done one side at a time simply because I ran out of clamps !

Once the sides had set up, I moved onto Formers F4, F5 & F6. The fuselage was set over the plans inverted with F1 & F2 overhanging the bench at the front. The sides of the fuselage were lined up with the plans using blocks and the formers were lined up with the locations I had previously marked on the fuselage sides. With the formers in place, I added triangular stock, the 3/32” cross sheeting and the 1/8” ply tailwheel mount to the aft belly. I did use one transition piece of 1/8” balsa between the 3/32” balsa and the 1/8” ply plate.

With the lower fuselage closed in, I removed it from the board and cleaned up the belly sheeting. The last step I did last night was to reattach the upper halves of F3, F4, F5 & F6 using some of the leftover 1/2”x 1/8” spar stock. Once I have the upper sheeting in place, I plan to remove the cross braces on F3 so that the tank will fit in place. I may also remove the braces on F4 and F5 if I need to mount the batteries that far aft.

In all, it was a very productive weekend! One thing that concerns me now is how I’m going to get the two halves of the rear fuselage perfectly vertical so that the vertical stab tailpost is vertical. The tailpost goes all the way to the bottom sheeting.

The other concern is that the tailwheel horn needs to be attached to the bottom of the rudder; which is 3/8” thick balsa. I’m worried that the balsa isn’t strong enough to support the screws in the horn and that a hard landing may pull out the screws out or break the balsa there. My plan is to carve out a section of balsa from the lower, forward part of the rudder and replace it with spruce. Thoughts?
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Old 02-05-2018, 02:30 PM   #25
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Re: IMAC DR-107 One Design Build

Looking great, keep it rolling along. Also you win the who has the most clamps contest. Ha Ha
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Old 02-05-2018, 05:40 PM   #26
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Re: IMAC DR-107 One Design Build

The clamps! All the clamps in Calgary are in Ken's basement
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Old 02-06-2018, 12:31 AM   #27
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Re: IMAC DR-107 One Design Build

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Originally Posted by Christavia View Post
What a great weekend! Tons of snow; city brought to a stand-still and a basement full of wood and glue… what else could you hope for!

The other concern is that the tailwheel horn needs to be attached to the bottom of the rudder; which is 3/8” thick balsa. I’m worried that the balsa isn’t strong enough to support the screws in the horn and that a hard landing may pull out the screws out or break the balsa there. My plan is to carve out a section of balsa from the lower, forward part of the rudder and replace it with spruce. Thoughts?
Making a hardpoint with a chunk of spruce would work but you could also router a shallow (1/16”) depression on both sides of the rudder and glue in 1/16” ply. The ply would spread the torque loads over a greater area and would provide a solid base for mounting the control horn. Both would be fine. Your build is looking great!
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Old 02-06-2018, 05:29 PM   #28
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Re: IMAC DR-107 One Design Build

The proportions for the DR-107 I'm building have been stretched to the maximum allowed by IMAC for competition. The true-scale fuselage is about 10% wider and shorter than this design. However, Dan Rihn (the DR-107 designer) also designed a plane that was proportionally longer and narrower than the 107: the 2-seat, DR-109.

I've been doing a little searching around to see if I could find enough information to draw up a set of 50cc - 70cc plans for the 109 but hadn't had much luck. I even tried to get a set of 3-views from the current owners of the full-sized design, but they weren't very forthcoming. Today, I happened to look at the Air Age Store (Model Airplane News plans) and found a set of plans for a .40-.50 sized DR-109 (I don't know why it didn't show up in a google search...) http://www.airagestore.com/dr-109.html . These plans plus a couple of basic line drawings I have of the ship should give me enough information to draw up some plans using the DR-107 plans as a structural guide.

At 27%, I'd have a 71.3" fuselage, 78" span and 1,200 sq in. of wing. That would fit nicely in the back of my Tacoma with a two-piece wing...
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Old 02-07-2018, 10:57 AM   #29
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Re: IMAC DR-107 One Design Build

Looks great Ken!!
Love the cleco clamps!!
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Old 02-09-2018, 01:20 PM   #30
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Re: IMAC DR-107 One Design Build

I’ve made a little more progress this week and have done a little “mocking up” to get a feel for the size of the new plane. I did a trial fid of the DA-50 on the nose primarily to see how well the wrap-around Slimline muffler was going to fit. There’s no interference, but it is REALLY tight to the firewall. The lower angled piece below the firewall has not yet been glued in. It goes in after the wing attach dowels have been drilled.

Being a bit concerned about airflow around the engine and muffler, I’ve pretty much decided to get a stock DA-50 muffler freeing up the space behind the engine and saving a couple of ounces of weight. I also confirmed that there is enough room to mount the ignition module on the firewall.

Wednesday night, I got the cockpit floor and instrument panel installed. The panel is installed at a 45-degree angle to the cockpit floor… not exactly scale, but it gives enough room to install the fuel tank.

Last night I added the rear cockpit bulkhead and all of the upper stringers. I did make a small change here substituting some 1/8” x 1/4” Sitka spruce for the balsa called out between the instrument panel and firewall. This was done to help reinforce the firewall and help take up the load of the DA-50. I was impressed just how much strength the stringers added to the forward section for the fuselage!

Before shutting down the shop for the night, I threw on the tail and cowling to see how it would look… I’m very happy with the results! This also marks the two-week point since starting construction.
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