TBD2 - Bridi Trainer 5 - RC Groups
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Mar 25, 2017, 09:53 PM
AndyKunz's Avatar
Build Log

TBD2 - Bridi Trainer 5


For the TBD2 contest I'll be building another Bridi Trainer 5 from RCM Plans.

Plans are found on Outerzone http://outerzone.co.uk/plan_details.asp?ID=5766

It will be electric again.

Andy
Last edited by AndyKunz; Mar 25, 2017 at 10:00 PM.
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Mar 26, 2017, 03:09 AM
I like real wooden aeroplanes!
Sundancer's Avatar
Is that a "V" tail adaptation of it in the photo Andy?
Mar 26, 2017, 07:59 AM
AndyKunz's Avatar
Yes it is. Plans are just suggestions, you know

Andy
Apr 02, 2017, 09:17 PM
AndyKunz's Avatar
This afternoon I didn't feel like working on the biplane, so I took a couple hours and made a laser cut short kit for it. It includes the sides, fin, rudder, and wing ribs. After I build this to check for errors, (which will probably only take a day) I'll post the final corrected files so others can cut them too. The attached file is subject to revision (I use TurboCAD 2016).

I'm using a Park 400 outrunner on it, so the firewall has been moved forward and the sides are keyed for the formers to plug in.

The wing as drawn used some odd sizes of wood for the spar, and there was lots of sanding for the LE and TE. Rather than keep those, I changed wing to use two 3/16" main spars (top and bottom), a 1/4" LE, and two sheets of 1/16 x 1" for the TE. I also added 1/8" sq spars up front to improve the airfoil. One thing I really dislike is a scalloped front view.

Andy
Apr 03, 2017, 07:20 AM
Sometime plane and heli flyer.
n0bbyUK's Avatar
Quote:
Originally Posted by AndyKunz
The wing as drawn used some odd sizes of wood for the spar, and there was lots of sanding for the LE and TE. Rather than keep those, I changed wing to use two 3/16" main spars (top and bottom), a 1/4" LE, and two sheets of 1/16 x 1" for the TE. I also added 1/8" sq spars up front to improve the airfoil. One thing I really dislike is a scalloped front view.

Andy
I'm doing the same on my 48" Achilles, I'm just drawing up the plan in CAD now and have put in an extra 1/8" spar on top between the 3/16" spar and the LE and one underneath towards the TE. I'll also be putting in some riblets (that should please George!!) to stop the sag between ribs, it'll also strengthen the wing (even though it's a floater not an aerobatic plane) for minimal weight gain.

Looking forward to seeing yours take shape...
Apr 03, 2017, 07:58 AM
AndyKunz's Avatar
Riblets are good, especially the barbecued type

Andy
Apr 04, 2017, 02:54 PM
AndyKunz's Avatar

Cut File Info


A bill of materials:

The cut file is 1 partial sheet of 1/8" balsa, 2 sheets of 3/32" balsa, and a 7x4" piece of 1/8" lite ply.

In addition you will need 2 strips of 1/16" x 1" x 36" for the TE, 1 strip 1/4" sq for the LE, 2 of 1/8" sq for the turbulator spars, 2 of 3/16" sq for the main spars, a portion of 1/16" x 3" x about 16" for main spar web, 2 sheets of 1/16" x 3" x 36 for fuselage top and bottom sheeting.

The horizontal stab is 3/16" x 1/2" x 36" with some 1/8" x 3/16" strips in it, which can easily be made or substituted with something almost the same size and be satisfactory.

The landing gear wire is 3/32" for the main and something .040" to .062" for the tail skid, but you can also use a nylon skid if you like.

You'll need two 3/4" or 1" control horns, plus pushrods.

Andy
Apr 07, 2017, 11:05 AM
AndyKunz's Avatar
I found a few more pictures of my second model.

I'm still gathering bits for this. I now have the ESC and servos from my box of scavenged parts, and the motor from a friend's scavenge box.

Andy
May 09, 2017, 09:57 PM
AndyKunz's Avatar
I set this project to the side while I finished up the construction of the Grandpa biplane.

Tonight I did the last bit of "construction" stuff on it, and that enabled me to get started on this plane. It's amazing how quickly this one is coming together - I may just put covering on them both at the same time!

I began by selecting some straight 3' sticks - (2) pcs 1/8" sq, (2) pcs 3/16" sq, and (1) pc 1/4" sq. I also cut (2) pcs 1/16" to 1" width for the trailing edge. The sticks were all cut to 18" to facilitate making the left and right wings.

These were pinned down to the plans and the ribs glued onto them.

While the right wing panel was drying, I cut a 3' length of 3/16" to 1/2" wide and some 1/8" scrap to 3/16" wide, then used that build the horizontal stab. The plans did not have equal left and right sides, so I marked the center and measured 6 1/8" to either side for the span, and marked the LE and TE. I also measured and marked so the angled bracing within the frame would be equal.

I should have started with the fuselage sides, adding the "cockpit" area first, but I did this last. The sides weren't as dry as I would have liked when I added the formers to it. Since everything is notched this went together just fine, but I would have preferred to sand the outside of the fuselage sides prior to making the fuselage. Note that the tail is taped together so things are even there.

What you see here was about 80 minutes of work.

This is going to be a quick plane!

Andy
May 10, 2017, 12:26 AM
I like real wooden aeroplanes!
Sundancer's Avatar
That is moving quickly Andy.
May 10, 2017, 07:03 AM
AndyKunz's Avatar
If I knew it was going to be this quick, I'd have started earlier. It could be a rainy day project, start to finish.

Andy
May 11, 2017, 10:33 PM
AndyKunz's Avatar
I was able to spend another 1.5 hours tonight on this model and got lots done.

First thing was a change. I really don't like gear that I can't remove if I need to. The plans show the old "glue the inverted V to the former" type of gear mount. Instead, I cut some 1/4" x 1/2" hardwood so it fit snugly between the fuse sides against F2. There's a slot in one piece where the gear will go. Later on I'll drill holes for them to plug into.

The elevator halves were cut from 3/16" sheet. To join them, I used to 3/16" x 1/2" pine from the scrap bin. This means I'll need to change the rudder notch, but that's not a big deal.

To get the correct size relief in the balsa, I first sanded the edges round so the sanding of the stab and elevator halves is essentially done. I then taped the halves so the outer edges match the stab span, and held the joiner in place as I cut around it with my knife. Then I just glued the piece in.

I started sheeting the bottom of the fuselage. I like to join all the cross-grain wood first so I can sand the joints smooth before putting on the plane. Since I didn't use my fuselage jig this time, I only put on the portion that is constant width. This will give me the strength I need to pull the tail together evenly without twisting anything.

The wing TE bottom portion was beveled down to about 1/32". While knife-edge would be perfect, that's neither necessary nor practical. After beveling I added the top 1/16" x 1" strip to each half and tape it down to the foam board so it dries straight.

I gotta run - it's way past my bedtime already!

Andy
May 12, 2017, 06:26 AM
Sometime plane and heli flyer.
n0bbyUK's Avatar
Looking good Andy, nice progress
May 12, 2017, 07:46 AM
AndyKunz's Avatar
Thanks. It certainly is a quick build. I'm hoping to start covering on this and the biplane Sunday after church.

Andy
May 12, 2017, 09:45 PM
AndyKunz's Avatar
Tonight was a bunch of little stuff.

I added the cross-grain sheeting to the rear of the fuselage. Tomorrow I'll do the top and make the hatch.

The wing center sections were sheeted top and bottom with some medium 1/16" balsa. I prefer slightly heavier balsa when I'm going to use rubber bands to hold the wings down. Trimming and inserting each piece takes more time than it did as a kid, but back then I didn't mind little gaps between the sheets and the spars. My sanding block is a good friend

The tips took a bit of work. I don't have 7/8" triangle stock laying around like the plans call for. I debated if I should build them up, but decided to just follow the way it was drawn. To make the triangle stock I first trimmed a 15/16" slab off a soft 3x3 block with the bandsaw, then cut it again to give a square.

To cut the diagonal, I CAd the square stock to a sheet of balsa at a 45 degree angle, set by a square. After that cured, I fed the assembly into the band saw, cutting right down the peak. A few swipes of the sander and I had two pieces ready to glue on.

Andy


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