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Old 03-12-2014, 02:11 AM   #1
Bald Paul
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Default The Boeing L15 project

Having finished my MidStar 40 conversion (nitro to twin electric), I felt the need to start building another.

I've been slowly teaching myself DesignCAD. I had already taken a set of plans and converted them into CAD, and built the plane from the resulting laser-cut short kit. That was (relatively) simple, since most of the details had already been worked out on the plan sheet, and I just measured and copied for the most part.

The MidStar required me to design some of my own pieces from scratch. That was a bit more challenging. You have to think about how it's supposed to look, how it has to be built to achieve that look, and not fall apart in the air!

This time, I decide to jump into the deep end of the pool. Not being an aircraft designer, I still needed a set of plans for general dimensions. I started scanning through some available plan sets and saw Bob Aberle's take on the Boeing L15. It is an intriguing aircraft, but the plans are for a very small backyard flyer. Scaling it up just wouldn't look right. A Google search led me to a set of plans from 1950 for the same aircraft in a free-flight version. The plans aren't really useable (or maybe I can't understand some of the build techniques used) but I got a good size reference for a 49" wingspan plane.

So, the process begins. This will be a 'sort of' scale version of the L15 scout plane. I intend to design the majority of the parts in CAD. When the plane is completed, and (if) it flys well, I'll offer up the CAD files to anyone who would like to build their own version. I've started a "build log" blog on (can I say this?) RCGroups.com under my forum name Stay Quiet. Pictures, notes, etc will be updated there.
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Old 03-12-2014, 09:20 AM   #2
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Old 03-21-2014, 10:43 PM   #3
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First batch of parts have arrived from the laser cutter. The 1/8" lite ply sheets contained the parts needed for fuselage and tailboom construction - at least most of it. The motor mount has to be cut from birch ply, and it seems I forgot to include a couple of minor pieces at the top of the fuse, on the wing mount, but they are no big deal (just rectangles with no fancy tabs or curves). I will, however, add them to an updated CAD cut layout file in the future.

I jigged up the fuselage bulkheads, sides, and floor sections using rubber bands. The tab and slot construction I designed into the parts works very, VERY well.
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Old 03-21-2014, 11:24 PM   #4
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Originally Posted by Bald Paul View Post
First batch of parts have arrived from the laser cutter. The 1/8" lite ply sheets contained the parts needed for fuselage and tailboom construction - at least most of it. The motor mount has to be cut from birch ply, and it seems I forgot to include a couple of minor pieces at the top of the fuse, on the wing mount, but they are no big deal (just rectangles with no fancy tabs or curves). I will, however, add them to an updated CAD cut layout file in the future.

I jigged up the fuselage bulkheads, sides, and floor sections using rubber bands. The tab and slot construction I designed into the parts works very, VERY well.
Cool We need Pictures, Lots of Pictures LOL

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Old 03-22-2014, 12:19 AM   #5
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Okay, if you insist!


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Old 03-22-2014, 12:30 AM   #6
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Great Start, nice laser cut pieces, Keep up the nice work with lots of Pictures, I Insist LOL


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Old 03-28-2014, 12:50 AM   #7
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Waiting for the remainder of my laser cut parts to arrive. Fuselage and boom assembly revealed one very small issue that will be corrected in Version 2. I'm using 4mm carbon fiber square tubing to reinforce the boom, sandwiched between two sections of 1/8" lite ply. I thought that would give me the space needed to run a Sullivan tube through the middle for elevator control. Well, almost. Version 2 will use 5mm carbon fiber square tubing. (I did get the control rod tube routed, but I had to groove one section of lite ply to do it.) So, a minor design modification of bulkheads 6 and 7, where the boom fits, will be in order.

Bulkhead 7 has sections glued to the rear to form the large rear observation window. I may tweak that a bit as well, as forming the rear and side glass looks like it may be a challenge. But, scratch building is all about the challenge, isn't it?

I'll add pictures when I make a bit more progress.
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Old 03-31-2014, 06:53 AM   #8
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Looks like an interesting project you have there. The twin boom and dual rudders, and just the overall aircraft in general are reminding me of the Miles Aerovan I took on last year. Endless possibilities working out those linkages.
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Old 04-05-2014, 03:04 PM   #9
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More changes due. Fuselage is assembled, but I'm not completely happy with it. The picture of bulkhead B7 with the rear "window frame" assembled may be redesigned, along with bulkhead B2, which will make battery installation a lot easier. The tailboom has been scrapped, as it was just too heavy being made of lite ply, and the carbon fiber reinforcement just didn't stick. (Side note: does anyone know of a good cement that will stick to carbon fiber? Apparently, epoxy won't!) Redesigns have been made in CAD for the future, and the new tailboom will be made of 1/4" balsa with a 6mm X 1mm CF reinforcement insert to prevent flexing. Landing gear has been built (amazing, since I am the world's worst wire bender) and the tailwheel, which will be steerable, is a Du-Bro 60 size with a 1.25" wheel.
The remainder of the laser cut parts arrived, and tail construction will begin as soon as I get my workbench cleaned off!


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Old 04-06-2014, 10:43 AM   #10
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Originally Posted by Bald Paul View Post
More changes due. Fuselage is assembled, but I'm not completely happy with it. The picture of bulkhead B7 with the rear "window frame" assembled may be redesigned, along with bulkhead B2, which will make battery installation a lot easier. The tailboom has been scrapped, as it was just too heavy being made of lite ply, and the carbon fiber reinforcement just didn't stick. (Side note: does anyone know of a good cement that will stick to carbon fiber? Apparently, epoxy won't!) Redesigns have been made in CAD for the future, and the new tailboom will be made of 1/4" balsa with a 6mm X 1mm CF reinforcement insert to prevent flexing. Landing gear has been built (amazing, since I am the world's worst wire bender) and the tailwheel, which will be steerable, is a Du-Bro 60 size with a 1.25" wheel.
The remainder of the laser cut parts arrived, and tail construction will begin as soon as I get my workbench cleaned off!
Epoxy and CA works great with CF, ONLY if you sand the CF Rough first, or its like trying to epoxy Glass together, Plastic and CF parts have to be made rough before gluing. Hope that helps, Chellie

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Old 04-06-2014, 09:36 PM   #11
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WEST epoxy sticks to carbon just fine. Kind of slow curing Re hobby style epoxies, but it sticks. As Chellie mentioned, sand the parts. And lose any 5 minute epoxy you have - useless stuff . . .
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Old 04-07-2014, 07:20 AM   #12
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5 Minute isn't much different than super glue.

slow stock prop reversal. it flies! easily! 543 watt dual motor bipe slow stick. push-me-pull-you. 242 watt 3 channel slow stick. 365 watt mini ultra stick. 415 watt mini contender. 810 watt ultra stick .25e. 220 watt alpha 450 sport (retired).
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Old 04-19-2014, 08:22 PM   #13
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Back to business.

I got slightly sidetracked. I was going through my 'junk' drawer, and found a motor, ESC, a couple of micro servos, another receiver, just sitting there. It just so happened that they all fit quite nicely into a Flite Test F22 Raptor kit. I actually built this plane in an afternoon. The quality of the kit (which was $28, by the way) was outstanding. Flite Test has a video build on their YouTube channel. I'll be flying this at a field 5 minutes from work - probably at lunch during the week!

The L15 flaperons are on the building board now. It's pretty straightforward, with the LE and TE laser cut and full size plans printed to build over. Just some 3/16" square balsa on the ends, and 1/16" strips cut to fit for the slots in the laser cut parts. A little sanding to round out the LE and taper the TE, and they will be ready for covering. Then I'll be moving on to the wing.


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Old 04-26-2014, 05:40 PM   #14
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Sorry I didn't take more pics as the wing was being built, but I think you've all seen that process, haven't you?

The wing has no dihedral, and a 5mm carbon fiber main spar is utilized. The horizontal stab also uses a carbon fiber main spar, this one is 4mm. The horizontal stab is really an inverted airfoil, per the 1950 drawings. Who am I to argue?

I test fitted the parts together today. Obviously, the LE sheeting and top rib caps of 1/16" balsa strips haven't been installed yet. The wing mount (1/4" ply) isn't in place as yet, and the flaperons and elevator aren't shown. The boom is made of 1/4" balsa, with a 6mm by 1mm carbon fiber reinforcement to prevent side flex. It will be round, true to the original, once I get the boom formers and sheeting in place.

Oh yeah, the flaperons. During my test fitting, I discovered I made a slight miscalculation in how long they were supposed to be. Luckily, they were a bit too long, and I could cut off and rebuild one end. As I find things that don't quite work, I go back to my CAD drawings and modify as needed, so that version 2 will go together nicely.

I also think I solved my flaperon hinge problem. The original (and thanks to Chellie for providing the pic) shows the flaperons mounted below the TE of the wing. Using pairs of 1/2A control horns, one up from the flaperon, one down from the TE of the wing, and hinged together, should solve that issue.

Elevator servo will be mounted at the bottom front of the boom, inside the fuselage. That's next, and then I can determine where the control rod tube has to be routed, so the proper holes can be drilled into the boom formers and bulkhead 7. Once done, those holes will be added to the CAD drawings for those parts.


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Old 04-27-2014, 04:51 AM   #15
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When I was about 15, (66 now) my dad somehow bought a model of the L15 that was used in Boeing wind tunnel tests. Then someone tried to convert it to control-line. Had a Enya .15 or .19 engine, but it didn't fly worth a dang.

I still have some parts of it left, I will try and find them, and send in a picture.

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Old 04-27-2014, 11:38 AM   #16
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Originally Posted by Wildflyer View Post
When I was about 15, (66 now) my dad somehow bought a model of the L15 that was used in Boeing wind tunnel tests. Then someone tried to convert it to control-line. Had a Enya .15 or .19 engine, but it didn't fly worth a dang.

I still have some parts of it left, I will try and find them, and send in a picture.
Well, that's encouraging!

Hopefully, it had more to do with weight than design.
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Old 04-27-2014, 07:03 PM   #17
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I'm sure it was excess weight in certain areas, and that caused balance problems.
It was not designed to fly in the first place, and whoever installed the bellcrank and other hardware for control-line, was not a real genius.

I found out that Stearman aircraft company, and Boeing were in some kind of partnership on the plane. I have a large book about the Stearman planes and this plane is in it.

The observer was supposed to sit in the large rear window. I think I would get sick, watching every thing backwards.

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