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46" DTFB Spirit of St Louis -Build

Tench745

Active member
#1
A quick summary:
-My 1/6th scale Spirit build for FFOH '17 was a deuce-and-a-half of work.
-I want to know how it flies before I fly it.
-I want something I can crash.
-I want to build something new to fly and none of the FT designs are really speaking to me.
-I want to design a plane that people know

For the above reasons, I took my CAD files for the Spirit, scaled them down to 1/12th scale and worked up the start of an FT style wing and fuselage.
This is my build thread for version 1.
 

Tench745

Active member
#2
A quick progress shot.
I'm using all Ft techniques for this build to make it a little easier for someone else to follow. There is some paper-off foam bending and I stole the gear mount from the FT Edge (and Simple Scout, and Simple Cub) the rest is classic FT.

The tail looks particularly small at this scale. I suspect it will give me problems, but we'll see.
IMG_1059[1].JPG
 

Tench745

Active member
#3
Quick Update:
I'm making slow but steady progress on the Small Spirit. These pictures are from the day after my last post. I opted for a rolled foam airfoil akin to the new FT Master Series Corsair. It's actually a bit of a hybrid between that and the folded FT airfoils. The first picture is of the wing with the forward and mid-chord spars. The mid-chord spar is doubled as it will take most of the loads; the forward spar helps form the curve of the leading edge. The last picture is of my test piece, not the final wing.
IMG_1062.JPG IMG_1061.JPG
IMG_1063.JPG
This method may have bit me as my table has a slight warp to it and without the creases of the folded airfoil to define things it's easier to accidentally set a warp into the wing when gluing it up. Bamboo skewer struts should help correct some of this.

The next day was spent locating aileron control horns and servo pockets. These were then added to the plans.

IMG_1065.JPG
Last night I soldered up a Y-harness for the aileron servos and realized that I probably should have done this before folding the wings up. It will not be easy to plug in a servo lead 3" into the wing. Of course, if I had put the servos in first the servo horns would have been in the way when folding the wing. Hmmm....
IMG_1066.JPG

Anyway, tonight I'll get the wings finished up minus control linkages and start figuring out attaching it to the fuselage.
 

Tench745

Active member
#4
Soooo... I may have hosed myself. Or at least I need to rethink some things. I drew this up to have a removable wing so the battery etc can be placed inside through the opening under the wing. Except, I also had been planning to have wing struts, a very notable feature of the Spirit of St Louis. Struts are usually glued in ala FT Mini Pietenpol, ie. permanent.

Right now I'm thinking about ways to make removable struts or other ways to install the battery. I have some ideas, but input is welcomed.

I'm also puzzling through servo mounts, motor mount, esc location, etc. Updates will continue as I try things.
 

Grifflyer

WWII fanatic
#5
Soooo... I may have hosed myself. Or at least I need to rethink some things. I drew this up to have a removable wing so the battery etc can be placed inside through the opening under the wing. Except, I also had been planning to have wing struts, a very notable feature of the Spirit of St Louis. Struts are usually glued in ala FT Mini Pietenpol, ie. permanent.

Right now I'm thinking about ways to make removable struts or other ways to install the battery. I have some ideas, but input is welcomed.

I'm also puzzling through servo mounts, motor mount, esc location, etc. Updates will continue as I try things.
If you could reinforce the wing enough to fly without struts, then you could just hold them in with small magnets.
 

Tench745

Active member
#6
More progress today, no time to post pictures yet.
The struts are purely aesthetic. Something simple, yet strong enough they don't get lost in flight is all I need to hold them on. It looks like Ben Harber @Mid7night has something similar on his new little Cessna150, but I can't see how it's done for sure.
 

Tench745

Active member
#8
Progress from yesterday:
I got the motor box glued in and the motor mounted. The ESC Velcros to the underside of the motor box where it can get some good cooling.
It's looking like this should fly pretty scale with a 2S.
I've built this from Ross foamboard and it is a radial-engined aircraft, so it is pretty tail-heavy by nature. Luckily my 2000mAh 2S fits perfectly inside the motor box for a good CG. A 3S might work okay too, but can't fit as far forward.

Pushrods and control horns were rigged for the ailerons with a little differential
Fuselage servos, pushrods, and control horns were installed for the tail
Simple foam circles on a brass bushing were fabricated for the gear.

I'm still puzzling through wing struts but have the start of an idea. A post on that will follow.
IMG_1067.JPG IMG_1068.JPG IMG_1069.JPG IMG_1070.JPG
 

Tench745

Active member
#9
Here's my idea for wing struts. A Piece of foam, in this case approximately 3/4" x 13", with a BBQ skewer glued to the leading edge for stiffness.

One end has all but the paper on one side removed and a bevel.
IMG_1071.JPG

The paper gets glued to the wing where the strut will mount.
IMG_1072.JPG
Then the strut gets folded back towards the fuselage, no extra glue.
IMG_1073.JPG

Pros:
The paper can act as a hinge, allowing the wing struts to fold flat when the wing is removed from the fuselage.
The paper wraps the bare end of the strut when attached to the plane, holding the strut-end together.

Downsides:
The strut sticks about 3" past the wingtips when folded flat, making it more prone to damage.
The paper hinge is only so strong.
I don't yet know how to do the fuselage side in a way that is easily removable.
 

Tench745

Active member
#10
A downside to this square fuselage thing is the engine. It looks all wrong.
This picture shows a front view of the engine; the box is the fuselage. Most-to-all of the cylinders will be covered by the fuselage, and to make a shape cut out to match the valve covers would just look weird on this fuselage.
IMG_1074[1].JPG
As such, I've just cut a couple circles of foam the diameter of the engine and I'm thinking I'll just glue a picture of a radial to it. IMG_1075[1].JPG

At this point the plane is flyable. Everything thing else is just cosmetic.
 

Tench745

Active member
#12
A couple updates; progress and disappointments included.

I did a couple tests with paint on ROSS foamboard.
The water-based polyurethane I have, when dried, works very well to remove paper. The water lifts the paper from the foam, and when dried the polyurethane works well to hold the paper together so it doesn't tear into bitty pieces on removal; this is not the intended effect.

Spray paint works like spray paint and all the caveats that go with it.

I was very happy to find, however, that my quart can of silver Rustoleum paint that I painted my big Spirit with will not peel the paper off the Ross board, and it doesn't harm the foam at all, so it looks like it can be used over papered or bare foam just as easily. In fact, it looks a little better over the bare foam in my tests.

So, the Small Spirit got a coat of silver, and for added flair the cowl was covered with aluminum tape. It was not burnished with machine turning though, because I'm lazy and expect this plane to crash.
IMG_1079.JPG

I'm sad to say that the printed engine on the foam rings looks quite silly now next to the aluminum cowl. The white foam between the cylinders didn't stand out much when the whole plane was white, but now it is very obvious.

Also, to save myself from having to hand paint or meticulously cut out the various markings for the Spirit, I opted to make vector graphics of all the text. I printed these on 8 1/2" x 11" clear shipping label stock. I thought I was being clever, but the matte nature of the label paper makes the decals stand out like a sore thumb. It's not quite as bad on the paint as the cowling, but it's still pretty noticeable.
IMG_1080.JPG

It's good enough for this build though and I'm glad I tried it. I suspect if one were doing nose art, or other things where you could cut most of the label away from the edges, it would look pretty good. I'll let you-all know if I have adhesion problems or anything.

I may play with a spinner, painting tires, and/or adding windows, but we'll see.
If anyone is interested I'd be happy to share the vector files and plans once this flies.
 

Tench745

Active member
#13
The Small Spirit had is maiden yesterday, sort of...
I "forgot" to secure the battery.
Truthfully, I knew it wasn't secured and I convinced myself it would be fine. It was not.