46" DTFB Spirit of St Louis -Build

[Tench745]

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.

Plans for Version 2 available here:
McB Small Spirit

 

[Tench745]

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.

 

[Tench745]

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.


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.


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....


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

 

[Tench745]

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]

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]

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.

 

[kilroy07]

This is very cool!

 

[Tench745]

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.

 

[Tench745]

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.


The paper gets glued to the wing where the strut will mount.

Then the strut gets folded back towards the fuselage, no extra glue.


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]

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.

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.

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

 

[Tench745]

Radial printed. Looks pretty good.

 

[Tench745]

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.


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.


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]

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.

 

[Tench745]

It was cold, gray, and windy today; a day where no one had any business flying. So naturally I decided to re-maiden the small spirit today.

The first flight was short and strange. I had her balanced on the aft CG position and that was clearly too far aft. The spirit was incredibly unstable in pitch, yaw, and roll. It was just as happy flying sideways, up, down, just about everything but straight.
I knew it would be a handful, but wasn't ready for just how bizarre it was to fly an aircraft that didn't mind flying at something like a 70° crab.
I was able to plant her softly enough that only the firewall broke free.
I took her home to the glue gun to repair the damage and add 2.15oz of lead to the nose to get her to balance at the forward CG point. I also tweaked the programming, dropping aileron rates and increasing elevator throw.

The wind was gusting to about 14 when I went out to remaiden, but I was itching to fly and to show off how weird this plane behaves. I'd already decided that larger tail surfaces were in order, which will necessitate a complete rebuild anyway, so if I wrecked her I was fine with it.
The nose weight definitely helped with pitch stability, but it was still really unstable.

On that note, my wife was able to come along and get some video. It's a bit blury in places, but you can see at least some of what I'm talking about.

She went down in a spiral dive into the trees, but survived with nothing more than a few scratches. I guess I'll just have to keep trying to kill it.

 

[Tench745]

Plans added to first post for version 2 with larger tail surfaces.

 

[Tench745]

The McB Small Spirit was re-maidened today with the larger tail surfaces, four rubberbands holding the wings on, and new wheels. All in all it was a much tamer experience than last time even with gusty winds above the trees.
I am definitely out of practice flying in general, but especially flying with rudder.
The Spirit actually managed a ROG takeoff with her new Dubro "micro sport" wheels. She still has a bad tendency to pitch up with throttle, so I'll have to add some down-thrust to the motor eventually. Pitch and yaw were much more stable. Roll felt sluggish except on high rates, but those made elevator and rudder too sensitive. I was fighting the wind, so I'll fly again on a calmer day before tweaking rates and expo. I don't think I ever went above 3/4 throttle because of the pitching issue, but with how she was trimmed climbing felt off. I suspect with some down thrust and full power available that will change.

I hurried a little too much getting it down and managed to crack the piece of foam that carries the elevator through the rudder. A little hot glue would have fixed it, but for some reason I never bring a glue gun when I fly. The flight only lasted 2 minutes and the battery was at 85% on landing.

 

[Tench745]

Got to fly the Small Spirit again today, this time there was a little less wind. I upped my low rates because they were so small I would never use them.
I got just over eight minutes of flying in two flights and landed after the second with 43% battery. I also managed to get some video of the first flight.
The plane was still is unpredictable in pitch but I believe I've solved it now. It would take a lot of back pressure to keep the aircraft level, and then as soon as it would try to climb it would pitch up abruptly. At low speeds it was more predictable. I realized that on this design I have the elevator servo pushing for up elevator and that even though I had some support on the pushrod it was flexing in flight so that only extreme elevator throws would actually deflect the elevator enough to pitch up, and as soon as it did the air pressure on the elevator lessened and it could go to full deflection. I added another pushrod support in the aft fuselage and expect it to fly much better. If all goes well I'll be testing it again tonight.

 

[Tench745]

I got to fly a couple planes again this evening and the extra pushrod support solved my elevator issues on the Small Spirit. It was a wonderful moment. Now I just need to fly the wings off it and actually become a good pilot...

 

[Tench745]

I finally got some good footage of the Spirit flying. And by "good" I mean the flying was good; the footage was only ok. I managed to override the auto focus on my phone, so it doesn't try to focus on nothing, but the footage is still a bit blurry.

 

[The Fopster]

Seems to fly really well. Must have been a challenge to get it to balance with such a short nose. Congrats!