Miny Morph Marathon Part I: Mini-Bip

Background

The Mighty Minies are adictive, they are so simple and cheap it is hard to not get on a binge of making several.  I was slightly disappointed that one of the first minis was not a bi-plane, but since I rarely build a plane 'to plan', this only set up a challenge to design my own bi-plane.

I started out building the Mini-Scout, but have still to actually fly it - other priorities took over.

Variations on a Theme

Because I cut my own foam, and prefer cutting straight lines, I tend to lay out parts as strips, cut out the strip from the foam board, then trim the corners and edges.  This approach also gets me seeing the similarities between planes; how the mini is like the Storch, or like the Spitfire.  The fuselages are all basically the same, with a variation in placement of the wing.

I tend to simplify planes for ease of construction, with less regrd to looks and stype.  With the Mini-Scout, I did not want to cut all the trailing edge scallops, so I modified the wing into a 6 x 11 inch rectangle (start by cutting a 6 inch strip of foam).  Almost all my wings have a simple tip.  For a 6 inch chord I mark a line one inch in from the tip, then cut off a triangle from the fold to the trailing edge mark, and round off the front tip. The tail for all these designs is the one from the Mini-Speedster.

Looking at the Mini-Scout, I started seeing that if I moved the wing down, I could end up with more of a warbird style, move the wind up and it becomes a trainer.  Move the wing down and split it in two and I have a bi-plane. Thus I ended up with an outline for a series of planes - and an interesting experiment to see how the flight characteristics would differ.

My actual build/fly sequence was not in logical order (since I started out wanting a bi-plane), but there is a progression of design.

The Mini-Bip

I started off by making the wings; cutting two 4 inch wide strips from the width of the foam board (20 inch length).  The fold was cut at 1 3/8 inch (about 2/3 of the 6 inch wing chord location).  For the bottom wing, I took a hack saw and cut the top of the wing part way through along the middle line, this made it easy to bend the wing and create a dihedral.  The angle was set just a little bit less that than of the Scout.

The hardest part was thinking through the adjustments to the fuseladge for the wing placement so as to keep the CG about the same as the Scout. Starting with the Scout fuseladge,  I dropped the wing placement down to the bottom and 'slid' the wing so the back edge would line up with the relative location of the original location, keeping the attack angle the same.  I designed the struts so that the top wing would be raised 4 inches, and the leading edge would align with the Scout's leading edge.  The spar placement was eye-balled for asthetics, your placement may vary.  There is a third, simple spar, between the center of the top wing and the fuseladge.

I am not into scale looks, so there is no turtle-deck or cockpit.  If you want one, the design is up to you.  There are plenty of ideas from the Spitfire through the Duster and the Minis.

These plans are not for printing and using as a pattern, but enlarge the image and read the measurements.  As you can see, most of this is simple strips with a few trimmings.

Warning: these plans are not for this plane (or at least some of the parts are not)!  These plans show the fuseladge, spar, top and bottom.  Make two of the wing on the right end and ignore the short wings in the middle.

Electronics 

I followed the suggestion for the Scout and got all the electronics from Ready to Fly, they are working nice and give plenty of power:

Motor - RTF Mini Motor X2204 v2 2300kv - House (swinging a 5x3 prop)

ESC - B12-A Ice Blue

Receiver - Lemon 6 Chanel

I used servos that were on hand - 9 gram Hextronix (HX900).  I was lazy and mounted them externally, with coffee stirrers as guides.  It doesn't look as nice as internally mounted,  but I don't think it affects the flight performance.

Set-Up

Most of my disasters have been from not spending the time to get the plane set up decently before I try to fly.  I now have a four step approach that tends to keep me safe:

1. Check the transmitter settings multiple time to make sure the surfaces are moving in the right direction, and with the right amount of throw (less is usually better, at least when beginning).  Walk through some flight manouvers (with the throttle switched off) and make sure the controls are doing what you think they should.  It is better to be surprised on the bench than in the air.
2. Make sure it taxies straight.  If it doesn't taxi straight, it won't fly straight.  I have damaged a lot of planes by thinking I had the rudder straight, only to toss it into the air and watch it take a hard left (or right) and nose into the ground.  Adjust the rudder so the plane travels straight, even if it doesn't look straight.  Especially when building like I do, it is too easy to not get the rudder glued exactly on the center line.
3. Do a chuck test or hop-flight.  Now that the plane should be flying straight, check the glide slope and make sure the CG is correct.  Apply just enough power to start a climb, cut the power and glide into a landing.
4. Finally, go for an easy flight to look for any strange behavior.  Make an easy take-off and climb to three mistakes high.  Check how 'twitchy' the controls are.  I tend to initially leave too much travel in the controls so that the plane over reacts, now is the time to find out and make adjustments.  Make sure the turns are smooth and responsive.  Check the stall characteristics.  Does it tend to climb (or turn) when throttled-up?  Work your way into the plane gradually - it pays off in how long the plane lasts, and how much you enjoy flying it.

Characteristic

I have put several flights on the Mini-Bip, it is fun, but not my ideal.  After flying some bigger trainers for a while (FoamCub), small planes tend to be a bit more eratic - especially when I am out in an 8 mph wind.  I also have to remind myself that a 'bank-and-yank' will never be as smooth as a plane with airelons.

The same day I was flying the Bip, another person was in the park with a hot-liner glider.  I thought he was crazy to try and fly such a big plane in such a small park, until I saw him take off and go vertical.  Needless to say, it was hard not to be comparing my flying skills and plane with his.  As long as I remind myself that this is a small foamy, it is a good little plane to play with, especially for a few minutes of fun in the local small park.

 I think a slightly larger wing would give it more drag, slowing it down an bit and making it a bit more stable - stay tuned for version II, it is built and waiting for some dry weather.