Mini Morph Marathon Part IV: Mini-Bip:B & C

Background

This series of articles has been about learning as much as coming up with a good airplane.  To be honest, the first three articles have been more on learning, and the results have been below what I was wanting.  When I have the time (and the weather cooperates), I plan on going back and revisiting the Mini-Spit and the Mini-Trainer, and from what I have learned about thrust angles, wing angle of attack and CG; I think I can improve their basic performance.

With this plane, the focus definitely changes to a well flying plane.  The Mini-Bip:C is a sweet plane, both in design and performance.  After initial set-up I tossed it into the air to adjust the throws, and it just flew straight and steady; I upped the throttle to a touch over 1/2 and it flew level.  I ran out the battery checking it out and had a delightful flight.  This is no acrobatic performer (at least on a 2s), but getting up three-mistakes high and putting it into a power dive it managed to make an awkward loop.  The glide slope was good, and it gracefully came into a smooth landing.

As I said in the first article of this series (Mini-Bip), I was thinking of extending the wing to make this plane a bit slower and more stable.  This article is the results of extending the wing and one other modifications. The only actual build information you will get here is for the top wing; everything else is exactly the same as the build in the first Mini-Bip article, and the specifics are covered there.

 Mini-Bip:B

The only difference between this plane and the first one is a lengthing of the top wing.  If you are starting from scratch, just cut it to 24 inches instead of 20.  Since I already had a plane with a good wing, and didn't want to butcher the plane in cutting it off.  I simply whacked off the wing tips and scabbed on some extensions.  I cut one inch off each end of the top wing, removing the curved tips.  I then cut two 3x3 pieces, curved the ends to the standard shape, and gave them the same cord as the wing.  These extensions were then glued flat and square to the cut-off ends (making the final wing 24 inches).  My attitude is that if you don't like the wing - change it.

Mini-Bip:C

While designing the bi-plane, I looked at a number of plans, the one that really caught my eye was the Aeromaster, with a swept top wing (Google for plans), which has similarities to the Pits.  The wing design is basically the same, only rather than being a single 6x24, it is made in three pieces: two 6x11 wings and a 3 inch center spacer.  Rather than a simple rectangle, the trailing edge 'pushed' out by 1/2 inches, producing the sweep angle.  The center spacer is the same wing chord, but only 3 inches wide, with a bit of decorative removal at the back edge.  Fold and glue up all three pieces, using the Mini-Scout angle gauges, then hold them flat to a table surface and glue them together.  The strut is glued to the exact same place on the lower wing as the Mini-Bip:A, and the top wing is centers on the struts (this is all easier to do than explain).

This is the same picture as on the first Mini-Bip, but now all the parts are used.

Flight Characteristics:

Set-up:

• 2 cell 500 mah battery
• 6x4 prop
• CG is just behind the wing fold (see marker in photo)
• Throws set at 12 degrees (less is better!)

Both planes fly nicely.  The Mini-Bip:C is described above.  It is a slow and gentle flyer, perfect for a soccer field sized park.