Mumbo Minor -- Electric Flight -- RC Plane

The Mumbo Minor is the second design I've built from http://www.flyelectric.ukgateway.net. (The first was my AND_NOW). It is made entirely from 3mm Depron, has a brushless CD-ROM motor from C&K Designs, and it has much more than a 100% thrust-to-weight ratio.

Shown to the left is the CD-ROM motor, weighing 20g excluding the prop and mounting tube. The propellor is a GWS 8x4.7"

The thing I like about this plane is that it is a 3D design, but actually has a proper fuselage, not just a profile thing like a "Shockie". The control surfaces are big, and the plan asks for "as much deflection as possible"!

I think that this design should be quite simple to put together, as it is a box fuselage made out of 4 pieces of depron, a flat plate depron wing, and not much else. In fact it took me ages to build, as most of the time was needed working out how to make the control surfaces function. The ailerons are straight-forward enough, but the rudder and all-moving tailplane are another story. After a test fit, I decided not to put the servos where they are shown on the plan, but to move them backwards so that the C of G balances in the right place without the battery in place. That way, I can just locate the battery in a convenient place somewhere around the balance point. I ended up with the servos much nearer the tail than the plan showed. I tried to use closed-loop controls using fishing line, but I had no success, so I changed the rudder to be operated by a piece of wire. It still has far too much slop though.

The motor is a C&K Designs CD-rom motor that I wound myself. It took me ages to do it, but in the end was quite satisfying. I wound it for 3 cells of Lipo. It claims to give over 300g of static thrust, but my crude measurements on an electronic balance I borrowed only showed around 250g. No worries, because the whole plane probably weighs around 170g with batteries in!

The fuselage is very solid, considering that it is made of 3mm depron, but I glued it all together, so there is no way to get at any of the equipment without cutting it open! I made a hatch in the bottom to get at the battery, which just fits below the wing, but without taking a knife to it, I have no way to even change the receiver crystal...

How does it fly?

It's great! On the very first flight I launched at about half throttle. It just cruised away, gaining plenty of height. It inspired such confidence in me that I was soon doing rolls, loops and mad stunts. It is the easiest plane to fly upside-down. In fact, perhaps because I forgot to put any down-thrust in there, and perhaps because the wing is just a flat plate and therefore totally symetrical, it is somehow slightly easier to handle when inverted than in normal flight!

I made this plane to learn 3D with, so I can't comment yet on it's abilities, as I don't know how to even fly knife-edge yet. I'm sure it is capable of a lot, because it is seriously over-powered. At full throttle it goes mad, just looping and corkscrewing like crazy.

It inspired such confidence in me that I was soon doing rolls, loops and mad stunts

It makes me feel that I'm a much better pilot when I fly this plane, because it can turn on the spot, do really quick rolls, and get out of trouble easily by just powering up into the vertical. Unfortunately I've made some pretty terrible control connections on it, so that the elevator wobbles up and down. I've also built it with a twisted fuselage, which is annoying.

On the fourth flight I crashed it (I'm using a REX4 receiver, which is annoyingly glitchy when flying near the ground). I discovered that Depron rips easily. So much for the C&K prop-saver, the prop just broke in half! It'll be back in the air again soon...

2006 Update

Well, it never did get back in the air... It was too badly damaged, but it remains a fond memory, and I'm tempted to build another, just to re-live those easy-flying moments.

[Thanks to Jon Moore for photos!]

Mumbo Minor technical details:

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