Albatros C III (oz16915)

About this Plan

Albatros C III. Radio control indoor scale model. Wingspan 27 in, for electric power with WesTechnik Micro DC1717 motor. Scale is 1/10.

Quote: "Indoor R/C scale Albatros CIII, by Ken Sheppard.

My last indoor R/C scale project, the Armstrong Whitworth FK3 (MF May 2002) flies well and has withstood the rigours of regular session flying all through last season heroically, but is now showing its age. I also wanted to see if I could get the next model to fly slower, as the FK3 flying speed was a little too high for realistic flight.

I didn't want to change my design philosophy of using a scale structure with double surface covering (a single surface and non-scale structure would have made it lighter), so I had to look at other ways of slowing the model down.

The span was restricted to about 30 in, the practical limit in the Furzefield Centre sports hall, in my opinion. To minimise wing loading - the key factor in getting slow flight - meant that another biplane was in order, preferably with parallel and wide chord to keep it simple. The lowest loading that I thought that I could achieve (realistically) was 3oz/sq ft - if I was lucky! This, combined with slightly increased wing incidence and motor downthrust - and a large wing area - should get me closer to that elusive goal of realistic flight speed.

The Albatros CIII immediately seemed a good prospect. A double bay, two-seater bipe, parallel chord wings, flat-sided but curvy fuselage, a nice deep nose to hold the motor and battery and a nice sized curvy tail. The downside was that the fuselage was sheeted and the rudder was rather small. What swung it was an interesting colour scheme for the CIII, featuring a dragon and a crocodile - sold!

I could have cheated and used an open structure for the fuselage which would have reduced the weight quite a bit (the model turned out at 170g, giving a wing loading of 3.6oz/sq.ft. - a bit off of the target!), but it wouldn't have looked right. I remembered seeing a F/F plan for a CIII some time ago and true enough a search through my plans file found the 39 inch Albatros CIII (oz1162) by John Watters. All the hard work had been done! It was a simple job to work out the reduction factor and start drawing out a simpler, lightweight structure - thanks, John!

Ribs: At this size and delicacy of model, the one job I don't like is cutting out all the wing ribs, so I called on the services of Chris Stewart at RCS Technik again, who CNC cut sheets of balsa ribs from the drawing that I sent him. The beauty of doing it this way is that not only are all the ribs exactly the same, the quality of the router cutting means that the spars are a perfect fit - the wing panels were assembled dry, in the air, before being pinned down and glued with a tiny drop of cyano at each joint, using Chris's Greven cyano hypodermic applicator. This way, each panel took literally just 15 minutes each to make. Chris will offer this service to anyone - and for quite a modest fee!

I have fitted adjustable ailerons to a couple of my OD indoor WC models, which makes trimming the model a doddle, so I incorporated them into the Albatros - the weight gain is easily offset by the ease of trim adjustment (to keep the inside wing up without having to resort to wing warping). The hinges are short pieces of soft wire and the ailerons are finally fixed in position when a satisfactory trim has been achieved. The ailerons are built separately to the panels and a tapered packer under the TE builds in the washout 'twist'. The trailing edge of the wing panels and ailerons is from 1/16 carbon rod (available also from RCS Techniks), which allows a really thin rib section, without sacrificing strength. This material is also used as wing joiners, glued along the wing spars over two rib bays and projecting out of the root ribs. The tips are simply 1/32" sheet balsa cut across the grain and glued to the end rib, giving a curved section. For strength, the outer edges of the tips were reinforced with some thin cyano. The wings are covered in Mylar film gently heat shrunk (see the RCS Technik catalogue for the method) and lightly sprayed with well thinned Humbrol enamel, building up the colour gradually with a few thin coats, to avoid paint runs - and unnecessary weight.

The curved edges of the tailplane, elevators and fin are from two laminations of 1/32 x 3/32 strips of balsa, soaked in water, then wrapped around a card template and cyano'd together, the ribs are simple strip. After covering and before painting, the elevators and rudder are fitted to the fixed surfaces using thread hinges in the time honoured 'control line hinge' method. The elevator joiner (I know it's not scale, but closed loop on the elevators as well as the rudder is just too complicated) is a short length of cocktail stick.

Dirty up the painted 'linen' surfaces with some artists chalk rubbed on using the tip of your finger - black for grime, brown for stains, etc.

The fuselage is made from the lightest grade of 1/32 balsa that you can find, reinforced with longerons and cross pieces of 3/32 square soft balsa. Make the two sides first then fit the horizontal cross pieces, pulling in the rear end and then the nose section. You will be wise to make up a temporary jig to do this so that the tail slot is square side to side and the vertical fuselage centre line is accurate. When fuselage top and bottom sheeting is fitted, the fuselage becomes quite a rigid unit. Both the upper wing cabane and the u/c assemblies were assembled on simple jigs made from sheet balsa..."

Albatross C III from R/C Model Flyer January 2003.

Direct submission to Outerzone.

Supplementary file notes

Article pages, thanks to RFJ.

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