Ages ago I came across this article by John Gallagher on wax paper bagging DLG tail surfaces, and ever since I have wanted to give it a go.
I'm working on a Fusion style pod and boom sloper designed by Leadfeather on RCGroups and thought bagged balsa tails would suit. My foam elevator is proving to be a bit delicate for repeated rough landings.
2.5mm x 75mm balsa sheet. Elevator will be 100mm wide so an extra strip needs to be glued on.
I'd probably use thinner balsa for DLG tails or sand down the 2.5mm.
Later I realised 100mm wide balsa is also sold at Bunnings.
A couple of things prompted me to try this traditional foam wing cutting method.
1. Thick boards of XPS insulation foam appeared in Bunnings. Either I have been unobservant or they have just recently added this stuff to the product line. 30mm and 50mm thick 1200mm x 600mm boards are available for $12 and $20.
2. There was an old PC power supply that was about to be trashed at work and I already had some 0.6mm MIG welding wire for the resistive wire.
I followed some online videos about getting 12V DC from the PC power supply. First time I turned it on the house safety switch tripped so it went in the bin.
Instead of a mains supplied power source I decided to try using a 3S LiPo, and it worked beautifully.
I'm using a watt meter to keep an eye on battery level, current and consumed mAh
The pine frame stretches the resistive wire across a 750mm span at the front. Tension is maintained by stretchy shock cord at the back.
Voltage is applied to heat the wire via alligator clips and I have an ON OFF switch on the frame. The LiPo connects via an XT60 plug.
Airfoil images and plots can be downloaded from The University of Illinois Airfoil Data Site. To make templates the airfoils need to be resized, printed then cut out of a rigid heat resisting material. I'm using 3mm MDF board but G10, formica and carbon fibre are also used.
The MIG wire broke mid cut a couple of times so I changed to 40kg stainless steel fishing wire and it's working well. It's 7 strand and nylon coated so the coating needs to be stripped off. I burned it off but it can also be easily peeled off using a knife.
Here's the "How to" video including a test flight.
As these wing cores are solid foam there is nowhere for the spar to fit.
This video shows three ways to form a spar channel.
UPDATE Jan 2016
I am now using a 4S Lipo for more heat in the wire, enabling a faster and smoother cut for 850mm wing halves.
I have changed to thin aluminium sheet (I think it's window flashing) for the templates. Can be cut out with scissors.
I was keen to try some aerobatics with powered planes but The Red was not quite up to the task. Too much of a glider and not enough rudder. So this is what I came up with.
It has a 1.2m x 180mm 12% chord Armin wing and a 700mm fuselage both made from 6mm depron covered with 75 micron document laminating film. That is the thicker laminate and it added lots of strength.
I also wanted to try a design with the tail as part of the fuselage, and test a full flying elevator setup. Both are working very well so far.
Fuselage construction started with the side and bottom panels in uncovered depron
The sides were glued on top of the bottom panel, which defines the width of the front area.
The tail halves were glued together giving the taper curve, then top and bottom panels added.
The fuselage was then covered with 75 micron laminate.
This added a great amount of strength, especially to the narrow tail area.
The 2826/10 1400kV motor is mounted to 5mm plywood with ventilation holes drilled out. Initially I built in some down thrust but I am still testing to find the right amount. Plastic washers can be added or removed to vary the angle.
The most radical feature of this design is the flying elevator. The whole horizontal stabiliser pivots on a 3mm carbon fibre rod which also acts as the spar. The rod passes through a brass tube glued into the tail. The inner diameter of the brass tube must be just bigger than the CF rod to give free movement but minimal wiggle. To hold the brass tube firmly there are 25mm discs of foam sandwiched between ID card plastic on either side.
Plans
Overview and build video
Field and slope flights
SPECS
Armin wing span - 1.2m (47")
Airfoil chord - 190mm (7") including 45mm (1.5") ailerons
Airfoil thickness - 23mm (12%) using 9mm formers
Spar - Skyshark P4X 7.5mm x 850mm, 57mm back from LE
Fuselage Length - 700mm (27.5")
Flying weight (2200mAh LiPo) - 770g
Full span Ailerons / Flaperons
Full flying Elevator
Large Rudder
TGY 9018MG servos x 4
Motor - Turnigy 2826/10 1400kV with 8x4 prop
ESC - Plush 40A
Skyshark P4X woven tubes - Wing spars and tail booms 7.54mm OD x 825mm (32.5") - Kites and fun things
US$3.50 each. Freight is about US$45 to Aus. These are woven carbon fibre tubes, which are lighter than pulltruded tubes and less prone to splitting. Great for big kite spars also. 6 x 1mm and 3 x 0.5mm CF strip - light weight spars and reinforcing
2 to 5mm CF rod and tube - wing tie downs rods and elevator axle 12k CF tow (ribbon of unwoven fibres) - reinforcing and repairs
Rubber bands Size 64 (87 x 6mm) wing tie downs - Officeworks
Buy a 500g bag, they need frequent replacing. Dont buy the coloured version, they are weaker and fail sooner.
Laminating film and Packing tape Iron-on document laminating film (covering) 3 mil (75 mic) is the most useful thickness, you can also use 1.7 mil (42.5 mic) for lighter builds. I bought 305mm wide rolls of GBC EZLOAD Lamination film but it may no longer be available This laminate from Bound to Impress may be suitable but not tried by me
75 micron laminate
This is my favourite reinforcing tape but it's more expensive. Strong holding, flexible and lighter than cloth tape. Used to join wings, hold landing gear on and to reinforce control horns and hinges. Use cheaper Bear cloth tape where weight and strength are not as crucial.
Hot gluegun- Crescent 60W Bunnings and this 12V battery one from Hobby King Brown Gorilla Glue Accent Polyeurethane Glue - Mitre 10 Z-Poxy Epoxy finishing resin - ebay and Tates Hobbies Geelong Foam Safe CA - Hobby King Thread locker (Blue = releasable) for motor bolts - Supercheap Auto
Genuine depron is stiffer and stronger than other uncovered foamboards.
Beware - Paper-covered foam boards in Australia, like Quill from Officeworks, are much heavier and way more expensive than Dollar Tree foam board used by Experimental Airlines and Flite Test. Dollar Tree foam board is not sold in Aus so I use depron with tape or laminate covering. Depron is waterproof and lighter and much more durable than paper covered foam board.
Hot wire cutting bits
Knauf XPS insulation foam 30mm and 50mm thick - Bunnings
Hotwire wire - 40kg (90lb) single strand SS fishing wire
Template aluminium - 0.3mm Weatherflash window flashing
Bits and pieces
Blank ID cards - Search Ebay for CR80 blank ID cards
Piano wire for Push rods (0.047" or 1.1mm) or Landing gear (2.5mm to 3mm) - Tates Hobbies
This twin boom pusher is similar to the 1.3m Depron Spectre, however it has a straight 1.65m (65") x 190mm depron Armin wing and twin rudders.
1.3m Depron Spectre and 1.65m Twin Boom pusher
Initially it was designed it as a 1.8m light-wind slope soarer but didn't perform as well as I wanted. The longer tail booms and larger wing span made it too flexy and delicate. I was also comparing the performance to a motorless Phoenix 2000, which is a sensational sloper.
Shortened tail booms and wingspan stiffened up the airframe nicely and the addition of a motor fuselage turned it into an excellent FPV cruiser and medium wind FPV sloper. It tracks well in a straight line and has a decent glide angle but is quite agile like the Spectre.
Instead of using packing tape to cover the depron I used document laminating film, often referred to as New Stuff in the RC world. It is ironed on with a warm iron before bending the airfoil and fuselage, and works very well. It's tougher and easier to apply than packing tape.
Additional strengthening ...
6x1mm CF strip glued along the front of the elevator.
Heat bent UPVC brackets for the rudder to elevator joins.
I used twin rudder servos rather than one servo and a long vulnerable connecting pushrod between the rudders. Full length wing spar made from 2 Skyshark P4X spars joined with an internal CF rod joiner and epoxy.
One of the cheapest and toughest foam covering materials is document laminating film. The RC community has nicknamed it New Stuff for some reason.
Initially I bought 10m each of 43 and 75micron laminate from www.aussieflight.com.au for $1/m. That amount covered Le Fish fuselage three times, the wing twice, and the wing of my next ultra light build.
If you want larger quantities you can buy full rolls from a laminating supplies business. It works out much cheaper per metre.
I bought two GBC EZload laminate rolls Updated GBC link (Thanks Lex_Dysia)
1.7mil (42.5micron) x 305mm x 100m
3mil (75micron) x 305mm x 60m
Price was $45/roll plus freight and GST and it's perfect. Goes on easily with a warm clothes iron (Wool setting) and it will cover many future planes.
