Simple 3 channel trainer

This design was inspired by a friend who wanted to take one of my "retired" planes to learn how to fly. So I gathered bits and pieces together and tried to come up with an easy to fly, crash proof trainer.

It only has rudder elevator and throttle, no ailerons. I wanted it to be as light as possible for slow and easy flight with a big energy absorbing nose and a tough fuselage.

The fuselage was shaped from a 50 x 100 x 370 block of XPS insulation foam and the tail planes are 8mm panels of the same foam. The boom is a Skyshark P4X 7.6mm tube.

The hotwire-cut 170mm clark y wing comes from rescued sections of the drowned Fokker (which now has new wings) Three x 360mm sections were glued together with the tips each raised 120mm. No spars are needed to hold the polyhedral due to the tape covering and large join surface area for gluing.

The nose is soft packing foam covered with tape and completely encases the 1300mAh Lipo battery.

The motor is the original Bixler 2, servos are cheap 9g HXTs, and it has a Plush 18A ESC and HobbyKing 3 channel receiver.

All up weight with the battery adds up to 550g, giving a slow continuous cruising flight time of over 30min.

This plane is very smooth and stable and with correct trim will fly hands off.

At this stage the nose, fuse and wings are almost bullet proof, but the tail planes are a bit too delicate. Thinner sheets of XPS foam are quite brittle so some kind of reinforcing is needed.  Both the elevator and rudder have cracked during the test flights so I have added a 0.5 x 3mm CF spars.

Might be better to use depron or corflute for the tail.

Dimensions

Flight video - motor slope soaring

Build video

UPDATE 30 March 2016 

After some tough flight testing by my dedicated student test pilot it became apparent that this tail

design was not crash proof enough.

So here is the new tougher tail design made from depron. The tail to boom join has extra foam fillets either side for more gluing area and to raise the elevator a little.

The new wing has more area and less polyhedral for smoother flight.

Update overview video

Tail build video

Dimensions for the updated tail design

MATERIALS

All my building materials and RC gear - http://newtonairlines.blogspot.com.au/2015/03/materials-and-links.html

Knauf XPS insulation foam - http://www.bunnings.com.au/our-range/building-hardware/building-construction/insulation/panels

Bulk Depron - http://www.tradewarehouse.com.au/more/depron-foam/white.html

Skyshark P4X spars - http://www.kitesandfunthings.com/ProductInfo.aspx?productid=SSP4XCAM0

New Stuff iron-on film - EZload laminate - http://www.neopostonline.com.au/lamination/ez-load-roll-film

Blank ID cards - Ebay http://www.ebay.com.au/usr/y2store?_trksid=p3984.m1439.l2754

BUILD VIDEOS

Hot wire cutting rig - https://www.youtube.com/watch?v=JIRzQO4F8ck

The Art of Hotwire - https://www.youtube.com/watch?v=_tt56xp2lQk

1.1m Fokker Dr 1 triplane

Two wings on the Tigermoth worked so well I had to take the next step...three wings.

The most famous triplane is the Red Baron's Fokker Dr1.

My wings are stiff enough not to need inter plane struts so I decided to stick to the familiar rubber band mounts. That meant I had to come up with a method for creating a rigid mount for the top wing. I recorded detailed build videos along the way.

SPECS
Top Wing - Top 1.1m, iron-on laminate and packing tape. 0.5 x 3mm CF spars
Middle and lower wings - 950mm and 900mm. packing tape. 0.5 x 3mm CF spars
Airfoil - 170mm Clark y
Fuselage - 6mm depron, 3mm ply nose, packing tape.

1.2m Tigermoth

I have never been much interested in scale model planes apart from the Tigermoth biplane. Tigermoth World is nearby and for my 40th Virginia and I went for aerobatic joy flights...great fun.

I already had enough practice hot wire cut wings laying around for the build so I decided to have a go. I gathered scale measurements from tiger moth photos and made the adjustments needed for a 1.2m wingspan model.

The fuselage is 6mm depron covered with yellow packing tape to mimic the plane I flew in. I added 3mm ply under the nose to take landing impacts and a 5mm ply motor mounting firewall.

The motor is a Hextronic DT750 which had plenty of thrust, especially with a 4S battery. Prop is 11 x 5.5", ESC 40A Plush. 3000 mAH 3S or 4S Lipo gives 20+ minutes of cruising.

Here are build and flight videos of this great looking vintage biplane. It flies just like the real thing, slow and steady with just enough aerobatic capability.

New DLG - Hobby King 1.5m V2

My much loved Versus DLG has been crashed and repaired many times and is looking a bit rough now. But it was a great intro to DLGs. Hobby King's big sale came along at just the right time. The updated Versus, now called the V2, dropped from A$450 to $280, couldn't resist that price.

The V2 has a disser construction wing, crossed CF ribbon reinforcing, and a kevlar pod but otherwise is identical to the Versus.

I bought the Plug N Fly version which is OK, but might have been wiser to get the ARF version and add my own servos.

Here are my detailed build videos showing strengthening and control mods.
After a few weeks the V2 is going well, feels like a better Versus. I wouldn't pay full price for it because there are many better alternatives available, but for the sale price it is excellent.

Balsa / fibreglass tails

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.

Landing Gear

Here's how I make landing gear using 2mm piano wire for the axle 

and 20 x 1.5mm aluminium flat for the struts. 

Wheels are pool noodle foam glued to bottle caps.

Piano wire axle has a bend on one end

Hot Wire foam cutting rig

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.

UPDATE 2025: Now replaced with Blue XPS boards at Bunnings. I have not tested it for hot wire wings yet.

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.

The wire needs about 5A to heat up enough for cutting. I use 4S for my 850mm big bow, and 2S for my 40cm small bow.

Also changed to single strand 40kg SS fishing wire, which has resistance value of 4 Ohms per metre.

I have changed to thin aluminium sheet (window flashing) for the templates. Can be cut out with scissors.

4S power and Aluminium template in use