Tuesday 25 November 2014

Ultra light slope soarer

The design for this lightweight aerobatic slope soarer was inspired by DLGs or discus launch gliders.
It will work in anything over 5kn on a decent slope and in 10kn it will work on any slope.

The rudder and elevator are operated by a pull line acting against a torsion spring.

This unique system means the servos can be forward in the fuselage and there are no pushrods going to the tail.

The trick is to make a torsion spring strong enough to operate the control surface against the airflow

but not so strong as to overpower the servo.

The 0.4mm SS wire provided as pushrods for the Versus DLG turns out to be perfect.

Wingspan - 1.5m (65") Armin wing
Length - 104cmm (38")
Flying weight (500mAh LiPo) - 410g
TGY 9018MG servos x 2 (elevator and rudder)
HXT900 servos x 2 (ailerons)


6mm depron
43 micron laminating film
60 micron clear packing tape
2 x Skyshark P4X spars (7.6mm x 820mm)
- Wing spar 820mm
- Tail boom 700mm
150lb Kevlar kite line (pull line)
0.4mm SS wire (torsion springs)
Soft packing foam (nose cone)
4mm CF rod (wing tie down bars)

Overview and build video

Aerobatics in 10kn

Testing with dihedral and no ailerons

New Stuff iron-on film - EZload laminate - GBC Australia

UPDATE March 2015: On really hot days the rudder and elevator servos have moved out of position as the glue softened. I have added more foam packing and glue to fix them securely. The trailing edge of the wing has also popped open twice. I removed the ailerons, re-glued then taped the join, then reattached the ailerons. In the original build, by cutting out the ailerons from the wing, I removed too much of the glue holding that join. 

Wednesday 12 November 2014

1.65m (65") Twin Boom pusher

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.

See the depron wing build and Spectre overview videos for the basics, and the Spectre post on this blog.

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. 

Wingspan - 1.65m (68")
Chord - 190mm (7.5")
Length - 100cmm (36")
Airframe weight - 840g
Flying weight (2200mAh LiPo) - 1040g
Motor - Turnigy 2836 1100kV (260W)
ESC 30A Plush
Prop - 10 x 6"
Twin rudders
TGY 9018MG servos x 2 (ailerons)
HXT900 servos x 3 (elevator and rudders)

I can email the Sketchup file if required

Initial slope soaring tests

Tuesday 14 October 2014

2m Parkzone Radian EP mods

Everyone has heard about the 2m Radian. It's a very simple no-aileron motor glider with graceful curved up wings and has fantastic thermalling abilities.

For A$200 the "Plug and Play" version comes with a good quality motor and servos fitted and not a lot of assembly required. Add your own receiver, battery and transmitter.

I bought mine from RCWorld in Geelong. They have all the spares too.

Like all planes there are a few issues to be sorted out before flying. It is very light and flexy, especially in the tail area, and some of the fittings are inadequate. Most owners carry out strengthening mods and Paul Naton, well known glider tutorial DVD producer, has published a mod video which is essential viewing.
Paul Naton's Radian mod video

Essential mods needed before the first flight

Pathetic plastic clevis connectors
The pin on mine broke just trying to clip on to the control horn the very first time! What were Parkzone thinking? These ridiculously weak plastic clevis connectors are just wrong. May be OK for a tiny indoor foamie but not a 2m thermal glider.

I couldn't find another connector to fit the pushrod thread so decided to beef up the existing one with a piano wire pin. Just needed to carefully drill holes in the cheeks using a piece of the wire as a drill bit. Tight fitting shrink wrap (not shrunk) keeps the pin in place and connector cheeks pulled in.

Staples into foam?
What is the purpose of these staples? They were straddling the pushrods where some sort of fixing structure should have been. I pulled them out, they were already floating loose, and threw them away because they offended me!

My solution was to use tough clear gaffer tape to fix the pushrods securely to the fuselage leading into the rudder and elevator.

Missing canopy magnet
The canopy is held in place by magnets front and rear. Unfortunately one of the fuselage magnets was missing. Luckily I had a replacement in my spares box and I glued it in with gorilla glue.

Changed ESC connector
The Parkzone ESC comes with an unfamiliar (to me) blue connector, to match Parkzone batteries I guess. All my LiPos have XT60 connectors so a little soldering was required to swap the ESC to XT60.

Receiver bay surgery
The receiver bay is made for a small Spektrum Rx but all I had was a bulky 8ch Turnigy Rx. All I had to do was cut out a little mound of foam to make it fit. 

After those easy repairs/mods it was airworthy and ready for the maiden flight. The day was windier than ideal but the Radian performed superbly. No thermalling on the first day but on subsequent days I climbed to frightening heights, lots to learn. 

I had previously checked the range of my Turnigy 9X transmitter with a 6ch Hobby King receiver. I got more than 800m at low altitude flying along coastal dunes. The highest I have had the Radian is 300m, and I wouldn't want to go too much higher at this stage, so it would have no problems with signal strength. At 800m the glider would not be visible anyway.

Optional performance mods - (inspired by Paul Naton)

Elevator control horn placement
The control horn was relocated inwards about 12mm to give the pushrod a straighter run. The control horn base was shaved off where it now overhangs the elevator. Elevator was stiffened along it's span using 12k carbon tow and epoxy.

Elevator hinge was taped both sides with clear packing tape for durability. Moulded foam hinges will fail eventually, they are not designed to last. Fixed the horizontal stab in its slot with clear gaffer tape both sides, above and below.

Fuselage stiffening
Added 3 strands of 12k carbon tow along the bottom of the fuselage boom to reduce tail flex. I covered that with clear packing tape for smoothness.

Wing slot top strengthening
I added 3 strands of 12k carbon tow over the top of the wing slot because this area is quite thin and prone to failure.

Wing leading edge tape
After a few flights I noticed that the leading edge was becoming dented and scratched so I added clear packing tape back to 50mm from the LE top and bottom

Wing retaining velcro / magnets
There are many horror stories on the forums about wings falling out in flight. They are very weakly held in with friction and slightly keyed foam blocks that do nothing at all.
Initially I used sticky back velcro on all the meeting surfaces of the two wing halves but that pushed the wings apart by almost 1cm. My current solution is magnets glued to 40mm dowel inserts. These are quite securely glued into the wing roots with epoxy also strengthening that area nicely.

Rudder root strengthening
To stiffen the area at the base of the rudder I cut a slot and glued in a 6x1mm carbon strip pushing it right down into the foam of the fuselage.

Decalage mod
All of these stiffening mods add a little tail weight moving the CG rearward. This is actually a good thing according to the experts. The stock CG of 70mm is too far forward requiring up elevator to fly level. The Radian is designed with lots of horizontal stabiliser decalage angle as seen below and performance can be improved by moving the CG back and reducing the decalage angle. Well that's the much-debated theory anyway.


I tried the decalage mod by slicing out the foam wedge (marked below) and repositioning the horizontal stab. At this early stage of my thermal gliding journey it felt like too much and I couldn't get it to fly smoothly. So I have gone halfway back. Seems like a good compromise now with my CG at 78mm or 3".

Painted bottom surface of the wing
For visibility and orientation. This glider starts to be difficult to see higher than 300m. Solid black seems to be the most visible colour at that distance.

Radian videos

Trying different camera mounting spots

Thermal flight in Google Earth, recorded with a GPS watch

Slope Soaring

and finally Stormy loves the box so all is good.

UPDATE: I left customer feedback on the Horizon Hobby site about the broken clevis connector and missing magnet and they sent me replacement pushrods and canopy, posted in two separate parcels from US to Australia. Now that is awesome customer service.  

Monday 13 October 2014

Red Sloper with added dihedral

Here's a demo video covering how I add dihedral to a depron Armin wing.
I show how to bend a 200mm length of ali tube to set the dihedral angle and hold the spars.

This video also shows my swappable motor mount for the Red Sloper and other construction tips.

Here's a slope soaring video showing how the dihedral makes the Red Sloper into a smooth and relaxing glider while slightly reducing the aerobatic capability.

Saturday 9 August 2014

Mobius anti-vibration mount

Here's a quick, cheap and easy vibration-damping camera mount using 2 cable ties and an ID card. It only takes a few minutes to make and greatly reduces those annoying jelly waves often seen in onboard video.

Tools needed are an office hole punch, scissors, side cutters and a marker pen. Materials needed are two small rubber bands, an ID card and two 4mm x 200mm cable ties.

Cut the card in half and punch 4 holes in each roughly 1cm in from the edges.

Double wrap the rubber bands on one card towards the middle from the holes.

Thread through the cable ties to form the springs. Start underneath and thread up out and around the card edges, then back through the bottom card into the middle. Continue on threading in and out the holes till you come back to the start. 

Adjust the size of the loops until the top deck is level or possibly tilted forward a little.

Clip off the excess and it's done.

You still need to balance your props but this mount takes care of the vibrations that you can't fix.

Velcro on the bottom is a good way to attach the mount to a plane or even electrical tape for temporary positioning.

Here is the full build in real time - about 4 minutes.

This video shows the comparison of with and without the anti-vibe mount.

Tuesday 8 July 2014

1.3m Twin-boom Pusher

Also called the Depron Spectre.

This was inspired by Alex Greve's (IBCrazy) EPP Specter designed for proximity and obstacle course FPV.

The twin boom configuration means the motor doesn't need to sit up high, which means the fuselage can be slimmer.

The forward swept wings give amazing anti-stall characteristics and increased grip in the turns. I suspect when the wing tips flex upward they give positive feedback to the turn, similar to snap flaps. A swept back wing would do the opposite. It also looks very cool in the air.

This plane can fly slow or fast and is crazy manoeuvrable even without movable rudders, and it can balance in it's tail.

The wing build is slightly different to my previous style, with cut out ailerons rather than full span. Wingspan is 1.3m or 53" compared to IBCrazy's 40" and 48" versions.

I made a 200mm (8") x 20mm flat bottomed airfoil in two 700mm halves, then cut a wedge from each inner end to make the forward sweep when glued and taped together. The tips are about 45mm forward of the root. I also cut wedges off the wingtips so they were parallel. Naturally I cut them the wrong way first.

I removed some of the forward former in the spar channel either side of the join so the Skyshark P4X spar had a wider bend curve.

Here it is in the air with 10-15kn wind

Wingspan - 1.3m (53")
Length - 80cm (32")
Airframe weight - 660g
Flying weight (2200mAh LiPo) - 850g
Motor - Turnigy 2822/14 1450kV (160W)
Prop - 7 x 4.5"
TGY 9018MG servos x 3

Depron Spectre plans and dimensions

Build overview video

UPDATE: Here are a two more recent Depron Spectre videos. Some aerobatics on a rare calm 13th Beach day and some slope soaring at Beacon Point in a lovely 10-15kn NW wind.

Friday 13 June 2014

Pusher with polyhedral

I have never tried a 3 channel rudder elevator throttle plane so thought I'd give it a go using the orange slim wing and pusher fuselage.

RET planes need some wing dihedral to enable turns due to the lack of ailerons.

I fixed the ailerons in place and removed the servos. This simplifies the plane greatly, the wing is just a wing, no servos or wires, apart from rudder and elevator.

The CF spar was removed and a bent 200mm x 10mm diam ali tube inserted to set the dihedral. The wing extensions were hot glued in place at the desired polyhedral angle. The wing seems to be strong enough without a CF spar.

I increased the rudder area, but after the maiden reduced the throws for smoother control.

The 1500mm x 200mm wing and flying weight of 630g gives a wing loading of about 21 g/sq dm (7oz/sq ft) which is great for gliding and slow flying.

This plane is a delight to fly, so slow and steady. If I had started with something like this the learning process would have been much quicker. I can trim it to fly hands off in big lazy circles and it takes care of itself.

Wingspan - 1.5m (59")
Chord - 200mm (8")
Elevator servo - TGY 900 9g
Rudder servo - TGY 500 5g (stronger servo might be safer)
Motor - Turnigy 2822/14 1450kV
Prop - 7 x 4.5"
Airframe weight - 520g
Flying weight - 630g with 1300mAh LiPo (gives 20 min slow flying)

Sketchup Plans

Friday 6 June 2014

Albatross 2m sloper

Before the Red Sloper came this 2m wingspan sloper. It actually started life as a motor glider but a dodgy ESC connector stopped that project from being fully realised. I'll revisit it soon.

I call this one the Albatross for obvious reasons.

The orange plane is the pusher trainer with a 1.5m polyhedral no-aileron wing adapted from the slim wing. I'll post about that one when we get a nice calm day to do a proper maiden.

The depron I use comes in 1000mm x 700mm sheets so I can make the 2m wing in 2 halves.

I used 3 Skyshark spars all up, 2 joined with a 10mm x 150mm ali tube for the main spar and another spanning the join closer to the leading edge. The spar layout is visible in this shot of the wing on an earlier version of the fuselage.

The wing has full span ailerons operated by TGY 9018MG metal gear micro servos. Total chord is 200mm including the 35mm ailerons. That gives a 10:1 aspect ratio.

I suspect 40 to 45mm ailerons would have been better to give a faster roll rate for some aerobatics but they are fine for smooth cruising.

Airfoil thickness is 23mm, formed by using a 3mm strip of depron over the main spar, giving an 11.5% airfoil.

The tail is just a little scaled up from the Red Sloper but basically the same shape.

Horizonal stab is 460mm wide x 90mm deep tapered to 70mm at the ends plus a 50mm elevator.

Vertical stab is 220mm high x 130mm at the base tapered to 60mm at the top plus a 50mm rudder.

Elevator servo, hidden inside the fuselage, is a TGY 9018MG and rudder servo is HXT 900.

Fuselage is a 1000mm long x 70mm square tube tapered towards both ends for looks, weight saving and aerodynamics.

Weight is 650g without battery and balance weights and 830g flying weight.

The big wing makes for an excellent light wind slope soarer which also works well in strong winds. It's smooth and languid in the air, not so aerobatic, but a delight to cruise along the ridge.

UPDATE: I made the nose removable so I could swap to a motor pod. Just have to pull off the tape around the join and re-tape the motor pod on. The motor glider version is 730g without battery and 925g flying weight.

It took some decalage adjustment to smooth out the tendency to loop up under power. I needed to tilt the wing forward by sticking about 8mm of packing under the rear mounting area. Then it tracked level and glided much better.

Thursday 29 May 2014

Red Sloper

Here are the specs for the Red Sloper fuselage, designed and built especially for the 1.5m depron 10% chord wing detailed in the previous post. 

Aileron servos - TGY 9018MG metal gear micros
Elevator and rudder servos - HXT900 9g
Receiver - Hobby King 6ch
BEC - Hobby King 5A

The 750mm fuselage is a square tube 50 x 50mm outer size constructed using Flite Test style joins rather than ExAir style bends. 

A 15mm x 350mm tapered slice is removed from each side, and the bottom bent up and re-glued to close the gap. That gives the tapered rear half.

Horizontal stabiliser is 440mm x 130mm, tapered to 100mm at the ends, and the 50mm elevator is cut from that. 

Vertical stabiliser is 200mm high, 120mm at the base (for a longer glue join) tapered to 40mm at the top. Rudder is 50mm tapering to 20mm at the top. 

The control surface tapers are just for looks, but looks are very important. A daggy tail ruins the overall impression of the plane.

Elevator servo is stuck inside the fuselage near the rudder servo. 

There is no need to have the tail servos mounted forward with long push rods. The amount of weight saving is not significant for a speedy slope soarer. In my normal 10-15kn flying conditions more weight is often needed.

The nose is soft EPP foam with a tongue extending into the fuselage. It holds the battery, nose weight (4 large washers), BEC and receiver. 

Nose is held on with 2 velcro tabs.

Wing tie-downs are 4mm carbon tubes glued in and reinforced with ID card plastic 

Here's the maiden flight of this excellent glider, probably my best design and build so far.