Cockatoo aka EPP Eagle Modification Notes

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Before choosing a supplier for the EPP Eagle READ THIS and THIS and make up your own mind. My kit had no instruction manual and the box had no cover label - clear alarm bells in hindsight.

The following are notes on construction and various modifications I made. There is however more information from the original designer. Also the extensive RC Groups Eagle Thread.

"Representational" Sulphur Crested Cockatoo with 10x6 prop @ Home 15 March 2008

There are more and photos of the build. Click thumbnails for a larger image.


Against all advice and common sense I started out using "WeldBond" adhesive to assemble the EPP components. When it dries, which it has on all of the fuselage seams, it makes an extremely strong and flexible bound. The problem is that it takes a very long time to dry especially inside wing cavities if it dries at all. I "helped" the drying process for the wings by placing them under weights and wrapping them in black plastic placed outside on a 25C day. I then put them in the boiler room which sits at around 30C most of the time because of the usual houshold routers/servers etc.

I did briefly use hot melt glue but it seemed to cool too quickly for my liking giving only a patchy bond on the fuselage doublers.

Clone Leton Motor and 25A Leton ESC

The motor in my clone kit had the retaining circlip missing from the rear of the motor.

The motor which had no documentation appears to be a Leton 201013 (400T) 1300 RPM/V. Nominal best current is 10A wiuth a maximum of 15A/30Sec. The Leton 201010 (400XT) @1000 RPM/V would probably have been more flexible. The prop brake on the Leton 25A ESC that came with the motor also failed for all props tested over my 6x3. It certainly did not stop the 10x6 prop.

Motocalc predicts that the GWS EP 8060 slow fly propellor will draw 16A at 11K RPM with 3S LiPo exceeding the recommended maximum current. I fleetingly saw significantly above this current probably because of the propellor.

The Motocalc Wizard recommended propellor is nominal 7x3.5 drawing 8A static at 13K RPM - not easily purchased! I will run the 6x3 Graupner folder on a 40mm Hub I have to hand.

I reduced the width of the nose of the fuselage by about 10mm overall so that the folder closes and starts cleanly with a 40mm hub. This may or may not be necessary but is at no cost depending on your motor diameter.

Improving the Clone Wings

Both wings were warped asymetrically as delivered.

Close inspection of the cores showed that a slot had been cut where a main spar would normally be. The slot is about 3x10mm or roughly the same dimensions as a typical top/bottom spar plate. I inserted and glued a full span spruce spar cap into the slot and this, at the current stage of drying after several days under weights, has removed the warps. If this ultimately does not work fully I will put an 8mm thin walled carbon tube in one of the lightening voids (see later).

The leading edge decorations are kicked down by several degrees into what hopefully will be nearly stagnant air at normal angle of attack. They may offer slight effective pseudo washout?

A have added a few turns of thread to the centre of the wing joiners and will, at the suggestion of Prof John Bird, add a couple of tube guides at the root of the wings to stop the joiners chewing out the EPP.

Just when you think it is going well you find that it is impossible with average size hands to connect the ESC to the motor. A bend up temporary hatch was required! A better idea is to make the whole front deck hinge.

The rest of the build is pretty much standard. A load distribution which places the battery over the CG is straightforward (no as the CG was not at 80mm!) with servos and receiver close to the TE wing mount. This also keep the pushrods short. Picture is with 2000mAH pack.

The overall all up weight with 800mAH pack is 505gm.

First Flight 26 February 2008 (Wrong CG and Negative Decalage)

What can I say - beautiful - straight and level from a gentle hand launch until the throttle was applied! Porpoising and extreme pitch up under power not helped by the CG being misread at 80mm rather than 60mm behind the LE. The GWS 8060 prop at full throttle sounded like it was going to self destruct as expected - throttling back to 50% helped, but only marginally - all VERY exciting. All landings though (3) were very gentle and SLOW as a consequence the Rx antenna does not stream behind all that well and seems to have a fatal attraction being drawn forward towards the prop.

There is almost no down-angle on motor mount which could be resolved by mixing throttle to elevator but better done mechanically. The V-Tail flexes easily and so the actual control being applied while the air craft was cavorting is anyone's guess - stiffening with bamboo skewers was considered but abandoned. There is possibly negative decalage as the tail incidence seems to be greater than that of the wing when it is fully seated as mine was. Most photos of the Eagle show the LE not seated fully but riding up on the front deck.

A check of the CG computation suggest that 80mm used on the first flight gives a stability margin of approx 2% - very very frisky and essentially unflyable. The wing plan is pretty convoluted so the MAC calculation is very approximate! The recommended 60mm gives a stability margin of approx 10% which is quite stable. Aircraft approximates a "plank" flying wing if you can work out what the effective chord is!

The initial improvements/corrections are:

There were 4 wedgetail eagles floating around the field today in the thermals.

Windy Flight March 2008

The wind was at around 8-10Kts from the North and so close to the nominal flying speed of the Eagle. Flat field launch uneventful with 6x3 thin Graupner folder propellor more than adequate with climb pretty much as predicted even with strong sink on occasion. Elevator response a little sluggish and sink a bit sad.

CG moved back to 70mm. Control response better, as is glide but as far back as I would go. No porpoising encountered so decalage fine. Performed one loop (or rather someone else did) inadvertently - tube spars held but should probably be replaced by solid rather than tube (see later).

Tried wide 7x3 Graupner folder. Climb faster but above say 70% throttle not useful because of drag. Reverted to thin 6x3 on 40mm hub for the balance of the day. Choice seems to be either a propellor for vertical performance or something more sensible to climb on the wing a little more slowly.

Aircraft looks good in the air and given the conditions more than acceptable to fly with some thermalling - quite satisfactory.

Final trim a few degrees of up.

Bolted Down Wing and Carbon Tube Spar

The rubber bands were replaced 3.5mm nylon hold down bolts at the main spar and a simple tongue arrangement at the rear. A light carbon arrow shaft was also installed (optionally) at the front of the rear lightening cavity as a more substantial spar (~15gm penalty). This is retained at the rear of the cavity using a piece of 5mm balsa.

Hyperion Brushless and 10x6 Prop 16 March 2008 - Dick Steel Day

Tried Hyperion Z2213/24 and 10x6 prop - vertical climb but control surfaces not really up to high-speed tearing about. Reverted to 6x3 with 40mm hub and Leton motor and kept the expensive bits for a more sophisticated aircraft. Wing and aircraft easily survived a vertical 100M or so dive avoiding a full-size Cessna. Pullout slow with bendy tail feathers. Terminal velocity was not very high as you may expect as it is no slick chick and was probably reached in the first 10M or so of the dive. Tail feathers now stiffened by painting with PVA as a skin and putting a strip of 0.5mm ply around the leading edges.

On/Off Switch 1 April 2008

On/Off "switch" (below) really required as connecting battery then screwing wings down is questionable safety wise. Not pretty but then neither is the aircraft now christened Cockatoo. Making all of the front deck a cover to get at the battery is also a good idea. Rubber band on beak to stop it biting.

Pendulum Effect 8 April 2008

I have lifted my battery up close to the underside of the wing ( block of light foam under the battery) to reduce the pendulum effect of the battery down in the bottom of the fuselage when doing some aerobatics. Of course if you just want to float around then having the battery in the bottom of the fuselage certainly improves stability.

Changed to a 7.5x4 propellor - same endurance as 6.5x3 but a bit stronger on climb when needed or when perhaps carrying a camera. Flight today excellent. Cockatoo flew itself for several minutes circling hands-off in light thermals under bird attack while I took some video - maybe post later.

Final Comments

Lots of useful stuff on RC Groups Eagle Thread.

My Flying Page

Before choosing a supplier for the EPP Eagle READ THIS and THIS and make up your own mind. Remember the Levi Strauss (?) maxim - "the original and the best".

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Copyright © G.K. & S.P. Egan - All rights reserved. Last updated 16 February, 2014.