I rather like the F4D Skyray


Master member
A Skyray was my first attempt at an EDF. Not being familiar with actual EDFs I reasoned the blended fuselage/wing layout of the Skyray would allow quite a big prop to be installed inside the fuselage to become an EDP and still be true scale.

The only concession would be an enlarged inlet and exhaust. Not an uncommon trade off with many EDFs.
With limited thrust this concept would only make sense if combined with a super light airframe made from Depron. Having built a number of planes from Depron I was happy I could handle that.
A quick check suggest at 36" span I could squeeze in 4.5" prop in the fuselage.

Actually a 5x7 Slightly trimmed to 4.4" but it would mean the duct would be nearly the size of the fuselage.
The duct was built with 3mm Depron planks around a 110mm plastic drain pipe as mandrel.

The centre section of the fuselage was built around the duct, indeed the whole plane was constructed around it in stages.
The wings have no ribs but the 3 mm Depron skins are drawn over two Depron shear webs to give near scale symmetrical wing section.

All the loads are taken by the skin and as a simple glued joint in Depron is as strong as the foam the wing can be simply glued on to the fuselage.
To cut a long story short I ended up with an "all Depron" EDP Skyray.

Very light it only needed a 1500mA 3s in the cockpit. Very simple electronically with just a micro servo for each elevon and no rudder.

To my surprise it actually flew beautifully needing no CofG adjustment a t all.
Why this 10 year old history? After 4 years of flying I literally lost it as a result of some sort of control failure.
Despite having since built several true scale and more complex EDFs I still miss its simplicity and delightful handling so this year I built another but this time making use of LW-PLA printed ducts with true scale inlets and exhaust with no cheat holes!
To be completed.


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Master member
The F4D did eventually get completed.
The complete light weight PLA duct.

Like my first Skray it to uses a motor and prop rather than an EDF although in this case an Emax 2205 'drone' motor driving a matching 5x3 three blade prop in an own design printed housing with a scale diameter exhaust nozzle.

This is how it ended up.

Very light at 455g (16 oz) with a 1000mAh 4s.
A radio problem terminated the otherwise successful maiden with a spectacular "lawn dart".

As is typical with a Depron stressed skin structure the remainder of the airframe was completely untouched although part of the LW-PLA printed duct was damaged. I feared this would make the repair rather difficult so I have to admit it lay untouched for 5 months!
Eventually the duct was repaired and the nose rebuilt.

One advantage this type of structure this is there is virtually no "repair" weight gain. The replacement bit is built in exactly the same way as the original.
However by the time it was complete the UK winter had set in with record breaking periods of rain and wind so it has not yet been tested.:(
Roll on 2024!
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Master member
Super calm today for the first time in 2024 so the 36" span Skyray got taken off the wall.
Tested had indicated that with a 3s there would be very marginal thrust so at the last minute the 1800mAh 3s was replaced with a 1300mAh 4s.
It flies quite nicely and ridiculously slowly! Not that surprising with a wing loading of 5oz/sqft.
Quite an eventful flight having to stay up longer than I really wanted from being chased by a large dog that decided the Skyray needed to be pulled out of the sky!
In faact I need not have worried. Subsequent testing showed it only takes 8.5A at full power so with any throttle management a 12 minute flight should be possible!