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Printed EDF casings


Simon Chaddock
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I found I had a spare Emax 2205 2300kV motor and four blade 3x3.5 prop so I decided to print an EDF casing to mount it in possibly to use as a power 'pod' for a light weight glider.

Obviously as an external pod it would need to have a streamlined external shape as well ab having an efficient internal duct profile. 3" (77 mm) is quite a big EDF for what is really only a 200W motor max so weight was an important issue.

At this stage more a printing design exercise than to create a finished article.

My first attempt followed the principle I used on my Airbus A350 which used the same motor and prop. In that case it used a scale RR Trent duct so was rather longer and had a specific outer profile. For the pod EDF it could have a more generous bell mouth and be rather shorter as well as a 85% FSA nozzle to give the maximum static thrust suitable for use as a low speed EDF.

The inner duct was made of 4 pieces glued together. Inlet duct, motor mount + exhaust tube, a tail cone and a ring former to support the Depron outer skin.

 EDF1Parts.jpg.512403e59c4737daaf731d3175f25206.jpg  

  The outer skin is made up of 27 2mm thick Depron formed planks.

EDF1Front.JPG.bd468aa7a23ff3d6aa96897b4355b52c.JPG

Although the 'over hung' motor and prop layout makes installation simple a disadvantage is the motor mount has to be particularly rigid to prevent the prop from hitting the duct wall at even a modest shock loading.

EDF1Rear.JPG.a9c32277a98eeccfb12b76235ed416b8.JPG

Such planking is a fiddley and time consuming process.

The complete duct without the motor and prop weighed 22.9 g. The motor, prop and leads add a further 35.0 g.

Even with a Depron outer skin the duct is remarkably strong and stiff.

On a 4s it generates nearly 250g of thrust drawing just under 10A.

The next question was would it be possible to print the outer skin as well and for maximum strength in conjunction with the inner profile but without a significnt weight penalty.

The parts of Duct2

EDF2Parts.JPG.1392df163e6ecf9e5565f7afe7124b38.JPG

The motor mount is printed separately but when glued in place is fully supported by both the inlet and exhaust ducts.

In fact the motor mount acts as the 'locating joiner' for the two duct parts.

EDF2Front.JPG.30b41fa780685ab7fb013a1a50493f0b.JPG

 

EDF2Rear.JPG.e792e95de73b77ae1d7ca695c9cec67c.JPG

It would use the same tail cone once the motor was installed.

The duct weighs 26.3 g an increase of just 3.4 g. Doesn't sound much but on such lightweight structures it is nearly a 15% weight gain.☹️

The unusual pattern on the duct surface results from the thin 0.3 mm single wall and the "gyroid" infill pattern. This infill works well on circular or irregular shapes with a better stiffness for a given weight.

The final exercise was to print a 'minimum' duct that could be used as an 'internal' EDF in a longer duct rather than as an external pod 

Duct3 parts.

EDF3Parts.JPG.7b54bfa44d1710330b0903db19eda900.JPG 

Using the same principle for the inlet and exhaust ducts to support the skinny motor mount but it is concentrated over a reduced length.

The duct is also a bit shorter but maintains the same bell mouth  

EDF3Side.JPG.937863402ad53c0971a43601ed0a7caf.JPG

In this case the exhaust is set to the full FSA to allow a parallel exhaust tube to mounted that can have the required reducing nozzle at its end.

This duct weighs 18.1 g.

Maybe not every ones "cup of tea" and these lightweight structures can be tricky to print successfully, you should see the waste bin, but at least they don't use a lot of filament.

Now I have just got to find/make a plane to put one in. 

 

 

 

    

Edited by Simon Chaddock
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Well Done!  A bit more adventurous than my printing for UAV's, but today I revived a couple of inherited TRex 450's that had broken or butchered tail stabiliser fin plates, horizontal and vertical.

 

Previous owner had a habit of cutting the vertical fins short and fitting a big ugly wheel  ?, then after landing poorly and breaking that in half, then "fixing" it by overlap gluing with copious epoxy.  No wonder he needed nose weighting, which he glued in the fragile canopy that is only held on by a couple of grommets.

 

Done in matching colour to the canopy, they are now lighter, stronger and look a lot less painful to the eyes............. 

 

Couple of months back I did similar to one of his 600's AND a 250, Yup, he certainly had a "house style" when it came to tail feathers..............  ?

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  • 2 weeks later...

Having printed the casing for the four blade 3x3.5 I wanted to measure reasonably accurately the thrust it generated so I printed this simple test stand.

ThrustStand2.JPG.03600d8ebc2edc81e8c5d54181b4edc6.JPG 

It clips onto the edges of the bell mouth. By holding the EDF over the weight scale I determined that at 40 mm above the scale surface the airflow into the fan did not alter the scale's reading. The three supports are removable so new can be easily reprinted for a different EDF bell diameter.

The EDF gave 249 g thrust drawing 4.77 A at 15.4V (71W) which gives a specific thrust of 3.5 g/w.

Not a lot of thrust but it is rather more efficient than a true EDF at what it does deliver. ?  

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  • 1 month later...

The next step was to make a simplified casing intended to be inserted in a duct with no bell mouth but a 'ring' to accept a lightweight inlet duct made from 2mm Depron.

NoBellEDF.jpg.8c169506d98b86facf768e784341ee7c.jpg

The Depron inlet duct is planked in 2 mm Depron using a pair of printed 'build' rings to hold the planks in place until the glue is dry

The Depron inlet duct on the EDF.

DepronDuct.JPG.ac3000d893c48700015ff4aa89a77f80.JPG

The intended plane is quite large so a second inlet section is required.

TwoSctnDuct.jpg.5af38c7be88818adb8b65b088f6305d6.jpg

Commendably light it weighs 69.3g. The EDF itself contributes 49g of that figure.

The plane requires a bifurcated inlet. A printed component could give an almost ideal flow path.

Single wall 'Vase' printed as left and right sides, they are identical, with a joining ring.

BiDuct2.jpg.260207f4f139413a5592d8d50c2c4f93.jpg

Impressive as it is it is also heavy. At 50 g very nearly the weight of the rest of the duct including the EDF! 😲

Fabricating this out of 2mm Depron would be light enough but how much of the ideal duct profile would have to be compromised to actually make it? 

 

By the way the intended plane for this EDF is a F4D Skyray.

I built one 11 years ago in the early days of 3mm Depron sheet. It was my first attempt at a "jet" although it actually used a ducted 4x4.5 2 blade prop squeezed inside the fuselage. 

 

 

 

 

 

  

Painted.JPG

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