Put a Swash plate into an EDF

[ÄlveKatt]

In your last episode you mentioned part of the reason EDFs are so inneficient att low speeds are the angle of attack of the blades. Can you try and put a Swash plate on an EDF, Like on the FT Viggen for example, hook it up to an air speed-meter, and control the angle of attack of the blades based on air speed? I realize you might need to make custom blades or modify the ones of some prop, but wouldn't it be awesome if it works?

Also, why didn't you use an FT foamboard plane to modify into your 3d-plane?

 

[kilroy07]

It would be awesome, but EDFs spin at very high RPMs, anything that will change the geometry and/or balance will most likely cause the unit to destroy itself in short order. You'll note that even on true jet engines, the vanes are fixed. Note this doesn't even address how complex such a mechanism would be.

I think (just my opinion) they ripped the EDF out of the F-22 because EDFs (as a whole) are quite a bit less efficient than props... That AND they just enjoy doing crazy stuff!

If you want a purpose built 3D plane made from Foam Board check out the FT Edge;
https://www.flitetest.com/articles/ft-edge-release
(I haven't built one yet, but it's on my short list.)

Or try their earlier design (and quite a bit less complex) FT3D
https://www.flitetest.com/articles/ft-3d-scratch-build

 

[Brett_N]

I love my FT3D's - have built and destroyed a half dozen of them by now and am still on the original power pod.

Biggest complaint is the VERY THIN connection between the L&R halves of the elevator. Mine ALWAYS break right there and you end up with a wonky tail - NOT GOOD on a 3D.

I may build another one (I've been flying 3D profiles from ValueHobby and my full balsa) but the FT3D is still a favorite. I may try a dual-reversing-motor version.....

 

[F106DeltaDart]

In your last episode you mentioned part of the reason EDFs are so inneficient att low speeds are the angle of attack of the blades. Can you try and put a Swash plate on an EDF, Like on the FT Viggen for example, hook it up to an air speed-meter, and control the angle of attack of the blades based on air speed? I realize you might need to make custom blades or modify the ones of some prop, but wouldn't it be awesome if it works?

Also, why didn't you use an FT foamboard plane to modify into your 3d-plane?

You could make a variable pitch EDF, but it would be large, extremely expensive, and require a lot of precision machine work. Lots of big scale helis have fenestron tail rotors, which are essentially a variable pitch EDF. However, for the expense and weight, I don't think you would see a tremendous benefit in performance either.

 

[ÄlveKatt]

You could make a variable pitch EDF, but it would be large, extremely expensive, and require a lot of precision machine work. Lots of big scale helis have fenestron tail rotors, which are essentially a variable pitch EDF. However, for the expense and weight, I don't think you would see a tremendous benefit in performance either.

Can't you just get a swashplate from an RC helicopter and mod it together?

 

[F106DeltaDart]

Can't you just get a swashplate from an RC helicopter and mod it together?

A swashplate for a helicopter is generally too large, and requires 3 servos, linkages, and mounting hardware behind it. All of this equipment in the down wash of a thin duct would kill efficiency pretty quick, and require a lot of extra weight.

 

[quorneng]

Much of this discussion is based on the premise "the reason EDFs are so inefficient at low speeds are the angle of attack of the blades"
The actual fan of an EDF is in a parallel duct so If you consider the airflow immediately in front and behind the blade the velocity of the air is, within the bounds of compress ability, exactly the same regardless of the speed at which the fan is travelling through the air.

Surely EDF inefficiency comes from the fact it is a small diameter and multi bladed when compared to same power going through a 2 bladed prop in 'free air'.