Could a sub250 EDF park flyer be a thing?

[quorneng]

UCDWino
Most people will agree that the maximum static thrust is obtained with a bare EDF with a bell mouth. The manufacturers certainly think so!
If you are using an inlet duct then the bell mouth technically becomes redundant although it may not be easily removable.
For a sub 250g flyer I suggest you arrange the layout so the EDF has no thrust tube whatsoever.
Best if it has no inlet duct either but if it does make sure it has an area at least the diameter of the EDF body (1.2 x FSA), is internally smooth and with the minimum of changes in shape and direction.
Not a sub 250g but an example of an EDF "at the back" with a very short thrust tube the diameter of the EDF body .

Despite its looks it is very light and a true slow flyer, as was the full size!

 

[LitterBug]

I have a 20mm that is just like that EDF. Should do something with it this winter.....

 

[L Edge]

You said to me(reply #19) that you have 127 grams for battery and airframe.

Related but seperate question for you guys.... I went to research how to design a thrust tube for the motor here and came across discussion saying that a thrust tube doesnt help.... Given that I have a weight limit im designing against, It might indeed nice to not to have to worry about adding a part downtstream of the EDF.... thoughts?

I have used a number of EDF's without worry about inlet or exit area designs. Still plenty of power and best of all, no additional weight. If fact, cut the bell inlet shape off yours if you want to reduce further weight. Here is a couple of samples.

A "STOL EDF" rotated by rudder input allowing short takeoffs and high alpha approaches. Proof enough.

 

[telnar1236]

The DJI o3 system is under 40 grams. That plus the 40mm fan, 4 servos, a flight controller and a receiver all sum up to 122g leaving 127 grams for the frame plus battery…. My thought is to try to design as efficient of a frame as possible and then pick a battery with the remaining weight budget…. Don’t know how that will turn out though…. Not until I try it at least.

It won’t be the end of the world to be a little over the weight at first and try to optimize…. I read The new 04 DJI unit is apparently going to have a “lite” variant which should bring the weight down even further… so while I don’t think this is going to be “easy”. I think it is probably “do-able”

Seems doable. Waterjet cut carbon fiber might be heavy for a plane this size, but foam board designs like what you see from Quorneng should definitely be light enough.

Related but seperate question for you guys.... I went to research how to design a thrust tube for the motor here and came across discussion saying that a thrust tube doesnt help.... Given that I have a weight limit im designing against, It might indeed nice to not to have to worry about adding a part downtstream of the EDF.... thoughts?

If you're desperately trying to cut weight, it should be ok. It depends on the specific EDF unit if a thrust tube helps or hurts static thrust, but it's not going to make a huge different for a slower plane. The big advantage is it lets you position the EDF further forwards to help with CG if you have a full length fuselage. As you go faster, you definitely lose out on thrust without a thrust tube though. They're not all that heavy, but with a design like this where every gram counts should be ok to leave it off.

 

[quorneng]

Do you really need 4 servos? Many EDFs manage without a rudder and fly "bank and yank" All but one of mine do!
Are they 9g servos? At sub 250g do you really need such power.
My sub 250g Venom uses three 2.5g servos and its 40mm EDF weighs just 30g!
To stand a chance of a practical sub 250g EDF you will have to use suitable light weight components.

 

[Mr Man]

Do you really need 4 servos? Many EDFs manage without a rudder and fly "bank and yank" All but one of mine do!
Are they 9g servos? At sub 250g do you really need such power.
My sub 250g Venom uses three 2.5g servos and its 40mm EDF weighs just 30g!
To stand a chance of a practical sub 250g EDF you will have to use suitable light weight components.

From some tinkering, 2.5g servos are stronger than they look.

 

[Marzipan]

Hey gang,

I’ve been thinking of designing a sub250 FPV park flyer for a while now, and have been playing with a variety of ideas in Cad and can never find something that ticks all the boxes. After getting my part107 recently I noticed that there are regs especially for flight over people that include references to prop guards. (Undoubtedly for intended multicopters in sure, but the regulation isn’t specific on that point). The intent here is to make something fun that is in zero way dangerous and complies with all the regs…. So I’m wondering if a sub250 EDF might be the combo we need for “anywhere” fpv fixed wing flying.

My question to you is: is this crazy?

I’m not necessarily looking to design something that is fast… I’m more interested in safety: finger safety on launch, and the ability to belly land without striking the prop, or heaven forbid, it gets flown into someone…. Maybe an EDF is the way to go?

Would be interested in your thoughts and even recommendations

yup, definitely possible; just take a look at MinimumRC and you'll see they have a big handful of options.