Which fan to use?

[Boots Whirlygig]

I purchased the Opterra 2m flying wing because I think it'd be cool to, through much surgery, install an edf. I've got three FreeWing edfs sitting in front of me and I think any one of them would work:
1. 64mm 4S 12-Blade 2836-3500kv
2. 70mm 4S 6-Blade 2839-3000kv
3. 80mm 4S 6-Blade 3536-2870kv
The wing will also have FW Super Scorpion retracts, but no fpv gear. I've decided not to take the easy route with pod mounting, it will be internally installed, so I'll be removing and adding foam. I plan on adding more carbon fiber reinforcement for the wing. Which would YOU choose and why?

[xviper]

The Opterra is not a light airplane (~2kg). Although it can glide better than most flying wings, it is NOT a glider. It needs power most of the time to stay up. IMO, the more thrust you can put on it, the better chance you have of it actually flying. Then you need enough battery to sustain a reasonable flight time. However, having said that, if you have a good runway, you can save a lot of power by not having to throw it. Something that would give you close to or slightly more than 2kg of thrust should it. The more battery, the heavier it will get, the more thrust you'll need.
I tried an experiment similar to this on the Eflite Scimitar years ago. I installed a 90mm EDF on it externally with a thrust tube and it was just barely enough to push it into the air. It needed to be flown at high throttle all the time and I tired of the short flight times and the constant max throttle usage.
Figure out what thrust you can get out of those choices you have and go with the one that gives you the thrust you need. There are site that will tell you thrust number for various types of fan units you choose.

[gooniac33]

the 6 blade 80mm fan could be a good option. Will this be a 4s or 6s set up? Also a 12 blade may be really good for this type of a plane too since you will get lots of thrust out of one of those...

[Boots Whirlygig]

I figured the opterra would be a good platform for edf, but it is large and heavy, and Horizon has quite a bit of lead weight in the nose for balance. The carbon fiber wing spars pass thru the center line where you'd like to see the fan, so the fan would have to go above or below them. A streamlined fairing on the main spar may work but would reduce thrust. The 3 edf are 4S.
Maybe I'll set it up for the 80mm fan, with the ability to install a smaller lighter fan, smaller thrust tube liner, etc.
Opterra has hollow molded wings. I have carbon fiber strips, like those used to reinforce the horizontal stabilizer on my FW f-16. I will have to pick the correct place to sink these vertically in the hollow wing, as I don't want flutter.
i wonder if the SAFE feature will work with this personality change?

[F106DeltaDart]

I would personally start out with an 80mm 12 blade fan on 6S. 4s will likely be enough to get it in the air, but not that far above stall. 2 3S 5000s could be easily hidden in the wing and connected in series. If you must have 4S maybe a twin setup with the 80s would work, but it would cost a lot, both in $ and weight penalty.

[xviper]

I'm not so sure a 4s system will have enough push for this plane. Also, I don't think you'd get this plane going fast enough to get flutter. I've had mine in a pretty fast dive coming out of a loop and there's no hint of flutter. On my old X8 wing, however, I could get flutter around 60 mph as did the other 2 X8's at my field. I've seen the inside of the wings when I installed spoilers. They're hollow but has cross braces everywhere and the main tube goes a long way towards the wingtips. It would take a very strong EDF to make this plane fly as fast as it does with the stock drive system. Going back to my old Scimitar, the stock prop system was by far the most efficient. The 90mm EDF on 6s couldn't come close in speed.

The weight in the nose is necessary for it to balance without the FPV gear. If you take out the weight, you'd need to replace it with battery or move other stuff around to put the weight back up there. A tail heavy flying wing is a disaster waiting to happen.

[Boots Whirlygig]

Thanks for all the input guys, as I've not flown in over thirty years, and have never flown edf! I don't know what kind of thrust, what the power to weight differences between these 3 units on 4s power to expect. I want to stick with the single tho a twin is intriguing I think the wing loading would make it a brick. Am I correct in assuming that twin 64mm would not match the thrust of a single 80mm? I think this wing will weigh less than the FW Super scorpion, but with the more efficient wing design and a much lighter wing loading. No it won't be as efficient as the stock propellor, no power off soaring, but I don't think it'll fall out of the sky like many small wing edf planes.

[xviper]

Am I correct in assuming that twin 64mm would not match the thrust of a single 80mm? I think this wing will weigh less than the FW Super scorpion, but with the more efficient wing design and a much lighter wing loading. No it won't be as efficient as the stock propellor, no power off soaring, but I don't think it'll fall out of the sky like many small wing edf planes.

This depends on the type and specs on the EDFs. They make some pretty powerful 64mm fans. The Opterra may weigh less than the SS but it's a large wingspan, very draggy plane, while the SS is small and sleek.
Can I assume the reason you want to convert to EDF is that you are worried about that prop carving up your hand? If that's what it is, then you should know that although the manual says you should use full throttle to launch it, with the "LAUNCH" mode engaged, it is possible to give it a good throw, with power off, then give 'er as soon as it's away from your hand. That has proven to work. Or, you could stand on a small hill and throw it power off. Converting any pusher prop to EDF has many challenges and limitations.

[Evoman]

Is the Opterra you first and only plane in 30 years? If it is I recommend starting out with something else that does not need to be modified just to get you stared out and up to pace.

As much as I wanted to start out with a beautiful EDF fighter Jet I had to take my time and start off training with a cheap and simple plane like the Dynam Hawk Sky. And I am glad I did because my first planes have been in many crashes and rebuilds.

[Boots Whirlygig]

No there is no practical reason to make it edf, such as the spinning prop! I have been out of the hobby for years, tho it was always in my thoughts! I was busy with work and raising a family. The boys are adults now and I lost wife two years ago to cancer and I am ready to get back to flying. I've always been more of a designer and tinkerer than a flyer, and have scratch built a few back in the day.
After getting the opterra pnp and looking it over, and knowing that I HAD to turn it into a military jet, I bought a second opterra, the bnf one, that I can fly now, or soon! I've been working out my thumbs on small quad copters.

[xviper]

A wonderful explanation. Tinker away and have fun. Enjoy yourself and best of luck. Would love to see your progress.

[Boots Whirlygig]

Hey xviper2, I am trying to remove the motor from the Opterra , and per the instructions, I removed the screw holding the spinner on.....the spinner won't come off! I don't know how aggressive to get, I haven't gotten out my dremel cut-off yet! Have you or any other Opterra owners encountered this?

[xviper]

Hey xviper2, I am trying to remove the motor from the Opterra , and per the instructions, I removed the screw holding the spinner on.....the spinner won't come off! I don't know how aggressive to get, I haven't gotten out my dremel cut-off yet! Have you or any other Opterra owners encountered this?

Yes, it was tight. This was the first time I removed the spinner to weigh and balance the blades. The center screw is completely out, right? Rather than using a Dremel, take a thin bladed flat screwdriver and slide it between the spinner and each blade base and pry from there. Work it from each side. The plastic on the spinner is very tight and holds on.

[Boots Whirlygig]

Thank you xviper2, I wasn't expecting it to be that deep on the shaft. I guess it had to be, otherwise it could 'wobble' and shake the whole plane apart! Using your suggestion had it off in a snap. I still ended up cutting the plastic tail piece off that houses the motor because you can't slide it out the back, and it won't fit forward either. So if you need or want to replace the motor you can carefully slide a butter knife under the plastic tailpiece/motor housing, cutting thru the soft adhesive and the foam stayed pretty much intact. Now I have a spare power plant for my other Opterra, or a nice motor for one of my old (old) balsa kits I've been hoarding!