Is This EDF Design Practical? - RC Groups
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Oct 18, 2017, 02:37 PM
Nu2RC
BSquared18's Avatar
Question

Is This EDF Design Practical?


Hi,

A couple years ago I was hot to build a twin-engine B-66/A3 bomber, using EDF motors and foam. To get advice from others, I started a thread at:

A-3 (Was B-66) Foam EDF Build Project

I'm returning to this project but thinking that I want to simplify the design. Instead of an engine in each nacelle, I'm thinking about having a single EDF buried in the fuselage. This idea comes from a B-66 plan published in Model Airplane News back in 1957 (see attached image). That was a gas-powered free-flight model.

I built that model back then, but it was too under powered to get off the ground. That whole incident is discussed in my video, B-66 "Destroyer" RC Model Planned Build and Phoenix Test Flight.

Basically, the air intake is an open bomb bay. The exhaust is through the tail, whose turret is missing. The engine nacelles are dummies.

Not having worked with the powerful EDFs of today, I'm wondering if that design is efficient enough to provide sufficient thrust. Are there any aspects of such a system that I need to be aware of? Or drawbacks, such is inefficiency because of the way the air is fed to the fan?

Of course, back in 1957, all I had to work with was tissue, balsa and hardwood. Using foam should reduce the model's weight. This, of course, would be an RC model, not free flight. I think I'd want to include ailerons, flaps and, possibly, retracts.

Would like to hear any suggestions.

Bill
Last edited by BSquared18; Oct 18, 2017 at 02:58 PM.
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Oct 19, 2017, 04:06 AM
jofro
It all depend on your AUW as fully complete model but I would definitely go for twin, compromise between 70&90, so 80mm set up on 6S might be just right.
I have recently upgraded one of my rather unique scratch build model from 70 to 80mm EDF set up on 6S with the short th/tube giving me 2.2 kilo static pull as fully complete model on the ground which translates to slightly more in the air.
Oct 19, 2017, 08:52 AM
Nu2RC
BSquared18's Avatar
jofro,

Could you please explain "set up on 6S might be just right." I'm still learning the lingo (I had to look up AUW. I was afraid it might mean "Absolutely Unworkable Weight.)

I suppose both the weight and drag of the dummy nacelles could be an issue. However, in the Model Airplane News article, they did show the model in flight, and that was with a primitive fan. (Pre-Photoshop, so I assume the image wasn't altered.) However, it was gas-engine powered, albeit a very small Cox motor.

Cool model! Do you happen to have any YouTube footage of it in flight?

Bill
Oct 19, 2017, 09:59 AM
SidGates
sidgates50's Avatar

B-66


Quote:
Originally Posted by BSquared18
jofro,

Could you please explain "set up on 6S might be just right." I'm still learning the lingo (I had to look up AUW. I was afraid it might mean "Absolutely Unworkable Weight.)

I suppose both the weight and drag of the dummy nacelles could be an issue. However, in the Model Airplane News article, they did show the model in flight, and that was with a primitive fan. (Pre-Photoshop, so I assume the image wasn't altered.) However, it was gas-engine powered, albeit a very small Cox motor.

Cool model! Do you happen to have any YouTube footage of it in flight?

Bill
==========================================
I would review this thread first.
https://www.rcgroups.com/forums/show...21-1-8th-Scale
Oct 19, 2017, 01:13 PM
Nu2RC
BSquared18's Avatar
Yes, Sidgates. I had been following that thread back in 2015 when I was researching making my model. He started his build thread about the same time I was thinking about my project.

I went to YouTube and found the following video on that model (maybe it had a link on the build thread, but I didn't see it):

Douglas EB-66C Maiden Flight! - 26SEP17

There is some drama on the maiden flight, but for anyone who hasn't watched the video yet, I won't be a spoiler by giving away the ending.

Of course, John's model is much bigger than the one I've been envisioning. Useful info though.

Bill
Oct 19, 2017, 07:30 PM
jofro
Quote:
Originally Posted by BSquared18
jofro,

Could you please explain "set up on 6S might be just right." I'm still learning the lingo (I had to look up AUW. I was afraid it might mean "Absolutely Unworkable Weight.)

I suppose both the weight and drag of the dummy nacelles could be an issue. However, in the Model Airplane News article, they did show the model in flight, and that was with a primitive fan. (Pre-Photoshop, so I assume the image wasn't altered.) However, it was gas-engine powered, albeit a very small Cox motor.

Cool model! Do you happen to have any YouTube footage of it in flight?

Bill
To make decision what power to use on such a model I would firstly like to know the size and the full weight, at least of the air frame. With single fan I would be concerned about intakes and ducting so twin would be my preference. I suggested 80mm as a compromise for easy installation in nacelles with ESCs and batteries somewhere in the fuse at CG position and to minimize the power leads length.
I'm using 10blade DR Max fan, 100A ESC and 6S/4-5.5Ah. My power leads are extremely long running along the fuse so numerous sets of capacitors were added to my 10gauge power leads along the line to minimize the voltage drop. My model is only 2.5 kilo take off weight so in the air I have one to one power to weight ratio. At 165cm (66.5") long and 126cm (52") W/span gives you some idea. With my original 70mm fan it was bit struggling on take off from the grass.
Now it moves very nicely even with that 'weird' wing design I personally hate but it is certainly something different. I loaded dozens of videos on the tube just check my Threads under / jofro/ for X-29.
Oct 20, 2017, 11:59 AM
Pro Hoarder
turbonut's Avatar
There is nothing wrong with the design as you show in the plans. Its not the most efficient way to go but would work well. think of it this way. If it can fly with a .049 Df then EDF will be more as much as 10 times better..that .049 would only make 100 watts on a good day...Today a 1000 watt 70mm is pretty normal...if you don't mind the non scale tail end just build it..Even some of the turbine guys do this so as not to have to install 2 engine at a high cost
Oct 21, 2017, 11:41 PM
Registered User
Bare's Avatar
It's Also :-) possible to insert an electric motor into Each Nacelle and run Props.
Easy Simple and Very! effective Props are barely visible at 50' and certainly so at speed
Oct 22, 2017, 01:44 AM
Registered User
Peacemakr40's Avatar
depending on the size aircraft, you might be able to get away with running a pair of smaller EDFs in the nacelles for power. It'll all come down to AUW and thrust from a pair of small EDF units.
Oct 22, 2017, 01:44 AM
Registered User
AntiArf's Avatar
I'd prefer the prop solution to over sized nacelles. Could build a light weight scale model with reasonably well powered 30 or 40mm fans, although things such as flaps and retractable gear would likely have to be scrapped. I've also built and flown 2 DH106 Comets with internal ducting. The idea would be more practical with the bomb bay intake notion, versus the restrictions/angles I had to deal with.
Oct 22, 2017, 10:27 AM
Nu2RC
BSquared18's Avatar
This hobby certainly has been made more fascinating with all the options now available.

So far, the following have been suggested:
  • Ducted fan in the fuselage, as I first mention in this thread.
  • Smaller EDFs in each nacelle, which I envisioned when I first considered this project.
  • Propellers on the nacelles.

Add to the list John Morgan's pusher B-66 he built (see attached image) to test CG requirements, etc. for the larger model whose video I linked to in an earlier post on this thread. The pusher video is at "John Morgan's EB-66C Pusher - 14OCT2016."

I think I'll pass on the propellers on the nacelles. If I was going to go that route, I think I'd just build something like a B-25 instead.

John's pusher eliminates landing gear and flaps and, as seen in the video, is hand launched. Once they got the CG right, it flew quite well. By the way, considering that this model is just for proof-of-concept purposes, he certainly did a great job on the paint scheme.

I'm leaning toward building a model similar in size and design to John's pusher (i.e., no flaps, no landing gear, hand launched) but with an internal ducted fan instead of pusher. And possibly a Navy A3 instead of B-66.

Because this would be my first RC build, simpler seems to make more sense. Save things like retracts and flaps for later projects.

Great discussion.

Bill
Oct 22, 2017, 04:20 PM
Registered User
Ed Waldrep's Avatar
Inlet diameter doesn't have to match the fan diameter. You aim for 100% FSA so the diameter of the inlet can be less than the fan. I've never built and used a nacelle like that but I know it would work fine, I've build plenty of airplanes with 100% FSA inlets and they fly fine ROG. You could even go less, as far down as 85% FSA, though acceleration would be less, it depends on where you're flying. A cheater hole (such a dirty word) or well designed secondary inlet on the bottom of the nacelle would work also if the inlet is really small. It's more drag but heck we have so much power with brushless and lipo you can get away with it. For a twin though I'd wire the motors in parallel with a high S count to keep the amps down. Asymmetrical thrust can be a killer.
Oct 22, 2017, 05:01 PM
Nu2RC
BSquared18's Avatar
Ed, just to clarify, I'm thinking of having the EDF in the fuselage with the exhaust going out a hole in the tail where the gun turret normally would be.

The intake would be in the belly of the model where the bomb bay door normally would be. The hole can be as small or large as necessary to provide the proper air flow.

I need to learn about how to calculate FSA. I googled it but haven't drilled down yet. I wanted to respond to your comment as quickly as possible.

Of course, the inlet won't be at right angles to the fan the way most inlets would be. I don't know what effect that will have on how large the hole (which I have envisioned being rectangular, but it could be circular if that works better) should be.

What kind of ducting would be necessary?

Any thoughts, Ed...or anyone else?

Bill
Oct 22, 2017, 11:01 PM
Pro Hoarder
turbonut's Avatar
As always the intake should have a smooth transition. But you would be surprised what can work.. just add a bell mouth intake ring on the fan and go for it
Last edited by turbonut; Oct 23, 2017 at 12:53 PM.
Oct 23, 2017, 04:25 AM
jofro
Q-I'm leaning toward building a model similar in size and design to John's pusher (i.e., no flaps, no landing gear, hand launched) but with an internal ducted fan instead of pusher. And possibly a Navy A3 instead of B-66.

Mate, it's a shame to go for such an inefficient option, it would be an art work on its own to build such a nice model , stick in couple of fans for each nacelle, nothing could be easier, just thing of that twin sound of the music.


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