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A10 Style Giant F14 power plant

#1
Hiya,

I’m looking to build a giant F14 in the style of the A10 from FT, though around 6-7ft long, not 10! I’ve had a rummage around the internet for EDF power plants but in my ignorance I had no idea how expensive they are! I basically wanna know if this would work.
I expect the flying weight to be 3kg and I would use power pack C (used in the first A10 video) with increasing pitched props through the duct for better efficiency. But I am thinking of adding a third motor into the duct to add extra power. Along with this i would do more with the ducting such as decreasing the size of the duct (Bernoulli’s principle). So using a similar concept to the first A10 video would the F14 have sufficient power to do high speed flying, not just about staying in the air like the A10 in the first video.
I am planning to use a 4S 35C 5000mAh

Thanks for any advice
Harry Karmel
 

JTarmstr

Elite member
#2
Hiya,

I’m looking to build a giant F14 in the style of the A10 from FT, though around 6-7ft long, not 10! I’ve had a rummage around the internet for EDF power plants but in my ignorance I had no idea how expensive they are! I basically wanna know if this would work.
I expect the flying weight to be 3kg and I would use power pack C (used in the first A10 video) with increasing pitched props through the duct for better efficiency. But I am thinking of adding a third motor into the duct to add extra power. Along with this i would do more with the ducting such as decreasing the size of the duct (Bernoulli’s principle). So using a similar concept to the first A10 video would the F14 have sufficient power to do high speed flying, not just about staying in the air like the A10 in the first video.
I am planning to use a 4S 35C 5000mAh

Thanks for any advice
Harry Karmel
The problem with an F-14 is the ducts on it are fairly small because the engines on a F-14 are really long and a bit thinner whereas the A-10 has a wider and shorter turbofan. On the other hand if you could get some smaller props on the C motors it might work. I am not an expert on setting up proper propellers for motors so i don't know if its possible. I wonder if you used F pack motors with 3 bladed propellers it would do a better job providing thrust in the space you would have. That's just an idea though, no guarantees on how it would work. Good luck!
 
#4
Yh I was thinking the props might be bit tight. Maybe if I added a 4th prop (because the duct is much longer) that might counter the smaller prop diameter. I might just scale up some of the areas of the duct to fit larger props if it doesn’t work.
 

Chuppster

Well-known member
#5
The "Props as an EDF" approach should be tested more, but I would say that buying four C-packs and expecting them to give you 3 kg of thrust in a series duct is perhaps a little... ambitious? EDF's have 6-12 blades for a reason, if you want a lot of thrust from a small diameter you need them! It is unfortunate that EDF's are so expensive but I have yet to see anyone replicate their power/diameter ratio with cheap electronics. I'm not saying you shouldn't try it, but don't expect it to work much better than two C-packs mounted on the wings in clean air.
 
#6
I’ll give it a test! I’ll see if I can find any 4 blade or even 6 blade props to help but I’ll see what I can do. I don’t necessarily need 3kg of thrust but I want enough for it to pick up decent speed.
 

d8veh

Elite member
#8
You'll probably need much higher voltage to run small props at the right speed to get full power. Alternatively, you can buy motors with a much higher kV than the C-pack ones. 4S with the 1180kV Emax motor will get you something like 10600 rpm at max power, which is nowhere near enough for a small prop. I'd say that you need at least 6S, which will get you 15,000 rpm, or a motor with a kV of 2000 and a 4S battery, would get you around 20,000rpm, which seems a lot more realistic.
 

quorneng

Elite member
#9
Next thing to think about is the maximum safe revolutions for such a prop. I suspect 20,000 rpm is beyond the capabilities of that 6 blade prop, after all it was intended for a quad.
On the other hand EDF fans are designed to handle such revs with big hubs and relatively short stubby blades.
 
#10
Ok thanks for that advice. I’ll look into the props from that perspective. I expect I’ll use 3 or 4 blade props or the final one but I’ll probably test with a few different types. And if all else fails, I’ll have to splash out on a quality EDF!
 

PsyBorg

Wake up! Time to fly!
#11
Next thing to think about is the maximum safe revolutions for such a prop. I suspect 20,000 rpm is beyond the capabilities of that 6 blade prop, after all it was intended for a quad.
On the other hand EDF fans are designed to handle such revs with big hubs and relatively short stubby blades.
Emax 2306 motors run in the 20 to 30k rpm range pushing up to 1700g thrust depending on voltage and kv rating running 5040 tri blades to 6040 bull nose bis

You are correct though with edf props meant to push more air at those rpms

@avpostter check the charts on the spec page. This may give you a better idea with already tested combinations.

https://www.emaxmodel.com/emax-rs2306-racespec-motor-cooling-series-2400.html
 
#12
That’s really helpful - I’ll definitely check those out.
I saw in the comments of the A10 video that someone was talking about the ducting, so I’ll probably be compressing the airflow, with a high pressure bypass region from the front prop as well.
 

kilroy07

Legendary member
#13
so I’ll probably be compressing the airflow, with a high pressure bypass region from the front prop as well.
That’s basically what the newer high efficiency engines on airliners do these days. Almost like a turbo prop (with a whole lot more blades).
 

quorneng

Elite member
#15
avpostter
Don't get to excited about compressing the airflow. Yes both a prop & EDF do compress the air but its actually only by a very small amount. Most of the work is put into accelerating the air.
Big airliner turbo fans on the other hand do compress the air but then they have to achieve sufficient exhaust velocity to provide useful thrust at a 600 mph cruising speed.
The fact that EDF only accelerates the air flow means the ducting has to be very carefully arranged or it simply slows the air down with a corresponding loss in thrust.
 
#16
Ok thanks for the advice. I have access to Solidworks (CAD rendering software) so I’ll try and model it on that and then use the wind tunnel rendering to find the optimal shape to achieve max thrust.
 
#18
Thanks! I’m afraid school got in the way so not brilliant at the moment. Potentially this Summer though! I want to try it out at some point but I’m afraid that isn’t going to be soon :(