telnar1236
Elite member
Didn't see this challenge until right before the end, so I don't have much time, and I'm mostly curious about how fast a 50mm EDF can go more than trying to win, but here is my design. It's meant to be able to be printed on my spare printer and in PLA so I can print it quite fast while also continuing to print my other projects. The structure is also mostly going to make use of infill instead of a modeled internal structure, but it's so small that I'm not adding much weight.
There are a few things I'm trying to do here. The basic design is a flying wing with a very thin streamlined wing wrapped as tightly as possible around the required electronics.
The control surfaces are designed to use fully internal linkages to reduce drag which is the main reason I went with a flying wing instead of more of a T-tail like a pylon racer. While I'm modeling it with a 4s 2200 pack and using that in my calculations to give me some room to add weight, the plan is for it to fly on a 4s 1550 mAh pack to keep the weight down which should give it a flying weight of about 600g with 950g of thrust.
The least conventional design feature is the location of the EDF. Its location behind and in line with the fuselage is selected so that it should ingest pretty much the entire fuselage boundary layer. Ultimately, drag comes from the airplane slowing the air down around it. Simultaneously, one of the limitations of any electric RC plane is the pitch speed of the power system. By letting the EDF ingest the air from the fuselage boundary layer, it mostly cancels out the drag from the fuselage which significantly reduces the drag of the airframe as a whole. At least that's the theory - we'll see how it works in practice.
This is CFD of it flying a 110 mph. You can see how the EDF keeps the flow attached resulting in high pressure on both the front and back of the fuselage.
And how the except for the stagnation point at the nose and the EDF lip, the air keeps moving smoothly without really being stopped or becoming turbulent anywhere.
I'm not really sure how fast this thing will end up being largely because I don't really have any data on the pitch speed or thrust curve for the EDF unit. If thrust remained constant at the static value, it could hit 270 mph, and if the pitch speed is the static efflux speed (66 m/s) it will top out at a more sedate 115 mph. This is also all assuming the surface is smooth and not accounting for the layer lines and imperfections from 3D printing which will add drag and not accounting for the outline of the hatch and trim drag from the elevons which will both also slow it down. I'm also not sure how turbulence from the boundary layer might impact the power output of the EDF.
Basically, this all goes to say, I don't really know what the top speed will be. I'm fairly sure it will be north of 100 mph but beyond that it's a bit up in the air. If I had to throw darts at a dart board and guess, my best estimate would be somewhere between 120 and 150 mph, but that could be quite wrong.
There are a few things I'm trying to do here. The basic design is a flying wing with a very thin streamlined wing wrapped as tightly as possible around the required electronics.
The control surfaces are designed to use fully internal linkages to reduce drag which is the main reason I went with a flying wing instead of more of a T-tail like a pylon racer. While I'm modeling it with a 4s 2200 pack and using that in my calculations to give me some room to add weight, the plan is for it to fly on a 4s 1550 mAh pack to keep the weight down which should give it a flying weight of about 600g with 950g of thrust.
The least conventional design feature is the location of the EDF. Its location behind and in line with the fuselage is selected so that it should ingest pretty much the entire fuselage boundary layer. Ultimately, drag comes from the airplane slowing the air down around it. Simultaneously, one of the limitations of any electric RC plane is the pitch speed of the power system. By letting the EDF ingest the air from the fuselage boundary layer, it mostly cancels out the drag from the fuselage which significantly reduces the drag of the airframe as a whole. At least that's the theory - we'll see how it works in practice.
This is CFD of it flying a 110 mph. You can see how the EDF keeps the flow attached resulting in high pressure on both the front and back of the fuselage.
And how the except for the stagnation point at the nose and the EDF lip, the air keeps moving smoothly without really being stopped or becoming turbulent anywhere.
I'm not really sure how fast this thing will end up being largely because I don't really have any data on the pitch speed or thrust curve for the EDF unit. If thrust remained constant at the static value, it could hit 270 mph, and if the pitch speed is the static efflux speed (66 m/s) it will top out at a more sedate 115 mph. This is also all assuming the surface is smooth and not accounting for the layer lines and imperfections from 3D printing which will add drag and not accounting for the outline of the hatch and trim drag from the elevons which will both also slow it down. I'm also not sure how turbulence from the boundary layer might impact the power output of the EDF.
Basically, this all goes to say, I don't really know what the top speed will be. I'm fairly sure it will be north of 100 mph but beyond that it's a bit up in the air. If I had to throw darts at a dart board and guess, my best estimate would be somewhere between 120 and 150 mph, but that could be quite wrong.
