What is the ratio of the drag from the arms compared to the overall thrust (they are situated right in the wind stream of the propeller). The drag on the arms may not have a significant effect on top speed but it might have an effect on the flight duration. With a more aerodynamic arm, you could also substitute a more efficient propeller that has less thrust for the same performance . I noticed that most arms of tri/quad copters have little to no consideration for aerodynamics. You end up having to put in more power into the system to overcome the arm drag. I was just curious if the effects of the arm drag is at all significant for duration/efficiency. Log In to reply
The drag ratio is based off of a low Re. The down wash from the propeller will far exceed the flow over the arms at max forward flight. From the prospective of parastic drag looking at the 2d surface area in forward flight it does have an effect on your speed, but you are going to slow(around 40mph) that it has little effect, more 1 or 2 mph if that. I was going to do a few more wind tunnel test on the shaped but I ran out of time. you are correct in your statment. Overall the best solution would be a tube arm (circular) cross section. A sysmetric airfoil would be ideal but not practical. Another example of this is in the eflite EDFs. The shoud that covers the motors cables is airfoil shape. This operation at a high exhaust speed increases the speed by 5mph. ( this info comes from testing someone else did a few years back). Same concept here fro the tricopter. If you have two of the same tricopteres with one of a tube and one with a square, with everything being equal I would bet the tube will fly slightly faster, with a slight increase in duration and efficiency. If I had to guess I would say about a 2 mph increase for max forward flight with a 5% increase in efficiency. Of course this may throw off the vibrations. Log In to reply
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