|Jan 27, 2014, 12:25 PM|
I understand your pain with the weather! Right now I'm supposed to be in Dayton but the plane was diverted last night to Columbus. Apparently the crosswinds were too much and after 3 aborted landings they rerouted us. It was a hairy flight. Lots of banking around the airport low and slow in dense fog was no fun!
Here is what a 1lb Electrolyte looks on final approach.
|Jan 28, 2014, 07:33 AM|
I have been following this awesome project for a while now and it's truly inspirational what you guys are achieving.
I'm hoping to pick you brain with regards to you super slick exhaust ducts as I'm just in the process of designing them for a 40mm Hunter. As you will probably guess I'm a relative newbie when it comes to EDF.
I have read that the ideal exit diameter of the exhaust is 85% FSA. From your pictures it looks like yours tapers down a lot more. Is this because you are looking to increase the efflux to increase top flight speed?
Am I correct in thinking that the trade off would be thrust, hence the bungee launch?
I hoping to keep the Hunter too scale and there is plenty of area to play with on the inlets. It's the exhaust nozzle thats driving the model's size. At the moment, with the exhaust area at 79%, my wing span is scaling to 540mm. I was hoping to get it to about 500mm, but that would mean reducing the nozzle area further if I want to keep things to scale.
I'm trying to get a feel for how much things weigh and what's acceptable. I appreciate you stuffs cutting edge, but do you have a weigh for your ductwork?
You mentioned that you included a fan faring over your motor. Do you feel that the improvement in EDF efficiency was worth the weight tradeoff?
The reason I ask is that I originally include a faring in my design but removed it because I felt that it could increase the chances of the motor over heating. There is also the weight issue. As it stands I just have the faring around the wires.
|Jan 28, 2014, 11:16 AM|
The Hunter should make for a great micro edf and your CAD drawings look great! If your finished model looks like the drawings you will have an extremely efficient edf!
Regarding the exhaust, The Electrolyte tailpipe works out to about 85% FSA when using a 40mm fan. Because the airframe is pretty slick, flight testing has demonstrated increased performance with the tailpipe further restricted to 75-80%.
The topic of the bungee launch method is an interesting debate. The issue is 2 fold for the Electrolyte. Most people assume its because there is not enough thrust. Actually the last 3 Electrolytes have over a 1:1 thrust to weight ratio despite the fact that I still bungee them. The bungee is a reliable method and I would hate to bust up the plane. The lack of control surface effectiveness at low airspeed is what make the bungee technique more reliable than a hand launch. If this were a prop plane there would be no issue with hand launch since the prop blast going over the elevator and wing is much greater than the actual airspeed. However, on a jet-like design you only get airflow from airspeed and maybe some headwind (which helps a lot). Have we hand launched an Electrolyte? Yes, many times but the success ratio is much lower than the bungee.
The split ducting on the Electrolyte is very light. It weighs a total of 4 grams. I am not sure what the weight of the 3D grown thrust tube is but its not very heavy. The most recent 121 mph flight this weekend represented an entirely new power system. I am very happy with the performance of the Dinogy 65C lipos but also believe the thrust tube contributed to the higher top speed.
For your design its hard to say whether the weight penalty is less than the efficiency gain. The only real way to find out is through flight testing. Best of luck with your project!
|Jan 28, 2014, 01:50 PM|
Cheers Bret, that explains alot.
You know I never gave a thought to the fact that there wouldn't be any prop wash. This is so challenging - there is so much to take into consideration.
I'm hoping to have all the ducting finished for testing over the weekend.
I have been watched the testing you did on the EDF units on your youtube channel - thanks for sharing the info.
Just the one question. Do you ballance you rotors for each motor / rotor combination?
Thanks again for the great reply.
|Jan 28, 2014, 10:11 PM|
i would balance each rotor you use ,if your using a out runner motor the bell some times needs to be balnced too ..but i think your using a inrunner so no worries there . Balance makes a big diff to EDf ,it changes the sound and add rpm and uses less amps and watts on a well balanced rotor ,we usally rotate the rotor after we balance it .so what i mean is we feel for a sweet spot ...balance the rotor .bolt it on run it ...if its ruff ,rotate the rotor a 1/4 turn .bolt it down and run again ...cont this untill you fine the "best " smoothest run . it takes time but is well worth it . if you watch some vids from last sat. you hear some jets that are very noisey ...these are not balanced well .Bret plane and C/N F-20 ,and even his huge T-38 run very smooth .
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