Just started a new project. It's my first edf build and I'm building it from scratch. It's not to first airplane I've build but it's the first one I haven't had any plans. If I've done the math correctly it will be 1/12 scale so I can convert the measurements in feet or the real aircraft directly to inches. I plan to do a complex normal mig 21 body and tail but have the wings of the j 7 because they are a bit bigger. I'm not currently planning on using a store bought edf motor. I staid I'm using the motor out of a discontinued parkzone typhoon 2 that the gear box broke on (I'm replacing the motor and gearbox with the modern more powerful motor). I 3d printed suports for the motor but I will need to buy a edf fan. Any recommendations for 70 mm edf fans or any thing els that I might be missing while building it would be appreciated. I plan on puting retracs on it but I don't have them yet so I'm not shure. In the one picture I atemted to draw about what the rest of the turtle deck and tail will look like.
Mig 21/J-7 70mm edf scratch build
- Thread starter Funky
- Start date
quorneng
Master member
Funky
If you can build light enough an EDF does not have to be fast and it does not need that much power either.
Just to give you an idea this 850mm span Hawker Hunter F6 uses a 50 mm EDF and a 1800mAh 3s.
easy hand launch and belly land on grass.
It is built entirely (no wood or carbon reinforcing) from 5mm XPS foam. It weighs 560g ready to go.
If you can build light enough an EDF does not have to be fast and it does not need that much power either.
Just to give you an idea this 850mm span Hawker Hunter F6 uses a 50 mm EDF and a 1800mAh 3s.
easy hand launch and belly land on grass.
quorneng
Master member
The Parkzone Typhoon 2 used a 20A ESC so it is reasonable to assume the motor drew less than this at full power and it used a 3 cell LiPo. That means a power of 12V x 18A or 200W max
Such a motor will not power a modern 70 mm fan effectively. Something like 400W would be needed.
As a guide an EDF is only about half as efficient as a prop in converting Watts into thrust. So using your motor with a fan you would have to build a plane that would fly on just 100W if using a prop. For a Typhoon 2 sized plane it would have to be a lot lighter.
If you are set on building an EDF plane then I suggest the best course of action is to buy a complete EDF unit. Even then success is not guaranteed.
Sorry but that is how I see it.
Such a motor will not power a modern 70 mm fan effectively. Something like 400W would be needed.
As a guide an EDF is only about half as efficient as a prop in converting Watts into thrust. So using your motor with a fan you would have to build a plane that would fly on just 100W if using a prop. For a Typhoon 2 sized plane it would have to be a lot lighter.
If you are set on building an EDF plane then I suggest the best course of action is to buy a complete EDF unit. Even then success is not guaranteed.
Sorry but that is how I see it.
I checked the parkzone i have and the esc is 30 amps and recommends a 9 to 12 cell battery. I don't know very much about how that changes things other than 30 amps means more power. The esc is stock. I think it was one of the last planes they produced as it has all modern electronics. I got a second typhoon 2 from a friend to use as parts and that one had 20 Amp esc.
L Edge
Master member
Ditto, agree with quorneng, buy a complete EDF unit to have a match motor/blade setup.
When completed, my approach to see the weight/thrust is in range is the following:
Apply 1/2 throttle, hold plane vertical, quickly let go and then grab to see if plane wants to drop, hover, or climb.
If it climbs--got a excellent chance of flying
if it hovers-- it should fly
if it drops--bad, add more throttle and redo again.
If you are at full throttle and it does hover -you have high odds against you-personally, I find ways to reduce weight.
My way of maiden launch to check CG and thrust--- Most flyers throw the plane avg-6 ft above ground and if nose heavy end up with nose damage or tail heavy it will go nose up and usually rotate causing major damage with EDF full speed.
What I do is to prevent major damage is set throttle(were it hovers) and use that hand to chop power if it necessary and with other hand launch
plane horizontal about a foot above ground. If it is nose heavy, the kinetic and potential energy is very little and worst case, it will have minor damage. If it tail heavy, it will nose up, tail will drag along and plop back on ground.
If CG is right on, throttle back and see your plane drop and slide along the ground.
So picture 6 ft above ground launch or 1 ft launch. I rest my case.
When completed, my approach to see the weight/thrust is in range is the following:
Apply 1/2 throttle, hold plane vertical, quickly let go and then grab to see if plane wants to drop, hover, or climb.
If it climbs--got a excellent chance of flying
if it hovers-- it should fly
if it drops--bad, add more throttle and redo again.
If you are at full throttle and it does hover -you have high odds against you-personally, I find ways to reduce weight.
My way of maiden launch to check CG and thrust--- Most flyers throw the plane avg-6 ft above ground and if nose heavy end up with nose damage or tail heavy it will go nose up and usually rotate causing major damage with EDF full speed.
What I do is to prevent major damage is set throttle(were it hovers) and use that hand to chop power if it necessary and with other hand launch
plane horizontal about a foot above ground. If it is nose heavy, the kinetic and potential energy is very little and worst case, it will have minor damage. If it tail heavy, it will nose up, tail will drag along and plop back on ground.
If CG is right on, throttle back and see your plane drop and slide along the ground.
So picture 6 ft above ground launch or 1 ft launch. I rest my case.
quorneng
Master member
Funky
With a commercially available EDF the motor and fan will be matched when used with the recommended LiPo cell count. The figure you need is the static thrust figure. As L Edge suggests if the published static thrust at full power is significantly above your planes "ready to fly" weight then it should be OK. If not then either find a more powerful 70mm EDF (it will be more expensive) or loose some weight from the plane.
It is possible to fly an EDF plane that has a static thrust less than it weight but to do so it is likely to be more of a 'light plane' configuration than a fast military jet.
With a commercially available EDF the motor and fan will be matched when used with the recommended LiPo cell count. The figure you need is the static thrust figure. As L Edge suggests if the published static thrust at full power is significantly above your planes "ready to fly" weight then it should be OK. If not then either find a more powerful 70mm EDF (it will be more expensive) or loose some weight from the plane.
It is possible to fly an EDF plane that has a static thrust less than it weight but to do so it is likely to be more of a 'light plane' configuration than a fast military jet.
L Edge
Master member
What is the distance between the inlet and position of the EDF? and distance of EDF to outlet(any reduction in size)?
L Edge
Master member
What do you think the total flying weight will be?
I think it should be about 800 g. The edf I ordered had a chart that said with the battery and esc I have it will produce 1130 g of thrust. I built it with a inner tube for the edf and a outer tube for the skin. The space between the tube and the turtle deck should alow me to put the battery and all electronics separated from the edf tube. The edf tube is completely clean except for a inlet cone and 2 wing spars that run through it.
