I wanted to try an EDF, so I bought a $33 50mm EDF on Amazon and made a simple adaptation to my FT Tiny Trainer 3 channel. To get an approximation of the correct thrust angle I set it 8 deg up and adjusted elevator trim to eliminate pitch over when at full throttle (holding the plane in my hand). Once I fly it I (soon as the weather allows) I suspect mixing throttle and elevator will work well. Any advice/suggestions would be appreciated.
Giving EDF a try
- Thread starter model14
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tamuct01
Well-known member
The biggest thing I've found with EDFs is that there is no instant power change. On a prop plane, when you apply throttle you almost instantly get thrust. The EDF must accelerate the air in the thrust tube before you see power changes (similar to spooling up a turbine). Just be aware of this tendency and don't get yourself in a situation where you need instant power. Your thrust tube in the photos is quite short, so you might not experience much of this tendency. However, as you move to more scale jets you'll notice the power lag more.
quorneng
Master member
Compared to a prop using the same power its more a lack of thrust than any delay in achieving what it does deliver.
At least with just the factory bell mouth you won't be suffering any of the dreaded inlet ducting losses.
Remember the fin/rudder will be in a much higher speed air steam than with a nose mounted prop. The rudder will be much more effective when the EDF is on.
The first thing I do with a new EDF is check the 'bare' EDF thrust using the intended flight battery. Then I know how much I have lost in the final installation. It can be quite disappointing!
Indeed you might find your relatively small EDF delivers virtually the same thrust without any exhaust tube on it at all.
Duct losses are primarily from wall skin friction. The thickness of the air slowed by it is more or less constant so a small diameter duct is proportionally more effected by it.
Do let us know how it goes.
At least with just the factory bell mouth you won't be suffering any of the dreaded inlet ducting losses.
Remember the fin/rudder will be in a much higher speed air steam than with a nose mounted prop. The rudder will be much more effective when the EDF is on.
The first thing I do with a new EDF is check the 'bare' EDF thrust using the intended flight battery. Then I know how much I have lost in the final installation. It can be quite disappointing!
Indeed you might find your relatively small EDF delivers virtually the same thrust without any exhaust tube on it at all.
Duct losses are primarily from wall skin friction. The thickness of the air slowed by it is more or less constant so a small diameter duct is proportionally more effected by it.
Do let us know how it goes.
L Edge
Master member
First thing, I like is that you will have full control of elevator due to the exhaust flow close to the surfaces. Don't know if the 8 degrees is right. I would try at 3 to 4 degrees. Way to determine that is when you have it flying trimmed at say 2/3 flying level, punch the throttle and if climbs/ nose down, you need to change angle of exhaust. Also, check if it skews off left or right. My slow flyer(EDF) ended up three degrees up and 1 degree right without an exhaust tube. Check out my SR-71 for comments on inlet ducts and exhaust ducts.
I would not do a mix of throttle to elevator.
Hold plane vertical, add throttle until it wants to hover(also an general indicator of 2 much or 2 little thrust angle side or up/down). A safe bet it should fly with 1/2 to 2/3 throttle.
Do an overhand throw and release level.
Do a short flight (1 to 2 min) for you will gobble up watts and you will have spare if you need to do a go around to land. Average flight is 3-4 min.
For the first landing, always have some power on until you are about a foot of the ground and then flare. EDF's need to spool up and if you are flaring and too high and decide to go around, !!!!!!!!!!! I use a modified throttle curve to offset spooling up.
Watch what happens for landing and watch the chucking at second time. Happy because it took me many moons to solve for no vertical stabs and no rudder where I used only 2 servo and a thrust vectoring unit to apply necessary yaw.
I would not do a mix of throttle to elevator.
Hold plane vertical, add throttle until it wants to hover(also an general indicator of 2 much or 2 little thrust angle side or up/down). A safe bet it should fly with 1/2 to 2/3 throttle.
Do an overhand throw and release level.
Do a short flight (1 to 2 min) for you will gobble up watts and you will have spare if you need to do a go around to land. Average flight is 3-4 min.
For the first landing, always have some power on until you are about a foot of the ground and then flare. EDF's need to spool up and if you are flaring and too high and decide to go around, !!!!!!!!!!! I use a modified throttle curve to offset spooling up.
Watch what happens for landing and watch the chucking at second time. Happy because it took me many moons to solve for no vertical stabs and no rudder where I used only 2 servo and a thrust vectoring unit to apply necessary yaw.
The Tiny Trainer EDF conversion flies very well. I had no major problems, but a few surprises. I just flew it off the short grass, and then once off of the paved strip. Both worked fine. The thrust angle was perfect for a smooth easy climb with up elevator. The first surprise was when I cut power and the nose pitched up at 45 degrees, but then settled back down to a manageable decent when I eased off the elevator. Obviously, I was carrying a lot of up elevator during level flight and this caused the pitch up on throttle cut. The other surprise was my battery only lasted for 2 quick trips around the pattern! Battery is a 1300 mah 80C 3S. I know it was fully charged on takeoff. I probably was flying at full throttle and didn't realize it. Power meter reads 30 amps so really not a surprise.
For the second flight I put in some down trim before takeoff and eased the throttle to about 1/2 around the pattern. This worked great. There were no surprises on a slow throttle decrease for landing, and landing trim was perfect. Flight time was about 2 minutes.
At home I remeasured the EDF thrust angle and it came out to be 6 degrees up.
No video, sorry, but I promise one after my Christmas trip away from home, and I get a decent camera.
For the second flight I put in some down trim before takeoff and eased the throttle to about 1/2 around the pattern. This worked great. There were no surprises on a slow throttle decrease for landing, and landing trim was perfect. Flight time was about 2 minutes.
At home I remeasured the EDF thrust angle and it came out to be 6 degrees up.
No video, sorry, but I promise one after my Christmas trip away from home, and I get a decent camera.
Last edited:
quorneng
Master member
model14
30A at 3s means maybe 300W and in a plane that is likely to fly perfectly well on less than 100W with a decent size 2 blade prop..
A perfect demonstration of just how inefficient EDFs are.
Substantially discharging a LiPo in 2 minutes won't be doing it any favours either.
Looking forward to the video.
30A at 3s means maybe 300W and in a plane that is likely to fly perfectly well on less than 100W with a decent size 2 blade prop..
A perfect demonstration of just how inefficient EDFs are.
Substantially discharging a LiPo in 2 minutes won't be doing it any favours either.
Looking forward to the video.
b-29er
Well-known member
Like Quorneng said, EDFs are great at two things, pitch speed and draining batteries. I might suggest putting this on something that either can maintain energy well at speed, like a flying wing, or to make the wings smaller. EDFs really shine at high speed, they don't have the instantaneous thrust of a prop, but they'll get stuff going faster. So sticking one on the back of an FT trainer...it will probably be fun, but it's not going to do much different.
quorneng
Master member
What many don't recognise is the big improvement in EDF efficiency (g thrust/Watt) as you throttle back.
In some cases the efficiency can actually double so if you can design an EDF plane light enough to fly well on a true half electrical power, note this can still mean as much as 70% of the full power thrust, then what might be 3 minutes flight becomes 6 minutes and still using the same battery. The light weight also improves the full power climb performance although the drag square law means only a modest increase in the top speed.
It is however rather more difficult to do this than to say it as the airframe has to be really light yet still be strong enough and aerodynamically efficient.
Can be worth considering if you are designing your own.
In some cases the efficiency can actually double so if you can design an EDF plane light enough to fly well on a true half electrical power, note this can still mean as much as 70% of the full power thrust, then what might be 3 minutes flight becomes 6 minutes and still using the same battery. The light weight also improves the full power climb performance although the drag square law means only a modest increase in the top speed.
It is however rather more difficult to do this than to say it as the airframe has to be really light yet still be strong enough and aerodynamically efficient.
Can be worth considering if you are designing your own.
Yeah!! I found the video I thought I had accidently deleted. Here is the EDF Tiny Trainer flying off pavement (second flight after trimming):
www.youtube.com/watch?v=FbPGMw9WG8o
It is edited to delete portions where the plane is too far out to see.
www.youtube.com/watch?v=FbPGMw9WG8o
It is edited to delete portions where the plane is too far out to see.
L Edge
Master member
Model 14
On the positive side, EDF"s are fun to do. You don't get lots of time but if you make your own, it happiness.
I have a transport YC-14 with blown flaps, Sr-71, forward swept wing, modified bobcat and many other EDF videos. The point is If you want to explore, have fun. Here's one flying a 64 EDF jet in winter month's in a confined area in a dome. Other is landing gear(large aileron horns) added to a ducted 64 jet to do takeoff and landings.
On the positive side, EDF"s are fun to do. You don't get lots of time but if you make your own, it happiness.
I have a transport YC-14 with blown flaps, Sr-71, forward swept wing, modified bobcat and many other EDF videos. The point is If you want to explore, have fun. Here's one flying a 64 EDF jet in winter month's in a confined area in a dome. Other is landing gear(large aileron horns) added to a ducted 64 jet to do takeoff and landings.
EDF powered FT Tiny Trainer flying is going well with one exception. The trainer wing will not take the additional flight loads of the much higher EDF powered speeds. Wing reinforcement is needed to prevent the wing from folding in a high-speed pullup. I solved this problem by gluing a Lowes thin paint stick to the wing underside. These sticks are very light.
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quorneng
Master member
model14
The thing to remember with an EDF is that it and its battery add quite a bit of weight so the plane have to fly faster. The aerodynamic forces for any manoeuvre will increase by the square of the speed increase so you have to consider both the strength and rigidity of the airframe.
Finally the increased flying speed means the drag and thus the power to fly increases by the same equation. With an EDF It pays to consider any aerodynamic refinement including setting up the CofG and wing/tail incidence so the control surfaces are at neutral for straight and level flight.
When this is done effectively you should find the EDF will actually glide better than its prop equivalent.
A by product of any improved aerodynamic efficiency is that you won't need to use full power all the time so flights can be that bit longer too.
The thing to remember with an EDF is that it and its battery add quite a bit of weight so the plane have to fly faster. The aerodynamic forces for any manoeuvre will increase by the square of the speed increase so you have to consider both the strength and rigidity of the airframe.
Finally the increased flying speed means the drag and thus the power to fly increases by the same equation. With an EDF It pays to consider any aerodynamic refinement including setting up the CofG and wing/tail incidence so the control surfaces are at neutral for straight and level flight.
When this is done effectively you should find the EDF will actually glide better than its prop equivalent.
A by product of any improved aerodynamic efficiency is that you won't need to use full power all the time so flights can be that bit longer too.
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