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OverTheTop

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First is probably a question with an answer that's obvious to anybody who knows the second thing about ducted fans, but I only know the first thing. So, could some sort of nozzle shape at the aft end where the air exits help increase the thrust?
With helicopters (this is essentially a helicopter with an enclosed rotor I think) the lift is mainly caused by mass airflow, and not so much exhaust velocity (secondary effect). If you can move more mass you get better lift.

I am not sure if increasing the exhaust velocity will gain you anything in this case, as it is more akin to a helicopter than a jet. I am happy for any aerodynamacists set me straight if I got this wrong.

As george mentioned upthread, if you treat the incoming air nicely and minimise pressure drops you can probably gain some improvements.

Have you thought of trying tethered flights with this? Might help save the airframe if something happens during a test that is unexpected, and keep everything safe in the early development. Will be good to see this fly!
 

Richard Dierking

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With helicopters (this is essentially a helicopter with an enclosed rotor I think) the lift is mainly caused by mass airflow, and not so much exhaust velocity (secondary effect). If you can move more mass you get better lift.
There are some good videos on YouTube that describe EDF's and how thrust is measured and factors that affect the thrust. For example, thrust decreases with the velocity of the craft. I don't think a comparison with helicopters and aircraft with EDF's would go very far. Maybe aircraft with high-RPM propellers, but I heard that props on airplanes become more effective when you feed them air, so static testing doesn't tell you much about performance.
I've thought about two inline EDF's counter-rotating so one is supplying air to the other. But, this project is complicated enough without me looking for things like that. ;-)

A bit of background: I started to do RC airplanes about 6 months ago because of my lifting body project. I wanted to learn about RC flight, control, FPV, and gain some degree of skill for landing. So far, that's going well, but there's a lot to learn. Figure if I can do some work on the EDF rocket, other's can refine and improve this, and there's sure to be improvements in things like EDF's and batteries in the future.

Just a side note here that's interesting. I call if a EDF rocket, but neither the State of California or the FAA would consider this a model or high-power rocket. We need to consider where this fits and how it would be accepted at NAR and TRA launches. I would be interested to hear your thoughts on this.
 

Rob Campbell

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There are some good videos on YouTube that describe EDF's and how thrust is measured and factors that affect the thrust. For example, thrust decreases with the velocity of the craft. I don't think a comparison with helicopters and aircraft with EDF's would go very far. Maybe aircraft with high-RPM propellers, but I heard that props on airplanes become more effective when you feed them air, so static testing doesn't tell you much about performance.
I've thought about two inline EDF's counter-rotating so one is supplying air to the other. But, this project is complicated enough without me looking for things like that. ;-)

A bit of background: I started to do RC airplanes about 6 months ago because of my lifting body project. I wanted to learn about RC flight, control, FPV, and gain some degree of skill for landing. So far, that's going well, but there's a lot to learn. Figure if I can do some work on the EDF rocket, other's can refine and improve this, and there's sure to be improvements in things like EDF's and batteries in the future.

Just a side note here that's interesting. I call if a EDF rocket, but neither the State of California or the FAA would consider this a model or high-power rocket. We need to consider where this fits and how it would be accepted at NAR and TRA launches. I would be interested to hear your thoughts on this.
That is an excellent question as to whether this is a rocket or a drone. The way you described your set-up, with an RC throttle, I believe the FAA and State of California will likely consider it a drone. One way to fly it legally, is to join the AMA, if you haven't already done so, and fly it at an AMA club field. This will exempt you from the remote ID requirement.

A good person to talk to is Ilona Maine at the AMA headquarters. She runs the insurance program and if she can't answer your questions, she can refer you to someone who can. She can be reached at 1-(800) 435-9262, ext. 251. I've talked to her several times regarding supplemental insurance for property owners when we are having RC events at venues other than our club field.

Rob
 

Richard Dierking

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That is an excellent question as to whether this is a rocket or a drone. The way you described your set-up, with an RC throttle, I believe the FAA and State of California will likely consider it a drone. One way to fly it legally, is to join the AMA, if you haven't already done so, and fly it at an AMA club field. This will exempt you from the remote ID requirement.

A good person to talk to is Ilona Maine at the AMA headquarters. She runs the insurance program and if she can't answer your questions, she can refer you to someone who can. She can be reached at 1-(800) 435-9262, ext. 251. I've talked to her several times regarding supplemental insurance for property owners when we are having RC events at venues other than our club field.

Rob
Thank you Rob! Yes, I just renewed my AMA membership. I joined AMA when I started to work on the lifting body project. I know that AMA also covers model rockets, but I haven't heard of a rocket launch at a AMA event - yet.

I'm also just starting my FAA Part 107 study and the material may help. I will call Ilona and ask for some guidance. The rocket is definitely a UAS but not RC guided in the traditional sense, just stabilized. It will be interesting to find out more about this. And, very important to know, because this is coming! Just like all the questions about actively stabilized amateur rockets. Think about all the raised eyebrows checking in a rocket with no fins and doesn't even require a regular launch pad. And, if I have my way, launch with a solid rocket motor and land using a EDF. ;-)
 

Richard Dierking

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Just completed another static test using the 70 mm Powerfun EDF from Amazon, a Avian 80 amp ESC, and 2200 mAh Turnigy 4 cell 40-50C battery. Also, using the 1" long tail cone with the diameter reduction based on the online exhaust calculator for a 70 mm EDF.

I ran the EDF with the control surfaces in a neutral position and then with them in the roll control config. Also, I used sub-trim on the control servos first so they were parallel to reduce as much drag as possible. Also, seemed like less vibration.

At full throttle, I obtained 1.70 Kg thrust with no roll control, and 1.53 Kg with the control surfaces active. So, again 0.17 Kg loss from the roll control.

The Powerfun cut sheet advertises 1.810 Kg max thrust at 75 amps and 16.8 volts. The motor is rated 3400 Kv (not kilovolts) so at 16.8 volts this would be 57,120 RPM no load. Wow, cranking!

I hope others try different brands, and better EDF's on future projects.
 

Richard Dierking

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I've increased the sampling frequency to 100 ms (0.1 sec) for the test stand and going immediately to full throttle. This first test was using a 64 mm 3S EDF, 60 amp Spektrum ESC, and the 1300 mAh 80 C battery. You can see the fluctuations that start at about 3 seconds. This is when the EDF starts to surge. Note: I over spec'd the EDF because it's a 3S EDF running a 4S battery. Just wanted to try. The surge is probably caused by the battery - EDF combination.

Still, the EDF comes up to full thrust (1.5 Kg) in 0.9 seconds and the thrust is pretty good for the EDF. I'll be trying some different configurations later today, then create a RASP engine file with the best one to try a simulation using Rocksim.

IMG_3898.jpg
 

Rob Campbell

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What is your amp draw? The fluctuations from the fan may be caused by your motor trying to draw more amps than the battery can deliver. Moving up to a 4S battery will not only increase the voltage, it will also cause an increase in amp draw. In my experience with electric RC, max amps for ESCs tends to be understated and "C" rating for batteries tend to be overstated.
 

Richard Dierking

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What is your amp draw? The fluctuations from the fan may be caused by your motor trying to draw more amps than the battery can deliver. Moving up to a 4S battery will not only increase the voltage, it will also cause an increase in amp draw. In my experience with electric RC, max amps for ESCs tends to be understated and "C" rating for batteries tend to be overstated.
I do have a way to measure the volts and current but it's presently bit of a pinch point for the current. It's made for a solar system and for one thing, I need to increase the wire gauge. Just got the 12 gauge silicone wire to do this. Still, every time the wire length increases it affects power.
I'm seeing some variation from the specification for batteries and ESC's but I think it's the brands. For example, I'm not a fan of the Eflite 80 amp ESC I was using. Even after repeated attempts to calibrate it, I'm still getting dead band when I start throttling up. I need a good ESC that can handle power surge.

I probably should not have used the 3S EDF with a 4 cell battery, but I was curious what the higher voltage would do, and it increased the thrust like 50%. I have some 64 mm 3S/4S EDF's coming, but they just departed China, so it's going to be awhile.

As far as the voltage and amp draw, my thinking is to use the 64 mm EDF that is spec at 3500 Kv with a 4 cell 80 C battery. I can still use the 60 amp ESC which has a lower mass than the 80 amp and get high RPM and thrust too. The maximum current is listed as 52 amps but I'm going pedal to the metal at launch. I really need the high thrust at launch for stability off the pad, then reduce during the cruise phase. At least that's my present plan. Does this seem reasonable?
 

Rob Campbell

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You should be fine running an ESC rated for 53 amps. I converted a World Models Rambler 45 to electric and flew it for several years with a Castle Creations 60 amp ESC drawing 74 amps at full throttle. They have margin built into them.
 

Richard Dierking

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You should be fine running an ESC rated for 53 amps. I converted a World Models Rambler 45 to electric and flew it for several years with a Castle Creations 60 amp ESC drawing 74 amps at full throttle. They have margin built into them.
Was that the Castle Creations 60 amp 6S?

I tried running the 70 mm EDF with a 4 cell battery and a 60 amp ESC (3s to 6s) and it was a no-go. The 70 mm EDF max amps is 75.
 

Richard Dierking

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That thing was a missile it was so fast!
I bet it was with that combination including the prop. For airplanes, you are doing pretty good if you are 1:1 with the thrust and weight. And, over that you can do tail stands and go ballistic.

I'm going to try the Avian 60 amp ESC in the rocket first. I will do a bunch of testing including measurements of voltage and current when I receive the 3S/4S 64 mm EDF.
If someone knows of a good battery with 1000-1500 mAh that's 4S and about 80C please let me know. The present battery I have is a Ovonic 1300 4s 80C and weighs 148 grams. I would like to keep under 150 grams.

Also, I'm considering some procedures for launching that may help get the most stable flight off the pad. For example, perhaps bring the motor up to under 1 to 1, then initiate the roll control servos and quickly increase to full throttle. This may help with minimizing the electrical power surge. Also, maybe reduce the throttle after launch when the rocket looks stable, and just cruising at that velocity.
 

Richard Dierking

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Update: I just ordered some Lumenier "Feather-lite" batteries 850 to 1300 mAh 4S and 120 to 150c. Mass looks pretty good, and this will give me a range to work with.
 

georgegassaway

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Since you have R/C deployment, maybe just go ahead and "launch" it.

If it starts to go badly early, you just "abort" and flip the eject switch.

Perhaps also program the eject switch to kill the throttle too.

Set up a ground camera to record the flight. Ideally two, one at the pad looking up, then one from the side.
 

Richard Dierking

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I think I'll be getting video from a drone along with the ground video. I'll have one switch for throttle cut and another for parachute deployment. I want to be able to turn the throttle cut back on to use the EDF to slow the descent if necessary. The parachute is only a 15".

I need to test the RC deployment switch; so much to still do.

If I do any launch testing, I'll post the video. Just going up to a couple hundred feet. But, I'll be doing the Rocksim simulations first.
 

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You mention wanting to be able to vary the deflection of the control surfaces... Is their movement directly related to throttle position? If so, does your Tx allow you to create a multi-point mix where you can mix control surface throw to throttle stick position (full throttle equals some amount of control surface deflection, 3/4 throttle a different amount, 1/2 throttle different still, etc)?

Or does the amount of deflection need to change dependent upon the amount of time the EDF has been running and the resulting rotational torque being experienced? Not sure there are mixes that can be activated which include time as a consideration... My R/C transmitters are older 72Mhz models that were capable in the day, but likely a far cry from what is out there presently (e.g. the Jeti).

r/
Dave
 

jqavins

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I fell a bit behind. Here are responses to a couple of things from earlier this week.
With helicopters (this is essentially a helicopter with an enclosed rotor I think) the lift is mainly caused by mass airflow, and not so much exhaust velocity (secondary effect). If you can move more mass you get better lift.

I am not sure if increasing the exhaust velocity will gain you anything in this case, as it is more akin to a helicopter than a jet. I am happy for any aerodynamacists set me straight if I got this wrong.
Well, I'm not an aerodynamics expert, or even a fraction of an expert. But basic physics I can handle. Thrust, whether in a jet, from a prop, from a rocket, or an EDF, comes from pushing a fluid; move fluid this way and feel the reaction force that way. And the reaction force is the product of the mass flow rate and the fluid's speed. Always. When the fluid has a constant density, like air that's not being substantially compressed or water exiting a hose, the mass flow is proportional to the speed squared and the stream area.

A reduction in diameter will decrease the mass flow and increase the speed, and the effect on the thrust, i.e. on the product of the two, depends on a lot of factors that I don't know more than the tiniest thing about.

Just a side note here that's interesting. I call if a EDF rocket, but neither the State of California or the FAA would consider this a model or high-power rocket. We need to consider where this fits and how it would be accepted at NAR and TRA launches. I would be interested to hear your thoughts on this.
This is truly not a rocket, since what makes something a rocket is the generation of thrust by expulsion of gas that is stored or generated on board. This is a rocket-shaped something. But then, it also gains aerodynamic stability by use of fins in the manner most frequently seen in rockets. And, notably, this is not the means of stabilization used in quad-copters and the like. This can't hover. So, I think it unequivocally not a rocket and not a drone; it's something else. What is it? I don't know, George, you give it a name. What is it in a legal and regulatory sense? Beats me! :questions:
 

georgegassaway

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What is it? I don't know, George, you give it a name. What is it in a legal and regulatory sense?
A flying Model Aircraft.

As kids, the Wright Brothers had a Penaud Helicopter, a rubber powered stick with a prop and a counter-rotating prop at the bottom, that climbed vertically,




A modern version, deleting the lower counter-rotating prop, that mostly keeps it from rotating the body but being flexible does produce a bit of crude propeller effect:

1635551562698.png


As a kid, I remember having a dime store helicopter using the same principle. Made by North Pacific, it used the same kind of props as their "Sleek Streak" planes, with the rear prop being fixed to the body, and with opposite twist. It didn't stay vertical for long, but then also those proper were smaller in diameter and spinning too fast to fly much like the Penaud copter.
 
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Richard Dierking

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You mention wanting to be able to vary the deflection of the control surfaces...
I will have full throttle control using the stick (0 to 100%). The internal control surfaces are controlled just like a elevon on the other stick. So, I also have full and independent control of their position. The throttle cut is a separate switch. It's basically a safety feature if somehow you lost control of the throttle control. The parachute deployment will be a separate switch. Initiate the transmitter switch and the channel sends a signal to the RC switch on board to fire the BP charge.

I'm only a novice at RC aircraft, although I'm learning. Again, I want to become proficient enough to fly the lifting body to landing.
 

Richard Dierking

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Well, I'm not an aerodynamics expert, or even a fraction of an expert. But basic physics I can handle. Thrust, whether in a jet, from a prop, from a rocket, or an EDF, comes from pushing a fluid; move fluid this way and feel the reaction force that way. And the reaction force is the product of the mass flow rate and the fluid's speed. Always. When the fluid has a constant density, like air that's not being substantially compressed or water exiting a hose, the mass flow is proportional to the speed squared and the stream area.
Exactly.
I believe the EDF is more like a turbo fan engine than a helicopter prop.
I also think an improved EDF could be created (with multiple fans) that would more suited for rocketry. Honestly, I don't think I have the skill and it would take a bunch of experimentation; but, I see a future for this.

A reduction in diameter will decrease the mass flow and increase the speed, and the effect on the thrust, i.e. on the product of the two, depends on a lot of factors that I don't know more than the tiniest thing about.
The thrust can be optimized including the distance after the fan, reduction/exhaust section diameter, and this may even vary for the volume and velocity of the air exiting the EDF, but as I'm finding out there are many factors, it takes some work.

After the launch and when I post some conclusions, I hope to provide some details on appropriate regulations. I need to do more research.
 

Richard Dierking

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One thing I didn't mention is the different control surfaces I tried. What I did is try different shapes and sizes of two control surfaces at full deflection and maximum thrust. I settled on the surfaces that stopped the roll and just started a reverse roll. So, I knew the surfaces were adequate for the ground test. No doubt the actual flight will be different. For example, I could have an induced roll that may increase or actually decrease the torque roll because the fin pitch. Very difficult to attach surface mount fins with no misalignment.
 

Richard Dierking

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I haven't posted for a couple days but I've been working on the rocket. Still waiting for the new 64 mm 4S EDF, so I decided to try and remove the housing on a 70 mm EDF to reduce the mass. It took some work to remove the plastic housing and replace with a lighter paper coupler and this reduced the mass from 178 to 148 grams.

However, a static test of this EDF showed a reduction of almost 0.7 Kg of thrust. I think the epoxy I used protrudes into the flow of air and creates turbulence. Not sure, but the reduction from 1.7 Kg to 1.05 Kg in thrust shows that I did something to affect the maximum thrust. Kind of bummed, but good to know I guess.

So, back to waiting for the new EDF's. Hopefully, they will be delivered on Monday.

Also, I have an idea for a new EDF rocket design I'm going to start working on.

IMG_3904.jpg

Removing the plastic housing reduced the mass 30 grams on the 70 mm EDF.

IMG_3902.jpg

Perhaps the epoxy in the paper coupling is causing turbulence and reducing the thrust.
 

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You do not have the smooth curved lip inlet. Very important.
 

OverTheTop

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What was the clearance on the tips of the blades to the housing on the original setup? It looks quite large on the cardboard version. I know on the big birds they go to great lengths to get this clearance down to a minimal distance.
 

Richard Dierking

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What was the clearance on the tips of the blades to the housing on the original setup?
Excellent question and I considered that. Both are 0.7 +/- 0.2 mm. However, the interior of the paper housing is considerably rougher. You would expect this from raw paper tube.

I guess I could have messed up the balancing, but I'm not detecting any imbalance (sound or vibration) at full throttle. I also tried a couple of different 80 amp ESC's with similar results. And different batteries too.
 

Richard Dierking

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What was the clearance on the tips of the blades to the housing on the original setup?
I took measurements again and compared to what the diagram on the spec sheet showed. My measurements were wrong in post #85.
The 70 mm EDF I have with the housing has a clearance of 0.75 mm and the modified one with the paper coupler housing average is 1.5 mm. And, may be as high as 1.7 mm. The paper coupler deflects easily. A lot more difference, so you are probably correct; the loss in thrust is the dimension change in the housing.

I think the important lesion for me is, don't mess with the manufacturer's housing set.

Maybe one could 3D print a close match to the original housing dimensions but I wonder if it would even be worth the effort.
 

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One could remove a strip from a second coupler the insert it (as one sometimes does with body tubes to make couplers) or just buy a thick wall stiffy coupler. I don't know if that would add enough thickness, but it couldn't hurt unless it adds too much.

One could coat the inside of the coupler sanding filler sealer and then sand it smooth.

One could cut the original housing and keep the little funnel front, with just enough of the original tube to slip into the front of the coupler like a nose cone shoulder.

One could attach the supports to the coupler with smaller and smoother fillets.

Or, one could could decide that a 30 gram mass reduction just isn't worth the effort and move on. Which is probably what I would do in your shoes.
 

Richard Dierking

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You do not have the smooth curved lip inlet. Very important.
Not on this static test. Since the original housing was removed it would have been difficult to reattach the inlet, which is removable because many applications require the EDF to be installed inside the aircraft.
But, I do see your point and this too may account for the loss of thrust.

I'm curious about the effect of intake air so I'm going to rig something up to supply a bit more air (with a fan) going into the EDF next time I do some static testing.

When I was at my local RC airplane flying field last week, someone had a large F86 that they had 3D printed and it had a 90 mm EDF that was installed internally, about at the location of the wings. The airplane seemed to develop lots of thrust and I noted that the intake on the forward end was about the same diameter as the exit. But, there was a smooth tube going forward to aft for the EDF.
Here's a photo of a F86.

F-86_Sabre_hertiage_flight.jpg
 

Richard Dierking

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I received the new 64 mm 3S/4S EDF and did some static testing. All my static testing is full-throttle for 30 seconds. Kind of disappointed in these results. I tried two different EDF/ESC/Battery systems with pretty much the same results:

System 1 (Higer mass):
1300 mAh Lumenier 4 cell 150c battery
60 Amp Avian ESC
64 EDF 3S/4S
Average 1.12 Kg
Minimum 1.08 Kg
Maximum 1.21 Kg
System mass 0.371 Kg
Thrust/mass is 3.02
End voltage: 15.74 V

System 2 (Lower mass):
1150 mAh Lumenier 4 cell 150c Battery
50 Amp Hobbywing ESC
64 EDF 3S/4S
Average 1.07 Kg
Minimum 1.03 Kg
Maximum 1.15 Kg
System mass 0.315 Kg
Thrust/mass is 3.40
End Voltage: 15.65 V

IMG_3915.jpg

System 1 right and System 2 on the left.

So, the second system is a bit better. I decided to use thrust/mass (no units) to compare the systems. This is important because all the other mass in the airframe, etc. stays the same. I also check how the battery recovers. You would expect that the smaller capacity battery would be less, but it was still OK.

But, I came to the conclusion that neither of these systems will be adequate. So, I decided to go back through the others I tested and perhaps even use the heavier 70 mm EDF again.

For example, look at the data for one of the 70 mm EDF tests I conducted:

System mass was 0.507 Kg and the average thrust was 1.70 Kg. So the thrust to mass was 3.35.
On the other hand, I got an excellent result from the 64 mm 3S EDF using a 4 cell battery. The rating on the motor is 3900 KV (again, not kilovolts) so with the higher voltage, this motor cranks. So, I did another static test this morning:

System 3:
1300 mAh Lumenier 4 cell 150c Battery
50 Amp Hobbywing ESC
64 mm EDF 3S
Average 1.38 Kg
Minimum 1.34 Kg
Maximum 1.47 Kg
System mass 0.351 Kg
Thrust/mass is 4.19
End Voltage: 14.81 V

It really discharged the battery to storage level, but wow, lots more thrust. The maximum is always at the start, so the 1.47 Kg thrust is going to help get the rocket going quickly off the pad. I will almost have the 2:1 thrust to mass I was trying to achieve.

So, I'm going with system 3, and I'm going to start the final assembly and test the deployment system.
 
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