HobbyKing 70mm EDF Thrust Tube Diameter Test

Doing a bench test for the 70mm edf combo to see what diameter thrust tube will provide best thrust. Discovered that most likely there will be a certain compromise between the best thrust and speed depending on model weight. On my Mig I probably could have had slightly better speed using a 58mm tube.

[@robajohnson]

Thank you! Excellent measurement of static thrust for this unit! Very helpful!

[@SohStress]

Great testing! There's something to keep in mind thought. You're testing static thrust, not dynamic one. At the same given power, a narrower tube makes speed go up and thrust go down, on the static test. Also, narrow cones increase backpressure on the EDF. This means less static test airflow, but, it gets up as soon as the plane speed goes up, a bit like high pitch props. Static thrust without speed, on jets, only helps on takeoff and landing. Once again, congrats on the tests!

[@RStephenLegge]

Good experiment with good relavent data. Thanks for taking the time to put this together. It is all I need to design my thrust tube.

[@jayrothwell]

I'll be adjusting my thrust tube according to the results of this vid! Great testing

[@urbanaeronautics7097]

Nice test and some great responses and comments. How well the manufacturer designs the thrust tubing is one of my criteria for buying a plane...except for the F-22, F-18 or other split tubing 64mm plane. My Freewing F-86 80mm EDF has the best overall design for moving high volumes of air, it has one long tube that gets about to that 80% FSA but it uses 18 inches to do it. I believe John Wells' comment is correct, we should be looking at EDF's more like tail pipe tubing or like turbo tubing. Thanks for the video.

[@GregStrysky]

Glad it was helpful! At some point the formulas have to be set aside and the scales have to come out! I learned a lot that night. I just did a twin edf su37 from Boxermad84 today.

[@MohitDewan]

Awesome vid! I'm not sure it's quite conclusive but it does seem that way.

[@hklausen]

Have you consitered the effect on the trust from the length of the trust tube?

[@doctorvox]

If you make the thrust tube like the tailpipe of a gas turbine (jet) engine, you may get better performance? The tailpipe is not fixed to the motor but is spaced an inch or two away and gently increases in diameter (like a megaphone) before continuing straight. This allows more air to be drawn into the tailpipe.

[@GregStrysky]

That's true. I never wanted to spend money on amp meters when there is all that depron to buy!! I usually don't push the systems too Much. But I was a bit surprised by the results. Thanks for watching!

[@yunanaminuddin8507]

Thank you very much your video is very helping me so much

[@wraith657]

No. You get increased velocity narrowing the tube, but you lose static thrust. You regain speed at the top end while flying with a narrower tube, but you lose it in the bottom end statically. It's just like gearing in a car. Top gear is capable of higher speeds once you get moving, but lower gear is better to get moving, which is why real jets can adjust their thrust orifices. The newest jets can adjust the pitch if their compressor blades, and stators.

[@GregStrysky]

Yes, this is a static test. Numbers would be different with airflow.

[@Asadullah21]

I think when air is flowing over the EDF when the plane is in the air the very last test without a thrust tube could look very different.

[@erh7771]

The compromise is between thrust and air speed from the exit of the exhaust tube, the plane can go no faster than the air speed or efflux. If there is a reduction in both then there's a loss in usable energy out and just waste watts.. To measure the airspeed there's the pitot tubes from Eagle Tree Test systems that is pretty inexpensive and will give you air speed or efflux from the end of the thrust tube

[@helijatek]

excellent job! you just saved me a lot of time testing. it would be nice to know how much of a change we can see in the amp drawing?

[@sidewayz180sx]

Conclusive and proven results! Great!

[@sotm6078]

NOTE: That you are measuring only Static thrust here. The smaller dia. will increase velocity and speed once you are airborne and accelerating!

[@RStephenLegge]

Even though the thrust is decreasing as the thrust tube outlet decreases, theoretically the exhaust speed would be increasing. More thrust would make for a shorter takeoff distance, and less thrust would increase the top speed. The sweet spot is supposed to be around 85 to 90% FSA (Fan Swept Area)

[@GregStrysky]

You are exactly riht-kfc cup but it does what it's supposed to do. Reduce the diameter for testing. I am not testing the optimal thrust tube design otherwise I would have used a longer tube done with rolled plastic like on my su37.

[@Kcburnit]

Smaller nozzles provide higher speed larger nozzles provide better acceleration. The trick is to find a balance. The best way to test this is with a radar gun or air speed sensor and an adjustable nozzle. measure the speed of your aircraft as it flies

[@SkipBuiltRC]

Didnt take into consideration air speed and the velocity of air being packed into the edf to produce more thrust with a slight restriction in the nozzle...??? Just a thought.

[@txtrm]

Hi, do you know which maximum static pressure this turbine (or other edf turbines) can build up? Thanks

[@moonscrafts8987]

Please explain it in grams which is international unit

[@bergfald]

Thanks for your effort, very helpful.

[@gisall8205]

The proof is in the pudding. GFREAT video.

[@robertxxx2076]

good video bro, it seems like you need some combustion in order to encrese the trust...

[@FairviewRCflier]

Loved this test!!! I wanna send you my 68mm unit to test... Maybe you can find a plane for it....RCLanders edf

[@GraemeRobinson]

Hi Greg - I use ear protection! Just did a static test of my 70mm HK set and I'm not getting anything like the thrust you are getting, unless I'm misunderstanding your US weights - what was your maximum thrust in grams? Something over a 1000grams? Thats my rough estimate on your numbers - I'm only getting 400grams of thrust so no wonder my Eurofighter isn't flying.

[@TheKindom767]

use a fan with more blades. they have more static pressure

[@GregStrysky]

No I don't nishbrown. Just my ears! I was a little nervous down there at 50 mm with the sound of the wash coming out!

[@nishbrown]

Do you have any tools to measure the velocity changes?

[@GregStrysky]

Hello Graeme, I'm getting almost 1200g but Jay says he's getting only 1000 or 1100. Are you using 4s?

[@mice1m1]

great i can show friends how 85% is the best spot ..(.for that fan ).lose a little bit of on the bench static thrust for some up in the air speed but still not enough to stall the fan..perfect...

[@rva1945]

He is using a scale, isn't he?

[@ArguZ72]

Please get the metric system ASAP...

[@thaister88]

Please try again with a better thrust tube looks like you just slapped a kfc cup on there with a zip tie