All FLPHG stuff goes here
User avatar
By Watson
#385907
Hi Jeff,

I've got 2 of the Schuebeler 12.8cm of diameter HST fans (with biggest engine). But I've ordered mine with a nice nacelle for even better performance on open airstream.

I work with real aircraft engines (Pratt & Whitney) and wouldn't be so concerned with blades flying off. They are very light because of high tiny they are and, the shroud should be strong enough to hold them if they break.

I would be more concerned with choosing the correct power system (ESC, batteries and cables) for the current that you intend to draw. The last think you want is to start a fire in flight because you cheaped out on a wire :D

One interesting thing that I saw after my first bench test is that the sucking power is usually overrated, you can only feel the wind when you are only close to the fans (like 1 or 2 inches).

These ducted fans tend to suck air from all around its front, so the speed is very low all around and having another one close won't cause any problems. However, the exit has a very distinct unidirectional flow, giving its extraordinary thrust for such a small thing.

Watson.
User avatar
By flyit
#385931
I noticed your engineering credentials after I had posted. I am so enthused to hear your progress and advice in this project. I told my wife Im not crazy there is somebody else out there trying this and he is an air space engineer !!

The units I have are spec. at 10# thrust. each , I did purchase the advised 120 amp opto ESC and Turingy multi rotor 6s 8k amp 22.4 volt battery iin series to get 48 v. My first EDF tested around 10# on bench as per the description on hobby king. I have not combined the units on the bench yet. or run extended time at max rpm for heat testing the entire system.

If i understand you correctly, there is little concern about the blades flying forward out of the fan in the event of turbine shattering during operation, and not much concern of intake air flow robbing the adjacent unit if I keep the units about a foot apart ?


Jeff
User avatar
By Watson
#385953
Jeff,

You are definitely not crazy, EDFs haven't been used by hang gliders yet because only recently the RC ones became powerful enough to push us. And we are not the only ones, look up for "paraglider thrusters" on YouTube and you'll find a guy that used the same engines as me for a paraglider and it worked!

About the concerns, you've got it right, at least in my opinion. Imagine throwing one fan blade of your EDF on someone with the full force of your arm, it is going to hurt, but it's not going to cut or pierce; however, if you had a regular jet engine fan on your hands, the damage would be quite different! :-o Because the RPMs are very similar (~30k), this is actually a good way to compare.

The robbing of airflow is a non-issue, but while we are in the subject, I'm concerned with where and how do you intend to attach your engines. In any aircraft, the best point to put them is in an imaginary line that crosses the center of gravity and points in the direction of the airflow. So, unless your glider is heavier than you, don't attach the engines to it, it is way more controllable to attach to you.

Another thing is that I had though before about using 4 of the same ones that you've got, but my idea was to have them around me while prone (2 in the back, plus 1 on each side) instead of a square. The reason for that is because when they are off, they become a nice drag component, so it is better to keep them close to you, where the airflow is already slower because of your harness drag.

Watson.
By DavidScott
#385959
What are the differences in efficiency between a larger propeller and an EDF? I think the propeller has a significant advantage.
User avatar
By drachenjoe
#385971
DavidScott wrote:What are the differences in efficiency between a larger propeller and an EDF? I think the propeller has a significant advantage.
I am afraid you are right.
Large Props (> 5ft) can give up to 75% Eta, smaller ones (3ft) around 50%, ( results from PropCalc...)
EDF maybe 25% or even less. ( my estimation...)

PS: still waiting for a battery with 500 Wh/kg :)
User avatar
By Watson
#385996
I'm sorry drachenjoe, but the EDFs with newer brushes engines are 92-97% efficient at design speed. Don't just take my word for it, look at the website of major manufacturers and you'll see by yourself. The truth is that propellers suck when compared to ducted fans, just check how many fuel efficient aircraft have propellers on them: none.

The physics behind it is that a propeller blade loses a lot of energy by pushing the air radially outward, while on ducted fans, the duct increases drag by a small amount but doesn't let the same thing happen. And if you have some stators to deswirl the flow after the fan, you get these amazing efficiency numbers.

However, ask any experienced RC hobbyist or pilot, the way they fly is significantly different. On a propeller, you have a feeling of immediate thrust, so you can pull up and up you go, but you reach max speed very quickly and, once you are there, the propeller acts as a drag feature stopping you from accelerating more. In the other hand, ducted fans seem to lag a bit on the power side because you have to use your wings to generate lift, in order to gain altitude, but the max speed of the flight is Mach 2!

Watson.
User avatar
By Wagner24314
#386003
Watson wrote:The physics behind it is that a propeller blade loses a lot of energy by pushing the air radially outward, while on ducted fans, the duct increases drag by a small amount but doesn't let the same thing happen. And if you have some stators to deswirl the flow after the fan, you get these amazing efficiency numbers.\

Watson.
I made a prop that fixed this issue https://www.youtube.com/watch?v=271cIlKqSr4

https://www.youtube.com/watch?v=Jk7sCCr-p-s
Attachments
20150902_184544.jpg
20150902_184544.jpg (2.43 MiB) Viewed 2435 times
20151004_123753.jpg
20151004_123753.jpg (3.2 MiB) Viewed 2438 times
20150407_070423.jpg
20150407_070423.jpg (2.54 MiB) Viewed 2456 times
User avatar
By Toomb
#386012
Would you guys hurry up and figure this out, so I can build one? Seriously, it would be amazing if you can actually do this with off the shelf parts. Best of luck, and please continue to share...........
User avatar
By flyit
#386063
I did a full bench test of my two 90mm dr mad thrust with 120amp turnigy OPTO esc, 2 x 8000 mha 22.4 volt multi roto 6s batts in series. ( two separate systems, all same components each system weighs 7 # all total everything on the scale )
The results are 9# thrust per EDF on fresh charge. First test , they we set 14 " apart, the best combined thrust was 18#, so they can be run closer together than I thought. I spread them to 32" apart for second test, and thrust was less at 14# combined( humm ) all I can figure was that I was loosing battery after several thrust test of 45 seconds on the first set up.
Total run time was about 7 minutes. 5 min, of that was wide open max both systems.
I Heat tested the edf, ecs and battery packs with digital thermal scanner several times during max rpm run ( 5 minutes ) and none of the components rose about 100f . except for one ESC ( 127 f ) I did not place that ESC in the thrust stream for cooling. that made a huge difference. ( Esc in jet stream remained at 78 f , 1 foot behind EDF directly in the stream, ). in fact the warmer system shut down first, I will post a vid. or still shots shortly.

They pulled the testing jig ( on casters ) straight ahead without yaw at same rpm. If one slows it will yaw the glider ( when other unit is putting out 25% more thrust ( I observed this only in my second test, at EDF width of 32" apart )
I doubt a yaw effect would be as significant at 14" apart.

My thoughts:
For sure the 2 EDF can be useful for assist in thermal hunting after mountain launch. It seems plausible that 4 of these 90mm aluminum Mad Thrust units would give 36# thrust off fresh batteries and may work for flat land foot launch ( my reason for this whole test )
The 4 unit harness would weigh about 30# and yes it would have some drag. but probably no more than a 36# prop. ( My EDF are about the size of a softball ) I now imagine my harness would look something like 10" wide belt around my upper thighs two EDF units on top , two on bottom. Yes a jet pack strapped to my ass. LOL. And the dreaming my become reality, low profile simple power assisted HG flat land launch.

woo hoo
By DavidScott
#386073
How many amps per kw of thrust? In the attached link Reidar Berntsen gets 3.4 amps per kw of thrust, total of 40 kw thrust, using a Rotormax 150 with a Mosie gear reduction and prop. When he rewound the motor he got 2.5 amps per kw of thrust, around 26 kw total thrust, direct drive with a 2 blade prop and better efficiency with a 3 blade prop. From what I have seen these setups are the gold standard for electric powered harnesses.

https://www.youtube.com/watch?v=WgNMc35zqYo
User avatar
By flyit
#386076
David , I mentioned earlier in this thread, I would like to find a source to buy the mossy reduction drive or even have one built, I don't think they are easy to find. but the down side of all this e stuff is that the flight time is very short. Period. If I were going to go with custom build reduction drive I would ago with gas.

Im not doing R+D. Radnier is an engineer, I would say 97% of pilots hoping to build an e help harness can't rewind their own rotomax.

I will avoid burring out esc and blowing up batteries and so on using off the shelf max output battery products Exactly as mfg recommends to connect these components up. so the kWh thrust is a moot point, not relevant in this test, not an issue, We can not change these components , and the actual thrust outcome of my test IS ALL THAT MATTERED to demonstrate that EDF can be ganged up, multiplied to achieve a functional level of thrust to merit full testing of this opportunity.

The goal of my putting the test into action is the hope is to achieve FLFL, bypass driving to the mountain and messing around with winch or aero tow.

We can achieve 5 to 7 min of good climb rate, get to altitude. Wallah.
If is does not happen... ok we tried. Didn't sit around blogging about other guys test. I have no doubt that EDF will be used to extend flight time for Mountain launch , ridge soaring, already gliding at altitude. it is neat, compact, no keel cut, just strap up and " FLy It " . awesum.

Kindly

Jeff
Last edited by flyit on Mon Apr 11, 2016 7:21 pm, edited 1 time in total.
By DavidScott
#386086
I posted Reidar's info since it is the best baseline I have found to compare for efficiency. Since the power source with batteries is pretty limited then you must maximize efficiency. Since you have an electric motor without power pulses the most efficient reduction method would be gears, v belts waste quite a bit of power.

In this video https://www.youtube.com/watch?v=PNnqWsAmvgs Reidar is able to launch from the airport and fly for 35 minutes in still air using 70% of his batteries, I think they have 47 ah of capacity, so longer flights are now possible with the right design.

I am curious if a power backpack "kit" would be popular enough to be viable? Everything but the power source. It would adapt to most harnesses, neutral cg, weigh around 6-8 lbs, be fully contained, and jettisonable in seconds if something went wrong. Say around $1000 or so without a prop if the kit idea would reduce liability enough.
User avatar
By flyit
#386118
I have followed his research fully, Even though he did get that 37 min flight on the E help 2, he goes on tho say the 150 rotomax / direct drive E help is barely enough to consider as a flat land foot launch design. I am still thinking EDF to get up to altitude can work. I will probably invest in the other units later this summer. Until then I will be using the two units as " zero sink system " after mountain launch.

I also am chomping at the bit to try two 100cc rotomax direct drive with 24x10 pusher props, one counter rotating , I think this can be more than enough to get to altitude. E help just published a traditional front side twin test. plenty of power, bulk clunky look. It looses the HG coolness.
A better version of this can be seen on youtube under wasp wing glider. Uses two 150 gas with 36" props, mounted closer to CG. I email the owner and he is very willing to share info.

I have been flying RC with lipoly batteries for about two years in a pitts biplane. never seen a fire, they do get hot, lol
So Im not really worried about the battery issue as long as you stick with the mfg specs and charge them with a balance charger. protect them from the obvious.

you will have about 22# battery weight in any scenario.
User avatar
By Watson
#386163
I'm sorry Wagner, but you haven't solved any problem, you just minimized with diminishing the airfoil profile, however the air will still get pushed a bit sideways, resulting in less total efficiency. By the way, you could improve your design by not using a flat bottom airfoil, but the problem that I was referring to is intrinsical of any wing.

Jeff, I've also sized my setup to be a winch replacement, so also only for 5 min of max power. However, with ducted fans, the more airspeed you have coming into the engine, the more trust it produces and, you might be able to ease on the throttle, so don't be surprised if you get a lot more juice on the batteries than what you sized for.

Remember the trusts that we are using for the calculation are static ones, once there is additional airflow coming into the engine, things change a lot and, that is where ducted fans will always outperform propellers.

Watson.
User avatar
By Wagner24314
#386177
watson ever heard of a flat winglet
User avatar
By flyit
#386184
Watson I love what your doing here, makes total sense and any additional speed gained as speed picks up more speed on the EDF, will keep me from landing on my face, lol

Look forward to discussing results further.

Jeff
User avatar
By flyit
#386259
Ok this is a Response from the Man, The Legend of E help. I have been on his youtube subscriber list for a while. I posed the question about my project. He was kind enough to weigh in on the subject.


Reidar Berntsen
Reidar Berntsen1 day ago
+Jeff Reynolds 36 ibs on that big 190 footer will be about what it takes to cruise. Depending on Your body weight above or under 80 kg. Above 80 do not try a flatland start. Too much drag in that wing to overcome high aoa periode in start. Fly it off from a ramp rather. Fuel burn/ ampere draw is high with ducted fans. Looked at the numbers before and it is not so efficient as props, big diameter props that is
User avatar
By W9GFO
#386455
Watson wrote:I'm sorry drachenjoe, but the EDFs with newer brushes engines are 92-97% efficient at design speed.


There is no way that an EDF is 90% efficient. Perhaps the motor itself converts 90% of the electrical energy into rotary motion, but that does not make a 90% efficient ducted fan.
Watson wrote:Don't just take my word for it, look at the website of major manufacturers and you'll see by yourself.


The people that are trying to sell you something are not necessarily the best source of unbiased information.

Thrust is produced by accelerating air rewards. You can either accelerate a little bit of air a lot (turbofans, EDFs) or you can accelerate a lot of air a little (turbo props, helicopters, pretty much every single engine aircraft). You need to match the thrust producer with the flying characteristic of the aircraft to get the best efficiency.

Consider boats. A racing hydroplane and a tug boat my have the same amount of horse power. The tugboat will have a huge prop, the hydroplane a tiny one. Each one is as efficient as can be designed. Swap the props between the two and neither would work. Putting a duct around the tiny prop would make no difference.
Watson wrote:The truth is that propellers suck when compared to ducted fans, just check how many fuel efficient aircraft have propellers on them: none.
Turbofans are not efficient at low speeds, that's why you see them on aircraft that move very fast. When you see them on slow moving craft it is a novelty. Turbo props and regular props are much more efficient than turbo fans at slower flying speeds. Thats why you see them on commuter aircraft and light aircraft. Many, many fuel efficient aircraft use props. Turbofans combine the benefits of a jet engine (high power, low weight) with the benefit of a large prop (efficient thrust).

You will NEVER get an EDF to be as efficient as an open prop at the low speeds that hang gliders fly at.