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Old Mar 30, 2012, 05:59 AM
The blade numbers go up to 11
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Originally Posted by monkamarm2000 View Post
As I posted above I asked the questions to learn more about the limits of our gear..Would I like to see a couple more pounds of thrust from the 70 or 80mm fan?Absolutely..Do others??Absolutely...Why would we be trying so many combinations of fans and motors to eek out those last grams of thrust from our present systems...Everyone wants a little more..Just human nature to push things ,within

Hover

Well I wouldn't, cause if I made more pounds, then it'd take more power to make those pounds. And now I added some power but added weight to just a 70mm fan. Now I have to ask how heavy can the 70 mm plane I'm putting it in weight, or can stand to weight. Now tell me a nice new way to have same weight but 1/2 pound more thrust and bump in efflux to match I'm in. Depends on what we want the fan to do really. If we're not caring bout weight and just how much air to push for thrust alone then that's one fan, if you want thrust and efflux in manage weight, and realistic to power with a motor you can get your hands on that's EDF. And yeah can't look at jets or bypass at all, different speeds and they really have 2 motors in one cause fans design is to get them up there, after that it's all efflux, so they don't care if pitchy fan falls off at altitude.

Barry


Barry, I'm gonna have to get my book out to help me understand all of that

Stu.
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Old Mar 30, 2012, 07:07 AM
it wasn't me flying that plane
Hover or die's Avatar
United States, NC, Wilmington
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Stu
Could you pass along a copy or at least post a translation..

can you imagine being stuck with the fans from just 7or8years ago..and being told that's all there is...it can't get any better..sheesh..
I am interested in what's next..not being told its senseless to want the next great thing to come along..there's always room to improve...
Can you imagine the 70mm only putting 2.8 to 3.0 lbs of thrust..I think not....
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Old Mar 30, 2012, 11:14 AM
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Better batteries, motors, ESCs and fans will certainly help, but I'm betting on better understanding of aerodynamics to be the biggy.

If you look at EDFs with 'new eyes', it is evident (at least to me), that there is a lot of improvement to be had from smoothing the air flow as it passes through the fan.

Stu made a big advance with his original fan, by putting the stators in front of the fan. This has a benefit of getting the stators away from the extremely turbulant air just downstream of the fan.

BV made a big advance by smoothing the air flow around the blunt spinner, right in the middle of the air stream. The inlet ducts now guide the air around the spinner, making for a smoother flow.

Then (my own personal favorite) there is the enigma of the bench test always showing the highest thrust figures, when it gets into the air, the thrust goes way down. Most of us know why this is so, but why do we accept it?
The good Doctor Einstein once said "given the same conditions, the physical realities are the same wherever you are in the universe"
Transfering this idea to EDFese; the good doctor says what you have on the bench, you should also have in the air. Providing , of coarse, that conditions are the same in both places.

So (in my view) the challenge is upon us; make airborne conditions the same as what you have on the bench, and you will have all the power that you could ever want.

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Old Mar 30, 2012, 11:19 AM
Carbon fiber is our friend
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Quote:
Can you imagine the 70mm only putting 2.8 to 3.0 lbs of thrust..I think not....
Yes, that's how minifans are supposed to work. We hear about 7lbs thrust, but it takes a huge battery, a motor running on the verge of meltdown and flies for 2 minutes.That's not efficient. If you're going for a speed record, then you do whatever it takes, but otherwise it seems silly.
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Old Mar 30, 2012, 01:01 PM
EDF rules... :)
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Joined Nov 1999
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Ron,

Considering that the aircraft can only fly as fast as drag will let it(The aerodynamic equation is thrust force/drag, lift/aircraft mass, when thrust force = drag of the airframe there is no more acceleration) then you must increase thrust force to get more speed, thrust force is a product of the air mass being moved thru the fan and its velocity. Increase the mass or increase the velocity and the thrust force will increase and thus more speed.

Cheers,
Eric B.
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Old Mar 30, 2012, 02:41 PM
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Yes Eric ~

The aircraft will accelerate until drag = thrust. Totally agree.

What I was refering to, is a loss of thrust while the aircraft is airborne.

Such loss of thrust being caused by relative motion of inlet air (air is already moving, so the fan can not get as good a grasp on it)
Conversely, surrounding air near the outlet is already moving away from the airplane outet, so there is less to push on.

Think of it like this; If the surrounding air was moving at the efflux velocity, how much thrust could the fan produce? To my way of thinking the answer is zero.
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Old Mar 30, 2012, 02:55 PM
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Quote:
Originally Posted by Ron Pogue View Post
Yes Eric ~

The aircraft will accelerate until drag = thrust. Totally agree.

What I was refering to, is a loss of thrust while the aircraft is airborne.

Such loss of thrust being caused by relative motion of inlet air (air is already moving, so the fan can not get as good a grasp on it)
Conversely, surrounding air near the outlet is already moving away from the airplane outet, so there is less to push on.

Think of it like this; If the surrounding air was moving at the efflux velocity, how much thrust could the fan produce? To my way of thinking the answer is zero.
then would it make sense to have larger inlets so that the air is forced to slow down as the size chokes down to fan diameter? (i realize this creates drag)
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Old Mar 30, 2012, 03:13 PM
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Inlet size is reduced on fast EDF airplanes, smaller than fan swept area. Outlet too.
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Old Mar 30, 2012, 03:16 PM
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Wind tunnels were created to help expand the test bench conditions for just these sorts of issues. It's just that most of us can't afford to have one in the garage or basement : o Too bad as it might help advance things a bit further in EDF or any sort of modeling for that matter.
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Old Mar 30, 2012, 03:35 PM
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Quote:
Originally Posted by Ron Pogue View Post
Inlet size is reduced on fast EDF airplanes, smaller than fan swept area. Outlet too.
yeah i know (i guess something to do with drag and creating a vacuum before the duct?!) which doesn't make sense if we think that the closer intake speeds are to eflux the less thrust we get!

right?
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Old Mar 30, 2012, 05:02 PM
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Yeah DB ~

Wind tunnels are good to have, even the Wright brothers had a home-brew wind tunnel.

Well Lightning ~

As a friend of mine used to say "Not knowing, I hesitate to say"
Thanks Mort
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Old Mar 30, 2012, 05:30 PM
it wasn't me flying that plane
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United States, NC, Wilmington
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Steve C,
I'll meet you halfway on that..I do agree on some points..My 70mm puts out 6 lbs in the aircraft,is it hard on batteries??Kinda..I did fly it on 2200 6s for many flights and yes they were 2-1/2 to 3 minutes..But we are talking 2200's and yes I got the 6lbs with the small batteries...45c thunder power..My new 3300 65c's seem to be just fine as long as I'm not running wide open the whole time..lol..(70mm 2900kv 2000watts,,,70mm 3300kv 2400watts)Through eflite delta V-15 fan
My 2200's are still going strong after being used in the jet for many flights,now on pusher apps..You do not have to have large batteries,just not abuse the smaller ones and not run combos that create extra-high amps..I think 5 to 6 lbs is fine for 70mm and 50,000 to 60,000 rpm..but i can see that there are applications where the 3.0 are enough,especially for those new to EDF,,I just need a little more...Everyones different I guess...I also now understand that the larger diameter EDf's do not need the high RPM of the smaller fans to "produce"..Just part of the learning curve..And I still have a lot to learn..
Take care.................Chris
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Old Mar 30, 2012, 05:44 PM
Capt. Z
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Tonopah, Nevada
Joined Dec 2004
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Quote:
Originally Posted by db_sonic View Post
Wind tunnels were created to help expand the test bench conditions for just these sorts of issues. It's just that most of us can't afford to have one in the garage or basement : o Too bad as it might help advance things a bit further in EDF or any sort of modeling for that matter.
Hey if this 8th grader can build a wind tunnel I would think we could build one for an EDF unit

http://www.youtube.com/watch?NR=1&fe...&v=UQsvIH4Of1U
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Old Mar 30, 2012, 06:14 PM
EDF rules... :)
AirX's Avatar
Joined Nov 1999
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Quote:
Originally Posted by Ron Pogue View Post
Yes Eric ~

The aircraft will accelerate until drag = thrust. Totally agree.

What I was refering to, is a loss of thrust while the aircraft is airborne.

Such loss of thrust being caused by relative motion of inlet air (air is already moving, so the fan can not get as good a grasp on it)
Conversely, surrounding air near the outlet is already moving away from the airplane outet, so there is less to push on.

Think of it like this; If the surrounding air was moving at the efflux velocity, how much thrust could the fan produce? To my way of thinking the answer is zero.
Hi Ron,
The airplane will never fly to the limits of available efflux, the thrust force will equalize to drag force well before that happens. Same thing happens with turbofans except that the core thrust will help continue acceleration again till the thrust force equals the airframes drag.

Cheers,
Eric B.
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Old Mar 30, 2012, 09:02 PM
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Quote:
Originally Posted by db_sonic View Post
Wind tunnels were created to help expand the test bench conditions for just these sorts of issues. It's just that most of us can't afford to have one in the garage or basement : o Too bad as it might help advance things a bit further in EDF or any sort of modeling for that matter.
+1

What would have to go into basement wind tunnel for EDF?

100 - 300mph wind to simulate EDF in air speed, a 12" clear tube and some heavy smoke?

I think tams A-4 on 4000 watts prove we're not using energy we're putting into these fans as efficiently as we can
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