Well it is kind of progress. I ran a test with 2 fans inline and got the following result. It was the max thrust of all tested configurations. The only one I was not able to test was 2 3blade 3pictch fans together.
Front fan
3 blade 3 pitch
Rear fan
5 blade 3 pitch
Thrust without inlet lip, thrust or tail cones
104g or 3.7 oz

Three blade 3 pitch fan in duct by itself
76g or 2.7 oz

Now the question I have.
With both fans inline I get 1 oz more thrust but 1 oz more auw.
Running the numbers 3.7/10 (auw) I get .37
2.7/9(auw) .3
Is the minor thrust gain from the extra fan worth it?

Thanks,
Isaac.S
Below are a couple of pictures of my plans

Close up

another

Originally posted by isaac-bees
Front fan
3 blade 3 pitch
Rear fan
5 blade 3 pitch
Thrust without inlet lip, thrust or tail cones
104g or 3.7 oz

Three blade 3 pitch fan in duct by itself
76g or 2.7 oz

Have you tried to reverse the fan order and measure thrust differences? It doesn't sound like you are getting that much more thrust from a second fan.
ps: where did you obtain the nice 3-view drawings for the XL? I have one in the works too.

I just came up with another idea for increasing the thrust for the edf50. Firstly will require one edf50 with motor CN12RXC and highest pitch 5 blade impeller, a second motor of identical model # and lastly about 50mm of 1.5mm dia s/s rod with the ends rounded.

First task is to dissassemble the two motors removing the shaft from themthen reassemble both motors onto the same shaft. Make some slight modifications to the duct to hold both motors stationary. assemble the whole thing and hey presto. Should not be above 50grams in wieght but should give about 150-170% thrust of original.

Can't seem to order the motor over here from my hobby shop or else I would already have ganged a handful of em.

Marc

Hi Isaac,

Some interesting results, but I don't think the inline EDF's is worth it. Not only do you have the increased weight of the EDF unit, but batteries and possibly a larger ESC (hey, every gram counts!)

I think you have shown something that hasen't been seen before...all the test results we've see so far are static thrust (the EDF unit stationary). What you've shown is the thrust of the EDF when it's "in motion" so to speak.

Static thrust only matters for the first second or two when the plane first starts accelerating. The thrust we should be most interested in is when the plane is in motion. You've shown that the thrust INCREASES cosiderably once the plane is in motion.

I'm going to have to get some of these 5x3 impellers myself!

Thanks for the info! Any info on the current draw of the 5x3 impeller on your inline setup?

Zbrubaker,
I am not sure that the thrust would increase.
It apears at first glance that it should but, if you have your influx is at say 30 mph, (from what I have heard the outflux of one fan is about 30mph) your little 5 blade impeller is going to spit out 3.7 oz of thrust. But when you consider what kind of airflow that 3.7 oz is going into would it really be a whole 3.7? I don't have physics yet so I don't know.
I got the 3 views from nasa just search for f-16xl 3 view and you'll find it. Does any one have any info on the wing? My views are not good enough and I would really like to make it scale.
Isaac.S

Isaac,

If you can spare the time, test the EDF with the 5 blade rotor by it's self (thrust & current draw). Then test it with another fan running in front of it to simulate forward motion, and check thrust and current draw.

Only problem, I don't have a current meter. I'll see if I can do it at a friend's place.
Isaac.S

If you use my previous idea in the previous post but instead of just adding the two motor togehter include the 5 bladed impeller as well so that all are on the same shaft. This will have the effect of using the rpm gained from the second fan to help with the first and as the two fans are doing the same rpm you should get increased thrust. Or somthing like that any way, with 50w going through it it must get better that 104g.

I am borrowing my friend's meter for the weekend. Hope to get some current draw stats. Oh by the way those results were using a 1100mAh 6 cell pack.
For those of you who wondered about reversing the order. 5 blade first 3 blade second. I got 94 g of thrust with that, and 100 g with 2 5 blade impellers.
marc I think if I was going to go that way I would try to build a impeller myself. I have been wanting to build a semi compressor setup using 2 motors, but since it is for the contest, it has to be commercially available.
Zbrubaker, I talked to a friend and he said in most system thrust increases with speed slightly. So, I was thinking, I wonder what the 2 fans would output in flight? Might be interesting! I unfortunantly don't have a 3rd fan to test it
Isaac.S

I finally got to testing the fans some more tonight. I realized the reason why the results are deceiving. The thrust measured was from BOTH fans. To really simulate thrust the 1st fan should not be considered. So I changed my setup. I held the 1st fan to the 4 inch duct were the other fan was running. Here is what I got.
with the 5 x 3 impeller, 30 g of thrust drawing 3.34A.
The fans were not both running through the amp meter, only the second one.
That is that bad news, not more thrust inflight. But the good news is that I think inline WILL produce twice the thrust in flight.
If one fan gives 30 g of thrust at the speed of say 30 mph, if you had two fans running inline they would both have 30 g each right?
At least it seems that way. What do you guys think?
With the long weekend I was able to spend some time cutting out formers. My dad looked at it and thought it looked like it was really going to be hard to do, but then again that is why I like the hobby. I do have to admit though, if I had seen the 3 views without any prior building experience I would be a little lost too. Who knows maybe I already am?
Isaac.S

Static thrust is not that important. It's the plane in motion that
matters. Perry at Aeromicro told me this. He said that an A-10
he saw fly on two EDF-50's did very well, better than they
expected because it's the moving through the air that makes
these little fans really shine.

(now let's see how my AN-225 will do soon! I sure hope so!)

Hey isaac-bees where ya fly at in newport. You are the closest e-zoner i have ever ran into

Here is what I got with the 5 x 3 impeller, 30 g of thrust drawing 3.34A

I dunno...something there doesn't seem quite right...30g of thrust? That's barely over 1 oz.

But the good news is that I think inline WILL produce twice the thrust in flight.
If one fan gives 30 g of thrust at the speed of say 30 mph, if you had two fans running inline they would both have 30 g each right?

providing that the second fan has a higher pitch that the first fan, there will be some increase of thrust, but not as much as your thinking.

Let's see if I can explain this simplistically (so I don't confuse myself)...if you have a car moving at 30Mph, and you put a car behind it moving at 30 Mph, they will be moving at??? You guessed it - 30 Mph.

With the EDF setup, the first fan gets the air moving at 30Mph...the second fan also wants to get the air moving to 30Mph, but the air entering it is already moving at 30Mph, so in effect, the second fan does nothing.