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Old Apr 20, 2011, 07:12 AM
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Old Sep 05, 2011, 06:43 AM
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Rock On- Damon Atwood
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Here is an update with the A7.

Over the last month I got most the the wing designed in Compufoil. The wing is very cool. I should start pulling the Compufoil info into CAD next month and then in to my 3D design after that.

Thanks, DAG
Old Nov 17, 2011, 04:24 PM
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Just noticed you were working on this plane while going back through the B-36 thread. You are crazy! Or a genius! A crazy genius And not evil Wishing I had your life sometimes.. thanks for sharing and remember to ignore the trolls because they are a very small annoyance compared to the inspiration and excitement your projects bring to so many.
Old Nov 18, 2011, 11:10 AM
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Rock On- Damon Atwood
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Originally Posted by seeingeyegod View Post
Just noticed you were working on this plane while going back through the B-36 thread. You are crazy! Or a genius! A crazy genius And not evil Wishing I had your life sometimes.. thanks for sharing and remember to ignore the trolls because they are a very small annoyance compared to the inspiration and excitement your projects bring to so many.
Thanks!!

Dag
Old Nov 19, 2011, 09:41 AM
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Originally Posted by seeingeyegod View Post
Just noticed you were working on this plane while going back through the B-36 thread. You are crazy! Or a genius! A crazy genius And not evil Wishing I had your life sometimes.. thanks for sharing and remember to ignore the trolls because they are a very small annoyance compared to the inspiration and excitement your projects bring to so many.
Can't say it any better than that!!!!!
Old Jan 19, 2012, 01:04 PM
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Rock On- Damon Atwood
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Well.......

Here is a real update.

Still on the ropes as if this will be next, but I have the wings about 65% design, and the fuse about 80%.

DAG
Old Jan 19, 2012, 10:11 PM
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Air flow adjustments


Dag; I have been silently following your B36 build and cannot fully express my amazement at you skill and audacity at even attempting such a project.

I think your A7D is just as brazen and I really want you to succeed at it. I was checking out your sketch of the A7D design and couldn't help but notice that you might experience some loss of EDF efficiency because of the uneven airflow pattern through your engine duct work.

At first glance, it appears that the air entering the two EDFs will be unevenly distributed and somewhat turbulent. The air exiting the fans will also experience some significant turbulence as it recombines to exit the exhaust nozzle.

Here is a sketch showing extensions to the inlet and outlet splitter vanes.

I would suggest that you do a wind tunnel mock-up study to fine tune the length and angle of the vanes. Find a way to measure the airflow through the two fans to equalize it and blow some smoke through the mock-up to study the turbulence and minimize it.

I doubt that it could ever be perfect but otherwise you may risk a significant loss of efficiency and thrust if you don't give it a try.
Old Jan 20, 2012, 08:58 AM
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Rock On- Damon Atwood
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Originally Posted by JohnSH View Post
Dag; I have been silently following your B36 build and cannot fully express my amazement at you skill and audacity at even attempting such a project.

I think your A7D is just as brazen and I really want you to succeed at it. I was checking out your sketch of the A7D design and couldn't help but notice that you might experience some loss of EDF efficiency because of the uneven airflow pattern through your engine duct work.

At first glance, it appears that the air entering the two EDFs will be unevenly distributed and somewhat turbulent. The air exiting the fans will also experience some significant turbulence as it recombines to exit the exhaust nozzle.

Here is a sketch showing extensions to the inlet and outlet splitter vanes.

I would suggest that you do a wind tunnel mock-up study to fine tune the length and angle of the vanes. Find a way to measure the airflow through the two fans to equalize it and blow some smoke through the mock-up to study the turbulence and minimize it.

I doubt that it could ever be perfect but otherwise you may risk a significant loss of efficiency and thrust if you don't give it a try.
111% agree.

This project will have most of it R&D in this ducting. As drawn does not reflect at all the ducting design I am working with, just airframe.

Thanks!!!!

DAG
Old Jan 20, 2012, 01:23 PM
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EDF rules... :)
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The dual fans using a common exhaust ducting has been done alread and has proven to work reliably. Ducted fans perform like positive displacement pumps at the levels we use them, as long as both run there can only be one direction the airflow will travel and that is thru the exit. It is imperative that the design of the outlet tube must be area ruled and the areas must coincide with the areas of the both fans tapering to ~85% of the total Fan Swept Area or the veloctiy out will either be low or there wont be enough area and back pressure will cause rotor efficiency to drop.

Tamjets already does this with thier 100mm sized fans in a large T45 they sell. I am sure Barry(Monkamarm2000) or Tam can help if you want the scoop on what they did.

https://www.rcgroups.com/forums/show...1&postcount=37

Cheers,
Eric B.
Old Jan 20, 2012, 05:51 PM
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Originally Posted by AirX View Post
The dual fans using a common exhaust ducting has been done alread and has proven to work reliably. Ducted fans perform like positive displacement pumps at the levels we use them, as long as both run there can only be one direction the airflow will travel and that is thru the exit. It is imperative that the design of the outlet tube must be area ruled and the areas must coincide with the areas of the both fans tapering to ~85% of the total Fan Swept Area or the veloctiy out will either be low or there wont be enough area and back pressure will cause rotor efficiency to drop.

Tamjets already does this with thier 100mm sized fans in a large T45 they sell. I am sure Barry(Monkamarm2000) or Tam can help if you want the scoop on what they did.

https://www.rcgroups.com/forums/show...1&postcount=37

Cheers,
Eric B.
Thanks, as I get the design more stream line I will start looking at options.

My rough estimates are she will be 32-36 pounds. So I need a good safe 15-20 pounds of thrust. Some of my calcs show her closer to 28 pounds.

Attached is what I got done late last night and this afternoon. I took off from work at 4 toady....... I needed to find more room for air tanks and by raising the motors a bit I actually helped with the ducting.....

DAG
Old Jan 20, 2012, 08:46 PM
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Rock On- Damon Atwood
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Well this kinda sucks,...... but you will understand just how much time it takes to design a fuse from the station lines from a A7 maintenance manual....

But at least my math is right and everything will fit perfect with the other components.

DAG
Old Jan 20, 2012, 08:49 PM
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EDF rules... :)
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Dag,

2-125mm fans from a reputable manufacturer ie Tamjets or similar vendor should be able to provide 30-36lbs thrust in a pair of 12s-6000mah systems.

Cheers,
Eric B.
Old Jan 20, 2012, 09:12 PM
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Dag,

2-125mm fans from a reputable manufacturer ie Tamjets or similar vendor should be able to provide 30-36lbs thrust in a pair of 12s-6000mah systems.

Cheers,
Eric B.
30-36 pounds....Really??

This is really looking like my next project........

I believe this summer after the 36 is done I will have to start setting up a mock-up fuse. If I can get everything I want to fit in the fuse then the only other challenge is the folding wings.....

I think this plane a 98-101" span would look sooooo cool.....

Thanks for all your input, I am very new, hell not even hatched into DF.....

DAG
Old Jan 20, 2012, 09:47 PM
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EDF rules... :)
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Yup 5 kw will give ~15lb thrust which would be average. Note this is bench thrust installed it would drop some due to duct losses.

Cheers,
Eric B.
Old Jan 21, 2012, 08:43 AM
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Rock On- Damon Atwood
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A bit more done... The ducts are not designed only for reference. I think you are all seeing inside how much it takes to get this all to fit, and know where the weight will be.

DAG

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