HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Oct 07, 2012, 09:52 AM
Registered User
Joined Jun 2006
95 Posts
Discussion
Need input on air pump for special use

I am trying to build a weird kind of propulsion system based on discrete co-flow jets. This system utilizes wings with discrete jets blowing from behind the leading edge, and a spanwise suction slot ahead of the trailing edge. The idea is to use an EDF, or perhaps some other design of mechanism, to provide air to the jets at a pressure ratio of at least 1.2.

To be more clear, I wanted to use an EDF mounted in semi-sealed ductwork to blow air forward to the jets, and suck the air to its intake from the rear slot. It would be a closed system except for the jets and slot. So the EDF or mechanism would be facing the opposite direction of normal inside the ductwork in the wing or fuselage.

Can current off the shelf EDFs work in such an application, where air velocity is less important than volume and light pressure? I am worried it will cause heat to build up due to flow restrictions. I have zero experience with EDFs, and hope to get some helpful advice about this here. I am open to designing new blades/rotors if necessary, or even exploring a mini roots type system. See below for details on how this works.

http://www7.miami.edu/ftp/acfdlab/pu...A2007-4442.pdf
UncleMatt is offline Find More Posts by UncleMatt
Last edited by UncleMatt; Oct 07, 2012 at 10:06 AM.
Reply With Quote
Sign up now
to remove ads between posts
Old Oct 07, 2012, 09:58 AM
Registered User
Joined Jun 2006
95 Posts
I wanted to add, I am working on a more typical kind of plane than the one discussed in the reference I posted. I am focused more on a flying wing kind of layout, similar to the X8, but using this propulsion system in place of a normal propulsion setup. Just want to see if I can make it actually work, with all the described benefits they claim.
UncleMatt is offline Find More Posts by UncleMatt
Reply With Quote
Old Oct 07, 2012, 10:17 AM
Registered User
BelgiŽ, Vlaams Gewest, Oostende
Joined Sep 2007
47 Posts
Turbo-fan. Weight and weight distribution will be your main headache.
sompop is offline Find More Posts by sompop
Reply With Quote
Old Oct 07, 2012, 10:23 AM
Registered User
BelgiŽ, Vlaams Gewest, Oostende
Joined Sep 2007
47 Posts
I suppose you will make a scaled version first. Look up the people from Wren turbines. I believe they are doing some tests mating a wren turbine to a Schubeler Ducted fan. The weight of the whole setup is very low compared to the thrust obtained.
sompop is offline Find More Posts by sompop
Reply With Quote
Old Oct 07, 2012, 02:36 PM
Registered User
Joined Jun 2006
95 Posts
The discrete jets I referred to are in a slot along the top of the wing, with obstruction tabs placed in that slot that obstruct .25 for every 1.0 of slot (factor of 3/4). So I need something that can push air through a row of slots that will be around 2 mm in width, and of various lengths. I would be happy to use an off the shelf EDF, and may do so just to see what happens, but just wanted to see if anyone had any alternatives.

I will check out what has already been suggested, and to clear things up this is definitely for an RC airplane.
UncleMatt is offline Find More Posts by UncleMatt
Reply With Quote
Old Oct 07, 2012, 04:10 PM
Do it Right, the first time!
CoolerByTheLake's Avatar
United States, MN, Hermantown
Joined Dec 2008
5,215 Posts
You might check out this thread-- How to compare fans

http://www.rcgroups.com/forums/showthread.php?t=1742680

There may be some "numbers" in there regarding air flows that could help.
CoolerByTheLake is offline Find More Posts by CoolerByTheLake
Reply With Quote
Old Oct 07, 2012, 05:50 PM
Registered User
Joined Jun 2006
95 Posts
Thanks for that link, I got the calculator Stu cooked up from it. I am still wondering if I can use an EDF, or if I will have to come up with some other means of compressing the air. In the reference I posted, they show a roots type air pump. I wonder if I could utilize a scaled down version of a roots type air pump for this application. Of course, I am open to any other ideas that might be presented. I have also looked at maybe cooking up an electric multi-stage axial compressor for this too, but want to take a simple approach until I know there is a payoff. I am also upping my target pressure ratio to 1.3, as they did in the reference I posted. So for example, I need to figure out if an existing EDF can raise ambient pressure by that amount, given the appropriate ducting to capture outflow.

To give some ideas of the benefits of using this kind of system for propulsion, it increase lift dramatically, it reduces drag in a big way, and also is very efficient at producing thrust. So even if you use a thicker wing to accomodate ducting and motors, the drag is reduced so much it won't have an impact on air resistance, and produces negative drag to produce thrust. I want to use a fairly thick profile on a flying wing design, and see what happens. Its a long winter ahead, and this is my cure to seasonal affect disorder.
UncleMatt is offline Find More Posts by UncleMatt
Reply With Quote
Old Oct 07, 2012, 09:47 PM
Not Funny......
Mike Warren's Avatar
United States, CO, Redstone
Joined Dec 2010
893 Posts
Quote:
Originally Posted by UncleMatt View Post
Thanks for that link, I got the calculator Stu cooked up from it. I am still wondering if I can use an EDF, or if I will have to come up with some other means of compressing the air. In the reference I posted, they show a roots type air pump. I wonder if I could utilize a scaled down version of a roots type air pump for this application. ..........(snip).......
............Its a long winter ahead, and this is my cure to seasonal affect disorder.
To shorten your quest:
Electric Ducted Fans do not ....... Can not......"compress air"......
They only move air/increase flow......they DO NOT compress.
If you restrict or block the airflow (attempt to compress air) the fan simply stalls (aerodynamic stall of the blades)

You are probably better off posing this type of question in the "modeling science" forum.
Mike Warren is offline Find More Posts by Mike Warren
Reply With Quote
Old Oct 08, 2012, 01:32 AM
Registered User
Brisbane, Australia
Joined Oct 2004
1,141 Posts
Quote:
Originally Posted by Mike Warren View Post
To shorten your quest:
Electric Ducted Fans do not ....... Can not......"compress air"......
They only move air/increase flow......they DO NOT compress.
If you restrict or block the airflow (attempt to compress air) the fan simply stalls (aerodynamic stall of the blades)

You are probably better off posing this type of question in the "modeling science" forum.
I think the question is perfectly fine here.

He asked about what or how he could use an EDF, not how to make his project on a larger scale work This IS the place to ask that type of question

Thanks

dave
ticketec is offline Find More Posts by ticketec
Reply With Quote
Old Oct 08, 2012, 06:50 AM
Life begins at transition
Australia, VIC, Sale
Joined May 2007
3,593 Posts
EDFs do compress air. How much by? Let's find out.

Something like an SM89-45, with a 4771mm2 fan area, putting out 4.5kg thrust with a 100% FSA exhaust.

4.5kg is 44.1N, 4771mm2 is 4771e-6m2. Simply, the pressure change is
dP=F/A
dP=44.1/4771e-6
dP=9243 Pascals.

For those not into SI units, that's 2.7inches, or 1.3psi, or around 1/10th of an atmosphere.
So, it's got a pressure ratio of 1.1. Not enough for the job at hand, but nothing to be sneezed at, no?

Three inline would obviously give around 1.33 ratio, but huge amounts of power.
Odysis is offline Find More Posts by Odysis
Reply With Quote
Old Oct 08, 2012, 11:36 AM
Not Funny......
Mike Warren's Avatar
United States, CO, Redstone
Joined Dec 2010
893 Posts
Quote:
Originally Posted by ticketec View Post
I think the question is perfectly fine here.

He asked about what or how he could use an EDF, not how to make his project on a larger scale work This IS the place to ask that type of question

Thanks

dave
Read his whole 1st post, he is expanding into roots type devices and lots of other issues.
So: my point is that he might get more and EXPANDED info over in the other forum.
(In simple words for you , it's just like politely redirecting some questions about small foamies to the "foamie forum")
Mike Warren is offline Find More Posts by Mike Warren
Reply With Quote
Old Oct 08, 2012, 11:45 AM
Registered User
Joined Jun 2006
95 Posts
Quote:
Originally Posted by Odysis View Post
EDFs do compress air. How much by? Let's find out.

Something like an SM89-45, with a 4771mm2 fan area, putting out 4.5kg thrust with a 100% FSA exhaust.

4.5kg is 44.1N, 4771mm2 is 4771e-6m2. Simply, the pressure change is
dP=F/A
dP=44.1/4771e-6
dP=9243 Pascals.

For those not into SI units, that's 2.7inches, or 1.3psi, or around 1/10th of an atmosphere.
So, it's got a pressure ratio of 1.1. Not enough for the job at hand, but nothing to be sneezed at, no?

Three inline would obviously give around 1.33 ratio, but huge amounts of power.
I love a man who knows his math! That was a very helpful rundown on EDFs and compression. I have seen other threads where a guy placed 2 EDFs so their impellers would emulate a multi-stage axial compressor, but the goal was additional air velocity, not pressure increase. I wonder if that would produce the 1.3 pressure ratio I am after here. But it will probably take an axial setup designed to compress more to get there without using too much power or adding too much weight.

If more ideas are out there, let them flow! Also, it may be off topic here, but if anyone knows of a scale roots type air pump that might work for this, let me know.
UncleMatt is offline Find More Posts by UncleMatt
Last edited by UncleMatt; Oct 08, 2012 at 11:50 AM.
Reply With Quote
Old Oct 08, 2012, 11:53 AM
Not Funny......
Mike Warren's Avatar
United States, CO, Redstone
Joined Dec 2010
893 Posts
Uriah?
Mike Warren is offline Find More Posts by Mike Warren
Reply With Quote
Old Oct 08, 2012, 12:16 PM
Suspended Account
Joined Dec 2011
104 Posts
Quote:
Originally Posted by Mike Warren View Post
Uriah?
My thoughts exactly Mike, and infact do you have Pics of Uriah's work?

I think you need to do a search for a user named Uriah. He has several different type of special propulsion systems. I would post pics but im not at my office, im on the road in a friends i-pad.

Uriah is the man for what you are looking to do. Nobody has come close to the achievements that he has done. Look up his name on here and research his old postings.

That or get yourself a Dyson fan.
Super Matt is offline Find More Posts by Super Matt
Reply With Quote  (Disabled)
Old Oct 08, 2012, 12:37 PM
Suspended Account
Joined Oct 2012
1 Posts
Subscribed for the win factor in this thread
Tardofunk is offline Find More Posts by Tardofunk
Reply With Quote  (Disabled)
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Help! Need inputs on winter build projects! RMCCOR7737 Scale Kit/Scratch Built 5 Oct 01, 2012 03:37 AM
Discussion Thread: Grand Cruiser Crash: Need input on investigation F1nut Electric Plane Talk 26 Jun 18, 2012 02:14 PM
Help! Need inputs on (re)building Piper Cub vijayfx35 Electric Plane Talk 9 May 26, 2012 10:02 AM
Found Air Pump for retract systems Doubledog Aircraft - Fuel - Airplanes (FS/W) 0 Apr 18, 2012 04:06 AM
Question Need input on AP build rgoins21 Multirotor Talk 12 Mar 15, 2012 01:27 PM