Thrust tube? - RC Groups
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Oct 17, 2012, 01:24 AM
right between the batteries
Justo23's Avatar
Discussion

Thrust tube?


I know i've heard the term "thrust tube" before, but being quite new to EDFs (still looking at buying a little fan for a small flying wing i built) was curious what exactly a "thrust tube" is, and what it's importance is...

I'm gonna laugh my backside off if i dont even have the right termanology xD

thanx m8's
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Oct 18, 2012, 08:38 PM
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LuvEvolution7's Avatar
the thrust tube has one simple job...................direct the thrust of the fan and put it to better use. it could be straight for maximum static thrust, or it could be conical to give the best compromise between higher speed and good static thrust. it's kinda like squeezing a water hose. you leave it wide open and the water just pours out. if you sqeeze it with your fingers, the water flow backs up a bit and comes out at a higher pressure. the more you squeeze, the higher the pressure becomes, but only to a certain point. this is the same thing that happens with the thrust tube and how we can get a bit higher top speed by choking the exit of the thrust tube. you can only go so far choking the exit though, before you lose all efficiency from the fan and the flow stalls out.

Rich
Oct 19, 2012, 10:13 PM
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Justo23's Avatar
ok, that makes sense. I was just currious why some use one, while products like the Zephyr 70 have no thrust tube.

I am looking to put a 50mm alloy from hobyking on a combat flying wing (for kicks and giggles) and i like to have as much understanding going into a project as possible. The wing has a 26" span... i hope the 50mm will be sufficent thrust. I've always wanted to play with EDFs.

eventually i want to put two "12 Blade Alloy DPS 90mm EDF unit - 6s 1620kv 2250watt" on a larger EPP foam combat wing, but that is money and time i have yet to find

Thanx again, Justin
Oct 19, 2012, 11:41 PM
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LuvEvolution7's Avatar
no problem Justin. I've seen guys use similar setups on flying wings and gliders. they use simple, ready-made thrust tubes................I've even used them myself. just go to Burger King/McDonalds. or just about any fast food joint and use one of their soft drink cups. they make great thrust tubes. I've even used coffee cups before too.
Oct 20, 2012, 01:32 AM
jofro
Quote:
Originally Posted by Justo23
I know i've heard the term "thrust tube" before, but being quite new to EDFs (still looking at buying a little fan for a small flying wing i built) was curious what exactly a "thrust tube" is, and what it's importance is...

I'm gonna laugh my backside off if i dont even have the right termanology xD

thanx m8's
Here are few pics of thrust tubes I make to suit all sorts of EDF's and to get the best performance from each model. Visit your stationary store and get some clear sheets of PVC and make it up to suit your set up using good quality tape, J.
Oct 20, 2012, 04:09 PM
right between the batteries
Justo23's Avatar
looks simple, does anyone know of a good ratio to use as a rule of thumb for thrust tubes?

For example, if the EDF is a 100mm...

Fan Dia. 100mm
Thrust Tube Length Xmm
Exhaust opening Xmm
Oct 20, 2012, 06:49 PM
Do it Right, the first time!
CoolerByTheLake's Avatar
As a rule of thumb, the starting point is 85% of FSA . This will vary on the fan. On my JetFan 90, suggested optimun exit dia is 75-76mm, which is around 90% FSA. Larger dia exit = more thrust, less speed. Smaller dia exit= more speed, less thrust. Too much of either is not good. Kind of trial and error to find what is best for your application. LuvEvolution7 gave a great description of this in his post.

Thrust tube length will vary depending on what your putting the fan into or onto, ie podded.
Oct 20, 2012, 11:39 PM
Registered User
LuvEvolution7's Avatar
if you want a good ratio for a podded application, your thrust tube length should optimally be about three fan widths. so if you use a 64mm fan, your thrust tube length should be about 190mm. now, that may not be good on the eyes a.s far as looks go, so you could shorten it to give the best look. your outlet should be about 56mm in diameter for a 64mm fan. for a 50mm fan, try about 43mm diameter and a thrust tube length of about 150mm.

you also want to put a lip on your fan for best performance, since a fan will suck air in from all directions, including from behind the lip itself.
Oct 21, 2012, 01:00 AM
right between the batteries
Justo23's Avatar
C17 Creates Tornado (0 min 9 sec)


Yes, having gone through school in Aviation Maintenance, I understand jet engine intakes (in this case the same thing as an EDF) suck from every direction... but jet engines and even turbo fans don't use thrust tubes, so i have been at a loss... until now

Thanks for all the GREAT info '

Justin
Oct 21, 2012, 02:46 AM
Registered User
LuvEvolution7's Avatar
but they do use thrust tubes...............sort of. the outer casing is optimized for maximum thrust, so in essence, they have a thrust tube. imagine the outer casing of an RB211, for example.
Oct 21, 2012, 03:24 PM
James L
TANGOSIERRAROM's Avatar
If you put this equation into the google search bar and swap the text for your fans figures it will spit out the diameter for an 85 % FSA thrust tube.

(sqrt ((((pi*fan radius^2)-(pi*hub or motor tube radius^2))*85%)/pi)*2)
Oct 22, 2012, 08:40 AM
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Justo23's Avatar
great info guys!
i did not know you could do math with google lol
Mar 07, 2013, 11:05 PM
Registered User
MJB9's Avatar
I just ordered this http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1

Expensive but cheaper than what other's on RCG are selling it for. Also, while what I got .005 is most common, they do have .007, .010, .015 and .020 as well, but not in the size I wanted. You could get .007 in 12 x 12 sheets for about $10 or $15 - I got 14inch x 17 inch because the habu 2 needs at least 14" to make it out the exit/rear of jet. And with 17inches, it should be enough for a 90/100mm fan too. They also have large 40" sheets by 12' but I'd rather a more manageable size.
Mar 07, 2013, 11:29 PM
Do it Right, the first time!
CoolerByTheLake's Avatar
Do you have this program? http://www.conelayout.com/purchase They have a free trial version. You would be surprise what size a thrust tube is!!


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