Hi folks , just wondering , since the ducting in my Airfield f4 phantom is over sized , should I maybe run the intake ring on my fan . the area right before the fan seems quite large and probably turbulent . Also what would be the correct size exhaust nozzles on a bifurcated setup ? I think the stock tail cones are oversized as well . Just trying to milk some extra speed out of this thing . I realize this is a foamy but I figured there might be more voices of experience in this forum .

Are all the gurus taking today off ?

The intake ring will definetly be a benefit. Tipically increase static thrust 10 %. As for the exhaust the best setup for speed is, take the swept area of the rotor, and reduce it by 10%, make that you total exhaust exit area.

Larry E.
SouthEast Model Products Inc.

Originally Posted by pencon

Hi folks , just wondering , since the ducting in my Airfield f4 phantom is over sized , should I maybe run the intake ring on my fan . the area right before the fan seems quite large and probably turbulent . Also what would be the correct size exhaust nozzles on a bifurcated setup ? I think the stock tail cones are oversized as well . Just trying to milk some extra speed out of this thing . I realize this is a foamy but I figured there might be more voices of experience in this forum .

Football Sunday or flying!

If you have just open ducting to the fan a ring might be a very good idea. Look up the FSA calc, plug in your shroud ID and motor tube OD. Will give all the info you need. Also gives bifurcated outlet dia. Start measuring.

Ok LJE4357 , but this has a bifurcated dual nozzles so if the normal exit size for a single 70 mm would be say 60mm does that mean 2 nozzles should be 30mm each ?Or does that logic not transfer directly ? Coolerbythelake , I don't know if you would call it open ducting but oversized would probably describe it .I found the FScalc but have absolutley no I dea how to use it .

OK what I meant by open ducting was, there is no separate intake,ie a fiber glass one. Yours just routes through the intakes back to the fan.

FSA calc is pretty simple. You will see (2) green sections. One for shroud inner dia, and bottom one for outside dia of the motor tube. Either metric or imperial measure works. Too make it easy just use metric. Just put those 2 numbers in, it automaticaly does the work. On far right side it will give the exhaust dia for the bifurcated ducts. From 100% to 70%, every 5%.

Bifurcated exhausts don't work that way. If I take my Jetfan 90, at 100% FSA is 77.94mm in dia.(Single) Bifurcated ducts at 100% FSA are 55.11 mm in dia. each!

You will have to measure your fan for any accurate results. Once you know exactly what your FSA is, measure the area of each intake WxL as close as you can. Then add the 2 together and see how that compares the what you fan FSA is. Exhaust is easier, the calc does most of it for you.

It's not 100% accurate, but close enough. Some measuring is involved, but once you figure it out it's easy.

The problem I'm having with FSAcalc is that it's not letting me write anything at all . It's asking me for a cd key , which I don't have ..

OK don't know where you got it from , but download this one. this is what I have. http://www.rcgroups.com/forums/member.php?u=114136

Scroll down about half way, it's a zip file. Download and SAVE it. If your like me, remember where you you put it!! I'll check back in a bit.

53mm each exit for a 90mm edf

Ok the new version works Thanks , However I'm technically inept and still have no idea how to use it ,I punch in the amount and there's an error exclamation point with no answer ..If you know how , what would be the right size for two exits keeping in mind I'm running a 10 blade 70 mm ?

Using 70mm as shroud ID, and guessing motor tube OD at 30mm. this is what you get. Measure the dia of exhaust to see where your dia falls. Post your results.



Exhaust Diameter (bifurcated outlet)
100% FSA44.72135955
95% FSA 43.58898944
90% FSA 42.42640687
85% FSA 41.23105626
80% FSA 40
75% FSA 38.72983346
70% FSA 37.41657387

Ok Cooler , so this being a changesun 10 blade 70mm I should go with 43 mm each ?I have read that the changesun doesn't like being compressed too much and the exhaust should be around 95% .

pencon what is the dia of your exhaust?

I have read that also. Never had a CS fan so I really can't comment. Alot of what needs to be done is trial and error now. First, you HAVE to get your exhaust diameters!! You have to know were you started from and go slow. Just a little at a time. As small as those exhausts are the difference between 90 and 95% is very,very small. The rest is in your court. I wish you well.
Mark

Hmm They're right at 40mm each .I wonder if I'mgoing to have to increase them?