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Old Feb 04, 2010, 06:52 AM
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Helge Sondresen's Avatar
Stavanger Sola, Norway
Joined Oct 2000
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Inlet opening J-29 tunnan

Hi ..
I started on a J-29f tunnan..Got inspired by Boogies Build from scratch.
Scale is 1/12..Wingspan 37inches(94cm)
It is based on Mike Stuart Plan enlarged 300%..

Power will be MMX Fan edf/motor HW combo.60mm fan.
Inlet tube length 12 inches(30cm)
Scale Inlet on plan is 44mm..I intended to stay as close as possible on opening.Maybe 50mm will be ok..
Hopefully it will be a light model around 30oz.
Any opinion ? Thanks

Helge
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Old Feb 04, 2010, 07:34 PM
Big gov never Works
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Skunk Water, Rhode Island
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I'm not familiar with this fan, Helge. What dia mtr does it use? Good to see another stick build!

Fuzz
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Old Feb 04, 2010, 07:50 PM
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United States, NJ, Frenchtown
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All fans NEED a correct sized inlet for efficiency. Inlets cause a suction on the inlet side of the blade. This is a worse problem than a restriction in the exhaust. Basic pump theory & design. So keep the inlets full sized diameter and short as you can with a COG.

Todays EDFs are strong enough to muscle alot of stick plane into the air.

I am always looking for a scale, small, Saab Draken J35. Any over there ?

Rich......USA.
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Old Feb 05, 2010, 05:20 AM
Da' Cajun
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Lake Charles, Louisiana
Joined Jun 2009
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What?!? I inspired somebody?
(this hobby is in big trouble)

Looks good Helge. Mike has a bunch of good planes. I may wind up building all of his designs.
And take my advice, follow whatever advice Fuzz gives you.

Keep the updates coming
Julian
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Old Feb 05, 2010, 06:05 AM
Claus at Area 52
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copenhagen Denmark
Joined May 2002
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Saab tunnan.

I have worked a little with this for a 70 mm project.
as long as you have a good soft (part of elipse) intake inwards the size is not that critical. one thing is the opening (throught of the duct) and one thing is the catch area (stagnation point).

as you can see i ended up with a nice round form, very close to scale of this model.
Claus
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Old Feb 05, 2010, 07:50 AM
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Helge Sondresen's Avatar
Stavanger Sola, Norway
Joined Oct 2000
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Hi,Thanks
Steve,dia mtr 25mm.The fan /motor combo are Hoffman magnetics Wild Migthy mite..Kv -5580 weight 116grams.
External diameter of fan 62mm.5 blade rotor 4 stator vanes.Preinstalled outrunner motor.says its good for 650watts..much more than i need.

Rich Draken here.MBS RC Models www.mbs-rcmodels.se
Kit but looks very good.

Helge
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Old Feb 05, 2010, 08:16 AM
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Thank you very much, Helge.
I e-mailed for a kit price.

Rich
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Old Feb 05, 2010, 08:51 AM
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Helge Sondresen's Avatar
Stavanger Sola, Norway
Joined Oct 2000
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Julian,yes have been following Fuzz`s informatives builds..
Have at least one plane with Tumb patch

Thanks Claus..its the top part of the drawing that is going inwards.
Should it be like that the full circle?

Helge
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Old Feb 05, 2010, 09:28 AM
Claus at Area 52
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Helge.
the top elipse is only there to show where i got the form from
the bottom part is done same way but no elipse shown.
Claus
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Old Feb 05, 2010, 09:35 AM
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Arngeir Blakseth's Avatar
Molde, Norway
Joined Jan 2001
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Hei Helge,

Artig prosjekt det der, jeg har endel Tunnan dokumentasjon liggende som du kanskje kan være interessert i? Jeg kan sende det til deg på mail.

If the fan has a 6cm diameter and a 2.5cm motor tube, it has a FSA of 23.36cm2. Using a 5cm diameter intake gets you to 19.63cm2, so if you add a nice rounded inlet lip to that you should be good. Area of the inlet should be measured from the middle of the lip, with a lip with a 5mm radius that means you have 23.75cm2 of area which is very good.
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Old Feb 05, 2010, 10:51 AM
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Stavanger Sola, Norway
Joined Oct 2000
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Claus, ok same toprofil full circle.hmm, maybe I need some fancy sanding tool.

Hei Arngeir Thanks for calculations,Maybe I can go for a smaller diameter and adjust later on(increasing) if performance is not satisfactory.. Inlet are made of 4 balsa rings 21mm thick..Og ja takk for dokumentasjon..helgson@online.no

Helge
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Old Feb 05, 2010, 11:07 AM
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Stavanger Sola, Norway
Joined Oct 2000
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Ok.some progress made..

covered some part of fuselage and started on second half lining up formers so
it will be equal.
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Old Feb 05, 2010, 03:03 PM
Big gov never Works
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Skunk Water, Rhode Island
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Helge, the info Arngeir gave, I had to change to imperial(I'm still slow on some metrics), I agree with. One rule of thumb I always use, is always have the exaust area less than the intake area. I usually use a 15% exaust decrease from 100% FSA intake, minus the mtr tube.
But I have noticed, that if the intake is reduced in area from FSA 100%, the exaust ratio is less. Expl: 90% intake FSA= only 10% FSA exaust(less than the intake area). I'm no flow expert like Claus, Stu, and others, so I cannot explain why, honestly.

And having no experience with your fan, these numbers may not be as valid as with the 70mm fans I normally use. I only know from experimenting with exaust cones.

I was eyeballing this plan also. I love the tubby Tunnan. I built Dave Ree's Tunnan back in the mid 90's. With the RFB 63mm fan it was not too bad. To bad brushless and lipos were not available. Hope your going to honor the balsa work with a nice silkspan and lacquer finish?

Fuzz
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Old Feb 06, 2010, 01:26 PM
Claus at Area 52
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Fuzz-
it is no big deal, neither rocket science.
if you think of the inlet size and make the outlet % down as usual(80%) the same based on the inlet then you will not go too wrong.
it is all about the amount of air comming in and the accelleration of it in the fan and the further accelleration from the narrowed excit tube.
Claus
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Old Feb 06, 2010, 02:52 PM
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United States, NJ, Frenchtown
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We are getting into a... speed versus thrust .....discussion ??
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