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Old Jan 05, 2005, 09:24 PM
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Quote:
Originally Posted by AirX
Looks good Mr. B.
The duct on the right is the F-35 and the one on the left is the ?
Sorry cant help on the heatshrink.

Eric B.
Hey AirX,

The ducts on the left are generic, the thought was to squeeze the inlets to shape afterwards.

B
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Old Jan 05, 2005, 09:30 PM
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Quote:
Originally Posted by winmodels
Hi Mr. B.

getting 2" heat shrink tube is not the problem, it's used for "confectioning" of battery packs. Shops who sell cells for battery construction should have it.
I still have plenty meters around - send me a PM, a letter to America shouldn't be a problem.
The real problem with the heat shrink tubing I know of is, that it is still pretty flexible after shrinking, and I fear that it would be sucked flat by the EDF, unless you reinforce it after forming and demoulding with some tows of glass or better carbon fibres and epoxy. That in itself causes problems since most of the heat shrink material is made of polyolefines which does not stick to epoxy .
A little hint to the shape of the ducting: it may be advantages if the front end of the duct again curves towards parallel to the centre line of the aeroplane, so the forward duct center line does not create an angle with the incoming air inflow. And don't forget to round off of the inlet lip.

Have fun with fans

Klaus

Thanks for the input Klaus.
As TN explained we are playing with some ideas, but are open to suggestions from those who have travelled this path already. In your layup of the ducts for your Cobra400, what weight glass are you using? and How do you close the seam afterwards?

Thanks,
B
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Old Jan 05, 2005, 09:42 PM
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Quote:
Originally Posted by Ed Waldrep
Mr. B, what's the plug made out of? If it's foam, you could encase the plug in a one of those long kiddy balloons that you find in supermarkets, then apply mold release and lay up a glass part with 3 oz cloth. You might be able to cut the dried inlets and re-use the plug if you are lucky but you may also end up destroying the plug. But now I see after posting that you have access to a rapid prototyping machine (that laser and wax thing or is it cnc machining foam?). If that's the case then I guess there's not need to worry about destroying a plug for a one off inlet duct.

A more permanent solution would be to glass the inlet plugs and lay up glass parts over that, but that's a lot of work for a one off solution and as Thomas said the goal is a one piece part with no cutting. I can see the appeal of heat shrink tubing but as mentioned the stiffness is not there with just the heat shrink and no reinforcement. I think CA might stick to the heat shrink though, so maybe wrapping it with carbon tow and CA would work.

The way your inlets are on the present model are could be modified a bit. In front of the fan you could make a section that transitions from the rectangular inlets to the round shape of the fan. Maybe you could use thin depron for this but thick card stock/cereal box cardboard or computer photo paper could be used as well. The transition would be formed between two bulkheads with the shape required cut into each end, then the paper is inserted and held in place while it's glued in position to hold it into shape. That wouldn't be a smooth as glass ducting but it would be easier.
Hi Ed,

The prototyping machine is actually a laser and photocurable polymer system. The parts are pretty solid and thermally stable to a point. I normally use the parts as canopy plugs for vacuum forming.

I would like to give the heat shink a shot first and then I figure waxing the part and doing a glass layup is the next logical step.

The inlets actually go from rectilinear to semi-circular. These pieces will mate with a straight run tube of heavy photopaper which in turn mates with the fan shroud.

I like the paper duct/bulkhead former idea and may try this as a quick evaluation of duct fitment.

I've included some pics of the prototyped duct masters.

Thanks,
B
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Old Jan 05, 2005, 09:47 PM
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Booh,

I know this is how Thomas constructed his F16 duct. If it comes down to it, we'll give it a try.

Charlye and Jorge,
Thanks alot for the heatshrink links!

Klaus,
You've got PM.

Boogie
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Old Jan 05, 2005, 10:31 PM
EDF rules... :)
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Mr. B.

That is just sweet. I think your on the road to acheiving your goals.

Cheers,

Eric B.
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Old Jan 06, 2005, 12:07 AM
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Oh man, those plugs are nice, and they look really smooth. If they are strong enough to withstand the heat and pressure of vacuum forming then they may work for fiberglassing plugs. I bet you could wet-sand those with up to 1500 grit paper and then start with the polishing compound to get them glass smooth, then several coats of wax, mold release, then lay up some glass parts. For my midi T-33 inlets I think I used 3 oz cloth. I wrapped them with carbon tow just in case, that really stiffened them up.

Man, I'm doing it the hardway.
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Old Jan 06, 2005, 12:40 AM
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Hey guys

The heat shrink idea was mine and I admit I've not tried it nor heard of it applied this way ... it may prove totally unusable. The reason behind it is to keep the duct fabrication as simple as possible, without ruining the plug. Here's what I envision:

1 Lightly shrink (minimal heat) the tubing over the FP plug. (They look great BTW, Mr. B! Had only seen the CAD images up 'til now) Leave some overhang at one end to tug on later.

2 Use the overhang to pull the heat shrink off the plugs. Since the ducts are fully area ruled, I'm hoping they'll slide off with minimal resistance - if they're not shrunk too tight in the first place!

3 Epoxy a couple of layers of either carbon tissue or glass directly on the heat "shrunk" tubing; I've no doubt it will not handle the suction without such re-inforcement. I am hoping, however, that it has sufficient rigidity to keep its shape through the glass or CF re-inforcing process. Thoughts?

4 If the tubing does not stick to the glass/CF - no biggie. Just peel it all out of the inside of the duct. I had to do similar with the Econocote on my F-16 duct.

5 And if the heat shrinkable tubing stubbornly refuses to slide off the plug, then cut it lengthways, remove it and rejoin the two halves.

So that's it. The goal is a lightweight, easy to make, accurate ... and hopefully efficient ducting for the Microfan. Thoughts? Comments? Pot Shots? Hysterical laughter?

Among the things Mr B and I have discussed trying at some point, might be a conical bulge inside the flat portion of each inlet duct, one which gradually reduces the FSA from some 140% at the inlet to 100% at the hub of the fan, and ensures minimum disruption of the air as it enters the rotor. The big end of the bulge will have the same diameter as the hub, reducing the turbulence the hub causes. It's the same thing shown in Klaus' drawing here, just approached "the other way 'round". Again, CAD will ensure that area ruling is maintained, and gradually applied to the dimishing FSA. Surprising (to me at least) was that this degree of complexity is totally doable with fast prototyping technology. "And for his next trick, Mr B is gonna replicate a phaser". (ummm ... any Trekkers out there?)

Given that textures are also possible with the FP approach, Mr Boogie could also test the effect of the roughness of the duct, leaving ALL other attributes unchanged.


PS: The LHS has some large, transparent heat shrinkable tubing Mr B. It comes flattened, and is sold on a roll. The flattened dimension is 2.875", which will yield a circumference of 5.75", resulting in an unshrunk diameter of 1.83". If this is big enough I'll go buy 10' or so and shoot it your way.
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Old Jan 09, 2005, 07:02 PM
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Quote:
Originally Posted by Ed Waldrep
Oh man, those plugs are nice, and they look really smooth. If they are strong enough to withstand the heat and pressure of vacuum forming then they may work for fiberglassing plugs. I bet you could wet-sand those with up to 1500 grit paper and then start with the polishing compound to get them glass smooth, then several coats of wax, mold release, then lay up some glass parts. For my midi T-33 inlets I think I used 3 oz cloth. I wrapped them with carbon tow just in case, that really stiffened them up.

Man, I'm doing it the hardway.
Thanks Ed,

Believe me, without access to the RP technology I'd be building stuff by hand as well. It's all fun doesn't really matter how you get there, as long as you enjoy the journey.

I plan to be polishing these plugs if the heatshrink experiment doesn't work.

Thanks,
B
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Old Jan 09, 2005, 07:15 PM
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Quote:
Originally Posted by Thomas Nelson
Hey guys

The heat shrink idea was mine and I admit I've not tried it nor heard of it applied this way ... it may prove totally unusable. The reason behind it is to keep the duct fabrication as simple as possible, without ruining the plug. Here's what I envision:

1 Lightly shrink (minimal heat) the tubing over the FP plug. (They look great BTW, Mr. B! Had only seen the CAD images up 'til now) Leave some overhang at one end to tug on later.

2 Use the overhang to pull the heat shrink off the plugs. Since the ducts are fully area ruled, I'm hoping they'll slide off with minimal resistance - if they're not shrunk too tight in the first place!

3 Epoxy a couple of layers of either carbon tissue or glass directly on the heat "shrunk" tubing; I've no doubt it will not handle the suction without such re-inforcement. I am hoping, however, that it has sufficient rigidity to keep its shape through the glass or CF re-inforcing process. Thoughts?

4 If the tubing does not stick to the glass/CF - no biggie. Just peel it all out of the inside of the duct. I had to do similar with the Econocote on my F-16 duct.

5 And if the heat shrinkable tubing stubbornly refuses to slide off the plug, then cut it lengthways, remove it and rejoin the two halves.

So that's it. The goal is a lightweight, easy to make, accurate ... and hopefully efficient ducting for the Microfan. Thoughts? Comments? Pot Shots? Hysterical laughter?

Among the things Mr B and I have discussed trying at some point, might be a conical bulge inside the flat portion of each inlet duct, one which gradually reduces the FSA from some 140% at the inlet to 100% at the hub of the fan, and ensures minimum disruption of the air as it enters the rotor. The big end of the bulge will have the same diameter as the hub, reducing the turbulence the hub causes. It's the same thing shown in Klaus' drawing here, just approached "the other way 'round". Again, CAD will ensure that area ruling is maintained, and gradually applied to the dimishing FSA. Surprising (to me at least) was that this degree of complexity is totally doable with fast prototyping technology. "And for his next trick, Mr B is gonna replicate a phaser". (ummm ... any Trekkers out there?)

Given that textures are also possible with the FP approach, Mr Boogie could also test the effect of the roughness of the duct, leaving ALL other attributes unchanged.


PS: The LHS has some large, transparent heat shrinkable tubing Mr B. It comes flattened, and is sold on a roll. The flattened dimension is 2.875", which will yield a circumference of 5.75", resulting in an unshrunk diameter of 1.83". If this is big enough I'll go buy 10' or so and shoot it your way.

TN Thanks for the assist!

and...

What colors and sizes do you want your phasers in?

B
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Old Jan 21, 2005, 10:05 PM
EDF rules... :)
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Joined Nov 1999
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Hi Mr. Boogie,

Just browsing the thread, working on a revised version of my S-54 and looking for ideas on former placement. Going Depron for faster prototyping. It can be made to look pretty good as has your F-35.

Cheers,

Eric B.
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Old Jan 21, 2005, 10:51 PM
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Eric a Copy of the Plans in a PDF can be found here http://www.parkfly.rchomepage.com/MBF35.pdf
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Old Jan 21, 2005, 11:09 PM
EDF rules... :)
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Thanks Tom, I will look over them, I want to build one later this spring from Boogies plans.

Cheers,

Eric B.
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Old Jan 22, 2005, 01:44 AM
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Quote:
Originally Posted by AirX
Thanks Tom, I will look over them, I want to build one later this spring from Boogies plans.

Cheers,

Eric B.
Those are Mr. Boogies Plans I'm hosting his F-18 and F-35 Plans on my RCHomepage site. Note the MB

"MBF35.pdf"
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Old Jan 22, 2005, 03:05 PM
EDF rules... :)
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Yep, I understood, your a great guy Tom...

I still need to learn how to make a web page..

Eric B.
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Old Jan 22, 2005, 07:04 PM
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The RC Homepages sites have a lot of features we would never use, but putting up a basic webpage is simple enough. Go and download a free copy of Netscape 7.2 I use the "Composer" to build my webpages, then I just create an index page on the RChomepage and copy and paste the Composer's HTML into the page. HECK of a lot easier than using that CAD stuff you do LOL
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